Search

[Display omitted] • Several protection strategies of MICP in civil engineering compared in detail. • To further investigate the key factors that influence the effectiveness of MICP. • Potential of application prospects of MICP in civil engineering discussed. Microbially induced calcium carbonate deposition is a ubiquitous phenomenon observed in nature. Adhering to the principle of "learning from nature and incorporating it into practice", the innovative technology of microbially induced calcium carbonate precipitation (MICP) has been employed in the field of civil engineering to address limitations associated with traditional cementitious materials. By manipulating the microbial metabolic processes, MICP technology offers solutions for mitigating these inherent drawbacks. Extensive research has demonstrated that this technology possesses numerous advantages, including cost-effectiveness, environmental sustainability, low energy requirements, and controllable processes. As a result, it has emerged as a prominent and captivating area of study within the civil engineering field in recent years, representing a significant advancement in the development of modern cementitious materials. Building upon the current research progress in this field, this paper provides a systematic summary of the fundamental principles of microbial-induced calcium carbonate precipitation. It also discusses and summarizes the engineering properties of microbial mineralization and the current status of its application in the field of civil engineering. [ABSTRACT FROM AUTHOR]

• Adopting the sugar-coating method to immobilize bacteria and nutrients. • EP particles after wrapping can enhance the crack-healing capacity of concrete. • The crack-healing of concrete peaked when EP particles wrapped with MKPC. • The values of completely healed crack widths were up to 1.24 mm. Microbial-induced carbonate precipitation (MICP) can realize self-diagnosis and self-healing of concrete to reduce the maintenance costs and extend the lifetime of concrete structures. However, the self-healing capacity of the cracks is below par using existing self-healing methods. Thus, adopting the sugar-coating method to immobilize bacteria and nutrients was proposed in this paper. The effect of expanded perlite (EP) wrapped with various materials as bacterial carrier and nutrient carrier on the crack-healing capacity of concrete has been investigated. The results indicated that after EP particles were coated, the numerical tube pressure was increased, and the water absorption was reduced. Wrapping materials can effectively reduce the breakage rate of the EP particles and resist the invasion of water in the process of mixing with concrete. The EP particles after wrapping process were found to enhance the healing capacity of concrete cracks. In particular, the crack-healing of concrete peaked when EP particles immobilized with bacterial spores were wrapped with a low-alkaline material (potassium magnesium phosphate cement). This result was also validated by the water permeability experiments. After 28 d of crack-healing, the maximum value of the completely healed crack width was 1.24 mm. EP is a low-cost material; thus, it can be used as a bacterial carrier for large-scale self-healing concrete applications. [ABSTRACT FROM AUTHOR]

In this work, the effect of physical properties of recycled coarse aggregate (RCA) on the workability and mechanical properties of recycled aggregate thermal insulation concrete (RATIC) was studied. Two kinds of RCAs from different concrete waste plants were studied and the density, water absorption and crushing index of RCAs were analyzed. Then, the workability and mechanical properties of RATIC having different gradations, original strength grades and degree of saturation of RCA were investigated. The results showed that the gradation and degree of saturation of RCA exhibited a significant influence on the workability and mechanical properties of RATIC. For the RATIC, the optimum A/B ratio was found to be 4/6. The original strength grade of RCA had little influence on the workability, though it exhibited a significant influence on the mechanical properties of RATIC. [ABSTRACT FROM AUTHOR]

• The S cr of GIC-0, GIC-50 and GIC-100 are about 76–78%, 84–86% and 89–91%. • When S > S cr, the supercooling phenomenon of the adsorbed water is obvious. • S < Scr specimens have virtually no hysteresis curves during freeze–thaw cycles. • Saturation(S) and GHBs content affect the freezing process of water in concrete. • S and GHBs content affect pore size distribution during concrete freezing. This paper uses experimental analysis to understand the freezing law of water to determine the freezing damage mechanism of Glazed Hollow Bead Insulation Concrete (GIC). The critical saturations of GIC with different Glazed Hollow Beads (GHBs) contents were obtained by the relative moving modulus after testing seven saturations of the concrete (70% to 100%, 5% interval). The critical saturation of GIC-0 (i.e., 0% GHBs content) occurred at ∼ 76–78%. GIC-50 occurred at about 86–88%. GIC-100 occurred at about 89–91%. GIC-0, GIC-50, and GIC-100 were then saturated to S 60 , S cr , and S 100 based on their respective critical saturation. Low-field nuclear magnetic resonance (NMR) was used to study the freezing process of different water types in GIC. The results showed that: 1) The water inside GIC was composed of adsorb water, pore water, and free water; 2) The whole freezing process could be roughly divided into four stages: subcooling stage, rapid freezing stage, stable freezing stage, and the end of the freezing phase; 3) During the freezing and thawing process, the change in unfrozen water content of GIC specimens had a hysteresis curve, while the specimens less than the critical saturation had almost no hysteresis curve. Moreover, the saturation significantly influenced the freezing process of different water types, which determined the proportion of them. This study also determined the evolution of the pore size of GIC, which provides a new idea for analyzing the freezing damage mechanism of porous GIC. [ABSTRACT FROM AUTHOR]

• GHBs are beneficial to improve impermeability of concrete after fire. • GHBs have great significance for improving the concrete resistance to thermal damage. • The chloride ion diffusion and remaining service life of GIC after fire was calculated. • A thermal damage permeability model was established. Concrete building structures often suffer serious damage after fire, which poses a great threat to the durability of structures. Due to the high thermal stability and pressure relief mechanism of glazed hollow beads (GHBs), GHBs are of positive significance in improving the concrete's resistance against high temperature. In this paper, the electric flux test was utilized to investigate the chloride ion transport behaviors of concrete containing insulating GHBs (GIC) after high temperature exposure. The electron probe micro-analysis (EPMA) combined with chemical titration method was adopted as a supplement to carry out a more in-depth analysis on concrete's permeability. The results show that the anti-chloride ion transport performance of GIC was significantly improved compared to normal concrete. Experimental permeation data were further used to prepare a thermal damage permeability model. That is then used to discuss the impact of including glazed hollow beads on concrete's residual service life after a fire. These data provide technical guidance for the engineering design and safe operation of undersea tunnels and other structures at risk of fire and subsequent saline water intrusion. [ABSTRACT FROM AUTHOR]