CHARACTERISTICS OF STONE MATRIX ASPHALT USING WARM MIX ADDITIVE

Abstract

Stone matrix asphalt (SMA) is a bituminous mix which consists of gap-graded coarse aggregate skeleton filled with rich asphalt matrix and stabilizer additive such as fibres. It provides stone on stone contact and gives tough, stable and highly rut resistant mixture. The major advantage of using stone matrix asphalt is the improved performance of the pavement and increase in its life. The polymer-modified bitumen is generally used in the production of SMA mixture due to their rut resistant and drain down properties. The increased viscosities of the binders are also beneficial to minimise drain-down in the mixture. These modified binders require high mixing and compaction temperatures. Warm mix asphalt is a new technology which allows the mixing, lay down and compaction of bituminous mixes at lower temperatures compared to hot mix asphalt without affecting the properties of the mix. Various WMA technologies involve the use of different additives. Most of the work on WMA has involved dense-graded mixture; however, in principle, WMA technologies are equally applicable to other types of asphalt mixture. In the present study attempt was made to use WMA technologies to produce stone matrix asphalt. Warm stone matrix asphalt will reduce the mixing and compaction temperatures with similar or better strength, durability and performance characteristics as conventional SMA. In this study the SMA gradation used is as per lRC:SP:79-2008 with 13 mm nominal maximum aggregate size. Tests are performed for binders VG 30, PMB-40 and CRMB-60 by using the warm mix additives. The warm mix additives used are sasobit, evotherm and rediset. The relationship between compaction temperature and density of the mix are found. The mixing temperature taken is 100 C higher than the compaction temperature. It is found that the density decreases with reducing temperature but warm mix can be compacted at lower temperatures. Moisture susceptibility tests for different binders were performed and tensile strength ratio was calculated.