2. opportunity cost is defined as
A: The cost of the second best option that will have to be forgone in order to select the best option .
3. Which of the following services is not available in a free market economy ?
- Defence services
4. In a free market economy , production resourcs are allocated through
- The power of supply and demand in the market
5. In a centrally planned economy , the problem of for whom a good should be produced is solved by
A : Rationing
6. In a mixed economy , the problem of how much of a good should be produced is solved by
A: Market mechanism
7. An economy reaches productive efficiency when
A : Production of a good cannot be increased without reducing the production of another good .
8. The figure below shows a production possibilitis curve for the production of good x and good y . The points that indicate achievable production levels are points .
A : P, F, and M
9. Of the following , which is not a merit of free market economy ?
A: Social welfare is prioritised .
10. Government intervention is necessary in the economy because
A : The government wishes to overcome weaknesses in the free market economy .
Friday, September 30, 2011
Economics is defined as
A study of social science that focuses on behaviour of individuals in the allcation of limited production factors to fulfil umlimited wants .
Thursday, September 29, 2011
James Tobin
Beginning with keynes at harvard
Rare is the child , I suspect who wants to grow up to be an economist , or a professor . I grew up in a university town and went to a university run high school , where most of my friend were faculty kids . I was so unfailing an A students that it was boring even to me . But I don't recall thinking of an academic career . I liked journalism , my father's occipation ; I had put out "newpapers" of my own from age six . I though of law : I loved to argue , and beginning in my teens I was fascinated by politics . I guess I knew that there was econoics at the university , but I didn't know what the subject really was . Of course , economic issues were always coming up in classes on history and goverment - civics , in thosedays . I expected economics to be among the social science course I would someday take in college, probably part of the pre-law curriculum .
I grew up happily assuming I would go to college in my hometown , to the University of Illinois . One month before I was scheduled to enroll as a freshman , I was offered and accepted a Conant Prize Fellowship at a voracious reader , the biggest customer of the Champaign Public Library , discovered in the New York Times that Harvard was offering two of these new fellowships in each of five midwestern states . President Conant wanted to broaden the geographical and social base of Harvard College . Having nothing to lose , I accepted my father's suggestion that I apply . University High School , it turned out , had without even trying prepared me superbly for the obligatory College Board Exams . uni High graduates only third to thirty-five persons a year , but it has three Nobels to its credit and , once I had broken the ice , many national scholarships .
Thus James Bryant Conant , Louis Michael Tobin , and Universit High School changed my life and carrerr , Illionois was and is great university . But I doubt that it would have led me into economics . For several reasons , Harvard did .
Harvard was the leading academic center of economics in north America at the time : only Columbia and Chicago were close competitors . Both its senior and junior faculty were outstanding . Two of the previous lecturers in this series were active and influential members of the community when I was a student , Wassily Leontief on the faculty and Paul Samuelson as a Junior Feloow , a graduate student free of formal academic requirements . Of the senior faculty of the 1930s , Joseph Schumpeter wuld have been a sure bet for a Nobel , Alvin Hansen , Edward Chamberlin , and Gottfried haberler likely choices . Haberler , still active , remains a possibility . Naturally , Harvard attracted remarkably talented graduate students . That able undergraduates might go on to scholarly careers was taken for granted .
When I arrived at harvard , I knew I would want to major - at Harvard the word is concentrate - n one of the social sciences or possibly in mathematics . By the end of freshman year I was leaning to economics . But I hadn't yet taken any . In those days even Ec A , the introductory course , was considered too hard for freshman . As a sophomore all of eighteen years old , I began Ec A in a section taught by Spencer Pollard , an advanced graduate students specializing in labour economics and writing a dissertation on John L . Lewis and the United Mine Workers .
Pollard was also my tutor . A Harvard undergraduate , besides taking four courses , met regualarly , usually singly , with a turtor in his field of concentration , generally a faculty member or graduate student associated with the student's residential house . Tutorial was not graded . It was modeled , like the house system itself , on Oxford and Cambridge . Pollard suggested that we devote our sessions to " this new book from England ." He had recently been over there and judges from the stir the book was creating even before publication that it was important . The book was the General Theory of Employment , Interest and Money by John Maynard Keynes , published in 1936 .
Rare is the child , I suspect who wants to grow up to be an economist , or a professor . I grew up in a university town and went to a university run high school , where most of my friend were faculty kids . I was so unfailing an A students that it was boring even to me . But I don't recall thinking of an academic career . I liked journalism , my father's occipation ; I had put out "newpapers" of my own from age six . I though of law : I loved to argue , and beginning in my teens I was fascinated by politics . I guess I knew that there was econoics at the university , but I didn't know what the subject really was . Of course , economic issues were always coming up in classes on history and goverment - civics , in thosedays . I expected economics to be among the social science course I would someday take in college, probably part of the pre-law curriculum .
I grew up happily assuming I would go to college in my hometown , to the University of Illinois . One month before I was scheduled to enroll as a freshman , I was offered and accepted a Conant Prize Fellowship at a voracious reader , the biggest customer of the Champaign Public Library , discovered in the New York Times that Harvard was offering two of these new fellowships in each of five midwestern states . President Conant wanted to broaden the geographical and social base of Harvard College . Having nothing to lose , I accepted my father's suggestion that I apply . University High School , it turned out , had without even trying prepared me superbly for the obligatory College Board Exams . uni High graduates only third to thirty-five persons a year , but it has three Nobels to its credit and , once I had broken the ice , many national scholarships .
Thus James Bryant Conant , Louis Michael Tobin , and Universit High School changed my life and carrerr , Illionois was and is great university . But I doubt that it would have led me into economics . For several reasons , Harvard did .
Harvard was the leading academic center of economics in north America at the time : only Columbia and Chicago were close competitors . Both its senior and junior faculty were outstanding . Two of the previous lecturers in this series were active and influential members of the community when I was a student , Wassily Leontief on the faculty and Paul Samuelson as a Junior Feloow , a graduate student free of formal academic requirements . Of the senior faculty of the 1930s , Joseph Schumpeter wuld have been a sure bet for a Nobel , Alvin Hansen , Edward Chamberlin , and Gottfried haberler likely choices . Haberler , still active , remains a possibility . Naturally , Harvard attracted remarkably talented graduate students . That able undergraduates might go on to scholarly careers was taken for granted .
When I arrived at harvard , I knew I would want to major - at Harvard the word is concentrate - n one of the social sciences or possibly in mathematics . By the end of freshman year I was leaning to economics . But I hadn't yet taken any . In those days even Ec A , the introductory course , was considered too hard for freshman . As a sophomore all of eighteen years old , I began Ec A in a section taught by Spencer Pollard , an advanced graduate students specializing in labour economics and writing a dissertation on John L . Lewis and the United Mine Workers .
Pollard was also my tutor . A Harvard undergraduate , besides taking four courses , met regualarly , usually singly , with a turtor in his field of concentration , generally a faculty member or graduate student associated with the student's residential house . Tutorial was not graded . It was modeled , like the house system itself , on Oxford and Cambridge . Pollard suggested that we devote our sessions to " this new book from England ." He had recently been over there and judges from the stir the book was creating even before publication that it was important . The book was the General Theory of Employment , Interest and Money by John Maynard Keynes , published in 1936 .
Wednesday, September 28, 2011
Deduction of liquidated damages
Client is entitled to recover liquidated damages from the contractor if he fails to complete by the "completion date " .
Architect will issue a "Non-Completion Certificate"
Client will notice the Contractor in writting - issues "notice of Liquidated Damages ' before the final date for payment on the "Final Certificate '.
Liquidated damages support by the 'Non-Completion Certificate.
Client is entitled to recover liquidated damages from the contractor if he fails to complete by the 'completion date' .
Architect will issue a "non - completion Certificate'
Client will notice the Contractor in writting - issues "notice of Liquidated damages ; before the final date for payment on the "final certificate '.
Liquidated damages support by the 'Non-Completion Certificate . '
Architect will issue a "Non-Completion Certificate"
Client will notice the Contractor in writting - issues "notice of Liquidated Damages ' before the final date for payment on the "Final Certificate '.
Liquidated damages support by the 'Non-Completion Certificate.
Client is entitled to recover liquidated damages from the contractor if he fails to complete by the 'completion date' .
Architect will issue a "non - completion Certificate'
Client will notice the Contractor in writting - issues "notice of Liquidated damages ; before the final date for payment on the "final certificate '.
Liquidated damages support by the 'Non-Completion Certificate . '
Concept and appication of liquidate damages
According to the principle of Law of contract , to succeed in a claim for damages for breach of contract , a claimant must prove to the satisfaction of the court that
- The defendant's breach of contract caused loss in the amount claimed .
-The loss not too remote at the time of formation of the contract .
-The claimant took all reasonable steps to mitigate his loss.
- The defendant's breach of contract caused loss in the amount claimed .
-The loss not too remote at the time of formation of the contract .
-The claimant took all reasonable steps to mitigate his loss.
Entitlement for E.O.T
- The 'nett effective' delay must be assessed based on the contractor's approved programme and the interdependence of the operations of the works in relation to the whole of the works . Consequential delays must also be considered .
- in the assement , a logical analysis must be undertaken in a methodical way of the impact which the relevant matters had or were likely to have on the contractor's planned programme .
- The overriding requirement is as to the satisfaction of the "Fair and Rasonableness Test' on part of assessor .
It should be noted that the contract adminstrator's ultimate decision as to the granting of any extension of time is subject to the important expectations that are highlighted in the "Standard Form of COntract . "
Entitlement for extension of time
- If the procedures which the contract las down are strictly followed .
- Can only be validly granted in respect of an event that is expressly included in the contract as a 'relevant event and which has delayed , or is likely to delay completion .
- The delay must be one affecting an activity / activities that are on the critical path . ie. One that is having 'little or no float ' that cannot be delayed without affecting the others.
benefits of exntesion of time
- obviously benefit the contractor who will not be liable to pay damages for delay during the period for which time is validly extended .
The purpose extension of time
- To retain a defined time for completion .
- To preserve the employer's right to Liquidated damages against acts of prevention
- To give the contractor relief from his strictly duty to complete on time in respect of Delays caused by designatd neutral events
Why extension of time ?
- To make contract valid
- To avoid penalty
- modifies the liability of the contractor to complete the works by the date for completion specified in the contract document and to liquidated damage to the client upon the failure of the contractor to meet the deadline.
Importance of the notice of delay
- To give the architect the opportunity to take all reasonables steps available to minimise the effect of delays .
- To alert the Architect to watch out for the reasonableness of the contractor endeavours to prevent / minimise delays .
- To alert the Architect to the effects of the delays as they occur .
- To allow the Architect to advise the client .
Delays
Time for completion of the Works is said to be delayed when the Contractor's obligation to complete the Works within the specified time or certified extended time is lost . That is to say , the Contractor is no longe bound by the contract provision that he has to complete the works by a certain date or extended date .
Delay in construction industry contractin can be both psychologically and financially desctuctive .
It xcan be resulted from an act of God , breach of contract by one of the party , or differing site conditions .
Delay in construction industry contractin can be both psychologically and financially desctuctive .
It xcan be resulted from an act of God , breach of contract by one of the party , or differing site conditions .
Obligations of the contractor
provide two copies of master work programme A.S.A.P after commencement date .
Contractor is not contractually bound to carry out work strictly in accordance with subnmitted work programme .
Contractor can amend the programme to take account of any extension of time (E.O.T) granted by Architect - submite revisions within 14 days of the awarded of E.O.T.
When the progress is likely to be delayed or is being delay , contractor must give written notice that comply .
Contractor is not contractually bound to carry out work strictly in accordance with subnmitted work programme .
Contractor can amend the programme to take account of any extension of time (E.O.T) granted by Architect - submite revisions within 14 days of the awarded of E.O.T.
When the progress is likely to be delayed or is being delay , contractor must give written notice that comply .
- Details of all the material circumstances surrounding the delay .
- State the cause of delay
- Identify which of the cause that the Contractor believes to be RELEVANT EVENTS . .
Issues of time
In most construction contracts , the contractor is expected to complete the contract works by a specified time .
Failure to complete the project by the due date of completion will result in liability for damages for breach of contract .
