Bacteria-based Self-healing Concrete Research Articles

Biomineralization and corrosion inhibition of steel in simulated bio-inspired self-healing concrete

The concrete possessing quasi brittle nature is always prone to the transport of aggressive ions leading to corrosion of embedded steel. The use of bacteria-based self-healing concrete has been tremendously practiced since the last decade to repair such blemishes of concrete. In this research, interaction of 2 gram positive Chryseomicrobiam species with the simulated concrete and reinforcing steel has been studied in the chloride's environment. The effect of chlorides and varying pH conditions on the microbially induced CaCO3 precipitation (MICP) capability was explored along with the forensic investigations of the precipitates. The biofilm formation potential and electrochemical measurements were done to assess the corrosion inhibition tendency of steel bars by bacteria. The MICP potential of Chryseomicrobiam amylolyticum (CA) was high at each pH compared to the Chryseomicrobiam imtechense (CI). However, both of the strains produced vaterite and maximum amount was observed at a pH of 10. The CI strain formed denser and 42.27 % thicker biofilm compared to the CA. The corrosion inhibition efficiency of the rebars by CA and CI was 6.62 % and 90.42 % more than the control sample, respectively.

Bacteria-based self-healing concrete− A life cycle assessment perspective

A life cycle assessment (LCA) was utilised to evaluate the environmental impact of bacteria-based self-healing concretes (BBSHCs), where non-ureolytic bacterial endospores are encapsulated in porous calcium silicate granules. Findings reveal that 1 m3 of BBSHC has an overall 85% higher environmental impact than equivalent conventional concrete, primarily due to calcium nitrate and polyvinyl acetate. Furthermore, BBSHC has a 36% larger embodied carbon footprint (120 kg CO2 eq) and a 51% larger water footprint (260 L). However, by selectively incorporating BBSHC in specific areas of reinforced concrete structures, leveraging its inherent self-healing properties to deliberately allow wider crack widths, and consequently, reduce the amount of non-structural steel needed to control early-age cracking, sustainability improvements ranging from 12% to 50% can be achieved depending on the impact category. In this regard, a BBSHC-structure can potentially save up to 51 kg CO2 eq per m3.

Laboratory analysis of self-healing cement composition based on calcium lactate and bacteria

The research aims to evaluate the feasibility of using bacteria-based self-healing concrete using Portland cement and assess the effect of temperature on its performance. The results showed that the inclusion of calcium lactate and bacteria in the mixture accelerates the gain in compressive strength, but after 28 days of curing, the healing agent has no impact on the overall compressive strength value of the mixture. The crack width distribution analysis revealed an inverse relationship between crack width and self-healed area, with wider cracks having lower self-healing rates. Most of the healing occurs within 15 days, with only a small fraction healing between day 15 and 60 days. The study also showed that low temperatures do not produce self-healing in tested samples, and 25°C increases the self-healed area for all crack widths. Finally, chromatography tests of submerged water reveal that reaction to seal the cracks takes calcium from some external source. Keywords: self-healing cement; carbon emission; bacteria; calcium lactate; Portland cement.

Alkali activated lightweight aggregate as bacterial carrier in manufacturing self-healing mortar

A bacteria-based self-healing concrete has been proposed for the autonomous repair of micro-cracks. However, the bacteria need protection to survive in concrete until cracks would appear. Here, vegetative cells of Bacillus sphaericus have been encapsulated into novel alkali activated lightweight aggregate (LWA) generated from fly ash and Sidoarjo volcanic Mud (Lusi). For the production of self-healing mortar, 30% by volume of the fine aggregates were replaced by bacteria impregnated LWA. The mechanical properties of the resulting mortar, the healing performance, sealing efficiency and healing product morphology were investigated. The results show that with vegetative cells as healing agent, a significant decrease in healing performance was observed when cracks were fabricated at later age. Furthermore, fly ash based LWA provided comparable healing and sealing performance as a commercial expanded clay carrier used for comparison. In addition, the fly ash-based LWA carrier provided excellent autogenous healing in young mortar.

