| Reactive Powder Concrete(RPC)is a new cement-based composite material,which has ultra-high strength and ultra-high toughness and durability.It has a broad prospect of application in the construction of marine infrastructure,chemical workshops,and salt lake areas and other highly corrosive environments.According to "Code of Reactive Powder Concrete"(GB/T31387-2015),RPC has a mechanical property grade of RPC100～RPC180,high strength of RPC,low water binder ratio,compact microstructure.In order to prevent RPC components or structures from bursting under fire,an appropriate amount of polypropylene(PP)fiber or steel fiber shall be mixed or mixed together during preparation.However,studies have shown that the stirrups do not necessarily yield when the confined concrete column reaches the peak compressive load.Lacking regulations on the extent to which the stirrup tensile stress can be exerted when the confined concrete column reaches the peak compressive load,the compressive strength of confined concrete calculated by the yield strength of stirrups is sometimes unsafe.Therefore,it will be necessary for application and generalization of RPC in ductile component to conduct a research of improving and avoiding high brittleness and high temperature burst of RPC,explore an exact solution of incorporation of macroscopic composite such as steel fiber,stirrups and pole constraints and inspect the axial load and seismic performance of RPC column.The detailed work is below:(1)58 groups of RPC ratio tests with different water-glue ratios,steel fiber content and conservation mode were completed.We have systematically explored the effects of factors such as cement,silica fume,fly ash,nano beads,steel fiber content,water-glue ratio,conservation mode on the strength and mobility of RPC.We have proposed a formula for calculating RPC mix ratio with main parameters such as water-glue ratio,conservation mode and steel fiber content.By using the optimized mix ratio,after curing for 7 hours in an autoclave with a temperature of 200°C and an air pressure of 1.3 MPa,the compressive strength of a cube of RPC with a side length of 70.7 mm can reach 215 MPa.(2)Based on the statistical analysis of the high temperature burst test results of ordinary concrete,high-strength concrete and RPC with a cube with a side length of150 mm and a compressive strength of 23MPa～238MPa,we have obtained the relationship curve between the amount of anti-cracking steel fiber and the compressive strength of concrete: as the compressive strength of concrete increases,the amount of steel fiber required for explosion-proof cracking increases exponentially.We have established the mathematical expression of the minimum amount of anti-high temperature bursting steel fiber content in concrete with different compressive strength.The minimum amount of steel fiber content recommended in this article is higher than the minimum steel fiber content given in GB/T 31387-2015.It is suggested that people adopt the minimum amount of the explosion-proof steel fiber content for fire-resistant RPC160 and related components.(3)An axial compression test has been carried out with 6 HRB600 spiral stirrup constrained RPC cylinders with a diameter of 250 mm,a height of 750 mm,a cubic compressive strength of 171 MPa,and a stirrup ratio of 0.68% to 6.78% as well as a plain reactive powder concrete cylinder with the same size and same strength.The test results show that the circular specimen of plain RPC undergoes brittle failure after reaching the peak axial load.With the increase of volumetric hoop ratio,the peak compressive strain and peak compressive stress of constrained RPC increase.The increase in the peak compressive strain and the compressive strain corresponding to 50% of the peak load in the descending section of the compressive loaddeformation curve is higher than the increase in the peak compressive stress.All the stirrups of the specimens did not yield when reaching the peak axial load.This paper analyzes the load-deformation curve under different confinement degrees,establishes the mathematical expressions of the RPC peak compressive strain,peak compressive stress,stirrup tensile strain and the minimum volumetric stirrup ratio when the stirrup under tension yield and proposes the stress-strain curve model of RPC tri-fold line constrained by stirrups.The model accords with the material characteristics of RPC type elastomer,with fewer parameters and good agreement with the test curve.(4)The axial compression test of 6 HRB600 RPC cubes with a compressive strength of 148 MPa,a side length of 250 mm and a height of 750 mm as grid stirrupconstrained reactive powder concrete square columns is carried out.The outcome of the test reveals that with the increase of volumetric stirrup ratio,the peak compressive strain and peak compressive stress of constrained RPC increase,and the increase range of deformation capacity and load-bearing capacity is lower than that of the spiral stirrup constrained RPC cylinder with the same degree of confinement.The stirrups are not yielded when the peak compressive load is reached,and the tensile stress level of the stirrups under the peak load is lower than the spiral stirrups of the RPC cylinder.The compressive load-deformation curve under different constraints is analyzed,and the mathematical expression of the peak compressive strain,peak compressive stress,and stirrup tensile strain of the RPC column constrained by the mesh stirrups is established.(5)Based on the limit equilibrium theory,the suggested formula of peak compressive stress of spiral stirrup confined RPC was substituted into the force balance relationship of steel pipe confined RPC,and the bearing capacity formula of circular steel pipe confined RPC was formed.The bearing capacity calculated by the formula was nearly equal to the axial compression performance test of 213 steel pipe RPC short columns with a 70.7mm side length cube with a compressive strength of76.6MPa ～ 178.2MPa and a hoop coefficient of 0.057 ～ 2.312.In view of the small aggregate added by RPC,the initial damage between the gel and the aggregate is small,and the lateral deformation under axial load is small,the experimental result of the compressive bearing capacity of the steel tube RPC column is lower than that in the "Code for Design and Construction of Concrete-Filled Steel Tube Structures"(CECS 28-2012).It is suggested to adopt the calculation formula of axial compression capacity of RPC with round steel tube constraint established in this paper. |
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