| With the development of construction industry, such as bridges, housing, roads and other civil constructions, prestressed high strength concrete pipe piles (PHC pipe piles) has become one of the main structural materials of foundation engineering. Nowadays most PHC piles are produced with the curing system which includes steam curing and autoclaved curing in domestic manufacturers. Because of the shortcoming of environmental pollution, poor security, large energy consumption and poor durability, this process is not suit for requirements of energy conservation, emissions reduction and sustainable development of the society. So the new process of PHC pipe piles production which does not contain autoclaved curing is the way of pipe pile industry for a sustainable development. In this paper, we studied the basic mix proportions for non-autoclaved PHC pipe piles through optimum selection of the raw materials, discussed the mechanical properties and resistance to chloride ion penetration, sulfate erosion resistance, frost resistance and sea water erosion resistance, and analyzed the microstructure of non-autoclaved PHC pipe piles which explains the macro performance of the PHC pipe piles. The main research contents and results are drawn as follows:(1) Research of the basic mix proportions for non-autoclaved PHC pipe piles. The results is:cement had better to use the grade P·Ⅱ 52.5; The superplasticizer is the type of polycarboxylic; The medium sand in area II is appropriate chooses; The coarse aggregate is 5～25 mm continuous gradation of granite stone with the sand ratio of 38%～39%; The total amount of gelled material should be controlled in 480 kg/m3～500kg/m3.(2) Preparation of the C80 non-autoclave PHC pipe piles. We studied the influence to the mechanical properties of admixtures added in the PHC pipe piles which includes S95 slag, S105 slag, gypsum and fly ash microsphere (FAM). The results show that when gypsum is added as a activator with the content of 10%～15% S95 slag added in the PHC pipe piles concrete,7d compressive strength is 81 MPa; When using equivalence S105 slag replace the S95 slag, the compressive strength is higher; When 10% S95 slag and 10% FAM are added in the concrete, the compressive strength and the workability are the best.(3) The research of the durability of non-autoclaved PHC pipe piles. Compared with the autoclaved PHC pipe piles, the non-autoclaved PHC pipe piles shows the superior properties on resistance to chloride ion penetration, sulfate erosion resistance, frost resistance and seawater erosion resistance, in which added with S95 slag, gypsum and FAM shows the best durability.(4) Research of the microstructure of the non-autoclaved PHC pipe piles. Based on the analysis of XRD, SEM and MIP in the microstructure of autoclave PHC pipe pile concrete, it is founded that S95 slag and FAM will promote the hydration process of cement because of the reaction with Ca(OH)2, and produce C-S-H to fill the internal porosity of concrete so to improve the strength and durability of the PHC pipe piles. The results show that the performance of the resistance to chloride penetration of PHC pipe piles concrete is mainly influenced by the pores with diameters between 10～100 nm.(5) Study the layer distribution and pore structures of PHC pipe piles under centrifugal system. By using the X-CT technology to analyze the layer distribution of PHC pipe piles, the results show that the thickest concrete layer of PHC piles is the addition of the S95 slag, gypsum and FAM, and the addition with S95 slag and gypsum take the second place. And the layer of autoclaved PHC pipe piles is the thinnest. It has been discovered that the larger pores are located in the middle of the PHC pipe wall, namely at the junction of mortar and concrete layer. |
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