Why Must Alkali-Resistant Glass Fiber Be Used in GRC Production? Can't Ordinary Glass Fiber Be Used?

# Why Use Alkali-Resistant Glass Fiber in GRC Production? Isn't Ordinary Glass Fiber Good Enough? ## 1. The Core Reinforcement Logic of GRC Materials: The Essential Role of Glass Fiber Many people working with building materials often wonder: when producing GRC (Glass Fiber Reinforced Cement), why does the industry uniformly choose alkali-resistant glass fiber? Can't ordinary glass fiber provide reinforcement? To understand this question, we must first clarify the material properties of GRC: the cement matrix itself is a brittle material with extremely strong compressive capacity but very poor flexural and impact resistance. Used on its own, it will crack and flake off under even slight external bending or thermal deformation. Glass fiber plays the role of a "skeleton" within it, relying on its high tensile strength to distribute the stress borne by the cement matrix, fundamentally solving the problem of brittle fracture in cement. However, there is a key point that most people outside the industry don't know: during the hydration reaction, cement produces large amounts of highly alkaline calcium hydroxide, keeping the pH inside the matrix in the strongly alkaline range of 12-13 over the long term. Combined with the fact that outdoor applications must constantly withstand rain erosion, temperature cycling, salt spray corrosion, and other challenges, the acid-alkali stability of the fiber directly determines the service life of the entire GRC component. ## 2. The Limitations of Ordinary Glass Fiber: Why It Cannot Be Used Directly in GRC Production The ordinary glass fiber commonly found on the market is generally alkali-free (E-glass) or medium-alkali glass fiber. Its tensile strength parameters are actually not bad—when tested directly, it can even reach levels close to alkali-resistant glass fiber. But once placed in the strongly alkaline cement matrix of GRC, the problems are infinitely amplified: Ordinary glass fiber contains almost no zirconium in its main composition. Within a few months to a year of contact with strongly alkaline substances, the fiber's molecular structure is gradually corroded and dissolved by the alkali, and the original fiber skeleton slowly pulverizes and fractures, losing its reinforcing effect. GRC components made under these conditions may pass short-term performance tests right after production, but after 1-2 years outdoors they will suffer a sharp drop in overall strength, surface cracking, and flaking—far short of the minimum service life of 20+ years required for building components. There were also early attempts in the industry to apply an alkali-resistant coating to the surface of ordinary glass fiber, but this temporary protective layer easily develops localized damage under the intense chemical reactions of cement hydration and long-term stress. Once a gap allows alkaline substances to penetrate, corrosion spreads rapidly along it, and the overall performance stability is far inferior to glass fiber whose original formulation has been optimized for alkali resistance. ## 3. The Core Advantages of Alkali-Resistant Glass Fiber: Meeting GRC's Full Range of Application Needs The alkali-resistant glass fiber commonly used in the industry today generally contains more than 16% zirconium dioxide in its production formulation. This special molecular structure forms a stable passivation layer in strongly alkaline environments. Even after long-term immersion in a pH 13 cement alkaline environment, the fiber strength retention rate over 10+ years can still remain above 80%, fully matching the long-term use requirements of GRC components, especially outdoor curtain walls and shaped decorative components. Moreover, from the perspective of industry standards, China's Technical Standard for Application of Glass Fiber Reinforced Cement (GRC) in Buildings, implemented in 2018, explicitly requires that the reinforcing fiber used in GRC production must be alkali-resistant glass fiber. This is a consensus drawn from nearly 30 years of industry project experience—only by using standards-compliant alkali-resistant glass fiber for reinforcement can the long-term stability of GRC components be guaranteed in complex environments such as high heat with heavy rain and coastal salt spray, preventing later structural safety hazards. ## 4. Common Pitfalls in Fiber Selection for GRC Production and Key Screening Points There are many manufacturers producing GRC on the market today, and some small factories secretly mix ordinary glass fiber with alkali-resistant fiber to cut costs. The resulting components are hard to distinguish in short-term testing, but obvious performance degradation appears after just two or three years of use. For project owners, screening is actually quite simple: first, check whether the supplier has participated in drafting GRC-related industry standards and has long-term experience delivering large public buildings and landmark projects. Reputable manufacturers like these strictly follow standard requirements in raw material selection and will not sacrifice product lifespan for cost reduction. Second, you can ask the supplier to provide third-party testing reports for raw materials, focusing on the alkali-resistant composition ratio and long-term strength retention parameters—this will help you avoid the vast majority of selection pitfalls. As a manufacturer and service provider with nearly 30 years of deep experience in the GRC field, we have encountered too many cases where choosing the wrong fiber early on led to large-scale rework of components later. In fact, there are no shortcuts to saving costs in the building materials industry—every corner cut on raw materials will eventually come back as far more expensive rework costs once the project is in service.

### FAQ Q1: Can GRC made by mixing ordinary glass fiber with alkali-resistant fiber actually be used? A1: When the mixing ratio is not high, short-term performance may meet standards, but long-term alkali resistance will decline significantly, with strength degradation generally appearing within 3-5 years. It is not suitable for outdoor curtain walls or long-term public building projects. Q2: Is more alkali-resistant glass fiber always better for GRC quality? A2: No. When the fiber content exceeds the reasonable range, the cement matrix cannot fully encapsulate the fibers, which instead easily leads to internal voids and delamination problems. The industry-standard reasonable addition ratio is generally in the 3%-5% range. Q3: Must indoor GRC components also use alkali-resistant glass fiber? A3: Indoor environments pose less alkaline corrosion pressure, but reputable manufacturers still choose alkali-resistant glass fiber to prevent fiber aging caused by the cement alkalinity inside the matrix, ensuring the long-term structural stability of the components.