1 Introduction

Concrete buildings frequently experience cracks during the hardening phases of the cement due to plastic and drying shrinkage, settling process, and loading [1, 2]. Cracks allow air and water to enter a building made of concrete with ease. Additionally, cracks allow harmful ions to enter concrete structures, such as CO2, sulphate ions, and chloride ions, resulting in strength loss and eventual structural collapse [3]. This also shortens the lifespan and strength of the entire concrete structure by causing the rebars to corrode. Hence, to prolong the life of the building, it is essential to prevent fractures from growing larger and to fix cracks as soon as possible. Surface treatment, injecting chemical adhesives, manual grouting, and route sealing are some of the methods for fixing these cracks [4, 5]. Recently self-healing mortars and concretes are subject of much attention since they extend the life of construction projects by repairing cracks on their own. Concrete that has the ability to repair cracks on its own, may extend the building lifespan by protecting the reinforcement steel and internal matrix [6].

Artificially or synthetically produced substance with the innate capacity to self-heal cracks without external assistance or human interaction are known as self-healing materials. Healing mechanisms are generally categorised into two categories, extrinsic healing mechanism and intrinsic healing, depending on the mechanism of repairing cracks. Studies found that the occurrence of chemical interaction, between matrix of cement and other components in the concrete which promotes the healing of fissures, shows intrinsic mechanism of healing. In contrast, an extrinsic self-healing mechanism occurs when the healing process that is dependent on external healing agent that exist in the form of a capsule, which does not perticularly interact with the matrix but will heal the fissures. Extrinsic is performed by physical filling of cracks [7, 8]. Cementitious materials can exhibit intrinsic self-healing through either autogenous/autonomous processes. Autogenous healing is an innate mechanism that occurs in presence of moisture or water. The process involves hydration of unhydrated cementitious materials inside the matrix or by the formation of calcium carbonates (CaCO3), when calcium hydroxide reacts with ambient CO2 [9,10,11]. However, autogenous healing can fill the cracks max up to 0.3 mm, also it’s filling of cracks depends on the quantity of water or unhydrated cement present in the matrix [11, 12]. Another process of self-healing were chemically produced reagents or adhesives are introduced to the cracked area, or these materials are put inside a capsule and subsequently inserted into the concrete before it solidifies, this process is chemical self-healing [13]. Although, the chemical healing method is expensive, and complicated and increases the difficulty of casting the concrete. It is crucial to pick a concrete crack repair method that's affordable, simple to apply, safe for the people and environment, and efficient at closing the fissures. A significant quantity of natural resources are consumed during the energy-intensive process of manufacturing OPC, and carbon dioxide gas is also released. Alkali-activated composites are seen to be a formidable rival to OPC concrete in several applications in recent years. It is observed that it takes 1.5 tonnes of raw material to produce 1 tonne of cement, which in turn releases 1 tonne of CO2 into the atmosphere [14, 15]. Alkali activation technology is currently under exploration as a viable alternative to traditional cement in 3D printable concrete, offering notable environmental advantages and less cement usage. The potential of utilizing agro-industrial byproducts to bolster sustainability in alkali-activated 3D printing concrete is acknowledged, albeit with a call for further investigation in this domain. Mix proportions in Alkali activated 3D printed concrete exhibit variability depending upon factors such as silica fume, fly ash, GGBS, type of aggregate, NaOH molarity, and the incorporation of reinforcing fibres and nano clay [16].

Bio-concrete has recently attracted a lot of attentiveness, due to its decreased repair costs, effectiveness in healing large crack width, the sustainable nature of the healing agent, and some bacteria which can live in extreme environments. Micro-organism-induced self-healing is more effective (up to 4 times) in filling micropores and sealing cracks than autogenous repair using unreacted cementitious materials, which can only heal fissures with crack width of 0.1 mm [17]. Fewer species of bacteria can survive in harsh concrete environments since it reduces their lifespan. The endospores of Bacillus pasteurii, also known as Sporosarcina pasteurii, can survive the extreme conditions of concrete, they are frequently used to produce self-healing concrete [18]. The bacteria which survive 1 or 2 pH below the neutral pH-7 are known as neutrophils. Salmonella spp., Staphylococci, and Escherichia coli are some examples [19]. Alkaliphiles are a type of bacteria that are suitable for use in highly alkaline environments like concrete. The ideal pH range for this kind of bacterium growth is 8 to 10. Extreme alkaliphiles have evolved to adapt to their extreme environment by changing the structure of proteins, lipids, and other biological processes to keep the proton motive force(PMF) in alkaline medium [19]. Most often, a high alkalinity is needed for the cementitious components to dissolve during the hydration process. Conventional concrete has a pH between 12 and 13, which is regarded as a rather alkaline medium [20]. The general process of bacterial self-healing of mortar/concrete is presented in Fig. 1.

Fig. 1
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Typical process of crack healing in bacterial concrete

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In order to promote the development and growth of bacteria in the concrete, nutrients are required, which usually comprise of nitrogen and carbon sources. These sources of nutrients, along with organic calcium salt, can be regarded as the growth media for the bacteria. A typical biological growth medium contains an approximate calcium acetate of 0.25–1.5%, glucose of 0.5%, and yeast extract of 0.4–0.5%. Growth mediums are often employed at a rate of 4–5% by mass of the cement. The most common method of providing all the nutrients is to utilise yeast extract in conjunction with a calcium salt [21, 22]. For bacteria to endure the extreme condition within concrete, they often injected as spores [23]. Once the bacterial spores are introduced into the concrete mixture, they activate when water is added, allowing the bacteria to use carbon dioxide activation to break down the bacterial substrate. The right pH and calcium-rich environment in concrete aid in the production of carbon dioxide, which then combines with calcium ions to produce calcium carbonates. Due to this the bacterial development may result in the accumulation of mineral precipitation in fissures, which could reduce the water permeability of healed concrete [24].

