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.

Microbially induced calcium carbonate precipitation (MICP) technology has attracted widespread research attention owing to its application in crack healing for cement-based materials in an intelligent and environmentally friendly manner. However, the high internal alkalinity, low nutrient content, and dense structure of cement-based materials have restricted its application in self-healing cement-based materials. Various carrier materials have been widely used for the immobilization of microorganisms in recent years. Carrier materials have significantly increased the ability of microorganisms to withstand extreme conditions (high temperature, high alkali, etc.) and have provided new ideas for the compatibility of microorganisms with cement-based materials. In this study, the basic principles of microbial self-healing technology in cement-based materials and microbial immobilization methods and the influencing factors are introduced, followed by a review of the research progress and application effects of different types of carrier materials, such as aggregate, low-alkali cementitious materials, organic materials, and microcapsules. Finally, the current problems and promising development directions of microbial carrier materials are summarized to provide useful references for the future development of microbial carriers and self-healing cement-based materials.

We propose and demonstrate a passively $Q$-switched Er-doped fiber laser based on pure water as the saturable absorber (SA). The SA is made of two optical ferrules matched with a cannula, and the gap between the end-facets is filled with pure water. The nonlinear response of this SA has been characterized, and stable $Q$-switching operation at 1558.03 nm has been achieved. The maximum output power is 21.1 mW with 65.0 kHz repetition rate. The duration is 1.44 μs, and the pulse energy reaches 324.8 nJ. To the best of our knowledge, this is the first demonstration of the passively $Q$-switched laser with pure water as the SA. It provides further evidence of the possibility of liquid as an effective SA for pulsed lasers.

Effect of Delaminated MXene (Ti₃C₂) on the Performance of Cement Paste: Delaminated MXene was incorporated into cement to improve the properties of cement composites, and its effects on the hydration process, microstructures, and mechanical properties were investigated, respectively. The investigation results showed that delaminated MXene was well-dispersed in the cement matrix and significantly reinforced the compressive strength of cement, especially when the addition is 0.01wt. Meanwhile, the total hydration heat of cement hydration and the quantity of hydration products were increased with the addition of delaminated MXene. In addition, the formation of HD C-S-H gel was promoted, and the microstructure of hydrated cement became more compact.

This present study mainly focuses on the influence of low-calcium circulating fluidized bed fly ash (LCFA) on the mechanical property and microstructure of cement-based materials under different curing conditions. The mechanical properties test was conducted by changing variable parameters, such as LCFA content, the internal mixing ratio of LCFA and fly ash (FA), and dry and water curing conditions. Further, the hydration products and pore structure were analyzed using XRD, FT-IR, TG-DTG, NI, SEM, and BET micro-testing technology. The strength development law of LCFA on cement-based materials is discussed. The research results show that LCFA has a certain degree of self-hardening and can be used as a cementitious material in cement-based materials. Still, the loose and porous microstructure of LCFA leads to higher water requirements, which reduces the fluidity of cement-based pastes. Water curing is favorable for promoting the development of LCFA on the long-term compressive strength of cement-based materials. When the LCFA was added to the cement, the optimal substitution ratio was 20%, and the compressive strength at 91 days reached 101 MPa. In the case of compounding LCFA and FA, when the internal mixing ratio of LCFA/FA was 3 and the total content was 20%, the mechanical properties were the highest, and the compressive strength at 91 days was 92 MPa. The microscopic analysis result shows that the cumulative hydration heat of the samples decreased significantly with the increase of dosage of LCFA. The main hydration products of cement-based materials mixed with LCFA were AFt, C-S-H gel, and Ca(OH)₂. AFt and C-S-H gels are critical to the strength development of OPC-LCFA samples. The active Al₂O₃ and active SiO₂ in LCFA were involved in hydration reactions to promote the formation of C-A-H and C-S-H gel and effectively promote the development of the mechanical properties. Overdosages of LCFA would reduce the ettringite formation rate. FA is not conducive to AFt formation in the hydration process of OPC-FA samples.