Bibliographic survey and comprehensive review on mechanical and durability properties of microorganism based self-healing concrete

Abstract

Concrete is the most widely utilized material for construction purposes, second only to water, in the ever-increasing need for construction globally. Concrete is a brittle material and possesses a high risk of crack formation and consequent deterioration. Cracking, which allows chemicals to enter and can cause concrete structures to lose their physico-mechanical and durability features. Repairing and rehabilitating concrete structures involves high costs and leads to various repair methods including coating, adhesives, polymers, supplementary cementitious materials (SCMs), and fibers. One of the latest technologies is the use of microorganisms in concrete. These added microorganisms lead to calcite precipitation and thereby heal the cracks effectively. This study presents a comprehensive literature survey on bacteria-included concrete, before which a bibliographic survey is performed using VOSViewer software. In addition to regular bacterial concrete, this study focuses on also using SCMs and fibers in bacterial concrete. A detailed literature review with data representation for various mechanical properties including compressive strength (CS), split tensile strength (SS), and flexure strength (FS), along with durability properties including carbonation, water absorption, resistance against chloride ion penetration, gas permeation, and resistance against cyclic freeze-and-thaw is presented. A study on the use of X-ray computed tomography (XCT) in bacterial concrete is highlighted, and the scope for future research, along with identification of the research gap, is presented.

Graphical abstract

Keywords

bacterial concrete / bibliographic survey / biomineralization / carbonation / fibers

1 Introduction

One of the main reasons for concrete deterioration is cracking, which allows the ingress of moisture and chemicals into the concrete, thereby reducing its durability and physico-mechanical strengths. The addition of polymeric resins (such as epoxy, polyester, and vinyl ester), adhesives [1], and autogenous healing of unreacted cement particles, usually in the ultra-high performance concrete (UHPC) structures [2], are just a few of the significant repair approaches used in recent decades. Alternative binding agents (such as alkali-activated compounds) [3–8] and waterproofing chemicals [1] have also been used. However, there are many situations where choosing the best repair method is difficult due to factors such as high cost, high environmental impact, lack of coherent and homogeneous interfacial transition zone delamination problems (especially for polymer-based materials), and difficulties with actual on-site applications (such as handling a liquid activator for alkali-activated materials) [9].

Current investigations have yielded encouraging findings regarding the potential application of microbial calcification for resolving cracking and durability problems [10,11]. The primary mechanism due to embedded bacteria in concrete is based on the breakdown of urea and calcium to form calcium carbonate (CaCO₃), so that the material is frequently referred to as self-healing, bio- or bacterial concrete/microbial concrete/bio-cement/microbial-induced calcite precipitation cement [12]. The precipitation methods of bio-CaCO₃ vary according to different bacterial metabolic pathways. Moreover, there are two main categories of autotrophic and heterotrophic CaCO₃ precipitation, both leading to the calcification and biomineralization of CaCO₃ [13,14]. Autotrophic bacterial action involves various processes such as non-methylotrophic methanogenesis, oxygenic, and anoxygenic photosynthesis. The nitrogen cycle, sulfur cycle and the utilization of organic carbon are the basis of pathways for heterotrophic precipitation. The nitrogen cycle involves numerous methods, like ammonification of amino acids, degradation of urea and uric acid and dissimilatory reduction of nitrates whereas sulfur cycle involves dissimilatory reduction of sulphates [15].

In accordance with studies [1,16], if bacteria are appropriately applied to the fractured area, they can seal cracks with a width section of 0.46 mm. Microorganism driven healing could be as much as four times more effective in filling micropores and repairing cracks than autogenous healing, utilizing unreacted cementitious materials, which can only repair cracks up to 0.1 mm wide [17,18]. Due to the filler effect of bacteria, bacterial concrete heals the microcracks and leads to a reduction in the porosity by an order of 28% to 50% [19,20] and an increase in the mechanical strengths (of the order of 42% and 72% for compressive strength (CS) and flexural strength (FS), respectively) [21,22].

Applying bacteria directly to the mixture, encapsulating bacteria in the mix to keep them latent until activation, and spraying or injecting bacteria onto the surface of the fractures are the three techniques used to apply microorganism-induced healing to concrete [23]. In each of these situations, a nearby supply of organic food, such as yeast extract [13] and a urea medium [24], is also necessary to provide the potential for the bacteria to develop and react.

The most common procedure for healing cracks in bacterial concrete involves the propagation of cracks, activation of bacteria, chemical reaction, precipitation of calcite, and finally sealing cracks. The bacteria can mainly be classified into three types, neutrophils (which exist and grow at a pH of approximately 7, e.g., Escherichia coli, Staphylococci, and Salmonella species), acidophiles (which optimally grow below pH of 5.5, e.g., Lactobacillus) and alkaliphiles (which grow best at a pH range of 8–10, e.g., Bacillus subtilis, Bacillus firmus, etc., and are suited to highly alkaline media such as concrete [25].

Though several papers were found showing exhaustive data on bacterial concrete, research on the property-based analysis of concrete is rare. There are few comprehensive examinations of the material qualities, mechanical properties, permeability properties, resistance against carbonation and cyclic freeze–thaw and addition of bacteria percentage, to determine which would make the best concrete. In this analysis, we seek to explore connections between the relevant parameters of the raw material’s physical and chemical qualities or its mechanical and durability properties as well as to focus on the effect of bacteria on the properties of blended concrete and fiber-reinforced concrete. The study examines the literature and analyzes the current trend of research on bacterial concrete, making use of VOSviewer software, and is intended to be a reference for future researchers. The current research gaps are highlighted in the conclusion of the study.

2 Bibliographic analysis

The bibliographic analysis is carried out using VOSViewer software, and the data are obtained from the Scopus search engine. The data are obtained from the Scopus search engine using the keywords “concrete” and “bacterial concrete” and the filter is limited to the subject area “engineering”. From this search, only 589 documents have been found to date. The types of the 589 documents are classified in Tab.1.

To analyze the data based on countries, the setting in the VOSviewer software is carried out by selecting the type of analysis as “bibliographic coupling” and the unit of analysis as “countries.” The visual network obtained based on this analysis can be termed country mapping (Fig.1). Along with country mapping, a network can be visualized concerning yearly publications. It is found that the contribution of developed countries in the last five years is less than that of developing countries.

Sources encouraging research on using bacterial concrete as supplementary cementitious materials (SCMs) are analyzed. The top 15 journals with the highest number of documents are listed in Tab.2, showing the number of documents, citations, and total link strength. It is observed that Construction and building materials published 36.6% of the total documents, and the total proportion of citations is about 56.0% (Fig.2).

