Bacillus subtilis bacteria used in fiber reinforced concrete and their effects on concrete penetrability

Abstract

Fiber-reinforced concrete has found wide applications in recent years as a remedy for compensating for the weak concrete tensile and flexural strengths. The use of fibers in concrete, however, increases its porosity. This drawback calls for remediation techniques to reduce concrete porosity and permeability in order to enhance its durability. Calcite sediments are capable of filling part of concrete pores to reduce its porosity. In the present study, use was made of bacteria as sediment producing agents in concrete specimens strengthened with different types of fiber. For this purpose, a strain of Bacillus subtilis was employed in its culture medium at a concentration of 107 cell/ml both as a replacement for the water in the concrete mixture and in a surface treatment gel. Moreover, polypropylene, steel, and barchip fibers were used at volume percentages of 0.3, 1, and 0.75%. The concrete specimens thus obtained were subsequently cured for 28, 56, and 90 days (depending on the type of experiment) in either plain water or the calcium lactate-urea solution. Measurements of water, CO2 and chloride ion penetration depths revealed that the use of bacteria in both curing environments led to reduced water, CO2, and chloride ion penetration depths in the bacteria-incorporated specimens, with the highest reductions of 64.75%, 39.77%, and 27.4% recorded for water, chloride ion, and carbonation depths, respectively. This is while the specimens subjected to surface treatment exhibited reductions of 57.75%, 24.94%, and 23.3% in their water, chloride ion, and carbon dioxide penetration depths, respectively, relative to those of the control specimens. Thus, the use of bacteria in the concrete mixture and its curing in the calcium lactate-urea solution were found capable of filling concrete pores to reduce porosity in fiber-reinforced specimens.