The role of nanomaterials in reducing moisture damage of asphalt mixes

Abstract

Interest of researchers in using nanomaterials in asphalt mixes is increasing rapidly. In this research, the effects of using various nanomaterials in asphalt mixes were investigated. In addition, the effects of two different types of fillers at their conventional size and their nano-size in asphalt mixes were tested. Four types of nanomaterials, namely nano-CaCO3, nano-hydrated lime, nano-bentonite and nano-silica, and two types of anti-stripping fillers, namely hydrated lime and CaCO3 were selected. Nano-hydrated lime was produced using a planetary ball mill apparatus. In producing nano-hydrated lime, optimum combinations of the main parameters that affect particle size reduction in milling process were determined applying trial and error procedure. Minimum particle size of the produced nano-hydrated lime was determined using Scanning Electron Microscope (SEM) and Dynamic Light Scattering (DLS) tests. From these tests, sizes of 125 and 208 nm were recorded, respectively.With applying Field-Emission Scanning Electron Microscopy (FE-SEM) technique, homogenous distribution of the additives in a 60–70 bitumen binder was verified. Asphalt concrete mixes were prepared using the above additives and a siliceous type aggregate. Moisture damage of different mixes was evaluated applying modified Lottman test at different Freeze-Thaw (F-T) cycles. F-T cycles results indicated that Indirect Tensile Strength (ITS) values were reduced appreciably at the first cycle. In fact, it was shown that 4% nano-hydrated lime exhibited the most resistance against different F-T cycles. In addition, Indirect Tensile Stiffness Modulus (ITSM) test was performed at 25 °C. From these tests, Tensile Strength Ratio (TSR) and Index of Retained Resilient Modulus (IRMr) parameters were determined. Testing results indicated that by adding 20% hydrated lime filler and 4% nano-hydrated lime to the binder, TSR values of mixes increased to some 60%. In the case of using CaCO3 filler and nano-CaCO3, 60% increase in TSR, was achieved when either 5% CaCO3 filler or 4% nano-CaCO3 were used. These results were validated performing resilient modulus test. IRMr of mixes containing 20% hydrated lime filler and 4% nano-hydrated lime increased to 56% and 60%, respectively. IRMr values of asphalt mixes increased to 48% and 54% where 5% CaCO3 filler and 4% nano-CaCO3 were added, respectively.