Microbial Induced Calcium Carbonate Research Articles

Impact of flow-direction and gravitational settling on microbially-induced calcium carbonate precipitation (MICP) in rock fractures

Impact of flow-direction and gravitational settling on microbially-induced calcium carbonate precipitation (MICP) in rock fractures

Generation of enhanced endospores for microbially induced calcium carbonate precipitation (MICCP) via thermal shock for concrete self-healing

Endospores are desirable phenotypes in Microbially-Induced Calcium Carbonate Precipitation (MICCP) for their durability in challenging environments. This study investigates the impact of various endosporulation methods on endospore morphology and their subsequent performance under harsh conditions. Results revealed that the Thermal Shock (TS) method produced larger endospores, possibly due to multi-layer encasement. Notably, endosporulation and germination ratios, besides MICCP effectiveness, achieved via TS-produced endospores surpass that of the Carbon Starvation method, both in vitro and within a cement-paste setting under freeze and thaw cycling. This outcome underscores the pivotal role of utilizing TS-produced endospores for concrete self-healing, particularly in cold areas.

Stress sensitivity of permeability in high-permeability sandstone sealed with microbially-induced calcium carbonate precipitation

Microbially induced carbonate precipitation (MICP) catalyzed by S. pasteurii has attracted considerable attention as a bio-cement that can both strengthen and seal geomaterials. We investigate the stress sensitivity of permeability reduction for the initially high-permeability Berea sandstone (initial permeability ∼110 mD) under various durations of MICP-grouting treatment. The results indicate that after 2, 4, 6, 8 and 10 cycles of MICP-grouting, the permeabilities decrease incrementally by 87.9%, 60.9%, 38.8%, 17.3%, and then 5.4% compared to the pre-grouting condition. With increasing the duration of MICP-grouting, the sensitivity of permeability to changes in stress gradually decreases and becomes less hysteretic. This stress sensitivity of permeability is well represented by a power-law relationship with the coefficients representing three contrasting phases: an initial slow reduction, followed by a rapid drop, culminating in an asymptotic response. This variation behavior is closely related to the movement and dislocation of the quartz framework, which is controlled by the intergranular bio-cementation strength. Imaging by scanning electron microscopy (SEM) reveals the evolution of the stress sensitivity to permeability associated with the evolving microstructures after MICP-grouting. The initial precipitates of CaCO3 are dispersed on the surfaces of the quartz framework and occupy the pore space, which is initially limited in controlling and reducing the displacement between particles. As the precipitates continuously accumulate, the intergranular slot-shaped pore spaces are initially bonded by bio-CaCO3, with the bonding strength progressively enhanced with the expanding volume of bio-cementation. At this stage, the intergranular movement and dislocation caused by compaction are reduced, and the stress sensitivity of the permeability is significantly reduced. As these slot-shaped pore spaces are progressively filled by the bio-cement, the movement and dislocation caused by compaction become negligible and thus the stress sensitivity of permeability is minimized.

High strength bio-concrete for the production of building components

The production of bio-concrete is based on the process of microbially-induced calcium carbonate precipitation (MICP), in which calcium carbonate (CaCO3) is formed as a binder. Bio-concrete is a potentially CO2-neutral alternative to conventional Portland-cement-based concrete, since no process-related carbon dioxide emissions are generated during biomineralization. Furthermore, CO2 is bound in the form of carbonate. However, achieving compressive strength values comparable to conventional concrete, in combination with sufficient component depth, has been a significant challenge in the MICP research. In the present study, a combination of methods was implemented, including the use of urease-active calcium carbonate powder (UACP) instead of free bacterial cells, optimization of aggregate packing density, and the implementation of an automated stop-flow pressure injection method. A variety of cementation parameters were tested to determine the optimal conditions for the production of homogeneously cemented high strength bio-concrete. Additionally, reproducibility and optimization studies have been conducted with selected parameter combinations. It was found that achieving homogeneous compaction with sufficient aggregate packing density played a crucial role in obtaining consistent and high-quality cementation results. A combination of a very high compressive strength of 52.5 MPa and a cementation depth of 140 mm has been reached, which has not been reported in previous publications. These findings might unveil new possibilities for bio-concrete to be used in the production of prefabricated load-bearing building components, where it could partially replace traditional concrete.

