A comparison of weathering process of andesitic UGMs in two quarries in New Zealand

•Short-term weatherability of road materials is confirmed in two quarries.•Laboratory tests may not reveal the weatherability of road materials.•Weathering of aggregates can result in production of detrimental swelling clays.•Marginal aggregates are more susceptible to weathering process. Environmental conditions can sufficiently degrade the properties of road aggregates below the design standards. To encourage more sustainable use of available aggregates in the pavement structure this investigates the weatherability of unbound aggregates within two andesitic quarries, under the complex in-situ environmental conditions. Both quarries produce Unbound Granular Materials (UGMs), Premium aggregates that are compliant with New Zealand specification and Marginal aggregates that have lower quality. In order to trace the variation in chemical and mineralogical characteristics of materials a variety of analytical methods, including X-Ray Fluorescence (XRF), X-ray Diffraction (XRD), thin section petrography, Clay Index (CI) test, and image processing were carried out on fresh and short-term weathered aggregates (less than 15 years). The results revealed a variety of degrees of weathering, which are comparatively more intense in Marginal materials. Overall, immediate loss of alkali and alkali-earth metals is the main result of chemical weathering in both quarries, which has been reflected in the XRF analysis and weathering indices. CI test and XRD analysis also revealed the production of clay minerals, kaolinite and smectites. Moreover, a significant change in the textural features of feldspar grains were observed in the thin-sections. Overall, it was concluded that the weathering behaviour of road materials primarily depends on their chemical composition and microstructural properties.