Influence of Lysinibacillus sphaericus on compressive strength and water sorptivity in microbial cement mortar

Bio-strengthening of cementitious composites from incinerated sugarcane filter cake by a calcifying bacterium Lysinibacillus sp. WH

This study investigated Microbially Induced Calcite Precipitation (MICP) technology to improve the mechanical properties of cementitious composites containing incinerated sugarcane filter cake (IFC) using a calcifying bacterium Lysinibacillus sp. WH. Both IFC obtained after the first and second clarification processes, referred to as white (IWFC) and black (IBFC), were experimented. This is the first work to investigate the use of IBFC as a cement replacement. According to the X-ray fluorescence (XRF) results, the main element of IWFC and IBFC was CaO (91.52%) and SiO₂ (58.80%), respectively. This is also the first work to investigate the use of IBFC as a cement replacement. We found that the addition of strain WH could further enhance the strength of both cementitious composites up to ~ 31%, while reduced water absorption and void. Microstructures of the composites were visualized using a scanning electron microscope (SEM). The cement hydration products were determined using X-ray diffraction (XRD) followed by Rietveld analysis. The results indicated that biogenic CaCO₃ was the main composition in enhancing strength of the IBFC composite, whereas induce tricalcium silicate (C₃S) formation promoting the strength of IWFC composite. This work provided strong evidence that the mechanical properties of the cementitious composites could be significantly improved through the application of MICP. In fact, the strength of IFC-based cementitious composites after boosting by strain WH is only 10% smaller than that of the conventional Portland cement. While using IFC as a cement substitute is a greener way to produce environmentally friendly materials, it also provides a solution to long-term agro-industrial waste pollution problems.

Effect of Immobilizing Bacillus megaterium on the Compressive Strength and Water Absorption of Mortar

The world’s growing population and industrialization have led to increased construction activities. This has increased the amount of waste aggregates which can be recycled in construction and cut the cost of infrastructure development. This study, therefore, reports the experimental findings for the effect of immobilizing Bacillus megaterium on the compressive strength and water absorption of laboratory prepared test mortar. Bacterial solution used in this work had a concentration of 1.0 × 107 cells/mL. The impact of recycled mortar impregnated with bacteria was studied after curing the specimens in water, saturated lime water, and 1.5% sulfuric acid. Compressive strength for test specimens cured in the three media was determined at the 2nd, 7th, 28th, and 56th day of curing. SEM analysis was done for mortars cured in acidic media and saturated lime water after curing for 28 days. The test results indicated that curing in water and saturated water improved the compressive strength, while the acidic medium lowered it. Recycled mortar is, therefore, an ideal material for immobilizing Bacillus megaterium before introduction into fresh concrete/mortar. The use of recycled mortar is a good strategy to reduce wastes from construction activities, save on the cost of construction materials, and enhance environmental conservation.

Kinetic model of a newly-isolated Lysinibacillus sp. strain YL and elastic properties of its biogenic CaCO3 towards biocement application

BACKGROUND

Biocement, calcifying bacteria-incorporated cement, offers an environmentally-friendly way to increase the cement lifespan. This work aimed to investigate the potential use of Lysinibacillus sp. strain YL towards biocement application in both theoretical and experimental ways.

METHODS AND RESULTS

Strain YL was grown using calcium acetate (Ca(C₂ H₃ O₂ )₂ ), calcium chloride (CaCl₂ ) and calcium nitrate (Ca(NO₃ )₂ ). Maximum bacterial growth of ~0.09 hr-1 and the highest amount of CaCO₃ precipitation of ~8.0 g/L were obtained when using Ca(C₂ H₃ O₂ )₂ . The SEM and XRD results confirmed that biogenic CaCO₃ were calcites. The bulk, Young's and shear moduli of biogenic CaCO₃ calculated via the VRH approximation were ~1.5-2.3 times larger than those of ordinary Portland cement. The Poisson's ratio was 0.382 and negative in some directions, suggesting its ductility and auxetic behaviors. The new model was developed to explain the growth kinetic of strain YL in the presence of Ca(C₂ H₃ O₂ )₂ , whose concentration was optimized for biocement experiments. Strain YL could increase the compressive strength of cement up to ~50% higher than that of the uninoculated cement.

CONCLUSION

Strain YL is a promising candidate for biocement applications. This work represents the trials of experiments and models allowing quantitatively comparison with large-scale production in the future.

Bioremediation of mortar made from Ordinary Portland Cement degraded by Thiobacillus thioparus using Bacillus flexus

