Microbial Mortars Research Articles

Enhancing the interfacial compatibility and self-healing performance of microbial mortars by nano-SiO2-modified basalt fibers

Fibers that enhance the self-healing ability of microbial mortar cracks have been widely studied. This study explored the impact of modified fibers on the self-healing performance and interfacial compatibility of microbial mortar by incorporating expanded perlite as a carrier of self-healing agents and basalt fibers modified with nano-SiO2. The effect of modified fibers on the mechanical properties of mortar was analyzed through compressive and flexural strength tests. The crack-healing effect of the specimens was evaluated using crack observation, UPV tests, and water absorption experiments, and the crack fillers were analyzed through SEM and XRD experiments to reveal the self-healing mechanism. The experimental results confirm that the nano-SiO2 loaded on the surface of the modified fibers exhibits Pozzolanic reactivity and can react with Ca2+ and OH− in the pore solution of the mortar to form secondary C-S-H on the fiber surface, which enhances the bonding ability between the fibers and the cement slurry, effectively improving the mechanical properties of the specimens. The rough surface of the modified fibers facilitates the deposition of calcite produced by microbes and hydration products, promoting the early-stage healing rate. Furthermore, due to the C-S-H shell on the surface of the modified fibers, the electronegativity of the fiber surface is improved, which is beneficial for bacterial adhesion and promotes the deposition of calcite, ultimately enhancing the self-healing capability.

Enhancing self-healing performance of microbial mortar through carbon fiber reinforcement: An experimental analysis

The incorporation of fibers has been shown to be an effective means to enhance self-healing properties of biomass self-healers in cementitious materials. In this study, the mechanism of carbon fiber-enhanced self-healing ability for self-healing agent made by straw charcoal adsorbed bacteria in mortars was investigated. Mechanical properties, compressive strength restoration properties and permeability testing of microbial mortars were evaluated. Our findings reveal a synergistic effect between carbon fibers and the self-healing agent, notably in crack repair. Although fibers alone did not significantly increase compressive strength, can play a crucial role in promoting Ca2+ aggregation and facilitating the transformation of spores into bacteria, which resulted in the formation of structurally intact and layered calcium carbonate, result in significantly enhanced the self-healing efficacy of microbial mortars. The results of this study show for the first time that carbon fibers have a significant effect on the self-healing capacity of biomass mortar.

Preliminary study on double-sided direct shear test of microbial mortar

A new method of strengthening masonry structures of ancient architecture has been proposed, which involves the use of microbial grouting to generate mineralized mortar. To study the shear mechanical properties of microbial mortar, a comparative experiment was designed with 9 groups of specimens, including acid washing method to test the amount of calcium carbonate, penetration method to test compressive strength of mortar, double-sided direct shear method to test shear strength of mortar and get shear stress-strain curve. According to the experimental results, when the brick joint is thick, more bubbles remain at the contact between the brick and the mortar, reducing the saturation of the grouting liquid and affecting the amount of calcium carbonate generated, thereby affecting the shear strength of the mortar. When the brick is placed vertically, the contact area between the brick and the mortar is on the side, and it is not easy for bubbles to remain, so the amount of calcium carbonate generated is high, and the corresponding shear strength of the mortar is high. Reducing the concentration of calcium solution and implementing bidirectional perfusion can slow down the deposition of calcium carbonate and blockage of perfusion pathways, thereby improving the homogeneity of the carbonate level. A well-graded filling of sand particles is an effective measure to improve the binding efficiency of calcium carbonate.These measures not only increase the production of calcium carbonate, but also result in higher compressive and shear strength.The shear stress-displacement curve of microbial mortar specimens with damagedmortar layer exhibits strain-softening behavior, while the specimens with inter facial damage show strain-hardening behavior.The shear strength of specimens with interface damage is lower than that of specimens with mortar layer damage, so measures should be taken to avoid interface damage.

Study on the prompting effect of basalt fibers on the change from two-dimensional to three-dimensional deposition of CaCO3 to improve the healing properties of microbial mortars

Microbial-induced calcium carbonate precipitation (MICP) is utilized to effectively seal microcracks in concrete. In this study, coconut shell charcoal was used as a carrier for adsorbed bacteria to act as a biomass self-healing agent, and the healing effect of microbial mortar was enhanced by the addition of basalt fibers. The effect of the combined action of biomass self-healing agents and fibers on the mechanical properties and healing ability of mortars has been investigated. The complete process of microbial metabolism in the cement matrix was firstly revealed by microscopic experiments. Optical microscopy was used observed the deposition paths of the fillers under multifiber conditions at different depths. The results showed that a large number of fibers changed the healing products that transformed from two-dimensional to three-dimensional due to the bridging effect between the calcium carbonate grown on the neighboring fibers, which enhanced the healing ability of the cracks.

