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Important Provisions of CBC for PSC

Important Provisions of CBC for PSC. Cement…. Portland Pozzolona cement (PPC) shall not be used for PSC works

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Important Provisions of CBC for PSC

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  1. Important Provisions of CBC for PSC

  2. Cement… • Portland Pozzolona cement (PPC) shall not be used for PSC works • However Portland Blast Furnace Slag cement can be used for PSC. As the rate of development of strength is less, as compared to OPC, this shall be kept in mind while determining stage of pre-stressing and period of curing • Compatibility of chemical admixtures and super plasticizers with Portland Blast Furnace Slag cement shall be ensured by trials before use ( admixture shall conform to IS : 9103) • Sulphate resistance cement ( IS: 12330) shall not be used under conditions where concrete is exposed to risk of excessive chloride and sulphate both

  3. Exposure Conditions The general environment to which concrete will be exposed during its working life is classified in three levels of severity

  4. Concrete Grade • Minimum Grade for PSC : • Moderate Exposure : M35 • Severe Exposure : M40 • Extreme Exposure : M45

  5. Permeability • Permeability is one of the main characteristics influencing the durability of concrete • Permeability tests shall be mandatory for concrete bridges ( both RCC and PSC ) under severe and extreme exposure conditions • Under moderate exposure, Permeability test shall be mandatory for all major bridges • Permeability test shall be carried out as per procedure prescribed in appendix G of CBC. The depth of penetration of moisture shall not exceed 25mm

  6. W/C Ratio Limits for maximum w/c ratio are based upon environmental conditions as defined below :

  7. Cementitious Material Content Depending upon the environment to which the structure is likely to be exposed during its service life , minimum cementitious material in concrete shall be : Maximum cementitious material content shall be limited to 500kd/m3

  8. Production and Control of Concrete • Competent person who has been issued certificate by Divisional Engineer for executing and supervising concreting shall only supervise all stages of production of concrete • Batching : IS 4925 • Cement and aggregate : By mass • Water : by vol or by mass • Solid admixture : by mass • Liquid and paste admixture : by vol or by mass

  9. Production and Control of Concrete • Where weigh batching is not practicable the quantities of FA and CA may be determined by volume batching for concrete of grade upto M25. • If FA is moist and volume batching is adopted , allowances shall be made for bulking as per IS : 2386(pt3)

  10. Ready Mix Concrete • Checking suitability of admixtures : admixtures like water reducing agents, retarder etc. are used in RMC for retention of desired workability and to avoid setting of concrete. Admixtures should be tested for their suitability as per IS:9103 at the time of finalising mix design • Re-tempering with concrete : under any circumstances , re-tempering i.e. addition of water after initial mixing , shall not be allowed , as it may affect strength and other properties of concrete • RMC shall be delivered within 1.5 hrs when atmospheric temperature is >20 degrees and within 2 hrs when temp is < 20 degrees • The speed of transit agitators during transit shall not be less than 2 rpm and not more than 6 rpm

  11. Pre-stressing Steel • The wire and strands as supplied , should be self straightening when uncoiled • In no case, heat shall be applied to facilitate straightening of pre-stressing steel • Strands and hard drawn wires , used in pre-stressed concrete work shall be continuous over the entire length of tendon • HTS bars may be joined together by means of coupling • Welding shall not be permitted in pre-stressing steel

  12. ARRANGEMENT OF TENDONS AND POSITIONING • Permissible tolerance in the location of pre-stressing tendons shall be 5mm • Method of supporting and fixing thye tendons (or the sheeths) in position should be such that they will not be displaced by heavy or prolonged vibration, by pressure of the wet concrete, including upward thrust of concrete

  13. THANKS

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