Durability and Mechanical Aspects of UHPC Incorporating Fly Ash and Natural Pozzolan

Silica fume (SF), an ultra-fine pozzolanic material that is a by-product of industrial processes, is essentially used as mineral filler in the manufacture of ultra-high-performance concrete (UHPC) at a high dosage. However, its high cost can be a significant barrier to UHPC production, particularly in areas where local sources are not available. The aim of this study is to investigate the feasibility of partially replacing SF with two other pozzolanic waste materials, fly ash (FA) and natural pozzolan (NP), for UHPC production. Six different mixes of UHPC were designed, produced and tested initially for workability and compressive strength, considering different constitutions of FA and NP to partially substitute SF. Based on fulfilling the minimum requirements of flow and compressive strength of a UHPC mix, three UHPC mixes, including the control mix with SF alone, were considered for a detailed assessment of their performance in terms of strength, shrinkage, and durability characteristics, including resistance against reinforcement corrosion. Results reveal that both pozzolanic waste materials can be used to replace SF up to 60% to produce UHPC mixes without compromising strength and durability. The outcome of this study would help in reducing the consumption of SF and produce UHPC by utilizing FA and NP as partial replacements of SF when SF is not available locally as a waste material.