The optimal formulation of bio-carbonate and bio-magnesium phosphate cement to reduce ammonia emission

Microbially induced calcite precipitation (MICP) has been regarded as a promising cementitious material to consolidate loose sand and soils for ground improvement. The main adverse effect of the urease driven MICP is the ammonia emission during bio-cementation process, which poses negative impact on environment when large dose of ammonia has been released. In order to create environment-friendly bio-cement materials, this paper presents series of experiments to select the optimal formulation of a new bio-cement that can convert ammonia into cementitious materials. Based on previous research, carbonate-mineralization microbe (also named as Sporosarcina pasteurii) has been adopted as the carbonate-mineral microbe. The bio-magnesium phosphate cement is obtained by selecting an optimal formulation (molar ratio), which is bio-carbonate cement: MgCl2: K2HPO4·3H2O = 1 : 2: 2. The ammonia fixation ratio achieved in solution test is up to 62.75%. This value increases to 75.12% when the formulation is applied to bind loose sand columns (sand column tests). For the purpose of increasing the ammonia fixation ratio, the effects of pH, temperature, dosage of additive ingredients, etc. have been investigated. In order to evaluate the performance of this formulation, the properties of sand column cemented by this formulation are studied by uniaxial compressive testing, micro-scale image analysis, chemical component analysis (X-ray diffraction, XRD), etc. Experimental results demonstrate that, the average permeability of the sand columns (3.97 × 10−2 cm/s, initially) is reduced to 2.37 × 10−2 cm/s and the achieved average uniaxial compressive strength of bio-sandstones is 1.43 MPa. SEM (Scanning electron microscope) images of sand column indicates that loose sand grains can well be filled through bio-magnesium phosphate cement.