On the performance of film formers versus penetrants as water-repellent treatment of High-Performance Concrete (HPC) surfaces

A common way to conserve the aesthetic appearance of High-Performance Concrete (HPC) surfaces against e.g. undesired changes in colour is to apply water-repellent treatment. For this purpose, two types of treatment i.e. film former and penetrants are commonly employed, with film formers developing a continuous film on the surface, whereas penetrants line the near-surface pores of the substrate. In this paper, the performance of these two types of treatment - when subjected to artificial weathering (IJV irradiation and humidity) - is assessed by colourimetry, static contact angle (CA) measurements, scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). The obtained results revealed that both types of treatment led to hydrophobic properties by reducing the surface free energy (SFE) with the extent depending on the chemical functionalities of the used waterrepellent agents. The film former successfully hindered water from extracting the soluble calcium bearing constituents from the hardened cement paste and, thus, prevented the deposition of efflorescence onto the HPC surfaces. The smaller penetration depths of the penetrants due to the low permeability of the investigated HPC, on the other hand, most likely allowed for the formation of transport pathways into the bulk material allowing water to extract the soluble calcium-bearing constituents. Based on the provided experimental basis, the underlying mechanisms of water-repellent treatment when applied to HPC are highlighted and guidelines for the proper selection of surface treatment according to the protection desired are given. (C) 2019 Elsevier Ltd. All rights reserved.