Performance of Two Bacteria-Based Additives Used for Self-Healing Concrete

Bacteria-induced mineral precipitation is an environmentally friendly technology to enhance the self-healing ability of concrete cracks. However, the self-healing capacity of concrete was improved at the expense of extra bacteria-based additives incorporated into a concrete matrix, and the influence of bacteria-based additives on a concrete matrix has not been fully understood. The objective of this work was to investigate the effects of bacteria-based additives on the properties of a cement paste matrix. Two types of bacteria-based additives (Type 1 and Type 2) were developed to improve the concrete self-healing capacity mainly achieved by bacteria-induced mineral precipitations. The mineral precipitations induced by two types of bacteria-based additives in the liquid medium were analyzed with a scanning electron microscope (SEM) and X-ray diffraction (XRD). Then, the crack-healing capacity of cement paste specimens with both bacteria-based additives was evaluated on the basis of area repairing rate. Moreover, the mechanical and carbonate resistance properties of cement paste specimens were investigated in detail. Experimental results showed that both bacteria-based additives could be utilized to design a self-healing cementitious material system. Incorporation of the Type 1 additive into cement paste resulted in a decrease of about 14.7%, 6.8%, and 0.1% in compressive strength after 3, 7, and 28 days of curing, respectively. However, incorporation of the Type 2 additive into cement paste resulted in a decrease of about 1.6% and 2.2% in compressive strength after 3 and 7 days of curing, respectively, and an 8.1% increase after 28 days of curing. The carbonation depths of control specimens, specimens with Type 1 and specimens with Type 2 were 6.6 mm, 7.0 mm, and 6.5 mm, respectively, after 3 days of accelerated carbonation. These results suggested that the two types of bacteria-based additives could be used to design a self-healing concrete system, though a slight compressive strength loss in early curing age was found.