Existing review articles frequently give a general overview of bacterial concrete, but they might not look closely enough at the particular bacterial strains that are combined with agro-industrial waste. This could include the methods used to produce bacterial concrete, a more thorough synthesis and comparison of these methods is required, especially with regard to how well they work with various kinds of agro-industrial waste. By synthesizing existing literature, this review provide insights into the diverse range of agro/industrial waste such as RHA, sugarcane bagasse ash, fly ash etc., and their potential as supplementary cementitious material in bacterial concrete production.

2 Bacteria types, culturing, and their blending in concrete

In recent years, numerous extensive studies of bio-based self-healing materials have been published. The term “Bacteria culture” describes the process of growing microorganisms under regulated conditions which has supplies like urea, peptone, and beef extract as a food source for the bacteria [25]. Self-healing can be achieved through various mechanisms, which include bacteria that are ureolytic, non-ureolytic, denitrifying, etc. Carbonate ions and ammonia/ammonium ions can be produced by ureolytic bacteria via urease activity by decomposing Urea [26]. When compared to other bacterial species, ureolytic bacteria exhibit rapid rates of CaCO3 precipitation [27]. Researchers found that in 24 h the bacteria isolation reach the high theoretical level of precipitates of calcium carbonate in presence of urea. Conversly, it took 13 days for the same amount of precipitation of CaCO3 without urea [28]. Despite the effectiveness of using ureolytic species, there are a few significant drawbacks such as release of nitrogen oxide into atmosphere as a result of ammonium ion production causing health and environmental issues [27, 29]. Furthermore, too much ammonium content in the concrete matrix raises the salt damage risk by converting it into nitric acid, which could worsen the corrosion of the steel reinforcing [12, 13, 26]. Few examples of ureolytic bacteria are Sporosarcina ureae, Sporosarcina pasteurii, Bacillus megaterium, and Bacillus sphaericus.

Non-ureolytic bacteria that can survive and precipitate calcium carbonate in high pH conditions have been identified and isolated from various location all over the world [30]. It was reported that three different species of alkali-resistant, non-ureolytic bacteria were extracted from natural alkaline lakes in Kulunda, Russia; Wadi Natrum, Egypt; and Chiprana-Playa, Spain. A phylogenetic study on these isolates indicated that they closely resemble the alkaliphilic species Bacillus alkalinitrilicus and Bacillus cohnii [30]. The Bacillus genus contains the majority of the non-ureolytic bacteria utilised in autonomous healing concrete. The gram-positive bacteria in this genus have rod-shaped, 1–10 μm long facultative anaerobic or aerobic cells [31]. For self-healing concrete, Bacillus species are the most suitable option because they can effectively provide the conditions for CaCO3 precipitation by producing CO2 through cellular respiration and increasing pH of surrounding environment at same time [32]. Their capacity to produce spores, and incredibly resilient surviving condition, is a significant additional factor in their utilisation. The bacteria as spores, may survive the initial challenging circumstances of the concrete environment, such as concrete's dense matrix, unsuitable humidity conditions, and high pH values (pH-13) [33].

Another process called biomineralization, a process of living organisms converting organic substances into inorganic derivatives. Biologically driven mineralization process can precipitate CaCO3 in presence of calcium. Figure 2 describes the process of biomineralization. In this process, carbonates are generated extracellularly by microbes through a variety of metabolic process, such as dissimilatory nitrate reduction, urea hydrolysis, oxygenic photosynthesis, reduction of calcium sulphate, and utilization of organic acid [34]. Methods of biomineralization involve autotropic and heterotropic calcium carbonate precipitation. The term "autotropic" refer to an organism that primarily uses light energy to make something from its own resources, such as carbon dioxide. Autotropic processes involve oxygenic photosynthesis (Cyanobacterium species) and anoxygenic photosynthesis (Halobacterium and the Heliobacterium species), as well as non-methylotrophic methanogenesis (Methanobacterium species), for the formation of CaCO3 [34, 35]. A condition known as "heterotrophic" occurs when an organism needs to obtain its resources and energy from a different medium to produce a necessary substance. This involves the utilizing organic acid, calcium sulphate reduction and reduction in dissimilatory nitrate, and ureolysis (Fig. 3).

Fig. 2
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a Structure of bacteria b presence of negative charged cell wall and positive charged ions, and c biomineral production employing binding of Ca ions to the cell wall [12]

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Fig. 3
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a Encapsulation of bacteria, b injection/spray of cultured bacteria, c direct blending of bacteria

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Following the culture phase, the bacteria can be sprayed directly into the concrete, encapsulated, or added directly into the mixture. These methods involve calcium lactate and bacterial spores which is the food source for bacteria added straight to the concrete after mixing [36]. Once the concrete mixing is complete, calcium lactate and bacterial spores are immediately incorporated into the slurry. Commonly utilized carrier media include water, various alternative carriers, expanded clay, lightweight aggregate, nano, and microparticles [37]. While adding bacteria with calcium lactate, concrete compaction tends to rise, whereas the basic characteristics of this concrete remains same [21].

Introduction of self healing technique to the 3D printing systems offers innovative solution for durability and longevity of structure and this method integrates advanced materials and engineering principles to autonomously repair cracks, enhancing structural resilience and reducing maintenance costs. Some researchers reviewed on the use of supplymental cementitious materials such as GGBS fly ash and micro silica in 3D concrete printing (3DCP) technology, aimed at enhancing sustainability and energy efficiency in construction practices [38]. Through a comprehensive analysis of physical, rheological, and mechanical properties of 3DCP, the study underscores GGBS's superior performance in both compression and flexural, while highlighting thermal conductivity reduction achieved through the incorporation of micro silica and fly ash [38]. Another study utilized numerical models to simulate and identify the mechanical responses of 3D-printed vascular-based healing concretes. By calculating the healing capacity of the vascular based healing concrete, it is discovered that the four acrylonitrile butadiene styrene (ABS) printed vascular based healing concretes have healing efficiencies of more than 150% [39]. It was observed that, in addition to having superior ductility and absorbing greater amounts of energy during deformation and fracture, horizontally printed vascular networks exhibited greater flexure compared to vertically printed ones after the healing process [39]. Despite the potential of Alkali acxtivated slag(AAS)as a groundbreaking solution to mitigate issues such as drying shrinkage and early-age cracking, there remains a lack of extensive research concerning its self-healing capabilities [40]. A study on AAS mortar specimens revealed that the inclusion of polyvinyl alchohol (PVA)fibres resulted in a maximum healing capacity of 65% for fissures upto 50 μm and a low healing rate of 18% for 150 μm fracture width [41].

