A sustainable approach to designing high volume fly ash concretes

The construction industry is one of the significant contributors to global warming and the depletion of natural resources. It also contributes to about 40% of global energy usage and 30% of greenhouse gas (GHG) emissions while being responsible for 8% of worldwide carbon emissions. Though concrete is the most sought-after building material for the infrastructural needs in India, its production is far from environmentally sustainable. The recent growth in the construction projects sector puts India at risk of increasing the GHG emissions and natural resource depletion. Such issues are exaggerated further by the generation of industrial byproducts such as fly ash. India produced 624.56 lakh tonnes of fly ash from coal/lignite-based thermal power plants in 2021, of which about 21% is unutilized. The choice of building materials concerning the local climatic conditions, assessment of life cycle costs, and thermal comfort of buildings help resolve the issue. In addition, it is imperative to design concrete that incorporates industrial byproducts such as fly ash more than current codal provisions. The study presents the design and early-age test results of self-compacting concrete (SCC) and no aggregate concrete (NAC). While the SCC uses crushed granite stones and river sand as aggregates and replaces 60% of ordinary Portland cement (OPC) with fly ash, the NAC replaces 80% of OPC with fly ash and is devoid of any aggregates. The present study uses class F fly ash sourced from a specific electrostatic precipitator (ESP) field. The physical tests viz., wet sieve analysis, specific gravity, and pozzolanic activity index (PAI) along with the chemical analysis demonstrate the fly ash's quality. The flowability, passing ability, and viscosity tests show that the designed SCC mix exhibits necessary fresh properties. The SCC achieves a compressive strength of 34.72 MPa at seven days curing age while achieving more than two-fold improvement at 56 days. NAC shows equivalent compressive and similar flexural strength while the splitting tensile strength is not comparable enough to that of the SCC.