Development and Evaluation of Stone Matrix Asphalt Containing Treated Recycled Concrete Aggregate

Abstract

The recycling or utilization of construction and demolition (C&D) waste in a developing country like India is important for sustainability in pavement construction. This study attempts to investigate the utilization of waste material such as recycled concrete aggregate (RCA) in stone matrix asphalt (SMA) mixes. Because of its higher water absorption, the use of RCA in bituminous paving mixes for the surface course of a bituminous pavement is limited. Also, it does not satisfy the criteria for abrasion and impact characteristics for preparation of bituminous mixes used in the uppermost layer of a bituminous pavement. Therefore, RCA was only limited to concrete production or application in the lower bituminous layer, sub-base or base courses.
It is obvious that RCA as a replacement of aggregates, may not be able to directly sustain heavy wheel loads and resist the moisture induced damage when used in the uppermost part of the bituminous pavement as an SMA layer. Therefore, in this study, various attempts have been made to pre-treat the RCA to modify its properties in order to enable RCA to be considered a suitable alternative to conventional coarse aggregates for preparation of SMA mix. After several trails, a proper procedure for pre-treatment of RCA was developed by mixing RCA with nanosilica modified emulsion-water solution, which not only resulted in satisfactory water absorption value but also improved the abrasion value and impact value. In this study, the resulting RCA is termed as pre-treated recycled concrete aggregate (TRCA). Like normal use of fibers in conventional SMA mixes, the present study involved the use of cellulose fibers as a stabilizer for the production of SMA mixes. SMA mixes were made in this study with TRCA, RCA, or conventional aggregate (CA) as coarse aggregates, and two types of widely used bitumen, VG 30 or VG 40 bitumen, with or without cellulose fiber. The SMA mixes thus developed were evaluated in terms of various engineering properties such as Marshall parameters, indirect tensile strength, moisture susceptibility, resilient modulus, fatigue life and rutting resistance using wheel tracking test. It was observed that the mixes involving CA, RCA or TRCA in general, meet the requirements of Marshall test parameters and rutting criteria. However, SMA mixes with RCA (RCA-30, RCA-40, RCA-30-F) fail to satisfy the required moisture susceptibility criteria in terms of tensile strength ratio (TSR) (≥ 85%). Further, the maximum resilient modulus value was observed for mixes prepared with
TRCA and VG 40 bitumen, and stabilized by cellulose fiber, at all three test temperatures (namely 150C, 250C and 350C). SMA mixes prepared with TRCA also showed reasonably higher fatigue life, followed by mixes prepared with CA and RCA. It is observed that all SMA mixes with VG 40 bitumen with or without fiber result in somewhat better engineering properties as compared with that made up of VG 30 bitumen, with or without fiber. After examining various engineering properties of the various mixes under consideration, it was observed that mixes comprising pre-treated recycled concrete aggregate and VG 40 bitumen, with and without cellulose fiber, yield results equivalent to those containing natural aggregates. Based on Indian Roads Congress (IRC) method of bituminous pavement design, it is observed that there has been a reduction in thicknesses of SMA layer made with TRCA alone, or TRCA and fiber. When TRCA alone with VG 30 and VG 40 bitumen is used in a SMA layer there is a cost saving of about 5.8% and 4.6% respectively, while there is a cost saving of about 3.4% and 4% respectively when TRCA with VG 30 or VG 40 bitumen is used in respect of a pavement designed on the basis of assumed design inputs for bituminous pavement with an analysis period of 20 years.