Study On Mechanical Properties And Durability Of Basalt Fiber Silica Fume Recycled Concrete

Due to the large crushing index and the old surface mortar of recycled aggregate,the mechanical properties and durability of the recycled concrete made from recycled aggregate are not ideal.Previous studies have shown that both basalt fiber and silica ash can improve the performance of concrete.In order to improve the mechanical properties and durability of recycled concrete,basalt fiber and silica ash were added to the recycled concrete to produce basalt fiber silica ash recycled concrete(hereinafter referred to as BFRAC).Through orthogonal test,the effects of basalt fiber,recycled coarse aggregate,silica ash and water cement ratio on the mechanical properties of basalt fiber recycled concrete was studied,and the values of four factors were determined when the mechanical properties were optimal.The effect mechanism of basalt fiber on the mechanical properties of BFRAC was analyzed by scanning electron microscopy(SEM)test.Moreover,based on the optimal values of each factor,the effect of basalt fiber on the frost resistance and sulfate erosion resistance of BFRAC were studied by setting a single variable.The main research contents and results are as follows:(1)The mechanical properties of BFRAC were studied by the method of orthogonal test.The range,variance,and multiple linear regression analysis were performed based on the results of the compressive strength,splitting tensile strength,and resistance strength tests of BFRAC.The influence degree of each factor was compared,the trend and mechanism of the four factors affecting the mechanical properties were analyzed,and the regression equation within the range of variables in this paper was obtained,and then the optimal value of the four factors was determined.The results showed that the water cement ratio is the most important factor affecting on the mechanical properties.Besides the water cement ratio,the content of basalt fiber and the replacement rate of recycled coarse aggregate also had a high influence degree.Basalt fiber can effectively improve the splitting tensile and folding strength of BFRAC.With the increase of the substitution rate of the recycled coarse aggregate and water cement ratio,the mechanical properties showed a downward trend.Silicon ash could improve the compressive and splitting tensile strength,but the improvemeng was relatively low.Finally,the optimal values of the four factors were determined when the mechanical properties were optimal.(2)Experimental studies on the frost resistance of BFRAC were carried out.According to the optimal values of the substitution rate of recycled coarse aggregate,substitution rate of silicon ash and water cement ratio determined by the mechanical properties test,the influence of basalt fiber on the frost resistance of BFRAC was studied with the basalt content as a single variable.The apparent shape of the specimen,mass loss rate,relative dynamic elastic modulus and compressive strength loss rate were used as the standards to evaluate the freezing resistance performance.It was found that basalt fiber could effectively improve the frost resistance of silica ash recycled concrete.The frost resistance was the best when the mixing content is 0.16%.(3)The sulfate resistance of BFRAC was studied.Similar to the test method of frost resistance,the influence of basalt fiber on the sulfate resistance of BFRAC was measured by the apparent form,mass loss rate,relative elastic modulus and compressive strength.The results showed that basalt fiber had an enhancement effect on the sulfate erosion resistance of BFRAC,and the content of 0.12% is more suitable.When the improvement of content was too high,the sulfate resistance was not obvious,and even decreased.