Durability and Microstructure Evolution of Graphene Oxide Modified Polymer Cement Mortar under Sulphate–Freeze–Thaw Cycle

In the northwest of China, the harsh service environment such as saline soil and large temperature difference leads to the serious salt corrosion and freeze-thaw damage of cement concrete structures, and even structural damage and eventually shortened service life. It is important to improve the durability of cement-based materials via introducing polymers into common cement-based materials. However, the shortcomings of high-temperature sensitivity and low compressive strength of polymer materials limit their further application. In recent years, the introduction of nanomaterials greatly enhances the durability of ordinary cement-based materials. However, the dispersion and dosage of nanomaterials in cement-based materials and their influence on the microstructure of cement-based materials still need a further study.

Combined with the advantages of polymer and graphene oxide, sulfate and freeze-thaw coupling were used to simulate the special natural environment in the northwest China. Ordinary cement mortar and ethylene vinyl acetate polymer rubber powder were prepared with graphene oxide (GO) and ethylene vinyl acetate polymer rubber powder (EVA), respectively. Polymer cement mortar, graphene oxide cement mortar and graphene oxide modified polymer cement mortar were tested for relative dynamic elastic modulus, mass loss and compressive strength under different freeze-thaw cycles by sulfate-freeze-thaw cycle test. The microstructure evolution of specimens was characterized by X-ray diffraction (XRD), Fourier infrared spectroscopy (FTIR), derivative thermogravimetric analysis (TG-DTG), low-field nuclear magnetic resonance (LF-NMR), and scanning electron microscopy (SEM).

For 0.03% GO modified with 4% EVA cement mortar, the freezing and thawing resistance of the sample can be improved. After the sulfate freeze-thaw cycle, the maximum mass loss rate of OCM group is obtained (i.e., 5.26%), and the minimum relative dynamic elastic modulus is achieved (i.e., only 56.27%). The minimum of G3ECM is only 3.75%, and the relative dynamic elastic modulus reaches 73.95. After 125 freeze-thaw cycles, the compressive strength of G3CM specimen is the largest, and the OCM of blank group is the smallest. When EVA is mixed alone, the compressive strength of the specimen reduces, while the synergistic effect of GO and EVA can increase the strength. GO can obviously promote cement hydration, and EVA can delay cement hydration to a certain extent, but GO and EVA can still promote cement hydration and optimize microstructure under the synergistic effect. 0.03% GO mono-doped has an optimum effect on the optimization of pore structure, and the polymer film made of EVA can still promote the durability via hindering water transport.

In this study, GO modified polymer was used to prepare GO modified polymer cement mortar. The results of sulfate freeze-thaw cycle test showed that GO and EVA could significantly improve the durability of ordinary cement-based materials via affecting the cement hydration of cement-based materials, optimizing the pore structure and improving the microstructure.