THESIS ABSTRACT

Abstract

Good quality stone chippings are the most important requirement in Double Bituminous Surface Treatment wearing course but mostly they fall short, that actually comply with the requirements of the Standard Specifications for Road and Bridge Works 2016 (with amendment 2021). The study aimed to evaluate the impact of Combined Flakiness Index and Elongation Index (CFEI) on mechanical properties -Los Angeles Abrasion (LAA), Aggregate Impact Value (AIV) and Aggregate Crushing Value (ACV) of stone chippings used in Double Bituminous Surface Treatment. Different combinations of flaky and elongated aggregates were added to natural stone chippings in increments from 0% to 50% to observe the effect in the mechanical properties mentioned earlier. Furthermore, the research involved blending of crushed aggregates containing different proportion of flaky and elongated aggregates with natural stone chippings, to observe their influence on CFEI of the resulting mix. The study revealed that as the percentage of CFEI is increased in natural stone chippings, the values of LAA, AIV and ACV is also increased. Moreover, the influence of flaky aggregates was found to be more remarkable compared to elongated aggregates while blending five different combinations with different percentages of flaky and elongated aggregates. Further, while blending crushed aggregates with natural stone chippings having higher volume of flaky and elongated particles, the CFEI of resulting mix decreased but necessary criteria for strength parameters were satisfied. As specified requirements of LAA, AIV and ACV was satisfied while increasing CFEI up to 42%, it is recommended that specification for CFEI can be relaxed up to 42%. It is also recommended to blend 50%-50% ratio of natural and crushed aggregate, with crushed aggregate having 30% CFEI and 40% CFEI in natural stone chippings, so as to minimize CFEI of the resulting mix, with strength criteria satisfied at the same time. This study did not investigate the effect of bitumen in DBST surfacing; so it is further recommended to study the effect of bitumen in DBST wearing course when CFEI is relaxed. For further studies, study on effect of flaky and elongated aggregates on different road components was recommended.

Keywords

Double Bituminous Surface Treatment, natural stone chippings, crushed aggregate, flaky, elongated, CFEI, LAA, AIV, and ACV