A Systematic Approach for Optimising Water to Binder Ratio for Low Carbon Concrete

Australia’s Net Zero 2050 policy has set an aggressive target of 43% reduction in greenhouse gas (GHG) emission by 2030. Embodied carbon (EC) constitutes a significant portion of GHG emissions, therefore, needs to be minimized for achieving the New Zero objectives. Concrete is the preferred construction material due to its better whole of life cycle performance and lower EC as compared to other construction materials such as steel, aluminum, timber etc. Portland cement (PC) is generally only 12-15% of concrete but is responsible for approximately 90% of concrete’s embodied carbon. The supplementary cementitious materials (SCMs) such as fly ash, ground granulated blast furnace slag (GGBFS), and metakaolin, are commonly used to replace a portion of PC in concrete for reducing EC and improving the performance. The strength and durability of concrete is influenced by the water and binder (w/b) ratio, which is used for customizing concrete to suit an application. The water demand varies with the binder composition and is generally determined by trial-and-error. The determination of optimum w/b becomes challenging when binary, ternary, and quaternary binders are used to lower the EC of concrete while complying with the performance requirements. This paper presents a systematic method for determining the optimum water demand for low carbon concrete mixes with minimal trials.