A new immobilization technique that encapsulates B. pasteurii in the fine waste cement mortar particles (FWM) was being investigated to induce CaCO3 precipitation in reducing porosity and refining pore size of old cement mortar (OCM), where FWM particles were crushed from old cement concrete and passed through a size of 5 mm sieve. The capillary water absorption test (CWA) and scanning electron microscopy (SEM) were carried out to evaluate the pore-refining effect of this bio-treated methods. X-ray diffraction analysis (XRD) was used to analyze the morphology and the composition of the treated OCM. The results showed that a larger quantity of calcium carbonate bio-depositions were formed and filled the pores of OCM. As a result, the capillary water absorption was decreased by 47% compared with untreated-OCM, respectively.

Based on the dominant mineral in barium-bearing sulfoaluminate calcium cement C2·75B1·25A3S¯, the calcium-barium sulfo-ferritealuminate series minerals were synthesised by replacing Al3+ with a different equivalent of Fe3+. The microstructure was investigated by means of X-ray diffraction, dynamic thermal analysis/thermogravimetric analysis, scanning electron microscopy–energy dispersive spectroscopy (SEM–EDS). The results indicated that the optimal molar composition of Fe3+ ions was from 0·5 to 1·7. The optimum composition was C2·75B1·25A1·5Fe1·5S¯. At this level, the strength at 1, 3 and 28 days could reach 64, 77·75 and 86·62 MPa, respectively.