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.

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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.

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