Experimental study on the mechanical properties of lightweight aggregate concrete mixed with fly ash and shells

In this study, lightweight aggregate concrete [LWAC] was prepared by partially replacing cement with fly ash and partially substituting river sand with shell. The effects of fly ash and shell on the mechanical properties of concrete were studied by compressive test, splitting tensile test and flexural test. In addition, the specimens were microscopically analyzed by SEM electron microscopy. The results showed that both the compressive strength and splitting tensile strength decreased gradually with the increase of fly ash replacement ratio, butthe maximum reduction was only 1.4 % and 3.1 % when the fly ash substitution ratio was 5 %. With the increase of shell replacement ratio, the compressive strength and splitting tensile strength of concrete increased first and then decreased, reached their maximum value at a substitution ratio of 10 %. The optimum fly ash substitution ratio and shell replacement ratio for LWAC were 5 % and 10 %, respectively. The compressive strength, splitting tensile strength and flexural strength of the experimental group under the optimum substitution ratio increased by 2.7 %, 0.6 % and 4.6 %, respectively, compared to the control group. The correlation coefficients of compressive strength with split tensile strength and flexural strength were 0.91 and 0.82, respectively. Finally, a compressive strength calculation formula related to fly ash substitution ratio and shell replacement ratio was proposed based on the Bolomy formula, and the correlation coefficient between the calculated value and the experimental value was 0.91.