Mineralization and cementing properties of bio-carbonate cement, bio-phosphate cement, and bio-carbonate/phosphate cement: a review.

Due to high pollution associated with traditional Portland cement and bio-carbonate cement, a new generation of cementitious material needs to be developed. Bio-barium phosphate, magnesium phosphate, and ferric phosphate are synthesized by bio-mineralization. Firstly, the substrate is hydrolyzed by alkaline phosphatase secreted via phosphate-mineralization microbes, obtaining phosphate ions. Micro- and nano-scale phosphate minerals are prepared by phosphate ions reacting with different types of metal cation. The setting time of bio-BaHPO4 has a greater effect on the strength of sand columns when a mixing precipitation process is innovatively adopted. The strength of the sand columns increases as bio-BaHPO4 content (10~50%) increases. The optimum content of bio-BaHPO4 is 60%. Porosity and permeability of the sand columns decrease as bio-BaHPO4 content (10~60%) increases. Ammonium and ammonia can effectively be synthesized to magnesium ammonium phosphate by adding K2HPO4·3H2O to Sporosarcina pasteurii liquid. Permeability, porosity, and compressive strength of the sand columns are close to CJ1, CJ1.5, and CJ2 cementation. However, the fixation ammonia ratio of CJ2 is bigger than CJ1 and CJ1.5 (The mixture solutions of Sporosarcina pasteurii and K2HPO4·3H2O (1, 1.5, and 2 mol/L) are named as CJ1, CJ1.5, and CJ2) cementation. The results show that the Sporosarcina pasteurii liquid containing K2HPO4·3H2O (2 mol/L) and the mixture solution of MgCl2 and urea (3 mol/L) cemented loose sand particles best. Two types of bio-cement are environmentally friendly and can partially or completely replace bio-carbonate cement.