What Alkalinity Issues Should Be Considered When Applying Sulphoaluminate Cement in GRC?

Sulphoaluminate cement is occasionally used in GRC production due to its rapid setting and hardening and high early strength. However, this type of cement has special alkalinity characteristics; if improperly controlled, it can easily cause fiber corrosion, strength degradation, and other problems. Mastering the key points of alkalinity control is essential to ensuring the quality of sulphoaluminate cement GRC products.

I. Alkalinity Characteristics and Potential Risks of Sulphoaluminate Cement

During hydration, sulphoaluminate cement releases alkaline substances, and its paste typically has a pH value between 11.5 and 12.5. Although this is lower than ordinary Portland cement, prolonged exposure to this alkaline environment can still erode the surface of alkali-resistant glass fibers and reduce the bond strength between the fibers and the cement matrix. Uneven alkalinity distribution can easily cause localized stress concentration, leading to micro-cracks in GRC components; in severe cases, fiber performance deteriorates, reducing the flexural strength of components by more than 15%. In early project practice, Qinglong found that sulphoaluminate cement GRC without alkalinity control is prone to surface powdering and strength degradation after 3-5 years of use, highlighting the importance of alkalinity control.

II. Core Technical Measures for Alkalinity Control

Adjusting the cement blend ratio is a fundamental approach. Mixing sulphoaluminate cement with ordinary Portland cement in a proper proportion can effectively reduce overall alkalinity. Qinglong's tests show that when the blend ratio is controlled at 1:3 to 1:5, the paste pH value can be stabilized between 10.5 and 11.5, meeting the requirements of alkali-resistant fibers. Adding mineral admixtures is equally effective; admixtures such as fly ash and slag powder can consume part of the alkaline substances and lower paste alkalinity, with a recommended dosage of 10%-20% of the total cementitious materials, while also improving component density. Using specialized alkali-resistant admixtures, such as silicone-based retarders, can both adjust setting time and inhibit alkali ion migration, reducing fiber erosion.

III. Alkalinity Monitoring and Control During Application

During production, paste alkalinity must be monitored in real time, with regular testing using a pH meter to ensure the pH value remains stable within a reasonable range. Qinglong's production lines are equipped with online monitoring equipment, and alkalinity data must be recorded for each batch of products. Control the water-binder ratio and curing environment; an excessively high water-binder ratio can easily lead to increased alkali ion concentration, so it is recommended to keep it below 0.35. During curing, avoid high-temperature and high-humidity environments and use constant temperature and humidity curing to reduce alkali solution migration. For thin-walled GRC components, such as decorative moldings and openwork panels, the fiber content should be appropriately increased to enhance alkali erosion resistance. Qinglong effectively mitigated the effects of alkalinity in the production of GRC European-style components for the Sanya Festival Plaza using this method.

IV. Application Scenarios and Limitations of Sulphoaluminate Cement GRC

This type of GRC is suitable for projects with tight schedules and high early strength requirements, such as emergency repair works and short-term display components, but is not suitable for harsh environments such as long-term outdoor exposure or coastal high-salt-mist conditions. Qinglong recommends that important buildings and landmark projects prioritize ordinary Portland cement combined with high-quality alkali-resistant fibers to ensure long-term product stability. If sulphoaluminate cement must be used, a professional manufacturer should be commissioned to customize the formulation; for example, Qinglong can provide targeted alkalinity control solutions, optimizing material combinations based on the project environment to avoid alkalinity risks.