PDMS-OH and nano-SiO2 Modified KH570-TEOS silica-sol coating and protective effect on concrete

Concrete structures fail when external water and aggressive particles penetrate and cause problems such as acidification and rusting of internal steel structures. Nowadays, surface protective coatings are mostly used to protect concrete. However, there are problems such as poor water resistance of inorganic coating and poor adhesion of organic coating. In this paper, we use sol-gel method to compound organic and inorganic materials with γ-methacryloyloxypropyltrimethoxysilane (KH570) using ethyl orthosilicate (TEOS) as the inorganic precursor, and combine the advantages of both to prepare a highly waterproof concrete surface coating. The composite coating was further modified using hydroxyl end-blocked dimethylsiloxane (PDMS-OH) as well as nano-SiO2. It was finally found that the best performance of the silica sol was obtained when HCl was used as the catalyst, the pH was adjusted to 3.5, and the mass ratio of KH570 to TEOS was 2:1. Its water absorption rate after seven days of immersion was only 0.36 wt%. Further modification of the composite sol was found that the addition of 30 wt% PDMS-OH and 0.5 wt% nano-SiO2 had the best effect on the modification of the composite sol. Its water absorption was only 0.09 wt%, which was 98.2% lower compared to the uncoated concrete, after 7 days of immersion in the seawater simulation solution. The internal Cl− content was only 20 mg/L after soaking in 5 wt% NaCl solution for seven days, and the Cl− concentration decreased by 95% compared with the blank concrete.