Admixtures are widely used to create high-performance concrete that is workable, strong, and durable at a low cost. However, improper usage of these admixtures can lead to adverse effects on the concrete. One such effect is rapid slump loss, which is commonly observed in rich mixes with higher cement content. This can be mitigated by adding booster dosages at different intervals. Another issue is severe segregation or bleeding, which is more frequently seen in lean mixes with low cement content. The extent of this effect depends on the dosage of the admixture used. To reduce segregation, one can either decrease the admixture dosage or increase the content of fine in the concrete.
Over-retardation is yet another effect observed when admixtures are added in excess of the specified dosage. This can affect the construction schedule, leading to low strength development at an early age. However, the ultimate strength of the concrete remains the same. Finally, plastic shrinkage is observed in large floor slabs with thin sections due to excessive water evaporation from the concrete surface at high temperatures or continuous breezing. These plastic shrinkage cracks can be harmful to structures.
Effect of CaCl2 on setting time of OPC
