Optimization of binary and ternary concrete composed of fly ash and ultra-fine slag using GRA

The paper presents the study of concrete made with supplementary cementitious materials such as Fly Ash (FA) and Ultra Fine Slag (UFS). Ordinary Portland Cement (OPC) is partially replaced with 20%, 30%, and 40% of FA by weight of cementitious content in three FA binary combinations. OPC is further replaced with 5%, 10%, 15%, and 20% of UFS to all three binary combinations forming twelve ternary combinations. The paper assesses workability, strength behaviour, chloride migration, water permeability, and cost aspect of all mixes. The results indicate that the use of FA binary combinations improves the workability but mechanical and durability properties are compromised. In case of FA-UFS ternary combinations, the compressive, flexural, and split tensile strengths have been observed to improve up to 36%, 13%, and 22%, respectively. Chloride migration and water permeability of ternary mix improve by 92% and 94% compared to reference concrete. An optimization technique using Taguchi-grey relational analysis (GRA) suggested that a ternary combination with 55% OPC, 30% FA, and 15% UFS qualify as an optimum mix combination.