To framework the research adequately to cover all the significant factors, the choice of keywords is very important. To study this, the type and unit of analysis considered are “co-occurrence” and “all keywords”. To have the maximum repeated keywords, the minimum number of occurrences of a keyword is set to 25 times. Based on this, the top 43 keywords are shortlisted, and their visualization network is presented in Fig.3. These keywords are classified under four major categories: self-healing mechanism of the bacterial concrete; process involved in bacterial concrete; effect on mechanical properties; effect on durability properties.

3 Cultivation of bacteria and their inclusion in concrete

Cultivating bacteria involves introducing them in a suitable medium comprising ingredients, such as peptone, beef extract, and urea, under sterile conditions [26]. After the cultivation stage, bacteria can be utilized in the concrete, most commonly in three ways: direct addition into the concrete, injection/spray of bacteria culture, or the encapsulation of the bacteria in the concrete (Fig.4) [23]. Calcium lactate and bacterial spores are directly added to the concrete after the concrete is mixed. The most commonly used carrier media that have been reported in the previous literature are water [27], aggregates (mostly coarse and light-weight aggregates) [28,29], expanded clay [30], micro and nanoparticles (e.g., nano iron oxide) [27,31] and others [32].

Surface treatment of concrete is a highly successful method for improving the overall durability of the material, as the majority of degradation processes primarily initiate from the surface. de Muynck et al. [33,34] were among the early researchers who implemented bacterial treatments on the surface of cementitious materials by a two-step immersion process. The mortar specimens were initially submerged in a culture of B. Sphaericus that had been cultivated for a period of 24 h. The presence of CaCO₃ precipitation on the surface of the mortar led to a reduction in the absorption of capillary water and in gas permeability. As a result, the mortar exhibited enhanced resistance to carbonation, chloride penetration, and the detrimental effects of freezing and thawing. Similar results were also reported by Nosouhian et al. [35]. In contrast, Qian et al. [36] employed a single-step bacterial treatment. The cement stones were immersed in a solution containing S. Pasteurii cells, urea, and Ca²⁺. Concrete was mixed, and the precipitation of carbonate primarily occurred on its outer surfaces, resulting in the formation of a compact and cohesive layer with a thickness ranging from 150 to 290 µm and in enhanced durability properties. Another such application of bacteria on the surface of concrete is the biofilm formation. According to research by Soleimani et al. [37,38], bacterial biofilms have the potential to exhibit antagonistic properties against sulfur-oxidizing bacteria (SOB), thereby serving as a protective barrier against SOB-induced deterioration of concrete structures.

Bacteria provide the basis for dealing with damage caused by cracks in general, involving ‘self-healing’. During the casting process, dormant bacteria, typically in the form of spores, as well as other necessary agents such as nutrients and precipitation precursors, are integrated into the concrete matrix. The activation of latent bacteria in the crack zone and subsequent precipitation of CaCO₃ to facilitate crack healing in situ only occurs when cracking takes place, typically in response to factors such as presence of moisture and oxygen. The most common mechanisms for such crack healing are bacterial oxidation of organic compounds [13], bacterial ureolysis [39–41] and denitrification [42–44].

4 Biomineralisation

The inclusion of bacteria in concrete is very effective in crack healing, producing calcite crystals that help in blocking pores and cracks in concrete [45]. Precipitation of calcite, to block cavities in concrete, can be linked with biologically induced mineralization in the presence of a calcium source. Calcium carbonate is produced by microorganisms through various metabolic processes that can mainly be classified into two types. The first of these is autotrophic precipitation of CaCO₃, which can be further classified into different methods like non-methylotrophic methanogenesis, oxygenic and anoxygenic photosynthesis [46]. The second is the heterotrophic precipitation of CaCO₃ which can further be categorized into various other processes like utilization of organic acid, reduction of calcium sulfate, nitrate reduction, and ureolysis. Fig.5 presents the different methods of biomineralization and the chemical reactions involved in those processes.

5 Mechanical properties

The general mechanism for strength development and healing of cracks in microbial concrete is the conversion of soluble organic compounds to inorganic crystals of calcite, which then seals the cracks [21,22]. Previous studies have demonstrated that strength restoration of cracks using CaCO₃ follows a multi-factor approach that can be classified into physical and chemical features. The most important variables for the development of strength, in terms of chemical properties, are the bacteria type and concentration [22], the medium’s pH [14], and the nucleation site for bacterial immobilization [47].

Tab.3 and Tab.4 provides the different types of bacteria used in previous literatures and detailed data analysis of mechanical properties reported in previous literatures, respectively. In previous research, the most optimal concentration of bacteria for greater CS has been found to be in the range of 10⁵–10⁸ cfu/mL, where cfu is ‘colony forming unit’. The type of bacteria also plays a vital role in the strength development of concrete. Rauf et al. [22] conducted research on application of different kinds of bacteria and reported that the higher strength was obtained with the inclusion of Bacillus sphaericus, rather than B. cohnii or B. subtilis, due to more significant calcium carbonate precipitation. Chen et al. [21] studied the influence of ceramsite sand, and Rauf et al. [22] used various natural fibers (coir, flax, and jute) as carriers for bacterial immobilization and their effect on the CaCO₃ precipitation. The latter study revealed that there can be as much as a 50%–70% rise in flexural strength.

Natural fiber inclusion can also result in concrete protection from an alkaline medium inside the concrete and around a 42% increase in CS values. An increase in strength can be linked with the formation of extra calcite from the carriers that already included nutrients [21,22].

Also, there are conflicting findings about how bio-based healing agents affect the strength of concrete. According to an investigation done by Wang et al. [48] adding encapsulated B. Sphaericus to mortar causes a 15%–34% reduction in CS. However, others have found that the CS was raised at 7 and 28 d when B. Sphaericus was used in a cube mortar [20]. The CS of the mortar decreased for greater cell concentration (5 × 10⁸ cfu/mL) even though the bio-based agent had a beneficial impact on the cell concentration of 5 × 10⁶ cfu/mL.

Bang et al. [49] investigated the impact of S. Pasteurii bacteria on CS at 7 and 28 d for mortar specimens. They discovered that the immobilized S. Pasteurii concentration at the most significant level on porous glass beads significantly increased the CS of the mortar samples by 24%. Additionally, the CS increased as the cell concentration rose from 6.1 × 10⁷ to 3.1 × 10⁹ cells/mL. Fig.6 and Fig.7 represent the CS and tensile strength (split tensile strength (SS) and FS) of concrete, respectively, with various bacterial concentrations.

Apart from the above factors, one of the governing factors affecting the strength of microbial concrete is the usage of different nutrients, such as calcium lactate, calcium formate, calcium nitrate, yeast extract, and urea as food source for bacteria. A study was performed on the behavior of various nutrient dosages (bacterial spore powder, calcium lactate, formate, and nitrate) on the CS of microbial mortar by Luo and Qian [50]. Results show decreased early strength gain by incorporating calcium lactate with bacterial spore powder. However, strength was found to be enhanced at later curing ages. Including calcium formate also produced an enhancement in strength; however, an increase in concentration resulted in a decrease in the enhancement effect. Contradictory to the effects of abovementioned nutrients, Calcium nitrate inclusion resulted in about a 17% decrease in CS after 28 d of testing. Another research performed by Schreiberová et al. [51], on the performance of nutrients on strength properties of microbial concrete demonstrated a drastic decrease in strength with the addition of yeast. Adding other nutrients like calcium formate, nitrate, lactate, and urea enhanced CS and FS.

