Use of Thermally Treated Bentonite as Filler in Hot Mix Asphalt

Abstract

Clays and clay minerals are widely used as raw materials in different industrial processes due to their abundance. Generally, in road construction projects, clays are considered waste materials because they have some undesirable engineering properties (e.g., plasticity and swelling properties). For this reason, this material is generally discarded in landfills or dumps. However, taking advantage of its abundance, this material could be used as a substitute for natural aggregates of hot mix asphalt (HMA) production as long as their undesirable properties are eliminated. In this study, a bentonite was thermally treated (subjected to high temperatures) in order to be used as replacement for the total filler content of a natural aggregate in HMA. X-ray diffractometry (XRD), X-ray fluorescence (XRF), Atterberg limits, and free swelling index tests were carried out on bentonite (with and without thermal treatment). Marshall, indirect tensile strength (ITS) (under dry and wet conditions), resilient modulus, permanent deformation, resistance to fatigue, and Cantabro tests were carried out on HMA mixtures using thermally treated bentonite (BT) as filler. On all test results an ANOVA test was carried out. When BT replaced the total fraction of the natural filler, its resistance under monotonic load, stiffness under cyclic loading, and resistance to moisture damage increased remarkably. A similar resistance to fatigue and abrasion in the Cantabro test was observed. Based on the results obtained, BT could be considered a technically viable alternative as a substitute material for natural fillers in HMAs.