How Do Admixtures Improve GRC Performance? Which Admixtures Are Prohibited?

Admixtures are key to optimizing GRC performance. Proper selection can significantly improve workability, strength, and durability, while some harmful admixtures can damage product performance. Based on 28 years of practice, Qinglong has developed clear selection and prohibition standards to ensure product quality.

I. Core Improvements of Admixtures to GRC Performance

Common admixtures can be divided into four categories by function, each targeting specific pain points in production and use. High-range water reducers: primarily improve workability and lower the water-binder ratio (from 0.5 to below 0.4), increasing density and strength. Qinglong uses custom polycarboxylate water reducers with a water reduction rate of over 30%, giving fresh GRC a spread of ≥700mm and making it suitable for complex shapes. Retarders: extend hydration time, prevent overly rapid setting in high-temperature environments, and ensure sufficient time for installation operations. During summer production, Qinglong adds retarders to extend the initial setting time to over 4 hours. Thickeners: improve the cohesion of fresh GRC and prevent fiber settlement and aggregate segregation, making them especially suitable for spray-up processes. Qinglong adds cellulose ether thickeners to its spray-applied GRC, resulting in no segregation after forming. Waterproofing agents: improve impermeability, raising the GRC impermeability grade from P8 to above P12. Waterproofing agents were added to Qinglong's GRC roof components for the Hainan International Convention and Exhibition Center, requiring no additional waterproofing measures and showing no water seepage in 10 years of use.

II. Types of Admixtures Strictly Prohibited in GRC

Admixtures are prohibited mainly due to performance damage and long-term risk considerations, in three categories. Chloride-containing admixtures: such as calcium chloride and ferric chloride, can cause excessive chloride ion content, leading to corrosion of metal connectors and degradation of GRC strength. Qinglong strictly prohibits the use of any chloride-containing admixtures. High-alkali admixtures: products with alkali content ≥5% intensify alkali-aggregate reactions and corrosion of alkali-resistant fibers, shortening GRC service life. All admixtures selected by Qinglong have an alkali content of ≤3%. Inferior retarders/accelerators: products containing formaldehyde or nitrites not only affect performance but may also cause environmental pollution and reduce the long-term durability of GRC. Qinglong only selects environmentally friendly admixtures that comply with the national standard GB 8076. Other prohibited types: admixtures containing air-entraining agents increase GRC porosity and reduce strength, and are prohibited across the board unless specially required.

III. Corporate Standards and Practices for Admixture Selection

Qinglong has established a three-tier "selection - testing - application" process to ensure admixture compatibility. Selection criteria: give priority to admixtures with good compatibility with low-alkali cement and alkali-resistant fibers; suppliers must provide third-party test reports. Small-batch testing: before a new admixture is used, mix proportion tests are conducted to verify that there is no negative impact on workability, strength, or durability; Qinglong's laboratory keeps more than 20 compatible admixture formulations in reserve. Project adaptation: admixture types are adjusted according to project environment and process, such as increasing the waterproofing agent dosage for coastal projects and using low-freezing-point antifreeze agents (non-chloride type) for winter production. Standard compliance: fully comply with the requirements for admixtures in the Technical Standard for Building Applications of Glass Fiber Reinforced Cement (GRC) (JGJ/T423-2018), preventing any prohibited products from entering use.