Applying the first microcapsule-based self-healing microbial-induced calcium carbonate materials to prevent the migration of Pb ions

Lead (Pb) accumulation can lead to serious threats to surrounding environments and damage to the liver and kidneys. In the past few years, microbial-induced carbonate precipitation (MICP) technology has been widely applied to achieve Pb immobilization due to its environmentally friendly nature. However, harsh pH conditions can cause the instability of the carbonate precipitation to degrade or dissolve, increasing the potential of Pb2+ migration into nearby environments. In this study, microcapsule-based self-healing microbial-induced calcium carbonate (MICC) materials were applied to prevent Pb migration. The highest sporulation rate of 95.8% was attained at 7 g/L yeast extract, 10 g/L NH4Cl, and 3.6 g/L Mn2+. In the germination phase, the microcapsule not only prevented the bacterial spores from being threatened by the acid treatment but secured their growth and reproduction. Micro analysis also revealed that cerussite, calcite, and aragonite minerals were present, while extracellular polymeric substances (EPSs) were identified via Fourier transform infrared spectroscopy (FTIR). These results confirm their involvement in combining Pb2+ and Ca2+. The immobilization efficiency of above 90% applied to MICC materials was attained, while it of below 5% applied to no MICC use was attained. The findings explore the potential of applying microcapsule-based self-healing MICC materials to prevent Pb ion migration when the calcium carbonate degrades under harsh pH conditions.

Development of a nature-inspired polymeric fiber (BioFiber) for advanced delivery of self-healing agents into concrete

In this study, we developed nature-inspired multi-functional polymeric fibers (called BioFiber) to deliver bio-self-healing agents into cementitious materials. BioFibers were manufactured using a load-bearing core-fiber, a sheath of endospore-laden hydrogel, and an outer damage-responsive polymeric shell layer. The innovative BioFiber integrates three key functionalities into the quasi-brittle matrix: (i) autonomous bio-self-healing, (ii) crack growth control, and (iii) damage-responsiveness. The hydrogel sheath contained endospores, as bio-agents, to establish microbially-induced calcium carbonate precipitation (MICCP) as a self-healing end-product. The core-fibers provided crack growth control functionality into quasi-brittle engineering materials. Additionally, the outer shell coating integrated a robust damage-responsive self-healing activation strategy in concrete. A comprehensive parametric study was conducted to explore material options and the influential parameters for tailoring the processing-compositions-structure properties of the developed BioFiber. The findings of this study revealed that a concentration of 8 w/v sodium-alginate crosslinked with calcium acetate provided higher solution uptake capacity required for MICCP. As for the shell, the polymer blend of polystyrene and polylactic acid (1:1 wt%), with polymer/solvent ratio of 18 w/v-single layer coating, effectively protected BioFibers during simulated concrete casting process. Lastly, each BioFiber was able to produce 40–80 mg of calcium carbonate within the first 30 h of activation.

Effect of a harsh circular environment on self-healing microbial-induced calcium carbonate materials for preventing Pb2+ migration

