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

The prohibition of sea sand in GRC is a red line for material safety, stemming from the lethal harm of chloride ions to glass fibers and steel reinforcement. Qinglong Group calls sea sand the “invisible killer” of GRC; the chloride ions it contains cause fiber degradation and steel corrosion, severely threatening structural safety. The selection of qualified silica sand must follow three major criteria: “chemical stability, particle gradation, and mud content.” In the Hainan International Convention and Exhibition Center project, we ensured the long-term durability of a 120,000-square-meter GRC roof in a marine environment through strict sand control, proving the importance of material purity.

The Destructive Mechanism of Chloride Ions in Sea Sand

Chloride ions in sea sand exist in the form of sodium chloride and become free chloride ions when dissolved in water. These ions penetrate the cement matrix, destroying the SiO₂ network structure of glass fibers and causing a sharp decline in fiber strength. More seriously, chloride ions destroy the passivation film of steel reinforcement, triggering electrochemical corrosion, and the volume expansion of corrosion products cracks the GRC protective layer. Qinglong laboratory data shows that GRC specimens made with sea sand lose more than 40% of their strength after one year, completely losing their service value.

Chemical Index Requirements for Qualified Silica Sand

Qinglong has strict requirements for the chemical purity of silica sand: silicon dioxide content of no less than 95%, mud content of no more than 1%, and water-soluble chloride ion content below 0.01%. We have established a supplier access system, and every batch of sand must be accompanied by a radioactivity test report and proof of chloride ion content. For major engineering projects, we even send personnel to sand quarries for on-site sampling and testing, ensuring material quality at the source.

Optimized Design of Silica Sand Particle Gradation

Reasonable particle gradation is key to ensuring GRC workability and density. Qinglong adopts a continuous gradation system, mixing 0.1-0.3mm fine sand with 0.6-1.2mm medium-coarse sand at an optimal ratio to ensure tight packing between particles. This gradation design allows GRC to achieve high density even with a lower cement content, improving mechanical properties and durability.

Full-Process Control of Sand Testing

Qinglong's laboratory is equipped with advanced instruments such as laser particle size analyzers and rapid chloride ion detectors to conduct full-index testing on every batch of sand entering the site. A sand quality traceability system has also been established, so that any issue can be traced back to the specific batch and supplier. This strict quality control system is the fundamental guarantee of the excellent performance of GRC products.