The Effect on Using Cells versus Spores of Bacillus Sphaericus on the Healing Performance of Self-Healing Mortar

Bacteria-based self-healing concrete has become an effective approach to mitigate microcracks in the concrete structure. However, there are still doubts about when to use vegetative cells or spores of Bacillus sphaericus as a healing agent. Thus, this research aims to give recommendations regarding this choice. Spores and cells were encapsulated into expanded clay aggregate to protect them from the harsh environment of fresh mortar. The viability of cells and spores after encapsulation was investigated. The 28- and 90-day mortar compressive strength was analysed. The healing performance of the resulting mortar samples that were cracked at the age of 28 and 90 days has also been observed. The results show that both cells and spores were still active after encapsulation. The yeast extract added to mortar containing spores decreased the compressive strength of the mortar compared to the reference sample. From the healing performance result, it seems that the spores are more suitable for mitigating microcracks in aged mortar, while cells are more suitable for mitigating early-age cracks in the mortar.

Encapsulation of fungal spores for fungi-mediated self-healing concrete

Although concrete is a prominent building material in nearly all construction applications, it is also known for its reinforcement corrosion and thus material degradation due to crack formation. These severe durability issues ignited the use of microorganisms to self-heal concrete cracks in a biological way by promoting the precipitation of CaCO3 on their cell walls. Filamentous fungi have recently emerged as high-potential self-healing agents because of their ability to grow in large mycelial networks providing abundant nucleation sites for CaCO3 precipitation. Based on the extensive research already conducted on bacteria-based self-healing concrete, protection of the microbial spores in the concrete mix is key to the survival of the microorganism. This research therefore applied a natural encapsulation technique derived from bacteria-based literature on fungal spores. The fungus Trichoderma reesei, already known in the field of self-healing concrete, was used to prepare the capsules. First results showed that the fungus was able to withstand the encapsulation process, yet could not survive when embedded in cement due to its harsh conditions. The possibilities to optimize the procedure are however discussed in the paper and give rise to a broad range of research opportunities.

Study on bacteria based self-healing properties of bio-concrete - An overview

The use of bacteria-based self-healing concrete has gained attention in recent years due to its potential to improve the durability and sustainability of concrete structures. This paper provides an overview of the research conducted on the self-healing properties of bacteria-based bio-concrete. The paper discusses the mechanism of bacterial self-healing in concrete, the types of bacteria used in self-healing concrete, and the methods used to introduce bacteria into the concrete. The paper also reviews comparative studies that evaluate the mechanical properties and durability of selfhealing bacterial concrete compared to traditional concrete. The results of these studies demonstrate that the use of bacteria in concrete can improve the self-healing capacity of the material, leading to better mechanical properties and a higher resistance to cracking and freeze-thaw damage. Furthermore, the paper discusses the potential environmental and economic benefits of using self-healing bacterial concrete. The self-healing capacity of the concrete can reduce the need for costly repairs and maintenance of concrete structures, resulting in lower costs and a reduced environmental impact associated with concrete production. Additionally, the use of waste materials as nutrient sources for bacteria can promote the circular economy and contribute to sustainable development. Overall, this paper highlights the promising potential of self-healing bacterial concrete to improve the durability, sustainability, and economic viability of concrete structures.

The effect of bacteria Bacillus Cohnii on the synthesised calcium silicate hydrate (C–S–H) with various calcium to silica ratio in nanoscale

Calcium silicate hydrate (C–S–H) is the main cement hydration product, providing the most mechanical strength to concrete structure. As per the previous studies of bacteria-based self-healing concrete using non-ureolytic bacteria, one of the main issues is that the amount of externally added calcium salt was restricted by the properties of carriers, limiting the content of precipitated calcium carbonate. In addition, previous studies barely investigated the potential impact of microbial activities on the individual cement hydration products. Therefore, in this study, for the first time, we investigated the individual impact of bacteria on synthesised C–S–H gel and the potential of biomineralisation of C–S–H gel. In light of results obtained in this study, we evidenced that C–S–H could be biomineralised to produce a considerable amount of calcium carbonate. Decalcification of C–S–H gel and microbial carbon-capture were simultaneously occurred prior to the precipitation of calcium carbonate, resulting in increase of calcium and bicarbonate ions in the solution. The amount of precipitated CaCO3 is closely in response to Ca/Si ratio in C–S–H, higher Ca/Si essentially led to more precipitates, whilst the remaining structure and mass of C–S–H gel that could not be further biomineralised was generally similar.

