THESIS ABSTRACT

Abstract

Many infrastructure projects in Nepal are located in remote mountainous terrain where the coarse aggregate available within an economic haul distance may not meet conventional quality limits, particularly the Los Angeles Abrasion (LAA) limits associated with the Department of Roads (DoR)/IS 383 two-tier convention. This study examined coarse aggregate from three sources at the Upper Arun Hydroelectric Project: Leksuwa, Namase and Rukuma and their effect on M25, M30 and M35 concrete, and tested whether a non-conforming aggregate can still reach target strength through mix adjustment. Aggregate physical and mechanical properties were determined by standard tests, and 21 trial mixes (126 cubes) were cast and tested at 7 and 28 days. Three objectives were pursued. First, a source-versus-strength comparison at each grade's baseline w/c ratio, with all other parameters held constant. Second and third, the non-conforming Leksuwa aggregate was evaluated by reducing the w/c ratio and by reducing the maximum aggregate size, holding cementitious content constant. All three objectives were analyzed by a two-factor analysis of variance without replication, with concrete grade as a blocking factor, and Objective 2 additionally by linear regression. Aggregate source had a modest but statistically significant effect on strength [F(2, 4) = 9.61, p = 0.030]; mean strength followed Rukuma > Namase > Leksuwa, with Leksuwa about 4–12% lower depending on grade. Reducing the water–cement ratio also had a significant effect [F(2, 4) = 15.60, p = 0.013] and followed Abrams' law, allowing Leksuwa to reach the M30 and M35 targets that its baseline mixes had failed. Reducing the nominal maximum aggregate size likewise had a significant effect [F(2, 4) = 14.02, p = 0.016], with 16 mm giving the highest observed strength at all three grades, with the 10 mm result essentially equal at M35. The findings indicate that a locally available aggregate whose LAA exceeds conventional limits carries only a small, quantifiable strength penalty and can still yield conforming M25–M35 concrete when the w/c ratio and aggregate size are adjusted. Because these 2 adjustments cost little relative to hauling conforming aggregate over long mountain distances. As LAA is fundamentally a durability (abrasion-resistance) index rather than a strength index, this acceptance applies to mass and structural concrete, not to abrasion- exposed surfaces such as rigid pavement, spillways and stilling basins. The study offers UAHEP and comparable other infrastructure projects a practical, evidence-based basis for accepting marginal local aggregate under controlled mix-design conditions. Limitations include the single-batch experimental design, the omission of durability testing, and the untested lowest-w/c mixes.

Keywords

coarse aggregate source; Los Angeles Abrasion; compressive strength; water–cement ratio; maximum aggregate size; trial mix optimization; Upper Arun Hydroelectric Project.