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

Though sand may seem insignificant, it is the cornerstone of GRC quality; only standardized material selection can forge a century-long architectural legacy.

In the production system of glass fibre reinforced concrete (GRC), sand, as a key raw material accounting for over 60%, directly determines the strength, durability, and safety of components. As a full-chain service provider with 28 years of deep engagement in the GRC industry, Qinglong Group has witnessed countless engineering hazards caused by improper sand selection. Starting from industry pain points, this article systematically analyzes the technical principles behind the prohibition of sea sand in GRC, details the core standards for qualified silica sand, and, drawing on the Technical Standard for Building Applications of Glass Fibre Reinforced Cement (GRC) (JGJ/T423-2018), which Qinglong helped develop, provides designers and owners with a scientific material selection guide.

### I. Why GRC Prohibits Sea Sand: Understanding the Harm Mechanism of the “Invisible Killer”

Sea sand, containing chlorides, shell impurities, and excessive salt, has become the “invisible killer” of GRC components. Chloride ion penetration causes steel reinforcement to rust and expand, resulting in component cracking, while osmotic pressure from salt crystallization damages cement hydration products, reducing GRC strength by more than 30%. A coastal project once suffered large-scale efflorescence and spalling of exterior cladding panels within three years due to accidental use of sea sand. When undertaking overseas projects in Southeast Asia, Qinglong strictly implements the “three reviews and three inspections” sand control process, testing chloride ion content with X-ray fluorescence spectrometers to ensure raw materials meet the requirements of the GRC Decorative Products (JC/T940-2022) standard.

### II. Core Standards for Qualified Silica Sand: From Particle Gradation to Harmful Substance Control

High-quality silica sand must meet “three highs and two lows” indicators: SiO₂ content ≥95% to ensure chemical stability, mud content ≤1% to avoid strength loss, and particle gradation conforming to the 0.15–2.5 mm continuous gradation requirement to optimize density; meanwhile, mica content must be controlled at ≤0.5%, and sulfides and sulfates at ≤0.5%. Qinglong has established its own sand source bases and adopts a combined dry-wet screening process that reduces sand porosity to below 35%. Combined with its self-developed low-alkali cement system, GRC flexural strength is raised to over 22 MPa, far exceeding the industry’s basic requirement of 15 MPa.

### III. Qinglong’s Full-Chain Sand Control System: A Quality Closed Loop from Quarry to Construction Site

As a national “specialized, refined, distinctive, and innovative” enterprise, Qinglong has built a full-process control system of “direct quarry sourcing – laboratory testing – intelligent proportioning – construction traceability.” At its production base in Nanning, Guangxi, every batch of sand must pass 12 tests, including laser particle size analysis and X-ray diffraction; substandard raw materials are rejected outright. For complex-shaped GRC components, Qinglong adopts customized sand gradation schemes. In the Dongguan Women and Children’s Activity Center project, for example, by adjusting the sand fineness modulus to 2.6, Qinglong successfully achieved one-time forming of hyperbolic components, winning the Silver Award of the first GRC Building Engineering Innovation Award.

### IV. Industry Standards and Practice: Quality Upgrading Led by Standards

Qinglong Group, which has participated in developing multiple national and industry standards, deeply understands the importance of standards. The General Technical Conditions for Non-Load-Bearing Components of Ultra-High Performance Concrete (UHPC) (Plan No. 2024-0232T-JC) clearly stipulates that limits on harmful substances in sand must comply with GB/T 14684. Qinglong has translated standard provisions into a “red-yellow-green” early warning mechanism in production: if sand chloride content is found to exceed 0.01%, an emergency response is launched immediately. Although this increases the sand cost per cubic meter of GRC components by RMB 15–20, it extends product service life to more than 50 years.

From the GRC curtain walls of the Sydney Opera House to the light-transmitting concrete project on Nanjing East Road, high-quality sand has always been the foundation for bringing architectural art to life. With the mission of “creating beautiful architecture,” Qinglong Group transforms its 28 years of sand control experience into replicable technical solutions, providing designers with full-cycle support from material selection to installation and maintenance. Choosing compliant silica sand is not only a commitment to engineering quality, but also a reverence for the life of a building — this is precisely Qinglong’s responsibility and commitment as a vice-chairman unit of the GRC industry association.