An Investigation on the Effects of Aggregates Properties on the Performance of Unbound Aggregate Base Layer

Abstract

<span>Unbound aggregates are the most common type of materials used for construction of the base layer of <span>flexible pavements in Iran and worldwide. Due to the lack of binder, the performance of the compacted <span>unbound aggregates is highly dependent on the properties of the gravel (particles remaining on sieve <span>4.75mm, sand (particles passing sieve 4.75mm and remaining on sieve 0.75mm), and fines (particles passing <span>sieve No. 200) fraction of the mixture. As the bearing capacity and permeability are the main properties <span>influencing the performance of the base layer; in this research, the effects of the angularity of gravel and <span>sand, and the content and plasticity of fines on the bearing capacity and permeability of the compacted <span>unbound aggregates have been investigated. The bearing capacity of the materials in dry and saturated <span>conditions has been measured using CBR test, and the permeability has been measured using constant head <span>permeability test method. The results showed that the CBR of the compacted mixture decreases with <span>decreasing the percentage of angular sand and gravel in the mixtures. The strength of the mixture was shown <span>to be optimum at a certain amount of fine content and decreases with increasing the plasticity of the fine <span>fraction. It was found that the saturated CBR of the mixtures with non-plastic fines is higher than that of the <span>dry CBR. It was also found that the angularity of the sand is more effective than the angularity of gravel on <span>the CBR. The permeability of the mixtures is shown to increase with decreasing the angularity of the gravel <span>and sand fraction in the mixture.</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span> </span>