Fiber-reinforced geopolymer concrete (GPC) is a green building material prepared from solid waste. At present, the research on its static and dynamic properties is relatively sufficient, but the mechanism of the effect of fiber on the mechanical properties of GPC after high temperature has not yet formed a perfect system. Therefore, this paper first analyzes the high temperature degradation mechanism of GPC under different material components. Then, the strengthening effect of two kinds of thermal characteristic fibers (steel fiber and polyvinyl alcohol fiber) on the mechanical properties of GPC after high temperature was discussed. Finally, a prediction model of compressive and tensile mechanical properties of GPC after high temperature considering the influence of fiber is proposed. The research results provide a reference for promoting the application of GPC in the field of structural engineering.

The low work hardening is a prominent deficiency for high-strength titanium (Ti) alloys. The gradient design of oxygen content was adopted to realize the coupling deformation of {332}<113> twinning and dislocation slip in the Ti-15Mo alloy. This oxygen gradient alloy exhibited an optimal balance of yield/tensile strength (700 and 848 MPa) and elongation (25%), with remarkable work hardening behavior. The dominated dislocation slip deformation and the solution strengthening of oxygen atoms in the oxygen-rich region resulted in a remarkable increase in yield strength. The successive formation of {332}<113> twins and piled-up geometrically necessary dislocations around the twin boundaries in the oxygen-free region induced remarkable back stress strengthening, maintaining the high work hardening rate, which resulted in a stable increase in strength. The twins and dislocations formed at the crack tips effectively hindered the cracking behavior, avoiding premature necking. The present study provides a novel idea for designing oxygen layer-distributed Ti alloys, which further improves the strength–ductility tradeoff.

This study investigates the wetting characteristics and kinetic behavior of amphoteric ionic surfactant on the microscopic "solid-liquid" interface of coal based on low-field NMR experiment combined with molecular dynamics simulations, since the basic research on the wetting mechanism of coal seam water injection is not systematic and in-depth enough, which restricts the further development of dust control technology in mines. Firstly, the wetting characteristics of amphoteric surfactant (CAB-35) on coal with different degrees of metamorphism and the dynamic spreading of the wetting range were obtained by low-field NMR experiment, revealing the microscopic wetting law at the "solid-liquid" interface of coal; In order to establish the numerical simulation operation system of interfacial wetting of coal macromolecular structure characteristics based on coal surface chemical parameters and using molecular dynamics theory, the wetting dynamic behavior of amphoteric ionic surfactants on coal dust is studied from microscopic perspective, and the law of influence of surface chemical characteristics on coal wetting characteristics is obtained, so as to improve and enrich the theoretical system of coal wetting, in order to promote the development and enhancement of coal mine water injection and wetting and dust control technology and clean production, and realize the clean production of mines.

Geopolymer is a kind of material with a better ability of high-temperature and corrosion resistance. Poor adhesion could easily lead to problems such as coating cracks, peeling at an early stage, and inability to work with the substrate. The adhesion depends on many factors such as chemical composition of the raw materials, the formulation of the geopolymer, the type of substrate, surface roughness of the substrate, etc. The higher the Si/Al ratio, the greater the shear strength of the coating. This is because geopolymers synthesized with different Si/Al ratios have different phases in the geopolymer binder. Each study uses different multi-parameter combinations selected by itself, which is not uniform and has no universal applicability. As the parameter Ra is determined by the profile centerlines of the substrate surface, it is difficult to get an appropriate value of Ra to represent the roughness of the substrate surface. The parameter-relative area, determined by area scale fractal analysis, can effectively characterize the surface roughness, predict the texture component of bond strength, and establish a connection between which and the bonding performance of the geopolymer coating at a high level of confidence. The bonding strength reduces with the decrease in the value of the relative area. The magnitude of scale employed should be seriously determined when characterizing the surface roughness.

Geopolymer is a promising fire-resistant coating material due to its admirable mechanical properties and thermal performance. This paper reviews the thermal performance of geopolymer-coating subjected to elevated temperature. Geopolymer coatings, geopolymer mortar, and concrete are with the similar fire- resistance performance, but with some differences. Size effects would affect the geopolymer coating in the ways of thermal expansion and shrinkage. The thermal expansion and mass loss of geopolymer coating are larger than that of geopolymer mortar and concrete. Chemical instability leads to weak volume stability and mechanical strength, whereas high chemical stability and microstructural performance may not result in positive volume stability and strength behaviors. The factors of Si/Al ratio, Al/Na ratio, water content, precursor type, alkali cation type, and curing conditions etc. are involved in mix ratio design which basically determines the performance of geopolymers. To improve the mechanical properties and fire-resistance capacity of geopolymers, slag, fibers, lightweight aggregates, inorganic fillers, and nano material would be considered in further studies. Furthermore, a further study is advised to be placed in the relationships between the microstructure changes, the macroscopic properties, and the reaction mechanism of geopolymer at high temperature still.

Geopolymers are considered to be green materials with excellent fire resistance performance and potential substitutes for ordinary Portland cement (OPC). This review article focuses on the adhesion of geopolymer coatings subjected to elevated temperature. Their high adhesion strength is the basis for geopolymers being used as coating materials to work with the substrate. The adhesion strength is related to many factors, such as chemical composition of the raw materials, the formulation of the geopolymer, substrate type, surface roughness of the substrate, etc. The Si/Al ratio has different effects on compressive strength and bonding strength. The water content affects the polymerization process—the adhesion strength decreases with increasing water content. Careful tailoring of the mix ratio design is essential to make the geopolymer coating have excellent adhesive performance. These mix design factors include Si/Al ratio, Al/Na ratio, water content, precursor type, alkali cation type, curing conditions, etc.