Common Causes And Solutions For Corrosion At The Contact Between Terrazzo Prefabricated Panels And Metal Components

Corrosion at the contact between terrazzo prefabricated panels and metal components is a common problem in construction, mainly due to material properties, construction defects, or environmental factors that cause metal oxidation reactions in humid environments. The following provides a detailed analysis from two aspects: common causes and corresponding solutions:

1, Common reasons
1. Moisture infiltration and humid environment
Terrazzo is a porous material (composed of cement, stones, etc.). If there are cracks or poorly sealed joints on the surface or inside, rainwater, moisture, or condensed water will seep in, forming a humid environment when in contact with metal components. Metals (such as iron and steel) undergo electrochemical corrosion (rusting) under the combined action of moisture and oxygen.
Typical scenario: At the connection between prefabricated panels and metal brackets, keels, and fasteners, if the sealant ages or is not filled tightly during construction, water will infiltrate along the gaps.

2. Poor material compatibility (electrochemical corrosion)
After hydration, cement in terrazzo becomes alkaline (with a pH value of about 12-13). If the metal in contact is an active metal (such as ordinary carbon steel), it will form a microbattery due to potential difference: in alkaline environment, the metal is oxidized as an anode (Fe → Fe ² ⁺+2e ⁻), and oxygen in water is reduced as a cathode (O ₂+2H ₂ O+4e ⁻ → 4OH ⁻), ultimately forming rust (Fe ₂ O ∝· nH ₂ O).
Key point: Direct contact between metals and alkaline cement-based materials can accelerate corrosion, and even in the absence of external moisture, free alkali in cement may slowly corrode metals through capillary action.

3. Construction defects
Metal components not treated with rust prevention: The metal surface was not derusted, galvanized, or coated with rust prevention paint before installation, resulting in direct exposure of the metal to the environment.
No isolation measures for the contact surface: Metal comes into hard contact with terrazzo, and friction occurs due to thermal expansion and contraction during temperature changes, damaging the protective layer (such as plating and paint) on the metal surface.
Sealing material failure: The sealant used at the joint (such as silicone glue) is not resistant to aging, water, or the gap is not filled during construction, resulting in water infiltration.
4. Environmental factors
High humidity or salt spray environment: The air in coastal or humid areas contains salt and acidic gases (such as SO ₂), which can accelerate metal corrosion.
Large temperature difference: Repeated thermal expansion and contraction lead to cracking of the sealing material at the joint, and water infiltration exacerbates corrosion.
5. Improper maintenance
Long term failure to clean the dust and debris at the joints has resulted in stagnant water.
Use acidic cleaning agents (such as hydrochloric acid) to clean the surface of terrazzo and corrode the protective layer of metal components.

2, Handling measures
(1) Preventive measures (during construction or maintenance)
Material selection and protection of metal components
Prioritize the use of corrosion-resistant metals: stainless steel (304/316), galvanized steel, or aluminum magnesium alloy (note the compatibility between aluminum and cement to avoid alkaline corrosion).
Surface treatment: Before installation, thoroughly remove rust from metal components (sandblasting or wire brushing cleaning), apply anti rust primer (such as epoxy zinc rich paint) and topcoat (such as polyurethane paint), or perform hot-dip galvanizing treatment.
Isolation and sealing design
Contact surface isolation: Add flexible materials (such as rubber pads, plastic gaskets) between metal and terrazzo to avoid hard contact and reduce friction damage to the protective layer.
Seam sealing: Use weather resistant and water-resistant sealant (such as polyurethane sealant or silicone structural adhesive) to fill the gap between metal and terrazzo, ensuring no gaps.
Terrazzo surface treatment
Apply permeable sealant (such as silane waterproofing agent) to the surface of terrazzo during construction to reduce water infiltration.
Chamfering treatment should be applied to the edges of prefabricated panels to avoid water accumulation and retention.
(2) Steps for treating corroded areas
Cleaning of corroded areas
Mechanical rust removal: Use a wire brush, sandpaper, or grinding machine to thoroughly remove the rust layer on the metal surface until the metal substrate is exposed (presenting a metallic luster).
Chemical rust removal: If the rust is severe, it can be treated with acidic rust remover (such as dilute phosphoric acid), then rinsed with clean water and neutralized (with alkaline solution such as ammonia water), and finally dried.
Repair and Protection of Metal Components
Apply anti rust coating: Immediately apply epoxy zinc rich primer (thickness ≥ 80 μ m) after rust removal, and then apply topcoat (such as polyurethane or fluorocarbon paint) after drying to ensure that the coating is complete and free of omissions.
Replace severely corroded metal components: If the metal has corroded extensively or the structural strength has decreased, it needs to be replaced with corrosion-resistant materials (such as stainless steel).
Surface repair of terrazzo
Cleaning rust infiltration: If rust has infiltrated the surface of the terrazzo, it can be cleaned with a stone specific cleaning agent (neutral or weakly alkaline), avoiding the use of acidic cleaning agents.
Repair cracks or holes: For cracks or damages at the contact between terrazzo and metal, fill them with epoxy resin or terrazzo repair mortar, polish them flat, and apply sealant.
Joint sealing reinforcement
Remove the expired sealant and use a dry cotton cloth to clean the dust and moisture in the gaps.
Re fill the weather resistant sealant (such as polyurethane adhesive) to ensure that the adhesive fills the gaps and firmly adheres to the materials on both sides, with a smooth surface treatment.

(3) Daily maintenance suggestions
Regular inspection: Check the joint sealant for aging and cracking every six months, and check for signs of rust on metal components.
Cleaning management: Use neutral cleaning agents (pH 7-8) to clean the surface of terrazzo, avoiding acidic or strongly alkaline cleaning agents from corroding the metal.
Drainage diversion: Ensure that there is no accumulated water on the surface of the terrazzo, no debris blocking the joints, and maintain smooth drainage.
summarize
The corrosion core at the contact between terrazzo and metal is a combination of "moisture+metal+alkaline environment", which needs to be comprehensively solved through material selection (corrosion-resistant metal), isolation sealing (reducing water penetration), surface protection (anti rust coating), and regular maintenance. When handling, it is necessary to first clean the rust, then repair the metal and terrazzo, and finally strengthen the seal to ensure long-term durability.