3 Mechanical and durability properties of self-healing concrete

3.1 Compressive and flexural strength

In a study conducted, Bacillus sphaericus demonstrated a greater regain of strength when compared to bacteria Bacillus subtilis & bacteria Bacillus cohnii, due to its high calcite precipitation. The conversion of soluble organic nutrients into inorganic CaCO3 crystals, which heals the fissures, is the fundamental mechanism of crack healing and strength restoration in bacterial concrete [42]. Physical and chemical characteristics are key factors in restoring the strength of cracked concrete by producing CaCO3 [42]. A study was conducted using ceramsite sand and natural fibers as carrier materials to promote microbial-induced calcite precipitation for bacterial immobilization [42, 43]. Through this analysis, it was found that that proper immobilization methods can enhance the flexural strength of bacterial concrete by 56–72%. Additionally, it was claimed that using natural fibers could increase compressive strength by 42% and provide additional protection from the alkaline medium [42]. It was explained that the increase in strength was due to the carriers' capacity to shield and provide the nutrients needed to produce CaCO3, which further filled the cracks and pores [43]. There have recently been some studies conducted on bacterial concrete, which examined the impact of calcium nitrate, calcium lactate and bacterial spore powder on the compressive strength [44]. It was seemed that utilising calcium lactate in conjunction with bacteria spore powder extended the setting time and slowed down the process of hydration. Conversely, it was discovered that adding calcium formate and nitrate to bacteria spore powder accelerated the process of hydration of concrete [44]. The variation of compressive strength on mortar and concrete and flexural strength of concrete with different dosages of bacteria Bacillus subtilis concentration is presented in Figs. 4, 5, and 6. It was observed that optimum bacteria concentration (Bacillus subtilis) for maximum strength was 106 cells/ml. Table 1 provides strength, water absorption and rapid chloride permeability test(RCPT) values of concrete with various species of bacteria. Bacteria bacillus cereus showed better result compared to other bacteria.

Fig. 4
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Compressive strength of mortar specimen [45]

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Fig. 5
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Compressive strength of concrete specimen [46]

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Fig. 6
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Flexure strength of bacterial concrete [47]

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Table 1 Compressive strength, RCPT and water absorption results of control and bacterial concrete
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The influence of Bacillus subtilis on the compressive strength of concrete with different dosages of bacteria is presented on Fig. 5. The bacterial concrete having cell concentration of 106 cells/ml has 22% higher strength compared to control concrete at 7 and 28 days. This is due to the precipitation that was deposited on cell surface and internal matrix which filled the smaller pores within the concrete. The impact of bacterial nutrients on mechanical characteristics of microbial concrete found that the addition of yeast caused a major reduction in compressive strength. However, other nutrients including urea, calcium nitrate, calcium lactate, calcium formate have helped in a slight increase in compression and flexural strength [48]. It was found that, regardless of the curing procedure, cracks wider than 0.4 mm had a significantly poorer healing capacity. This was likely due to a potential lack of bacterial immobilization and adequate minerals [49].

3.2 Modulus of elasticity (MOE)

The concrete's modulus of elasticity is its ability to deform within the elastic stress-strain zone without breaking. It was noted that elastic modulus primarily relied on the aggregate's shape and size distribution, reinforcement, and type of curing. Microbial concrete with biochar-immobilized bacterial spores was observed to have shown better MOE after undergoing healing cycles. Autogenous healing, which results from dehydrated cementitious particles, has been observed to have a tendency to lower the elastic modulus compared to healing caused by bacteria [50]. An investigation demonstrated on how the modulus of elasticity is affected on bacterial concrete containing different dosages of Bacillus sphaericus. Elastic modulus of microbial concrete was found to be significantly influenced by the number of bacteria present. For bacterial dosages up to 105 cells/ml, the modulus of elasticity improved by up to 9.5%. However, dosages of 103 and 104 cells/ml exhibited lower modulus of elasticity, as depicted in Fig. 7. This was due to the fact that at lower concentrations, the precipitation of CaCO3 was less, whereas at a concentration of 107 cells/ml, the precipitation was high. This filled all the voids completely, resulting in the blockage of nutrient supply to the bacteria, thereby affecting their growth. It was noted that up to a certain point, an increase in bacterial dosage to 105 cells/ml corresponded with a rise in the elastic modulus [51].

Fig. 7
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Variation of Modulus of elasticity for different dosage of bacteria [51]

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3.3 Shrinkage

Concrete drying shrinkage, defined as the variation in length caused by moisture loss, was primarily influenced by factors such as the curing period, the quantity of admixture used, and the water-to-cement ratio [52]. It was noted that the drying shrinkage of bacterial concrete was significantly influenced by the curing regime. Additionally, it was observed that the incorporation of bacteria and the presence of other substances, such as nutrients and ions, increased the early drying shrinkage of the concrete [53]. The drying shrinkage of biobased concrete is presented in Fig. 8. A study on bacterial mortar revealed that traditional mortar repair was reduced by approximately 4.5 times compared to bio-based mortar. This finding was attributed to the enhanced creep and stress relaxation properties of bacterial concrete, which made it more suitable for composite material repair by mitigating drying shrinkage stress [54].

