Search Results (36)

This study investigated the technical feasibility and antimicrobial potential of incorporating ornamental rock, limestone, and ginger waste into coating mortars with the aim of developing an innovative and sustainable solution for civil construction. This study evaluated the synergistic action of these materials on the microbiological and mechanical resistance of mortar, contributing to the greater durability and efficiency of the coatings. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) analyses were performed to characterize the morphology, chemical composition, and crystalline structure of the added materials, confirming their suitability for the cement matrix. Tests in the fresh state evaluated parameters such as density, consistency index, and entrained air content, demonstrating the viability of the formulations, whereas flexural and compressive strength tests indicated significant improvements in the mechanical performance of the modified mortar. Microbiological tests demonstrated a significant reduction in microbial colonization, indicating the action of ginger’s bioactive compounds, such as gingerol and shogaol, which have antimicrobial properties and are effective in inhibiting the growth of pathogenic microorganisms, as confirmed by the reduction in the bacterial colony count from 4 × 10² to 1 × 10² CFU mL⁻¹. Comparisons with conventional compositions indicate that the proposed approach outperformed traditional formulations in terms of both mechanical resistance and microbiological control. Thus, the results validate this research as a promising strategy for improving the durability and performance of coating mortars, reducing maintenance costs, and promoting the sustainable use of alternative materials in civil construction. Full article

Negative temperature environments inhibit bacterial survival in cementitious materials and reduce the self-healing ability of bacteria. To address this challenge, acid-etched alumina hollow spheres are proposed as carriers to encapsulate microorganisms in cementitious materials. The effects of these carriers on the mechanical properties, thermal conductivity, self-healing properties, and self-healing products of specimens after exposure to −20 °C were investigated. Finally, the self-healing mechanism was examined and analyzed. The results demonstrated the effectiveness of the acid-etched hollow microbeads as bacterial carriers. The addition of the alumina hollow spheres participating in the cement hydration reaction enhanced the mechanical properties of the mortar and reduced its thermal conductivity, which supported bacterial survival in the negative temperature environment. Although negative temperature environments may reduce bacterial populations, the hydrolysis of aluminum ions in the alumina hollow spheres during bacterial metabolism resulted in the precipitation of aluminum hydroxide flocs. These flocs adsorbed free calcium carbonate in the pores, converting it into effective calcium carbonate with cementing properties, thus enhancing the crack healing capability of the examined specimens. This microbe-based self-healing strategy, utilizing alumina hollow spheres as bacterial carriers, is anticipated to provide an effective solution for achieving efficient crack self-healing in mortars that is resistant to the detrimental effects of negative temperature conditions. Full article

The use of recycled coarse aggregates (RCA) in concrete production offers significant environmental and economic benefits. However, the high water absorption and low mechanical strength of RCA, caused by residual mortar and internal cracks, severely limit its application. This study employed microbial-induced calcium carbonate precipitation (MICP) technology to improve RCA performance, systematically investigating the effects of key parameters such as bacterial strains, bacterial concentration, modification duration, and urea addition sequence. This study employed microbial-induced calcium carbonate precipitation (MICP) technology to enhance the performance of RCA. The investigation systematically examined the effects of key parameters, including bacterial strains (Bacillus subtilis, urease mixed bacteria, and Bacillus pasteurii), bacterial concentrations (0, 2.4 × 10⁷ cells/mL, 9.3 × 10⁷ cells/mL, 2.49 × 10⁸ cells/mL, and 2.36 × 10⁹ cells/mL), modification durations (0 d, 3 d, 7 d and 14 d), and urea addition sequences (urea added to the calcium source, urea added to the culture medium, and added to the bacterial solution followed by 2 h of incubation). The impact of MICP treatment on RCA’s water absorption, apparent density and resistance to ultrasonic impact was analyzed. Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) were used to characterize the microstructure and composition of calcium carbonate deposits, revealing the mechanisms by which MICP enhances RCA performance. The results showed that optimized MICP treatment reduced RCA water absorption by 32.5%, with the optimal conditions being a bacterial concentration of 2.4 × 10⁷ cells/mL, a modification duration of 7 days, and a two-hour urea resting period. It is primarily due to calcium carbonate filling pores and sealing cracks, which significantly improves the structural integrity of RCA. This study demonstrates that MICP is an effective and sustainable method for RCA modification, providing theoretical support and practical insights for the recycling of construction waste and the promotion of green building materials. Full article

