Study on effect of fly ash and limestone powder on compressive strength of roller compacted concrete for dam construction

Abstract

Roller compacted concrete (RCC) is a special concrete having similar ingredients as in the case of conventional concrete, but in different proportions. Use of fly ash to replace significant proportion of Portland cement (PC) for RCC mix is very popular. However, use of limestone in RCC is not so popular. Limestone can act as an inert filler as well as can take part in hydration process and development of different hydration products to a limited extent. The study attempts to determine the optimal replacement levels of PC using fly ash and limestone for development of high volume fly ash based roller compact concrete with limestone filler for use in construction of dams in India by evaluating the fresh properties (in terms of Vee Bee time, density and setting time) and compressive strength (at 7, 28, 56, 90 and 180 days) for different RCC mixes having varying proportions of PC, fly ash and limestone. The study evaluation of 17 RCC mixes prepared by replacing PC to an extent of 72% (by weight of total cementitious content) using two types of fly ash and two types of limestone from different sources to observe the variations in setting time, short and long-term strength for the concrete. For RCC mixes having ternary cementitious systems (combination of OPC, fly ash and limestone), setting time values were observed to be in between setting times of mixes made with binary cementitious systems (i.e. OPC and limestone & OPC and fly ash). Optimum performance in terms of compressive strength at all the ages was observed for mixes with ternary cementitious system due to the synergistic contributions (physical and chemical) of both fly ash and limestone.