Research On Mechanical Properties And Pore Structure Of Reactive Powder Concrete

Reactive Powder Concrete(RPC)is a kind of cement-based composite material with super high strength,high toughness and excellent durability.RPC can effectively reduce the amount of concrete used in components,lighten the structure and greatly improve the durability of buildings.It has broad application prospects in the fields of civil engineering and marine engineering.Domestic and foreign scholars have achieved many research results in the mechanical properties of RPC,but the performance of RPC is obviously affected by the variety of raw materials,and different curing temperatures have a significant impact on the strength and pore structure of RPC.The effects of local raw material mix proportion and curing temperature on mechanical properties and pore structure of RPC were studied.In this paper,the effects of water-binder ratio,sand-binder ratio,silica fume and Ground granulated blast furnace slag on the compressive strength of RPC were investigated by orthogonal test.Based on the orthogonal test results,the influence of water-binder ratio,silica fume,quartz powder and steel fiber on the flexural strength and compressive strength were studied,and the optimal proportion of RPC with high strength and good workability is obtained.The effects of different curing temperatures on the strength of RPC were studied.The effects of steel fiber type,polypropylene fiber or it with steel fiber blending on RPC fluidity,flexural strength and compressive strength were also studied.The results show that the compressive strength of RPC increases first and then decreases with the increase of curing temperature,and reaches the maximum value of 303.5MPa under high temperature curing at 250?.The RPC strength is greatly affected by the steel fiber variety,and the contribution rate of steel fiber to RPC compressive strength and flexural strength is greater than that of polypropylene fiber.On this basis,X-ray computed tomography(X-CT),mercury intrusion porosimetry(MIP)and nitrogen adsorption method(BET)were used to study the pore structure of RPC at different curing temperatures,and the infrared spectrum(IR)and scanning electron microscopy(SEM)were used to study the degree of hydration and microscopic appearance of RPC respectively.The results show that X-CT measured the pores with a hole radius of 6?220?m,and the number of holes was mainly distributed in the range of 10?40?m.The pore radius measured by MIP ranged from 0.003 to 60?m,and the pore volume in the slurry was mainly distributed in the range of 3 to 10nm.Three test methods showed that high temperature curing can refine pores,and MIP is good at measuring nano-scale pores,while X-CT is more suitable for measuring micron-sized pores.However,BET is more accurate for mesopores..In addition,IR analysis showed that the degree of hydration of the RPC gelling system increased with increasing the curing temperature.It was found by SEM that acicular calcium silicate was formed on the inner wall of the slurry hole at the curing temperature higher than 250?.Obviously,high temperature curing can improve the degree of hydration,refine the pore structure of RPC,improve the microstructure,and thus improve the compressive strength,but the compressive strength decreased slightly when the curing temperature was higher than 250?.