Effect of environmental pH value on mechanical properties and microstructure of hardened sulphoaluminate cement paste

In order to analyze the influence of environmental pH value on the properties of hardened sulphoaluminate cement (CSA) paste, the cement samples are cured with different pH regimes (pH = 3, 7 and 12). The effect of pH value on mechanical properties, hydrated phase, morphology and microstructure is studied by compressive strength, XRD, TG-DTG, SEM and electrochemical impedance spectroscopy (EIS). Additionally, a new equivalent circuit is built to calculated the electrochemical parameters (R-s, R-ct, R-ccp and R-cp). Meanwhile, a proposed evolution model for pore network is used to analyze and explain the mechanical properties and microstructure of hardened CSA paste exposed to different pH curing conditions. The results show that the compressive strength, amounts of hydration products and EIS parameters are obviously affected by different environmental pH values. With the increasement of pH value, AFt morphology change from rod to needle-like increased in number and the gel products of AH3 decrease, accompanied by increasing continuous connected pores increase in the matrix and decreasing the discontinuous connected pores decrease, which result in the weakness of matrix strength, which can be further proved by the evolution model of pore structures with pH value as a function of curing age.

Automated summary

This study explores the influence of environmental pH value on the properties of hardened sulphoaluminate cement paste. The results show that different pH values significantly affect the compressive strength, hydration products, and electrochemical parameters. An increase in pH value leads to the formation of more continuous connected pores and a decrease in matrix strength.