Very few studies have been done on blended concrete. The inclusion of various waste materials, such as fly ash (FA), silica fume, and rice husk ash, in bacterial concrete has been reported in previous literature. Significant findings of earlier literature on blended microbial concrete are tabulated in Tab.5. Fig.8 represents blended bacterial concrete’s CS, SS, and FS with different SCMs at 28 d. The table data confirm that the effect of bacteria concentration is dependent on type and concentration, so it is necessary to optimize these factors, to help researchers to standardize the mix design process. Some studies exist in the literature on the efficiency of different supplementary materials like FA and silica fume [64–66] but no research has been found on the efficiency of bacteria to achieve equal 28 d strength, and there is scope for future research.

Studies on the inclusion of different fibers like coconut fibers [72], polyvinyl alcohol (PVA) [73], polypropylene (PP) [74,23], steel fibers [2], glass fibers [75], waste tire rubber fibers [76], natural fibers like coir, flax, jute [22], etc. in concrete have been done on the literature. However, in bacterial concrete, very few studies [22,62,75–81] have been done so far involving fibers. Including glass fibers (3% by volume of cement) [75] and steel fibers (2%) [77] in bacterial concrete resulted in a 12%–16% increase in CS. In addition, FS was enhanced by 50% in a study conducted by Zhang et al. [77]. In a study conducted by Rauf et al. [22], different natural fibers (coir (1.19%), flax (0.31%), and jute (0.38%)) were used as carriers for bacteria immobilization. Compared to other fibers, flax fibers have proved to protect bacteria more efficiently, whereas coir fibers imparted greater mechanical strength than the other fibers [22]. A summary of the effects of fibers on bacterial concrete is presented in Tab.6. Fig.9 portrays CS, SS, and FS at 28 d in fiber-reinforced bacterial concrete, as reported in previous literature.

6 Durability properties

6.1 Carbonation

Carbonation is a process of reaction of CO₂ with the hydration products of concrete, leading to reduced reserve alkalinity [83]. One of the most critical factors affecting the carbonation is the porosity of concrete. Greater porosity leads to the increased diffusion of CO₂, resulting in a faster reaction of CO₂ with hydration products [84].

Out of the various methods, one method for reduction of the porosity of concrete is by adding bacteria [53,85]. Although very few studies have been performed on the impact of bacteria on concrete carbonation, some research has shown positive results regarding carbonation resistance. A recent study by Joshi et al. [86], has shown the positive impact of bacteria (admixed and sprayed) on the carbonation of concrete, with about a 50% reduction in carbonation depth compared to that in normal concrete. Adding fibers in bacterial concrete has also demonstrated a promising result against carbonation compared to behavior of non-bacterial concrete [87]. Tab.7 presents the literatures on the carbonation performance of bacterial concrete.

Curing conditions have also impacted concrete carbonation [62,79]. Concrete cured in the urea-lactate medium has shown poor resistance against carbonation, leading to increased carbonation depth than in concrete cured in tap water. This might be because of the acidic nature of lactate, which leads to reduced pH of concrete pore solutions [62].

Chen et al. [88] studied the carbonation behavior by using Paenibacillus bacteria (3.1 × 10⁸ cells/mL) in different water-to-cement ratio (w/c) (0.3, 0.4, and 0.5) concrete. The bacteria were added in four different amounts (0.4%, 0.6%, 0.8%, and 1.5% by weight of cement) in the concrete and tested for carbonation after curing age of 14, 28 and 60 d. The optimum bacteria content is 0.6% for 0.4 to 0.5 w/c, and 0.4% for 0.3 w/c. The optimum bacteria content contributes to an increase in carbonation depth, while a greater bacteria concentration prevents such an increase. This is due to the fact that the biomineralization rate is greater during the preliminary phase of hydration, and increased CaCO₃ synthesis causes the porosity of the surface layer to drastically decrease, making it more challenging for CO₂ to continue to diffuse in the sample, leading to prevention of further biomineralization [88].

A study on the efficient application of B. Sphaericus (10⁷ cells/mL) has been conducted on mortar samples with the different w/c values (0.5, 0.6, and 0.7) by de Muynck et al. [89]. The samples were exposed to 10% CO₂ concentration and tested after 2, 4, and 6 weeks of exposure and resistance to carbonation were quantified in terms of carbonation rate constant (K) (mm·s^−1/2) [90]. Results demonstrated that after two weeks of accelerated carbonation, there were already evident changes in the carbonation depth between treated and untreated specimens. When compared to untreated cubes, the carbonation rate was significantly reduced by the added bacterial biomass. With increasing w/c (0.5, 0.6, and 0.7), this addition had a better effect, resulting in a decrease in K of roughly 24%, 30%, and 37%, respectively, and with the combination of calcium source and bacteria, a further drop in carbonation rate is observed [89].

6.2 Permeation properties

Permeability is regarded as the critical characteristic for illustrating the durability of concrete since it determines how quickly aggressive substances can penetrate concrete and cause degradation under pressure gradients. It depends on the characteristics of the materials’ pore network, which can be measured in terms of pores, tortuosity, specific surface, distribution of size, connectedness, and microcracks. These features are influenced by various factors, including the age of hardened cementitious materials, their particle size distribution, the water/binder ratio, and the presence of aggressive compounds [92]. Precipitation of calcite due to biomineralization has proved beneficial in the resistance against water permeability and absorption. Deposition of CaCO₃ decreased water absorption and permeability, resulting in enhanced durability properties [93,94].

Chahal et al. [10] in their study on the behavior of microbial concrete blended with various percentages of FA, reported that the concrete showed 4-fold reduced water absorption at a concentration of 10⁵ cells/mL S. pasteurii. In bacterial concrete, pores are filled with calcite resulting in decreased water absorption [95]. The addition of Bacillus Megaterium at a concentration of 5 × 10⁷ cells/mL resulted in about threefold decrease in water absorption in FA-concrete. An overview of various water absorption tests conducted on concrete with the addition of different types of bacteria and their concentration is presented in Tab.8.

The reduction in water absorption can also be influenced by the bacteria type and its concentration, presence of different nutrients, etc., as reported in various literatures [92,93,98]. In a long-term study of durability performance of concrete conducted by Bhaskar et al. [103], it was reported that the greatest reduction of 90% was obtained for the specimens containing S. pasteurii bacteria immobilized in Zeolite at a duration of 8 months. When it comes to bacterial concentration, it is seen that greater concentrations resulted in the most significant reduction in water absorption because higher precipitation slows down the water flow inside the matrix of concrete [94,98].

