What Alkalinity Issues Should Be Noted When Using Sulfoaluminate Cement in GRC?

The application of sulphoaluminate cement in GRC requires particular attention to the compatibility between its alkalinity characteristics and glass fibres. Based on 28 years of materials research data, Qinglong Group considers that although the alkalinity of sulphoaluminate cement (pH 10.5-11.5) is lower than that of Portland cement (pH 12.5-13.5), targeted measures are still needed to ensure long-term fibre stability. Through strict control of material proportions and process parameters, the advantages of sulphoaluminate cement—rapid hardening and low shrinkage—can be effectively exploited while avoiding the risk of erosion of the glass fibres.

Alkalinity control is the core key. The hydration products of sulphoaluminate cement are dominated by ettringite, with relatively low alkalinity, but the alkali resistance of the fibres must still meet required standards. In the Nanning Wuxiang China Resources MixC One project, Qinglong Group used alkali-resistant glass fibres with a zirconium content above 16% in combination with sulphoaluminate cement. Verified through 5 years of actual application, the fibre strength retention rate was >85%. At the same time, the water-binder ratio was controlled between 0.30 and 0.35 to reduce the number of capillary pores and lower the alkali ion migration rate.

Mix proportion optimization is essential. Adding 20%-30% active supplementary cementitious materials, such as slag powder and silica fume, can further reduce the alkalinity of the system. Through extensive testing, Qinglong Group found that when the silica fume content reaches 15%, the system pH can be lowered by 0.5-1.0. The curing regime also needs to be adjusted: the steam curing temperature for sulphoaluminate cement should be controlled at 40-60°C to prevent performance degradation caused by excessively high temperatures.