International Journal of Science, Engineering and TechnologyAuthors: Sayyad Khasim, Dr.K.Naga Sreenivasa Rao
Abstract: High-strength concrete (HSC) is widely used in modern construction for high-rise buildings, long-span bridges, and other infrastructure requiring superior mechanical and durability performance. The early age properties of HSC, including workability, setting time, and early strength development, play a critical role in ensuring the quality, placement efficiency, and structural integrity of concrete structures. The incorporation of chemical admixtures, such as high-range water-reducing agents (superplasticizers) and accelerators, has become a common practice to enhance the fresh and early age properties of concrete, particularly in mixes with low water-to-cement ratios and high cement content. This study investigates the influence of chemical admixtures on the early age properties of HSC, focusing on their impact on workability, setting characteristics, and early compressive and tensile strength development. Laboratory investigations were carried out using ordinary Portland cement, well-graded fine and coarse aggregates, and high-range water-reducing admixtures conforming to IS: 9103–1999. Concrete mixes were prepared with varying dosages of superplasticizers to assess the effect on workability, measured using the slump test, and flowability, measured using the compacting factor test. Early age strength development was evaluated by casting cube and cylindrical specimens and testing them for compressive and split tensile strength at 1, 3, and 7 days of curing. Additionally, the setting time of cement paste with and without admixtures was determined using Vicat apparatus in accordance with IS: 4031–1988. The experimental results indicate that the inclusion of chemical admixtures significantly improves the workability of HSC, allowing a reduction in water content without compromising fluidity. Superplasticizers were observed to maintain a uniform, cohesive mix, reduce segregation, and facilitate proper compaction at early ages. Early age strength results demonstrated that appropriate admixture dosages accelerate hydration and improve initial compressive and tensile strength, which is critical for formwork removal, prestressing operations, and early load application. Setting time measurements showed that admixtures can either retard or accelerate initial and final setting, depending on their chemical composition, allowing better control over placement and finishing operations. The study highlights the importance of optimizing admixture type and dosage to balance workability, early age strength development, and setting time for high-strength concrete applications. Overall, this research confirms that chemical admixtures are essential for enhancing the early age performance of high-strength concrete, contributing to improved constructability, structural reliability, and long-term durability in modern construction projects.
