Performance studies on Stone matrix asphalt mixes utilizing recycled asphalt pavement materials and warm mix additive

Abstract

Road development is an essential element for economic growth, trade and social integration. About 64.5% of freight and 90% passenger’s traffic is carried by the roads and annual growth is projected at 12-15% for passenger traffic, and 15-18% for cargo traffic. Considering the needs, a total of 200,000 km of national highways is expected to be completed by 2022. These road modernizations exposes challenges pertaining to depletion of natural resources like soil, aggregates and increase in liberation of greenhouse emissions during road construction. In this context, Recycling of existing bituminous mixes is one of the alternatives to reuse aggregates and bitumen [1]. In order to reduce CO₂ emissions, warm mix asphalt (WMA) technology is used to construct pavement at lower temperature, typically 30⁰C lesser than conventional hot mix technology without compromising the quality of mixes [2-4]. In recent years, several studies focused on utilization Recycled asphalt pavement materials (RAP) and WMA additives at high temperature performance and moisture sensitivity [5]. However, RAP gradation and RAP binder quality are the major concern in adopting appropriate quantity of RAP in construction. Hence in this study, an attempt is made to determine amount of RAP that can be utilized for SMA mixes with focus on mix performance using warm mix technology.

The RAP material aged about 5 years was collected from arterial road section in Bengaluru city, India. The RAP binder was extracted by centrifuge method and tested for its basic physical properties. Rheological parameters were determined for recovered binder using complex modulus test. The RAP materials were blended at varying proportions of 0, 10, 20 and 30% for conventional SMA mixes using VG 30 binder. Zycotherm is used as warm mix additive. Marshall method of mix design was carried out as per Asphalt Institute -Sixth edition (MS 2). Further, the Indirect tensile test was carried out as per AASHTO T283 at 7% air voids content for conventional and warm SMA mixes using RAP materials. Rutting tests were conducted on bituminous slab specimen of dimensions 600mm × 200mm × 50mm at 60 degree in immersion wheel tracking machine. The number of wheel passes was recorded up to 20mm rut depth.

The binder rutting parameter G*/Sinδ improved with increase in RAP percentage due to  increase in stiffness of binder and decreased with addition of  warm mix additive due to increase in viscosity of binder. However, G*/Sinδ values are within the permissible limit. The fatigue parameter G*Sinδ increased with increase in RAP percentage indicating possibility of fatigue cracking due to stiffening of binder. Therefore it may be necessary to rejunavate the binder if either the percentage or age exceeds. Indirect tensile strength and rutting of SMA mix increased with increase in RAP percentage for hot mixes. Decreasing trend is observed for same mixes with warm mix additive. However, the performance of warm SMA  mixes are within specified limits. Combining Warm mix technology, RAP materials   in bituminous mixes may be important towards optimizing the advantages of WMA technology and use of recycled materials towards sustainable pavements.