THESIS ABSTRACT

Abstract

Coarse aggregates constitute around 70–80% of concrete's total volume, and therefore their properties and gradation significantly affect the performance of the material as a main structural material. A number of studies have been conducted with respect to different aggregates and their contribution to the concrete strength. However, the influence of aggregate gradation on the mechanical characteristics and plastic properties of concrete has not yet been extensively explored. This study, therefore, examines the effect of different coarse aggregate gradation concerning the workability, compressive strength, and void ratio of concrete grades M20 and M25 with an aim of deriving valuable insights into optimum concrete mix design. A systematic investigation was carried out with five different coarse aggregate gradations (single-size (10, 20, and 40 mm) and well graded (20 and 40mm) aggregate) collected from Dukuchhap. The coarse aggregates were subjected to mechanical and physical tests that included sieve analysis, flakiness index (FI), elongation index (EI), and aggregate crushing value (ACV). Concrete specimens have been cast with controlled water to cement ratios. Assessment on workability was done by slump test, and the cube test was carried out on the 7th day and again on the 28th day for test compressive strength. Statistical Interpretation was carried out in terms of analyses such as ANOVA, Tukey Post Hoc Test and correlation on gradation, void content, workability, and compressive strength. The results highlight the crucial impact of aggregate gradation on concrete performance. Workability, measured by slump, increased with larger aggregate sizes due to the reduction in specific surface area, which lowered water demand. Among the tested samples, 20mm well-graded aggregates (70% 20mm down and 30% 10mm down) exhibited the highest compressive strength at both 7 and 28 days. This was attributed to their optimal packing density, reduced void content, and improved paste-aggregate bonding. Statistical analysis, including ANOVA and correlation studies, confirmed a strong negative relationship between void ratio and compressive strength, reinforcing the significance of well-graded aggregates in mix design. vi It shows the importance of aggregate gradation for optimal concrete performance and givesrecommendations on optimizing mix design. It identifies future research work on long- lasting durability assessments and field studies under actual site conditions, preparing the ground for improved construction practices and more resilient built environments.

Keywords

Concrete; Aggregate Sizes; Workability; Compressive Strength; Void Ratio