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
