Why Is Sea Sand Prohibited in GRC? What Are the Standards for Qualified Silica Sand?

Aggregate is a key component of GRC materials, and the quality of silica sand directly affects product strength, durability, and safety. Sea sand is strictly prohibited in GRC production due to its inherent characteristics; selecting qualified silica sand that meets standards is a fundamental step in ensuring GRC product quality.

1. Core Reasons Why Sea Sand Is Prohibited in GRC

The biggest hazard of sea sand is excessive chloride ion content. Seawater contains large amounts of sodium chloride, and even after simple washing, the chloride ion content in sea sand remains far above standard requirements. Direct use in GRC production leads to chloride ion enrichment within components. Chloride ions severely corrode alkali-resistant glass fibres, reducing fibre tensile strength and bonding performance, causing a sharp decline in the flexural strength of GRC components and shortening their service life. Data from Qinglong's laboratory shows that the 28-day flexural strength decay rate of GRC products made with sea sand can exceed 30%. For GRC components containing steel reinforcement cages, chloride ions accelerate steel corrosion, causing volume expansion that leads to surface cracking and spalling, and in severe cases, structural failure. In addition, sea sand contains impurities such as shells and salts, which affect the workability and compactness of GRC slurry, causing pores and defects on component surfaces and reducing impermeability and durability. In coastal areas, using sea sand in a salt spray environment further exacerbates the risk of damage.

2. Core Technical Standards for Qualified Silica Sand

Qualified silica sand must meet strict technical indicators. First, chloride ion content must be ≤0.02% (by mass), which is the most critical indicator and must be confirmed by silver nitrate titration testing; mud content must be ≤1% and clay lump content ≤0.5% to prevent impurities from affecting slurry bonding performance and compactness. Particle gradation must be reasonable, with particle size controlled within 0.15-1.2mm, of which particles in the 0.3-0.6mm range must account for no less than 50%, ensuring full bonding with the cement slurry and enhancing component strength. The silica sand selected by Qinglong undergoes precisely screened particle gradation to suit GRC production requirements. Silica sand must have SiO₂ content ≥95%, with high hardness and good wear resistance to improve the durability of GRC components; harmful substance content must meet standards, such as sulfide and sulfate content ≤0.5%, to avoid chemical reactions that damage components. In addition, silica sand must have a uniform colour without obvious colour difference, ensuring consistent surface texture across GRC products.

3. Quality Inspection and Control Process for Silica Sand

Silica sand entering the plant must undergo comprehensive testing. First, visual inspection screening is performed to remove obvious impurities such as shells and stones; then indicators such as chloride ion content, mud content, and particle gradation are tested, and only qualified sand may be stored in the warehouse. Qinglong has established a dedicated silica sand testing mechanism: each incoming batch must be sampled and sent to the provincial R&D centre for testing, with test reports archived for reference to ensure traceable quality. During production, silica sand must undergo pretreatment including washing, drying, and screening to remove surface impurities and moisture. Qinglong uses automated pretreatment production lines to improve the cleanliness and uniformity of silica sand. During storage, silica sand must be stockpiled by category and kept separate from sea sand and chlorine-containing materials to prevent cross-contamination, while proper moisture-proofing measures are taken to prevent caking that would affect usability.

4. Qinglong's Silica Sand Selection and Application Practice

Qinglong insists on using natural quartz sand as GRC aggregate, sourced from high-quality quartz sand mines in non-coastal regions to ensure chloride ion content meets standards. It has established long-term strategic partnerships with major silica sand suppliers, signing quality assurance agreements to control silica sand quality at the source. Particle gradation is customized to the requirements of different projects: for example, the finely carved GRC panels for the Wuhan Han Show Theatre use fine-particle silica sand to enhance surface smoothness, while the double-curved GRC curtain wall for Poly Peninsula No. 1 in Hainan uses silica sand with optimized gradation to enhance component strength and forming performance. Backed by a strict silica sand control system, Qinglong GRC products deliver outstanding performance in strength, durability, and other aspects, and have been successfully applied in thousands of major projects at home and abroad, earning high recognition from customers.