Decarbonizing concrete: A comprehensive review of fly ash and silica fume for low-carbon, durable, and sustainable cementitious systems

The construction industry has an imminent obligation to adapt to climate change and work to diminish carbon emissions through innovative sources and alternatives to traditional Portland cement. Between numerous alternatives, construction materials like fly ash (FA) and silica fume (SF) work as supplementary cementitious materials (SCMs). FA and SF construction materials are a viable alternative considering their potential environmental impact and construction performance. The present study analyzes literature published from peer-review journals from 2000 and a projected 2025 to understand the performance of FA and SF in the construction of low carbon and durable concrete systems. From the synthesis of various studies, it has been found that substituting FA and SF as partial cement replacements leads to a large reduction of CO2 emissions that are a direct result of the reduction of clinker production and an increase in the strength and durability of concrete. It has also been found that up to 15-30% FA as a partial cement substitute improves long-term strength as well as improves workability of concrete which is due to the spheroidal shape of the particles and the slow pozzolanic reaction. In addition, up to 10-20% of SF as a partial cement replacement will increase the early ages strength of concrete and reduce the permeability of concrete due to the smaller sizes of the SF particles and the rich silica content. It is also found that the use of both SF and FA improves the long-term durability of concrete structures and reduces the intent of chloride and sulphate ions. SF and FA further control the density of the cement and reduces permeability as well as the intent of ailed ions. Besides the technical benefits, the use of these industrial by-products also fosters waste valorization and the construction of resource-efficient buildings. Broadly, the review outlines the synergistic potential of FA and SF along with their positive impact on developing sustainable, high-performance concrete, and highlights the potential of these materials in the construction of resilient, low-carbon infrastructure systems.