Failure to complete the project by the due date of completion will result in liability for damages for breach of contract .
Interpretation of Grading Charts
Fine aggregate gradings , and coarse aggregaes grading charts are shwon in Fig . 15.3 to 15.7 . These charts have been produced considering grading of fine and coarse aggregates given in Table 15.8. In these graphs lower limits of grading aggregates are marked by L and uphttp://says.my/tankahban/invite
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Grading limits for fine aggregates
The grading of fine aggregates as specified by IS : 2386 -1965 , ( part I ) are given in Table 15.8 below . ISI has specified fine aggregates grading into four zones , namely zone 1,2,3,and 4 . Where the grading falls outside the limits of any particular zone of sieves other than 600 mic by a total amount not exceeding 5 percent it should be regarded as falling within that grading zone .
Grading of Aggregate
Grading of agregates means particle size distribution of the aggregates . If all the particles of an aggregates are of one size , more voids will be left in the aggregates mass . On the other hand an aggregates having particle of varying sizes will exhibit smaller voids . Principle f grading is that the smaller size particles fill up the voids left in larger size particles . By adopting proper percentages of various sized aggregates , composite aggregate mix can be developed which will be thoughly graded . Properly graded aggregates produces dense concrte and needs smaller quantities of fine aggregates and cement .
The grading of aggregates is expressed in terms of percentages by weight retained on a series of sieves , 80mm , 40mm , 20mm , 10mm and 4.75mm sieves are used for grading of coarse aggregates while 10mm , 4.75mm , 2.36mm , 1.18mm , 600mic , 300 mic , 150mic are used for grading the fine aggregates .
Grading determines the workability of the mix , which controls segregation , bleeding water and cement requirements , handling , placing and other characteristics of the mix . These factors alsoaffect economy , strength , volume change and durability of hardened concrete .
There is no universal ideal grading for the aggregates . Howwever , IS has specified certain limits , within which a grading must lie to produce a satisfactory concrete . But these limits depend upon the shape , surface texture , type of aggregates and amount of flaky or elongated material . Variation in grading of sand cause great variatiation in the grading of coarse aggregates does not effect thse properties to the extent of fine agggregates .
Coarse aggregates are supplied in nominal sizes . Coarse aggregregates and their grading as suggested by ISI are given in Table 15.5.
Coarse single sized aggregate nominal size and gradings as suggested by ISI are given in Table 15.6. Aggregates having all its particles predominantly of one uniform size , is known as single sized aggregates .
The grading of aggregates is expressed in terms of percentages by weight retained on a series of sieves , 80mm , 40mm , 20mm , 10mm and 4.75mm sieves are used for grading of coarse aggregates while 10mm , 4.75mm , 2.36mm , 1.18mm , 600mic , 300 mic , 150mic are used for grading the fine aggregates .
Grading determines the workability of the mix , which controls segregation , bleeding water and cement requirements , handling , placing and other characteristics of the mix . These factors alsoaffect economy , strength , volume change and durability of hardened concrete .
There is no universal ideal grading for the aggregates . Howwever , IS has specified certain limits , within which a grading must lie to produce a satisfactory concrete . But these limits depend upon the shape , surface texture , type of aggregates and amount of flaky or elongated material . Variation in grading of sand cause great variatiation in the grading of coarse aggregates does not effect thse properties to the extent of fine agggregates .
Coarse aggregates are supplied in nominal sizes . Coarse aggregregates and their grading as suggested by ISI are given in Table 15.5.
Coarse single sized aggregate nominal size and gradings as suggested by ISI are given in Table 15.6. Aggregates having all its particles predominantly of one uniform size , is known as single sized aggregates .
Deleterious materials in the aggregates
Iron pyrites , coal , mica , shale , clay , alkali , organic impurities are some of the materials whose presence in the aggregates is viewed as harmful . These materials should not be present in such quantity which may affect the strength and durability of the concrete . They should also not be attacking the reinforcement embedded in concrete . Aggregates which are chemically reactive with alkalies of cement are harmful as they may cause cracking of concrete . Deleterious materials cause followig affects :
(i) They interfere with the hydration of cement
(ii) They affect bond between aggregates and cement paste .
(iii) They reduce the strength and durability of cement concrete .
(iv) They modify the setting action and contributes to efflorescene .
Maximum quantities of deleterious materials in the aggregates should not exceed the limits given in Table 15.4 as per IS : 383 -1963 .
As a Thumb rule , the sum of percentages of all the deleterious substances , should not exceed 5 percent
(i) They interfere with the hydration of cement
(ii) They affect bond between aggregates and cement paste .
(iii) They reduce the strength and durability of cement concrete .
(iv) They modify the setting action and contributes to efflorescene .
Maximum quantities of deleterious materials in the aggregates should not exceed the limits given in Table 15.4 as per IS : 383 -1963 .
As a Thumb rule , the sum of percentages of all the deleterious substances , should not exceed 5 percent
Porosity and absorption 2
In field conditions nearly all the aggreate have some moisture . Fine aggregates increase in volume due to presence of moisture . Fine aggregates increase in volume due to presence of moisture . and hence suitable allowance must be made while taking amount of it . Also free moisture must be considere as a part of the mixing water and must be subtracted from the required amount of water to water and must be subtracted from the required amount of waer to be added . WHile batching the materials the weights of aggregates must be increased to compensate for the moisture they contain . However , in field , effort should be made to bring the aggregates to saturated surface dry condition , by sprinking water on coarse aggregates heap few hours before using the aggregates .
To maintain the w/c ratio , the knowledge of moisture content of an aggregates is important . Total water required for a constant w/c ratio will depend upon the type of moisture content prsent in the aggregates and is computed as follows :
(1) In bone -dry aggregates - Total water to be added = water absorbed by aggregates in 24 hours + Effective water .
(ii)Air dry condition . Total watr to be added = water absorbed by aggregates in 10 to 15 minutexs + effective water .
(iii)Saturated dry condition . Total water to be added = efective water
(iv) Moist aggregate - Total water to be added = Effective water - water available at aggreate surface .
(vi) Bulking of sand . Bulking means increase in volume . Fine aggregates bulk i volume when they possess some moistuee . Bulking is due to the formation of a thin film of water around the fine aggregate or sand particles . Tickness of water film goes on increasing with more and more moisture and consequently increase in volume continue . But after certain percentage of water , increae in volume completely vanishes and volume occupied by sand becomes equal to the volume of dry sand . Percentage moisture content and percentage bulking of sand is exhibited in Fig 15.2
To compensate the bulking effect , extra sand should be added in the mix so that the ratio of coarse to fine aggregates is maintained at a specified value . if this effect is not taken into consideration , the amount of and in the mix will be less than the required amount and the resulting concrete becomes harsh . Finer sands exhibit greater percentage of bulking than the coarser ones . Increase in moisture content may vary 25 to 40 percent when moisture content is 5 to 8 percent by weight .
To maintain the w/c ratio , the knowledge of moisture content of an aggregates is important . Total water required for a constant w/c ratio will depend upon the type of moisture content prsent in the aggregates and is computed as follows :
(1) In bone -dry aggregates - Total water to be added = water absorbed by aggregates in 24 hours + Effective water .
(ii)Air dry condition . Total watr to be added = water absorbed by aggregates in 10 to 15 minutexs + effective water .
(iii)Saturated dry condition . Total water to be added = efective water
(iv) Moist aggregate - Total water to be added = Effective water - water available at aggreate surface .
(vi) Bulking of sand . Bulking means increase in volume . Fine aggregates bulk i volume when they possess some moistuee . Bulking is due to the formation of a thin film of water around the fine aggregate or sand particles . Tickness of water film goes on increasing with more and more moisture and consequently increase in volume continue . But after certain percentage of water , increae in volume completely vanishes and volume occupied by sand becomes equal to the volume of dry sand . Percentage moisture content and percentage bulking of sand is exhibited in Fig 15.2
To compensate the bulking effect , extra sand should be added in the mix so that the ratio of coarse to fine aggregates is maintained at a specified value . if this effect is not taken into consideration , the amount of and in the mix will be less than the required amount and the resulting concrete becomes harsh . Finer sands exhibit greater percentage of bulking than the coarser ones . Increase in moisture content may vary 25 to 40 percent when moisture content is 5 to 8 percent by weight .
Porosity and absorption
Due to the presence of air bubles left during the formation or on account of the decomposition of certain minerals by atmospheric effect , small holes are formed in the rock which are known as pores . All the aggregates irrespective of their source have some percentage of these pores , through which water can penetrate . An aggregates which does not have an moisture content either in the pores or on the surface is said to be bone dry aggregate . When all the pores are filled with moisture but surface is dry , it is known as saturated surface dry aggregates . When along with all the pores filled with moisture but surface is dry , it is known as saturated surface dry aggregate . When along with all the pors filled with water , surface is also wet , the aggregate is said to be moist aggregate .
Surcface texture
Bond between aggregates particles and cement paste is greatly dependent on the surface texture of the aggregates paticles . Roughness of surface and surface porosity of the aggregate particles ar the main elements on which bond depends . An aggregate with rough surface will have a better bond than with a smooth surface aggregate . Similarly an aggregates with account of suction of cement paste into these pores . Surface of the aggregate as per IS : 383 -1963 may be glassy , smooth , granular , crystalline or honey combed . Aggregate having glassy surface should not be used . All other types of surfaces exhibit good bond .
Characteristics of Aggregates
A good aggregates should not contain ant deleterious materials which may cause physical and chemical changes in the concrete . An aggregates should have clean , uncoated , properly shaped particles of strong , dense , durable mineral and rock materials . Some of the important characteristics of aggregae are given below which may affect the performance of the concrete .
1. shape of the particles . As per IS : 383 - 1963 shape of the particle of the aggregate may be classified as rounded , regular , angular and flaky .
Rounded aggregates have about 35 percent of voids . It gives minimum ratio of surface area to a given volume of aggregates and hence require minimum water for lubricant . it gives good workability for the specified amount of water and also requires less cement for a particular w/c ratio . But such an aggregates does not have good interlocking effect and hence bound between aggregate and cement plaster is low and hence it does not give high strength concrete .
Irregular aggregates gives higher percentage of voids which may be as much as 37 percent . This aggregates exchibits lesser workability and requires more of cement . Its interlocking effect is better than rounded aggregates , but still not adequate enough for high strength concrete .
Angular aggregates have void percentage up to 40percent or 41 percent . it requires more water for lubrication and exhibits least workability for a specific /c ratio . it has very good interlocking effect and hence most suitable for high strenght concrete .
Flat , elongated or flaky particles in aggregates , are objectionable . besides decrease in workability , flaky particles in the aggregates should not be more than 10 to 15 percent .
1. shape of the particles . As per IS : 383 - 1963 shape of the particle of the aggregate may be classified as rounded , regular , angular and flaky .
Rounded aggregates have about 35 percent of voids . It gives minimum ratio of surface area to a given volume of aggregates and hence require minimum water for lubricant . it gives good workability for the specified amount of water and also requires less cement for a particular w/c ratio . But such an aggregates does not have good interlocking effect and hence bound between aggregate and cement plaster is low and hence it does not give high strength concrete .
Irregular aggregates gives higher percentage of voids which may be as much as 37 percent . This aggregates exchibits lesser workability and requires more of cement . Its interlocking effect is better than rounded aggregates , but still not adequate enough for high strength concrete .
Angular aggregates have void percentage up to 40percent or 41 percent . it requires more water for lubrication and exhibits least workability for a specific /c ratio . it has very good interlocking effect and hence most suitable for high strenght concrete .
Flat , elongated or flaky particles in aggregates , are objectionable . besides decrease in workability , flaky particles in the aggregates should not be more than 10 to 15 percent .
Aggregates
Mineral filler materials , used in cement concrete ,m are known as aggregates . Sand , gravel , crushed rock and other mineral fillers are used as aggregates . In cement concrete volume occupied b aggregates is about 75 percent of the total volume of the concrete . Almost any material , provided it hs required strength , durability and sound , can be usd as an aggregates for making concrete .
