| Three vital factors, namely environmental protection, savings in costs, and strength/durability benefits, make it advantageous to incorporate fly ash of controlled quality and composition in all concrete made from construction demolition (C&D) recycled aggregate. The specific objective of this research was to compare the performance characteristics of High-Volume-Fly-Ash (HVFA) structural concrete containing C&D aggregate with that of normal recycled aggregate concrete containing no fly ash.; A coordinated experimental program was undertaken which comprised of (1) Compressive and Split Tensile strength tests; (2) ASTM durability tests by measuring resistance to chloride-ion penetration; and (3) Flexural strength tests on reinforced concrete beam specimens. Three mix designs were used, all of which had the same water/cement ratio of 0.45 and the same amount of recycled aggregate/yd3. Mix 1 contained cement and no fly ash, Mix 2 contained 16% replacement of cement by weight, and Mix 3 contained 40% replacement of cement, called a HVFA mix. Results indicate that fly ash increases compressive strength, improves both moment carrying capacity and tension resistance, and increases resistance to chloride-ion attack. |
