Experimental and statistical investigation on strength and microcracks remediation in cement mortar using expanded vermiculite as a bacterial carrier

Abstract

Cement based building materials have been used in the field of construction for decades. Among the various applications, lightweight aggregates are very common for thermal insulation, improved acoustic performance, and lightweight construction. This study reported the healing of micro-cracks using expanded vermiculite as a bacterial carrier for crack healing. The expanded vermiculite was adsorbed with bacterial cells and subsequently coated using sodium silicate as the first layer and cement slurry as the second layer. The cement mortar was prepared using dual-coated expanded vermiculite as a bacterial carrier. The expanded vermiculite's water holding capacity and bacterial immobilization capacity were 180% and 1.62×109 cells/gram, respectively. The fine aggregate was replaced in the cement mortar using expanded vermiculite in 0%, 10%, 15%, 20%, and 25% to find the optimum replacement percentage for crack remediation without compromising strength and durability. The performance of this cement mortar in terms of strength, durability, and crack remediation capacity was assessed. The test results showed that 20% replacement with a 5% silica fume combination was effective. The crack area and width were determined by using ImageJ analysis. The bacteria remediated a crack width of 0.92 mm by precipitating calcite crystals was observed under FESEM and confirmed using EDS. For each test process, regression equations were formed by taking into account the variables that influence the compressive strength and healing efficacy. The variables' significance and the optimum vermiculite proportion were determined using ANOVA analysis. The factors were significant with a p-value less than 0.05, and the experimental and ANOVA general linear model predicted that 20% replacement is optimum.