What Problems Can Non-Standard Reinforcement Around Component Screw Holes Cause? Risk Analysis of Qinglong GRC Joint Reinforcement Technology

Screw holes (or anchorage zones for embedded inserts) on GRC components are areas of highly concentrated stress. If the hole edges are not reinforced according to standards, radial cracks can easily develop under service loads, and brittle spalling at the hole edge may even occur, leading to connection failure. This type of failure is localized and sudden, making it a safety hazard that cannot be ignored in GRC curtain wall projects. Qinglong GRC has established mandatory standards for hole-edge reinforcement across three stages—design, molds, and production—and verifies them through destructive testing.

Formation and Propagation of Radial Cracks at Hole Edges

When a screw is subjected to tension or shear, the force is transferred through the washer to the area around the GRC hole edge. If that area consists only of plain slurry with no fiber reinforcement or insufficient reinforcement, its tensile and shear strength is very low and cannot withstand the concentrated stress. The stress is released radially from the hole edge, producing cracks visible to the naked eye. These cracks not only weaken the connection strength at that location but also become channels for water and corrosive media to penetrate, accelerating corrosion of internal metal parts and deterioration of the matrix.

Concrete Spalling at Hole Edges and Connection Failure

Under alternating actions such as wind loads, cracks at the hole edge continuously propagate and interconnect, eventually causing the local GRC material at the hole edge to completely crumble and break away. The washer loses its support, the effective clamping length of the bolt is shortened, the connection loosens rapidly, and load-bearing capacity drops sharply. For anchor bolts under tension, such spalling can cause them to be pulled out entirely, resulting in serious accidents such as falling components.

Correct Methods for Standard Hole-Edge Reinforcement

To prevent the above problems, systematic reinforcement of hole edges is essential: Structural reinforcement: At the screw hole location, an embedded steel backing plate (typically 4-6mm thick) must be installed on the back of the GRC panel, with an area larger than the load-bearing washer, to spread the concentrated force over a larger area of the GRC panel. Material reinforcement: Within a radius of at least 50mm around the hole, an additional 1%-2% of chopped glass fibers should be added, or a small piece of alkali-resistant glass fiber mesh should be laid, to improve the crack resistance and toughness of this area. Process control: Holes should be pre-formed during production or drilled with dedicated tooling after curing; rough hole opening is strictly prohibited. Hole walls should be smooth and perpendicular.

Quality Inspection and On-Site Treatment

Before leaving the factory, specimens with embedded inserts or pre-formed holes should undergo pull-out testing, and the failure mode observed must be tensile breakage or pull-out of the metal part, not failure of the GRC at the hole edge. During on-site installation, if minor spalling or cracks are found at the hole edge, installation must be stopped immediately. Small defects can be repaired with epoxy mortar, while larger defects require replacement of the component. Flat washers and spring washers of appropriate size must be used during installation to ensure even distribution of pressure.

Although the screw hole edge is small, it is the vital “throat” of force transmission. Qinglong GRC treats hole-edge reinforcement as a “critical process point” in quality control. Through standardized design, mold positioning, production control, and factory inspection, we ensure that every connection node is safe and reliable, eliminating the risk of overall failure caused by local damage.