Effects of bacterial remediation on compressive strength, water absorption, and chloride permeability of lightweight aggregate concrete

Structural lightweight aggregate concrete (LWAC) offers such advantages as reduced dead load and decreased slab and beam size of concrete structures. To this may be added the economic advantages of artificial lightweight aggregates (LWA). However, LWAC basically suffers from higher porosity and water absorption compared to normal-weight concrete. Due to the negative side-effects of certain chemical techniques, biological methods have been proposed as an environmental friendly strategy for reducing concrete porosity and diminishing water absorption. In this regard, calcium carbonate precipitation induced by micro-organisms has found wide applications in construction technology for its effect on improved quality of building materials. This paper presents the results of an experimental investigation carried out to evaluate the influence of Sporosarcina pasteurii at cell concentrations of 106 cells ml−1 on water absorption, water permeability, compressive strength, and rapid chloride permeability (RCP) of LWAC. For the purposes of this study, Leca aggregates were left to soak in a solution of urea-CaCl2 containing bacteria for 6 days to investigate biological improvement of aggregate quality. Next, four types of LWAC were made under the three treatments of bacterially-treated aggregates, bacteria inoculated in the concrete mix water, and both techniques employed simultaneously and with no bacteria used in either the aggregate or the concrete mix solution as the control. The results revealed an average reduction of about 10% in water absorption, 20% increase in compressive strength, and 20% reduction in chloride penetration in the experimental specimens relative to the same properties in the control ones. Furthermore, scanning electron microscopy (SEM) analysis revealed denser and lower porosity of LWAC specimens with bacteria in their concrete mix water and aggregates as compared to those with bacteria used only in their concrete mix water.