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The self-healing of cracks via biomineralization in bacteria-based concrete has shown remarkable results in recent decades. This novel technique uses the ability of bacteria to precipitate CaCO3 for sealing cracks, and is termed microbially induced calcite precipitation (MICP). However, most previous studies focused on extensive laboratory-based procedures before incorporating them into concrete. This investigation developed a ready-to-use silica fume (SF) based bacterial agent that can be used directly to achieve CaCO3 precipitation. This will aid in the use of MICP for field-scale repair in concrete structures. Furthermore, most previous studies addressed crack remediation in the horizontal orientation of concrete structures. This study developed a remediation strategy to repair realistic cracks in existing concrete structures. The developed SF-based inoculum at an age of 180 days stored at 4°C was used to design biocementitious grouts. Various biogrouts were examined for fresh and hardened properties in order to develop the most effective biogrout. The effectiveness of the surface restored using biogrout was evaluated in terms of mechanical and watertightness properties. Microstructural analysis was conducted at the end of testing to evaluate its physicochemical attributes. The electromechanical impedance technique was used to quantify the microbial activity in the biorestored concrete during curing. The results suggested that precipitates led to the densification of pores, ultimately lowering the water permeability and the recovery of mechanical strength of the repaired specimens. Conclusively, the SF-based bacterial agent can increase MICP activity to seal cracks in actual concrete structures. [ABSTRACT FROM AUTHOR]

Microbially induced calcium carbonate precipitation (MICCP) is widely employed in various engineering applications, including repairing cracks in cementitious materials. Many of these studies were performed using heterotrophic bacteria that utilize urea and releases harmful foul-smelling environmental pollutant. Cyanobacteria have emerged as potential substitutes for heterotrophic bacteria to overcome this concern. This study used photosynthetic cyanobacteria Synechocystis pevalekii to develop an ecofriendly and sustainable grout for crack remediation in concrete. To improve the fluidity characteristics of the grout, fly ash was incorporated as a partial cement replacement in the cementitious grout. The cementitious grouts were tested for fresh properties at different dosages of fly ash (0%–50%) by keeping water (or bacterial culture) to binder ratios of 0.45, 0.47, and 0.50. Based on flowability results, a 0.47 culture/binder ratio was selected to examine different FA dosages for hardened properties. A 40% FA substituted cementitious biogrout was selected for repairing cracks at the lab scale. Different cracked concrete specimens were repaired and cured using ponding and spray treatment for 28 days. At the end of the experiment, a significant improvement in strength and permeability was recorded in biogrout-remediated cracked specimens. The sample was collected from healed cracked region to confirm the healing mineral using field emission surface electron microscope (FESEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The developed fly ash incorporated biogrout will help as an economical and ecofriendly MICCP technology for the remediation of existing cracks in the concrete structures. [ABSTRACT FROM AUTHOR]

Due to anthropogenic activities, heavy metals such as cadmium (Cd) and arsenic (As) are one of the most toxic xenobiotics contaminating water, thus affecting human health and the environment. The objective of the present investigation was to study the effect of ureolytic bacteria Bacillus paramycoides-MSR1 for the bioremediation of Cd and As from contaminated water. The B. paramycoides showed high resistance to heavy metals, Cd and As, with minimum inhibitory concentration (MIC) of 12.84 μM and 48.54 μM, respectively. The urease activity and calcium carbonate (CaCO3) precipitation were evaluated in artificial wastewater with different concentrations of Cd (0, 10, 20, 30, 40, 50, and 60 μM) and As (0, 20, 40, 60, 80, and 100 μM). The maximum urease activity in Cd-contaminated artificial wastewater was observed after 96 hours, which showed a 76.1% decline in urease activity as the metal concentration increased from 0 to 60 μM. Similarly, 14.1% decline in urease activity was observed as the concentration of As was increased from 0 to 100 μM. The calcium carbonate precipitation at the minimum inhibitory concentration of Cd and As-contaminated artificial wastewater was 189 and 183 mg/100 ml, respectively. The percentage removal of metal from artificially contaminated wastewater with varied concentrations was analyzed using atomic absorption spectroscopy (AAS). After 168 hours of incubation, 93.13% removal of Cd and 94.25% removal of As were observed. Microstructural analysis proved the presence of calcium carbonate in the form of calcite, confirming removal of cadmium and arsenic by microbially induced calcium carbonate precipitation (MICCP) to be promising technique for water decontamination. [ABSTRACT FROM AUTHOR]

Microbially induced calcium carbonate precipitation (MICCP) is considered a novel eco-friendly technique to enhance the structural properties of cementitious-based material. Maximum studies have emphasized using ureolytic bacteria to improve the durability properties of building structures. In this study, the role of photoautotrophic bacteria Synechocystis pevalekii BDHKU 35101 has been investigated for calcium carbonate precipitation in sand consolidation, and enhancing mechanical and permeability properties of cement mortar. Both live and UV-treated S. pevalekii cells were used to treat the mortar specimens, and the results were compared with the control. The compressive strength of mortar specimens was significantly enhanced by 25.54% and 15.84% with live and UV-treated S. pevalekii cells at 28-day of curing. Water absorption levels were significantly reduced in bacterial-treated mortar specimens compared to control at 7 and 28-day curing. Calcium carbonate precipitation was higher in live-treated cells than in UV-treated S. pevalekii cells. Calcium carbonate precipitation by S. pevalekii cells was confirmed with SEM-EDS, XRD, and TGA analysis. These results suggest that S. pevalekii can serve as a low-cost and environment friendly MICCP technology to improve the durability properties of cementitious materials. Keypoints: Cyanobacterial Synechocystis pevalekii cells induced calcification on cement mortar. Both live and UV-treated cells increased the compressive strength and reduced the water absorption. Biomineralization by S. pevalekii serves as a low-cost and eco-friendly MICCP technology. [ABSTRACT FROM AUTHOR]

