Evaluation of the durability and the performance of an asphalt mix involving Aramid Pulp Fiber (APF): Complex modulus before and after freeze-thaw cycles, fatigue, and TSRST tests

Abstract

The main deteriorations of asphalt pavements in cold regions are due to the effect of heavy traffics, water action, low-temperature fluctuations, freeze-thaw cycles and the combination of all these factors together. Fiber additives are mainly used as reinforcement materials in asphalt pavements to improve the tensile properties and increase the strength against low-temperature cracking and potholes. Aromatic polyamide fiber (aramid fiber) is used in advanced composite materials since it has a very high tensile strength, modulus, and high cohesiveness. Whether the addition of Aramid Pulp Fiber (APF) can effectively improve the fatigue life, thermal performance, and durability of asphalt mixture under repeated freeze-thaw cycles are also major problems needed to be investigated properly. In this regard, thermo-mechanical analyses (complex modulus, fatigue, and thermal stress restrained specimen test (TSRST)) have been conducted on the asphalt mix with a nominal maximum aggregate size of 20 mm, known as Grave Bitume (GB20) in Quebec, Canada. The improvement effect of APF incorporation is assessed to compare the stiffness variation before and after 300 rapid freeze-thaw cycles, fatigue behavior, and thermal strength. The results indicate the ability of APF to increase the durability of the GB 20 mix against freeze-thaw cycles. The TSRST and fatigue results also show that the APF additives can increase the performance of the GB 20 mix against low temperature cracking and heavy truckloads.

Introduction

Hot Mix Asphalt (HMA) is a complex material that consists of asphalt binder, aggregate, and air voids, which is used as the first layer in flexible pavements. HMA is a typical viscoelastic material that has different behavior during different seasons of a year [1]. The main deterioration of HMA in cold regions is due to the effect of heavy traffics, water action, low-temperature fluctuations, and freeze-thaw cycles. Researchers and engineers are trying to improve the performance and durability of HMA and consequently increase the service life of flexible pavements considering those deterioration factors.

Premature cracking and potholes are very common problems in Quebec and other regions in Canada [2], [3], [4]. Canada ranks seventh in the world in terms of road network length. More than 90 percent of the paved roads in Canada are flexible pavements. More than 50 percent of municipal roads are in fair, poor, or very poor conditions [5]. Pavement structures in Canada experience severe temperature variations in a year [1]. These significant temperature variations in combination with the moisture inside the pores result in the development of premature deterioration of asphalt pavements [6], [7], [8].

Fiber additives are mainly used as reinforcement materials in Portland cement concrete and asphalt mixes [9], [10]. Fibers are added to HMA to improve the tensile properties and performance [10]. Fibers are added to open-graded-friction-course (OGFC) mixes and stone matrix asphalt (SMA) mixes during transportation and laying to prevent draindown and leakage [11]. The dynamic modulus, viscoelasticity, moisture susceptibility, and reflective cracking would improve with the addition of fibers [9], [11], [12], [13]. It can also enable multifunctional applications, increased durability, increase fatigue and rutting performance of asphalt mixes [13], [16].

Previous research demonstrated the importance of using Aramid Pulp Fiber (APF) in road construction [13], [14], [17], [21]. Kevlar® is the trademark of a para-aramid synthetic polymer fiber, which can be used in advanced composite materials since it has a very high tensile strength, modulus, and high cohesiveness. It was introduced in the early 70 s by DuPont production. According to NCHRP synthesis 475, aramid fiber brings many advantages to asphalt mixes including increase the performance (rutting and fatigue), improve the strength and stability [13]. Kaloush et al. [22] investigated the performance of an asphalt mix with and without using polypropylene and aramid fibers. The final results concluded that the reinforced mix had better performance in terms of permanent deformation and thermal cracking [22]. Bennert [36] investigated the polyolefin and aramid fibers in the plant produced mixes. Mixes were produced in the same batch plant using the same mix design. The control mix was slightly stiffer than the reinforced mix at low temperature. On the other hand, phase angle analysis showed that the fiber mix is more viscous than the control mix. Beam fatigue test also indicated that both mix had the same fatigue resistance [13].

A recent study in the laboratory of LCMB at the Ecole de Technologie Superieure conducted the indirect tensile strength test (ITS) on APF mixes [17]. It was found that the addition of the APF could increase the ductility and tensile strength even at minus temperatures [19]. Previous studies demonstrated some advantages of using APF in asphalt mixtures such as better rutting resistant and delay in cracking propagation [15]. The research of the performance of an APF mix under cold region environment conditions such as the freeze-thaw cycles and thermal stress restrained specimens (TSRST) are crucial to carrying out. Whether the addition of APF can effectively improve the fatigue life; thermal performance, and the durability of asphalt mix under repeated freeze-thaw cycles are also major problems needed to be investigated properly.

HMA in pavements is usually divided into three sublayers with different thicknesses into cold regions. Base asphaltic layer plays a crucial role in bottom-up fatigue cracking [8]. This is while, at the bottom of the base layer, the percentage of air voids is higher, which is usually due to a poor compaction during road construction, and also the tensile strain is higher because of the behavior of flexible pavements in terms of traffic, especially heavy vehicles. This can be getting worse during thaw periods when there is a high potential for the capillary rise. Water can penetrate through the saturated granular base layer. On the other hand, the bearing capacity of underlying granular layers reduces considerably during the thaw periods due to insufficient pavement drainage and melting of ice [1], [8]. Therefore, reinforcing the asphaltic base-layer can be one of the effective solutions to improve the quality of pavement structures.

In view of this, the primary objective of this paper is to study the thermo-mechanical analyses (complex modulus, fatigue, and TSRST tests) on the asphalt-base mix (which is known as GB20 mix in Quebec, Canada) and improvement effect of APF incorporation are studied to compare the stiffness variation before and after 300 rapid freeze-thaw cycles, fatigue life, and thermal strength.