Research On Material Design And Energy-saving Manufacturin Techniques For High Performance Concrete Pipe Piles

Prestressed high-strength concrete (PHC) pipe piles are the most widely used concrete members in building foundations nowadays. They are widely used in all kinds of engineering projects, such as industry and civil buildings, highway and railway, port and wharf constructions, due to the advantages of high strength, high density and high bearing capacity. In traditional manufacturing process, the curing condition of PHC piles is consist of steam curing and autoclaved curing, which requires large amount of energy. At the same time, the resources shortage and environmental pollution are more and more serious due to the development of economy and society. Energy conservation and pollution reduction become the focus of the construction industry and society. In addition, the concrete engineering environment is becoming more and more complex. Further investigation is needed about whether PHC piles can be applied to some harsh environmental conditions, such as sea water, saline-alkali and cold.Therefore, the paper focuses on the high energy consumption and insufficient durability of PHC piles, and an energy-saving manufacturing technique of high performance piles concrete with high strength is studied. A new concrete materials system and energy-saving curing process of PHC are designed. The setting and hardening performance and durability development of PHC under steam curing condition are investigated. An energy-saving manufacture technique of high performance PHC is obtained.The main work and results of the paper may be summarized as follows.(1) The influence of metakaolin to the setting and hardening performance of concrete is investigated, and the results indicate that concrete setting time is shortened by metakaolin and the early and latter strength can be enhanced. The appropriate dosage of metakaolin is between10%and15%. In addition, the water demand of concrete is increased by metakaolin and it is not appropriate to use metakaolin as the only mineral admixture in the preparation of high performance PHC.(2) Cementitious materials composite technique and particles density packing model are adopted to design the high performance PHC materials system. It is concluded that the complex cementitious material systems, consist of cement, metakaolin, slag, flay ash and limestone powder, may exhibit satisfied pozzolanic activity and filler effect. Concrete with the complex cementitious material systems perform high and early strength. Meanwhile, the workability of the concrete is satisfied.(3) Influence of steam curing parameters such as delay time, heating-up rate, thermostatic period and thermostatic temperature on hardening performance of high-strength concrete is studied. The results reveal that concrete strength can be improved with a longer delay time, a lower heating-up rate, an appropriate thermostatic period and thermostatic temperature. Furthermore, it is noted that the influence of delay time and heating-up rate on concrete strength are prominent, followed by thermostatic period and thermostatic temperature. Based on the systematic research, a non-autoclaved energy-saving curing technique for the manufacture of PHC piles is obtained.(4) The whole materials system of high performance PHC is designed in the paper. The mixture parameters and preparation process under energy-saving curing condition are researched. Based on the research above, a new energy-saving manufacture technology of high performance PHC is conducted.(5) The durability of high-strength concrete subjected to steam curing and standard curing is investigated comparatively. The influence of cementitious system and curing conditions on high-strength concrete durability is studied. It is concluded that permeability resistance, frost resistance and sulphate resistance of concrete is decreased by steam curing. However, the application of complex cementitious materials system can improve the durability of steam cured high-strength concrete and the durability of the PHC prepared with the energy-saving technique is satisfied.(6) The microstructure of steam cured high-strength concrete is researched systematically. The influence of the complex cementitious materials system on microstructure of steam cured concrete is investigated. The results show that the complex mineral admixtures promote concrete hydration, improve the composition and structure of hydration products. Pore structure is refined and improved while the damage to pore structure caused by steam curing is eliminated. The ITZ performance is improved and the bong performance of the pate and aggregate is enhanced. Meanwhile, the porosity of interface between paste and aggregate is decreased.(7) The energy-saving manufacture technique of high performance PHC was adopted in the practical production. The pilot test shows that the energy-saving manufacture technique can be conducted successfully. The mechanical properties and appearance quality of the energy-saving produced PHC piles are satisfied. The energy consumption in the curing process is decreased by70%, compared with the traditional curing condition. The promotion and application prospect of the new technique is optimistic.