Empirical correlation of the Modified Wheel Tracker (MWT) and the dynamic creep test for evaluating the permanent deformation of HMA

The Wheel Tracking Test (WTT) has been extensively used for laboratory characterization of permanent deformation of Hot Mix Asphalt (HMA). However, the fully-confined setup of the device is unable to capture the tertiary zone where shear deformation takes place. This makes the permanent deformation resistance characteristics of HMA difficult to analyze. Hence, a modified wheel tracker (MWT), with unconfined lateral sides along the wheel tracking direction was utilized in this study, which can capture the tertiary flow [referred to as the Flow Number (FN)]. The dynamic creep test, which yields FN, is a common laboratory test which has the ability to characterize permanent deformation considering the shear behavior. The study investigated the relationship of the MWT and the dynamic creep test utilizing the permanent deformation and permanent micro-strain data from the respective tests. A novel parameter, FN-Index was explored. The permanent deformation parameters derived from the MWT were well correlated with the dynamic creep test. The MWT showed promising repeatability for the FNs.

Ethylene Propylene Diene Monomer (EPDM) Effect on Asphalt Performance

The asphalt industry is increasingly developing with greater focus on sustainability. This study focuses on the benefits of a binder modification of stone mastic asphalt (SMA) by adding a rubber—ethylene propylene diene monomer (EPDM)—into a class 320 bitumen. This study observes the advantages that occur for the rutting and fatigue performance of the samples. The binder modification was made by incorporating 0, 2, 4 and 6% binder weight into each sample. The tests performed on the samples were the wheel-tracking test and the four-point beam bending test. The results revealed varied outcomes, with the four-point beam bending test showing the 6% sample having the highest initial stiffness and modulus of elasticity but the lowest cycle to failure. Therefore, the best performer was determined as the 4% sample, which performed consistently throughout, having the highest cumulative dissipated energy and second-highest initial flexural stiffness, modulus of elasticity and cycle to failure results. There was a clear indication of the best performer for the wheel-tracking test, with the 4% sample having the lowest rut depth, although there were signs of further improvement to be achieved within the 4–6% range. In addition, drain-off tests were conducted on the mixtures, and the addition of EPDM significantly reduced the SMA drain-off values. Overall, the best improvements through binder modification for an SMA mix with EPDM concerning fatigue and rutting resistance came from a 4% incorporation.

Performance Evaluation of Warm Asphalt Mixtures Containing Chemical Additive and Effect of Incorporating High Reclaimed Asphalt Content

Reclaimed asphalt (RA) and Warm mix asphalt (WMA) are two widely used environmentally friendly mixtures in the paving industry. This study compares the laboratory performance of conventional hot mix asphalt (HMA) with virgin WMA, and WMA containing 60% RA content, using thermal stress restrained specimen test, wheel tracking test, and indirect tensile strength test. Based on test results, a reduction of 15 °C in mixing temperature was achieved for WMA mixtures compared to HMA using the given chemical additive. The virgin WMA mixture showed superior cracking resistance but lower rutting resistance than HMA, and incorporation of RA material without any further modification in the binder, deteriorated both cracking and rutting performance of WMA. It was also shown that laboratory short-term aging can significantly affect the performance of the mixtures.

Establishment of Rutting Model of Wheel-Tracking Test for Real-Time Prediction of Rut Depth of Asphalt Layers

The construction process control of asphalt layers directly affects the road service life and quality. The objective of this study was to establish a rutting model of the wheel-tracking test used for the real-time prediction of the rut depth of asphalt layers in the construction process. The gradation of asphalt mixture, asphalt content, and molding temperature were considered in the development of the new rutting model of the wheel-tracking test. The effects of these three factors on the high-temperature performance of asphalt mixture were analyzed. The order of importance of the factors affecting the high-temperature performance of asphalt mixture is the gradation of asphalt mixture, asphalt-aggregate ratio, and molding temperature. Overall, the predicted values of the rut depth of the wheel-tracking test are very close to the measured values. Furthermore, the difference between the rut depths of asphalt layers of the test group and the control group is small. These comparison results indicate that the new rutting model of the wheel-tracking test has high accuracy and good applicability for the test road.

Performance Evaluation of Cold Bituminous Mix Reinforced with Coir Fibre

Cold bituminous mix (CBM), which is a mixture of bitumen emulsion and aggregate that is mixed together at ambient temperature, has several advantages like energy savings, easiness in preparation, environmental benefits, and high production at low investment. But there are certain limitations of CBMs like inferior mechanical properties, high air voids, weak early life strength, long curing time and poor coating that hinder its extensive usage. The possibility of improving mechanical performance of CBMs by the addition of coir fibre is attempted in this study. The objectives of the study are to assess the improvement in performance of CBM due to addition of coir fibre and to identify the optimum length and optimum content of coir fibre for CBMs. Three coir fibre contents and three coir fibre lengths were used in this study. Performance evaluation of CBM modified with coir fibre was done through Retained Marshall Stability (RMS) test and Hamburg wheel tracking test. Coir fibre was added to the aggregates and mixed before the addition of pre-wetting water and emulsion, to achieve uniform distribution and to avoid balling of coir fibres. When coir fibre was added to the mix, Marshall Stability increased up to a certain level of coir fibre content depending on fibre length. Highest Marshall Stability value was obtained at 0.2% content (by weight of total mix) of coir fibre of 15 mm length. Resistance to moisture damage was assessed by RMS test. It was observed that the addition of coir fibre improved the RMS value. From the Hamburg wheel tracking test, it was observed that the addition of coir fibre improved rut resistance. For all fibre lengths, CBM with 0.2 % coir content showed the highest rut resistance, with 10 mm fibre length showed the best performance. Hence, coir fibre is recommended as a feasible additive for mechanical performance improvement of CBMs.