Microbially induced carbonate precipitation (MICP) is increasingly being explored for Pb-contaminated water bodies and soil remediation. However, the Pb-related precipitate resulting from the MICP process can possibly leach acid over time when subjected to harsh environments, causing serious threats to human health. In this study, for the first time, self-healing microbial-induced calcium carbonate (MICC) materials are proposed and applied to prevent Pb2+ migration where the Pb-related precipitate is acid leached after spore germination, spore-vegetative cell transformation, urease secretion, and urea hydrolysis, thereby producing spore-containing precipitation. This process was repeated five times to explore the effect of a harsh circular environment on self-healing MICC materials. Results indicated that Pb immobilization would have deteriorated if the inosine and trace elements had not been intervened during spore germination and spore-vegetative cell transformation, respectively. The spores and vegetative cells provided extra nucleation sites for Pb2+ and minerals to attach. The extracellular polymeric substances (EPSs) combined Pb2+ with functional groups and chemical bonds to prevent their migration to surrounding environments. The scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM–EDS) images also indicated that the cerussite mineral was precipitated prior to the calcite mineral because Pb2+ had more affinity to combine with CO32- and OH-. An immobilization efficiency of greater than 95% remained nearly the same after five cycles, while it reduced very quickly to less than 10% after three cycles when neglecting the self-healing MICC materials, thus highlighting their relative merits.

State of the art on factors affecting the performance of MICP treated fine aggregates

Microbially-induced calcium carbonate precipitation (MICP) is a promising technique for enhancing the mechanical and durability properties of fine aggregates used in the construction industry. However, several factors affect the success of MICP treatment, including chemical and physical factors, which can impact the treatment's effectiveness. This review paper comprehensively analyzes such factors influencing the effectiveness of MICP treatment. The mechanisms of the MICP process, including enzymatic and non-enzymatic pathways, are discussed in detail. The paper also highlights the challenges and limitations of the technique and identifies research gaps and future directions. This review provides valuable insights into the potential benefits and challenges of using the MICP technique for improving the performance of fine aggregates in concrete and will be of interest to researchers, engineers, and other professionals working in the construction industry.

Microbially-Induced Calcium Carbonate Precipitation Test on Yellow Sandstone Based on LF-NMR Monitoring

The microbially-induced calcium carbonate precipitation (MICP) technique has shown great robustness in dealing with soil and groundwater contamination problems. A typical result of the implementation of MICP technique is a change in the pore structure. In this study, the effects of MICP on the pore structure of yellow sandstone from the Zigong area, Sichuan, China under different conditions, (e.g., temperature, pH, and calcium ion concentration) are investigated using LF-NMR resonance. The pore network of yellow sandstone is accurately measured using the peak area of the T2 spectral signal. The distribution of calcium carbonate in the pores of the yellow sandstone is characterized by the magnitude of the T2 signal variation. The results show that the precipitation of calcium carbonate caused by MICP tends to be deposited in relatively large pores. However, the calcium carbonate precipitates in the smaller pores at a higher temperature. A higher pH considerably enhances the precipitation, and the alkaline environment tends to cause the precipitation of the calcium carbonate in the large pores. Although the amount of produced calcium carbonate continuously increases as the MCIP process continues, which is expected, the production efficiency decreases steadily.

Evaluation of the bonding properties between low-value plastic fibers treated with microbially-induced calcium carbonate precipitation and cement mortar

Plastic fiber reinforced cementitious materials offer the potential to increase the reusability of plastic waste and create lower-CO2 cementitious composites. However, the bonding properties of many plastic types with ordinary Portland cement (OPC) are largely unknown. This work employs single fiber pullout (SFPO) tests to quantify the interfacial bonding properties of polyvinyl chloride, low-density polyethylene, polypropylene, polystyrene, and acrylonitrile butadiene styrene embedded in OPC mortar. The interfacial bonding properties were compared for fibers either treated with microbially-induced calcium carbonate precipitation (MICP) or left untreated. SFPO tests revealed that plastic type had a large influence over bonding properties. Specifically, the fiber surface energy, as estimated from water contact angle measurements, was found to be the driving factor of bond strength. ABS had the highest surface energy and demonstrated the strongest bonding out of all plastic types studied. However, MICP treatment of fibers did not increase the interfacial bond strength for any of the plastics studied. The thick and inconsistent coverage of biomineral over the fiber surface from MICP is likely attributed to preventing an increase in bond strength. These results contribute to the design and application of plastic-reinforced mortars by comparing bonding properties for a range of typically low-value, unrecycled plastic types.