Fig. 8
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Drying shrinkage comparison between control concrete and bioconcrete [53]

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3.4 Chloride and sulphate resistance

Another durability property known as chloride resistance in concrete, typically in the form of chloride ions, could penetrate concrete and cause various forms of deterioration, such as corrosion of reinforcing steel. The RCPT test was used to measure the pore structure and pore solution, which determined the concrete's resistance to chloride penetration [55]. It was suggested that bacteria could act as filler material to reduce the values of coulomb and ensure a decrease in the permeability of concrete. The presence of bacteria in concrete was found to have resulted in improved compactness of the microstructure and increased strength [56]. It was observed that the addition of bacteria resulted in a reduction in the chloride ingress capacity of concrete containing fly ash which is presented in Fig. 9. The concrete’s physical and chemical tolerance to sulphate crystals was a primary cause of cracking, spalling, and efflorescence. The sulphate present in seawater, sulphate-containing soil, and sewage combined with calcium hydroxide to generate sulphate salt crystallization, leading to salt accumulation. This reaction could induce significant pore stress in concrete [57]. Researchers investigated the potential of sulphate attack on bacterial concrete by curing it in water submerged in MgSO4 solution and urea and CaCl2 solution. They demonstrated that, compared to concrete cured through water immersion, concrete cured in urea solution was more susceptible to sulphate attack and exhibited mass variation. This susceptibility was attributed to the reaction between urea and CaCl2 with magnesium sulphate in the concrete [58].

Fig. 9
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Variation of RCPT values for different dosages of bacteria and fly ash [56]

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4 Agro/industrial waste types, availability and utilization in concrete

The integration of agricultural and industrial waste into self-healing concrete presents an innovative and sustainable solution for the construction field. This method not only addresses the inherent vulnerabilities of concrete but also aligns with the broader goals of environmental conservation and resource efficiency. Ongoing research in this field holds the potential to revolutionize the way we approach concrete construction, fostering a more resilient and eco-friendlier built environment. It was observed that the increase in population and industrial production had resulted in the generation of a significant amount of waste [63]. It was noted that wastes produced by industries and agriculture were used as binders in concrete. Ashes obtained from burning of Coffee husk, sugarcane, sawdust, rice husk are some of the agricultural wastes and fly ash, ground granulated blast furnace slag (GGBS) are some of the examples of industrial waste as such. It was highlighted that the key difference in obtaining these wastes was in where they were collected and how they were converted into binder material. It was noted that rice husks and sugarcane are produced globally, while coffee husks are available in some regions. These materials were processed similarly by being burned to produce sugarcane bagasse ash, rice husk ash, and coffee husk ash. Fly ash was produced by steam-generating plants and coal-fired electricity. Coal was crushed and blown into the boiler’s combustion chamber with air, where it immediately caught fire, producing heat and generating molten mineral residue. GGBS was obtained as a by-product of iron in blast furnaces. The shape, size, and availability of some waste materials were then discussed along with physical and chemical properties which is provided in Tables 2 and 3 respectively.

Table 2 Physical properties
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Table 3 Major chemical composition
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4.1 Coffee husk ash (CHA)

Coffee plantations generate massive volumes of coffee husk as a result of the global trade in coffee beans, which are eventually dumped in landfills [64]. The image of coffee husk/pulp and burnt coffee husk are presented in Fig. 10. It was estimated that for every ton of fresh coffee produced, 0.18 tons of coffee husk and 0.5 tons of coffee pulp weres obtained [65]. It was recommended that coffee wastes not be composted or dumped in landfills due to their high polysaccharide content and significant fire risk, which posed environmental hazards [66]. The organic chemicals in coffee husk oxidize when burned as fuel in a variety of small-scale industries and farms, leaving behind minerals that are inorganic and elements that comprise the ash It was noted that the composition of CHA was influenced by various factors, including the variety of coffee beans, the processing technique, the temperature, and the length of combustion [67]. It was determined that the ideal burning rate for coffee husk was 600 °C. This temperature was found to simplify the removal of impurities from CHA and affect the ash's silica content [68]. Recently, CHA was the subject of pozzolanic property tests in a few countries. These tests revealed that CHA developed certain characteristics of mortar and concrete when used in various substitution percentages, including improvements in durability, compressive strength, flexural strength, and splitting tensile strength [69]. The processing factors of CHA, which include bulk density, particle size, surface area, specific gravity, and texture, essentially determine its physical attributes as reported by various scholars [70]. A small amount of SiO2, Al2O3, Fe2O3 and a larger amount of calcium oxide make up CHA. Various other oxides are also present, with 45–65% alkali content of K2O which is shown in Table 3. Due to the actual incineration and processing, the value of loss on ignition(LOI) on coffee husk ash is substantial up to 20% [71,72,73]. It was noted that, to be used as a pozzolan in cement, CHA needed to meet specific chemical composition standards outlined in ASTM C618-19. As per ASTM C618-19, it was stated that any material with a pozzolanic index of 70% or higher could be used as an additive to cementitious materials. Numerous studies have been conducted on the use of coffee husk ash in partially replacing cement in concrete. It was found that the optimal level for replacing cement with coffee husk ash is significant, up to 10% [71, 74]. According to some researchers, as CHA percentage increased, the workability of CHA determined by the slump and compacting factor tests decreased [74, 75]. Some researchers observed a decrease in water absorption on cement mortar blended with more CHA [76]. Up to the optimum level of 10%, compressive strength, flexural strength, and splitting tensile strengths met the design requirements of concrete after 28 days of curing. It was observed that when CHA was used beyond the optimum level, the strength of concrete was reduced [71, 74, 76].

Fig. 10
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a Coffee husk/pulp, b Coffee husk ash [71]

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4.2 Sugarcane bagasse ash (SCBA)