According to the size , aggregates may be classified under two categories :
Coarse aggregates - It is the aggregates whose particles completely pass through 75 mm mesh sieve and are entirely retained on 4.75mm mesh sieve . Aggregates having its particles greater than 75mm is known as cyclopean aggregates .
Fine aggregate . It is the aggregates whose particles pass through 4.75 mm mesh sieve but are completely retained on 0.07 mm mesh . Particles finer than 0,06 mm come under silts and clays and are considered as harmful ingredients .
According to the size , aggregates may be classified under two categories :
Coarse aggregates - It is the aggregates whose particles completely pass through 75 mm mesh sieve and are entirely retained on 4.75mm mesh sieve . Aggregates having its particles greater than 75mm is known as cyclopean aggregates .
Fine aggregate . It is the aggregates whose particles pass through 4.75 mm mesh sieve but are completely retained on 0.07 mm mesh . Particles finer than 0,06 mm come under silts and clays and are considered as harmful ingredients .
Chemical Requirement of Cement
Chemical composition of ordinary or rapid-hardening cements when tested accroding to IS : 4032 - 1968 should be as follows :
1. Ratio of percentage of lime to percentage of silica , alumina and iron oxide when calculated by formula ,
CaO - 0.7 SO3 / 2.8 SiO2 + 1.2 Ai2 O3 + 0.65 Fe2 O3
2. Weight of insoluble residue not more than 1.5 percent
3. weight of magnesia not more than 6 percent
4. Ratio of percentage of alumina to that of iron oxide not less than 0.66
5. Total sulphur content in form of S03 not more than 2.75 percent
6. Total loss on ignition not more than 4 percent
In the case of low heat cement the percentage of lime , after deduction of that necessary to combine with sulphuric anhydride ( S03) , present in cement shall be as follows :
Not more than 2.4 SiO 2 + 1.2 A12o3 + 0.65 Fe2O3
In all other chemical composition , low heat cement shall comply the requirements specified in 2, 3 , 4, 5 , and 6
1. Ratio of percentage of lime to percentage of silica , alumina and iron oxide when calculated by formula ,
CaO - 0.7 SO3 / 2.8 SiO2 + 1.2 Ai2 O3 + 0.65 Fe2 O3
2. Weight of insoluble residue not more than 1.5 percent
3. weight of magnesia not more than 6 percent
4. Ratio of percentage of alumina to that of iron oxide not less than 0.66
5. Total sulphur content in form of S03 not more than 2.75 percent
6. Total loss on ignition not more than 4 percent
In the case of low heat cement the percentage of lime , after deduction of that necessary to combine with sulphuric anhydride ( S03) , present in cement shall be as follows :
Not more than 2.4 SiO 2 + 1.2 A12o3 + 0.65 Fe2O3
In all other chemical composition , low heat cement shall comply the requirements specified in 2, 3 , 4, 5 , and 6
Heat of hydration
Chemical reaction between water and cement compounds is known as hydration . Druing hydration of the cement , sufficient heat is generated . The process of heat generation is quite rapid in the initial phase of the setting but its rate diminiseh with the passage of time . Special care has to be taken to dissipate this heat otherwise mass concrete works are likely to developed cracks . For mass concrte works low heat cement should be used . heat of hydration for low heat cement should be as follows . This recommendation is based on IS: 4031 -1968 .
After 7 days not more than 65 calories per gram and after 28 days not more than 75 calories per gram of cement .
All the physical requirement of cement are given in Table 15.3 as per the recommendations of IS : 269 - 1967 .
After 7 days not more than 65 calories per gram and after 28 days not more than 75 calories per gram of cement .
All the physical requirement of cement are given in Table 15.3 as per the recommendations of IS : 269 - 1967 .
soundness
Presence of excess quantities of free lime and magnesia in the cement , causes unsoundness in the cement . These substances slake very slowly and cause volumetric expansion in already set concrete , which may result in the distegration of the concrete . Soundness of the cement is measured either by Lechateliar method or by Autoclave method . All the sound cements should not exhibit expansion of more than 10mm by Le-chatelier method and 0.5 % by Autoclave method . Le-chatelier method of test is done as given is done as given is IS : 4031 -1968 .
Tensile strength
For assessing tensile strength of the cement , six standard briquettes are made from cement mortar . ALl these briquettes are made from cement mortar . All these briquettes are fratured after 1 day , 3 days and 7 days of immersion in water . The average strength of briquettes ater 1 , 3 and 7 days immersion should be as follow :
Time immersion Ordinary cement rapid hardening cement
after 1 days - 20kg/cm3
after 3 days 20kg/cm2 30 kg/cm3
after 7 days 25 kg/cm2 -
Time immersion Ordinary cement rapid hardening cement
after 1 days - 20kg/cm3
after 3 days 20kg/cm2 30 kg/cm3
after 7 days 25 kg/cm2 -
Tuesday, September 27, 2011
compressive strength
The quality of cement is judged from the compressive strength of the cement and sand mortar . 1: 3 cement sand mortar is used for assessing compressive strength of the cement . The compressing strength at the time of failure for ordinary cement should not less than the followingt values :
After 3 days 160 kg/cm2
After 7 days 220kg/cm2
After 3 days 160 kg/cm2
After 7 days 220kg/cm2
Monday, September 26, 2011
setting time
In order that the cement concrete may be palced in position of its use suitably and coveniently it is essential that the initial setting time is not too small . Similary after concrete has been placed and finisehd at its appropriate place , it should harden as early as possible so that the structure is put to use at the earliest . This cement should not lose its plasticity till various operations such as mixing , transporting ,placing and finishing are completed . The initial setting is a stage in the process of hardening that after this any crack in the concrete will not reunite .
1. Fineness
Rate of chemical reaction depends largely upon the fineness of grinding of cement . Finer the grinding , greater is the rate of reaction which hastens the early development of strength / Coarser cement particles also settle down in concrete which cause bleading . Too much fineness is also undersirable because it generates greater heat and concrete is likely to develop cracks . Fineness is emasured either in terms of percentage of weight retained after sieving or surface area in cm2 per gram of cement .
Physical specifications for cement
The physical properties of Portland cement are the fineness of grinding , the setting time , the strength , the soundness and heat of hydration . All these properties have been given in IS : 269 - 1967 and are briefly discussed here :
Storage of cement
Cement has to be stored in factories where it is manufactured and also at field construction sites where it is to be used . Moisture is the greatest enemy of cement . Cement has great affinity for moisture and hence it should be stored in such a way that moisture may not reach it . If somehow moisture happens to approach cement , it gets set , in form of lumps . If lumps formed are so hard that they cannot be pressed to powder between the fingers , it should be taken for granted that cement has been rendered useless . hence cement should be stored in specially constructed stores having damp proof floors , water proof walls and leak proof roofs . Cement stakes should be raised leaving a clear distance of 30 cm from the walls of the room . height of the stake should not exceed the height of 15 bags . Width of the stake should be limited to 3m . Stocks received first should also be issued first . All the doors , windows and ventilators should also be issued first . All the doors , windows and ventilators should be effectively sealed to prevent ingress of moisture in the store .
Water proofing cement
It is ordinary cement mixed with small percentage of some metal (AI and Ca ) stearate , at the time of grinding . Concrete made with such a cement is more resistant to water penetration and is used for the construction of water retaining structures like tanks , reservoirs , swimming pools , dams , bridge piers , retaining walls etc. This concrete is also more resistant to the corrosive action of acids and alkalies which are mostly found in the industrial waters .
Water repellent cement
This cement is used where water tight conditions are predominant . This cement is nothing but an ordinary cement mixed with small percentage of water-proofing compounds in suitable proportion . This cement is manufactured under trade name of "Aqua-crete"
Quick setting cement
When concrete has to be laid under water , quick setting cement can be advantageously used . The setting action of this cement starts within five minutes and it becomes stone-hard in less than one hour . This property of cement is developed by adding small percentage of aluminium sulphate and also by grinding this cement much finer than ordinary cement .
Expansive cement
This cement has a property of expanding while hardening whereas other cement shrink . Shrinkage cracks of ordinary cements may be eliminated by adding suitable proportions of expansive cement to it . In repair works also this cement is quite useful . Opened up joints can be repaired with this cement to make them water tight .
Super-sulphate cement
This cement is made by grinding a mixture of well granulated blast furnance slag ( 80 to 85 percent ) calcium sulphate (10 to 15 percent ) and ordinary cement ( 1 to 2 percentg ) . This cement is ground finer than the Portland cement . One of the significant properties of this cement is its low total heat of hydration . It is therefore very useful for mass concrete works . This cement is highly restaint to chemical attack . Concrete made from this type of cement expands if curing is done under water and shrinks if curing is done in air .
OIl well cement . This cement is usee for cementing oil wells
Oil wells are very deep . ordinary cement if used at sucvh depths will harden before it could reach its place of use . Oil well cement should be capable of being pumped for about 3 hours when subjected to high pressure and temperature . Thus cement to be used for this purpose should have the property of slow setting and must harden quickly after settting . This is accomplished by adjustingthe compound composition of cement or by adding retarders to the ordinary cement . This is possible by adjusting the proportion of iron oxide so that all the alumina is converted to Tetra calcium alumino ferrite ( C4AF) . The proportion of tri-calcium aluminate ( C3A) formed is , therefore , very small and setting time of cement is increased .
The function of cement in oil well is to fill the space between the steel lining tube and wall of the well and also to grout porous strata to prevent water or gas from gaining access to the oil bearing strata . Oil well cements besides prventing water from infilterating the oil bearing strata also protect the oil well casing from corrosion , help support the oil well casing , and thus reduce the tension in steel pipe .
The function of cement in oil well is to fill the space between the steel lining tube and wall of the well and also to grout porous strata to prevent water or gas from gaining access to the oil bearing strata . Oil well cements besides prventing water from infilterating the oil bearing strata also protect the oil well casing from corrosion , help support the oil well casing , and thus reduce the tension in steel pipe .
Pozzuolanic Cement
This cement is produced by grinding together a mixture of 80 to 60 percent of Portland cement and 20 to 40 percent of Pozzuolana . Pozzuolana may be a natural active material , such as volcanic ash or pumice or an artificial product such as burnt clay or shale containing silicious and aluminous mineral substances . The rate of development of strength is lower than that of normal Portland cement , especially at low temperatures .
Pozzuolana in optimum proportions with cement (20 to 30 percent of Pozzuolana ) improves the quality of concrete . it increases the workability , lowers heat of hydration and increases the water tightness . This cement has got greater resistance against sulphatic action and sea waters. Moreover it decreases the cost and is usefu; in the mass concreting works .
Pozzuolana in optimum proportions with cement (20 to 30 percent of Pozzuolana ) improves the quality of concrete . it increases the workability , lowers heat of hydration and increases the water tightness . This cement has got greater resistance against sulphatic action and sea waters. Moreover it decreases the cost and is usefu; in the mass concreting works .
Sunday, September 25, 2011
High alumina cement
This cement is very much resistant to sea water attack .
Its comprssive strength is nearly double of that of ordinary cement /
Thereis no trace of free lime and hence this cement is more sound than ordinary cement .
There is no trace of free lime and hence this cement is more sound than ordinary cement .
It is highly resistant to sulphate bearing waters and sea waters and is used for constructions near sea shore and also under water .
It is also used for making refractory and heat resistant concrete .
It is used for sealing rocks or concreteing against internal water flow .
It is not used for mass concrete works as it generates rapid heat of hyration .
This cement is called cement Fondu in France , "lighting " in England and "lumnite" in united states . While using , this cement must not be mixed with any other types of cement as heat evolved during setting is greater than any other cement .
Its comprssive strength is nearly double of that of ordinary cement /
Thereis no trace of free lime and hence this cement is more sound than ordinary cement .
There is no trace of free lime and hence this cement is more sound than ordinary cement .
It is highly resistant to sulphate bearing waters and sea waters and is used for constructions near sea shore and also under water .
It is also used for making refractory and heat resistant concrete .
It is used for sealing rocks or concreteing against internal water flow .
It is not used for mass concrete works as it generates rapid heat of hyration .
This cement is called cement Fondu in France , "lighting " in England and "lumnite" in united states . While using , this cement must not be mixed with any other types of cement as heat evolved during setting is greater than any other cement .