Effect of basalt fibers on the mechanical and self-healing properties of expanded perlite solid-loaded microbial mortars

Microbial-induced calcium carbonate precipitation (MICP) is an environmentally friendly technology to repair cracks. In this study, expanded perlite was used to adsorb bacteria as a self-healing agent, and basalt fibers were used for the first time to enhance the healing effect of microbial mortar. The mechanical properties and impermeability of fiber-reinforced bacterial concrete were investigated, the macroscopic crack healing effect and the precipitation path of generates were observed by optical microscopy, and the coupling effect of fibers and bacteria was studied and revealed by microscopic experiments. It was shown that the addition of a self-healing agent made the self-healing performance of mortar significantly enhanced, and the incorporation of fibers enhanced the mechanical properties and impermeability of the mortar. The basalt fibers provided the location for calcium carbonate precipitation, and its bridging action provided the pathway for precipitation. The fibers offered the possibility of healing cracks larger than 300 μm in width.

Self-healing mortar using different types, content, and concentrations of bacteria to repair cracks.

The creation of cracks, which are the most common cause of structural failure, has a significant impact on the structure's strength and durability. As a result, effective repair and maintenance are vital and unavoidable for treating any of these issues. Self-healing mortar holds promising benefits for reducing the cost of repair as cracks are autonomously repaired without any human intervention. This study investigated the effect of bacteria type, bacteria content, bacteria concentration, and nutrient type on the properties of the self-healing mortar. Three types of bacteria, Bacillus sphaericus, Bacillus Megaterium, and Bacillus subtilis encapsulated in calcium alginate beads, were introduced into the mortar. Two concentrations of bacteria, 2× 108 and 2× 109 Colony Forming Units per milliliter, and different percentages of bacteria of cement weight were selected for the study. In addition, calcium lactate and calcium acetate were used at 0.5% of cement weight as nutrition for bacteria. Tests were performed for compressive strength, bending strength, SEM, EDX, and TGA/DTG. The results show a significant development in the mechanical behaviour of mortar, especially with Bacillus Megaterium using a 2.5% bacterial proportion with a concentration 2× 109 CFU/ml. This can be related to the filling of voids and cracks in microbial mortar by calcite, which was confirmed by SEM and EDX.

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.

Influence of Starkeya novella on Mechanical and Microstructural Properties of Cement Mortars

Cement-based materials are subject to degradation during their service life. Most of the structural failures have been associated with corrosion of the rebar due to chloride ingress, alkali aggregate reaction, and/or sulfate attack. Microbial activities, especially in waste water collection points such as sewer lines, may compromise the integrity of concrete structures. This study reports an experimental work carried out to determine the effect of Starkeya novella bacteria species on mechanical and microstructural properties of cement mortars. Mortar prisms were prepared from selected ordinary Portland cement (OPC) and Portland pozzolana cement (PPC) in Kenyan markets. Bacterial solution of 1.0 × 107 cell/mL concentration was used as either mix water, curing media, or both. Distilled water was used to prepare mortar prisms for control samples. Compressive strength was determined after the 7th, 28th, 56th, and 90th day of curing. Scanning electron microscopy (SEM) was tested on both bacterial and control mortar prisms after the 28th day of curing. Both PPC and OPC exhibited significant decrease in compressive strength for bacterial-prepared mortars as compared to controls. SEM analysis showed extreme erosion on the microstructure of the microbial mortars. This was denoted by massive formation of ettringite and gypsum which are injurious to mortar/concrete.

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

Cement structures are subject to degradation either by aggressive media or development of micro/macro cracks which create external substance ingress pathways. Microbiocementation can be employed as a self-intelligent solution to this deterioration process. This paper presents study results on the effects of Lysinibacillus sphaericus microbiocementation on Ordinary Portland cement (OPC), normal consistency, setting time, soundness, compressive strength and water sorptivity. Microbial solutions with a concentration of 1.0 × 107 cells/ml were mixed with OPC to make prisms at a water/cement ratio of 0.5. Mortar prisms of 160 mm × 40 mm x 40mm were used in this study. A maximum compressive strength gain of 17% and 19.8% was observed on the microbial prism at the 28th and 56th day of curing respectively. A minimum of 0.0190 and a maximum of 0.0355 water sorptivity coefficient was observed on the OPC microbial prism and OPC control prism, after 28th day of curing respectively. Scanning electron microscope images taken after the 28th day of curing showed formation of vast calcium silicate hydrates and more calcite deposits on microbial mortars. Statistical findings of this study indicate that Lysinibacillus sphaericus significantly retarded both the setting time and normal consistency, but has no influence on the mortar soundness.

