The geopolymer uses fly ash, slag, and other solid wastes as raw materials and is widely used in building repair, but it is brittle and can be made tougher by incorporating fibers. In this study, polyvinyl alcohol (PVA) fibers, polyoxymethylene (POM) fibers, and polypropylene (PP) fibers were incorporated into the geopolymer mortar repair material, and the geopolymer was tested by changing the amount of fibers incorporation as well as the type. The effect of different fibers on the geopolymer mortar repair material was analyzed by comparing the flexural strength, compressive strength, flexural toughness, shrinkage, and bonding properties with cement mortar of different samples. The geopolymer was analyzed by Diffraction of X-rays (XDR) and Scanning Electron Microscopy (SEM) to further understand the hydration products and microstructure of the geopolymer. The results showed that the incorporation of fibers reduced the flexural strength and increased the compressive strength of the geopolymer mortar repair material; the mechanical properties of the geopolymer mortar repair material decreased with the increase in fiber incorporation, and the best mechanical properties of the geopolymer mortar repair material incorporated with 1.0% PP fibers; the toughening effect of PVA fiber was best when the amount of fiber incorporated was the same; the shrinkage properties of the geopolymer were good and had little effects on the building repair; the bonding properties of repaired specimens repaired with geopolymer mortar repair materials depended on the bonding area of the fracture surface, and the bonding area was enhanced with the increase in fiber incorporation; the XRD pattern showed that the hydration products of the geopolymer were mainly CaCO₃ and C–S–H gels.

By adjusting the content of geopolymer in geopolymer stabilized phosphogypsum (GSP) as roadbed filler, along with the mixing ratio, this paper mainly explores tendencies in the mechanical properties and water stability of GSP. This research is based on macro-mechanical properties such as unconfined compressive strength, resilience modulus, California bearing ratio and shear strength. It is also based on water stability tests, such as the water soaking test, dry and wet cycle test and expansion test, to explore changes in water stability. As for the durability of GSP, this paper is mainly based on the realization of a long time observation of mechanical properties and water stability. In the existing research, most of the stabilized phosphogypsum (PG) base material or roadbed filler consists of cement, lime, etc. In this paper, a new exploration is carried out on the composition of stabilized PG material, realized without the participation of cement. The 28 d compressive strength of GSP reaches 2.5 MPa, and over time this strength grows, which prevents the phenomenon of strength inversion that may occur in conventional cement-stabilized PG. In addition, a long-term soaking experiment was designed in this study based on the material after the strength was stabilized for up to 90 d. After the strength was steady, the GSP with the best water stability still had a softening coefficient of 80% after experiencing water immersion for 7 d. After determining the feasibility of the mechanical properties and water stability of GSP as roadbed filler, we further explored the strength formation mechanism of GSP by microscopic tests (XRD and SEM). This shows that geopolymer can stabilize PG in two main ways: one is the hydration reaction with PG to generate C-S-H gel and ettringite, and the other is to connect PG not involved in the chemical reaction to form a dense whole through generated hydration products. Geopolymer, stabilizing a high amount of PG, not only provides a new method for the consumption of PG, but also has more stable performance than cement, and has certain advantages in economy. In addition, the advantage of this study is that good performance can be achieved by simply sieving PG and adjusting the geopolymer ratio in practical engineering projects.