Bacteria-based self-healing concrete: Effect of bio-agents on the cementitious matrix

In this paper, the influence of the specific bacterial nutrient (yeast extract) and the precipitation precursors (urea and Ca-nitrate) on cement hydration and mechanical properties were first investigated. Meanwhile, the availability of the nutrient after being mixed into the cementitious matrix was examined. Due to the harsh conditions of concrete (high alkalinity and small pore size), bacteria need to be immobilized beforehand. Therefore the properties of the carrier candidates used for immobilization were also evaluated on the aspects of the pore properties and the compatibility with the cementitious matrix. Experimental results show that yeast extract greatly retarded cement hydration and had a remarkable negative effect on the strength of the mortar. The strength was greatly decreased when the addition was higher than 0.34%. The precipitation precursors had moderate effect on the strength and the optimal dosage was 4% for urea and 8% for Ca-nitrate by the mass of cement. Argex had a much higher porosity (50%) than that of Lava (16%), and had a more suitable pore size distribution for immobilization of bacteria. Both of them had a good compatibility with the cementitious matrix.