What Is the Mechanism by Which Steel Reinforcement Corrosion Causes GRC Component Cracking?

The core mechanism by which rebar corrosion causes GRC component cracking is “electrochemical corrosion → volume expansion → stress concentration → crack formation”. Corroded rebar expands 2-3 times in volume, generating tensile stress on the GRC matrix (exceeding the GRC tensile strength of 2MPa) and ultimately leading to cracking. Through its full-process anti-rust technology, Qinglong has achieved a rebar corrosion rate of ≤0.02mm/year in coastal projects such as Hainan Poly Peninsula No. 1, eliminating the risk of corrosion-induced cracking.

I. Electrochemical Corrosion: The Initiation Stage of Rebar Corrosion

Electrochemical corrosion is the root cause of rebar corrosion. Corrosion conditions: when moisture and oxygen are present inside GRC and the passivation film (Fe₂O₃) on the rebar surface is destroyed, a corrosion system of “anode (rebar) - cathode (GRC matrix) - electrolyte (moisture + chloride ions)” forms. Qinglong's tests show that when GRC moisture content >10% and chloride ion content >0.06%, the corrosion rate accelerates significantly. Corrosion process: an oxidation reaction occurs at the rebar anode (Fe→Fe²⁺+2e⁻), while a reduction reaction occurs at the cathode (O₂+2H₂O+4e⁻→4OH⁻). Fe²⁺ combines with OH⁻ to form ferrous hydroxide (Fe(OH)₂), which is further oxidized into ferric hydroxide (Fe(OH)₃) and ultimately becomes rust (Fe₂O₃·nH₂O). Qinglong's inspection of corroded rebar surfaces shows that rust thickness can reach 0.5-1mm.

II. Volume Expansion and Stress Concentration: The Key Process Leading to Cracking

The stress generated by volume expansion is the direct cause of cracking. Volume expansion effect: the density of rust (2.5-3.0g/cm³) is far lower than that of rebar (7.85g/cm³), so corroded rebar of the same mass expands 2-3 times in volume. Qinglong's measured data show that a 12mm-diameter rebar corroded to a depth of 1mm expands 2.2 times in volume. Formation of stress concentration: GRC has high compressive strength (≥30MPa) but low tensile strength (≤2MPa). The expanding rust generates outward tensile stress on the surrounding GRC, with stress concentrated in the 5-10mm zone around the rebar. When the tensile stress exceeds the GRC tensile strength, micro-cracks (width ≥0.1mm) appear. Crack propagation: as corrosion intensifies, stress continues to accumulate, and micro-cracks propagate from around the rebar to the GRC surface, forming through cracks (width ≥0.3mm). Qinglong tracked a component without anti-rust treatment: after 3 years, the crack width reached 0.8mm, with a rebar section loss rate of ≥15%.

III. Factors Affecting Corrosion-Induced Cracking and Qinglong's Prevention and Control Measures

Environment and workmanship affect the corrosion rate, so prevention must start at the source. Environmental factors: coastal salt spray, industrial pollution, and high-humidity environments accelerate rebar corrosion; the corrosion rate in coastal areas is 3-5 times that of inland areas. Qinglong uses 316 stainless steel for rebar in its coastal projects, reducing the corrosion rate by 80%. Workmanship factors: low GRC density (<2.1g/cm³) and a high water-cement ratio (>0.45) increase the penetration of moisture and chloride ions and accelerate corrosion. Qinglong controls the water-cement ratio at ≤0.40 and applies high-pressure vibration, achieving a density of ≥2.2g/cm³. Prevention and control measures: anti-rust paint (epoxy zinc-rich primer) applied to rebar surfaces, silane impregnation agent applied to GRC surfaces, and sealed joints to prevent moisture ingress. Qinglong's anti-rust technology keeps the rebar corrosion rate at ≤0.02mm/year. Project case: the GRC components at Hainan Changying Global 100 Fantasy Park, using stainless steel rebar + anti-rust coating + sealing treatment, have shown no corrosion-induced cracking and remain in good rebar condition after 8 years of use.