Steel reinforcement corrosion is caused by ion transport, and concrete’s resistance to this process depends on the pore structure [104] and can be measured through Rapid Chloride Permeabilty Test (RCPT) [105]. The ASTM C1202 code provides a qualitative demonstration of chloride ion penetrability based on measured values (charge passed) from the test and is presented in Tab.9.

The improvement of particle packing density of the material also results in a reduction of chloride permeability [106]. Additionally, bacterial precipitation enhances the aggregate-cement interface, which lowers the chloride permeability [20]. That research also showed that inclusion of bacteria in concrete can result in the enhancement in the permeation resistance of chloride ions. Around 12% reduction in average charge passed is observed for the concrete containing bacteria compared to bacteria-less concrete. Addition of S. pasteurii and B. subtilis has reduced the penetration of chloride ion in concrete [107]. Inclusion of B. aerius bacteria in the concrete has reduced the charge passed in both control and rice husk ash (RHA)-concrete. Reductions of 55%, 50%, and 48% in the charge passed are observed for bacterial concrete compared to that in normal concrete after 7, 28, and 56 d, respectively [56]. Another study conducted by Chahal et al. [95], on the inclusion of S. pasteurii bacteria on the silica fume (SF) based concrete, demonstrated excellent resistance against chloride penetration (380 coulombs passing level) at a concentration of 10⁵ cells/mL for 10% SF concrete. Tab.10 presents details from the literature survey, and Fig.10 presents a graphical representation of the RCPT behavior of bacterial concrete.

According to Rao et al. [106], bacterial concrete has shown an improvement in resistance to chloride migration of 85%–90% compared to conventional cementitious composites. Joshi et al. [108] and Achal et al. [20] reported similar findings in their studies. A study conducted by Bhaskar et al. [103] on the long-term durability properties of concrete has demonstrated reduction in chloride permeability of about 30% at 120 d, 44% at 180 d, and 54% at 240 d. Ling and Qian [109] studied the behavior of bacteria inclusion for reinforcement protection in concrete. Chloride concentration at various depths revealed that the presence of bacteria prevented chloride from penetrating the cracks, prevented corrosion products from spilling into the cracks, and reduced the weight-loss ratio of the reinforcements, thereby slowing the progression of reinforcement corrosion [109].

The evaluation of gas permeability in concrete is important in the assessment of the long-term durability and overall performance of concrete structures. Gas permeability quantifies the degree to which gases can traverse the porous and fractured structure of concrete and has implications for many concrete degradation mechanisms, such as reinforcement corrosion, concrete carbonation, and infiltration of deleterious compounds [110]. de Muynck et al. [34] in his study of bacterial carbonate precipitation using B. Sphaericus, found that gas permeability decreased with the addition of bacteria at all w/c due to the presence of precipitated calcite. In another study, greater gas permeability is reported in samples with greater w/c. The use of biodeposition treatment in the presence of calcium chloride led to reductions in permeability of approximately 31%, 47%, and 63% as the w/c increased from 0.5 to 0.6 and 0.7, respectively. The application of traditional surface treatments, such as acrylate-based surface coatings or the use of penetrating sealants like silanes or siloxane mixtures, led to more significant decreases in gas permeability than occurred with biodeposition treatment [92]. Nguyen et al. [111] had also reported the similar behavior of concrete treated with B. subtilis bacteria.

6.3 Freeze–thaw resistance

The experimental findings by de Muynck et al. [34], demonstrated that cementitious composites enhanced with bacterial technology, with a w/c of 0.7, and exhibited a notably greater SS following 21 freeze−thaw cycles than occurred in the composites with a lower w/c. This improvement can be attributed to the presence of a higher quantity of water capable of freezing within the pore system. Bang et al. [49] studied the performance of S. pasteurii bacteria cells (8.6 × 10⁸ cells/cm³) in cement mortar beams, cured in urea-CaCl₂ medium for 7 d, prior to 14 d of air curing, and subjected to 300 cycles of freezing–thawing. Throughout the test cycles, there were notable decreases (ranging from 44% to 73%) in the average expansion of mortar beams containing bacteria, in comparison to the control specimens. The average expansion of control specimens was found to be 0.054% after being subjected to 300 cycles of freeze–thaw. In contrast, the expansion of bacterial mortar beams was seen to be just 0.03%. The specimens containing bacteria exhibited a retention rate of 98% in terms of their initial weight after undergoing 300 cycles of freezing and thawing. In contrast, the specimens lacking bacteria displayed a significantly lower retention rate of just 69% of their original weight [49]. The better performance of the bacterial mortar specimens was because of the formation of an impermeable calcite layer on the surface of samples which resisted the samples to an adverse environmental condition.

7 Material characterization: X-ray computed tomography (XCT)

XCT is a non-destructive method used to examine the internal microstructure of materials. The emitter, which releases X-rays at a specific intensity, and the detector, which measures the X-ray reception intensity, make up the tomography apparatus. The outcome is a three-dimensional image in gray scale, where each area of gray corresponds to a different level of absorption of X-rays by the material, which is related to material density. Lighter greys represent higher densities of material, whereas lower densities are described by darker tones [112]. Although reports of XCT studies on concrete appear in the literature, only some were on bacterial concrete [35,88,113]. Wang et al. [113] conducted X-ray μ-CT to understand the microstructure and deposition of self-healing materials in concrete with bacteria encapsulated in hydrogel. The precipitation of calcite on the surface and inside the specimens could be seen clearly in the X-ray tomography images. The generated precipitates can be seen by subtracting the two-dimensional (2D) X-ray images taken before and after the healing process. Results show that no significant difference was found in ‘before’ and ‘after’ images for the sample with no nutrients (Reference sample, R). However, samples with hydrogel incorporation (m-H) and bacteria encapsulated in hydrogels (m-HS) show significant differences before and after the healing process. A larger amount of precipitation was formed in M-HS samples after the healing process than in the m-H sample.

To get a clearer idea about the precipitation of calcite, 2D reconstructed slices were rendered in three-dimensional (3D) (with the help of VG Studio) to learn more about the precipitation distribution in a 3D concrete matrix.

Even though there was little precipitation seen in the 2D images, there was some precipitation visible in sample R. There was a little concentration near the sample’s surface. The precipitation was dispersed randomly across the remainder of the sample, not confined to the cracks. A dense deposition was discovered at the surface of sample (m-H). The quantity significantly decreased inside the matrix and in the subsurface layer. It appears that more precipitation was generated for the sample m-HS.

Likewise, in sample m-H, a substantial layer was seen, but it was more prominent on the sample’s surface and less inside the body of material. Quantitative data of the produced precipitation were acquired using the software Morpho+. Results show 0.21%, 1.37%, and 2.2% precipitation by volume of the samples (R, m-H, and m-HS, respectively).

