Abstract
Due to the porous characteristics of cement-based materials, they are often corroded by salt solutions, which results in decreased durability, especially against damage under freeze-thaw cycles (FTCs). Improving surface properties is an effective way to improve the durability of these materials. In this study, a hydrophobic coating was applied to the surface of cement mortar by chemical modification of low surface energy materials. Fourier transform infrared spectroscopy (FT-IR) showed that low surface energy substances are linked to hydration products through chemical bonds. A water contact angle test indicates that the surface of cement mortar changed from hydrophilic (θ = 14°) to hydrophobic (θ = 140°) after chemical modification. The cumulative water uptake of hydrophobic samples decreased by 90%. Meanwhile, the wear resistance of the hydrophobic coatings was excellent. Compared with the baseline sample, mass loss rate, flexural strength, and compressive strength of hydrophobic coating samples increased several-fold in the FTC test. Microstructural changes of the mortar were characterized by scanning electron microscopy. The results show that a hydrophobic coating can significantly improve the freeze-thaw resistance of cement-based materials. The formation of a hydrophobic layer on the surface of cement-based materials can improve their durability. The research results not only have applications in civil engineering but will also have great impact in the restoration of historic structures.
Highlights
Concrete is a type of building material based on cement with highly effective mechanical properties; it is widely used as a structural material for buildings, bridges, undersea tunnels, etc
Both modern and historical buildings are usually corroded by salt solutions, by which water penetrates the concrete, which is a factor contributing to concrete degradation. e freeze-thaw cycle (FTC) in severely frozen regions will cause sustained damage to concrete due to osmotic pressure, water expulsion, and inpore crystallization during the FTC process [1,2,3,4,5,6]
Ordinary Portland cement (OPC) was used as the binding material in all mortar specimens. e chemical composition of the OPC is shown in Table 1. e aggregates were acquired from Xiamen ISO Standard Sand Co., Ltd., with particle diameters ranging from 0.5 to 2.0 mm
Summary
Concrete is a type of building material based on cement with highly effective mechanical properties; it is widely used as a structural material for buildings, bridges, undersea tunnels, etc. A water absorption test and FTC resistance test were used to evaluate the protective effect of the hydrophobic coating on mortar blocks. Is phenomenon can be explained by the Wenzel theory that a hydrophobic surface can be obtained by modifying the rough mortar sample with low surface energy materials.
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