MICROSTRUCTURE AND MECHANICAL PROPERTIES OF CONCRETE WITH TREATED RECYCLED CONCRETE AGGREGATES
Keywords:Recycled concrete aggregates, RCA treatment, Sulfuric acid, Silica fume, RCA concrete, SEM
Recycled concrete aggregates (RCA) are sourced from construction demolitions. Weaker
concrete, however, often resulted when using RCA as partial or full replacement of coarse aggregates due to
old mortar in RCA. Several treatment methods target this old mortar to completely remove it, or enhance its
properties, to make RCA suitable for construction use. Three treatment methods were employed in this study:
(1) sulfuric acid (SA), (2) silica fume impregnation (SF), and (3) the combination of both sulfuric acid and
silica fume (SASF). Experimental investigation showed improvement in the physical properties of RCA
compared to untreated RCA, however, statistical tests showed that these improvements were not significant.
SA treatment was found to have a detrimental effect on the surface of RCA, which developed a weaker layer
of adhered mortar on the RCA surface resulting to a reduction in the mechanical strength of the concrete thus,
its strength is lower compared to concrete with SF-treated RCA. SF treatment resulted in improved
compressive strength in comparison to untreated RCA concrete, SA-treated RCA concrete, and SASF-treated
RCA concrete. It was also observed that 50% RCA replacement in all concrete mixes with treated RCA resulted
to highest obtained compressive strength.