Properties of polymer-cement coatings for concrete protection

An acrylic polymer was mixed with fine sand and cementitious binders. The mixtures were studied as rubber-like coating to protect reinforced concrete specimens. Three coatings (all with water-binder ratio of 0.50, polymer-binder ratio of 0.50 and sand-binder ratio of 2) were produced by changing the type of binder: Portland cement, pozzolan-portland cement with metakaolin and slag-based cement. The coatings were applied to a porous concrete substrate with a water-cement ratio of 0.80. Preliminary tests on uncoated and coated concrete specimens were carried out to study the penetration of water, carbon dioxide, chloride, and sulphate ions. The resistance to penetration of these aggressive agents was very poor in the uncoated specimens and became as good as that of a watertight and durable concrete in the coated specimens. Coated beam specimens were kept for 24 months in three different environments (laboratory at 20°C and 60% R.H.; outdoors environment exposed to natural changes in temperature and relative humidity; under water) in order to examine the influence of the binder type on the bond strength and the flexibility of the coating in terms of ability to bridge the cracks of the concrete substrate. Bond strength of the coatings was substantially unchanged or improved by the exposure to the three different environments. Initial flexibility of the coating was improved by the addition of metakaolin or slag. However, at later ages there was some flexibility loss, for coated concrete specimens exposed to water, when portland cement was used specially in the presence of metakaolin. No flexibility loss was found in the polymer-cement coating in the presence of slag.