Aging effect on the properties of flexible surface coating for concrete protection

In the present work an acrylic polymer (based on 2-ethylhexyl acrylate) was mixed with cement and fine aggregate and was studied as rubber-like coating to protect reinforced concrete beam specimens. Two acrylic polymer-cement coatings (both with water-cement ratio of 0.50, polymer-cement ratio of 0.50 and fine aggregate-cement ratio of 2) were produced by changing the type of the cementitious component (Portland cement or high alumina cement). The two coatings were applied to a porous concrete substrate with a water-cement ratio of 0.80. Preliminary tests on the uncoated and coated concrete specimens were carried out to study the penetration of water, chloride, sulphate and carbon dioxide. 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. Then coated beam specimens have been kept for 1 year in three different environments (laboratory at 20°C and 65% R.H.; outsides environment exposed to natural changes in temperature and relative humidity; under water) in order to examine the influence of the ageing on the bond strength as well as the flexibility and therefore the ability of the acrylic coatings to bridge the cracks of the concrete substrate. The bond strength of the two coatings was substantially unchanged by the exposure to the three different environments. The flexibility of the polymer-cement coating remained substantially unchanged when portland cement was used independently of the exposure environment. On the other hand, when high-alumina cement was used there was a flexibility loss of the coating in humid environment, particularly in the underwater exposure.