Faculty Publications
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Item Stone matrix asphalt using aggregates modified with waste plastics(American Society of Civil Engineers (ASCE) onlinejls@asce.org, 2014) Goutham, G.; Lekha, B.M.; Ravi Shankar, A.U.R.Stone matrix asphalt (SMA) is a gap-graded asphalt mixture performing better than conventional dense-graded mixtures. It contains a high concentration of coarse aggregates (forming stone-on-stone contact between them) and high asphalt content. The coarse aggregate skeleton results in better load distribution and the high asphalt content adds durability to the mixture. Due to the high mastic (filler and asphalt) content, there is possibility of drain down during various stages in construction. SMA mix should be prepared with a suitable stabilizing additive to prevent the drain down of mastic material from the mixture. In this study, SMA mixtures are prepared in a Super pave Gyratory Compactor (SGC) with shredded waste plastics, which are mixed with aggregates prior to the addition of Viscosity Graded (VG) - 30 asphalt. Mixtures are prepared with asphalt contents of 5.0 to 7.0 per cent (by weight of aggregates) and stabilizer contents of 0, 4, 8, 12 and 16 per cent (by weight of asphalt). Volumetric and Marshall properties, tensile strength, and moisture susceptibility characteristics are determined. From the laboratory studies, it is observed that addition of waste plastics in shredded form can be used instead of stabilizers by controlling the drain down and enhancing the performance. © 2014 American Society of Civil Engineers.Item SMA mixtures with modified asphalt and treated aggregates(American Society of Civil Engineers (ASCE) onlinejls@asce.org, 2014) Goutham, G.; Lekha, B.M.; Monisha, M.; Ravi Shankar, A.U.Stone Matrix Asphalt (SMA) is a gap-graded asphalt rich mix with a high concentration of coarse aggregates. In the present investigation, SMA mixtures were prepared with chemically treated aggregates and Crumb Rubber Modified Bitumen (CRMB), and were compared for various characteristics. SMA samples were prepared in conventional Marshall and Superpave Gyratory Compactor (SGC) methods. Volumetric and Marshall properties, Indirect Tensile Strength (ITS), rutting and moisture susceptibility, fatigue behaviour and permeability characteristics were determined for these mixtures. From the laboratory studies it is evident that, chemically treated aggregates with normal bitumen (Viscosity Graded (VG) 30) and CRMB with normal aggregates can be used in SMA to meet the drain down requirements. CRMB mixes were observed to be having an upper hand in performance, even though treated aggregates mixes showed better moisture resistance properties. © 2014 American Society of Civil Engineers.Item Laboratory Performance of Superpave Mixes for Perpetual Pavements(American Society of Civil Engineers (ASCE), 2017) Priyanka, B.A.; Goutham, G.; Lekha, B.M.; Ravi Shankar, A.U.Long life asphalt pavement, also known as "Perpetual Pavement", is a pavement with design life more than 50 years and needs only periodic surface renewal. It works on the concept of controlling horizontal tensile strain at the bottom of the asphalt layer and vertical compressive strain at the top of the subgrade to a particular limit. This can be achieved by increasing the binder content of the mix over the optimum binder content (OBC) and by increasing the overall pavement thickness. In the present study two Superpave mixes were prepared using conventional binder at OBC (optimum binder mixture [OBM]) and also at 0.5 % extra binder over OBC (rich binder mixture [RBM]) which can be used in Perpetual Pavements. The mixes were tested for indirect tensile (IDT) strength, moisture susceptibility, fatigue and rutting resistance. From the results it was observed that, OBM performed well as compared to RBM. However the fatigue life of RBM was more compared to the OBM and this helps in reducing the horizontal tensile strain at the bottom of the asphalt layer which in turn increases the life of the pavement. © ASCE.Item Investigation on the Effect of Anti Stripping Additives on the Moisture Sensitivity of Bituminous Concrete(Springer Science and Business Media B.V., 2018) Ravi Shankar, A.U.; Goutham, G.; Lekha, B.M.; Carlton-Carew, C.Moisture damage is one of the most common reasons for the premature deterioration of Hot Mix Asphalt (HMA) pavements. Over the years, extensive research has been carried out by scientists and engineers on this subject; however, pavements still succumb to early failure from infiltrating moisture. A very popular method of minimizing the moisture susceptibility of asphalt pavements is by the use of anti-stripping agents. These additives are chemical substances that alter the physicochemical properties of the asphalt by making it more hydrophobic. This study focuses on the effect of anti-stripping agents on the moisture susceptibility of Bituminous Concrete (BC) mixture. The anti-stripping agents used were hydrated lime and Zycosoil. Three mix types were studied, namely: BC mix without additive, BC mix with hydrated lime and BC mix with Zycosoil. Viscosity Grade (VG) 30 bitumen was used in all three groups of samples. Marshall mix design method was adopted and specimens were prepared at bitumen contents 4.5, 5.0, 5.5, 6.0, 6.5 and 7.0% by weight of mixture. Volumetric properties and Marshall characteristics were determined for each specimen, and using them, the Optimum Binder Content for each mixture was obtained. Moisture susceptibility of mixtures was assessed using Tensile Strength Ratio, Retained Stability and Stripping Value. From the experimental results, it is observed that the addition of anti-stripping agents had a significant positive influence on the results of the test properties being evaluated in each test. © 2018, Springer International Publishing AG.Item Fatigue and Engineering Properties of Chemically Stabilized Soil for Pavements(Springer, 2013) Lekha, B.M.; Ravi Shankar, A.U.; Goutham, G.Soil stabilization is a technique to improve the weak soils and making them to meet certain requirements of the specific engineering projects. The type of soils available in Dakshina Kannada region of Karnataka State is laterite and Lithomarge clay. Its Plasticity Index is very high due to the presence of high percentage of silt and clay content. In the present investigation, an attempt is made to study the behaviour of laterite with and without adding chemicals. A chemical named