Reinforcement of Recycled Aggregate by Microbial-Induced Mineralization and Deposition of Calcium Carbonate—Influencing Factors, Mechanism and Effect of Reinforcement

Abstract

Recycled aggregate is aggregate prepared from construction waste. With the development of a global economy and people’s attention to sustainable development, recycled aggregate has shown advantages in replacing natural aggregate in the production of concrete due to its environmental friendliness, low energy consumption, and low cost. Recycled aggregate exhibits high water absorption and a multi-interface transition zone, which limits its application scope. Researchers have used various methods to improve the properties of recycled aggregate, such as microbially induced calcium carbonate precipitation (MICP) technology. In this paper, the results of recent studies on the reinforcement of recycled aggregate by MICP technology are synthesized, and the factors affecting the strengthening effect of recycled aggregate are reviewed. Moreover, the strengthening mechanism, advantages and disadvantages of MICP technology are summarized. After the modified treatment, the aggregate performance is significantly improved. Regardless of whether the aggregate was used in mortar or concrete, the mechanical properties of the specimens were clearly improved. However, there are some issues regarding the application of MICP technology, such as the use of an expensive culture medium, a long modification cycle, and untargeted mineralization deposition. These difficulties need to be overcome in the future for the industrialization of regenerated aggregate materials via MICP technology.

Effect of the Composition of Mixed Recycled Aggregates on Physical–Mechanical Properties

“…Regarding the drd and the dssd, three homogeneous groups without statistically significant differences can be observed (Figure 4a,b): the group of natural aggregates (CNA, Ru), Rb and masonry mortar (Rc2), and concrete particles (Rc1). It has been proven that cementitious particles (Rc1 and Rc2) present lower values than natural aggregates in drd and dssd [21][22][23][24][25][26][27]. However, natural aggregates, Rb, and Rc1 had similar dap, while Rc2 had the lowest value (Figure 4c) and presented significant differences.…”

Research status and development of microbial induced calcium carbonate mineralization technology

“…Concurrently, the urea in the solution environment is continuously decomposed into CO 3 2- and NH 4+ under the action of urease produced by microorganisms, and the CO 3 2- is transported to the cell surface and chemically reacts with the enriched Ca 2+ to form calcite precipitation ( Fig 1 ) [ 20 , 21 ]. The main biochemical reactions during mineralization can be expressed by the following equation [ 22 ]: …”

Critical Review of Solidification of Sandy Soil by Microbially Induced Carbonate Precipitation (MICP)

“…Nevertheless, the cost of a urea-producing culture medium is high. In order to reduce the cost of culture medium for urea-producing bacteria, researchers have found economical alternative culture mediums [67]. The urease activity of the urease bacteria cultured by the alternative culture medium is almost the same as that of the urease bacteria cultured by the standard culture medium.…”