Effective Protection of Concrete Against Carbonation by a Protective Render Coating
Lukáš Húlek, Michal Bačuvčík, Ivan Janotka, Jakub Gašpárek, Peter Paulík
Appears on pages(s):
cementitious render coat; concrete; carbonation; non-permeability; microstructure; barrier
During the diagnostics of 100-year-old concrete bridges carried out between 2014 and 2022-4 mm (0.078- 0.157 in.) protective render coats (PRC) were found on nine bridges in Slovakia. Most of the PRCs measured appeared almost impermeable, showing a permeability coefficient below 0.246 × 10-16 m2 (0.293 × 10-16 yd.2). At these sites, the underlying concrete was carbonated to a depth of 0 up to 2 mm (0.078 in.), while under spalled PRC was the measured depth of carbonation of concrete up to 80 mm (3.15 in.). The field experiments were followed in a laboratory by the development of PRC from currently available materials. The newly-developed PRCs are characterized by a high weight ratio of ordinary Portland cement (OPC) to natural silica sand, low water content, and, at the same time, capable of being applied in thin layers. The PRCs were applied to a surface of a concrete panel and were tested for permeability (the Torrent method), adhesion (the square target method), crack propagation, microstructure, and pore structure. The resistance to carbonation of the C20/25 strength class (2900/3625 psi) base concrete and those that were PRC-protected were verified by an accelerated carbonation test [20 °C (68 °F)/60% RH/20% vol. CO2].