In the application of hot-mix asphalt pavement (HMA), tension at the bottom of the HMA layer creates one of the most challenging distresses to pavement structures, fatigue cracking. Adding rubber to the asphalt mix can extend the life of a pavement and provide an end use for old tires that would otherwise end up in a landfill. It is already known that the initial construction cost of an asphalt rubber mix will be higher than that of a conventional mix. However, the purpose of this article is to investigate if the reduced layer thickness and improved fatigue life will offset the initial cost. After completing a mechanistic analysis using the FHWA software package named 3D Move (University of Nevada, Reno, NV), the pavement thickness required to last for 50,000,000 cycles (the estimated endurance limit) was found to be much less for asphalt rubber mixes as opposed to the reference HMA. The cost to construct one lane mile of the reference mix pavement designed for 113 kph traffic was $190,031, while the cost for asphalt rubber mix at the same speed came out to be $187,629. This is a $2,402 difference. Additionally, the cost to construct 1.6 km of lane of the reference mix and asphalt rubber mix for four more different vehicle speeds was calculated. Overall, analysis showed that Asphalt Rubber (AR) modified asphalt mixtures exhibited significantly lower cost of pavement per 1,000 cycles of fatigue life per mile compared to the conventional HMA mixture.

Aggregates constitute a major part of pavement construction. The strength, durability, and quality of the aggregate affects the overall performance of the pavement structure. Materials sourced near a construction site do not always meet the strength required for pavement construction, however, and haulage of aggregates of the required quality is often costly. For better use of locally available materials, stabilizing agents such as lime, cement, asphalt cement, and fly ash are often used to enhance the strength of the local aggregates. Pavement performance is influenced by both the structure itself and the layer materials present in it. The stiffness of the base layer, for instance, influences the tensile strain in the asphalt layer and compressive strains in the subgrade soil. The tensile strains at the bottom of the asphalt layer and compressive strains in the top zone of the subgrade soils are the main response components affecting fatigue cracking and rutting, respectively. In this study, field performance [rutting, cracking, and roughness measured in relation to the International Roughness Index (IRI)] of pavement sections with treated and untreated base layers were compared to determine the effects of stabilizing agents. In relation to fatigue cracking and pavement surface roughness, the treated sections outperformed the untreated sections. The average values of all three distresses showed better performance for the treated base layer sections with fatigue cracking averaging 2.2 times lower than the untreated sections. The combined rutting and IRI of the treated base layer sections averaged about 0.10 in. and 1.4 times lower than those of the untreated base layer sections, respectively.

No abstract

One of the important aspects of highway design is aggregates. Aggregates strength and consistency has an effect on pavement structure’s overall performance. The consistency of the base material near the site of the construction doesn’t always match the requirements of pavement construction and carrying quality aggregate raises the cost of construction. Stabilizing agents such as asphalt cement, lime, fly ash were used to improve the strength of these materials in order to make greater use of locally available materials. Layer materials present in the pavements and the structure of them influence pavement performance. The compressive strain and the tensile strain in the layer of subgrade and asphalt layer respectively are influenced by the stiffness of the base layer. The important aspects causing rutting and fatigue cracking are compressive strain in the top region of the subgrade layer and tensile strain at the bottom of the asphalt layer, respectively. In this research study, field performance (cracking, rutting, and surface roughness) of pavement sections with untreated and treated bases were collated to assess the impact of the stabilizing agents. The treated sections performed well significantly compared to the untreated sections in terms of pavement surface roughness and fatigue cracking. The treated sections performed higher than the untreated sections in terms of the cumulative average values of all 3 distresses with fatigue cracking averaging 5 times lower than the untreated sections. The combined IRI and rutting of treated sections averaged about 1.5 times and 0.11 inches smaller, respectively than those of untreated sections.

Fatigue cracking, which is commonly associated with repeated traffic loading, is considered one of the major distresses occurring in asphalt pavements because of the low tensile strength of hot mixed asphalt (HMA). Studies have shown that introducing modifiers, such as rubber and polymers, increases the tensile strength of HMA, prolonging the fatigue life of pavement. Although research in the past has studied the effect of added rubber and polymers on the long-term fatigue performance of newly constructed pavement, few studies have shown the effect of those modifiers on the fatigue life of an asphaltic overlay and their associated cost-effectiveness. In this study, the long-term fatigue performance of asphalt overlay was constructed utilizing three different mixtures, conventional HMA, asphalt rubber (AR), and polymer-modified mixtures, which were evaluated utilizing 3D Move Analysis software. In addition, cost-effectiveness analysis was performed. Eighteen 3D Move Analysis scenarios were run including two different overlay thicknesses, three different vehicle speeds, and three different overlay mixtures. The tensile strain at the bottom of the overlay was determined and the number of fatigue loading cycles to failure (Nf) was calculated based on strain-Nf relationships of the three asphalt mixtures. Based on these analyses, use of modified mixtures as an overlay resulted in a significant increase in the service life of the overlay. It was demonstrated that AR and polymer-modified mixtures had better fatigue life and were more cost-effective than the conventional HMA mixtures.