Contribution of reactive aggregates towards the performance of in-service asphalt pavements
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International Journal of Pavement Research and Technology Journal homepage: www.springer.com/42947
Contribution of reactive aggregates towards the performance of in-service asphalt pavements Rodgers Bangi Mugumea*, Steven Musumbab a
Transport Research Laboratory, Wokingham, Berkshire, RG40 3GA, United Kingdom National Roads Authority, Department of Quality Control, Kampala, Uganda
b Uganda
Received 15 April 2020; received in revised form 13 September 2020; accepted 11 October 2020
Abstract
This paper presents an assessment of the contribution of reactive aggregates on performance of asphalt pavements in service i n order to better understand how to mitigate likely asphalt pavement failures resulting thereof. A petrographic and mineralogical analysis was done on rocks that were used in the asphalt mix as well as their mineral composition. Also, a visual condition survey, deflection testing and coring of the asphaltic su rfacing for further analysis and testing were conducted to establish the extent of the distresses. Results showed that though aggregates tested were meeting the criteria required of a good quality asphalt concrete in relation to mechanical properties, they did not satisfy the other criteria in relation to their mineralogical composition and adhesion. Aggregates were found to be reactive and contained pyroxenes and feldspar which were responsible for deterioration in form of ‘blows ups’ and indentations observed on the pavement surface. Pyroxenes oxidised when they combined with atmospheric components due to their high iron content to form hydrated iron oxides. Feldspars experienced a hydrolytic reaction when they reacted with water to form clay minerals, potassium ions, and silica in solution. Continued exposure of reactive aggregates through water and air permeating into the open textured and cracked asphalt surface will result into total transformation of the pyroxenes into erodible iron oxides and hydroxides hence leading to further deterioration of the asphalt pavement. It is recommended that engineers consider conducting petrographic and mineralogical analysis when sourcing quarries for production of aggregates to be used in asphalt mixes. Keywords: Reactive aggregates; Pyroxenes; Feldspars, Oxidation; Petrography; Pavement deterioration
1. Background One of the key parameters in the performance of asphalt mixes is the type of aggregates incorporated in the mix. Aggregates make up the largest part of the mix of approximately 95 % by weight and act as the framework of the mix, hence making them a fundamental component of the mix design. However, the behaviour of asphalt mixes in relation to aggregates is usually associated with the physical and mechanical properties of aggregates with little or no emphasis being given to their petrographic and mineralogical properties. When selecting mineral aggregates for use in asphalt mixes to achieve well performing Hot Mix Asphalt (HMA), asphalt mix design methods such as the Marshall and Superpave methods are focused on ‘consensus’ and source aggrega
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