Mineralogy, morphology, and reaction kinetics of ureolytic bio-cementation in the presence of seawater ions and varying soil materials

Microbially-induced calcium carbonate precipitation (MICP) is a bio-cementation process that can improve the engineering properties of granular soils through the precipitation of calcium carbonate (CaCO3) minerals on soil particle surfaces and contacts. The technology has advanced rapidly as an environmentally conscious soil improvement method, however, our understanding of the effect of changes in field-representative environmental conditions on the physical and chemical properties of resulting precipitates has remained limited. An improved understanding of the effect of subsurface geochemical and soil conditions on process reaction kinetics and the morphology and mineralogy of bio-cementation may be critical towards enabling successful field-scale deployment of the technology and improving our understanding of the long-term chemical permanence of bio-cemented soils in different environments. In this study, thirty-five batch experiments were performed to specifically investigate the influence of seawater ions and varying soil materials on the mineralogy, morphology, and reaction kinetics of ureolytic bio-cementation. During experiments, differences in reaction kinetics were quantified to identify conditions inhibiting CaCO3 precipitation and ureolysis. Following experiments, scanning electron microscopy, x-ray diffraction, and chemical composition analyses were employed to quantify differences in mineralogical compositions and material morphology. Ions present in seawater and variations in soil materials were shown to significantly influence ureolytic activity and precipitate mineralogy and morphology, however, calcite remained the predominant CaCO3 polymorph in all experiments with relative percentages exceeding 80% by mass in all precipitates.

Effects of Chloride, Sulfate and Magnesium Ions on the Biomineralization of Calcium Carbonate Induced by Lysinibacillus xylanilyticus DB1-12

Microbially-induced calcium carbonate precipitation (MICP) has been studied extensively. However, the effect of different sources of magnesium ions on calcium carbonate biomineralization has rarely been examined. In this study, Lysinibacillus xylanilyticus DB1-12 bacteria isolated from petroleum samples were used to biomineralize calcium ions under the action of different sources of magnesium (magnesium chloride and magnesium sulfate). The results show that calcium ion precipitation ratios were much higher in MgSO4 group experiments than in the MgCl2 group (p < 0.01). The mineral phases in the MgCl2 group experiments were the same as those in MgSO4 group at each Mg/Ca ratio. Minerals with a ‘twisted’ shape were much more common in the MgSO4 group; the protein secondary structures hidden in minerals were much more abundant in the MgCl2 group, and the activation energy of biotic monohydrocalcite at a Mg/Ca ratio of 11 was also much higher in the MgCl2 group than in the MgSO4 group. The main reasons for these differences are closely related to the lower magnesium content and the more common protein secondary structures in the monohydrocalcite in the MgCl2 group. The shift of Mg1s XPS spectra suggests that the chemical interactions occurring on the monohydrocalcite surfaces in the MgCl2 group were different from those in the MgSO4 group. The δ13CPDB values of the biominerals in the MgSO4 group are in the range of −16.93 to −18.87‰, lower than those in the MgCl2 group (-15.77 to −18.69‰). The morphology of L. xylanilyticus DB1-12 became deformed and some rod-shaped protrusions developed on the cell surface during the process of biomineralization. This study not only contributes to the understanding of biomineralization mechanisms generally, but is also helpful in the interpretations of paleo-environmental conditions.

Permeable rock matrix sealed with microbially-induced calcium carbonate precipitation: Evolutions of mechanical behaviors and associated microstructure

