The Preparation And Research In Performance Of The Hpc For The Wide Cast-in-situ Box Girder

Supported by Tianhe Airport two-channel, the mix design of box girder concrete is made according to big width, high strength, difficult construction and crack prevention of cast-in-place box girder. The pouring of concrete can be completed on time by the experiments of workability, physical and mechanical properties and durability, and controlling the temperature of concrete.In this paper, the mix design of high performance concrete can be made by two different fine aggregate, fine sand and medium sand. The mix proportion that meet the high flowing of concrete and the compressive strength of concrete should be designed by working performance test and mechanical properties test. Then the mix proportion can be optimized by admixture, cementing material and aggregate. The mix proportion also can be optimized by durability analysis, such as frost resistance, carbonation resistance and impermeability. Finally, in concrete engineering application, concrete quality should be strictly guaranteed by water consumption test and temperature monitoring.Research indicates that,(1) The fine sand possesses high mica content and large specific surface area, both of which will induce a decrease of high performance concrete strength and larger water reducing agent dosage. When the amount of cementing material in the fine concrete increased, the strength of concrete was not necessarily increasing. But when the content of cementing material reaches a certain value, the strength of concrete would decrease. The optimal amount of cementing material was445kg/m3in concrete. When preparing high performance concrete with fine sand, the sand ratio should decrease, and the optimal sand ratio was36%. Fly ash can improve the performance of concrete, but lower the early strength. The recommend amount of fly ash was18%. Different maintenance way had certain fluctuation. Outdoor natural curing could lower the strength. Preparation of concrete with later admixing could decrease the water reducing agent dosage significantly, but it easily caused bleeding.0.01%welan gum could prevent bleeding efficiently.(2) Preparation of concrete with medium sand could greatly increase the strength of concrete compared with that containing fine sand, and the content of water reducing agent would decrease. So the sand ratio should properly increase. When the water cement ratio fixed and the content of cement material increased, the strength of concrete would increase firstly, then it tends to increase gently. The critical point was465kg/m3. Fly ash had certain influence on the performance of concrete. The recommend amount of fly ash was18%. The pozzolanic effect of fly ash is not obvious at earlier stage but more prominent at later stage. So it could greatly improve the later strength and durability of concrete.Through the optimization of admixture, cement materials and aggregate, it could make high strength and high durability high performance concrete with medium sand.(3) Through the detection of the water consumption of concrete could monitor the mix proportion of concrete, ensuring the quality of concrete. Detecting the temperature of concrete could control temperature difference between internal and external of the concrete, preventing the early temperature crack.