Study On The Influence Of Limestone Powder And Stress Damage On The Performance Of Lightweight Aggregate Concrete

In this paper, the enriched natural pumice in Inner Mongolia is taken as coarse aggregate first, and then industrial waste limestone powder is used as admixture. Meanwhile, the internal mixing method is adopted to replace 0%,10%,20%,30%and 40% of cement mass by limestone powder for preparing lightweight aggregate concrete. Through mechanical performance test and freezing-thawing resistance performance test with the aid of scanning electron microscope, internal microstructures of concrete have been analyzed to explore the influence mechanism of limestone powder on the mechanical performance and durability of lightweight aggregate concrete, so as to obtain the appropriate mix content of limestone powder in pumice lightweight aggregate concrete. By analyzing the stress-strain relationship of lightweight aggregate concrete with different limestone powder content, the constitutive equations were built. The test results show that when the mix content of limestone powder is 10%, the mechanical performance of lightweight aggregate concrete in all ages will be improved significantly; limestone powder can accelerate early hydration of cement, while itself has later hydration activity to improve the compactness of cement matrix and pumice-cement interface transition zone; the internal mixing of 10% limestone powder can effectively upgrade the freezing-thawing resistance performance of lightweight aggregate concrete in the early stage of freezing-thawing cycle, while degrade the freezing-thawing resistance performance in the late stage of freezing-thawing cycle.Secondly, through repeated loading of initial stress damage to lightweight aggregate concrete precast, the "quick freezing method" is adopted with relative dynamic elastic modulus and mass loss rate as evaluation indices to analyze the freezing-thawing resistance performance of lightweight aggregate concrete with damage degrees of 0,0.05, 0.12,0.19 and 0.27 respectively. With the aid of scanning electron microscopy (SEM), the microstructure characteristics of lightweight aggregate concrete with stress damage have been analyzed prior and posterior to freezing-thawing, so as to explore the influence mechanism of initial stress damage on the freezing-thawing resistance performance of lightweight aggregate concrete. According to the related theory of damage mechanics. through the analysis on the freezing-thawing damage evolution process of lightweight aggregate concrete. Loland concrete damage model is based to establish the mechanical damage evolution equation of lightweight aggregate concrete with initial stress damage and freezing-thawing damage. Finally, the measured relative dynamic elastic modulus of lightweight aggregate concrete with stress damage under different freezing-thawing cycles is used with the aid of MATLAB software for fitting the freezing-thawing damage prediction model of lightweight aggregate concrete with stress damage. The results show that the existence of initial stress damage will accelerate the development of freezing-thawing damage of lightweight aggregate concrete. The larger the initial stress damage is, the more serious the freezing-thawing damage will be. The fitting values of mechanical damage evolution equation are very consistent with experimental values, providing a theoretical basis for prediction on freezing-thawing resistance performance, maintenance and reinforcement of lightweight aggregate concrete posterior to damage.