Effect of aggregate shape on the strength of bituminous mixes

Abstract

In Bangladesh, roads are usually constructed of flexible pavement. The most important factors influencing the design of flexible pavements for given traffic and environmental conditions is the type and quality of aggregates used and also the properties of the bitumen incorporated in the bituminous mixes ..To ensure satisfactory and desired performance of the pavement it is, therefore, an utmost necessity to have a prior knowledge about the selected aggregates and .bitumen properties used in the mix. Since Bangladesh is a developing country and its road network demands an. everincreasing expansion, a study was made to evaluate the effects of the shape of aggregates as manifested in flakiness and elongation indices used in conjunction with the bitumen generally used in roads in Bangladesh to achieve' a durable and functional bituminous mix in pavement constructions. In the present study, a systematic laboratory investigation was made to. evaluate the effects of flakiness and elongation indices of available aggregates in order to examine their influence on the properties of bituminous mixes and also to ,examine the suitability of using them in road construction. . Aggregates with varying shapes in respect of flakiness and elongation were used with a commonly used grade of bitumen and their effects on the overall I perfonnance of the mixes in terms of stability and flow values were detennined. Allalysis of data gleaned from laboratory tests tends to indicate that both stability and flow values increase with the decrement of flaky and elongated particles from the aggregate matrix. At a mix temperature of 3000 F and when no elongated and flaky particles were used in the mix, the stability value was around 1800 pounds and the flow value was around 19. The highest value (around 3150 pounds) of stability was found when flakiness index of ~e coarse aggregate was 35% with no elongated particles .in mix. The corresponding flow value was around 18. At a mix temperature of 3200 F, the stability increased by 18.5% to nearly 2140 pounds and flow values decreased to around 17 when no flaky and elongated coarse aggregate was used in the mix.