Polymer for Internal Hydrophobization of Cement-Based Materials: Design, Synthesis, and Properties.

Xiao Liu,Shanshan Qian,Ziming Wang,Chunlei Xia,Xiaofei Song,Qian Xu,Suping Cui,Xiaoning Li,Ting Li

doi:10.3390/polym13183069

Abstract

A series of novel comb-like poly(butyl acrylate)-g-poly(dimethylaminoethyl methacrylate) (PBA-g-PDMAEMA) with different side chain lengths were designed and successfully synthesized by the “first main chain then side chain” method. Infrared Spectroscopy (IR), 1H Nuclear Magnetic Resonance (1H NMR), and gel permeation chromatography (GPC) were used for structural confirmation and molecular weight characterization. This polymer exhibited responsive behavior from hydrophilicity to hydrophobicity under the alkaline environment of cement-based materials, with the contact angle of 105.6°, a decreased evaporation rate, and a hydrophile–lipophile balance (HLB) value. A significant internal hydrophobic effect on cement mortar was shown in the water absorption rate, which decreased by 75.2%, and a dry shrinkage-reducing rate of more than 30%. Furthermore, this polymer can effectively slow the exothermic rate, reduce the heat release, and delay the exothermic peak of cement hydration. It was interesting that these properties showed a direct correlation with the side chain length of the comb polymer. The aims of this study are to provide a new avenue to synthesize polymers with the spontaneous hydrophilicity–hydrophobicity transition in the cement system, achieving excellent internal hydrophobicity of cement-based materials, and to offer a promising alternative to resist external erosion for improving the durability and service life of cement-based materials.

Highlights

With the development of construction engineering technology, concrete materials play a very important role in the construction of modern projects, and have become more indispensable [1] due to the advantages of a high strength, easy casting, low cost, etc
Compared with the blank sample, the compressive strengths of sample 25:1 at 14 days and 28 days decreased by 3.1% and 2.1%, respectively, but the flexural strengths of the samples decreased slightly more. These results showed the same trend of the water absorption rate and the dry shrinkage rate of cement mortars, that is, the longer the side chain length of comb-like poly butyl acrylate (PBA)-g-PDMAEMA was, the higher the mechanical strengths of cement mortars were
Its main chain can hydrolyze under the alkaline environment of cement-based materials to produce anchoring groups that can adsorb on the surfaces of cement particles, and its side chains can achieve the conversion from hydrophilicity to hydrophobicity in an alkaline environment and produce an internal hydrophobic effect in cement-based materials

Summary

Introduction

With the development of construction engineering technology, concrete materials play a very important role in the construction of modern projects, and have become more indispensable [1] due to the advantages of a high strength, easy casting, low cost, etc. The shrinkage of concrete leads to internal cracking [3,4], which will reduce the strength, make it easier for external harmful substances to enter the interior, and accelerate the deterioration of the durability of concrete, affecting the quality of the project and the service life of the building [5,6]. To reduce the shrinkage and cracking of concrete and extend its service life, water-tight and self-compacting concrete [12] can be used to reduce the entry of water and other corrosive substances. The more effective technical approaches to protect the concrete structures mainly include: a coating surface protection layer [13,14] to avoid or limit water into the concrete interior, or adding an emulsion admixture [15] to reduce internal capillary pressure

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Conclusion