Microbially induced carbonate precipitation (MICP) has emerged as a promising solution in enhancing the durability of concrete structures in the recent decade. Bio-grout is generally developed by incorporating bacterial culture which further requires extensive bio-based laboratory facilities which limits its practical implementation for civil engineers. In this study, a ready-to-use fly ash (FA) based bacterial inoculum with shelf life of 180 days was prepared that could be directly used to prepare bio-grout. This would help in executing MICP for field scale repair of concrete elements. The prepared bio-grouts were tested in terms of flowability, mini-slump, bleeding, setting time, mechanical strength and drying shrinkage to design the best-performing cementitious bio-grout. The best cementitious bio-grout was used to repair cracks in concrete structures. An attempt was made to develop a procedure for the remediation of cracks in three varying orientations, i.e. horizontal, vertical and inverted, to target actual cracks that might exist in the structures. The performance of the repaired surface was assessed in terms of recovery in flexural strength and water tightness. The mineral composition of the healing product was examined by FESEM-EDX and XRD; results clearly indicated the presence of calcite crystals inside the pores. Also, to quantify the calcium carbonate precipitation in the bio-repaired specimens during curing, electromechanical impedance technique was employed. Overall, it can be concluded that FA-based inoculum can effectively promote MICP activity to seal the fractured crack of any orientation in existing concrete structures. 

Development of field applicable remediation procedure using bio-cementitious grout for concrete cracks in variable orientations

Superplasticizer (SP) is essential to enhance the groutability of microfine cement (MC) in civil engineering, however, combined effects of cement type, SP type, amount of SP and water-solid ratio (W/S) on engineering performance of MC are not clear currently. In this research, workability and mechanical properties of superplasticized microfine cement grouts (SMCG) with various SPs are evaluated systematically. Three different MCs (CEM I, CEM II/B-M and CEM III/B based on EN 197-1) and four SPs (one naphthalene-based (N), one melamine-based (M) and two polycarboxylate-based (PCE)) were used to study the effect of grout formulation. The properties investigated included rheological behavior (mini-slump, flowability, time-dependent viscosity and initial viscosity), fresh-state property (bleeding, effective W/S and final setting time), mechanical performance (shrinkage, flexural strength (FS), unconfined compressive strength (UCS), and FS/UCS) and microstructure. The new method of static viscosity was adopted and viscoelasticity was evaluated. The ranges of W/S and SP content were 1.0–2.0 and 0–2.5%, respectively. The results show that the dispersion effects of SP on rheological behavior were followed by PCE, M and N in order of the influence degree. The instability, long-setting and oversaturation were easily caused by excessive SP. SP could be helpful for improving FS or bending toughness. Considering workability and mechanical performance of SMCG, the W/S is suggested to be within 1.5, the optimal amounts of N, M and PCE are recommended as 1.5–2.0%, 1.2–1.5% and 0.9–1.2%, respectively.

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Workability and Mechanical Properties of Superplasticized Microfine Cement Grouts

Strengthening effect of sulphoaluminate cementitious grouting material for water-bearing broken rocky stratum

To develop high-performance microfine cementitious grout (HPMCG), the matrix [microfine Portland cement clinker (MPCC) + flue gas desulfurizing gypsum (MFGDG) + calcium carbonate (MCC)], mi...

Fei Sha

Papers

Development of High-Performance Microfine Cementitious Grout with High Amount of Fly Ash, Silica Fume, and Slag