High alumina cement 2
These pigs are broken up and ground to required finess . The fineness of grinding of this cement is to 8 to 10 percent higher than that of ordinary cement . This cement is very dark in colour , almost black powder . in this cement setting time is controlled by the rate of cooling of the fused product and not by adding gypsum . Following are the special characteristics of this cement :
- Its initial setting time is 3 to 6 hours and finals etting takes palce within 2 hours of the initial setting . .
- Due to high percentage of aluminates being present this cement develops stength very fast . In 24 hours it develops as muich strength as an ordinay
High alumina cement
This cement is also known as aluminous cement . it contains as high as 35 percent to 45 percent of aluminates . This cement is manufactured from Bauxite and chalk or lime stone . bauxite and chalk or lime stone are first of all mixed dry and then heated until molten mass is obtained , which is later casted into pigs .
White and coloured cement
It is an ordinary Portland Cement having pure white colour . it is very costly cement since lot of precautions have to be taken in its manufacture . It is use for terrazzo flooring , face plasters , traffic curbs , aerodrome markings and other ornamental works .Snow crete , silvi -crete , Atlas etc . are the patented forms of white cement . Strength of this cement is slightly less than that of ordinary cement but it is 4 to 5 times costlier than ordinary cement .
Grey colour of the cement is due to the presence of iron oxide . In the manufacture of white Portland cement , iron oxide is limited to less than 1 percent . Also superior raw materials such as china clay and pure lime stone are choosen in its manufacture . For clinkering or klining process , oil is used in place of powdered coal to avoid adulteration by coal ash . In the absence of iron oxide sodium aluminium fluoride ( cryolite ) is added to act as a fluxing agent .
Coloured cement are produced by adding suitable minerals pigments to ordinary , or white cements . Oigments 5 to 10 percent , free from soluble slats are added to the cement during grinding . Following pigments are commonly used :
Red , Yellow , Brown , Black - iron oxide
Black , Brown - manganese dioxide
Green - Chromium dioxide
Blue - cobalt blue , ultra -marine blue
Black - carbon pigments .
Colourd cement are sold in the market under the patented names of colour-crete , rain bow ' , 'snow em' etc . They are mostly used for giving decorative finishes to buildings , swimmings pools floors , fountains etc .
Grey colour of the cement is due to the presence of iron oxide . In the manufacture of white Portland cement , iron oxide is limited to less than 1 percent . Also superior raw materials such as china clay and pure lime stone are choosen in its manufacture . For clinkering or klining process , oil is used in place of powdered coal to avoid adulteration by coal ash . In the absence of iron oxide sodium aluminium fluoride ( cryolite ) is added to act as a fluxing agent .
Coloured cement are produced by adding suitable minerals pigments to ordinary , or white cements . Oigments 5 to 10 percent , free from soluble slats are added to the cement during grinding . Following pigments are commonly used :
Red , Yellow , Brown , Black - iron oxide
Black , Brown - manganese dioxide
Green - Chromium dioxide
Blue - cobalt blue , ultra -marine blue
Black - carbon pigments .
Colourd cement are sold in the market under the patented names of colour-crete , rain bow ' , 'snow em' etc . They are mostly used for giving decorative finishes to buildings , swimmings pools floors , fountains etc .
Air entraining cement
Air entraining cement is just the ordinary cement in which 0.01 to 0.05 by weight of air entraining agents have been added . Air entraining agents are foaming agent such as vinsol , resin and darex . Air entraining foaming made with such a cement contains munute , well distributed air bubbles throughtout the concrete mass . Due to air bubbles strength of this concrete gets reduced by 10 to 15 percent . Air content in the form of the concrete . Such a cement is resistant to severe frost action and is immune to surface scaling due to application of coomon salt or calcium chloride used for de-icing purposes of the concrete pavements . Concrete made from this cement is more plastic and workable and develops less segregation .
sulphate resistant cement
Ordinary Portland cement does not resist the sulphatic action to a large extent . Disintegration due to sulphatic action is due to the presence of tri-calcium aluminate which reacts with sulphates and forms sulpho-aluminates and causing swelling and disintegration . To make cement more sulphate resistant percentage of C3A is reduced whereas C2S is increased . Rate of hardening of this cement is slow and requires longer period for curing . To offset the slower rate of hardening duew to changed chemical composition , sulphate resistant cements are ground a little finer than ordinary cements .
Blast furnance slag cement
It is a cement manufactued by grinding specifically proportioned amounts of ordinary cement clinkers , with granulated blast furnance slag of selected quality . When Portland cement and slag are ground together , the resulting cement is known by the name Portland -sLAG CEMENT . When lime and slag are ground together it is called lime -slag cement . The percentage of slag in Portland slag cement varies from 40 to 70 percent whereas it varies from 70 to 90 percent in the case of lime slag cement . Lime slag cement is not very good resistat of air and frost and hence its use is restricted to only damp situation . Portland slag cement offers goof rsistance to corrosion and good bond with steel reinforcement . This cement is extensively used in the manufacture of pre-fabricated reinforced concreete units . There is one more cement in which slag is used . it is a sulphate-slag cement . in this cement slag varies from 80 to 90 percent . It also contains about 5 percent Portland cement clinkers . This cement is highly resistant to sulphate action and hence recommendd to be used in martine works and other underground works .
Low Heat Cement
In the case of mass concrete structures such as dams , retaining walls , bridge abutments , rate of loss of heat of hydration from the surface is much lower than that generated . This causes rise in temerature inside the mass of concrete and may develop thermal and shrinkage cracks if proper precautions are not taken . Under such cricumstances low heat cement . Calcium aluminate and tri-calcium silicate ar reduced while those of di-calcium silicate and Tetra-calcium alumino ferrite increased . By this measure the rate of evolution of heat of hydration is considerably reduced . Low heat cement has not only slower rate of heat generation but also greater resistance to cracking . In the initial stage of setting and hardening , rate of heat evolution of heat evolution is small as rate of chemical reaction is slow . But in the later stage rate of setting and hardening is faster than ordinary cement . The ultimate strengrth attained by this cement is practically the same as that attained by an ordinary cement . The heat generated by ordinary cement in three days is nearly 80 calcories per gram of cement whreas for low heat cement it is of the order of 50 calories per gram of cement . This cement is manufactured only to special order and its initial setting time should not be less than 60 minutes . This cement offers greater sulphate resistance , due to decresed amount of tri-calcium aluminate . This cement is however not suitable for ordinary structure
Rapid hardening cement
This cement is use for cold-weather concreting because its rapid rate of strength development and consequent high rate of heat evolution , protects concrete against freezing . This cement is also useful in the manufacture of precast elements .
Ordinary Portland Cement
This cement is also know as normal setting cement and is recommended for adoption for all types of structures . it is used in pavements , reinforced concrete buildings , tanks , culverts and all such structures where heat of hydration will not cause any defeact . This cement has low resistance to sulphate reaction / Its rate of gaining strength , heat of hydration , drying shrinkage and resistance to cracking are ,moderate .
Saturday, September 24, 2011
Types of Cement
Most commonly used cement in structures is the ordinary Portland cement . But for use under specific conditions , a number of special types of Portland cements have been developed . Following are some of the cements in most common use under oridnary as well as specific conditions :
1. Ordianry Portland cement .
2. Rapid hardening Cement
3.Low heat cement
4.Sulphate resistant cement
5.Blast furnance slag cement
Air entraning cement
7. White and coloured cement
8.High alumina cement
9. Pozzuolanic cement
10. Oil well cement
11. Super sulphate cement
12. Expansive cement
13. Quick setting cement '
14. Water repellent cement '
15. Water proofing cement
1. Ordianry Portland cement .
2. Rapid hardening Cement
3.Low heat cement
4.Sulphate resistant cement
5.Blast furnance slag cement
Air entraning cement
7. White and coloured cement
8.High alumina cement
9. Pozzuolanic cement
10. Oil well cement
11. Super sulphate cement
12. Expansive cement
13. Quick setting cement '
14. Water repellent cement '
15. Water proofing cement
Prcentage of Bogue Compound
During manufacture of cement , if there is free lime left in the cement due to under burning of clinkers , and amount of this uncombined lime (CaO) in the finished cement is considerable , expansion and disruption of concrete may evenrtually occur .
Different types of cements can be developed by changing the relative proportions of the four Bogue compounds and also fineness of the cement . This variation can be achieveced by suitably changing the composition of raw materials .
Different types of cements can be developed by changing the relative proportions of the four Bogue compounds and also fineness of the cement . This variation can be achieveced by suitably changing the composition of raw materials .
Friday, September 23, 2011
Responsibilities
Traditional Method
This method can be clear cut division of design and construction works . The client will engage different architects or engineers to design the works and they will take full responsibilities for construction of the works from the pre-tender stage until the completion stage .
Design and Build Method
This method provides a single point contact and responsibility by the contractor . Therefore the contractor is solely responsible for failure in design or the construction . In short , the client has only one person to deal with if the project is faced with an problems .
Management Contracting method
- The client will have to choose the professional team who will be well coordinated through all the stages . The success of the project will depend on the management contractor's skills and an element of trust is essential .
This method can be clear cut division of design and construction works . The client will engage different architects or engineers to design the works and they will take full responsibilities for construction of the works from the pre-tender stage until the completion stage .
Design and Build Method
This method provides a single point contact and responsibility by the contractor . Therefore the contractor is solely responsible for failure in design or the construction . In short , the client has only one person to deal with if the project is faced with an problems .
Management Contracting method
- The client will have to choose the professional team who will be well coordinated through all the stages . The success of the project will depend on the management contractor's skills and an element of trust is essential .
Risk
Design and Build Method
- All the risks can lie almost wholly with the contractor
Management Contracting method
- The client ratain most of the risks .
Traditional method
-The risks are generally fair and balanced between the parties to the cotnract .
Price Completion
Traditional method
This method allows certainty in cost and time before coimmitment to build . There will be clear accountability and cost minitoring at all stages .
Management Contracting Method
-The client is committed to start building on a cost plan , project drawings and specifications only .
Design and Build Method
The client can expct a guaranteed cost and completion date .
- All the risks can lie almost wholly with the contractor
Management Contracting method
- The client ratain most of the risks .
Traditional method
-The risks are generally fair and balanced between the parties to the cotnract .
Price Completion
Traditional method
This method allows certainty in cost and time before coimmitment to build . There will be clear accountability and cost minitoring at all stages .
Management Contracting Method
-The client is committed to start building on a cost plan , project drawings and specifications only .
Design and Build Method
The client can expct a guaranteed cost and completion date .
Design and Manage Process
Project brief and clients require
Feasibility study
Concept design
Detail Design
Bidi=dding and Contracting
Construction
Commission and hand over
The Process of Project Designing and Construction in the Design and Manage Procurement System .
Feasibility study
Concept design
Detail Design
Bidi=dding and Contracting
Construction
Commission and hand over
The Process of Project Designing and Construction in the Design and Manage Procurement System .
Management Contracting and Construction Management Process
Project brief
Feasibility study
Tender doc & client require
Concept deisgn
Biding & contracting
Construction ( detail deisgn and / or shop drawings ) - package conbtractors responsibility
Commission and hand over
The process of project Designing and Construction in the Management Contracting and Professional Construction Management Procurement System .
Feasibility study
Tender doc & client require
Concept deisgn
Biding & contracting
Construction ( detail deisgn and / or shop drawings ) - package conbtractors responsibility
Commission and hand over
The process of project Designing and Construction in the Management Contracting and Professional Construction Management Procurement System .
Design and Build Procurement Process
Project brief
Feasibility study
Tender documentation 'Concept design
Tender and contracting
Construction
Commission and hand over 'Detail design
The Ubtegrated Process of Project Designing and Construction in the Design and Build Procurement System .
Feasibility study
Tender documentation 'Concept design
Tender and contracting
Construction
Commission and hand over 'Detail design
The Ubtegrated Process of Project Designing and Construction in the Design and Build Procurement System .
Traditional Procurement Process
- Project brief
- Feasibility study
- Concept deisgn Detil deisg
- Tender and contract
- construction
- Commission and handover
The linear or sequential process of the Traditional Procurement System .
