Abstract
This study is to investigate the effect of recycled fine aggregate on the properties of alkali activated slag-based concrete. In the review of the literature, NaOH and KOH are the common alkali activator for alkali activated concrete, but have a number of problem including safety issues. This study firstly used recycled fine aggregate that contains high alkalinity, in order to activate the hydration of blast furnace slag. In addition, ordinary Portland cement was used as a replacement of blast furnace slag, in order to increase the level of alkalinity. In the experimental test, the recycle fine aggregate replaced natural fine aggregate (RA) and the ordinary Portland cement (OPC) replaced blast furnace slag. The replacement ratios of both alkali activators were equally 0, 10, 20, 40, 60, 80 and 100%. Test results showed that the increase of RA and OPC increased slump flow and dramatically accelerated initial and final setting times. In particular, replacement with RA of over 60% accelerated final setting time faster than the concrete with OPC of 100%. By replacing NA with RA, later compressive strength of all concrete specimens increased. pH value sharply rises in early age, regardless of the replacement ratio for OPC and RA, and as far as curing temperature is concerned, OPC shows no big difference in proportion to the increasing pH, whereas RA shows the higher value of compression strength at $35^{\circ}C$ than at $20^{\circ}C$, provided pH remains the same. In conclusion, despite of low initial strength, RA of an eco-friendly material is more efficient than OPC as an alkali activator in terms of developing later strength of alkali activated concrete.