The fibrous remains of sugarcane, constituting 40 to 45% after extracting its juice, are referred to as 'bagasse.' It was noted that these bagasses were subsequently used as fuel for heat generation, resulting in 10–12% ash, known as sugarcane bagasse ash [77]. In India, bagasse ash was regarded as waste, amounting to about 10 million tons, while global sugarcane production exceeded 1500 million tons [77]. Studies found that 25–40 kg of SCBA was produced from one ton of bagasse fibers [78]. It was determined that sieving through a 300 μm sieve and grinding the SCBA to a fineness equal to that of cement was suitable for processing the SCBA to increase its pozzolanic activity [79]. The image of raw bagasse and bagasse ash is presented in Fig. 11. It was also noted that, to be characterized as a class F pozzolanic material, a material must contain a minimum of 70% of SiO2, Fe2O3, and Al2O3 combined, as described in ASTM C618. A material's mechanical strength and durability are increased if the silica content is higher [80, 81]. A research revealed that the main oxide component available in SCBA with maximum content is silica. Iron oxide and alumina still make up the majority of the SCBA, even though they are much smaller amounts than silica [82]. Bagasse ash properties can change depending on the machinery and power plant's operations as well as the source. Improved consistency and pozzolanic characteristics of the material are often achieved by processing the SCBA by calcination, grinding, screening, or by chemical addition [83]. It was observed that there was a gradual rise in water demand to attain the normal consistency of pastes. For instance, a 20% replacement of SCBA required an increase of 40%, 50%, or 70% more water compared to the control paste [84,85,86]. It was found that mortars containing SCBA, replaced up to 15–20%, gained more compressive strength over the curing time but did not affect the mixture's workability [87]. A study found that although the strength of mortars increased with the replacement of up to 20% with laboratory-produced SCBA, a greater amount of superplasticizer was required as the SCBA replacement increased to maintain constant flow, indicating a higher water demand [88] (Figs. 12, 13, 14).

Fig. 11
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a Sugarcane bagasse, b Sugarcane bagasse ash

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Fig. 12
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a Rice husk, b Rice husk ash

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Fig. 13
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Burning sawdust to obtain ash [101]. a Burning sawdust b Powder (SDBA)

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Fig. 14
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Fly ash [109]

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4.3 Rice husk ash (RHA)

Rice husk is a hard covering of rice grain that is separated by the milling process [89]. Over the years from 1960 to 2013, rice production has raised from 150 million tonne to 740 million tonne all over the world as per the Food and Agriculture Organisation. Studies found that each tonne of paddy generates up to 18–21% of rice husk generation of paddy in 2014 was found to be 741.3 million tonnes which resulted in production of 148 million tonne of rice husk [90]. It was noted that burning husks yielded ash with a higher silica content. Pozzolan was identified as a siliceous substance with limited reactivity once fully burned, and RHA was found to be finer compared to cement [89]. It was observed that RHA exhibited significant pozzolanic and reactive qualities when incorporated into concrete [91]. It was found that varying the substitution of RHA for cement affected the workability of concrete [92]. Since RHA has a low specific gravity, it reduced the weight of the concrete, thereby decreasing the dead load on the structure [93]. A study on the hardening characteristics of concrete was conducted using 10% RHA. Concrete samples were cured and analysed after 7, 28, and 56 days using a 1:2:4 mixing ratio and water-cement ratios of 0.45, 0.5, and 0.6. The results indicated that when 10% rice husk ash was added to concrete and cured for 56 days, the compressive strength improved by 14.51%, and the splitting tensile strength increased by up to 10.71% at 0.45 water to cement ratio [94]. RHA can be an essential filler in cement with a particle size of only about 25 microns in size [95]. Another study conducted on rigid pavement concrete with cement partially replaced with RHA upto 50%. It was observed that, for rigid pavements, the optimum replacement level of RHA was 20%. The values of compressive, splitting tensile, and flexural strengths were found to increase at all curing periods as the RHA content rose from 10 to 20% [96].

4.4 Saw dust ash

Sawdust is a waste generated by timber working processes (furniture and wood), that is produced during sawing, crushing, routing, drilling, and sanding [97]. Recently, studies were conducted to determine whether using saw dust ash as a substance partially substitutes the hydraulic cement used to produce concrete. The experiments yielded positive results, suggesting that sawdust ash could be used as a suitable constituent material for producing structural concrete with good mechanical and durability characteristics [98, 99]. The majority of carbonate and bicarbonate, especially calcite, were found in sawdust ash obtained from burning wood waste at temperatures below 500 °C. However, at higher temperatures—above 1000 °C, which is a standard operating temperature for most wood-fired boiler units, oxides like quicklime predominated in the chemical composition of wood ash [100]. The alkalinity of sawdust/wood ash decreased as the amount of carbonates and bicarbonates, which are chemical species that increase the ash's alkalinity at higher combustion temperatures, decreased. Additionally, as the temperature of combustion rose, the content of light metallic elements like sodium(Na), potassium(K), and zinc(Zn) decreased in saw dust ash [100]. These discoveries offer a solution to the issues of waste management associated with saw dust ash and also helps to lower the quantity of energy-intensive hydraulic cement used in the manufacture of greener concrete material, which meets the construction industry's rise in demand.

4.5 Fly ash (FA)

Fly ash is produced from burning ground or powdered coal (ACI 116R). Bottom ash (BA) and fly ash (FA) are two types of coal ash that are formed. It was noted that these were among the most common and complex anthropogenic elements. The majority of coal ash was classified as FA (80%), with the remaining portion categorized as BA [102, 103]. It was observed that fly ash exhibited pozzolanic characteristics similar to those found in naturally occurring pozzolans of sedimentary or volcanic origin, which are present in various parts of the world [104]. ASTM C618-2009 classified fly ash into two categories, "class C fly ash" and "class F fly ash". It was noted that "Class F" fly ash is primarily produced by burning bituminous or anthracite coal, where the combined amount of SiO2, Fe2O3, and Al2O3 exceeds 70%. Conversely, burning sub-bituminous or lignite coal containing between 50 and 70% of these compounds produces “Class C” fly ash. Class F was classified as a typical pozzolan, defined as a substance composed of silicate glass modified with iron and aluminium [105]. It was observed that fly ash comprised three types of constituents: crystalline minerals, non-crystalline aluminosilicate glass, and unburnt carbon particles, each of which could be used as a substitute for cement in concrete with unique reactivity [105]. It was indicated by research that unburnt carbon should not be present in FA. It was also found that the unburnt carbon could be eliminated through a calcination process, which partially converted the amorphous phases found in FA into crystalline phases [106]. The majority of fly ash was composed of glassy materials containing amorphous constituent materials with a poorly organized atomic structure involved in the chemical reaction. Thus, fly ash with higher amorphous content was found to effectively accelerate the pozzolanic reaction [107]. Therefore, fly ash with more amorphous content works effectively to quicken the pozzolanic reaction. It was found that the addition of FA or SCBA as cement-replacing materials increased strength up to replacement levels of 20%. However, with a further increase in FA and SCBA as cement-replacing materials, the strength of the mixes was found to reduce [108].

