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• Effect of biogenic healing agents on crack-healing crystal polymorph was studied. • MC-Ao based bioconcrete exhibited better healing potential. • 82% of aragonite-form CaCO 3 was introduced in the MC-Ao based bioconcrete. • Mixed cultures resulted in a 61% decrease of production cost versus pure cultures. Microbially induced CaCO 3 precipitation (MICP), mainly in the form of calcite, has been reported to be an efficient approach for self-healing cracks in concrete. However, little is known about the implementation of aragonite, the other common crystalline form of CaCO 3 , in bioconcrete. Therefore, a systematic investigation of the crystal polymorphs and the healing efficiency of different cultures, i.e., two microbial consortia under anaerobic (MC-Aa) and anoxic (MC-Ao) conditions and nonureolytic pure-culture bacteria (Bacillus cohnii), was conducted in this study. The results showed that the MC-Ao agent exhibited the maximum values of completely healed crack widths (1.22 mm) after 28 d of healing, which is larger than the values of 0.79 and 0.73 mm for B. cohnii and MC-Aa, respectively. Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) analyses confirmed that the biominerals induced by MC-Aa and B. cohnii are calcite, while those of MC-Ao were 82% aragonite and 18% calcite. It is noteworthy that this proportion of aragonite is the highest reported level for the MICP system to date. In addition, economic evaluation verified that the microbial consortia resulted in a 61% decrease in production costs compared to pure cultures. The intriguing findings obtained in this study may provide a scientific basis for the potential implementation of microbial consortia under anoxic conditions, such as a new self-healing agent, in bioconcrete. [ABSTRACT FROM AUTHOR]

Immobilization has been reported to be an efficient approach for bacteria-based self-healing concrete to maintain the high-efficiency mineral-forming capacity of incorporated bacteria over a period of time. However, the relatively high-cost, local unavailability, and low adsorption capacity of the current bacteria carriers make them impractical for potential implementation in large-scale concrete structures. In this study, the feasibility of expanded perlite (EP) as a novel bacteria carrier on quantifying cracks-healing in concrete via immobilization of Bacillus cohnii was demonstrated. The effects of two other self-healing techniques, i.e., direct introduction of bacteria and expanded clay (EC) immobilized bacteria, on the efficiency of crack-healing were also investigated. Experimental results showed that specimens incorporated with EP-immobilized bacteria exhibited the most efficient crack-healing after each healing time. The values of completely healed crack widths were up to 0.79 mm after 28 days of healing, which is larger than the value of 0.45 mm for specimens incorporated with EC-immobilized bacteria. Field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD) analysis confirmed that mineral precipitations on their crack surfaces are calcite crystals. The findings obtained in this study may provide a scientific basis for the potential implementation of expanded perlite, as a new microorganism carrier, in bacteria-based self-healing concrete. [ABSTRACT FROM AUTHOR]

• Enhanced RCAs as a novel bacteria carrier on crack-healing in concrete was studied. • Enhanced RCAs exerted equal effect on crack-healing capacity of concrete to ceramiste. • Microstructures of precipitations on RCAs and inside concrete cracks were analyzed. • Practical and cost-effective characteristics exhibited for proposed bacteria carrier. Immobilization is used to protect incorporated bacteria to maintain its high efficiency on the microbially induced carbonate precipitation (MICP) capacity in self-healing concrete over a period of time. However, several unfavorable characteristics of current bacterial carriers, such as poor compatibility with the cementitious matrix, relatively high cost, and potential decrease in mechanical properties of concrete, may limit their potential implementation in reinforced concrete (RC) construction. The objective of this study was to demonstrate the feasibility of microbial consortia-enhanced recycled concrete aggregates (RCAs), immobilizing bacteria to form self-healing cracks. The effectiveness of two other immobilization techniques (RCAs and ceramsite particle-immobilized bacteria) on the self-healing efficiency of concrete was also investigated. Experimental results showed that the physical and mechanical properties of RCAs could be markedly enhanced with extension of the biodeposition enhancement time. Concrete specimens incorporated with enhanced RCA-immobilized mixed cultures exhibited a 0.47-mm-wide crack that healed after 56 days of curing, which was equal to the 0.48-mm-wide crack that healed for specimens with ceramsite particle-immobilized mixed cultures. Mineral precipitations at the crack surfaces of self-healing concrete were calcite crystals and had regular cubic shapes. Results from this study provide a promising potential of mixed culture-enhanced RCAs for a wide range of engineering applications. [ABSTRACT FROM AUTHOR]

• Enhanced RCAs as a novel bacteria carrier on crack-healing in concrete was studied. • Enhanced RCAs exerted equal effect on crack-healing capacity of concrete to ceramiste. • Microstructures of precipitations on RCAs and inside concrete cracks were analyzed. • Practical and cost-effective characteristics exhibited for proposed bacteria carrier. Immobilization is used to protect incorporated bacteria to maintain its high efficiency on the microbially induced carbonate precipitation (MICP) capacity in self-healing concrete over a period of time. However, several unfavorable characteristics of current bacterial carriers, such as poor compatibility with the cementitious matrix, relatively high cost, and potential decrease in mechanical properties of concrete, may limit their potential implementation in reinforced concrete (RC) construction. The objective of this study was to demonstrate the feasibility of microbial consortia-enhanced recycled concrete aggregates (RCAs), immobilizing bacteria to form self-healing cracks. The effectiveness of two other immobilization techniques (RCAs and ceramsite particle-immobilized bacteria) on the self-healing efficiency of concrete was also investigated. Experimental results showed that the physical and mechanical properties of RCAs could be markedly enhanced with extension of the biodeposition enhancement time. Concrete specimens incorporated with enhanced RCA-immobilized mixed cultures exhibited a 0.47-mm-wide crack that healed after 56 days of curing, which was equal to the 0.48-mm-wide crack that healed for specimens with ceramsite particle-immobilized mixed cultures. Mineral precipitations at the crack surfaces of self-healing concrete were calcite crystals and had regular cubic shapes. Results from this study provide a promising potential of mixed culture-enhanced RCAs for a wide range of engineering applications. [ABSTRACT FROM AUTHOR]