Study On Flexural Performance Of Steel Fiber Reinforced Magnesium Phosphate Cement Concrete Beams

Magnesium Phosphate Cement Concrete(MPCC)has the advantages of rapid setting,early strength,good durability,good bonding performance and low volume shrinkage,which makes it show great development prospects in the fields of concrete bridge construction.How-ever,MPCC has brittle damage characteristics,so steel fibers are added to improve its brittle-ness problem.At present,there are very few experimental studies on the flexural performance of steel fiber reinforced MPCC beams.Therefore,this paper adopts a combination of test,finite element simulation and theoretical analysis to study the mechanical properties of steel fiber reinforced MPCC and flexural properties of steel fiber reinforced MPCC beams,in order to accurately understand the influence law of steel fiber dosing on the mechanical properties of MPCC and flexural properties of steel fiber reinforced MPCC beams,and to provide some reference for the engineering application of steel fiber reinforced MPCC beams,the main con-tents and conclusions of this paper are as follows:(1)MPCC mix ratio design tests are carried out to test its compressive strength.The results showed that:with the increase of water-cement ratio,the strength of MPCC increases first and then decreases.With the decrease of the content of small aggregates in coarse aggregate,the strength of MPCC decreases first and then increases.With the increase of water reducing agent,the strength of MPCC gradually increases.The optimum ratio of MPCC is obtained as follows:water-cement ratio is 0.16,small aggregates is 915kg/m~3 and water reducer is 15kg/m~3.Through the mechanical properties test of steel fiber reinforced MPCC,it is concluded that the basic mechanical properties of steel fiber in the range of 0%to 2.0%increase with the increase of steel fiber content.(2)Four-point bending tests of steel fiber reinforced MPCC beams are carried out to reveal the damage process and morphology of the beams,and to analyze the strain,deflection and ductility of the beams,etc.The effects of steel fiber dosing and reinforcement rate on the flex-ural properties of steel fiber reinforced MPCC beams are investigated.With the increase of reinforcement rate,the cracking load of the beam is slightly increased,and the yield load and ultimate load are greatly improved,but the ductility shows a decreasing trend.The digital image correlation technology is used to track the scattered spots on the surface of the beam in real time,and the strain field and displacement field on the surface of the beam are obtained.Com-pared with the traditional measurement results,the accuracy of the digital image correlation technology for the measurement of this test is verified.The failure mode of the steel fiber MPCC beam during the loading process is further analyzed,and the initial cracking position of the beam is located at a deeper level,and reveal the development and evolution of the cracks on the surface of the beam.(3)The finite element model of steel fiber MPCC beam is established.Compared with the experimental results,the accuracy of the model is verified,and then the parameters of the key materials are analyzed.The results show that the maximum stress of the steel fiber reinforced MPCC appears in the compressive region at the top of the span,and the maximum stress of the steel reinforcement appears in the tensile region at the bottom of the span.Both the longitudinal reinforcement strength and reinforcement rate will have important effects on the flexural per-formance of steel fiber reinforced MPCC beams,among which the reinforcement rate has the most significant effect on the ultimate bearing capacity.(4)Based on the experimental results and basic assumptions,the theoretical analysis of the flexural performance of steel fiber MPCC beams is carried out.Considering the influence of steel fiber content and reinforcement ratio,the calculation formulas of cracking moment,flexural bearing capacity,short-term stiffness and maximum crack width of steel fiber MPCC beams are proposed.Compared with the experimental results,the average values of the ratios are 1.00,1.00,1.07 and 1.03,and the mean square errors are 0.021,0.035,0.051 and 0.047,re-spectively,indicating that the theoretical calculation formula has high accuracy.