HIGH RANGE WATER REDUCING ADMIXTURE FOR CONCRETE
High range water reducing admixture (ASTM C494 types F and G) decreases the water/cement ratio and provides high-performance, particularly at early ages. Matching the chemical admixture to the cementitious materials, both in type and dosage rate is important. Slump loss characteristics of the concrete will determine whether the high range water reducer should be introduced at the plant, at the site, or both locations. However, with the advent of newer generation products, sufficient slump retention can be achieved through plant addition in most cases. High range water reducers can be used in one or a combination of the following ways while minimally affecting setting time:
- Reduce the water-cement ratio while maintaining slump.
- Increase slump while maintaining a constant water-cement ratio.
- Reduce the cementitious materials content and water content while maintaining constant slump and strength.
High range water reducers may serve the purpose of increasing strength through a reduction in the water-cement ratio while maintaining equal slump, increasing slump while maintaining equal water-cement ratio or a combination thereof. The method of addition should distribute the admixture uniformly throughout the concrete. Adequate mixing is critical to uniform performance. Problems resulting from non-uniform admixture distribution or batch-to-batch dosage variations include inconsistent slump, rate of hardening, and strength development.
Most of the commercial formulations of high-range water-reducers belong to one of the following categories:
· Sulfonated melamine-formaldehyde condensates.
· Sulfonated naphthalene-formaldehyde condensate
· Modified lignosulfonates.
· Polycarboxylate derivatives.