8 Conclusions

1) The most popular ways to incorporate bacteria into concrete are to spray it on the surface, add it to the mix, and encapsulate it there so it stays dormant until a crack forms; at that point the bacteria become active and begin the biomineralization process. Although most of the examined articles added the bacteria to the mixture, spraying the bacteria onto the mixture may be more appropriate because it keeps the bacteria out of the concrete mixture’s heavily alkaline media.

2) Bacteria can produce calcium carbonate both autotrophically and heterotrophically as part of the biomineralization process. The heterotrophic method primarily depends on utilizing other nutrients and minerals for biomineralization, whereas the autotrophic pathway occurs when the bacteria use carbon dioxide or light to generate calcium carbonate.

3) Three criteria are determined to be the main determinants of the CS of microbial concrete: the type of bacteria, the application process, and the concentration of bacteria in the concrete matrix. Most researchers have also noted that the most significant improvement in CS is found at an intermediate bacterial cell concentration of 10⁵ cells/mL.

4) Use of various SCMs such as FA, RHA, SF, have also enhanced mechanical and durability properties at an optimum replacement level.

5) As much as a 50% increase is observed in FS with the addition of fibers in bacteria-based self-healing concrete with significant enhancement in durability properties.

6) Although very few studies have been performed on the carbonation of bacterial concrete, as much as a 50%−60% reduction in carbonation depth is observed for bacterial concrete compared to the depth in control concrete because of the densification of concrete matrix and pore filling. Contradictorily, concrete cured in a nutrient medium like calcium lactate-urea is subject to increased risk of carbonation because of acidic nature of lactate media.

7) As much as 60% reduction in water absorption is observed for bacterial concrete due to intense pore filling with the calcite precipitates, thereby leading to more durable concrete. Similar trends have also been observed in the case of gas permeability.

8) Bacterial concrete is also effective against the penetration of chloride ions in concrete. As much as 57% reduction is observed in charge passed (RCPT) for bacterial concrete compared to that in normal concrete. Most of the bacterial concrete samples were found falling in the region of “very low−low−moderate” range as defined for chloride ion permeability by ASTM C1202, making the bacterial concrete more durable against chloride ion penetration.

9) Bacteria induced mortar/concrete samples have shown better resistance against cyclic freezing and thawing. About 44%–73% reduction in expansion of bacterial concrete/mortar specimens is observed. A retention rate of about 98% in their initial weight is also reported in the bacterial concrete samples subjected to cycles of freezing and thawing.

10) XCT is a technique which gives us an idea about the microstructure of concrete. With the help of XCT technology in bacterial concrete, we learn about the amount of precipitates formed and its distribution along the concrete matrix.

9 Research gaps and recommendation for further studies

1) The majority of the research being done now is on a laboratory scale. As a result, more extensive outside experiments are required to be conducted.

2) Unlike concrete, mortar has been the subject of the majority of experimental work until now. The behavior of bacteria in concrete needs to be thoroughly investigated because mortar and concrete behave differently due to the influence of particles and different fracture patterns.

3) The behavior of bio concrete in actual environmental conditions, such as when the concrete gets old, has multiple cracks or faces a variety of prolonged loads, has to be studied further.

4) Carbonation of concrete is an essential aspect of the durability of concrete. Extensive research should be performed on the bacterial concrete regarding its behavior against carbonation.

5) Use of SCMs and fibers in bacterial concrete needs further research to encourage sustainable practices in construction industry.

6) It is crucial to consider ways to cut costs of producing bacterial concrete, including consideration of nutrients as well as bacteria.

References

[1] Wiktor V, Jonkers H M. Quantification of crack-healing in novel bacteria-based self-healing concrete. Cement and Concrete Composites, 2011, 33(7): 763–770

[2] Wille K, Naaman A E, El-Tawil S, Parra-Montesinos G J. Ultra-high performance concrete and fiber reinforced concrete: Achieving strength and ductility without heat curing. Materials and Structures, 2012, 45(3): 309–324

[3] Schuab M R, José dos Santos W, Borges P H R. On the development of MK/BFS alkali-activated materials as repair mortars: Performance under free and restrained shrinkage tests. Construction and Building Materials, 2021, 275: 122109

[4] SinghNAnkurNHaqueM MGuptaA. Influence of coal bottom ash and copper slag on permeation of fly ash based geopolymer concrete. In: Proceedings of the 7th International Conference on Civil Structural and Transportation Engineering (ICCSTE’22), 2022, 1–8

[5] Singh N, Haque M M, Gupta A. Reviewing mechanical performance of geopolymer concrete containing coal bottom ash. Materials Today: Proceedings, 2022, 65: 1449–1458

[6] Singh N, Gupta A, Haque M M. A review on the influence of copper slag as a natural fine aggregate replacement on the mechanical properties of concrete. Materials Today: Proceedings, 2022, 62: 3624–3637

[7] Srikanth G, Safiuddin M, Haque M M, Rizwan M. Study on mechanical properties of concrete using different types of coarse aggregates. Materials Today: Proceedings, 2022, 65: 2029–2033

[8] Haque M M, Ankur N, Meena A, Singh N. Carbonation and permeation behaviour of geopolymer concrete containing copper slag and coal ashes. Developments in the Built Environment, 2023, 16: 100276

[9] Luukkonen T, Abdollahnejad Z, Yliniemi J, Kinnunen P, Illikainen M. One-part alkali-activated materials: A review. Cement and Concrete Research, 2018, 103: 21–34

[10] Chahal N, Siddique R, Rajor A. Influence of bacteria on the compressive strength, water absorption and rapid chloride permeability of fly ash concrete. Construction and Building Materials, 2012, 28(1): 351–356

[11] Wei S, Sanchez M, Trejo D, Gillis C. Microbial mediated deterioration of reinforced concrete structures. International Biodeterioration & Biodegradation, 2010, 64(8): 748–754

[12] Vijay K, Murmu M, Deo S V. Bacteria based self healing concrete––A review. Construction and Building Materials, 2017, 152: 1008–1014

[13] Jonkers H M, Thijssen A, Muyzer G, Copuroglu O, Schlangen E. Application of bacteria as self-healing agent for the development of sustainable concrete. Ecological Engineering, 2010, 36(2): 230–235

[14] Gao M, Guo J, Cao H, Wang H, Xiong X, Krastev R, Nie K, Xu H, Liu L. Immobilized bacteria with pH-response hydrogel for self-healing of concrete. Journal of Environmental Management, 2020, 261: 110225

[15] Wang J, Ersan Y C, Boon N, de Belie N. Application of microorganisms in concrete: A promising sustainable strategy to improve concrete durability. Applied Microbiology and Biotechnology, 2016, 100(7): 2993–3007

[16] Alghamri R, Kanellopoulos A, Al-Tabbaa A. Impregnation and encapsulation of lightweight aggregates for self-healing concrete. Construction and Building Materials, 2016, 124: 910–921

