Recent Advances and New Discussions on Superhydrophobic Coatings and Admixtures Applied to Cementitious Materials

Laísa Do Rosário Souza Carneiro,Péter Ludvig,Manuel Houmard

doi:10.2174/1874836802014010400

Abstract

Increasing the durability of buildings is one of the biggest challenges of the construction industry of the 21st century. The problems concerning durability are usually related to the presence of humidity or to water infiltration in the porous cementitious materials used in buildings. Advances in biomimetics have allowed the development of superhydrophobic surfaces and materials, with contact angles greater than 150°, which are able to repel water and aqueous products. In this context, this work summarizes the recent advances on superhydrophobic coatings and admixtures applied to cementitious materials. Recommendations for the future improvement of such products are made. The synthesis of superhydrophobic coatings generally includes the deposition of a low surface energy material (LSEM), especially fluoroalkylsilanes, on a microroughened surface, which, in cementitious materials, is usually achieved with the help of nanoparticles or micrometric molds. In this sense, variables as the spraying time duration, and the nanoparticles concentration, surface area and average particle size were identified as directly influencing the surface superhydrophobicity. Functionalized nanoparticles can also be introduced in cement matrix during the paste mixing in order to obtain a longer lasting waterproofing effect. In this case, hybrid nanosilica may react with Ca(OH)2 through pozzolanic reaction. The C-S-H formed may incorporate the organic group of hybrid nanosilica, and might present superhydrophobicity as well, modifying the composite’s microstructure. Besides, the cost of fabricating hydrophobic materials is decisive for their market entry. Hence, the partial or total replacement of fluoroalkylsilanes with less expensive LSEMs seems promising and needs to be further explored.

Highlights

One of the greatest technological challenges of the 21st century construction industry concerns the improvement of durability of the buildings
A surface is characterized as hydrophobic when the water contact angle (WCA) on it exceeds 90o
Table 1. – Water contact angles (WCA) and sliding angles (SA) of hydrophobic cementitious coatings synthesized by the single use of low superficial energy materials (LSEMs) or by combining low surface energy material (LSEM) with nanoparticles to reach the superhydrophobicity

Summary

INTRODUCTION

One of the greatest technological challenges of the 21st century construction industry concerns the improvement of durability of the buildings. In the adapted Cassie Baxter model, a heterogeneous wettability state is reached, in which air is trapped between the solid surface and the water droplet (Fig. 1b) [9 - 13]. Such former state usually allows reaching the highest contact angles and, the superhydrophobicity. Some researchers have explored the use of superhydrophobic admixtures in concrete, which are incorporated during the paste mixing [25 - 28] This method aims to prolong the hydrophobic effect in cement-based materials, since coatings tend to lose their efficiency over time. With the aim to promote the technological improvement of such materials, research gaps are identified and recommendations for future work are made

SUPERHYDROPHOBIC COATINGS APPLIED TO CEMENTITIOUS MATERIALS

RESEARCH GAPS AND RECOMMENDATIONS FOR

Findings

CONCLUSION