A compatibility study of ordinary Portland cement and flyash based cement with nano-silica

With the advent of 21st century, the construction industry faces a broad range of challenges from the new advanced materials like ‘nano’ materials in terms of applications, dosage, compatibility etc. Nanomaterials have very interesting properties as their size dictates its physical and chemical properties, while bulk materials have constant physical properties regardless of size. Also, Fly ash, a coal combustion product, primarily generated from the thermal power plants and originally considered a hazardous waste, which was previously normally discarded into the atmosphere, now requires that it be captured prior to release, as per new pollution norms. Looking at the future projections of flyash generation it is expected that, in spite of the massive initiatives taken by the government, there will be continued dependence on high ash coal to meet the future targets of power generation to achieve the objective of ‘power to all’. But going by the current rate of 33.5% flyash utilization the cent percent utilization as prescribed by the government remains a distant dream. As of now, there is not much literature available regarding the compatibility of these two materials i.e. nano-materials with fly ash. Our paper reports that with small addition of nano particles viz. Nano-silica (nS) to ordinary Portland cement(OPC) have enhanced both the short term & medium term strength of cement mortar when added in optimized quantities with respect to the weight of cement & water added as per the normal standard consistency formula of the Indian standards but their long term strength remains inconsistent. The OPC mortar compressive strength determined as per IS:4031 shows a 32.55% increase in strength at 0.75% nS (optimized addition) at 28 days, with the rate of strength gain increasing up to 59.8% at 90 days but then falling by 8.4% & 4.96% at 180 & 365 days, at same optimization. This optimization varies with Portland Pozzolona Cement (PPC) with 1% nS w.r.to cement wt. where it is observed that the consistency in gain of strength at 28 has been retained in the long term of 365 days showing a strength of 35.5N/mm2 which is more than 12% increase over that of OPC (31.5N/mm2) at same optimizations. Thus this Paper aims to explore the fact that fly-ash based cement containing 15%-35% fly-ash (as per Test Certificate), like Portland Pozzolona cement (PPC) have arrested this long term inconsistency to a certain appreciable extent due to its pozzolanic activity, finely divided