[17] Reinhardt H W, Jooss M. Permeability and self-healing of cracked concrete as a function of temperature and crack width. Cement and Concrete Research, 2003, 33(7): 981–985

[18] Maes M, Snoeck D, de Belie N. Chloride penetration in cracked mortar and the influence of autogenous crack healing. Construction and Building Materials, 2016, 115: 114–124

[19] Li M, Zhu X, Mukherjee A, Huang M, Achal V. Biomineralization in metakaolin modified cement mortar to improve its strength with lowered cement content. Journal of Hazardous Materials, 2017, 329: 178–184

[20] Achal V, Mukerjee A, Sudhakara Reddy M. Biogenic treatment improves the durability and remediates the cracks of concrete structures. Construction and Building Materials, 2013, 48: 1–5

[21] Chen H, Qian C, Huang H. Self-healing cementitious materials based on bacteria and nutrients immobilized respectively. Construction and Building Materials, 2016, 126: 297–303

[22] Rauf M, Khaliq W, Khushnood R A, Ahmed I. Comparative performance of different bacteria immobilized in natural fibers for self-healing in concrete. Construction and Building Materials, 2020, 258: 119578

[23] Gupta S, Pang S D, Kua H W. Autonomous healing in concrete by bio-based healing agents––A review. Construction and Building Materials, 2017, 146: 419–428

[24] Tayebani B, Mostofinejad D. Penetrability, corrosion potential, and electrical resistivity of bacterial concrete. Journal of Materials in Civil Engineering, 2019, 31(3): 04019002

[25] Nodehi M, Ozbakkaloglu T, Gholampour A. A systematic review of bacteria-based self-healing concrete: Biomineralization, mechanical, and durability properties. Journal of Building Engineering, 2022, 49: 104038

[26] Grabiec A M, Klama J, Zawal D, Krupa D. Modification of recycled concrete aggregate by calcium carbonate biodeposition. Construction and Building Materials, 2012, 34: 145–150

[27] Shaheen N, Khushnood R A, Khaliq W, Murtaza H, Iqbal R, Khan M H. Synthesis and characterization of bio-immobilized nano/micro inert and reactive additives for feasibility investigation in self-healing concrete. Construction and Building Materials, 2019, 226: 492–506

[28] Liu C, Lv Z, Xiao J, Xu X, Nong X, Liu H. On the mechanism of Cl⁻ diffusion transport in self-healing concrete based on recycled coarse aggregates as microbial carriers. Cement and Concrete Composites, 2021, 124: 104232

[29] Alazhari M, Sharma T, Heath A, Cooper R, Paine K. Application of expanded perlite encapsulated bacteria and growth media for self-healing concrete. Construction and Building Materials, 2018, 160: 610–619

[30] Han S, Choi E K, Park W, Yi C, Chung N. Effectiveness of expanded clay as a bacteria carrier for self-healing concrete. Applied Biological Chemistry, 2019, 62: 19

[31] Seifan M, Sarmah A K, Samani A K, Ebrahiminezhad A, Ghasemi Y, Berenjian A. Mechanical properties of bio self-healing concrete containing immobilized bacteria with iron oxide nanoparticles. Applied Microbiology and Biotechnology, 2018, 102(10): 4489–4498

[32] Jiang L, Jia G, Jiang C, Li Z. Sugar-coated expanded perlite as a bacterial carrier for crack-healing concrete applications. Construction and Building Materials, 2020, 232: 117222

[33] de Muynck W, Cox K, de Belie N, Verstraete W. Bacterial carbonate precipitation as an alternative surface treatment for concrete. Construction and Building Materials, 2008, 22(5): 875–885

[34] de Muynck W, Debrouwer D, de Belie N, Verstraete W. Bacterial carbonate precipitation improves the durability of cementitious materials. Cement and Concrete Research, 2008, 38(7): 1005–1014

[35] Nosouhian F, Mostofinejad D, Hasheminejad H. Influence of biodeposition treatment on concrete durability in a sulphate environment. Biosystems Engineering, 2015, 133: 141–152

[36] Qian C, Wang J, Wang R, Cheng L. Corrosion protection of cement-based building materials by surface deposition of CaCO₃ by Bacillus pasteurii. Materials Science and Engineering: C, 2009, 29(4): 1273–1280

[37] Soleimani S, Ormeci B, Isgor O B. Growth and characterization of Escherichia coli DH5α biofilm on concrete surfaces as a protective layer against microbiologically influenced concrete deterioration (MICD). Applied Microbiology and Biotechnology, 2013, 97(3): 1093–1102

[38] Soleimani S, Isgor O B, Ormeci B. Resistance of biofilm-covered mortars to microbiologically influenced deterioration simulated by sulfuric acid exposure. Cement and Concrete Research, 2013, 53: 229–238

[39] Wang J Y, Soens H, Verstraete W, de Belie N. Self-healing concrete by use of microencapsulated bacterial spores. Cement and Concrete Research, 2014, 56: 139–152

[40] Wang J Y, de Belie N, Verstraete W. Diatomaceous earth as a protective vehicle for bacteria applied for self-healing concrete. Journal of Industrial Microbiology & Biotechnology, 2012, 39(4): 567–577

[41] Wang J, Niu D, Zhang Y. Mechanical properties, permeability and durability of accelerated shotcrete. Construction and Building Materials, 2015, 95: 312–328

[42] Erşan Y Ç, da Silva F B, Boon N, Verstraete W, de Belie N. Screening of bacteria and concrete compatible protection materials. Construction and Building Materials, 2015, 88: 196–203

[43] Erşan Y Ç, de Belie N, Boon N. Microbially induced CaCO₃ precipitation through denitrification: An optimization study in minimal nutrient environment. Biochemical Engineering Journal, 2015, 101: 108–118

[44] Erşan Y Ç, Gruyaert E, Louis G, Lors C, de Belie N, Boon N. Self-protected nitrate reducing culture for intrinsic repair of concrete cracks. Frontiers in Microbiology, 2015, 6: 1228

[45] Khushnood R A, Ud Din S, Shaheen N, Ahmad S, Zarrar F. Bio-inspired self-healing cementitious mortar using Bacillus subtilis immobilized on nano-/micro-additives. Journal of Intelligent Material Systems and Structures, 2019, 30(1): 3–15

[46] Seifan M, Samani A K, Berenjian A. Bioconcrete: Next generation of self-healing concrete. Applied Microbiology and Biotechnology, 2016, 100(6): 2591–2602

[47] Siddique R, Chahal N K. Effect of ureolytic bacteria on concrete properties. Construction and Building Materials, 2011, 25(10): 3791–3801

[48] Wang J Y, Snoeck D, van Vlierberghe S, Verstraete W, de Belie N. Application of hydrogel encapsulated carbonate precipitating bacteria for approaching a realistic self-healing in concrete. Construction and Building Materials, 2014, 68: 110–119

