Preparation of Rapid Hardening Concrete by Using Locally Available Additives or Admixtures

Abstract

For accelerated strength development of concrete, while maintaining durability and workability, rapid hardening concrete (RHC) is increasingly finding its use in construction industry worldwide. However, its use in Pakistan is limited due to higher cost. The higher cost is due to the constituents’ i.e. higher quantity of cement contents and use of costly accelerating additives. This research work was designed to develop rapid hardening concrete, using locally available materials and accelerators. This research was conducted in three phases. In first phase, survey was carried out for availability of accelerating additives in local market. Sodium carbonate and Calcium nitrate were selected based on their availability and cost. In second phase the initial and final setting times of cement with various proportions of the additives were determined. On the basis of the initial and final set different proportions were selected. Final phase includes the lab work. Trial mixes were prepared by varying accelerator type and accelerator dosage. Tests were conducted to evaluate the properties of concrete prepared using accelerators and it was compared with the properties of normal concrete. The tests clearly revealed that by using the 5% dosage of calcium nitrate produces 86% strength in 72 hrs with initial setting time as 52 minutes and final setting time as 135 minutes. The concrete prepared from 5% calcium nitrate retained its workability for 40 minutes. Comparative cost analysis indicated that, although RHC is costly but the advantages which we can achieve can cover its cost to normal concrete