Microbially-induced calcium carbonate precipitation (MICP) is a promising grouting material for subsurface remediation due to its water-like viscosity and excellent penetration. Current studies of MICP-grouting for subsurface remediation of both rock fractures and highly-permeable rock matrix focus on the spatio-temporal distribution of precipitated bio-CaCO3 and the resulting reduction in permeability. Conversely, we focus on the improvement of mechanical response following MICP-grouting. We contrast the improved mechanical response of MICP-treated Berea sandstones with distinctly contrasting initial mechanical properties - contrasting associated pre- and post-treatment microstructures with various durations of MICP-grouting. Results indicate that although the precipitated CaCO3 mass with time within these two rock types is similar, significant differences exist in the evolution of mechanical properties (UCS, Young's modulus and brittleness). The evolution of mechanical properties for the low-strength sandstone (initial UCS 25.7 MPa) exhibits three contrasting phases: an initial slow increase, followed by a rapid-increase and then saturation and asympotic response. After ten cycles of MICP-grouting, UCS, elastic modulus and brittleness index for low-strength sandstone increase by 229%, 179% and 177% compared with before grouting. In contrast, the mechanical properties for the high-strength sandstone (initial UCS 65.1 MPa) are not significantly enhanced, increasing UCS by only 22%, 14% and 12%. Imaging by scanning electron microscopy (SEM) indicates that the cementing minerals fill the quartz framework for the high-strength sandstone but are sparse for the low-strength sandstone. Sandstone is a clastic sedimentary rock consisting of a framework of quartz grains bonded by cementing minerals. For the high-strength sandstone infused with a large mass of cementing minerals, the calcium carbonate crystals only precipitate in the gaps between the cementing minerals or adhere to the cementing minerals. This is only capable of relatively limited enhancement in the bio-bonding strength and volume of the quartz framework. For the low-strength sandstone with fewer cementing minerals, the precipitated calcium carbonate is evenly distributed on the surfaces of the quartz gains. The bulk strength is progressively increased with the ongoing bio-cementation between quartz gains. Cementing mineral contents not only exert a considerable control on the integral mechanical properties and penetration for the sandstone, but also have a direct influence on the microscopic distribution of bio-accumulated CaCO3, controlling the effectiveness of bio-cementation by incrementing the mechanical properties.

RESEARCH PROGRESS ON MICROBIAL SELF-HEALING CONCRETE

Crack formation in concrete is inevitable. The cracks allow the penetration of harmful substances which may decrease the durability and the service life of concrete structures. Self-healing concrete is therefore emerging as an innovative construction material to tackle the cracking issues. In recent years, microbial self-healing concrete is garnering interest from many researchers due to its environmentally-friendly nature and the concrete compatibility of microbially-induced calcium carbonate precipitation. Various metabolic mechanisms have been used for microbial self-healing concrete production and urea hydrolysis is the most preferable metabolic pathway due to its fast and high precipitation of calcium carbonate. In this paper, a comprehensive review on the research progress on microbial self-healing concrete is presented together with the numerical modelling of microbial self-healing concrete. The challenges and limitations of microbial self-healing concrete are discussed along with the recommendations for its prospective uses in the construction industry. It is found that the survival of bacteria through direct addition technique is limited and needs further investigation. The immobilization technique gives a promising result in durability properties but doesn’t reach the mechanical requirement. Moreover, a comprehensive assessment of self-healing efficiency is required, and more efforts are needed to improve from laboratory scale to large-scaled application.

Comparison of bacteria-based self-healing methods in metakaolin geopolymer mortars

This study aims to compare the bacteria-based self-healing methods in metakaolin-based geopolymer mortars. In addition, the effects of Microbially-Induced Calcium Carbonate Precipitation (MICP) on the mechanical properties of metakaolin-based geopolymer mortars were determined in this study. For this purpose, the submersion, spray, and injection methods were utilized for bacteria-based self-healing. The bacterial and bacteria-free medium solutions were used in these methods. In addition, the samples without Sporosarcina pasteurii (S.pasteurii) cells (H), the samples with S.pasteurii cells (M), and the samples with both S.pasteurii cells and the nutrient medium (Z) were prepared according to the microbiological content. Metakaolin-based geopolymer cubes and prisms samples using these contents were produced and cured at room temperature (20 ± 2 °C) for 28 days. Then, cracks were formed in the samples. These cracks on samples were healed using different self-healing methods. Lastly, the mechanical properties of samples were determined. This study showed that the injection method was the most effective method for completely closing cracks. Also, this study found that the M series healed with the injection method had the highest recovery percentage for flexural strength, and it was about 29.69%.

