The Precast Concrete industry is one of the thriving industries in the wake of faster development with high quality standards. The initial capital cost for precast construction is higher than for conventional concrete. The chief requirement in precast concrete is high early strength. It becomes a challenge to reduce costs, while maintaining the high early strength, durability, workability, and environmental soundness.
In the investigation work presented in this paper, mix design was developed with 25 per cent replacement of OPC with fine reactive powder (GGBFS) at water-powder ratio of 0.27 with an objective to reduce costs and make concrete green. The concrete thus designed for wet properties and compressive strength at 10 hours, 12 hours and 14 hours was to be tested and expected to meet the requirements of high early strength for precast industry.
Precast concrete has different requirements from normal concrete in terms of workability, water-cement ratio and early strength. Within the precast industry, the rheology of concrete varies with different precast elements and structures. These variations can be brought about in the concrete with the addition of the right type and dosage of chemical admixtures. Chemical admixtures play a pivotal role in developing the concrete to required rheology.
Governing factors in precast concrete are:
- Low water-cement ratio
- Medium workability
- Need for high early strength for early de-moulding to increase productivity
- Compatibility with cement replacements
- Compatibility with 100% crushed sand / manufactured sand.