Experimental Study On The Late Performance Degradation And Inhibition Of High Performance Concrete In Wet Conditions

The effect of a humid environment on high strength concrete,increases with the service period progression.Macro-performance during this growth period will increase till it gets to best intensity at a given age,after which the phenomenon of macro-performance degradation sets in,putting it at great security risk especially under earthquake loading.At present,the studies on the late stage performance degradation of high strength concrete in moist environment are at the initial stage.Therefore,the current research status,the strength,permeability and microstructure of the high strength concrete in the later stage of the heat curing conditions and seal curing conditions are studied.The fly ash and silica fume are mixed to optimize the attenuation of the strength of high strength concrete to provide scientific basis for further research and application.The specific research contents are as follows:This thesis studies the effect of moist environment on the macroscopic and microscopic properties of high strength concrete.A total of five concrete mix ratios were designed.The cementitious materials were cement,25% fly ash,22% fly ash + 3% silica fume,19 % fly ash + 6% silica fume and 16% fly ash +9% silica fume replaced the cement in the same amount.After the standard curing for 7d,28 d and 60 d,heat curing and sealing maintenance were conducted for 1d,2d,3d,5d,9d,and 14 d.Compressive strength tests and splitting tensile tests were performed on each group of high strength concrete specimens.The test results show that the strength of high strength concrete will first reach the peak strength with the increase of age,and the strength of concrete will decrease after a certain degree.Among them,the mechanical properties of the concrete mixed with fly ash 16% and silica fume 9% are optimal,and the peak compressive strength and split tensile strength are 121.9 MPa and 8.47 MPa,respectively.At the 14 d of heat and humid curing,the intensity of contraction was the least,which was 15.5% and 23.25%,respectively.At the same time,seal curing can also effectively reduce the intensity of contraction.Electrical flux tests and water absorption tests were performed on each group of high strength concrete specimens.The experimental results show that with the increase of the age of heat and humid curing,the electric flux decreases first and then increases.The concrete impregnated with 16% of fly ash and 9% of silica fume has the best impermeability,and its electric flux minimum value is 67.7 C.With the increase of the age of heat and humid curing,the water absorption rate changes little before 9d.On the 14 d,the water absorption rate of concrete mixed with fly ash 16% and silica fume 9% is significantly reduced,but the water absorption rate of other concrete increases greatly.SEM and mercury injection tests were used to characterize the microstructure of high strength concrete.The results of the study indicate that the increase of harmful pores and the secondary hydration of the later-staged cementitious material lead to micro-cracks in the pores and through-passages,which deteriorate the strength and impermeability of the concrete.