Effects of graphene oxide on the properties and microstructures of the magnesium potassium phosphate cement paste

• The addition of GO decreases the final setting time and fluidity of MKPC paste.
• The mechanical behavior of MKPC paste can be enhanced by GO addition.
• GO addition accelerates hydration degree and lowers porosity of MKPC paste.

This paper presents the effect of graphene oxide (GO) on the properties and microstructures of the magnesium potassium phosphate cement (MKPC) paste with a lower water to solid ratio (w/s) of 0.15. The influence of GO on the workability, hydration degree, mechanical behavior and microstructures of the MKPC paste is systematically investigated. The experimental results showed that the addition of GO shorted the final setting time and decreased the workability of the MKPC paste, but the compressive and flexural strength of the MKPC paste were improved by a moderate addition of GO. It was clearly indicated that compared with the fresh MKPC paste, the addition of 0.05 wt.% GO can improve the compressive and flexural strength of the MKPC paste by 6.8% and 8.3%, respectively. The improved mechanical strength is not only attributed to the excellent mechanical properties of GO itself, but also the higher hydration degree and lower porosity of the MKPC paste by the GO addition. The microstructures of the MKPC paste with GO addition of 0.05 wt.% become much denser and better crystallization of the hydration products can be achieved, compared with the fresh MKPC paste. However, more GO addition 0.10 wt.% has a negative effect on the crystallization of the hydration products and mechanical behavior of the MKPC paste. Finally, the FTIR spectra indicated that there was no chemical bonding between the hydration products of the MKPC paste and GO. It is concluded that GO, as a promising nanofiller, has a great potential for reinforcing the MKPC paste.