Partnering ( advantages )
- Encourages the parties to work together to attain the same desired result - contract completion - instead of engaging in fingerpointing whenever problem occur
- Helps eliminate surprises through increased communications . Surprises can lead to delays and additional costs
- Can minimise litigation by establishing informal conflict management procedures
- Avoid disuputes throught the establishment of informal conflict management procedures . oarties are able tpo anticipate and resolve problems before they become formal " disputes
Partnering ( consideration )
- All parties seek a win-win solution
- Each partner is aware of the other's needs , concerns , objectives and is interested in helping their partner to achieve this
- Value is placed on long-term relationship
- Overall performance is improved
- All understand the no one benefits from exploiting the other
- Innovation is encouraged
Partnering
Commitment from top management
Free and open exchange of information
Based on equality of all partners
Keeps project team together
Interest in mutual profitability
Problem Resolution .
Free and open exchange of information
Based on equality of all partners
Keeps project team together
Interest in mutual profitability
Problem Resolution .
Partnering
The creation of a special relationship between contracting parties in the design / construction industry .
This relationship encourages the parties to change their traditional adversarial relationship to a more co-operative , team based approach , which promotes the achievement of mutually beneficial goals , including the prevention of major disputes .
This relationship encourages the parties to change their traditional adversarial relationship to a more co-operative , team based approach , which promotes the achievement of mutually beneficial goals , including the prevention of major disputes .
Construction Management
project Manager
May be an organisation or an individual
Guides the client in the selection of a suitable procurement system , appoint all members of the construction team and control and organise the project .
Appointed on a fee basis , which is not dependent on the cost of the contract . This tends to ensure that the project manager works solely for the client's interest , as he earns no commision .
May be an organisation or an individual
Guides the client in the selection of a suitable procurement system , appoint all members of the construction team and control and organise the project .
Appointed on a fee basis , which is not dependent on the cost of the contract . This tends to ensure that the project manager works solely for the client's interest , as he earns no commision .
Construction Management
Construction management is similar in most respects to management contracting exept that whereas with managment contracting the contract is between the client and the contractor ( the subcontractors are engaged through the main contractor) in construction management the contracts for the work packages are with the client .
The construction manager is employed to maanage the construction work . this sytem tends to be used only on large , specialist technical projects such as power stations .
The construction manager is employed to maanage the construction work . this sytem tends to be used only on large , specialist technical projects such as power stations .
Advantage of management contracting
To developer
- work can start early
- allowing design adn construction to overlap
To contractor
-very few risks
The PM and Qs control costs '
- Cost exceed the budget are borne by the client .
- work can start early
- allowing design adn construction to overlap
To contractor
-very few risks
The PM and Qs control costs '
- Cost exceed the budget are borne by the client .
Sub - contractor
Subcontractors enter into a standard JCT type of contract with the management contractor carry out construction work
It is the management contractor who has a contractual relationship with the subcontractors who carry out the work , not the client .
If any problems arise it is the management contractor who must pursue the subcontractor for a remedy .
Subcontractors are normally appointed by competitive tendering based on the drawings and bills of quantities .
It is the management contractor who has a contractual relationship with the subcontractors who carry out the work , not the client .
If any problems arise it is the management contractor who must pursue the subcontractor for a remedy .
Subcontractors are normally appointed by competitive tendering based on the drawings and bills of quantities .
Management
"Fast - tracking " procurement approach
A contractor is contracted and paid a fee to manage , procure and supervise the construction of a project rather than to build the project .
The actual construction works are contracted out to many package or specialist contractors/ sub contractors .
The mnanagement contractor is employed as a construction consultant to be part of the client's team
The package contractors are in contract with the management contractor .
A contractor is contracted and paid a fee to manage , procure and supervise the construction of a project rather than to build the project .
The actual construction works are contracted out to many package or specialist contractors/ sub contractors .
The mnanagement contractor is employed as a construction consultant to be part of the client's team
The package contractors are in contract with the management contractor .
Advantage of develop and construct
The developer is only dealing with one organisation that has sole responsibility for the success or failure of the design and construction .
It allows the developer to be aware of the total amount of financial commitment prior to the commencement of construction .
It allows the developer to be aware of the total amount of financial commitment prior to the commencement of construction .
Develop and Construct
develop and construct is anither of the integrated procurement approach which is very much similar to design and build .
The contractor is still given the responsibility for both the design and construction of the project .
The difference is that , under this method the client's design consultants prepare the concept sketches or designs and passed them to the contractor who will develop them and produced the detailed working drawings . The contractor will then construct and complete the project based on what it has developed and produced .
The contractor is still given the responsibility for both the design and construction of the project .
The difference is that , under this method the client's design consultants prepare the concept sketches or designs and passed them to the contractor who will develop them and produced the detailed working drawings . The contractor will then construct and complete the project based on what it has developed and produced .
Turnkey Contract
Turnkey contract is an American term for " all in " or package contract . Under this arrangement , a contractor is commissioned to undertake the responsibilities for everthing necessary and required for the construction , completion , comissioning and hand over the project .
The word "turnkey" means that , upon completion , the client is given the key and he can then enter the project by "turning the key " . The contractor will have to do everthing from preparing project brief , getting approval , designing , financing , construction , furnishing and decorating to commissioning and handing over completed , cleaned and ready for use project .
The word "turnkey" means that , upon completion , the client is given the key and he can then enter the project by "turning the key " . The contractor will have to do everthing from preparing project brief , getting approval , designing , financing , construction , furnishing and decorating to commissioning and handing over completed , cleaned and ready for use project .
Design and Build Uses
Normally used for standard tyoe building i.e. industrial units
Useful for repetitive types of buildings , which the contractor has constructed previously .
Past experience and familiarity of the design and construction should result in cost savings for the client
Useful for repetitive types of buildings , which the contractor has constructed previously .
Past experience and familiarity of the design and construction should result in cost savings for the client
Design and Build
Design and build is under integrated procurement system
Under this system , the client together with is / her consultants will prepare a tender or bidding document that include the project brief and client's requirements and invite a number of contractors to bid .
For the purpose of submitting tenders , the invited contractors will produce their own design , construction and cost proposal . Very often the successful contractor will into a contract based on lump sum price and a fixed duration .
The contract may be on a fixed price or cost reimbursement basis , which may be either negotiated , or subject to tender
Under this system , the client together with is / her consultants will prepare a tender or bidding document that include the project brief and client's requirements and invite a number of contractors to bid .
For the purpose of submitting tenders , the invited contractors will produce their own design , construction and cost proposal . Very often the successful contractor will into a contract based on lump sum price and a fixed duration .
The contract may be on a fixed price or cost reimbursement basis , which may be either negotiated , or subject to tender
Integrated
Package deal
Commonly called the ' all in' contracting
A contractor is given the responsibility for everthing that is required and necessary for the design , construction and delivery of the project .
The services of the contractor will include the preparation of project brief , sketch and final working drawings , getting all the approval from authorities , project financing , construction , furnishing and commissioning of all equipments and acessories and handing over the project to the client .
Commonly called the ' all in' contracting
A contractor is given the responsibility for everthing that is required and necessary for the design , construction and delivery of the project .
The services of the contractor will include the preparation of project brief , sketch and final working drawings , getting all the approval from authorities , project financing , construction , furnishing and commissioning of all equipments and acessories and handing over the project to the client .
Traditional Method ( disadvantages )
-Length of time taken in the design and preparation of the Bill of Quantities
-Cost of preparation for the Bill of Quantities ( approximately 3.5 percent of the contract sum ) .
-Cost of preparation for the Bill of Quantities ( approximately 3.5 percent of the contract sum ) .
Advantage of traditional Method
- All parties have a clear picture as to the extent of their commitments . it gives a clear breakdown of the cost of all aspects of the projects .
- The unit rates allow ease of valuation for the stage payments of work carried out and for any variation to the original design .
- The unit rates allow ease of valuation for the stage payments of work carried out and for any variation to the original design .
Traditional method
When constructing new building it is possible to assess the cost of the work to be done , in which case a fixed price can be the basis for the contract
A fixed price can , however , be on the whole copntract ,a section of work or can apply to a unit rate . The price is fixed although the amount of work is not know .
The building owner will appoint a team of consultants to act on his behalf to produce construction drawings , specification and tender document and to administrator the tendering processes to selecta contractor
Once selected and awarded the contract , the contractor will carry out based on the drawings and specification prepard by the client's consultant .
Negotiated Tender
- Can be considered as an innovative approach to speed up the selection of contractor and the commencement of construction
-Involve preliminary discussion with selected few contractors , submission of fixed tender and / or cost negotiation
A fixed price can , however , be on the whole copntract ,a section of work or can apply to a unit rate . The price is fixed although the amount of work is not know .
The building owner will appoint a team of consultants to act on his behalf to produce construction drawings , specification and tender document and to administrator the tendering processes to selecta contractor
Once selected and awarded the contract , the contractor will carry out based on the drawings and specification prepard by the client's consultant .
Negotiated Tender
- Can be considered as an innovative approach to speed up the selection of contractor and the commencement of construction
-Involve preliminary discussion with selected few contractors , submission of fixed tender and / or cost negotiation
Thursday, September 22, 2011
Traditional Method
-A Fixed Price Contract involves the contractor agreeing to construct the building as specified in the drawing and Bills of Quantities ( B&Q) for the client for an agreeed suym , by an agreed date .
Although it is called a fixed price contract it does allow for the contractor to claim additional costs for any variations to the specification .
Although it is called a fixed price contract it does allow for the contractor to claim additional costs for any variations to the specification .
Allowance can also be claimed by the contractor for an extension of time if there is a delay which beyond his control .
When constructing new building it is possible to assess the cost of the work to be done , in which case a fixed price can be the basis for the contract .
A fixed price can , however , be on the whole contract , a section of works or can appl to a unit rate . The price is fixed although the amount of work is not nown .
tRADITIONAL mETHOD
Traditional Method - ( sequential method - tendering process )
- Accelerated Method - negotiated tender
This method usually uses the standard form of contract by the joint Contract Tribunal ( JCT) or a smilar .
The contract requires the contractor to carry out the construction accroding to the drawings and specification drawn up by the design team .
All work is supervised on behalf of the client by the design team leader , which is normally the architect or on civil engineering projects , the consultant civil engineer .
- Accelerated Method - negotiated tender
This method usually uses the standard form of contract by the joint Contract Tribunal ( JCT) or a smilar .
The contract requires the contractor to carry out the construction accroding to the drawings and specification drawn up by the design team .
All work is supervised on behalf of the client by the design team leader , which is normally the architect or on civil engineering projects , the consultant civil engineer .
Post titleTYPES OF PROCUREMENT
aPART FROM THE TRADITIONAL APPROACH , THERE ARE NOW OTHER "FAST-TRACKING " OR INNOVATI PRCUREMENT SYSTEMS USED BY THE CONSTRUCTION INDUSTRY WORLD WIDE .
tHE DIFFERENT PROCUREMENT SYSTEM DIFFER FROM EACH OTHER IN TERM OF ALLLOCATION OF RESPONSIBILITIES , ACTIVITIES SEQUENCING , PROCESS AND PROCEDURE AND ORGANIZATIONAL APPROACH N PROJECT DELIVERY .
pROCUREMENT SELECTION
- tHE FOLLOWIG NEED TO BE CONSIDERED WHEN CHOOSING THE MOST APPROPRIATE PROCUREMENT PATH FOR THE PROPOSED PROJECT :
- TIME
- eCONOMIC
-SIZE
--COMPLEXITY
-FINANCE
-ACCOUNTABILITY
-POLITICAL
-LEGAL
-COST
-RISK
-TYPE OF CLIENT '
-DESIGN
-QUALITY ASSURANCE
-TECHNOLOGICAL
-ORGAISATION
-MARKET
- TIME
- eCONOMIC
-SIZE
--COMPLEXITY
-FINANCE
-ACCOUNTABILITY
-POLITICAL
-LEGAL
-COST
-RISK
-TYPE OF CLIENT '
-DESIGN
-QUALITY ASSURANCE
-TECHNOLOGICAL
-ORGAISATION
-MARKET
Procurement Selextion
- The selection of appropriate contract arrangement is difficult owing to the diverse range of options and professional advice is available .
