Alkalinity Issues and Countermeasures When Using Sulphoaluminate Cement in GRC

In the application of GRC (Glass Fiber Reinforced Concrete) materials, sulfoaluminate cement, with its early-strength and rapid-hardening properties, demonstrates unique advantages in specific engineering scenarios. However, if its alkalinity issue is not properly addressed, it may directly affect the durability and safety of GRC components. As an industry leader with 28 years of full-chain experience in UHPC/GRC/GRG/GRP materials, Qinglong Group, drawing on the practice of hundreds of benchmark projects, provides an in-depth analysis of the key alkalinity control points and systematic solutions for sulfoaluminate cement in GRC applications, offering professional technical reference for designers and owners.

I. Potential Impact of Sulfoaluminate Cement Alkalinity on GRC Performance During hydration, sulfoaluminate cement releases hydroxide ions, keeping the pH of the slurry typically at 10-11. Although this is lower than ordinary Portland cement (pH≈13), it may still trigger two core problems: first, chemical corrosion of glass fibers in the high-alkalinity environment, causing fiber strength loss and affecting the flexural performance of GRC components (quality GRC requires a flexural strength of over 20MPa); second, the risk of alkali-aggregate reaction (AAR), especially when the aggregate contains reactive silica, which may produce expansive products and cause component cracking. In a commercial complex project, failure to control the alkalinity of sulfoaluminate cement led to surface powdering and exposed glass fibers in GRC decorative moldings after 2 years—typical manifestations of alkali corrosion.

II. Key Technical Measures for Alkalinity Control in Sulfoaluminate Cement GRC **1. Raw Material System Optimization** Through precise control of material proportions, Qinglong Group adopts a composite cementitious system of "sulfoaluminate cement + slag powder + fly ash," using the pozzolanic effect of slag powder to neutralize part of the alkali ions and bring the slurry pH stably down to the 9-10 range. At the same time, low-alkali-reactivity aggregates (such as quartz sand) are strictly selected, and aggregates are tested for alkali reactivity (with reference to the Test Method for Alkali Reactivity of Aggregates for Concrete), blocking the alkali-aggregate reaction path at the source. In the Dongguan Women and Children's Activity Center project, this solution increased the alkali corrosion resistance of GRC exterior wall panels by 40% and passed 1,000 freeze-thaw cycle tests.

**2. Compatibility-Based Selection of Glass Fiber** To address the alkaline environment of sulfoaluminate cement, Qinglong gives priority to alkali-resistant glass fiber (AR glass fiber), whose surface zircon coating forms a chemical barrier that effectively resists hydroxide ion attack. Practical data show that AR glass fiber achieves a 28-day strength retention rate of over 90% in sulfoaluminate cement GRC, far higher than ordinary alkali-free glass fiber (retention rate of only 60%). In addition, by controlling the fiber volume content (typically 3-5%), uniform fiber dispersion is ensured to avoid excessively high local alkali concentration.

**3. Coordination of Forming Process and Curing Regime** In the production stage, the vacuum extrusion forming process is adopted to improve density, reduce porosity, and slow the migration of alkali ions; during curing, a combined "steam curing + natural curing" mode is implemented, with the steam curing temperature controlled at 60-80℃ for no more than 8 hours to avoid a sudden rise in alkalinity caused by over-hydration. In the Nanjing East Road Century Plaza renovation project, Qinglong used this process to keep the alkali content of translucent GRC components below 0.6%, meeting the stringent requirements of the Technical Standard for Building Application of Glass Fiber Reinforced Cement (GRC) (JGJ/T423-2018). For more industry information: Add WeChat qlfsbl123

III. Full Life-Cycle Alkalinity Management and Quality Assurance As a National High-Tech Enterprise, Qinglong has established a whole-process alkalinity control system covering design through after-sales: in the design stage, BIM technology is used to simulate alkali ion distribution and optimize component cross-sections and reinforcement; during production, RFID chips trace the alkali content of raw materials; during construction and installation, on-site alkalinity testing is carried out (portable pH meter testing of surface alkalinity values); and after-sales maintenance provides 5 years of alkali corrosion monitoring services. This closed-loop management of "prevention-control-monitoring" ensures that sulfoaluminate cement GRC components achieve a service life of more than 20 years in high-end projects such as grand theaters and commercial complexes.

The application of sulfoaluminate cement in GRC requires not only leveraging its material property advantages but also being supported by scientific alkalinity control technology. With its outstanding contributions to the development of GRC standards (such as JC/T940-2022) and an accumulation of 58 patented technologies, Qinglong Group has formed mature solutions. In the future, as UHPC/GRC composite systems develop, alkalinity control will become one of the core directions of material innovation, helping the architectural decoration industry achieve a dual breakthrough in "safety and aesthetics." For more industry information: Add WeChat qlfsbl123