The effect of weathering on the engineering properties of laboratory compacted unbound granular materials (UGMs)

Abstract

Unbound Granular Materials (UGMs) are extensively used in pavement construction practice. These materials are uncoated, and their durability can be easily affected by the frequent variations of moisture content in the service life of the pavement. To this end, the effect of Wetting and Drying (W-D) cycles on the performance of two sources of andesite aggregates are investigated by conducting California Bearing Ratio (CBR) alongside Repeated Load Triaxial (RLT) tests. One source of aggregate characterised to be of high quality, indicates premium aggregates, and the other of more marginal in terms of engineering performance. It is observed that CBR results of Marginal aggregates are more dependent to moisture content. Additionally, W-D cycles have a damaging effect on CBR values of Marginal aggregates (up to 55% reduction in CBR results after 16 cycles of W-D), whereas, CBR results of Premium aggregates show a subtle increase after conditioning. The W-D cycles also affect the properties of fine portion of both aggregates and control the swelling trend of Marginal materials. Application of 16 cycles of W-D result in 64% and 29% increase in the proportion of fine materials in Marginal and Premium aggregate, respectively, and almost 60% increase in Clay Index (CI) test results of both sources of aggregates. Moreover, W-D cycles have been shown to have a considerable effect on permanent deformation behaviour and resilient modulus of aggregates in the RLT test. W-D process could potentially result in more than 40% increase in overall permanent deformation of aggregates. In addition to that, the permanent deformation performance of Marginal aggregates considerably depends on the state of stress and variation in moisture content. Overall, in order to achieve more sustainable use of available aggregates it is essential to incorporate the ageing characteristics of UGMs into selection procedure of road materials.