The estimation of the cost design of bacteria-based self-healing concrete

This research aims to estimate the design costs of implementing the bioconcrete samples suitable for structural purposes. The bioconcrete samples were produced by adding specific bacteria, Sporosarcina pasteurii. The specimens were submitted to tests of resistance to axial compression according to ABNT NBR 5739 under water-curing periods of 7, 14, and 28 days. To the implementation of this research, it was necessary execution of some stages: bibliographic research, and the providing of better visualization of the theme. The initial acquisition of bacteria, then the cultivation of bacteria to incorporate in the concrete. The third stage was laboratory tests to analyze the new concrete and make reports and data tabulation. The early costs results are encouraging further study.

Machine learning and RSM models for prediction of compressive strength of smart bio-concrete

In recent years, bacteria-based self-healing concrete has been widely exploited to improve the compressive strength of concrete using different bacterial species. However, both the identification of the optimal involved reaction parameters and theoretical framework information are still limited. In the present study, both experimentally and numerical modelling using machine learning (ANN and ANFIS) and response surface methodology (RSM) were implemented to evaluate and optimse the evolution of bacterial concrete strength. Therefore, a total of 58 compressive strength tests of the concrete incorporating new bacterial species were designed using different concentrations of urea, cells concentration, calcium, nutrient and time. Based on the results, the compressive strength of the bacterial concrete improved by 16% due to the decrement of the pore percentage in the concrete skin; specifically, 5 mm from the concrete surface, compared to that of the control concrete. In the same context, both machine the learning and RSM models indicated that the optimal range of urea, calcium, nutrient and bacterial cells were (18-23 g/L), (150-350 mM), (1-3 g/L) and 2×107 cells/mL, respectively. Based on the statistical analysis, RMSE, R2, MPE, RAE and RRSE were (0.793, 0.785), (0.985, 0.986), (1.508, 1.1), (0.11, 0.09) and (0.121, 0.12) from both the ANN and ANFIS models, respectively, while; the following values (0.839, 0.972, 1.678, 0.131 and 0.165) was obtained from RSM model, respectively. As such, it can be concluded that a high correlation and minimum error were obtained, however, machine learning models provided more accurate results compared to that of the RSM model.

Effects of carrier on the performance of bacteria-based self-healing concrete

To prolong the survival time of microorganisms in concrete, a new type of core-shell carrier was designed and prepared. Then, the mechanical properties, porosity, protection performance, and distribution in the concrete of the carrier were tested. After the healing agents were mixed into concrete, the influences of the carrier on the self-repairing performance, workability, mechanical properties, durability, and repair products in cracks of the concrete were studied. Finally, the mechanism of carrier protection and crack self-healing was inspected and analyzed. The results show that the batch prepared carrier has good quality stability, can achieve secondary strength growth, has low porosity and small pore size, and can greatly extend the survival time of microorganisms. The self-repairing capability of the later cracks was greatly improved, and there was no obvious negative impact on the basic performance of concrete. The resistance to chloride ions and carbonization can be improved to a certain extent. The invading alkaline substances would be consumed by fly ash, and the pores of the carrier would be filled by the produced gelled products, which is the trigger mechanism of the protective and secondary strength increase. The carrier provides a stable physical and chemical environment for the spores, ensuring that it can effectively play a role in the later cracking behavior of concrete. This research provides a technical choice for the low-cost preparation of the carrier and is expected to promote microbial self-healing concrete into engineering applications.

Compatibility and Biomineralization Oriented Optimization of Nutrient Content in Nitrate-Reducing-Biogranules-Based Microbial Self-Healing Concrete

Microbially induced calcium carbonate precipitation (MICP) can be mentioned among the popular approaches to develop a self-healing concrete. The production of dissolved inorganic carbon through microbial activity is the main precursor for MICP in concrete and it is limited by the bioavailability of the nutrients. When nutrients are added to the mortar as admixtures, their bioavailability becomes more significant for crack repair because nutrients disperse in the mortar and considerable fraction stays far from a single crack. Therefore, the determination of bioavailability of nutrients and its variation with the initial nutrient content and crack age is essential to optimize a recipe for bacteria-based self-healing concrete. This study presents the optimum nutrient content defined for nitrate-reduction-based self-healing bioconcrete. In the tests, calcium nitrate (CN) and calcium formate (CF) were combined with a CF:CN w/w ratio of 2.50. Mortar properties and bioavailability of nutrients were analysed at different nutrient doses. Moreover, the bioavailability of nutrients at different crack ages changing between 3 and 56 days was monitored. Finally, resuscitation, microbial activity and the MICP performance of nitrate reducing biogranules were tested at defined nutrient bioavailabilties. The optimum nutrient content was determined as 7.00% (CF 5.00% and CN 2.00%). The leaching rates of formate ions were twice the leaching rate of the nitrate ions at similar initial concentrations, which led to a bioavailable HCOO−/NO3-N ratio of 23 g/g in cracked mortar. Under optimum nutrient conditions, the CaCO3 precipitation yield of nitrate reducing biogranules was recorded as 1.5 g CaCO3/g HCOO− which corresponded to 68% C precipitation efficiency.

