Evaluation of Impact of Mixing Method on Laboratory- and Plant-Produced Fiber-Reinforced Asphalt Mixture

Abstract

The addition of fibers to asphalt mixtures has the potential to improve the resistance of asphalt mixtures to cracking and permanent deformation (rutting). However, the state (distribution) of fibers in the asphalt mix is critical parameter in determining performance enhancement. This study evaluated the impact of different laboratory mixing methods (mainly Hobart and bucket) on fiber distribution and selected a method comparable to plant-produced fiber-reinforced mixes. The laboratory performance of plant-mixed lab-compacted (PMLC) and lab-mixed lab-compacted (LMLC) fiber-reinforced mixtures was compared. Four types of laboratory and plant mixtures [unreinforced, polyolefin and aramid (PFA) fibers at 0.05% dosage, and Sasobit-coated aramid (SCA) fibers at 0.01% and 0.02% dosages] were produced to compare the laboratory performance of asphalt mixtures. The cracking resistance [evaluated using indirect tensile strength (ITS) and semicircular bend (SCB) tests], rutting susceptibility [evaluated using flow number (FN) and the Hamburg wheel tracking test (HWTT)], durability (evaluated using Cantabro loss), and fatigue (evaluated using a uniaxial fatigue test) performance of control and fiber-reinforced asphalt mixtures were evaluated. Among laboratory mixing methods, a bucket mixer was selected to produce LMLC samples because it produced the maximum fiber distribution (87% of fibers in the individual state). Laboratory performance testing results showed that PFA-reinforced mixtures enhanced the rutting performance regardless of mixing method. The mixtures with PFA 0.05% and SCA 0.01% fibers were highly durable and had better dynamic modulus (|E*|) at low frequency and high temperature. Cracking performance was improved with the addition of SCA fibers into the mix; however, fiber-reinforced mixes (PFA 0.05% and SCA 0.01%) had higher fatigue damage tolerance, except SCA 0.02% reinforced mix. The laboratory bucket mixing method is representative of plant-produced fiber-reinforced mixtures, and laboratory performance results were consistent for laboratory bucket and plant produced mixtures. This paper showcases laboratory mixing method equivalent to fiber distribution that produce fiber-reinforced asphalt mixtures comparable to those produced at an asphalt plant. Different laboratory mixing equipment, including Hobart and bucket mixers, was used to produce fiber-reinforced asphalt mixtures in the laboratory. Aramid fibers were added into these mixers after separation by hand. In addition, the same fiber-reinforced mixtures were produced at a batch plant for comparison purpose. Fibers and binder were extracted from all mixtures and individual fibers (indicating better fiber distribution) were quantified. According to the results, the use of a bucket mixer led to better fiber distribution within the produced asphalt mixtures than did a Hobart mixer. Laboratory performance comparison results showed that the mixes produced using the bucket mixer had identical results to plant-produced mixtures. Hence, using a bucket mixer and introducing aramid fibers after hand separation is an effective way to produce plant-representative fiber-reinforced asphalt mixtures. This is a major step toward designing and producing fiber-reinforced asphalt mixtures and enhancing the cracking performance of asphalt mixtures.