- In the past few years there has been a significant shift in the way that that construction project are procured .
-This partially response to the changes which have occured within the construction industry . Individuals experience , prejudices , vested interests , the desire to impove the system and familiarity with paritcular methods influenced procuirement recommendations .
-Those who had bad experiencewith a particular procurement method will
-In reality too little is known and too little rersearch has been undertaken properly to evaluate the various procurement options .
-In practice , there are both sucessful and unsuccesful projects that have used identical mneans and methods of contract document .
-Procurement advisers should offer advise in the absence of any vested interests or personal gains .
-Sound , reliable and impartial advise necessary from those who have the proficient skills , knowledge and expertise .
- In the past few years there has been a significant shift in the way that that construction project are procured .
-This partially response to the changes which have occured within the construction industry . Individuals experience , prejudices , vested interests , the desire to impove the system and familiarity with paritcular methods influenced procuirement recommendations .
-Those who had bad experiencewith a particular procurement method will
-In reality too little is known and too little rersearch has been undertaken properly to evaluate the various procurement options .
-In practice , there are both sucessful and unsuccesful projects that have used identical mneans and methods of contract document .
-Procurement advisers should offer advise in the absence of any vested interests or personal gains .
-Sound , reliable and impartial advise necessary from those who have the proficient skills , knowledge and expertise .
What is Procurement
Procurement comes the word procure which literally means " to obtain by care or effort " , to bring about " and " to acquire "
System is about organized method , approach , technique , process or procedure
Project procurement has been described as an organized methods or process and procedure for clients to obtain or acquire construction products .
Projects procurement has been described as an organized methods or process and procedure for clients to obtain or acruire construction products .
Projects procurement is very much concerned with the organized methods or process and procedure of obtaining or acquiring a construction product such as a house , shopping complex or road and jetty .
System is about organized method , approach , technique , process or procedure
Project procurement has been described as an organized methods or process and procedure for clients to obtain or acquire construction products .
Projects procurement has been described as an organized methods or process and procedure for clients to obtain or acruire construction products .
Projects procurement is very much concerned with the organized methods or process and procedure of obtaining or acquiring a construction product such as a house , shopping complex or road and jetty .
Constraints and problem encountered :
- Long and costly negotiation process
- Suspicion and lack of trust
- Financial
- legislation
- Risks
Benefit of B.O.T
- Obtaining efficiency as private sector will apply commercial discipline in the executive of project budget aand timetables .
- Market competition andommercial manaementis introdEnsure long term investment by investor .
- Reducing the size oif the public sector .
- Relievingfinancial and public sector brrowing
- Economical viable projects are undertaken in the private sector .
- Transfer industrial risks ( investment cost , operating cost , etc ) to the private sector .
- An exceptional opportunity for the country to recover and explore unused productivity source .
- Accelerating growth .
- Obtaining efficiency as private sector wll apply commercial discipline in the execution of project budget and timetables .
- Market competition and commercial management is introduced .
- Ensure long term investment by investor
- Reducing the size of the public sector .
BUILT , OPERATE , transfer (B.O.T)
- As one method of privasation in our country
- Privitasation policy started in 1983
- Only in 1985 - serriouslyffortury goverment
- Malaysiadefines privatization as the transfer of the goverment's obligation in providing goods and servic that aronally within its domain to the private sector .
- In the process the goverment transfer its ownership of assets or rights to use to the private sector together wwith its other commitment , rights , 'liabilities .
- Can take the form of : B.O.T ( Built , Operate , Transfer. E.g. PLUS , B.O.O.L ( Built , Operate , Transfer . E.g. : Plus , B.O.O.L ( built , operate , Own , Licence , - TV3 , ) T.O.O ( Transfer , Operate , Own , - TELEKOM ) .
- B.O.T is a concept of development where private sector is given a CONCESSION of sponsoring and subsequently operate a certain project ( usually infrastructural projects ) which traditionally is the domain of the goverment with their own cost .
- The Project us then transferred back to the goverment then may decide whether to further extend the concession to the original promoter with some return or may decide to operate on its own .
- .O.T has been widely practised especially in many developed countries such as United State , Uk , Switzerland .
- Uk - EUROTUNNEL ( British & French Promoter ) .
- Australia -Sydney Harbour Tunnel .
Wednesday, September 21, 2011
Setting and Hardening of cement
During burning and fusion , all the above listed ingredients undergo chemical combination and form , what are knows as Bogue compounds , in the finely ground cement . Bogue compounds and their accepted abbreviated forms are given below :
Name of Bogue compound
1. Tri-calcium silicate ( 3 Cao , SiO )
Di- calcium silicate
3. Tri - calcium aluminate
4. Tetra -calcium alumino ferrite
The proportion of above stated Bogue compunds vary , in various types of cement . Tri-calcium silicate ( CaS ) and di-calcium silicate are the compounds mostly responsible for the strength characteristic of the cement .
Tri-calcium hydrates first and is responsible for most of early strength of the concrete . Strength acquired during frist 7 days is mostly due to hydration of tri-calcium silicate . Di-calcium silicate reacts with water at a very slow rate and hence strength of the concete after first 7 days , is mainly due to hydration of theis compounds . Di- calcium silicate starts contributing strength after 7 days of its placement and continues for about one year , though rate of getting strength from this compounds goes on decreases with passage of time . Tetra-calcium alumino -ferrite is more or less in - active compounds and does not play any significant role in setting properties or hardening properties of tyhe cement . After addition of water in cement , tri-calcium aluminate is the first compounds which starts hydrating and is responsible for early setting of the cement . Hydration of tri-calcium aluminate does not contribute any strength to the concretye . It is mainly responsible for setting action of the cement .
Although the processes of setting and hardening of cement take place simultaneously , yet there is difference between the two . Setting of the cement is changing plastic state of cement paste , to stiff solid state which is not strong enough and has a very small compressive strength . Hardening of the cement concrete is the rtate o gaining stength .With the passage of time as the hydration proceeds , the compressive strnegth of the product goes on inc
Tri-calcium aluminate . As soon as wtert is added to the cement , hydrolysis of this compounds immdediately starts . This process may be delayed for about 30 to 40 minute by adding 2 to 3 percent poweder gypsum . This delay is essential to gain time for mixing water with the cement , transportation of mix to the place of use and finishing processes . It is the compounds responsible for early setting of the cement . It does not contribute any strength to the concrete . Setting effect is maximuym during first 24 hours and it does notextend beyond 28 hours . A cement havinh low percentage of crack development . It is generates low heat , resissts better sulphate action and possesss high ultimate strength .
Tri-calcium silicate . This compounds is next to set a harden . First 7 ir 8 days stnregth , is imparted by the hydration of thjis compounds only . During the reaction again considerable heat of hydration is generated .
Di-calcium silicate . Hydrolysis of this compounds is cimparatively slow . Hydration of this compounds starts about 7 days after mixing water in the cement concrete and continues for a bout a year .
It is clear from above mentioned discussions that setting and hardening of cement paste is mainly due to the hydration and hydrolysis action of the above mentioned four compounds Out of the four Tetra calcium Alumino Ferrite is pradctically inactive and does not contribute to any strength and setting of the cement . Tri-calcium silicate is the best cementing materials and greater percentage of it in the cement result in a type of cement which develops high early strength . Higher percentage of tri-calcium aluminate results in a type of cement which sets immediately . Hence in short it can be said that the rapidity of intialsetting of the cement is controlled by amount of tri-calcium silicate . Strength of cement concrete , developing after 7 or 8 days of its placement is depndent on the amount of Di-calcium silicate . As already strated earlier , setting gypsum poweder in the cement . Percentage contents of Bogue compouns and composition of some of the important cement are given in TABLE 15.1 AND 15.2 .
Name of Bogue compound
1. Tri-calcium silicate ( 3 Cao , SiO )
Di- calcium silicate
3. Tri - calcium aluminate
4. Tetra -calcium alumino ferrite
The proportion of above stated Bogue compunds vary , in various types of cement . Tri-calcium silicate ( CaS ) and di-calcium silicate are the compounds mostly responsible for the strength characteristic of the cement .
Tri-calcium hydrates first and is responsible for most of early strength of the concrete . Strength acquired during frist 7 days is mostly due to hydration of tri-calcium silicate . Di-calcium silicate reacts with water at a very slow rate and hence strength of the concete after first 7 days , is mainly due to hydration of theis compounds . Di- calcium silicate starts contributing strength after 7 days of its placement and continues for about one year , though rate of getting strength from this compounds goes on decreases with passage of time . Tetra-calcium alumino -ferrite is more or less in - active compounds and does not play any significant role in setting properties or hardening properties of tyhe cement . After addition of water in cement , tri-calcium aluminate is the first compounds which starts hydrating and is responsible for early setting of the cement . Hydration of tri-calcium aluminate does not contribute any strength to the concretye . It is mainly responsible for setting action of the cement .
Although the processes of setting and hardening of cement take place simultaneously , yet there is difference between the two . Setting of the cement is changing plastic state of cement paste , to stiff solid state which is not strong enough and has a very small compressive strength . Hardening of the cement concrete is the rtate o gaining stength .With the passage of time as the hydration proceeds , the compressive strnegth of the product goes on inc
Tri-calcium aluminate . As soon as wtert is added to the cement , hydrolysis of this compounds immdediately starts . This process may be delayed for about 30 to 40 minute by adding 2 to 3 percent poweder gypsum . This delay is essential to gain time for mixing water with the cement , transportation of mix to the place of use and finishing processes . It is the compounds responsible for early setting of the cement . It does not contribute any strength to the concrete . Setting effect is maximuym during first 24 hours and it does notextend beyond 28 hours . A cement havinh low percentage of crack development . It is generates low heat , resissts better sulphate action and possesss high ultimate strength .
Tri-calcium silicate . This compounds is next to set a harden . First 7 ir 8 days stnregth , is imparted by the hydration of thjis compounds only . During the reaction again considerable heat of hydration is generated .
Di-calcium silicate . Hydrolysis of this compounds is cimparatively slow . Hydration of this compounds starts about 7 days after mixing water in the cement concrete and continues for a bout a year .
It is clear from above mentioned discussions that setting and hardening of cement paste is mainly due to the hydration and hydrolysis action of the above mentioned four compounds Out of the four Tetra calcium Alumino Ferrite is pradctically inactive and does not contribute to any strength and setting of the cement . Tri-calcium silicate is the best cementing materials and greater percentage of it in the cement result in a type of cement which develops high early strength . Higher percentage of tri-calcium aluminate results in a type of cement which sets immediately . Hence in short it can be said that the rapidity of intialsetting of the cement is controlled by amount of tri-calcium silicate . Strength of cement concrete , developing after 7 or 8 days of its placement is depndent on the amount of Di-calcium silicate . As already strated earlier , setting gypsum poweder in the cement . Percentage contents of Bogue compouns and composition of some of the important cement are given in TABLE 15.1 AND 15.2 .
Chemical Composition of Cement
Silica , lime and alumina are the three basuc raw materials of cement . Iron oxide , sulphur trioxide , and other alkalies are alsomaterials are intimately mixed and then burnt at a clinkering temperature of about 1400 C .
Clinkers are lastly gound to a fine powser toi get cement . Following are the chief chemical ingredient and their proportions in an ordinary portland cement :
Lime 60-67 percent '
Sikica 17 to 25 percent 'Alumina 3 to 8 percent
Magnesia 0.1 to 4 percent
Sulphur trioxide 1 to 3 perent
Iron oxide 0.5 to 6 percent
Soda and potash alkalies 0.5 to 1 percent
Clinkers are lastly gound to a fine powser toi get cement . Following are the chief chemical ingredient and their proportions in an ordinary portland cement :
Lime 60-67 percent '
Sikica 17 to 25 percent 'Alumina 3 to 8 percent
Magnesia 0.1 to 4 percent
Sulphur trioxide 1 to 3 perent
Iron oxide 0.5 to 6 percent
Soda and potash alkalies 0.5 to 1 percent
Portland cement
Ordinary cement is mostly called portland cement . The ordinary cement , after setting , resembles in colour to that of a stone quarried near portland in England and hence called portland cement . Cement was first introduced in use by a Leeds ( Englsih ) brick layer named Joseph Aspdin in 1824 .
cement
Cement is a binding material which is obtained by burning together at high temperature calcareous , siliceous and argillaceous raw materials mixed in definite proportion and crushing the resulting clinkers to a fine powder . It is the most costly ingradient in the concrete and is available in variety of forms . The properties of various cement are dependent upon chemical composition , the process adopted in manufacture and degree of fineness .
