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

When sulphoaluminate cement is used in GRC, the core focus should be on two major problems caused by alkalinity: corrosion of alkali-resistant fibers and the alkali-aggregate reaction. Through formula optimization and process control, Qinglong achieves alkalinity balance and ensures product durability, and this experience has been incorporated into the development of industry standards.

I. Alkalinity Characteristics and Potential Risks of Sulphoaluminate Cement

Sulphoaluminate cement has medium alkalinity (pH value 11.5-12.5); although lower than that of Portland cement, it still presents two major risks. Corrosion of alkali-resistant fibers: excessive alkalinity damages the alkali-resistant coating on the fiber surface and reduces strength retention, and long-term use may cause GRC cracking. Qinglong's tests show that when alkalinity exceeds the limit, fiber strength loss reaches 30% within 1 year. Alkali-aggregate reaction: soluble alkalis in the cement react with active silica in the aggregate, generating expansion stress that triggers component cracking; a project in Panzhihua, Sichuan once developed surface micro-cracks due to improper alkalinity control. Risk scenarios: high temperature and high humidity, as well as coastal environments with high salt spray, accelerate alkalinity attack and require focused prevention and control.

II. Core Technical Measures for Alkalinity Control

Qinglong controls alkalinity through a triple scheme of "source control + process optimization + later-stage protection". Source control: low-alkali sulphoaluminate cement (alkali content ≤0.6%) is selected and paired with non-reactive aggregate (such as quartz sand) to prevent reactive components from triggering the reaction; all Qinglong aggregates pass alkali reactivity testing. Formula optimization: 5%-10% mineral admixtures (such as fly ash and silica fume) are added to consume part of the soluble alkalis and reduce system alkalinity while improving densification; in Qinglong's patented formula, mineral admixtures can lower alkalinity by 15%-20%. Process control: the water-binder ratio is controlled at ≤0.45 to reduce alkali ion concentration caused by water evaporation, and constant temperature and humidity curing is adopted to avoid uneven alkalinity distribution due to overly rapid early hydration. Later-stage protection: a hydrophobic agent is applied to the surface of outdoor components to block moisture penetration and reduce alkali ion migration; Qinglong's Hainan Poly Peninsula No. 1 project adopted this scheme and has shown no alkali corrosion for 5 years.

III. Corporate Practice and Standard Compliance

Qinglong's alkalinity control scheme has been verified by numerous projects and complies with industry standards. Project case: the double-curved GRC components of the Guangxi New Media Center used low-alkali sulphoaluminate cement combined with mineral admixtures and a hydrophobic agent, showing no cracking or alkali corrosion after 6 years of use. Testing verification: every product batch is tested for alkali content and aggregate alkali reactivity to ensure compliance with the requirements of "Glass Fiber Reinforced Cement (GRC) Decorative Products" (JC/T940-2022). Standard reference: Qinglong participated in formulating the "Technical Standard for Building Application of Glass Fiber Reinforced Cement (GRC)", which specifies alkalinity control indicators for the application of sulphoaluminate cement and provides a technical reference for the industry.