This research aims to study the bacterial healing process of cement mortar samples exposed to durability effects using bacteria characterized by their ability to precipitate calcium carbonate. Sporosarcina pasteurii is widely used for bacterial healing. This research investigates the performance of S. pasteurii with five types of bacteria isolated from caves (Viridibacillus arenosi, Streptomyces spororaveus, Bacillus zhangzhouensis, Stenotrophomonas rhizophila, and Serratia quinivorans). Cement mortar samples were exposed to high temperatures and freeze–thaw effects to create microcracks. Microcracks were also induced by applying flexural strength loads. Then, the formed microcracks were healed using spraying and injection of the bacterial solution for the first group for 90 days. The control and healed samples were assessed using flexural and compressive strength, water absorption, capillary water absorption, and ultrasonic pulse velocity (UPV) tests. Microstructural analysis was also conducted to evaluate the bacterial healing products. Subsequently, statistical analysis was performed using the results of these tests to compare the various bacterial efficiencies. As a result of the statistical analysis, the total efficiency scores obtained in the statistical analysis were 119 for Stenotrophomonas rhizophila, 112 for Viridibacillus arenosi, and 105 for S. pasteurii. Thus, Stenotrophomonas rhizophila and Viridibacillus arenosi showed the best healing performance compared to the other types of bacteria. Full article

Microbial-induced calcium carbonate precipitation (MICP) is an environmentally sustainable technology for the self-healing of concrete cracks. In this experiment, expanded perlite was used as a bacterial carrier. It can facilitate the adsorption of bacteria and serves as a self-healing agent when incorporated into cement mortar. Two different sizes of silica were simultaneously added to evaluate the combined effects of the self-healing agent and varying silica sizes on the mechanical and self-healing properties of cement mortar. The objective is to determine the optimal dosage for each silica size. The results show that the self-healing agent can improve the density and strength of the structure in the early stages of maintenance and realize the self-healing of microcracks after the cement mortar has cracked. Adding a single particle size of silica at the optimal dosage can effectively improve the strength of cement mortar. Adding two different sizes of silica can optimize the particle grading of silica. Nano-sized silica is beneficial to improving the early compressive strength of cement mortar, and micron-sized silica is beneficial to improving the self-healing efficiency of cement mortar and completely sealing cracks at an early stage. The interaction between silica particles of varying sizes can further enhance the mechanical and self-healing properties of cement mortar. Microscopic observations and tests provide effective support for these conclusions and elucidate the mechanism of interaction between the self-healing agents and silica. Full article

Concrete, as the most widely used construction material globally, is prone to cracking under the influence of external factors such as mechanical loads, temperature fluctuations, chemical corrosion, and freeze–thaw cycles. Traditional concrete crack repair methods, such as epoxy resins and polymer mortars, often suffer from a limited permeability, poor compatibility with substrates, and insufficient long-term durability. Microbial biogrouting technology, leveraging microbial-induced calcium carbonate precipitation (MICP), has emerged as a promising alternative for crack sealing. This study aimed to explore the potential of Bacillus pasteurii for repairing concrete cracks to enhance compressive strength and permeability performance post-repair. Experiments were conducted to evaluate the bacterial growth cycle and urease activity under varying concentrations of Ca²⁺. The results indicated that the optimal time for crack repair occurred 24–36 h after bacterial cultivation. Additionally, the study revealed an inhibitory effect of high calcium ion concentrations on urease activity, with the optimal concentration identified as 1 mol/L. Compressive strength and water absorption tests were performed on repaired concrete specimens. The compressive strength of specimens with cracks of varying dimensions improved by 4.01–11.4% post-repair, with the highest improvement observed for specimens with 1 mm wide and 10 mm deep cracks, reaching an increase of 11.4%. In the water absorption tests conducted over 24 h, the average mass water absorption rate decreased by 31.36% for specimens with 0.5 mm cracks, 29.06% for 1 mm cracks, 27.9% for 2 mm cracks, and 28.2% for 3 mm cracks. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses confirmed the formation of dense calcium carbonate precipitates, with the SEM–EDS results identifying calcite and vaterite as the predominant self-healing products. This study underscores the potential of MICP-based microbial biogrouting as a sustainable and effective solution for enhancing the mechanical and durability properties of repaired concrete. Full article