4.6 Ground granulated blast furnace slag (GGBS)

Slag from the production of pig iron (smelted iron ore byproduct) is specifically referred to as "blast-furnace slag". When molten slag is quickly quenched, it forms glassy substance known as "ground granulated blast-furnace slag" when it is finely ground [110]. For many years GGBS had been used as a cementitious binder of concrete and in composite cement [110]. Granulated ferronickel slag boosted the strength of mortar up to 50% replacement level, further replacement showed a reduction in the strength [111]. The replacement of fine-aggregate by GGBS in alkali-activated mortar was advantageous in high-temperature areas [112]. Increases of GGBS percentage in concrete were found to reduce its workability; however, the density of fresh concrete was either slightly higher or comparable to the control mix without GGBS [113]. In an experiment conducted on concrete’s durability for varying GGBS (%), it was noted that reference concrete without GGBS had lower durability than concrete containing GGBS. Other properties of concrete that were investigated included the effect of freeze–thaw resistance, high temperature, and sulphate resistance [114].

4.7 Silica fume

Micro silica, also known as silica fume, typically created from silicon or ferro-silicon alloys, such as those that make ferro-manganese and ferro-chromium. The smoke from the electric arc furnace is utilized as microsilica [116]. Calcium hydroxides are formed when Portland cement reacts chemically with water in concrete. Microsilica which was partially replaced by cement, reacts with calcium hydroxide and produce C-S-H which acts as a major cause for the hardening of concrete [117]. Studies have been conducted to investigate the workability of high-performance concrete having silica fume replaced partially by 0, 6, 10, and 15% by weight of cement. Due to the silica fume's tiny particle size, some superplasticizers will be adsorbed on its surface. It was found that mixtures with higher silica fume content typically needed increased superplasticizer dosages [118]. Studies carried out on the resistance of concrete to chloride penetration have demonstrated that, among other pozzolanic materials, silica fume, is most effective at preventing chloride ingress, when partially replaced by the weight of cement [119]. Silicafume paste with cement had lesser strength compared to silicafume concrete which was attributed to the difference in the function of aggregates in the concrete. Although the aggregate in concrete serves as an inert filler, because of the existence of a weak-interfacial zone, composite concrete is weaker than cement paste. However, silicafume removes this weak point in concrete by enhancing the cement-paste aggregate bond & creating a more uniform and less porous microstructure in the contact area [120].

5 Morphological study of self-healing concrete

For concrete surface micro-structural analysis, SEM (scanning electron microscopy) was utilized. It offered magnified high-definition images of bacteria, materials, and failure mechanisms involved in the bioconcrete that could be observed. SEM test that is conducted on non-conductive materials requires coating of silver, gold or chromium [132]. Figure 15 shows the SEM images of various agro/industrial waste particles, which are used as partial replacements for cement in concrete.

Fig. 15
figure 15

Ground granulated blast furnace slag [115]

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A study indicated that SEM images revealed the micromorphological properties of coffee husk ash, magnified up to 10μm, which is presented in Fig. 16a. Microscopy study reveals that, surface of CHA is corrugated, and ash particles have rough surfaces, modular morphologies, and are crushed and jagged [133]. It was observed that the surface of bagasse ash had numerous elongated oval-shaped pores, indicating its capacity to absorb oxygen or water. The SEM image of bagasse ash is presented in Fig. 16b [134]. A study on bacterial mortar with bagasse ash revealed the formation of CaCO3. The optimal microscope and SEM image of a cracked mortar sample is presented in Fig. 17, suggesting that bacterial activity promotes the mortar's ability to heal itself by CaCO3 precipitation. The particles of precipitated CaCO3 crystals most likely filled the cracks on the mortar surfaces as well as some of the gaps and spaces inside the mortar samples [138].

Fig. 16
figure 16

SEM images of waste materials. (a) CHA [133] (b) SCBA [134] (c) MICRO SILICA [135] (d) RHA [61] (e) GGBS [136] (f) FLY ASH [137]

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Fig. 17
figure 17

Calcite precipitation of cracked bacterial mortar [138]

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The SEM image of the RHA particle is shown in Fig. 16d. A study was conducted on bacterial concrete with cement replaced partially by RHA. 5%, 10%, 15%, and 20% of RHA were replaced, with and without bacteria. Maximum strength was observed at a 10% replacement of RHA without bacteria. Bacterial concrete with 10% RHA displayed an increase in strength up to 6.2%, 10.7%, and 13% at 7 days, 28 days, and 56 days respectively [61]. Figure 16 provides SEM image of bacterial concrete with cement replaced partially by RHA. SEM image depicts calcium silicate hydrate (C-S-H) gel formation and calcite precipitation which is responsible for increase in the strength of bacterial concrete [61] (Fig. 18).

Fig. 18
figure 18

SEM image of RHA replaced bacterial concrete [61]

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A study on fly ash(FA) based concrete demonstrated that use of bacteria at W/C ratio 0.6 showed optimum strength with 10% fly ash as binder replacement. The SEM image of fly ash based concrete with bacteria is shown in Fig. 19. the image shows several openings were packed and filled by calcite crystals precipitation [139].

Fig. 19
figure 19

SEM image for bacterial Fly ash concrete [139]

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6 Self-healing/bio-concrete with agro/industrial waste

The concept of self-healing concrete with agro-industrial waste is promising, challenges such as material compatibility, standardization, and long-term performance assessments need careful consideration. Research and development in this field aim to address these challenges and further optimize the formulation of autonomous concrete mixes. Some researchers examined self-healing mortar by substituting part of cement with bagasse ash and without bagasse ash. Self-healing mortar samples were created using cement (OPC), fine aggregate, water, bagasse ash, calcium lactate, and Bacillus subtilis bacteria 10−7 and 10−9 cells/ml [138]. Self-healing mortar samples with average humidity levels ranging from 31 to 46% and room temperature were produced utilising the normal procedure. The samples had water, sand, Bacillus subtilis bacterium 10−7/10−9 cells/ml, regular Portland cement and calcium lactate powder, (100%) [138]. The type bacteria and their dosage, material used and mix proportions are given in Table 4.