Compressive Strength of MICP-Treated Silica Sand with Different Particle Morphologies and Gradings

Microbially-induced calcium carbonate precipitation (MICP) can enhance the stiffness and bulk strength of sand aggregates via calcium carbonate cementation. This study explores the mechanical strength of silica sand aggregates with different particle morphologies and sizes following MICP treatment. Specifically, unconfined uniaxial compressive strength (UCS) of MICP-treated spherical, near-spherical, and angular aggregates are measured for four separate size fractions (18–25, 25–40, 40–60, and 60–80 mesh). Scanning electron microscope (SEM) imaging is performed on post-treatment samples to investigate the difference in cementation morphology and failure mechanisms. The experimental results indicate: (1) given identical cycles of MICP treatment, the UCS of treated spherical and near-spherical sands peaks at 25–40 mesh particle size, while the treated angular sands show increasing UCS with decreasing particle size; (2) spherical sands have the highest calcium carbonate (CaCO3) content given identical MICP cycles; and (3) higher post-treatment CaCO3 content does not correlate to higher UCS—implying that the distribution and morphology of CaCO3 precipitation exert crucial control. SEM analysis shows that CaCO3 fully encapsulates spherical sand particles uniformly, forming point contact bonds. In contrast, CaCO3 precipitations show a patchy distribution on near-spherical and angular sand grain surfaces. Unlike treated spherical sands, treated near-spherical sands feature a mixture of point and planar contact bonds while treated angular sands feature predominantly planar contact bonds. Planar contact bonds provide a larger effective cementation area between sand particles and thus result in higher bonding strength. The particle morphology and resultant inter-particle bonding morphology help reconcile higher ensemble UCS with lower CaCO3 content of treated angular sands.

Microbially-induced calcium carbonate precipitation by a halophilic ureolytic bacterium and its potential for remediation of heavy metal-contaminated saline environments

Heavy metal contamination is widespread in the environment and has resulted in numerous adverse consequences for the ecosystem. Ureolytic microorganisms are known to immobilize heavy metals by co-precipitation with calcium carbonates, which are formed during microbial hydrolysis of urea. In this work, we described a novel halophilic ureolytic bacterium (Exiguobacterium sp. JBHLT-3) and examined the relationship between ureolytic-driven mineralization of CaCO3 and heavy metal mitigation. The growth of strain JBHLT-3 occurred at salinities between 3 and 12% with an optimum at 6%. This strain was capable of precipitating calcite and vaterite under non-growth conditions. Lead (Pb) was selected as a model heavy metal for this study and amended into the bio-precipitation systems at a starting concentration of 1 mM. The strain JBHLT-3 efficiently removed Pb from saline solutions via incorporation within microbially-induced calcium carbonates. Mineralogical analysis showed that calcite had higher uptake of Pb2+ than vaterite. The increasing solution salinity progressively increased the vaterite fraction in the bio-precipitates but reduced the removal efficiency of Pb2+. Nevertheless, the removal efficiency could be still as high as 89% in the cultures incubated in a 12% salinity medium. Our results highlight the positive role of halophilic ureolytic microbes in remediating heavy metal-contaminated saline environments.

Augmentation of physico-mechanical, thermal and biodegradability performances of bio-precipitated material reinforced in Eucheuma cottonii biopolymer films