Recycled microbial mortar: Effects of bacterial concentration and calcium lactate content

This study investigated the optimum bacterial concentration and calcium lactate content in mortars containing recycled concrete aggregate (RCA) as full replacement of natural fine aggregate (NFA) for the first time. For this purpose, bacterial mortars with cells concentration of 103, 105 and 107 cells/ml were prepared. Calcium lactate was used as the organic precursor at dosages of 1%, 3%, and 5% of cement weight. The mechanical, durability, crack healing, and microstructural characteristics of the bacterial mixes were examined and compared to those of the control mix. The results indicated that incorporating bacterial cells with concentration of 105 cells/ml treated with 1% calcium lactate led to the optimal mix. The 28-day compressive strength of the optimal mix increased by 21% over that of the control mix. The lowest water absorption was also recorded for this mix, which was about 7% lower than that of the control mix. The scanning electron microscopy (SEM) images of the optimal mix showed a dense and compact microstructure as a result of calcite precipitation, which filled the air voids and reduced the pore size. Increasing the calcium lactate content lowered the quality of the pore system due to overproduction of calcium carbonate (CaCO3) crystals. This was confirmed by the results of porosimetry test using mercury injection method where the sample prepared with 5% calcium lactate and bacterial concentration of 103 cells/ml showed 450% higher total porosity as compared to the control sample. On the other hand, crack healing analysis revealed that the maximum healing in surface cracks occurred at the maximum bacterial concentration and calcium lactate content.

Enhanced crack closure performance of microbial mortar through nitrate reduction

Microbial self-healing of concrete has been widely investigated, yet the suggested microbial pathways are limited to ureolysis and the aerobic oxidation of carbon sources. Each of these pathways has certain environment and process related drawbacks which arise a need for an alternative pathway to proceed further. This study presents the NO3− reduction as an alternative microbial self-healing strategy. In the tests, we used previously described NO3− reducing bacteria, and two different porous protective carriers. The highest crack width healed by the bacteria was 370 ± 20 μm in 28 days and 480 ± 16 μm in 56 days. Water tightness regain up to 85% was achieved at the end of 56 days for 465 ± 21 μm crack width. Precipitates were identified as forms of CaCO3 and were abundant in microbial specimens particularly on the inner crack surface. The findings evidence the potential of the NO3− reduction pathway for development of microbial self-healing concrete.

Role of calcium sources in the strength and microstructure of microbial mortar

This study investigated the uniaxial compressive strength, splitting tensile strength and water absorption ratio of microbial mortars treated with three different calcium sources (CaCl2, Ca(CH3COO)2 and Ca(NO3)2). The results showed that the uniaxial compressive and splitting tensile strengths of microbial mortars treated with Ca(CH3COO)2 were about twice those of the microbial mortars treated with the other two calcium sources (‘the others’ hereafter). The results of mercury intrusion porosimetry analysis showed that the pore size distribution in the microbial mortar treated with Ca(CH3COO)2 was much more uniform than that of the others. The mineralogical compositions and the microstructure morphology of the microbially induced calcium carbonate precipitation were analyzed in detail. Scanning electron microscopy and X-ray diffraction revealed that the calcium carbonate cemented in the microbial mortar treated with Ca(CH3COO)2 were different from others. Besides the calcite and the vaterite crystals, aragonite crystals with an acicular mineral morphology were observed.Calcium acetate is a more appropriate calcium source than calcium chloride for the application of MICP technology in reinforced concrete structures because it avoids the corrosion of steel bars caused by chloride ion.

Experimental study on performance of high strength microbial mortar

Traditional repair materials for masonry structures, such as the mixed mortar, cannot meet the general requirements of material strength and durability. Based on the biochemical actions of urea hydrolysis, certain types of urease producing microbes can significantly accelerate the precipitation of calcium carbonate in porous media, given that the environment is rich in calcium ions. The calcium carbonate crystals then bind the sand particles together to form the microbial mortar, which can be used to fill in the cracks of the deteriorated masonry structures. The paper studies the controlling factors of the strength of the microbial mortar, which controls the uniaxial compressive strength of the microbial mortar to be within 2–55 MPa. By X-ray diffraction, scanning electron microscopy and mercury intrusion tests, it is found that the microscopic pore structure of the microbial mortar is significantly different from that of the mixed mortar, which makes the former more suitable for the restoration of masonry structures.

A performance study of high-strength microbial mortar produced by low pressure grouting for the reinforcement of deteriorated masonry structures

Abstract Microbial grouting reinforcement to repair the deterioration of masonry structures involves injecting microorganisms and nutrient solution (a cementation solution) into existing granular system pores to induce the generated calcium carbonate cementation to form a microbial mortar of certain strength. Microbial grouting reinforcement is used when traditional grouting materials, such as lime, cement and epoxy, cannot be employed. In this paper, based on experimental study, the main biochemical factors that affect microbial mortar strength were investigated. In addition, the mixture ratio and laboratory preparation method for high-strength microbial mortars were determined. Microbial mortars of different strengths were successfully produced, through which the maximum uniaxial compressive strength reached 55 MPa. The mechanical properties of the microbial mortar, such as uniaxial compressive strength, splitting tensile strength, compressive strength under cyclic loading and uniaxial compressive fatigue, were tested, and the crystal structure of the carbonate cementation and pore-size distribution of the microbial mortar were analyzed. The results indicate that in strength, deformation and durability, this new material is superior to conventional cement–lime mortar. This new type of grouting is ideal for the in situ reinforcement of deteriorated masonry structures. The preparation method for high-strength microbial mortar, the material’s tested mechanical properties and the quantitative relationships of the material’s grouting parameters are reported. The material provides a novel method to reinforce deteriorated masonry structures, particularly historical masonry structures.