Plain Concrete
Cement concrete is an artificial material obtained by mixing together cemen , coarse aggregte and water , in suitable proportions . All these ingredients , when freshly mixed , produce a plastic mass which can be poired into suitable forms or moulds , to give a desire shape to the rtesultingh solid mass . Plastic mass gets converted innto solid stone like hard mass with passage of time , due to chemical action taking place between cement and water . Aggregate ( btoh coarse as well as fine ) which are mineral materials like sand , gravel , crushed stone etc . do not undergo any chemical change . They simply provide mass volume to the concrete and reduce shrinkage effect in it . Hardened cement concrete resembles stone , in weight , strength and hardness .
A chemical reaction between cement and water is responsible for setting and hardening of cement concrete. Setting of cement concrete is the stage or phase when concrete mass changes from plastic stage to a non-flowing mass . Process of gaining strenbgth by the mass of cement concret3 is known as hardening of cement concrete . In short , the process of loosing plasticity is known as setting ,whereas process of gaining strength is nown as hardening of the cement concrete . The process of setting of cement concrete can be divided into three distinct stages . The first stage of setting is known as initial setting of the cement concrete . . The first stage of setting is known as initial setting of the cement concrete . This pohase of setting may take from 45 minmuits to about 8-10 hours in completion . In this stage of setting , plasticity of concrete is dexreased markedly and concrete develops considerable resistance to flow . The second stage or phase of setting is known as final setting of the concrete . This phase of setting is known as final setting of the concrtete . The phase may last 5 to 20 hour after mixing of water , depending upon the type of cement used and other weather conditions . During this period concrete looses all its plasticity and gets converted into relatively soft solid mass , whose surface is not very hard . The last or third stage envolves progressive hardening and increase in strength of the concrete . The process of setting of concrete is almost completed within 24 hours of miux ing water , but process of hardening or gaining strength contuinues for years . In the initia stage of hardening , rate of gaining strength by the concrete is quite rapid , but with passage of time it goes on slowing down . it is seen that cement concrete . The process of setting of concrete is almost completed within 24 hours of mixing water , but process of hardening or gaining strength by the concrete is quite rapid , but with passage of time goes on slowing down . It is seen that cement concrete acquire almost 80-90 percent of its potential strength within first 30 days after mixinh water in it .
The prperties of cement concrete are dependent upon the quantity and proportions of the ingredients use in th mix . The controls exercised during various operations starting from mixing of aggregates to the placement in the forms or moulds , also greatly influence the proprties of the concrete . Plain cement concrete is very strong in compression but has little strength in tension . Due to weakness in tension , plain concrete is also weak in tortision , shear and bending . Hence use of plain cement concrete is advocated only.Howecer it is seen that in most of the cases , structural members are subjected to shear , bending and torsion . Concrete is quite strong in compression and its weakness in tenion can be made good by embedding steel bars in the tensile zones of the structural members . Cement concrete , in which steel rods are embedded is called reinforced cement concrete or R.C.C.
A chemical reaction between cement and water is responsible for setting and hardening of cement concrete. Setting of cement concrete is the stage or phase when concrete mass changes from plastic stage to a non-flowing mass . Process of gaining strenbgth by the mass of cement concret3 is known as hardening of cement concrete . In short , the process of loosing plasticity is known as setting ,whereas process of gaining strength is nown as hardening of the cement concrete . The process of setting of cement concrete can be divided into three distinct stages . The first stage of setting is known as initial setting of the cement concrete . . The first stage of setting is known as initial setting of the cement concrete . This pohase of setting may take from 45 minmuits to about 8-10 hours in completion . In this stage of setting , plasticity of concrete is dexreased markedly and concrete develops considerable resistance to flow . The second stage or phase of setting is known as final setting of the concrete . This phase of setting is known as final setting of the concrtete . The phase may last 5 to 20 hour after mixing of water , depending upon the type of cement used and other weather conditions . During this period concrete looses all its plasticity and gets converted into relatively soft solid mass , whose surface is not very hard . The last or third stage envolves progressive hardening and increase in strength of the concrete . The process of setting of concrete is almost completed within 24 hours of miux ing water , but process of hardening or gaining strength contuinues for years . In the initia stage of hardening , rate of gaining strength by the concrete is quite rapid , but with passage of time it goes on slowing down . it is seen that cement concrete . The process of setting of concrete is almost completed within 24 hours of mixing water , but process of hardening or gaining strength by the concrete is quite rapid , but with passage of time goes on slowing down . It is seen that cement concrete acquire almost 80-90 percent of its potential strength within first 30 days after mixinh water in it .
The prperties of cement concrete are dependent upon the quantity and proportions of the ingredients use in th mix . The controls exercised during various operations starting from mixing of aggregates to the placement in the forms or moulds , also greatly influence the proprties of the concrete . Plain cement concrete is very strong in compression but has little strength in tension . Due to weakness in tension , plain concrete is also weak in tortision , shear and bending . Hence use of plain cement concrete is advocated only.Howecer it is seen that in most of the cases , structural members are subjected to shear , bending and torsion . Concrete is quite strong in compression and its weakness in tenion can be made good by embedding steel bars in the tensile zones of the structural members . Cement concrete , in which steel rods are embedded is called reinforced cement concrete or R.C.C.
Tuesday, September 20, 2011
Macadam ( Pre-mix )
- Macadams are materials which rely on particle interlock to provide strength and stiffness .
- They normally contain a wide range of particles sizes .
- Macadams coated with a bituminous binder are described as coated macadams .
- The bitumen acts as a lubricant as well as binder during compaction .
- Macadams use smaller quantities of bitumen than asphalt . Hence , cost is cheaper than asphalt .
pitch
- Pitch is the residue adter distilling tar from coal .
- Coal tar and pitch soften at lower temperature , are less plastic , are able to resist temperature variation .
- Less costly than bitumen product .
- Application : - Pitch mastic flooring , paints , damp-proof membranes , felt saturant ( Materials for damp-prrof membrane ) .
Tar / Coal Tar
- Produced by destructive distillation of organic materials .
- Coal tar run at a lower temperature than asphalt
- Resistant to petroleum - based solvents
- Has a low bitumen content generally has high specific gravity and v iscosities , and good adhesive properties .
- Oxidizes more easily .
- Ordinary coal tar is suitable for many of the applications of bitumen due to it has the advantages of superior adhesion in damp situation .
- Example : Tars for road purpose , damp -proof couse .
Asphalt
- Dark brown or black solids or sem i-solids which are found in natural state or the residue obtained in refining / distillation of petroleum .
- is readily soluble in most petroleum products .
- Composed almost entirely ob bitumen
- Asphalt are bituminous mixtures containing substantial amounts of fine material in the form of sand and filter .
- The sand and filler , together with binder , form a stiff 'mortar ' which provides strength and stiffness for the final product .
Bitumen
- Bitumen is a generic name applied to various mixture of hydrocarbon
- Non-crystalline solid or viscous material
- Soluble in carbon disulphide (CS2)
- ALl bitumen are thermoplastic i.e. soften when it is heated
- Bitumen lacks of stability .
- Waterproof .
- Not to be used by itself only .
- Normally serve as a material in mastic asphalt , adhesive and paints as a saturant .
- Application : Paints , damp-proof membrane , waterproof building papers , adhesive for woodblock flooring , curing membrane in concrete road base .
Types of bituminous product
- Bitumen
- Asphalt
-Cut-back asphalt : repair work
-emulsion asphalt : dampproofing purposes , and as tact - coat during road surfacing .
2. Macadam ( pre-mix )
Properties of Bituminous product
- Although bituminous materials are combustible , composite product such as mastic asphalt and pitch mastic are not combustible .
- Durable to resist acids , alkalis .
- Particularly pitch , are damaged by heat and sunlight .
- Embrittle at low temperature
- Flow under mechanical stress , particularly at high temperature .
- Naturally bituminous products is poisonous .
Properties of Bituminous product
- Bituminous products are usually dark brown or black and rely on pigments to give colour .
- All types are completely soluble in carbon disulphide (CS2) .
- They resist the passage of water and moisture .
- Materials applied in hot condition .
Disadvantages / problems of bituminous product
- They tend to become brittle at low temperatures and soft at high temperatures .
- They subject to creep ( Shear )
- They have low inherent stiffness .
Bituminous product offer following general attractions
- Excellent resistant to absorption / passage of water .
- Good adhesion to many material .
- Resistance to dilute acids and alkalis .
- Good flexibility at normal temperatures .
- Properties can be varied to suit application .
Bituminous Product
Generally usage of the term 'bituminous' covers product on bitumen , coal tar and pitch .
It can be natural or derivative from particular substance such as petroleum , natural sources , coal . Mostly in liquid form which serve as binder while ready to be used .
It can be natural or derivative from particular substance such as petroleum , natural sources , coal . Mostly in liquid form which serve as binder while ready to be used .
Monday, September 19, 2011
Plastic from Fruist waste
- USM reaserches have invented that could apparently use as plastic bags .
- Fruits skin (rambutan , bananas and jackfruit
-Cost effective ( 1o percent less )
-Naturally degrades within 3-6 months while they can last from 1-2 years o the shelve .
-More cost effective than biodegrable plastic made from sugar cane and husks .
Recycling Plastics
- There are some strong reasons for recycling plastic wherever possible .
- One of the biggest environmental prblems that the world faces is plastic waste .
- Most plastic do not degrade or deteriorate in the ground , hence lead to enrionmental hazard when used in landfill .
- Organic polymwers are a precious and finite resource
- Most of the plastic is made from petroleum which makes them difficult to break down and degrade .
Most of the plastic in construction can be separated from other easily .
Properties of Plastics
- Tensile strength : COmpare to same weight ratios , it has higher strength than most metals . Howevers , the elasticity is lower .
- Fire /heat : Thermoplastic soften at high temperature . And all plastic are combustible .
- No treatment can be done to prevent plastic become non-combustible . However , if fire-retardant additives is added , some plastic can be very difficult to ignite . e.g. PVC .
- Thermal Conductivity : Almost same as timber , which is comparatively low if compare to materials such as metal .
- Electrical Properties : Plastic are excellent insulators but electrostatic charges attract dust .
- Thermal expansion Generally , most of the plastics have several times expansion ability (Compare to steel ) while heat applied .
- Moisture Movement : Most plastic are resistant to water absorption , and therefore do not exhibit moisture movement .
- Durability : Mostl of the plastic do not rot or corrode . Generaally , they have good resistance on chemical substance in building works . Ultra-violet (UV) from sunlight is the chief factors that causing plastic product to deteriorate .
Types of Thermoplastic
- polyethylene , (PE)
- Polypropylene , (PP)
- Polyvinvyl chloride , (PVC)
- Polystyrene , (PS)
- Acrylonitrile-butadiene-styrene , (ABS)
- Styrene acrylonitrile , (AS)
- Polymethyl methacrylate , (PMMA)
- Polyvinyl alcohol , (PVA)
- Polyvinylidene chloride , (PVDC)
- Nylons .
- phenol - formaldehyde , (PF) .
- Urea - formaldehyde , (UF) .
- Melamine - formaldehyde , (MF)
- Epoxy , (EP)
- Unsaturated polyester , (UP)
- Polyurethane , (PU) .
- Silicones
- Polydiallyl phthalate , (PDAP) .
Types of Plastics
1. Thermoplastics
- Chemical structure remains unchanged during heating and shaping .
- More commercially used , comprising more than 70 percent of total plastics tonnage .
- Group of plastic that will be soften when heated and hard when cooled , regardless of the number of times the process is repeated .
- Can be reshaped and recycled .
- Having long chain-like molecular structure .
-
Undergo a curing process during heating and shaping , causing a permanent change ( called cross-linking ) in a molecular structure . - Group of plastic that will be formed permanently when cured .