Green reinforcement in biopolymer for enhanced industrial application is on the increase. Bio-precipitated CaCO3 was synthesised via the process of microbially-induced calcium carbonate precipitation using Bacillus sp. strain. The bio-precipitated CaCO3 (B-PCC) and conventional CaCO3 precipitates (C-PCC) reinforcement effect on the properties of Eucheuma cottonii film was analysed and compared. The biocomposite films were fabricated using a solvent casting technique. The physicomechanical, thermal and biodegradability performances of B-PCC and C-PCC incorporated E. cottonii film with increasing fillers' contents [0.05, 0.10, 0.50, 1.00, 2.00 (wt.%)] were determined and compared through a range of testing include water vapour permeability (WVP), contact angle using sessile drop method, scanning electron microscopy (SEM), tensile, elongation, Young's modulus, thermogravimetric analysis (TGA), and soil burial test. A further comparison was made between the E. cottonii biocomposite film with the existing biodegradable mulch films to evaluate its potential application using wet cup method. Results revealed that biocomposite films embedded with 0.1% B-PCC appeared to exhibit higher water barriers and hydrophobicity behaviours than those embedded with C-PCC. However, the mechanical strength and thermal stability were slightly lower than those embedded with C-PCC. E. cottonii biocomposite films, especially those embedded with 0.1 wt. % B-PCC has shown the potential in agricultural mulch film as it promoted better biodegradation and tensile strength by 34.24% and 20% respectively compared to the existing biodegradable PLA/PBAT mulch film, making it a promising alternative to the conventional plastic to mitigate plastic pollution.

Addressing wellbore integrity and thief zone permeability using microbially-induced calcium carbonate precipitation (MICP): A field demonstration

Microbially-induced calcium carbonate precipitation (MICP) is an emerging biotechnology for wellbore integrity applications including sealing defects in wellbore cement and modifying the permeability of rock formations. The goal of this field demonstration was to characterize a failed waterflood injection well and provide proof of principle that MICP can reduce permeability in the presence of oil using conventional oilfield fluid delivery methods. We compared well logs performed at the time the well was drilled with ultrasonic logs, sonic cement evaluation, and temperature logs conducted after the well failed. Analysis of these logs suggested that, rather than entering the target waterflood formation, injectate was traveling through defects in the well cement to a higher permeability sandstone layer above the target formation. Sporosarcina pasteurii cultures and urea-calcium media were delivered 2290 ft (698 m) below ground surface using a 3.75 gal (14.2 L) slickline dump bailer to promote mineralization in the undesired flow paths. By Day 6 and after 25 inoculum and 49 calcium media injections, the injectivity [gpm/psi] had decreased by approximately 70%. This demonstration shows that 1) common well logs can be used to identify scenarios where MICP can be employed to reduce system permeability, remediate leakage pathways, and improve waterflood efficiency, and 2) MICP can occur in the presence of hydrocarbons.

The Application of Lysinibacillus sphaericus for Surface Treatment and Crack Healing in Mortar

Micro-cracks, which develop during the service life of reinforced concrete structures, reduce the durability of concrete through the penetration of fluids. Microbially-induced calcium carbonate precipitation (MICP) occurs naturally in the presence of ureolytic bacteria which precipitate calcium carbonate (CaCO3) through urea hydrolysis. This deposition leads to the filling of micro-cracks and sealing of pores, reducing ingress of fluids into the concrete. The research aims were to assess the potential of Lysinibacillus sphaericus for healing cracks in concrete and to study the effects of this treatment on the absorption properties of treated concrete. Lysinibacillus sphaericus was cultivated in vitro and induction of MICP through urea hydrolysis was tested on cement paste with two different calcium sources. The calcium precipitates where characterised by light microscopy, Scanning Electron Microscopy, Energy Dispersive Spectroscopy and Fourier Transform Infrared Spectroscopy. The final phase of the study involved testing of the crack healing capacity and the effect on absorption of the MICP process on mortar samples. These parameters were measured by means of visual examinations, light & digital microscopy, Ultrasonic Pulse Velocity (UPV) and absorption tests. The study confirmed that MICP is induced successfully on concrete using Lysinibacillus sphaericus. Samples exposed to repeated treatment cycles of Lysinibacillus sphaericus in the presence of a calcium source, exhibited a more extensive and even coating of CaCO3 crystals on the surface confirming that repeated cycles of treatment are more effective in increasing the amount of CaCO3 deposition and therefore increasing crack healing capacity. Digital microscopy and UPV analysis proved that this precipitate was successful in partially healing cracks in samples. Sorptivity tests confirmed this and showed that it was also successful as a surface treatment to reduce absorption.