Influence Of Coarse Aggregate Size On Early Disturbed Performance Of Concrete

At present,a large number of infrastructure is built in our country,and construction disturbance inevitably exists around the pouring concrete,which will lead to the decline of mechanical properties and durability of concrete in the later stage.As an important part of the concrete structure,the performance characteristics of coarse aggregate determine the micro structure and macro performance of concrete.The research on the disturbed performance of concrete during the setting and hardening period is mostly focused on the single coarse aggregate size,without considering the influence of coarse aggregate size.At present,there is no clear research result about the influence of disturbance on concrete when the size of coarse aggregate is different.Therefore,the research on the disturbed performance of concrete based on the particle size difference of coarse aggregate is more in line with the actual situation of the project,which has a positive guiding significance for the performance evaluation of concrete in disturbed environment.According to the different maximum particle size of coarse aggregate,the test is divided into five groups.The particle size ranges from ?(5~10 mm),?(5~16 mm),?(5 ~ 20 mm),?(5 ~ 25 mm),?(5 ~ 31.5 mm).In the hardening stage with penetration resistance value of 10.7 MPa-14.8 MPa,the concrete specimen is disturbed by amplitude of 4 mm,frequency of 15 Hz and duration of 40 min.The influence of disturbance on the macro mechanical properties of concrete with different coarse aggregate size was analyzed by compressive strength test,flexural strength test and ultrasonic test.The microstructure of disturbed concrete was analyzed by SEM and MIP.The results show that: 1)there are significant differences in the macro mechanical properties and micro structure morphology between the disturbed concrete and the benchmark concrete,which affect the hydration reaction process of concrete.After the disturbed concrete,the strength decreases,the defects increase,and the compactness decreases.2)The influence of disturbance on the strength of concrete varies with the size of coarse aggregate.Among them,The maximum and minimum loss rates of compressive strength of disturbed concrete are 18.5% and 4.9% respectively,and the maximum and minimum loss rates of flexural strength are 30.0% and 9.2% respectively;the effect of coarse aggregate size on the mechanical properties of early disturbed strength of concrete is significant.3)The loss rates of compressive strength and flexural strength of 5~20 mm coarse aggregate concrete disturbed are 4.9% and 9.2% respectively,both of which arewithin 10%,and the degree of disturbance is relatively small.The ultrasonic wave velocity of 5~20 mm coarse aggregate concrete is the largest,and the disturbance has the least influence on the ultrasonic wave velocity and SEM micro morphology of this group of concrete,under the condition of this test,the particle size of this group is the optimal coarse aggregate particle size distribution affected by the disturbance of concrete.4)Combined with SEM and MIP micro test results,it can be seen that the average pore volume,average pore area and porosity of the disturbed concrete increase,the average pore diameter decreases,and the pore level distribution tends to be uniform,which leads to the deterioration of the micro structure density and macro mechanical properties of the disturbed concrete.The experimental results can provide theoretical support for the performance evaluation of disturbed concrete with different coarse aggregate sizes,and provide reference for related practical projects.