Microbial induced calcium carbonate precipitation study using Bacillus subtilis with application to self-healing concrete preparation and characterization

This study aimed to develop novel bacteria-based self-healing concrete by microbial induced calcium carbonate precipitation mechanism. A group of spore-forming bacterium related with gen Bacillus subtilis were selected for cultivation at elevated pH solution. The derived alkali-resistant Bacillus subtilis M9 was applied for biomineralization test whereas the precipitate mineral was calcium carbonate in calcite phase according to X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) results. With B. subtilis M9 as the healing agent, the self-healing concrete beam specimens were then prepared by incorporating polyvinyl alcohol fibers. Air-entraining agent was utilized to yield micro pores in cement paste mixture to provide ecological niches for microbe. 3-point-bending test was conducted to form 0.3-mm-width cracks on the beam bottom. After 28 days curing, the micro cracks were autonomously healed with calcium carbonate precipitation fillings due to the bacteria metabolic activity. The sequent SEM tests implied that calcite is the dominant mineral phase with some bacterial imprints on the crystal surface. Furthermore, flexural strength of the sealed beam subjected to repeated bending was enhanced by about 14% compared to residual flexural strength. The beam flexural strength recover was realized by remediation of the cracks in matrix as well as repairing of fiber–matrix interface bond.

On the Applicability of a Precursor Derived from Organic Waste Streams for Bacteria-Based Self-Healing Concrete

Bacteria-based self-healing concrete has the ability to heal cracks due to the bacterial conversion of incorporated organic compounds into calcium carbonate. Precipitates seal the cracks, theoretically increasing the service life of constructions. The aim of this paper is to propose a precursor for bacteria-based self-healing concrete derived from organic waste streams, produced is in line with the circular economy principle and ideally more affordable than other substrates. To verify the applicability of the proposed healing agent, some fundamental requirements of the proposed system are studied, such as its influence on functional properties, crack sealing capacity and evidence of bacterial activity in concrete.

A review of bacteria-based self-healing concrete

A review of bacteria-based self-healing concrete

Bacteria-based self-healing concrete: evaluation of full scale demonstrator projects

Bacteria-based self-healing concrete is an innovative concrete that contains a self-healing agent that provides the material with enhanced autonomous crack-sealing performance. A specific type of this concrete, based on a healing agent composed of bacterial spores and lactate as carbon source, has been developed and applied by the Delft University of Technology for over ten years. Under laboratory conditions it was proven that, depending on the dosage of healing agent, self-healing of cracks up to 0.8 mm widths occurs. As such the material potentially allows reduction of steel reinforcement used for crack width limitation in watertight constructions. Application of self-healing concrete would therefore not only result in a reduction of costs but also in improvement of environmental performance (lower CO2 footprint) and ease of in situ casting due to reduction of use of steel in waterproof applications. However, according to the EN 1990 Eurocode (Basis of structural design), customary application of a novel type of concrete must be preceded by full scale demonstrators proving evidence for safe and functional performance. In this contribution we portray full scale application of bacteria-based self-healing agent as developed by the Delft research group in two repair mortar- and in two concrete construction demonstrator projects. These demonstrator projects show that addition of the bacteria-based self-healing agent to the concrete mix is safe as no negative side effects on construction performance was observed. However, it also proved difficult to find evidence for increased crack-healing performance as cracking in the demonstrator constructions hardly occurred. In further full scale demonstrators we therefore plan to drastically reduce amount of crack width-restraining reinforcement to show crack-healing capacity and potential to save on use of reinforcement steel in watertight concrete constructions.

Complementing urea hydrolysis and nitrate reduction for improved microbially induced calcium carbonate precipitation.

