3. Introduction Advantages Dis-advantages Methods of Pre-stressing Mix Design Curing Laboratory Test Visit Report

4. Pre cast concrete members are assembled and fastened together on the jobsite. They may be unreinforced,reinforced or prestressed. Precasting is beneficial because higher quality control and higher strength concrete. Prestressing is the deliberate creation of internal stress in a structure or system to improve its performance.

5. Very fast Construction. Less Man Power. High thermally insulated Better shear resistance High strength steel and concrete PC : 20-35 % reinforcement in RC Lighter section, Longer spans PC depth ~ 65-80% of RC depth Lighter foundations possible Crack less Better corrosion resistance, better durability Deflection control

6. Higher material costs. Higher material costs. Pre-stressing is an added cost. Pre-stressing is an added cost. PC Form work is more complex than RC PC Form work is more complex than RC PC is Not as ductile as RC. PC is Not as ductile as RC.

7. Prestressing is applied to concrete by means of high strength tendons (usually steel) in tension, passing through the concrete. This can be achieved in one of two ways, namely pretensioning and post tensioning, the main distinction between the two methods being weather the steel is tensioned before or after the concrete is cast, hence the terms “pre” and “post ”.

8. Pre-tensioning : Pre-tensioning : Steel tensioned before casting of concrete. Steel tensioned before casting of concrete. Strands are tensioned – concrete is cast around the strands- strands are released when concrete attains required strength. Strands are tensioned – concrete is cast around the strands- strands are released when concrete attains required strength.

9. Summary : 1.Stress strands. 2.Cast concrete. 3.Cut strands 3.Cut strands. 4.Force transferred to concrete by bond.

10. Post-tensioning : Post-tensioning : Steel tensioned after concrete is cast. Steel tensioned after concrete is cast. Post-tensioning is primarily an in situ operation uese in large span bridges. Post-tensioning is primarily an in situ operation uese in large span bridges. Prestress force is transferred to concrete via the end anchorage. Prestress force is transferred to concrete via the end anchorage.

11. Summary: Summary: 1. Provide tendon inside duct. 2. Cast concrete. 3. Tension tendon after concrete attains required strength. 4. Inject grout into duct.

13. All precast elements prestressed and nonprestressed elements are cured by steaming. The reason for curing by steaming is to accelerate the curing by heating without drying. The process takes place by covering the elements with canvas and then leading steam from a boiler plant to the elements under the canvas. The steam curing cycle is given on the below :

15. (1) (1)Pre-steaming period. Must never last less than 3 hours.Too early steaming of fresh concrete can adversely affect the final strength of the concrete. (2) (2)Temperature rise period. The length of this period is until max temperature is reached. With an idealized temperature rise rate of 20 deg C per hour it will typically last 2 - 3 hours. (3) Period at max temperature. The length of this period is practically until the needed concrete strength for demoulding / detensioning is reached. Typically 6 hours for nonprestressed concrete and 12 hours for prestressed concrete.

16. (4) Cooling period. The cooling period before uncovering of canvas should for good economy and to avoid the risk of cracks last at least one hour. However if needed for recast and if experience says that it can be done without risk of cracks then the period can be shortened down.

17. Procedure for steam curing

18. Compression test : Compression test :

19. Shear test : Shear test :

20. Aggregates properties test : Aggregates properties test :

21. Company system: Company system: 1. Sales 2. Estimation 3. Contracting 4. Design 5. Approval 6. Fabrication 7. Delivery 8. Erection

22. Some of the company products: Some of the company products: 1. Hollowcore slab 2. Double tee(TT) slab 3. Columns 4. Beams 5. Walls

24. HCS 150 HCS 185 HCS 200 HCS 265 HCS 380 HCS 320 HCS 300 HCS 400

25. LOAD BEARING CAPACITY GRAPH

26. DEFLECTION

28. LOAD BEARING CAPACITY GRAPH

29. DEFLECTION