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

The use of sea sand is strictly prohibited in GRC, because excessive chloride ion content in sea sand (typically 0.1-0.3%) causes catastrophic consequences: chloride ions destroy the zirconia protective layer on the surface of glass fibers, causing the fibers to corrode and powder within a few years and depriving GRC of its reinforcement effect; meanwhile, chloride ions react with tricalcium aluminate in cement to form expansive products, causing matrix cracking. Qinglong Group's 28 years of quality control experience show that even after washing with fresh water, the chloride ion content of sea sand can hardly be stably kept below the 0.01% safety limit. We strictly select qualified silica sand, with standards including: SiO₂ content ≥95%, mud content ≤1.0%, chloride ion content ≤0.01%, fineness modulus 1.8-2.2, and continuous particle gradation. In a post-evaluation of a project in Hainan, GRC panels that illegally used sea sand suffered a flexural strength loss of 60% after 3 years, while similar products using standard silica sand retained over 90% of their strength. Sand source selection is the first line of defense for GRC durability.

The Hazards of Sea Sand Are Latent and Irreversible

Chloride ions in sea sand exist in both free and bound states. Even if fresh water washing removes part of the free chloride ions, the bound chloride ions will gradually release in the alkaline environment of GRC, forming a long-term corrosion source. This corrosion begins at the fiber-matrix interface and is difficult to detect with the naked eye; by the time rust stains and cracks appear on the surface, the structural damage is already irreversible. Qinglong Group has established a sand source traceability system, strictly prohibiting sea sand and river sand that may be affected by seawater from entering the plant.

Physical and Chemical Requirements for Qualified Silica Sand

High SiO₂ content ensures chemical stability; low mud content guarantees interfacial bond strength; the 0.01% chloride ion limit is an absolute bottom line; a fineness modulus of 1.8-2.2 achieves optimal particle gradation and reduces cement consumption. Qinglong Group conducts full-item testing on every batch of sand and firmly rejects any that fails. At our Nanning production base, we work only with certified, high-quality sand mines to ensure a stable and reliable sand supply.

Particle Morphology and Gradation Affect Workability and Strength

Well-rounded sand grains are preferred while needle-like and flaky particles are avoided, to ensure good flowability and compactness. By blending sands of different particle sizes, the tightest packing is achieved and porosity is reduced. Qinglong GRC adopts a three-grade sand system with a maximum particle size of no more than 1.2mm, giving the mix both flowability and stability.

Enhanced Controls in Special Environments

For projects in coastal areas, in addition to strict sand control, migrating corrosion inhibitors can be added to the mix to provide extra protection for the fibers. At the same time, increasing the cover thickness and adopting a low water-binder ratio to increase density provide multiple layers of protection to ensure fail-safe performance.

Sand is the raw material used in the largest quantity in GRC, and its quality directly affects the performance of the final product. Qinglong Group selects every grain of sand with the most stringent standards, building a solid quality foundation for our customers.