Faculty Publications
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Item Laboratory Evaluation on the Use of Natural Fibre in Gap-Graded Asphalt Mixtures(Springer Science and Business Media Deutschland GmbH, 2023) Chinnabhandar, R.K.; Ravi Shankar, A.U.; Sai Ganesh, V.; Cleetus, A.; Chourasia, S.Stone Matrix Asphalt (SMA) is a gap-graded mixture that consists of a high concentration of coarse aggregates, which imparts strength and rut resistance and a high binder content, making the mixture durable. The high binder content mortar consists of fine aggregates, filler, bitumen and stabilising additive. One of the limitations of SMA is it suffers from draindown of binder mortar which can be reduced by adding a mineral fibre, natural fibre or synthetic fibre. The addition of a stabilising additive not only controls the draindown but also improves the tensile strength because of the network of fibres in the mixture. In the present study, an attempt is made to determine the effect of Areca fibre, a natural fibre abundantly available in the southern Indian region. A comparison between two SMA mixtures prepared with and without stabilising additive is made. The Superpave mix design method was adopted, and tests such as draindown, fatigue, rutting and moisture-induced damage properties such as tensile strength ratio (TSR) were evaluated. The results indicate that the mixture with Areca fibre effectively controls the draindown and satisfies the volumetric and mix design criteria as per IRC SP 79. However, the performance of SMA without stabilising additive was better than the mixture with the stabilising additive with respect to resistance to rutting, fatigue and moisture-induced damage. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.Item 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. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.Item Laboratory performance of stone matrix asphalt mixtures with two aggregate gradations(Springer Science and Business Media Deutschland GmbH, 2015) Goutham, G.; Lekha, B.M.; Geethu, J.S.; Ravi Shankar, A.U.Stone matrix asphalt (SMA) is a gap-graded bituminous mixture which can be used in surface layer of high volume pavements. The mixture has higher concentrations of coarse aggregates, providing strength and rut resistance to the mixture, and higher asphalt content giving durability. There must be a proper stone-to-stone contact between the coarse aggregates of SMA, and hence aggregate gradation is an important factor in this mixture. In the current study, two aggregate gradations, with nominal maximum aggregate sizes (NMAS) 16 and 13 mm were adopted to prepare SMA mixtures and their laboratory performances were compared. Polymer-modified bitumen (PMB) was used as the binder material and no stabilising additive was used, since drain down was within permissible limits for both mixtures with PMB. Conventional cylindrical specimens were prepared in superpave gyratory compactor with bitumen contents 5.0 %, 5.5 %, 6.0 %, 6.5 % and 7.0 % by weight of aggregates, and volumetric and Marshall properties were determined. Tensile strength, behaviour to repeated loading etc. were checked for cylindrical specimens prepared at optimum bitumen content, whereas specially prepared slab specimens were used to check the rutting resistance of SMA mixtures. From the laboratory study, it was observed that, out of the two SMA mixtures, the one with NMAS 16 mm performed better compared to the other. These improved properties may be attributed towards the larger coarse aggregate sizes in the mixture. © 2015, The Author(s).Item Comparison of Stone Matrix Asphalt mixtures with polymer-modified bitumen and shredded waste plastics(Taylor and Francis Ltd. michael.wagreich@univie.ac.at, 2016) Goutham, G.; Lekha, B.M.; Krishna, G.; Ravi Shankar, A.U.Stone Matrix Asphalt (SMA) is a gap-graded bituminous mixture characterised with its improved rut resistance and durability. It has comparatively higher proportion of coarse aggregates and binder mastic with bituminous binder and mineral filler. Drain down of mastic content at various stages of construction is a common issue with SMA, and generally, some fibre additives are used to stabilise the mixture or a modified bitumen is used as the binder material. In this study, shredded waste plastics (SWP) are used instead of other stabilising additives, to prepare SMA mixtures with conventional viscosity graded (VG) 30 bitumen. Mixtures were prepared with four different levels of SWP content, and another mixture without any stabilisers was also prepared using polymer-modified bitumen (PMB). Specimens were prepared in superpave gyratory compactor (SGC) for all mixtures at different bitumen contents to determine volumetric and Marshall properties, and optimum bitumen content (OBC) was calculated for each mixture. Tensile strength, moisture susceptibility, rutting resistance and fatigue behaviour were also determined for all mixtures at corresponding OBC. From the available results, the optimum level of SWP in SMA mixture was determined as 8% by weight of bitumen. The study showed that even though mixture with PMB performed the best, SMA with 8% SWP provided comparable results. Based on the present investigation, waste plastic in suitable dosage can be recommended in SMA, instead of a stabilising additive. © 2015 Informa UK Limited, trading as Taylor & Francis Group.Item Laboratory Evaluation of SMA Mixtures Made with Polymer-Modified Bitumen and Stabilizing Additives(American Society of Civil Engineers (ASCE) onlinejls@asce.org, 2019) Shiva Kumar, G.; Ravi Shankar, A.U.; Ravi Teja, B.V.S.Stone matrix asphalt (SMA) is a gap-graded mixture that consists of two parts, a high concentration coarse aggregate skeleton and a high binder content mortar. The coarse aggregate skeleton provides the mixture with stone-on-stone contact, giving it strength, while the high binder content mortar adds durability. The mortar is typically composed of fine aggregate, mineral filler, asphalt binder, and a stabilizing additive. A stabilizing additive such as natural fibers, mineral fibers, or polymers is added to SMA mixtures to prevent draindown. In addition, it has the potential of reinforcing and improving the tensile strength and cohesion of SMA mixtures. In this study, banana fiber (BF) and pelletized fiber (VP) are used as stabilizing additives to prepare SMA mixtures with conventional viscosity-graded (VG) 30 bitumen. Mixtures were prepared with different levels BF and VP content, and another mixture without any stabilizers was also prepared using polymer-modified bitumen (PMB). Superpave mix design, draindown, fatigue, rutting, workability, and moisture-induced damage properties were evaluated. Results indicated that addition of natural and pelletized fiber controls binder draindown and improves resistance to rutting, fatigue, and moisture-induced damage of SMA mixture. Further, polymer-modified SMA mixtures take less energy for densification compared to SMA mixtures with natural and pelletized fiber. Results also showed that even though polymer-modified SMA mixtures performed better, SMA mixtures with pelletized fiber provided comparable results. © 2019 American Society of Civil Engineers.Item Evaluation of Workability and Mechanical Properties of Stone Matrix Asphalt Mixtures Made With and Without Stabilizing Additives(Springer, 2020) Shiva Kumar, G.; Ravi Shankar, A.U.Stone matrix asphalt (SMA) is a gap-graded mixture which is the combination of higher concentration of coarse aggregate and binder mortar. The coarse aggregate skeleton provides the mixture with stone-on-stone contact, giving it strength, while the high binder content mortar adds durability. The mortar is typically composed of fine aggregate, mineral filler, binder, and a stabilizing additive. A stabilizing additive such as cellulose fibers, mineral fibers, or polymers is added to SMA mixtures to prevent draindown of the mastics. In addition, it has the potential of reinforcing and improving the tensile strength of SMA mixtures. This paper presents the findings of performance of SMA mixtures with and without stabilizing additive. Superpave mix design, draindown, fatigue, rutting, workability, and moisture-induced damage properties of the SMA mixtures was evaluated. Three types of stabilizing additives (B, S, and V), one nominal maximum aggregate size (NMAS) 13.0 mm, and an unmodified asphalt binder (VG-30) were used in the study. Results indicate that the addition of stabilizing additive controls binder draindown and mix design properties of SMA mixtures satisfies the IRC SP 79 requirements. Resistance to rutting, fatigue, and moisture-induced damage of SMA with stabilizing additives were higher than SMA mixture without stabilizing additive. Further, SMA mixture without stabilizing additive takes less energy for densification compared with SMA mixture with stabilizing additives. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.Item 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.Item Synergistic effects of natural fibres and agro-waste ash on the engineering and sustainability of stone-matrix asphalt mixes(KeAi Communications Co., 2025) Akarsh, P.K.; Marathe, S.; Sapal, H.K.; Akshaya Krishna, N.This study investigates the use of non-traditional natural fibres, specifically sisal plant fibres (SF) and coconut coir coir fibres (CCF), in Stone Matrix Asphalt (SMA) mixtures. The objective was to evaluate the optimal binder content, assess Marshall properties, and investigate drain-down, indirect tensile strength, fatigue, and rutting characteristics of the SMA mixes. Additionally, the study explores the use of sugarcane bagasse ash (SBA), an agro-waste, as a substitute for Ordinary Portland Cement (OPC), aiming to promote sustainability and waste management optimization. The research identified the optimal SMA mix with a 0.30% fibre dosage and 10% SBA, demonstrating favorable mechanical properties with Marshall stability and tensile strength ratio exceeding 90%, alongside satisfactory rutting and fatigue performance. The results showed that SF and CCF provided comparable, or even superior, performance to traditional cellulose fibres (CF), positioning them as sustainable alternatives for pavement construction. Further, a Life Cycle Cost Analysis (LCCA) was conducted on conventional and modified SMA mixes, revealing substantial long-term economic benefits. Although SMA mixes incurred slightly higher initial costs, their superior durability and reduced maintenance needs resulted in a 13.6% cost reduction for SMA-CCF and 11.1% for SMA-SF over a 20-year period. Environmental assessments confirmed that substituting synthetic fibres and OPC with SF, CCF, and SBA substantially lowered carbon emissions and enhanced sustainability, with reductions in Global Warming Potential of up to 50%. These findings highlight the potential of natural fibres and SBA in reducing costs and environmental impacts, offering a sustainable solution for future pavement construction. © 2025 Tongji University and Tongji University Press