Microbially induced calcium carbonate precipitation (MICP) presents a sustainable, environmentally friendly solution for repairing cracks in cement-based materials, such as mortar and concrete. This self-healing approach mechanism enables the matrix to autonomously close its own cracks over time. In this study, specimens (50 mm in diameter and 25 mm in height) were exposed to submersion and a wet–dry cycle environment. The solution considered a nutrient-rich suspension with calcium lactate, urea, calcium nitrate, and Bacillus subtilis or Sporosarcina pasteurii in a biomineralization approach. The self-healing efficiency was assessed through optical microscopy combined with image processing, focusing on the analysis of the superficial crack closure area. S. and B. subtilis exhibited notable capabilities in effectively healing cracks, respectively, 8 mm² and 5 mm² at 35 days. Healing was particularly effective in samples placed in a submerged environment, especially with a 69 mM concentration of calcium lactate in bacterial suspensions containing B. subtilis, where 87.5% of a 4 mm² crack was closed within 21 days. In contrast, free calcium ions in the solution, resulting from anhydrous cement hydration, proved ineffective for S. pasteurii biomineralization in urea-rich environments. However, the addition of an external calcium source (calcium nitrate) significantly enhanced crack closure, emphasizing the critical role of calcium availability in optimizing MICP for bio-agents in cement-based materials. These findings highlight the potential of MICP to advance sustainable self-healing concrete technologies. Full article

In a concrete beam, cracking is generated on the tension side under the effect of flexure, shear, and torsional loadings. Accordingly, these weak concrete members require repair and/or strengthening to increase or restore their internal load capacity. In the current experimental and numerical investigations on concrete beams, the impact of using notches with different width to depth ratios on the ultimate flexural load under a three-point test was considered. Further, the flexural behavior performance of a notched concrete beam repaired using the three repair materials—cement mortar, bacterial mortar, and adhesive—was also examined. Consequently, a comparative study was implemented between the experimental and numerical results. A concrete damage plasticity (CDP) model was used for the finite element numerical analysis of the beams. The differences in numerical and experimental measured results ranged from 0.65 to 22.20% for the ultimate load carrying capacity. As the notch size increased, the ultimate load carrying capacity of the beam reduced. Additionally, a linear regression model was used to predict the ultimate load values at a notch width interval of 5 mm up to a maximum notch width of 100 mm. It was observed that the ultimate load capacity for a repaired beam increased as compared to the notched beam for all three repair materials under consideration. And the maximum ultimate load increased in the case of notched beams repaired using adhesive. Furthermore, in comparison to the cement mortar, the performance of the bacterial mortar in terms of the ultimate load was more. The bacterial mortar was found to be more sustainable and more durable as a repair material for concrete structures. Full article

It has previously been shown that epilithic bacterial biopolymers used as coatings influenced the physical properties (surface hardness and color change) at different levels and decreased the surface disaggregation of experimental limestone when evaluated at the laboratory level. A short-term study (30 days) was conducted to evaluate the performance under natural conditions of limestone blocks exposed to tropical conditions of a selected bacterial biopolymer (TM1B-488, after the producing bacterium) and a previously unreported Mayan plant biopolymer known as “Escobilla”, Sida rhombifolia (Malvaceae) used in conservation procedures. Surface hardness (Leeb units) and color (L*a*b* coordinates) were measured and statistically tested for two types of limestone blocks (sound and deteriorated limestone). Both biopolymers increased surface hardness, decreased surface disaggregation, and did not alter color. Escobilla polymer is a carbohydrate-rich biopolymer characterized by tangential filtration, global chemical composition, and monosaccharide composition of hydrolyzed polymer. These results indicate that biopolymers of a heteropolysaccharide nature are constituted by some anionic charge residues that could contribute to surface stabilization and consolidation, but compatibility with traditional building materials (mortars) and longer time of exposure (a year) are necessary to fully assess their applicability in the restoration of architectural heritage. Full article

