Study on early strength and workability of high volume fly ash and nanosilica mixes

Abstract

Global cement production contributes around 7% of annual CO, emissions, not only through energy consumption but also through the calcination of limestone. Hence, the use of high volumes of supplementary cementing materials in cement mixes is considered strategic to reduce environmental degradation. In commercial practice, the dosage of fly ash is limited to 30-40% by mass of the total cementitious material. Larger percentages of fly ash will be more environmentally friendly but may diminish quality. The focus of this research is to recover diminished properties of High Volume Fly Ash (HVFA) mixes by adding nano silica. Preliminary results of the investigation such as early strength gain and workability aspects are addressed in this paper. Early strength (3 day and 7 day) of cement paste mixes with fly ash replacement of 30%, 50% or 70% -and 3% or 6% nanosilica were investigated to identify effect on nanosilica on HVFA mixes. The flows of each mix were measured to get an insight about an adequate superplasticizer dosage for sufficient workability for different proportions of flyash and nanosilica. It was found that 3% nanosilica provided superior results than 6% nanosilica for all flyash percentages. The 70% Flyash series exhibited lower 3 day strength even but rose considerably at 7 days. Sufficient workability can be achieved in 3% and 6% NS cement paste mixes when superplasticizer dosage is 1200ml and 1500ml respectively per 100 kg of cementitious material.