Table 4 Mix proportions of waste-based bio concrete
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In self-healing mortar samples, surface fissures were healed up to 0.6 mm by calcite precipitation. Higher replacement of bagasse ash decreased the efficiency of crack healing [138]. SHM were thermally stable but lost more weight as temperature increased. Compressive strength was higher than traditional mortars and by incorporating 5% bagasse ash, flexural strength was greater than the standard mortars. Self-healing mortar absorbed less water compared to conventional mortar samples [138].

A study conducted on the autonomous healing mechanism of concrete with coarse aggregate partially replaced by FA(fly ash) aggregate. As shown in Table 4b the bacteria blended in this work is Bacillus subtilis. Specimen prepared with coarse aggregate replaced by 0, 30, 40, 50, 60, 70, and 100% of fly ash aggregates [140]. 100% natural aggregate offers the highest strength for both conventional and self-healing concrete, while 30% fly ash aggregate in concrete mix produced positive results for strength recovery after healing [140]. Concrete's ability to mend itself was facilitated by the addition of Bacillus subtilis. Concrete with a 30% fly ash aggregate replacement demonstrated a significant 61.37% increase in strength. Maximum crack healing of the 0.25 mm crack width was accomplished by concrete containing fly ash aggregates. The use of fly ash aggregates in replacement of natural aggregates showed promising results [140].

Another study demonstrated the strength properties of self-healing concrete by replacing a part of cement with SCBA and GGBS. This research highlights the relationship between agricultural waste products which include sugarcane bagasse ash (SCBA) and industrial waste products like GGBS. SCBA and GGBS are substituted for the cement with Bacteria Bacillus subtilis in the M30 mix [141]. GGBS was utilized with 20% and 40% by weight of cement, SCBA in 10% of cement, and Bacillus subtilis by 10% of cement weight shown in Table 4c. The mix with 30% of the cement is replaced with SCBA, GGBS, and bacteria showed better results on compressive and tensile strength [141]. This may due to the CSH gel's high composition and good quality when produced at this proportion. The strength of concrete containing bacteria, GGBS 20% and GGBS 40% was greater than that of standard concrete and concrete having only bacteria [141]. In an investigation of optimum use of RHA in self-healing concrete, cement is replaced partially by RHA at 0%, 5%, 10%, 15%, 20%, 25%, and 30% by weight [142]. Furthermore, all mixes received an addition of micro silica, 10% by weight of binder material. Bacterial cells were added to the mixture with the ideal RHA content at 103, 105, and 107 cells/ml as given in Table 4d [142]. Compared to the control mix, the optimal mix having 15% RHA had 12% more compressive strength at day 28, also when bacteria added at the ideal concentration, the strength gain reached 21% [142]. Figure 19 displays the variation in compressive strength for all the mixes having curing period of 7, 28, 56, and 91 days. From the figure, at 15% RHA content without bacteria had higher compressive strength and with addition of 105 cells/ml bacteria showed 21% peak strength (Figs. 20, 21).

Fig. 20
figure 20

Compressive strength variation of Bagasse ash-based concrete [140]

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Fig. 21
figure 21

Compressive strength of control concrete, concrete with different RHA mix, with and without bacteria [142]

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The splitting tensile strength of the different mixes is presented in Fig. 22. It is observed that the inclusion of 15% RHA resulted in a max value of splitting tensile strength. Also, bacterial concrete having 15% RHA for bacterial dosage of 105 cells/ml showed an increase in splitting tensile strength by 29.2% compared to control concrete [142].

Fig. 22
figure 22

Splitting tensile strength of RHA based concrete mix with and without bacteria [142]

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The addition of RHA was found to increase the modulus of elasticity (MOE), as illustrated in Fig. 23. This increase reached up to 14% compared to the control specimen. Furthermore, the inclusion of bacteria with RHA led to a further rise in elastic modulus.

Fig. 23
figure 23

Modulus of elasticity of control, RHA and bacterial concrete with RHA at 28 days curing period [142]

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The desired mechanical properties and maximum durability are obtained at cell concentration of 105 and 107 cells/ml respectively. There is a 70% reduction in permeability-related parameters and improved resistance to water intrusion by utilizing maximum bacterial concentration. The proper ratio of RHA content resulted in reduced pores and also had a denser matrix [142].

Another study investigated bacterial concrete by partially replacing cement with fly ash. This research highlighted the effects on compressive strength, splitting tensile strength, and flexural strength over 3, 7, and 28 days. The study used a bacterial concentration of 105 cells/ml and replaced 0%, 10%, and 30% of the cement with fly ash by weight [143]. It was observed that both bacterial and conventional concrete exhibited higher compressive and flexural strength when 10% of the cement was replaced with fly ash, compared to a 30% replacement with fly ash [143]. The enhancement in strength and durability of the concrete was attributed to the filling of voids within the cement matrix by fly ash particles. Figure 24 provides the compressive strength of flyash concrete with and without bacteria [143] (Figs. 25, 26).

Fig. 24
figure 24

Variation of compressive strength on concrete having fly ash [143]

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Fig. 25
figure 25

Compressive strength of optimum fly ash content M30 mix

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Fig. 26
figure 26

Compressive strength of optimum fly ash content M40 mix

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The concrete with bacteria was found to exhibit more splitting tensile strength than regular concrete. By filling the voids, bacterial calcite precipitation indirectly strengthens the concrete. Bacterial concrete is expensive. Therefore, aiming for greater RC structures is profitable [143]. A study on bacterial concrete, partially replacing cement with GGBS and dolomite powder were examined. Two separate mixes were prepared: M30 and M40 [144]. For both mixes, cell concentrations of 103, 105, and 107 cells/ml of Bacillus pasturii were added for the healing process. The test was conducted to analyze the compressive strength and durability of the concrete mixture [144]. Results showed that the optimum replacement of GGBS+dolomite powder and the optimum concentration of bacteria were 30% and 105cells/ml, for both M30 and M40 mixes [144]. Compressive strength increased up to 13.22% for M30 and 10.52% for M40. Bacterial concrete exhibited good resistance to acid attack when 30% of the cement was replaced. Cracks were healed upto 0.4 mm [144].

