The compatibility of concrete release agents and polyurethane sealants directly impacts the sealing effectiveness and durability of concrete joints, requiring a comprehensive analysis based on chemical composition, construction techniques, and long-term performance.
The primary function of concrete release agents is to form a barrier on the formwork surface, preventing concrete from adhering to the formwork and protecting it from corrosion. Its composition typically includes a water-based polymer, mineral oil, or silicone oil; some products may also contain additives such as rust inhibitors and thickeners. Polyurethane sealants, on the other hand, are based on a polyurethane prepolymer and cure by reacting with moisture to form an elastic sealing layer, exhibiting excellent adhesion, elastic recovery, and weather resistance. Direct contact between the two can lead to interfacial reactions due to compositional differences. For example, the oily components in the release agent may hinder the sealant's bond to the concrete, creating a weak layer.
From a chemical reaction perspective, the mineral oil or silicone oil in oil-based release agents easily remain on the concrete surface, forming a hydrophobic layer. Polyurethane sealants, on the other hand, rely on reactions with hydroxyl groups or moisture in the concrete to achieve adhesion. Excessive release agent residues can significantly reduce the sealant's interfacial adhesion, leading to bond failure. Furthermore, the rust inhibitors in some release agents may contain heavy metal ions, which can catalyze reactions with the isocyanate groups in polyurethane, accelerating sealant aging and shortening its service life. Therefore, thoroughly removing any release agent residue from the formwork surface before application is crucial for ensuring effective sealing.
Application techniques also significantly impact the compatibility of the two. Uneven or excessive application of release agent can result in an excessively thick oil film on the concrete surface, making it prone to rolling during sealant application and preventing the formation of a continuous bond. Conversely, poor film-forming properties may cause partial peeling during formwork removal. Debris remaining on the concrete surface can become embedded in the sealant, creating stress concentration points and reducing the fatigue resistance of the joint. Therefore, it is important to strictly control the amount of release agent used during application and select a water-based release agent that is more compatible with polyurethane sealants. Its residue is easier to clean and minimizes the impact on sealing effectiveness.
Regarding long-term performance, release agent residue can accelerate the aging process of polyurethane sealants. Organic solvents in oil-based release agents can penetrate the sealant, disrupting its cross-linking structure, resulting in reduced hardness and loss of elasticity. If water-based release agent residue is not completely removed, it can breed microorganisms in humid environments, causing mold and mildew on the sealant surface, impacting its appearance and durability. Furthermore, certain components in the release agent may migrate with the plasticizer in the sealant, causing the sealant to harden or soften, losing its original performance.
To improve compatibility between the two, the following measures can be taken: First, thoroughly clean the concrete surface before construction by using a high-pressure water jet and wire brushing to ensure no release agent residue remains. Second, choose a concrete release agent specifically formulated for use with polyurethane sealants. Such products are typically tested for compatibility, and residues have minimal impact on sealing performance. Finally, apply the sealant promptly after construction to avoid prolonged exposure of the concrete surface and secondary contamination.
In actual application, the appropriate release agent type should be selected based on project requirements. For projects requiring extremely high sealing performance, such as bridge expansion joints and underground engineering joints, it is recommended to prioritize water-based release agents and strictly control the application process. For general building joints, oil-based release agents with better compatibility can be used, provided they are kept clean.
