Effect of Surface Modifications of Recycled Concrete Aggregate on Concrete Properties

Abstract

The experiment aims to test the specific way of producing concrete with recycled concrete aggregate (RCA). To reduce its negative impact on the concrete properties, two different ways of treatment of the RCA with geopolymer slurry were applied—coating during the mixing using the specific mixing approach and coating prior to the mixing of concrete. As control samples, a mixture prepared by natural aggregate only and a mixture with RCA that was prepared by standard mixing with no coating process were tested as well. The results of density, total water absorption, and compressive strength in periods of 28, 90, 180, and 365 days of curing are presented and evaluated. Both methods of coating of the RCA with geopolymer slurry allow for the preparation of concrete with properties comparable to those of normal concrete (prepared by standard mixing with natural aggregate); thus, it seems to be a promising way to enhance the rate of RCA application. The positive effect of coating is clearly visible after a longer period of curing (180 days). When comparing the methods of RCA coating, coating directly during the mixing yields somewhat better results; it is also positive from the technological point of view, since the process is simpler in practice.