This study explored self-healing in geopolymer mortar cured at ambient temperature using polypropylene fibers and bacterial co-cultures of Bacillus subtilis and Bacillus megaterium. Damage degree, compressive strength, ultrasonic pulse velocity (UPV), strength-regain percentage, and self-healing percentage were evaluated. A full factorial design was used, which resulted in an eight-run complete factorial design with four levels in the first factor (polypropylene content: 0%, 0.25%, 0.5%, and 0.75%) and two levels in the second factor (bacteria concentration: 0 (without) and 1 (with)). The results indicate that increasing the polypropylene fiber content enhanced strength regains up to 199.97% with 0.75% fibers and bacteria. The bacteria alone improved strength-regain percentages by 11.22% through mineral precipitation. The analysis of variance (ANOVA) showed no interaction between fibers and bacteria, but both independently improved the compressive strength. Only bacterial samples exhibited positive self-healing, ranging from 16.77 to 147.18%. The analysis using a scanning electron microscope with energy dispersive X-ray (SEM-EDX) and X-ray fluorescence (XRF) also revealed greater calcite crystal formation in bacterial samples, increasing the strength-regain and self-healing percentages. The results demonstrate that polypropylene fibers and bacteria cultures could substantially enhance the strength, durability, and self-healing percentage of geopolymer mortars. The findings present the potential of a bio-based self-healing approach for sustainable construction and repair materials. Full article

Cracking is an inevitable feature of concrete, typically leading to corrosion of the embedded steel reinforcement and massive deterioration because of the freezing–thawing cycles. Different means have been proposed to increase the serviceability performance of cracked concrete structures. This case study deals with bacteria encapsulated in cementitious materials to “heal” cracks. Such a biological self-healing system requires preserving the bacteria’s viability in the cement matrix. Many embedded bacterial spores are damaged during concrete curing, drastically reducing efficiency. This study investigates the viability of commonly used non-ureolytic bacterial spores when immobilized in calcium alginate microcapsules within self-healing cementitious composites. Three Bacillus species were used in this study, i.e., B. pseudofirmus, B. cohnii, and B. halodurans. B. pseudofirmus demonstrated the best mineralization activity; a sufficient number of bacterial spores remained viable after the encapsulation. B. pseudofirmus and B. halodurans spores retained the highest viability after incorporating the microcapsules into the cement paste, while B. halodurans spores retained the highest viability in the mortar. Cracks with a width of about 0.13 mm were filled with bacterial calcium carbonate within 14 to 28 days, depending on the type of bacteria. Larger cracks were not healed entirely. B. pseudofirmus had the highest efficiency, with a healing coefficient of 0.497 after 56 days. This study also revealed the essential role of the cement hydration temperature on bacterial viability. Thus, further studies should optimize the content of bacteria and nutrients in the microcapsule structure. Full article

Microbial treatment of recycled concrete aggregate (RCA) may improve the quality of the aggregate, and enhance its use in the production of structural concrete and promote the recycling of concrete waste. The mortar phase of the RCA is responsible for the poor performance of the aggregate. Treating the old adhered mortar or removing it from the natural aggregate (NA) is an option to make RCA beneficial for the production of quality recycled aggregate concrete (RAC). Removing the adhered mortar from recycled concrete aggregate using silicate-solubilizing bacteria was investigated. The bacteria could synthesize the silicates in the calcium silicate hydrate phase of the cement paste leading to the breakdown of the old adhered mortar. Four SSB strains were tested for survivability and activity in an alkaline medium to simulate the concrete environment. The Serratia marcescens bacterial strain, which survived the environment, was inoculated into screw-cap glass vials containing recycled concrete aggregate fragments and glucose-enhanced nutrient broth and then incubated for 14 days. Partial removal of the old adhered mortar was observed based on the weight lost from the RCA. The S. marcescens bacterial strain could survive the alkaline concrete environment and solubilize the silicates present in cement paste resulting in the removal of the old adhered mortar. Full article