Microbial-induced CaCO3 precipitation has been widely applied in bacterial-based self-healing concrete. However, the limited biogenetic CaCO3 production by bacteria after they were introduced into the incompatible concrete matrix is a major challenge of this technology. In the present study, the potential of combining two metabolic pathways, urea hydrolysis and nitrate reduction, simultaneously in one bacteria strain for improving the bacterial CaCO3 yield has been investigated. One bacterial strain, Ralstonia eutropha H16, which has the highest Ca2+ tolerance and is capable of performing both urea hydrolysis and nitrate reduction in combined media was selected among three bacterial candidates based on the enzymatic examinations. Results showed that H16 does not need oxygen for urea hydrolysis and urease activity was determined primarily by cell concentration. However, the additional urea in the combined medium slowed down the nitrate reduction rate to 7days until full NO3- decomposition. Moreover, the nitrate reduction of H16 was significantly restricted by an increased Ca2+ ion concentration in the media. Nevertheless, the overall CaCO3 precipitation yield can be improved by 20 to 30% after optimization through the combination of two metabolic pathways. The highest total CaCO3 precipitation yield achieved in an orthogonal experiment was 14g/L. It can be concluded that Ralstonia eutropha H16 is a suitable bacterium for simultaneous activation of urea hydrolysis and nitrate reduction for improving the CaCO3 precipitation and it can be studied later, on activation of multiple metabolic pathways in bacteria-based self-healing concrete.

Synthesis and characterization of bio-immobilized nano/micro inert and reactive additives for feasibility investigation in self-healing concrete

Bacteria-based self-healing concrete can be made more efficient by using immobilization techniques, hence shielding the bacteria from crushing during mixing to remain dormant till the development of concrete cracks for the uniform healing of developed cracks. In this study, two intrusion approaches, direct induction and immobilization, are deliberated by using ‘Bacillus subtilis’ bacteria for self-healing concrete. Furthermore, for immobilization’s evaluation, two media namely iron oxide nano/micro particles (INMPs) and bentonite nano/micro particles (BNMPs) were selected. Compressive and tensile strengths were computed at 3, 7 and 28 days. Moreover, field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), X-ray fluorescence (XRF) and thermo-gravimetric analysis (TGA) were employed for monitoring self-healing efficiency. Results revealed that immobilization through INMPs media was best among all intrusions ensuing successive healing of cracks up to 1.2 mm width having 85% recovery in compressive strength after pre-cracking. Whereas, BNMPs immobilization and direct induction exhibited crack healings up to only 0.15 mm and 0.45 mm crack healing widths with 45% and 65% strength recovery, respectively.

Self-Healing Concrete Using Rubber Particles to Immobilize Bacterial Spores.

Bacteria-based self-healing concrete is a construction material used to repair cracks in concrete, in which the bacterial spores are immobilized by bacteria carriers. However, the currently available bacteria carriers are not always suitable due to a complicated procedure or high cost. To develop a more suitable bacteria carrier as well as improve the anti-crack capability of self-healing concrete, in this study we evaluate the feasibility of using rubber particles as a novel bacteria carrier in self-healing concrete. Two types of self-healing concrete are prepared with rubber particles of different sizes to quantify the crack-healing effect. In addition, the fluidity and mechanical properties of the self-healing rubber concrete are compared with those of plain concrete and normal rubber concrete. The experimental results show that the self-healing rubber concrete with a particle size of 1~3 mm has a better healing capacity than the self-healing rubber concrete with a particle size of 0.2~0.4 mm, and the width value of the completely healed crack is 0.86 mm. The self-healing rubber concrete has a higher slump than the plain concrete and normal rubber concrete. According to the strength tests, the compressive strengths of the self-healing rubber concrete are low early on but they exceed those of the corresponding normal rubber concrete at 28 days. Moreover, the self-healing rubber concrete has higher splitting tensile strengths than the plain concrete and a better anti-crack capability. The results of a comparison to the other two representative bacterial carriers indicate that rubber particles have potential to be a widely used bacteria carrier for practical engineering applications in self-healing concrete.

Bacteria-Based Self-Healing Concrete: Towards Standardization

Bacteria-based self-healing concrete is an innovative concrete that contains a self-healing agent that provides the material with enhanced crack-sealing performance. A specific type of this concrete, based on a healing agent composed of bacterial spores and lactate as carbon source, has been developed and applied by the Delft University of Technology for over ten years.