Why Is Sea Sand Prohibited in GRC? What Are the Standards for Qualified Silica Sand? Understanding Sand Selection Requirements and Specifications for GRC

In the field of architectural decoration, material selection directly affects a project's quality, safety, and durability. As an industry leader with 28 years of full-chain experience in UHPC/GRC/GRG/GRP materials, Qinglong Group deeply understands how material details determine project success. Today we focus on the selection of sand for GRC, providing an in-depth analysis of why sea sand is strictly prohibited and what standards qualified silica sand must meet, offering designers and owners a professional material selection guide.

I. Why Does GRC Material Have Strict Requirements for Sand?

As a lightweight, high-strength composite material, GRC (Glass Fiber Reinforced Concrete) relies heavily on the quality of its raw materials for its performance. Sand, as the main aggregate of GRC, accounts for approximately 60%-70% of the volume and directly affects the strength, durability, and surface texture of the products. When Qinglong Group participated in drafting the Technical Standard for Building Application of Glass Fiber Reinforced Cement (GRC) (JGJ/T423-2018), sand standards were explicitly listed as core technical indicators, reflecting the decisive role of sand in the structural stability of GRC.

II. Sea Sand Prohibition: Eliminating Construction Hazards at the Source

Sea sand is strictly prohibited in GRC production due to impurities such as chlorides and shells. Specifically, chloride ions in sea sand penetrate the cement matrix and corrode glass fibers, causing a sharp decline in the material's flexural strength (high-quality GRC can reach over 20MPa), and in severe cases leading to cracking and falling off of components. In addition, impurities such as shells in sea sand reduce the interfacial bonding force between the aggregate and the cement paste, affecting product density. Qinglong Group's production base (Nanning, Guangxi) has established a strict raw material screening mechanism; all sand undergoes dual testing for chloride content (≤0.03%) and shell content (≤1%), avoiding sea sand risks at the source.

III. Core Standards for Qualified Silica Sand: Comprehensive Control from Particles to Performance

High-quality silica sand is key to ensuring GRC performance. Based on industry standards and 28 years of practical experience, Qinglong Group has summarized the following core indicators:

1. Mineral composition: SiO₂ content must be ≥95% to ensure chemical stability and avoid adverse reactions with cement hydration products. The silica sand selected for Qinglong GRC all comes from specific mining sources, with composition purity verified by X-ray fluorescence spectrometry.

2. Particle gradation: Continuous gradation (e.g., 0.15-2.36mm) is adopted with a void ratio ≤35% to improve concrete density. Particle size distribution is precisely controlled with a laser particle size analyzer, ensuring the sand gradation curve deviates from design requirements by no more than 5%.

3. Harmful substance control: In addition to chloride ions, sulfide and sulfate content (calculated as SO₃) must be ≤0.5% and mica content ≤1% to eliminate the risk of alkali-aggregate reaction. Qinglong's laboratory is equipped with an atomic absorption spectrometer to conduct full testing on each batch of sand.

4. Physical properties: Apparent density ≥2500kg/m³ and mud content ≤3% ensure aggregate strength and compatibility with cement paste. In projects such as the Nanjing East Road Century Plaza renovation, Qinglong's customized silica sand solution enabled GRC light-transmitting components to achieve a perfect balance between strength and light transmittance.

IV. Qinglong's Full-Process Control of GRC Sand Selection

As a national high-tech enterprise, Qinglong Group has established a full-chain quality control system from sand source exploration to finished product testing: long-term cooperation agreements with high-quality silica sand mines ensure stable raw material supply; automated sand processing lines enable grading, screening, and impurity removal; and the provincial-level R&D center conducts research on sand-cement-fiber interface optimization, keeping GRC products continuously leading the industry in flexural strength, weather resistance, and other indicators. For example, in the Dongguan Women and Children's Activity Center project, strict sand quality control helped the project win the Silver Award of the First GRC Construction Engineering Innovation Award.

Choosing qualified silica sand is the first line of defense in ensuring the safety and durability of GRC products. Qinglong Group has always maintained a meticulous and excellence-pursuing attitude, integrating material detail control into every step of detailed design and manufacturing, providing reliable support for designers to realize their creative visions, and creating architectural works that combine aesthetics and durability for owners. In the application of GRC materials, scientific material selection is the foundation, and professional service is the guarantee—this is Qinglong's responsibility and commitment as an industry leader.