Laboratory and field performance of biodegradable release agents for hydraulic concrete

Raw vegetable oils and their emulsions have been used as biodegradable release agents for concrete. However, there is no scientific explanation linking the chemical composition to their release performance. The present study was divided into two phases. In the first phase, different vegetable oils with varying degrees of refinement were chemically characterized by middle range Fourier transform infrared spectroscopy (Mid-FTIR), and their viscosities were measured. For comparison purposes, two commercial release agents based on mineral oil were used. In the second phase, emulsions containing bleached soybean oil, water and some emulsifiers were prepared. The performance of the oils and emulsions as demolding agents in steel/concrete interfaces was measured by visual rating, image analysis and bond strength. The results indicate that almost all of the vegetable oils showed better performance than that of the two mineral oil-based agents, which is explained by the higher affinity of glycerol esters for metal surfaces and higher intermolecular interactions. The Mid-FTIR espectrum analysis indicates that oils having larger absorption areas under the curve at the methylene group exhibit better performance as release agents. In addition, the Mid-FTIR analysis allowed identification of the main molecular groups and differentiation between oil samples. In the second phase, the water/oil emulsion stabilized with organophilic clay performed the best. In addition to the lubricating effect of the emulsion, the better performance was also due to the saponification reaction between the acylglycerides and the Ca(OH)₂. The tangential adhesion was reduced to approximately 64 % compared to that of a mold without a release agent.