[49] Bang S S, Lippert J J, Yerra U, Mulukutla S, Ramakrishnan V. Microbial calcite, a bio-based smart nanomaterial in concrete remediation. International Journal of Smart and Nano Materials, 2010, 1(1): 28–39

[50] Luo M, Qian C. Influences of bacteria-based self-healing agents on cementitious materials hydration kinetics and compressive strength. Construction and Building Materials, 2016, 121: 659–663

[51] Schreiberová H, Bílý P, Fládr J, Šeps K, Chylík R, Trtík T. Impact of the self-healing agent composition on material characteristics of bio-based self-healing concrete. Case Studies in Construction Materials, 2019, 11: e00250

[52] Khushnood R A, Qureshi Z A, Shaheen N, Ali S. Bio-mineralized self-healing recycled aggregate concrete for sustainable infrastructure. Science of the Total Environment, 2020, 703: 135007

[53] Huynh N N T, Phuong N M, Toan N P A, Son N K. Bacillus subtilis HU58 immobilized in micropores of diatomite for using in self-healing concrete. Procedia Engineering, 2017, 171: 598–605

[54] Jena S, Basa B, Panda K C, Sahoo N K. Impact of Bacillus subtilis bacterium on the properties of concrete. Materials Today: Proceedings, 2020, 32: 651–656

[55] Khaliq W, Ehsan M B. Crack healing in concrete using various bio influenced self-healing techniques. Construction and Building Materials, 2016, 102: 349–357

[56] Siddique R, Singh K, Kunal P, Singh M, Corinaldesi V, Rajor A. Properties of bacterial rice husk ash concrete. Construction and Building Materials, 2016, 121: 112–119

[57] Saxena S, Tembhurkar A R. Developing biotechnological technique for reuse of wastewater and steel slag in bio-concrete. Journal of Cleaner Production, 2019, 229: 193–202

[58] Siddique R, Jameel A, Singh M, Barnat-Hunek D, Kunal A, Aït-Mokhtar R, Belarbi A. Effect of bacteria on strength, permeation characteristics and micro-structure of silica fume concrete. Construction and Building Materials, 2017, 142: 92–100

[59] Siddique R, Nanda V, Kunal E H, Kadri Khan M, Iqbal M, Singh A. Influence of bacteria on compressive strength and permeation properties of concrete made with cement baghouse filter dust. Construction and Building Materials, 2016, 106: 461–469

[60] Sahoo K K, Arakha M, Sarkar P, P R D, Jha S. Enhancement of properties of recycled coarse aggregate concrete using bacteria. International Journal of Smart and Nano Materials, 2016, 7(1): 22–38

[61] Pei R, Liu J, Wang S, Yang M. Use of bacterial cell walls to improve the mechanical performance of concrete. Cement and Concrete Composites, 2013, 39: 122–130

[62] Salmasi F, Mostofinejad D. Investigating the effects of bacterial activity on compressive strength and durability of natural lightweight aggregate concrete reinforced with steel fibers. Construction and Building Materials, 2020, 251: 119032

[63] Afifudin H, Nadzarah W, Hamidah M S, Hana H N. Microbial participation in the formation of calcium silicate hydrated (CSH) from Bacillus subtilis. Procedia Engineering, 2011, 20: 159–165

[64] Madhan Kumar M, Vijaya Ganapathy D, Subathra Devi V, Iswarya N. Experimental investigation on fibre reinforced bacterial concrete. Materials Today: Proceedings, 2020, 22: 2779–2790

[65] Shelote K M, Meera M, Supravin K, Gupta S. Study on modified water permeability method for fly ash concrete in comparison with DIN 1048 (part 5). Arabian Journal for Science and Engineering, 2023, 48(10): 13337–13352

[66] Shelote K M, Bala A, Gupta S. An overview of mechanical, permeability, and thermal properties of silica fume concrete using bibliographic survey and building information modelling. Construction and Building Materials, 2023, 385: 131489

[67] Jafarnia M S, Khodadad Saryazdi M, Moshtaghioun S M. Use of bacteria for repairing cracks and improving properties of concrete containing limestone powder and natural zeolite. Construction and Building Materials, 2020, 242: 118059

[68] Shanmuga Priya T, Ramesh N, Agarwal A, Bhusnur S, Chaudhary K. Strength and durability characteristics of concrete made by micronized biomass silica and Bacteria-Bacillus sphaericus. Construction and Building Materials, 2019, 226: 827–838

[69] Kunal S R, Siddique R, Rajor A. Strength and microstructure analysis of bacterial treated cement KILN dust mortar. Construction and Building Materials, 2014, 63: 49–55

[70] Chahal N, Siddique R. Permeation properties of concrete made with fly ash and silica fume: Influence of ureolytic bacteria. Construction and Building Materials, 2013, 49: 161–174

[71] Achal V, Pan X, Özyurt N. Improved strength and durability of fly ash-amended concrete by microbial calcite precipitation. Ecological Engineering, 2011, 37(4): 554–559

[72] Khan M, Ali M. Improvement in concrete behavior with fly ash, silica-fume and coconut fibres. Construction and Building Materials, 2019, 203: 174–187

[73] Li F, Chen D, Yang Z, Lu Y, Zhang H, Li S. Effect of mixed fibers on fly ash-based geopolymer resistance against carbonation. Construction and Building Materials, 2022, 322: 126394

[74] KashiyaniBpitrodaJShahB. Effect of polypropylene fibers on abrasion resistance and flexural strength for interlocking paver block. International Journal of Engineering Trends and Technology, 2013: 2231–5381

[75] Manojkumar C, Ramesh B, Kumar G B R. Proceedings Study on the compressive strength of glass fibre reinforced M20 grade self-healing concrete using a novel technique microbial induced calcite precipitation. Materials Today: Proceedings, 2023, 79: 53–58

[76] Thakare A A, Gupta T, Deewan R, Chaudhary S. Micro and macro-structural properties of waste tyre rubber fibre-reinforced bacterial self-healing mortar. Construction & Building Materials, 2022, 322: 126459

[77] Zhang D, Shahin M A, Yang Y, Liu H, Cheng L. Effect of microbially induced calcite precipitation treatment on the bonding properties of steel fiber in ultra-high performance concrete. Journal of Building Engineering, 2022, 50: 104132

[78] Su Y, Qian C, Rui Y, Feng J. Exploring the coupled mechanism of fibers and bacteria on self-healing concrete from bacterial extracellular polymeric substances (EPS). Cement and Concrete Composites, 2021, 116: 103896

[79] Karimi N, Mostofinejad D. Bacillus subtilis bacteria used in fiber reinforced concrete and their effects on concrete penetrability. Construction and Building Materials, 2020, 230: 117051

