Evaluating the Use of S. pasteurii on Mitigating the Damage Response of Cementitious Materials Exposed to Calcium Chloride

Deterioration of concrete pavements in the United States has increased over the past decade and is becoming a common occurrence. This damage is triggered by two possibilities: classic freeze-thaw behavior, as well as the formation of calcium oxychloride from a reaction between calcium hydroxide in the concrete and chloride-based deicing salts. Calcium oxychloride (CAOXY) is an expansive phase that may lead to significant damage in the cementitious matrix and result in cracking. This study investigates the use of alkaliphilic, spore-forming bacteria to mitigate the formation of calcium oxychloride. Mortar and paste samples were made with ordinary portland cement; ordinary portland cement combined with nutrients; and ordinary portland cement combined with bacteria and nutrients. Low-temperature differential scanning calorimetry (LT-DSC), thermogravimetric analysis (TGA), sorption analyzer (SA), and acoustic emissions (AE) were used to quantify the amount of calcium oxychloride, calcium hydroxide, microstructural change, and damage caused by CaCl2 salt in the cementitious samples, respectively. It was shown that the addition of bacteria significantly reduces the formation of CAOXY in the cementitious matrix. The bacteria were shown to utilize not only calcium hydroxide from cement hydration products, but also calcium chloride salt solution as sources to produce microbial induced calcium carbonate, thereby lowering the formation of CAOXY. This resulted in reductions in both calcium hydroxide and calcium chloride and an increase in the amount of calcium carbonate precipitated in the microstructure of cementitious materials. As a result, damage created due to CAOXY was substantially mitigated in the bacteria samples when exposed to calcium chloride deicing salt. It was also found that the addition of bacteria to cementitious system created a change in the micropore structure and pore size distribution of cement paste.