Study On The Key Technology Of Non-steam Cured High Strength Concrete Used For PHC Pipe Piles

Prestressed high strength concrete pipe pile(PHC pipe pile)is important foundation material,which is widely used in high buildings,long-span bridges,highways and ports,etc.The steam curing of PHC pipe pile with high temperature consumes a lot of energy and has a bad effect on the durability of the concrete.The non-steam cured PHC pipe pile concrete was investigated in south China,in which the climate was hot and wet.The research is mainly divided into three parts:the preparation of non-steam cured PHC pipe pile concrete;the durability of non-steam cured PHC pipe pile concrete;the impact resistance of fiber reinforced non-steam cured PHC pipe pile concrete.The conclusions are as follows:(1)The early strength Polycarboxylate Superplasticizer,early strength agent and superfine mineral admixture were chosen to do the mix optimization test of the non-steam cured PHC pipe pile concrete in this paper.The slump of fresh concrete was restricted into 30mm-70mm.The concrete after casting was cured at room temperature.The compressive strength of the concrete block cured different ages was tested.It requires that the compressive strength of the non-steam cured PHC pipe pile concrete cured 18 hours should reach 45MPa and the compressive strength cured 3 days should get 80MPa.Two groups were chosen to made the centrifugal forming concrete piles.The results show that the workability of fresh concrete meets the requirements of non-steam cured PHC pipe pile concrete.The compressive strength of the pipe piles’ cores was 94.6MPa and 99.1MPa,respectively.The porosity of cores detected by X-CT were 0.0013%and 0.0005%.It shows that the preparation of non-steam cured PHC pipe piles concrete can be achieved in the south China area.(2)The RCM test and natural immersion test(3.5%NaCl solution and natural sea water)were carried out for the non-steam cured PHC pipe pile concrete.The results of MIT and SEM showed that the concrete had a low porosity and compact microstructure.The results of RCM test and natural immersion test showed that the non-steam cured PHC pipe pile concrete had a low chloride ion diffusion coefficient and the loss of compressive strength of concrete block was less than 1%after 180 days seawater immersion.It showed that the non-steam cured PHC pipe pile concrete had good resistance to chloride ion erosion and seawater erosion.(3)The workability,mechanical properties and impact resistance of non-steam cured PHC concrete with basalt fiber(BF),polypropylene fiber(PP)and steel fiber(SF),respectively,were investigated.The results show that the incorporation of BF and PP fibers increased the total water of requirement of the mix which had the same workability,and the incorporation of SF,however,had little effect on the total water requirement.The compressive strength of concrete incorporated with BF and PP fiber,respectively,was decreased by the increase of fiber content.The compressive strength of concrete incorporated with SF was however increased with the increase of fiber content.The results of falling ball impact test show that the incorporation of fiber improved the bending load at the single impact of concrete slab,while the displacement of the slab during the impact process was reduced.The concrete with SF showed the highest repeated impact resistance.For concrete with PP fiber,the impact number was slightly higher than that of reference concrete.For concrete with BF,the number of repeated impacts was similar to that of reference concrete.