Faculty Publications

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Unmodified Bitumen in SMA: A Sustainable and Cost-Effective Approach
(Springer Science and Business Media Deutschland GmbH, 2025) Arun, U.; Chinnabhandar, R.K.; Talkeri, H.T.; Yatish, R.G.; Ravishankar, A.U.
Stone Matrix Asphalt (SMA) is a Hot Mix Asphalt (HMA) mixture consisting of a discontinuous aggregate gradation characterised by a high coarse aggregate content (between 70 and 80%), a high percentage of binder (typically between 6 and 7%) and a filler content as high as about 10%. SMA has an aggregate skeleton which imparts high strength and rutting resistance to the mixture. The high binder content though provides the mixture with durability, it also drains through the void spaces in the aggregate skeleton during production, transportation and placement of the mixture in the field. Hence, to reduce the drainage of bitumen and bitumen mortar, the SMA guidelines suggest using a modified bitumen or pelletised cellulose fibres in the mixture when a conventional bitumen such as Viscosity Graded (VG 30) is used. However, the production of cellulose fibres is not only expensive but also requires trees to be cut since cellulose is obtained from plant sources leading to deforestation. Due to the high cost of Polymer Modified Bitumen (PMB), the SMA mixtures prepared with the modified bitumen are also expensive. Hence, the present study focuses on the laboratory evaluation of SMA mixes using a conventional Viscosity Graded bitumen (VG 40) without the use of pelletised cellulose fibres. The results indicated that the susceptibility of mixtures to drainage of binder and/or binder mortar was within the permissible limit of 0.3% by weight of the mixture. The mechanical and moisture susceptibility tests conducted on compacted specimens indicated that the performance is comparable to that of the mixtures prepared using PMB. Further, it was noted that only the grades of bitumen softer than VG 40 required cellulose fibres to reduce drain-down. The study also revealed a reduction in cost due to not using cellulose fibres with VG 40 bitumen or modified bitumen, which makes it more environmentally friendly and sustainable. Â© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.
Laboratory evaluation of use of areca fibres in SMA mixes
(Taylor and Francis Ltd., 2023) Chinnabhandar, R.K.; Kumar, H.K.; Yatish, R.G.; Ravi Shankar, A.U.
One of the problems associated with Stone Matrix Asphalt (SMA) mixes is the drain down of binder mortar during production, transportation and placement of the mixes. A commonly adopted method to control the drain down is to add a stabilising additive such as natural, synthetic or mineral fibres to the mixture, which is also known to improve the mechanical and volumetric properties of SMA. The present study evaluates the feasibility of using areca fibres extracted from areca husk in SMA as a stabilising additive. Three SMA mixtures were prepared with Viscosity Grade VG 30 bitumen using areca fibre (SMA-AF), coconut fibre (SMA-CF) and cellulose fibre in pelletised form (SMA-PF) and their performance was compared with a control SMA mixture prepared using Polymer Modified Bitumen (SMA-PMB). The prepared SMA specimens were evaluated for volumetric and Marshall properties, workability characteristics, Indirect Tensile Strength (ITS), fatigue, rutting and moisture susceptibility. The drain down test results indicated that the fibres controlled the drain down, and the optimum fibre content was 0.3% for the mixes with fibres. All the mixtures satisfied the requirements of SMA per IRC:SP 79-2008. The statistical analysis conducted revealed that the fibre type had a significant effect on the properties of SMA mixes. The SMA-PMB and SMA-CF mixes required the least and the highest energy for compaction. Among the mixes with natural fibres, SMA-AF performed better than SMA-CF. © 2022 Informa UK Limited, trading as Taylor & Francis Group.

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