Effects of Water-Binder Ratio and Fine Aggregate-Total Aggregate Ratio on the Properties of Hwangtoh-Based Alkali-Activated Concrete

Fifteen hwangtoh-based alkali-activated concrete mixes were tested to explore the significance and limitations of the development of cementless concrete without carbon dioxide emissions while maintaining various beneficial effects. Hwangtoh, which is a kind of kaolin, was incorporated with inorganic materials, such as calcium hydroxide, to produce a cementless binder. The main variables investigated were the water-binder ratio and fine aggregate-total aggregate ratio to ascertain the reliable mixing design of hwangtoh-based cementless concrete. The variation of slump with elapsed time was recorded in fresh concrete specimens. Mechanical properties of hardened concrete were also measured, including compressive strength gain, splitting tensile strength, moduli of rupture and elasticity, stress-strain relationship, and bond resistance. In addition, mechanical properties of hwangtoh-based cementless concrete were compared with those of ordinary portland cement (OPC) concrete and predictions obtained from the design equations specified in American Concrete Institute 318-05 and Comite Euro-International du Beton-Federation International de la Precontrainte for OPC concrete, wherever possible. Test results show that the mechanical properties of hwangtoh-based concrete were significantly influenced by the water-binder ratio and to less extend by fine aggregate-total aggregate ratio. Based on the measured mechanical properties and code provisions, it can be proposed that the hwangtoh-based alkali-activated concrete is practically applicable as structural concrete when the water-binder ratio is less than 40%.