- Cannot be reshaped or recycled .
- Having cage-like molecular structure .
- To shape a thermoplastic polymer it must be heated so that it softens to the consistency of a liquid .
- Are long-chain polymers in which helical or zig-zag molecular chains are free to strighten when the material is stretched , and recover when the load is removed .
Plastic Shaping Processes are Important
- Almost unlimited variety of part geometries .
- Less energy is required than for metals because processing temperat ures are much lower .
- Handling of product is simplified during production because of lower temperatures .
- Painting or plating is usually not required .
Sunday, September 18, 2011
Plastic products
- Applications of plastics have increased at a much faster rate than either metals or ceramics during the last 50 years .
- Many parts previously made of metals are now being made made of plastics .
- For example : plastic containers have been largely substituted for glass e.g. bottles and jars .
- Plastics can be shaped into a wide variety of product :
-Extruded section
Films
-Sheets
-Insulation coating on electric wires
-Fibers for texties
-Flooring and partition
- In addition , plastics are often the principal ingredient in other materials , such as
- Paints and varnishers
- Adhesives
- Various polymer matrix composites
- Many plastic shaping processes can be adapted to produce items made of rubbers and polymer matrix composites .
Double Glazing
- Reducing thermal loss and condensation and in providing sound insulation .
- Outer pane has a heat reflective layer on its inner surface , the reduce emissivity of the coated surface reduces transmission through the air space
- Gaps filled suitable gases can further reduce thermal transmittance .
- Double glazing with 6mm gap may be equivalent to a brick cavity wall .
- In extreme conditions differences between the atmospheric pressure , enclosed air can cause explosion or implosion .
Laminated Glass
- Consist of 2 sheets of annealed glass cemented together with a polyvinyl butyral interlayer .
- More resistant to breakage than wired glass
- Can be describes as a safety glass ( Wire glass is not ) .
- Special purposes such as security , one-way vision , solar radiation control , anti-fading , obscuration , fire resitance , manufestation , and alarm
Solar heat resisting glass
- Ordinary glass can only block long wave solar radiation from passing through
- But allow short wave solar radiation through objects on which solar radiation falls reradiates the heat .
- Used in Hot House or Green House .
- Act mainly by either reflection or absorption .
- Therefore is used to reduce the cost of air conditioning and reduce sun glare .
Special Glass
2. Diffused Reflection Glass
- It is used for glazing pictures and instrument dials .
- Both the surfaces of sheet , plate and float glass are lightly textured .
- So that within 20mm of the object to be viewed .
- It's completely transparent and non-reflective .
- It is also called Non-Reflective Glass .
- No glass gives one way vision .
- One way glass depends upon the lighting condition .
- On the viewing side , it should be less intense than the reverse .
- In most one way glass , a metallic film is applied .
- The glass either to float or plate glass reflects most of the light that falls ipon it .
- This film must be protected from abrasion .
Toughened Glass
- made in either plate , sheet or float glass .
- The glass is heated and suddenly cooled by jets of cool air .
- The cooled surface is put to compression while the interior is still in tension .
- There may be some distortions but the glass becomes stronger , tougher and flexible than the original annealed glass .
- Toughened glass is de-toughened by exposing to temp of about 300 celcius for long duration or too frequently and it is not fire-resisting .
- It is also called tempered glass .
Patterned Glass
- The glass has patterns impressed on it by rollers .
- In selecting this pattern , ease of cleaning must be considered together with obscuration and diffusion pattern .
Transparent glass
Float glass
- It is produced by the recently developed floating and continuous ribbon method
-Both sides are flat and parallel .
- It is produced by the recently developed floating and continuous ribbon method
-Both sides are flat and parallel .
Saturday, September 17, 2011
Translucent glass
- Rough Cast Glass
- It is called so because it was formely cast on sand bed .
- It is also known as frosted glass .
- Now is made by passing molten glass between rollers which impart a characteristic pattern on one side with the other side being smooth .
- The most commonly available size is in 6mm thick .
- Rough cast glass allow light to penetrate but causes images to be distorted .
- it is necessary where privary is the main consideration , eg . Bathrooms and gazed panels , doors .
- Wire mesh embedded centrally in the thickness of the glass
- The function of the wire mesh is to hold the glass fragments in the event of breakage but not to reinforce glass .
- it is usually in public buildings & for roof lights or doors . The wired glass is made in 2 patterns .
ii) Diamond - 20mm sided square .
Transparent glass
1. Clear sheet glass - Also called Drawn sheet glass
(ii) SA- Selected Glazing quality
(iii) SSQ - Special selected glazing quality .
2.Clear plate glass
(ii) SG - Selected glazing quality - suitable for superior work to make mirrors .
(iii) SQ - Silvering quality - Suitable for high class mirrors .
- B.S. 952 state
- Sheet glass has natural fire - finished surfaces but because of the 2 surfaces are never perfectly flat and parallel .
- There is always some distortion of vision and reflection
- There are mainly 3 main B.S. Grades :
(ii) SA- Selected Glazing quality
(iii) SSQ - Special selected glazing quality .
2.Clear plate glass
- B.S. 952 plate
- This glass has "flat & parallel" surface producing clear vision and reflection .
- Wired clear plate glass .
- 27 is 6mm thick & the normal size of the plate is 330 x 183 mmm , both Georgian & diamond pattern's of plate glass specified in the B.S. 952
(ii) SG - Selected glazing quality - suitable for superior work to make mirrors .
(iii) SQ - Silvering quality - Suitable for high class mirrors .
Types of glass
- Glass used in buildings may be classified into 3 general categories :
2) Translucent glass
3) Special glass .
Transparent
-Clear sheet glass
-Clear Plate Glass
-Float Glass
Translucent glass
-Rough cast glass
-Patterned glass
-Wired rough cast glass .
Special glass
- Toughening /Tempered glass
-Diffuse reflection glass
-One way glass
-Solar heat resisting glass
-X-ray resisting glass
-Heat resisting glass
-Antique glass .
Glass-recyclable Product
Re-cycling and environmental considerations includes :
- Glass is very suitable for recycling .
- Glass is an essential part of the glass-making process since it has a relatively low melting point .
- Conversely , if not recycled , glasss does not readily break down over time and can be hazard .
- High temperature are required for its manufacture .
Disadvantages of glazing (problem area )
- There are serious injury risks due to the sharp edges exposed by cutting or breakage
- Ordinary glass has poor thermal insulation properties leading to high heating gain in summer and high heat loss in winter .
Glazing
Glazing , which forms a very important part of most building , has the form of attractions :
Aa) It admits daylights while providing a weather proof barrier .
B) Daylight is known to have psychological benefits for people compared with artificial light source .
C) Plain glazing provides the interest of an external view .
D) Glazing provides an increased feeling of spaciousness in a room of a given size .
Glass is the most traditional material for glazing , offering the following benefits :
Aa) It admits daylights while providing a weather proof barrier .
B) Daylight is known to have psychological benefits for people compared with artificial light source .
C) Plain glazing provides the interest of an external view .
D) Glazing provides an increased feeling of spaciousness in a room of a given size .
Glass is the most traditional material for glazing , offering the following benefits :
- Glass is quite cheap to produce .
- glass is relatively hard and generally scratch resistant .
- Glass is quite inert and largely unaffected by exposure to normal atmospheres .
- The material is easy to cut .
- It has excellent optical properties .
Manufacture of Glass
The manufacture process :
Glass products are produced by several basic processes , or method such as .
2) Drawing
-Used to make sheet glass ( for window ) .
- The basic ingredients used in manufacture of glass are silica , limistone and soda ash .
- These ingredient are first ground finely and mixed in a proper proportion . The mixture is known as frit
- Cullet (broken or scrap glass )are fed also into the furnace to cause initial melting action , resulting in a sticky mass full of bubble .
- Further heating will cause loosing its viscous nature and become watery liquid , allowing all bubble to rise to the surface .
- The molten glass is cooled and it is worked and shaped (formed ) when it is viscous .
Glass products are produced by several basic processes , or method such as .
- Blowing by mouth
- Drawing
- Casting by float
- Rolling
- Pressing or Extrusion .
- Blowing + Moulding (blowing by mouth )
- This process is used to make small glass product . This involves blowing the viscous glass into shapes .
- Used to make / manufacture : Antique sheet glass and sand bottles .
2) Drawing
- The molten glaurs is put into a tank .
- An iron grille known as a 'bait" is lowered into the tank .
- The molten glass sticks to the grille and it is slowly lifted up , thereby drawing with it a sheet glass .
- The sheet of glass passes through annealing tower as it is pulled up .
- The glass is then gradually cooled as it get higher .
- The glass is cut , inspected , stored and dispatched .
-Used to make sheet glass ( for window ) .
Disadvantages of timber products over solid timber
- Rely a lot on the adhesive - some products deteriorate quickly in damp conditions eg kitchen and bathrooms
- Some products not as aesthetically attractive
- Adhesive may increase wear and tear on cutting tools used for processing products .
- Weaker bending strength .
- Creep levels may be increased .
Advantages of timber products over solid timber
- Competitive in price
-smaller section of tree
-pieces cut off or not suitable for solid timber may be suitable for timber products .
- Can be produced in larger sizes eg sheets , long length
- Less defects associated with solid timber .
- Weakness and distortion associated with grain can be overcome .
Advantages of plywood
- Better apperance
- Strong (a 3-ply board is 3 times as strong as solid board of the same thickness ) .
- Easily bent to given shape .
- Not much affected by climate change .
- Large size .
- Low expansion and shrinkage .
- Do not split easily when nailed near edge .
Wafer and orient strand board (OSB)
- Similar to chipboard but using larger flakes of wood , less adhesive required , improved strength and stiffness .
- Strength performance between plywood and chipboards
- Glued Laminated timber (Glulam )
- Large structural members produced by joining small strips of wood together with glue to size , shape and quality .
- Obtained by cutting rotary veneers from timber logs and bonded together , alternate layers being crossed .
- Glued wood panels comprising outer and inner sheets .
- Odd number of plies is usually used , so that symmetrical distribution of piles about the centre sheet
- High strength in both directions .
- If moisture content changes , equal and opposite bending effect occur , due to differential movement of symmetrically opposed sheets .
- Can be used in situation with variable moisture content with minimum distortion .
- For cladding , form facing for concrete .
- Expensive
- Commonly use as formwork , cladding and decoration purposes .
Timber product
- Fibre building boards
- Produced by pulverising of wood down to individual fibres and then compressing them to form large sheets .
- Small % of adhesive may be used as binder
- Various types of product obtained based on degree of compression of fibres .
- Eg Hardboard (highest density ) , medium density fibre board (MDF) and Softboard (lower density ) .
- Strength increases with density .
- Particle boards (chipboard )
- Advantages
-Dimensional stability
-A smooth splinter free surface
- Disadvantage
-Difficult to nail and can be quite bristle edges
-Access to the undefloor space can be difficult due to T&G edges for fire resistant .
-Health hazard if excess formaldehyde is been used during manufacture .
- Water and orient strand board (OSB)
- Similar to chipboard but using larger flakes of wood , less adhesive required , improved strength and stiffness .
- Strength performance between plywood and chipboard
- Glued Laminated timber (Glulam )
- Large structural members produced by joining small strips of wood together with glue to size , shape and quality .
Timber products / Application
- Timber in Malaysia are classified into the following strength groups :
- Certain types of timber are naturally durable : ( does not require treatment )
- Example Balau, Bitis , Chengal , Penaga (SG1) Belian , Mala Ulat , Kekatong (SG2) , Bekak , Delek , Keranji (SG 3) Giam , Malabera , Merbau , Resak (SG4) Tembusu (Sg 5) .
- From SG1 to SG7
- The applications of the timber are also specified with their respective strength group
-Example Structural components such as columns , beams , bearer , studs , joists , ties and struts -SG1 , SG2 , SG3 and SG4
- (refer to Malaysian Timber Industry Board for more information ) .
Construction Precautions Pressure -treated timber
- Avoid inhaling saw dust during cutting of pressure -treated timber
- Hands should be washed after handling the timber .
- Clothes should be washed separately from other items .
- Waste much be disposed off properly , it should not be burned .
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