Cement is widely used as a construction material in the construction industry. However, there are challenges affecting its durability efficacy. Cement mortar/concrete is subject to degradation by aggressive ions such as sulphates and chlorides. Sulphates can be introduced into the concrete or mortar by Sulphur producing bacteria of the species Thiobacilli. Microbiologically induced CaCO₃ precipitation (MICP) has found its application in bioremediating cement based materials. It has been found to be environmental friendly. However, no work has been reported on bioremediation of biodegraded cement based materials. This paper presents findings of possible bioremediation of mortars after undergoing biodegradation. Bacillus flexus, a beneficial bacterium was used. The control mortars were prepared using Ordinary Portland Cement (OPC). The test mortars were prepared and cured in a solution of Thiobacillus thioparus, a Sulphur oxidizing bacteria, deleterious bacterium for 14, 28, 56 and 90 days. Compressive strength analysis was conducted on the 14^th, 28^th, 56^th and 90^th day of curing. Results showed that the lowest compressive strength was recorded on the 90^th day as 31.02 MPa. This was a 34.17 % loss in compressive strength. Another category of mortar cured in Thiobacillus thioparus for 28 days was bioremediated for 28 days using Bacillus flexus solution. Compressive strength and Scanning Electron Microscopy (SEM) analyses were then done. The results show a compressive strength of 45.83 MPa at the 56^th day. This represents a 99.91 % strength recovery from biodeterioration. The SEM analysis results revealed a denser material. This was due to massive precipitation of calcium carbonate in the mortar matrix and pores/voids for bioremediated mortars as opposed to the biodegraded mortars. The results further revealed reduced ettringite crystals on the bioremediated mortars. Bacillus flexus could perhaps be used in restoring lost compressive strength as well as in sealing voids in degraded concrete in sewer lines and other cement based materials. This could improve on its efficacy with minimal repair.

Investigating mechanical properties and biocement application of CaCO3 precipitated by a newly-isolated Lysinibacillus sp. WH using artificial neural networks

A newly-isolated Lysinibacillus sp. strain WH could precipitate CaCO₃ using calcium acetate (Ca(C₂H₃O₂)₂), calcium chloride (CaCl₂) and calcium nitrate (Ca(NO₃)₂) via non-ureolytic processes. We developed an algorithm to determine CaCO₃ crystal structures by fitting the simulated XRD spectra to the experimental data using the artificial neural networks (ANNs). The biogenic CaCO₃ crystals when using CaCl₂ and Ca(NO₃)₂ are trigonal calcites with space group R3c, while those when using Ca(C₂H₃O₂)₂ are hexagonal vaterites with space group P6₅22. Their elastic properties are derived from the Voigt–Reuss–Hill (VRH) approximation. The bulk, Young's, and shear moduli of biogenic calcite are 77.812, 88.197, and 33.645 GPa, respectively, while those of vaterite are 67.082, 68.644, 25.818 GPa, respectively. Their Poisson’s ratios are ~ 0.3–0.33, suggesting the ductility behavior of our crystals. These elastic values are comparable to those found in limestone cement, but are significantly larger than those of Portland cement. Based on the biocement experiment, the maximum increase in the compressive strength of Portland cement (27.4%) was found when Ca(NO₃)₂ was used. An increased strength of 26.1% was also found when Ca(C₂H₃O₂)₂ was used, implying the transformation of less-durable vaterite to higher-durable calcite. CaCO₃ produced by strain WH has a potential to strengthen Portland cement-based materials.

Effect of Bacillus cohnii on Some Physicomechanical and Microstructural Properties of Ordinary Portland Cement

Cement-made materials face durability and sustainability challenges. This is majorly caused by the presence of cracks. Cracking affects the mechanical strength of cement-based materials. Microbiologically induced calcite precipitation (MICP) has been found to enhance compressive strength, thus enhancing on the mechanical and durability properties of these materials. This paper presents the findings of a study conducted to investigate the effect of Bacillus cohnii on compressive strength development of OPC mortar prisms and the effect of Bacillus cohnii on cement setting time and soundness. Microbial concentration of 1.0 × 107 cells·ml−1 was used. Compressive strength tests analyses were carried out for each category of mortar prisms. Compressive strength tests were carried out on the 2nd, 7th, 14th, 28th, 56th, and 90th day of curing in distilled water and microbial solutions. All microbial mortars exhibited a greater compressive strength compared to the control with the highest observed at 90 days. Highest percentage gain in compressive strength was observed at 90 days which is 28.3%. Microstructural analysis was carried out using a scanning electron microscope (SEM) after 28 days of curing. The results indicated the presence of calcium carbonate and more calcium silicate hydrate (CSH) deposits on the bacterial mortars. The bacteria did not have an effect on cement soundness. Setting time was significantly accelerated.

Study on the effect of Thiobacillus intermedius bacteria on the physico-mechanical properties of mortars of ordinary portland cement

Most of concrete structural failures are attributed to poor workmanship and poor engineering designs. Some microorganisms present in sewer systems can degrade the concrete and/or mortar. Concrete failures due to microbial attack has not attracted much attention especially in developing countries such as Kenya. This study investigated the effect of Thiobacillus intermedius bacteria on the performance of Ordinary Portland Cement (OPC). Preparation of test mortar prisms was done using the bacterial solution as either mix water, curing water or both. The control mortar prisms were prepared and cured in distilled water. Compressive strength test was done after 7^th, 28^th, 56^th and 90^th days of curing respectively. Results showed significant drop in compressive strength for the mortar prisms prepared and cured in bacterial solution as compared to the control mortar samples. Soundness and normal consistency increased significantly for the bacterial treated cement paste as compared to the control sample. Scanning Electron Microscopy (SEM) analysis showed severe damage on the bacterial treated cement mortar. This was characterized by formation of deleterious expansive products like ettringite and gypsum. Control mortar sample exhibited even formation of hydration products within the pore system.