What Are the Consequences of Not Applying Anti-Rust Treatment to Embedded Rebar After Welding? Corrosion Risk Warning for Qinglong GRC Embedded System

In GRC components, leaving embedded rebar (or steel plates) without anti-rust treatment after welding is equivalent to planting a "time bomb" inside the component. Welding completely destroys the original galvanized layer or anti-rust coating, forming oxide scale and micro-cracks under high temperature, making this area the weakest link in corrosion resistance within the entire embedded system. The consequences are severe, hidden, and delayed. Through failure analysis of multiple engineering accidents, Qinglong GRC has clearly revealed the development path and failure modes of this risk.

In a large commercial complex in a southern Chinese city, sections of the GRC cornice decorative lines fell six years after completion. Post-incident inspection revealed that the fall was caused precisely by this: after the embedded steel plates were welded to the connecting angle brackets, the weld points and heat-affected zones had received only a simple coat of paint, and the paint film had long since deteriorated. In the long-term damp environment, the steel plates at the weld points corroded severely, with cross-section loss exceeding 50%, ultimately leading to brittle fracture under wind load. More seriously, the corrosion products expanded in volume (up to 2-7 times the original volume), generating enormous expansion stress on the surrounding GRC matrix, causing radial micro-cracks inside the GRC panel centered on the weld points and accelerating media intrusion.

Corrosion Drastically Reduces the Load-Bearing Capacity of Embedded Parts

Once the welded area loses its protection, corrosion spreads outward from the weld point. Corrosion reduces the effective cross-section of the rebar/steel plate, significantly lowering its tensile and shear load-bearing capacity. Under alternating stresses such as dynamic wind loads, the corroded area is prone to stress concentration, triggering fatigue fracture—a failure that often occurs suddenly without obvious warning signs.

Rust Expansion Causes Cracking and Spalling of the GRC Matrix

The volume of rust is far greater than that of the original steel. When this expansion force is restrained by the dense GRC matrix, it generates enormous internal stress (up to tens of MPa). When the internal stress exceeds the tensile strength of GRC, it causes cracks along the rebar or spalling of the cover layer centered on the corrosion point. This not only compromises the integrity of the component but also provides a fast channel for corrosive media such as moisture and chloride ions to reach the rebar and the deeper matrix, forming a vicious cycle.

Accelerates the Overall Durability Degradation Process

Water and ions penetrating from the corrosion point diffuse along the capillary pores or micro-cracks inside the GRC, potentially triggering electrochemical corrosion of other non-corroded metal parts, or reducing the alkalinity of the GRC matrix and weakening its protection of the glass fibers. The failure of anti-rust protection at a single weld point can become the "breach point" leading to premature failure of the entire component or even a local system.

Increases High Later-Stage Repair Costs and Safety Risks

Corrosion of the embedded system is hidden internally and difficult to detect during routine inspections. Once external signs such as cracking or spalling appear, internal corrosion is often already very severe, requiring the complete removal and replacement of the component—at high cost and disrupting normal building use. More seriously, components may fall without any warning, causing safety accidents.

Anti-rust treatment of embedded rebar after welding is a "mandatory" process in GRC component production and must never be omitted or handled perfunctorily. Qinglong GRC's standard process requires: after welding, weld slag, spatter, and oxide scale must be thoroughly removed, followed by two coats of epoxy zinc-rich primer for sealing, with a paint film thickness of no less than 120μm. For critical projects, embedded parts that are welded first and then hot-dip galvanized as a whole are even required, eliminating this risk at its source.