The influence of surface treatment on the transport properties of hardened calcium sulfoaluminate cement-based materials

Abstract In this study, the efficiency of surface treatment in the calcium sulfoaluminate (CSA) cement-based materials were explored. Several frequently used surface treatment agents (sodium silicate (NS), and magnesium fluorosilicate (MFS), tetraethyl orthosilicate (TEOS), poly-methyltriethoxysilane (PMTS)) were applied on hardened CSA mortar and concrete. The penetration depth of these agents and their influence of the treatment on the properties of water sorptivity, carbonation resistivity, mechanical property, and pore structure was investigated. Results showed that the penetration depth of NS and MFS was around 60-85um, and that PMTS, MFS, TEOS, and NS could reduce the water sorptivity by 94.0%, 17.0%, 11.0% and 7.8%, respectively. PMTS and TEOS could reduce the carbonation rate by 38.7% and 14.3%, respectively, but NS and MFS could not reduce it. In addition, PMTS can reduce the pores less than 50 nm (S pores) significantly, whereas has little influence on pores between 50 nm and 1 μm (M pores). NS, MFS and TEOS would reduce M pores, but increase S pores. By the combination of permeability and pore structure test, it was found that volume of S pores was positively correlated to the carbonation rate and the volume of M pores was positively correlated to the water sorptivity. Furthermore, it was found that surface treatment had little influence on the compressive strength, but it could increase flexural strength slightly. This work evidenced the effectiveness of surface treatment on CSA cement-based materials and highlighted the critical role of fine pores (less than 50 nm) in their transport properties.