Microbially induced calcium carbonate precipitation (MICP) is emerging as a sustainable technology for improved construction materials. In this technique, calcium carbonate is deposited in the pores of substrates such as sand and concrete. As the technology moves from laboratory to field new metrics and field measurement techniques are required to ensure that the results achieved at the laboratory are replicated. In the scaled up technique it is not possible to collect samples from deep inside the substrate for direct measurement. This paper explores some indirect indicators of MICP that can be easily monitored in large scale applications. Bacterial fluid has been passed through sand columns of varying grain sizes. The rate of flow is monitored for ten days. The effluent has been tested for pH and electrical conductivity to evaluate their potential for ensuring MICP. The residual urea and calcium in the effluent has been monitored to have a quantitative estimate of MICP. At the end of the tests the quantity of carbonate deposited in the sand columns is measured. A correlation between the residual reactants and the carbonate deposition is developed. An approximate expression for different grain sizes has been developed. This study demonstrates the utility of indirect measurement techniques as flow rate, pH, conductivity, urea and calcium consumption as potential indicators of efficient MICP in sand media. [ABSTRACT FROM AUTHOR]

Microbially induced calcium carbonate precipitation is a biomineralization process that has various applications in remediation and restoration of range of building materials. In the present study, calcifying bacteria, Bacillus megaterium SS3 isolated from calcareous soil was applied as biosealant to enhance the durability of low energy, green building materials (soil–cement blocks). This bacterial isolate produced high amounts of urease, carbonic anhydrase, extra polymeric substances and biofilm. The calcium carbonate polymorphs produced by B. megaterium SS3 were analyzed by scanning electron microscopy, confocal laser scanning microscopy, X-ray diffraction and Fourier transmission infra red spectroscopy. These results suggested that calcite is the most predominant carbonate formed by this bacteria followed by vaterite. Application of B. megaterium SS3 as biogenic surface treatment led to 40 % decrease in water absorption, 31 % decrease in porosity and 18 % increase in compressive strength of low energy building materials. From the present investigation, it is clear that surface treatment of building materials by B. megaterium SS3 is very effective and eco friendly way of biodeposition of coherent carbonates that enhances the durability of building materials. [ABSTRACT FROM AUTHOR]

Phenotypic mutants of Sporosarcina pasteurii (previously known as Bacillus pasteurii) (MTCC 1761) were developed by UV irradiation to test their ability to enhance urease activity and calcite production. Among the mutants, Bp M-3 was found to be more efficient compared to other mutants and wild-type strain. It produced the highest urease activity and calcite production compared to other isolates. The production of extracellular polymeric substances and biofilm was also higher in this mutant than other isolates. Microbial sand plugging results showed the highest calcite precipitation by Bp M-3 mutant. Scanning electron micrography, energy-dispersive X-ray and X-ray diffraction analyses evidenced the direct involvement of bacteria in CaCO3 precipitation. This study suggests that calcite production by the mutant through biomineralization processes is highly effective and may provide a useful strategy as a sealing agent for filling the gaps or cracks and fissures in any construction structures. [ABSTRACT FROM AUTHOR]

Application of microbial induced carbonate precipitation in cement-based materials has become substantially popular. In the present investigation, effect of nutrient components of media such as carbon and nitrogen content of organic nutrients and bacterial cells on the chemical and structural properties of concrete were studied. The retarding effect of organic nutrient medium on setting property of cement paste and decrease in compressive strength of concrete was observed. However, no impact on setting property of cement paste admixed with bacterial culture was observed. Significant increase in compressive strength and reduction in permeability was observed with bacterial admixed and surface treated concrete specimens. Carbon and nitrogen content were significantly increased in bacterial treated specimens compared to control. No significant variation in pH was observed from the samples collected from different depths of the concrete specimens both in bacterial treated and control specimens. Present study results suggested that biogenic precipitations of CaCO 3 by bacterial cells counteract the retarding effect of organic nutrients of concrete and enhance the durability properties. [ABSTRACT FROM AUTHOR]

Highlights • Sulfate attack (chemical and physical) causes severe damage to concrete structures. • Surface deterioration & strength loss of concrete was not found in bacteria treated specimens. • Mortars showed no surface scaling and salt efflorescence due to bacterial treatment. • Bacteria improved the lifecycle performance of concrete in sulfate environment. Abstract Application of microbial induced calcium carbonate precipitation (MICP) via biomineralization process has been considered as a novel method in improving durability properties of concrete. This bio-based treatment had been extensively targeted to improve the overall performance of concrete at lab scale experiments. Durability of microbial treated concrete under aggressive environments is still unexplored. In the current study, the durability properties of microbial treated concrete structures were studied after exposure to chemical and physical sulfate salt solutions (5% Na 2 SO 4 and 5% MgSO 4). It has been observed that sulfate attack damaged the untreated concrete specimens causing ultimate failure due to expansion under both exposure regimes. Thick salt efflorescence and severe surface scaling was observed in untreated mortar during physical sulfate attack. However, specimens treated with bacteria (Bacillus sp. CT5) significantly improved the resistance towards sulfate ingress. The experimental results indicate the extensive reduced expansion rate, salt efflorescence and surface scaling in bacterial treated concrete in sulfate exposure. The present study results indicates the potential of this technology in the overall improved resistance of microbial concrete against sulfate environment. [ABSTRACT FROM AUTHOR]