Why Is Sea Sand Prohibited in GRC? What Are the Standards for Qualified Silica Sand? Qinglong's Iron Rules for GRC Aggregate Quality Control

In the GRC material system, aggregates (usually silica sand) occupy about 30%-40% of the volume, and their quality is of vital importance. Among the rules, “the strict prohibition of sea sand” is an iron law recognized throughout the industry, because the chlorides in sea sand are the “Trojan horse” behind durability disasters in GRC. By contrast, selecting qualified natural silica sand or manufactured quartz sand and rigorously enforcing standards is the foundation for ensuring the long-term performance stability of GRC. Qinglong GRC's control over aggregates is so strict as to be nearly exacting, rooted in a deep understanding of material failure mechanisms and lessons summed up from extensive engineering experience.

A coastal city once saw a failure case: a local GRC manufacturer, in order to cut costs, illegally used insufficiently desalinated sea sand to produce window casing profiles. Only three years after installation, the products exhibited extensive map cracking and surface powdering, with fibers that broke at a touch. Diagnosis by Qinglong's technical experts identified the root cause as the chloride ions and salts enriched in the sea sand, which continuously attacked the glass fibers and cement hydration products in the humid environment and generated expansive stress through salt crystallization, leading to the accelerated breakdown of the material. This painful lesson confirmed the absolute correctness of Qinglong GRC's “prohibited raw materials” principle.

The Scientific Basis and Multiple Risks of Banning Sea Sand

Chloride attack: The chloride ions (Cl⁻) abundant in sea sand are the core killer. They rapidly destroy the SiO₂ protective layer on the glass fiber surface and react with the alkali metal ions in the fiber network, causing fiber strength to deteriorate rapidly. At the same time, chlorides also intensify corrosion of the cement matrix.
Salt crystallization damage: The soluble salts in sea sand (NaCl, MgCl₂, etc.) repeatedly dissolve and crystallize within the internal pores of GRC as humidity changes, generating enormous crystallization pressure that is enough to split the matrix and the fiber interface.
Hydration interference: Certain salts interfere with the normal hydration process of cement, affecting early strength development and long-term stability.

Selection Criteria and Key Indicators for Qualified Silica Sand

Qinglong GRC's screening standards for silica sand are far stricter than those for ordinary concrete sand:
1. Chemical composition: SiO₂ content should be ≥90% to reduce reactive impurities. Chloride ion content is strictly tested and must be below 0.01% (by mass). Aggregates suspected of alkali reactivity are strictly prohibited.
2. Particle gradation: It must be optimized; the ideal range is a fineness modulus between 1.8-2.2, with particle sizes mainly concentrated between 0.15mm-1.18mm, to achieve the tightest packing, reduce the amount of cement paste, and improve matrix density and strength.
3. Silt content and impurities: Silt content (particles smaller than 0.075mm) must be strictly controlled at ≤0.5%. Silt coats sand grains, hinders the bond between cement paste and sand, greatly reduces strength, and increases drying shrinkage.
4. Particle shape and soundness: Natural silica sand or high-quality manufactured quartz sand with well-rounded, clean-surfaced grains is preferred. Aggregates must have sufficient hardness and soundness to avoid fracturing during production.

Qinglong GRC's Aggregate Quality Control System

The company has established stable procurement channels for high-quality sand sources and conducts a “full physical examination” of every batch of silica sand entering the plant, including sieve analysis, silt content measurement, rapid chloride ion testing, alkali reactivity assessment, and more. Only aggregates meeting all indicators may enter the production process. The central laboratory regularly uses electron microscopy to observe sand grain morphology and surface cleanliness, ensuring aggregate quality at the micro level.

Aggregates are the “skeleton” of GRC, and their purity determines the “healthy” foundation of the entire material system. In GRC production, there must be no compromise whatsoever on the ban on sea sand, and the standards for qualified silica sand must be strictly enforced. Qinglong GRC upholds this fundamental principle of materials science, eliminating hidden dangers at the source and safeguarding the ultra-long service life of its products.