[80] Feng J, Su Y, Qian C. Coupled effect of PP fiber, PVA fiber and bacteria on self-healing efficiency of early-age cracks in concrete. Construction and Building Materials, 2019, 228: 116810

[81] Sierra-Beltran M G, Jonkers H M, Schlangen E. Characterization of sustainable bio-based mortar for concrete repair. Construction and Building Materials, 2014, 67: 344–352

[82] Kua H W, Gupta S, Aday A N, Srubar W V. Biochar-immobilized bacteria and superabsorbent polymers enable self- healing of fiber-reinforced concrete after multiple damage cycles. Cement and Concrete Composites, 2019, 100: 35–52

[83] Shah V, Bishnoi S. Carbonation resistance of cements containing supplementary cementitious materials and its relation to various parameters of concrete. Construction and Building Materials, 2018, 178: 219–232

[84] Shah V, Scrivener K, Bhattacharjee B, Bishnoi S. Changes in microstructure characteristics of cement paste on carbonation. Cement and Concrete Research, 2018, 109: 184–197

[85] Smitha M P, Suji D, Shanthi M, Adesina A. Application of bacterial biomass in biocementation process to enhance the mechanical and durability properties of concrete. Cleaner Materials, 2022, 3: 100050

[86] Joshi S, Ahn Y, Goyal S, Reddy M S. Performance of bacterial mediated mineralization in concrete under carbonation and chloride induced corrosion. Journal of Building Engineering, 2023, 69: 106234

[87] Vijay K, Murmu M. Evaluating durability parameters of concrete containing bacteria and basalt fiber. Journal of Building Pathology and Rehabilitation, 2022, 7: 1–6

[88] Chen Y, Qian C, Hao Z, Zhou H. Effect of bio-mineralization on concrete performance: Carbonation, microhardness, gas permeability and Cl⁻ migration. Biochemical Engineering Journal, 2021, 171: 108024

[89] de MuynckWde BelieNVerstraeteW. Improvement of concrete durability with the aid of bacteria. In: Proceedings of The First International Conference on Self-Healing Materials. Cham: Springer, 2007

[90] Roy S K, Poh K B, Northwood D O. Durability of concrete––Accelerated carbonation and weathering studies. Building and Environment, 1999, 34(5): 597–606

[91] RILEM Recommendation. CPC-18 Measurement of hardened concrete carbonation depth. Materials and Structures, 1988, 21: 453–455

[92] de MuynckWCoxKde BelieNVerstraiteW. Bacterial carbonate precipitation reduces permeability of cementitious materials. In: Sustainable Construction Materials and Technologies. Boca Raton, FL: CRC Press, 2020, 411–416

[93] Sadeghpour M, Baradaran M. Effect of bacteria on the self-healing ability of fly ash concrete. Construction and Building Materials, 2023, 364: 129956

[94] Tabalvandani M N, Tajabadi-Ebrahimi M, Sarafraz M E, Sepahi A A. Investigation of self-healing properties in concrete with Bacillus licheniformis isolated from agricultural soil. Journal of Building Engineering, 2023, 67: 106057

[95] Chahal N, Siddique R, Rajor A. Influence of bacteria on the compressive strength, water absorption and rapid chloride permeability of concrete incorporating silica fume. Construction and Building Materials, 2012, 37: 645–651

[96] Wang X, Xu J, Wang Z, Yao W. Use of recycled concrete aggregates as carriers for self-healing of concrete cracks by bacteria with high urease activity. Construction and Building Materials, 2022, 337: 127581

[97] Mondal S, Das P, Datta P, Ghosh A D. Deinococcus radiodurans: A novel bacterium for crack remediation of concrete with special applicability to low-temperature conditions. Cement and Concrete Composites, 2020, 108: 103523

[98] Mondal S, Ghosh A. Investigation into the optimal bacterial concentration for compressive strength enhancement of microbial concrete. Construction and Building Materials, 2018, 183: 202–214

[99] Wang W, Lu C, Li Y, Yuan G, Li Q. Effects of stress and high temperature on the carbonation resistance of fly ash concrete. Construction and Building Materials, 2017, 138: 486–495

[100] Nugroho A, Satyarno I, Subyakto S. Bacteria as self-healing agent in mortar cracks. Journal of Engineering and Technological Sciences, 2015, 47(3): 279–295

[101] Xu J, Yao W, Jiang Z. Non-ureolytic bacterial carbonate precipitation as a surface treatment strategy on cementitious materials. Journal of Materials in Civil Engineering, 2014, 26(5): 983–991

[102] Kunal S R, Siddique R, Rajor A. Influence of bacterial treated cement kiln dust on the properties of concrete. Construction and Building Materials, 2014, 52: 42–51

[103] Bhaskar S, Anwar Hossain K M, Lachemi M, Wolfaardt G, Otini Kroukamp M. Effect of self-healing on strength and durability of zeolite-immobilized bacterial cementitious mortar composites. Cement and Concrete Composites, 2017, 82: 23–33

[104] Choi Y S, Yang E I. Effect of calcium leaching on the pore structure, strength, and chloride penetration resistance in concrete specimens. Nuclear Engineering and Design, 2013, 259: 126–136

[105] ASTM C1202. Standard Test Method for Electrical Indication of Concrete’s Ability to Resist Chloride Ion Penetration. West Conshohocken, PA: ASTM, 2012

[106] Rao M V S, Reddy V S, Sasikala C. Performance of microbial concrete developed using Bacillus subtilus JC3. Journal of The Institution of Engineers: Series A, 2017, 98(4): 501–510

[107] Nosouhian F, Mostofinejad D, Hasheminejad H. Concrete durability improvement in a sulfate environment using bacteria. Journal of Materials in Civil Engineering, 2016, 28(1): 04015064

[108] Joshi S, Goyal S, Reddy M S. Influence of nutrient components of media on structural properties of concrete during biocementation. Construction and Building Materials, 2018, 158: 601–613

[109] Ling H, Qian C. Effects of self-healing cracks in bacterial concrete on the transmission of chloride during electromigration. Construction and Building Materials, 2017, 144: 406–411

[110] BakhshiMMahoutianMShekarchiM. The gas permeability of concrete and its relationship with strength. In: Proceedings of the fib 2nd International Congress. Naples: fib, 2006

[111] Nguyen T H, Ghorbel E, Fares H, Cousture A. Bacterial self-healing of concrete and durability assessment. Cement and Concrete Composites, 2019, 104: 103340

[112] VicenteM AMínguezJGonzálezD C. The use of computed tomography to explore the microstructure of materials in civil engineering: From rocks to concrete. In: Halefoğlu A M. Computed Tomography––Advanced Applications. London: IntechOpen, 2017

[113] Wang J, Dewanckele J, Cnudde V, van Vlierberghe S, Verstraete W, de Belie N. X-ray computed tomography proof of bacterial-based self-healing in concrete. Cement and Concrete Composites, 2014, 53: 289–304

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