What alkalinity issues should be noted when using sulphoaluminate cement in GRC?

Sulphoaluminate cement, with its early strength and rapid hardening characteristics, holds certain application value in GRC product manufacturing. However, its use in GRC requires particular attention to alkalinity matching, which is closely related to the long-term durability of GRC. Based on years of materials research and practical experience, Qinglong Group believes that the application of sulphoaluminate cement in GRC requires focused control of the following alkalinity-related issues.

The alkalinity (pH value) of the hydrated liquid phase of sulphoaluminate cement is typically lower than that of traditional Portland cement, which is the core difference requiring attention in GRC applications. The pH of the hydrated liquid phase of ordinary Portland cement can exceed 13.5, while that of sulphoaluminate cement generally falls between 11.5 and 12.5. This relatively low-alkalinity environment may weaken the long-term protection of alkali-resistant glass fibres. Qinglong Group conducts rigorous alkalinity testing at the material selection stage to ensure that the alkalinity of the cement raw material matches the alkali resistance of the fibres.

The alkalinity stability of sulphoaluminate cement requires particular attention. In multiple GRC projects in which Qinglong Group has participated, we have found that the later-stage carbonation rate of sulphoaluminate cement products may be relatively fast, which further reduces the alkalinity within the material and weakens the protection of glass fibres. To address this issue, we optimize the pore structure by incorporating appropriate amounts of active admixtures (such as silica fume and slag) into the mix proportion, slowing the carbonation process while increasing matrix density and thereby indirectly enhancing the protection of the fibres.

The compatibility of sulphoaluminate cement with admixtures is also an extension of the alkalinity issue. The effectiveness of certain high-range water reducers may be compromised in low-alkalinity environments, potentially leading to poorer workability. Through extensive testing, Qinglong Group's technical team has screened admixture types compatible with sulphoaluminate cement, ensuring that GRC mixes have good workability without compromising the mechanical properties of the final product. In the Algeria hotel project, we successfully overcame construction adaptability challenges under local climate conditions by optimizing the admixture formulation.

Despite the challenges related to alkalinity, sulphoaluminate cement still holds value in specific GRC applications, such as precast components requiring rapid demoulding. Qinglong Group recommends that when using sulphoaluminate cement to produce GRC, a comprehensive durability assessment, including accelerated aging tests, should be carried out to verify its long-term performance. Through scientific proportioning and strict process control, its strengths can be leveraged and its weaknesses mitigated, unlocking the application potential of sulphoaluminate cement in GRC.