What Alkalinity Issues Should Be Considered When Using Sulphoaluminate Cement in GRC? Low-Alkali Cement Technology and Durability Assurance Strategies

The application of sulphoaluminate cement in GRC requires particular attention to alkalinity control; improper alkali content accelerates glass fiber corrosion, causing a sharp decline in material durability. Based on 28 years of research and practice, Qinglong Group strictly controls the alkali content of sulphoaluminate cement below 0.6% and, through multiple measures such as incorporating active admixtures and optimizing curing regimes, ensures that GRC products maintain stable performance throughout a 50-year design life. In the Wuhan Hanxiu Theater project, the GRC curtain wall formulated with low-alkali sulphoaluminate cement achieved a strength retention rate of over 95% after 8 years in service, confirming the importance of scientific alkalinity management.

Corrosion Mechanism of Alkalinity on Fibers

Ca(OH)₂ generated by cement hydration raises the pore solution pH above 12.5, and such a highly alkaline environment attacks the SiO₂ network of glass fibers, causing fiber strength degradation. Through experiments, Qinglong Group found that when the cement alkali content exceeds 0.8%, the long-term strength retention rate of GRC drops below 70%. Therefore, we prefer sulphoaluminate cement with an alkali content of ≤0.6% and incorporate 20-30% silica fume, consuming Ca(OH)₂ through the pozzolanic reaction to stabilize the pore solution pH below 11.5.

Technical Measures for Alkalinity Control

Qinglong Group adopts a triple strategy of "raw material selection + mix proportion optimization + process control": using low-alkali cement (Na₂O equivalent ≤0.5%); incorporating active admixtures such as fly ash and slag powder (total ≤40%); and controlling the steam curing regime at 60-80℃ with humidity ≥95% to promote secondary hydration reactions. In the Nanning Wuxiang China Resources MixC One project, these measures kept the annual growth of carbonation depth in GRC panels at ≤0.1mm.

On-Site Construction Precautions

During construction, avoid using alkali-containing admixtures such as early-strength agents and antifreeze agents. Qinglong Group recommends testing the alkali content of every batch of cement upon delivery and regularly monitoring the pore solution pH. Through full-process control, we ensure that the alkali resistance of GRC products reaches its optimum.