Zycosoil, when added to water and mixed with soil alters its engineering properties that depend upon the type of the soil and dosage of chemical. These chemicals are liquid additives, which act on the soil to reduce the voids between soil particles and minimize adsorbed water in the soil for maximum compaction. In the present study, the effectiveness of Zycosoil in stabilizing the laterite soils of South Canara district is investigated through laboratory experiments. Various geotechnical properties are studied and correlations between different geotechnical properties and improvement in the soil properties with different percentages of chemical additions are derived. The important properties such as index properties, compaction characteristics, unconfined compressive strength parameters, California bearing ratio values and fatigue behaviour were studied. The results obtained indicate that there is an improvement in almost all properties with the addition of Zycosoil. © 2012 Indian Geotechnical Society.Item Evaluation of lateritic soil stabilized with Arecanut coir for low volume pavements(Elsevier Ltd, 2015) Lekha, B.M.; Goutham, G.; Ravi Shankar, A.U.Soil stabilization is a common method used by engineers and designers to enhance the properties of soil with different stabilizers. From ancient times, usage of natural fiber in soil as reinforcement is an effective technology adopted. This paper presents the effect of including randomly spaced Arecanut coir to the soil mix. The engineering properties and bearing capacity of a soil get enhanced by stabilizing it with Arecanut coir and a binding material (cement). The information available on experiments and research on the behavior of soil cement mixtures were collected and a few studies conducted on fiber reinforcement were referred. The current study mainly focuses on the durability test and physical evaluation of soil cement mixtures reinforced with Arecanut coir. Coir content was varied from 0.2% to 1% with an increment of 0.2%. For further improvement, a uniform dosage of 3% cement was added to soil. Laboratory tests including the Unconfined Compressive Strength (UCS), California Bearing Ratio (CBR), durability and fatigue behavior, were conducted as per standards. The test results indicated that the improvement in characteristics of the soil cement coir mixtures were functions of coir dosage, soil type and curing days. Durability test satisfied at 1% Arecanut coir with 3% cement. The stress-strain values were determined and damage analysis was conducted for the higher dosage of Arecanut coir using KENPAVE software. From the results it is observed that, the Arecanut coir reinforced cement soil mix can be used for low volume roads (traffic ?1 million standard axles) and few design cases have been discussed. © 2014 Elsevier Ltd.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 Effect of Electrolyte Lignin and Fly Ash in Stabilizing Black Cotton Soil(Springer US, 2015) Lekha, B.M.; Goutham, G.; Ravi Shankar, A.U.Subgrade is one of the important layers of any pavement. It must be able to support loads transmitted from pavement structure without excessive deformation under adverse climatic and traffic conditions. In this investigation, laboratory studies were carried out to evaluate the influence of a commercial electrolyte lignin stabilizer (ELS), fly ash (FA) and a combination of both, on black cotton (BC) soil procured from North Karnataka region in India. Basic geotechnical and engineering properties like unconfined compressive strength (UCS), California bearing ratio (CBR), etc. were determined for both untreated and treated soil. Dynamic repeated load test was conducted to examine the fatigue behaviour of the soil. Durability of the soil was checked by wet-dry (WD) and freeze-thaw (FT) cycle tests, and swelling properties by free swell index test. From the studies, it was observed that consistency limits, dry density, UCS and CBR values were improved for treated soil, with curing periods of 1, 7 and 28 days. Weight loss in FT test was less than 14 % for 12 cycles, which ensures that the stabilized soil has become durable. But none of the samples were observed to be withstanding above five cycles in wet-dry test. Soil stabilized with ELS and FA showed better results compared to soil with only ELS. Swelling was reduced to a great extent with 28 days curing period for the former one. From the experimental results, it can be concluded that this chemical can be used as a stabilizer for existing BC soil in site to enhance its subgrade strength. © 2015, Springer New York.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 Evaluation of Superpave mixtures for perpetual asphalt pavements(Taylor and Francis Ltd. michael.wagreich@univie.ac.at, 2019) Priyanka, B.A.; Goutham, G.; Ravi Shankar, A.U.Early deterioration of flexible pavements, due to increased traffic volume, environmental conditions, poor maintenance and construction quality, causes difficulties to road users, all around the world. The structural failures such as fatigue and rutting demand the reconstruction of the pavements which further leads to significant construction cost. One potentially sustainable solution to this problem is to adopt perpetual pavement technology. The fatigue and rutting distresses in the pavements can be minimised to some extent by utilising Superpave mixtures with perpetual pavement concept. This paper proposes two polymer-modified Superpave mixtures, one with optimum amount of binder and the other with rich binder content, for the asphalt intermediate and base layers of perpetual pavement, respectively. The optimum mixtures were prepared with two aggregate gradations having nominal maximum aggregate sizes 25 mm and 19 mm for the intermediate layers to enhance the rutting resistance. Rich mixtures were prepared with the same gradations for the asphalt base layer to improve the fatigue resistance. Laboratory tests were conducted on these mixtures to determine moisture susceptibility, rutting resistance, fatigue behaviour and resilient modulus. The fatigue and rutting criteria of perpetual pavement sections were evaluated using KENPAVE software and the critical strains were found to be within the limits. The experimental results and analysis on perpetual pavement sections with proposed mixtures for the intermediate and base layers show that they can be considered as a better alternative for conventional pavements. © 2018, © 2018 Informa UK Limited, trading as Taylor & Francis Group.