Reducing the costs of repairing concrete structures damaged due to the appearance of cracks and reducing the number of people involved in the process of their repair is the subject of a multitude of experimental studies. Special emphasis should be placed on research involving industrial by-products, the disposal of which has a negative environmental impact, as is the case in the research presented in this paper. The basic idea was to prepare a mortar with added granulated blast furnace slag from Smederevo Steel Mill and then treat artificially produced cracks with a Sporosarcina pasteurii DSM 33 suspension under the conditions of both sterile demineralized water and water from the Danube river in order to simulate natural conditions. The results show a bio-stimulated healing efficiency of 32.02% in sterile demineralized water and 42.74% in Danube river water already after 14 days. The SEM images clearly show calcium carbonate crystals as the main compound that has started to fill the crack, and the crystals are much more developed under the Danube river water conditions. As a special type of research, microscopic images of cracks were classified into those with and without the presence of bacterial culture. By applying convolutional neural networks (ResNet 50), the classification success rate was 91.55%. Full article

The study evaluated the impact of graphene powders used as additives in the recipe of the experimental lime mortar to a mixture ratio of 1:2.5 of NHL3.5 hydraulic lime:fine sand. The content of binder, aggregate and water was kept constant, varying only the amount and the type of the added additives in relation to the amount of natural hydraulic lime NHL3.5. The following five types of experimental mortars were prepared as follows: reference mortar (without additive); mortars containing 1 wt.% GO and 5 wt.% GO powder; mortar with the following GO powders mixture: GO powder functionalized with silver nanoparticles and with fly ash (GO-Ag + GO-fly ash); mortar with the following GO powders mixture: GO with zinc oxide and with titanium oxide (GO-ZnO + GO-TiO₂). The influence of the GO-based additive addition on the porosity, surface microstructure, and water sorption coefficient of the mortar samples was evaluated. The antibacterial effect of the mortar samples against three bacterial strains was also investigated. The best results were obtained for the experimental mortar containing GO-ZnO -TiO_2, which showed improved experimental properties that potentially allow its use for the rehabilitation of heritage buildings. Full article

This study determined the influences of Bacillus sphaericus Laboratorium voor Microbiologie Gent (LMG) 22257 bacteria activity on mortar samples cured in various media regarding compressive strength, porosity, water absorption, and water permeability. Three types of curing media were utilized, namely distilled water (D.W.), deposition water (D.M.), and run-off water (R.W.). The compressive strength was measured using 100 mm mortar cubes. The water porosity, water absorption, and water permeability were analyzed using the Leeds permeability cell with dimensions of the mortar cylindrical specimens of 55 mm diameter and 40 mm thickness. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDX) were utilized, respectively, for microstructure analysis and quantifying the elements with atomic numbers. The results indicated the presence of calcium carbonate and more calcium silicate hydrate (CSH) depositions on bacterial mortars. The inclusion of Bacillus sphaericus LMG 22257 bacteria activity and curing media type affected mortar properties through compressive strength and durability improvements, as well as the reduction in water porosity, water absorption, and water permeability of mortar. The comparison of CaCO₃ precipitation, such as a sufficient growth nutrient requirement and hostile bacteria environment, was observed. Curing in R.W. produced the most significant bio-based cement (BBC) mortar improvement, followed by D.M. BBC curing in runoff water had a 40% improvement in strength compared to normal curing. As a conclusion, runoff water is a highly promising sufficient nutrient to bacteria for the biomineralization process to produce CaCO₃. This work also aims to apply this approach in the field, especially in sewerage and drainage systems. Full article