Four-year behavior of polymer-cement coatings for concrete protection

An aqueous emulsion of an acrylic polymer (based on 2-ethylhexyl acrylate) was mixed with cement and fine aggregate and was studied as rubberlike coating to protect reinforced concrete beam specimens. Three 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, 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. Coated beam specimens were kept for 4 years in three different environments (laboratory at 20°C and 65% R.H.; natural environment exposed to 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 crack of the concrete substrate. The latter was determined by measuring the crack width of the concrete substrate beam when the coating started to break under flexural stress. Bond strength of the coatings was substantially unchanged or slightly improved by the exposure to the three different environments. On the other hand, the crack-bridging ability of the polymer-cement coating remained substantially unchanged up to 4 years in laboratory conditions, whereas there was a small flexibility loss of the coating in humid environment, particularly in the permanent underwater exposure. However, even in these less favorable conditions the crack-bridging ability of the three coatings was still satisfactory after 4 years.