Resistance of Bio-Based Cementitious Material to Acid Attack

Concrete although is a mechanically strong construction material, but suffer from several inherent drawbacks, such as low tensile strength, permeability to liquid and consequent corrosion of reinforcement, susceptibility to chemical attack and low durability, ultimately reduced service life. Therefore, properties such as strength, permeability, crack formation and corrosion properties defines the overall quality of concrete. To improve the overall performance of concrete from these deficiencies, microbial mineral precipitation resulting from metabolic activities of some specific microorganisms in concrete has been attempted. Concrete incorporated bacteria can produce copious amounts of minerals which can potentially seal freshly formed cracks. However, its performance in presence of acid need to be understood. This paper reports the effects of microbial calcite precipitation on parameters affecting the transport processes and durability of mortar. To study the effect of durability, mortar cubes with and without Bacillus cohnii were cast and subjected to acid attack. Treatments were evaluated by visualizing and calculating the extent of acid attack in terms of % strength loss and % weight loss on 0.5%HCl and H2SO4 exposed mortar specimens. The durability of the bacteria treated specimens have been studied by measuring the resistance against acid attack in terms of acid attack factor and increased durability in terms of acid durability factor. Microbial calcite precipitation was quantified by X-ray diffraction analysis and visualized by SEM. Bacterial deposition of a layer of calcite on the surface of the specimens resulted in reduction in pore percentage and therefore, a decrease of acid ingress inside the mortar specimen was detected. From all the aforesaid studies it was revealed that bio-concrete is more durable.