Research On The Development For The Mechanical Properties Of Fly Ash Concrete Under Sustained Load

Concrete in real structures works with loads.With the development of engineering techniques,the action of loading keeps shifting to an ever earlier age which has given birth to the possibility that the mechanical properties of premature concrete continues to develop under loads.Mechanical properties of concrete under sustained loads are different from those of load-free,results of many experiments have proved the reinforcing effect of concrete under low level of stress.However,few researches into the mechanical properties of concrete has considered the effect of loading.On the other hand,mixture design of concrete is getting complicated,new admixtures,like fly ash,are added to concrete which is to bring a significant change in the properties of concrete.Specifically,fly ash changes the reaction mechanism of concrete,making late-age mechanical properties of concrete different from ordinary ones,moreover,the effects of loads will further complicate this problem.This paper has studied the mechanical properties of fly ash concrete under sustained loads,primary work are shown as follows:1.Experiment was conducted to test the compressive strength and elastic modulus of fly ash concrete with different fly ash replacement(40%and 60%),a loading device is designed,and some specimens were loaded on the 28th day,the loading level is 20%of 28-day prism compressive strength of the load-free specimens,loaded and load-free specimens were tested for their compressive strength and elastic modulus at different ages.2.Analyzing the mechanism of sustained loads under which the mechanical properties of concrete increase.Two effects of extra hydration and pozzolanic reaction degree under sustained load and the change of aggregate concentration due to this extra reactions are considered.Two representative volume elements of different sizes were built by using the shrinking core model of hydration and pozzolanic reaction.3.A strength development model was established considering the effects of aggregate size and volume fraction,and analysis was made on the influence of loading age and loading level.4.An elastic modulus development model based on the framework of continuum mechanics was established,the homogeneous stiffness of two RVE were calculated and analysis was made on the influence of loading age and loading level.