Another study conducted on partial replacement of micronized biomass silica by cement in self-healing concrete. The strength characteristics of concrete specimen by introducing bacteria along with an appropriate alternate binder such as micronized biomass silica was evaluated [145]. In this paper, three different concrete were prepared that is control, concrete having bacteria, and concrete made by substituting 8% of Micronized Biomass Silica for cement. Bacillus sphaericus is a type of bacteria that is utilized, and it is added to the concrete specimens in varied amounts 10, 20, and 30 ml [145]. The compressive and splitting tensile strengths of M60 grade high-strength concrete were assessed using cubes and cylinders, comparing them with concrete that did not contain bacteria at 7 days and 28 days of age. The results showed that the splitting tensile strength increased by 16.60% and the compressive strength increased by 13.53%. However, when more than 20 ml of bacteria Bacillus sphaericus was added, the compressive strength decreased [145]. Some researchers investigated the effects of partially replacing cement with superabsorbent polymer (SAP) and rice husk ash (RHA) on the crack-repairing ability of mortar. For comparison, high-calcium fly ash was also used. Concrete mixtures were prepared by substituting 20% of the cement mass with either RHA or fly ash [146]. It was noted that SAP concentrations of 3% and 4% by cement weight were utilized. Six mortar mix proportions were prepared, with the mortar's flowability adjusted to remain nearly constant. Pre-cracked specimens were subjected to either wet/dry conditions or continuous submersion in water for healing [146]. Results showed the existence of reactive amorphous silica of RHA in concrete resulted in increased compressive strength [146]. Calcium carbonate is formed enabling cracks to heal, and this process was aided by carbonation, leaching, and interactions with cement matrix particles. It was found that the early production of ettringite in high-calcium fly ash reduced crack transit by filling the cracks and causing closure. It was observed that a significant reduction in Portlandite and the enhanced pozzolanic qualities of RHA led to a remarkable recovery of compressive strength compared to fly ash [147]. It was noted that the formation of C-S-H was greater in RHA, while fly ash excelled in permeability recovery. Superabsorbent polymers (SAPs) were added to mortar to enhance hydration by supplying moisture, and their absorption aided in permeability recovery by generating an insoluble, water-resistant gel [146]. The variation in compressive strength of agro-based bioconcrete for various grades of cement is presented in Figs. 27 and 28 and splitting tensile strength is presented in Fig. 27 for 7 days and 28 days of curing. It was observed that the maximum strength was obtained with the utilization of micronized biomass silica up to an 8% replacement with the bacteria Bacillus sphaericus. A reduction in strength was noted for bagasse ash-replaced bioconcrete compared to other agro/industrial waste-based concrete (Fig. 29).

Fig. 27
figure 27

Compressive strength of bacterial concrete having agro waste after 7 days of curing [141, 144, 145, 147, 148]

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Fig. 28
figure 28

Compressive strength of bacterial concrete with agro waste after 28 days of curing [141, 144, 145, 147, 148]

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Fig. 29
figure 29

Splitting tensile strength strength of bacterial concrete with agro waste after 28 days of curing [141, 142, 145, 149, 150]

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7 Critical summary

The self-healing properties in concrete with agro-industrial waste arise from various mechanisms. One way to promote self-healing properties is by partially replacing cement with agro-industrial waste materials. This sustainable practice not only contributes to the efficient use of resources but also enhances the durability and resilience of concrete structures. Some waste materials contain reactive compounds that can participate in further hydration reactions, filling microcracks.

  • The investigation of self-healing concrete with cement partially replaced by agro-industrial waste has a promising and sustainable avenue for the construction industry.

  • The inclusion of agricultural-industrial waste such as, RHA, sugarcane bagasse ash, or other agricultural residues, provides benefit of waste utilization and improved self-healing properties, aligning with the principles of environmental protection.

  • The optimum replacement level for coffee husk ash in M25 concrete was observed to be 10%. No research has yet been conducted on bacteria-based concrete with cement partially replaced by CHA, presenting an exciting opportunity for pioneering research in sustainable construction materials.

  • Rice Husk Ash (RHA) was found to exhibit superior pozzolanic properties compared to fly ash. The analysis indicated that RHA led to significant reductions in calsium(Ca)/silicates(Si), Portlandite, and Ca/(Si + Al), underscoring its effectiveness in pozzolanic reactions. The presence of amorphous silica in RHA was directly attributed to the generation of C-S–H, which explained the substantial compressive strength recovery observed in concrete specimens mixed with RHA.

  • The pozzolanic reactions of RHA results in the formation of supplementary cementitious materials, enhancing the overall durability and resistance of the concrete. This advantage of waste utilization and self-heal aligns with the principle of sustainable and environmental friendly construction.

  • The presence of Fly Ash and Bacillus Subtilis bacteria in concrete beams at optimal levels resulted in enhancing the ultimate load-bearing capacity, mechanical properties, and decrease in deflection.

  • The incorporation of SCBA (10%) and GGBS (20%) in the concrete mix, along with bacteria, was deemed essential for achieving a balance between improved workability, compressive strength, and overall performance compared to traditional concrete mixes.

8 Future scope of work

  1. 1)

    Conducting in-depth research to understand the mechanisms of self-healing in concrete by including agro-industrial waste. Explore the mutual action of chemical and physical properties that helps in self-healing process.

  2. 2)

    Comprehensive field studies and rapid aging tests to investigate the long-term performance of self-healing concrete with agro-industrial waste in real-world case

  3. 3)

    Research using nanomaterials, such as nano-silica or nano-clays, with agro-industrial waste to boost self-healing process and to study their importance on the microstructure and healing kinetics.

  4. 4)

    Engage machine learning and predictive model techniques to enhance the composition of self-healing concrete with agro-industrial waste. This can help in predicting long-term performance, identifying potential issues, and optimizing material formulations.