Journal Articles
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Item PFWD, DCP and CBR correlations for evaluation of lateritic subgrades(2009) George, V.; Rao, N.C.; Shivashankar, R.The evaluation of subgrade strength plays a major role in pavement design. An understanding of subgrade properties enables the selection of road materials for sub-base and base courses. In developing countries like India, apart from the use of well-established traditional pavement evaluation techniques such as the California bearing ratio (CBR) test and the dynamic cone penetrometer (DCP) test, the use of non-destructive testing devices such as the portable falling weight deflectometers (PFWDs) has gained popularity in recent years. This is mainly because of the inherent capability of PFWDs in obtaining quick estimates of the modulus of subgrade in addition to their simplicity in design and portability. Thus, there exists a need to correlate the results obtained using PFWDs with those obtained using traditional approaches such as the CBR and the DCP for the benefit of road engineers. This work focuses on exploring the correlations between these approaches for lateritic soils in Dakshina Kannada district, India.Item Evaluation of properties of porous friction course mixes for different gyration levels(2009) Suresha, S.N.; George, V.; Shankar, A.U.R.Porous frictions courses (PFCs) are characterized by high percent air voids content, and are widely used as pavement surface drainage layers. This paper presents details on the laboratory investigation performed on evaluation of properties of PFC mixes using the Superpave gyratory compactor. It also, provides a brief review of the latest specifications related to standard practices for mix design and the uses of these mixes adopted by various agencies. Major differences were observed in the design gyrations (Ndesign) and the design aggregate gradations. In this study, six gradations (G) were investigated with binder contents (BCs) ranging between 4.0 and 5.0% by mass of the total mix, for various gyration levels (N). The effect of N, G, and BC on the volumetric properties, unaged abrasion loss, permeability, and the permanent deformation characteristics of PFC mixes were investigated. The experimental results were statistically analyzed to identify the major influencing factors and their significance. © 2009 ASCE.Item Laboratory and theoretical evaluation of clogging behaviour of porous friction course mixes(2010) Suresha, S.N.; George, V.; Ravi Shankar, A.U.The clogging of porous friction courses (PFCs) plays a major role in their resulting performance. Clogging occurs due to deposition of external and internal materials, leading to the loss of permeability and drainage characteristics of PFCs. In this study, investigations were conducted to determine the effect of clogging and de-clogging on the permeability of PFC mixes. Tests were conducted to study the effect of three different clogging materials on PFC mixes prepared using four different aggregate gradations. Permeability tests were conducted using the falling-head concept on cylindrical PFC specimens. The influence of the particle size ratios and the effective air voids on the permeability of fresh, clogged and de-clogged PFC specimens was analysed. Experimental results on the permeability observed were compared with those predicted using theoretical models. Although, the theoretical models tend to overestimate the permeability values, statistical analyses indicate good correlations with the observed results.Item Studies on iron tailings towards usage for paving blocks manufacture(2010) Mangalpady, M.; Sampath Kumar, N.N.Disposal of mill tailings is one of the major problems in mining industry. Investigations are being done all over the world to utilize tailings for useful purposes. The scope of this work is to study the utilization of iron ore tailings in manufacture of concrete paving blocks. Five reference mixes were prepared using cement, jelly dust and baby jelly. Ten paving blocks were prepared from each type of mix, out of which five specimens were cured for 7 days and five were cured for 28 days. By using sand and tailings as fine aggregates, two modified mixes were prepared by replacing jelly dust partly in reference mixes. Similar to reference mix, five mix ratios were made and ten paving blocks were prepared from each type of mixtures. From each set of paving blocks, five specimens were cured for 7 days and the other five specimens were cured for 28 days. Laboratory tests were conducted to assess water absorption and compressive strength of specimens, and graphs were plotted for their comparison among each type of respective mix ratios. In all the comparisons, compressive strength of tailing based mix was higher than the respective reference mix. Similar trend is shown by the graphs plotted for water absorption. © 2010 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved.Item A model study on accelerated consolidation of coir reinforced laterite and blended shedi soil with vertical sand drains for pavement foundations(2012) George, V.; Santosh, G.; Hegde, R.N.; Durga Prashanth, L.; Gotamey, D.; Ravi Sankar, A.U.Sub-grade soils of lateritic origin are frequently encountered in the construction of highway embankments in various regions of India, often comprise intrusions of soft lithomargic soils that result in large settlements during constructions, and differential settlements at later stages. This necessitates the use of appropriate soil improvement techniques to improve the load-carrying capacity of pavements. Coir is a natural fiber that can be used in place of geosynthetics and geogrids, and it is biodegradable and environment friendly. This work deals with the accelerated consolidation of un-reinforced and coir-reinforced laterite and blended lithomargic soils, provided with three vertical sand drains. The load-settlement characteristics were studied for various preloads ranging from 50kg (0.0013 N/mm2) to 500kg (0.013N/mm2) using circular ferro-cement moulds. It was observed that at lower preloads up to 300kg, the relative increase in consolidation (Cr) for randomly reinforced soil with vertical drains was significantly higher than that of un-reinforced soil without vertical drains. Also, the Cr for un-reinforced soil with vertical drains was quite higher than that of un-reinforced soil without vertical drains, with values above 38.71%. However, in the case of higher preloads of 450kg and 500kg, the Cr for randomly reinforced soil with vertical drains was insignificant, and the Cr for un-reinforced soil with vertical drains remained slightly higher at around 9.59% for similar comparisons. The aspect-ratio of coir fibers used was 1: 275. © 2012 Cafet-Innova Technical Society. All rights reserved.Item Accelerated consolidation of coir reinforced lithomargic laterite soil blends with vertical sand drains for pavements(2012) George, V.; Hegde, R.N.; Vardhana, M.V.; Santosh, G.; Gotamey, D.It is found that sub-grade soils of lateritic origin encountered in the construction of highway embankments in various regions of India, often comprise intrusions of soft lithomargic soils that result in large settlements during constructions, and differential settlements at later stages. This necessitates the use of appropriate soil improvement techniques to improve the load-carrying capacity of pavements. This work deals with the accelerated consolidation of un-reinforced and coir-reinforced laterite and blended lithomargic soils, provided with three vertical sand drains. The load-settlement characteristics were studied for various preloads ranging from 50kg (0.0013 N/mm2) to 500kg (0.013N/mm2). Studies were performed using circular ferro-cement moulds. It was observed that at lower preloads of up to 250kg, the relative increase in consolidation (Rct) for randomly reinforced soil with vertical drains was significantly higher than that of un-reinforced soil without vertical drains. Also, the Rct for un-reinforced soil with vertical drains was quite higher than that of un-reinforced soil without vertical drains, with an average value of 20.84%. In the case of higher preloads the Rct values for randomly reinforced soil with vertical drains were moderate with an average value of 22.67%. An additional increase of up to 27% at lower pre-loads and 11.83% at higher pre-loads was observed due to the effect of random reinforcement when compared to use of vertical drains alone. © 2012 ejge.Item A study on the factors influencing the load transfer efficiency in concrete block pavements(2012) Thameel, S.S.; Amar Kumar, D.S.N.V.; Pancharathi, P.Concrete Block Pavements (CBP) are essentially precast blocks arranged in a specific pattern over a sub base and interlocked with graded bedding and jointing sand. The block size and shape, joint gap and joint filling sand size and laying pattern influence the effectiveness of the interlocking or the distribution of wheel loads. The measure of effectiveness - Load Transfer Efficiency (LTE), is the ratio of deflection between a loaded block to an adjacent unloaded block. In the present LTE study, joint filling sand of three particle sizes (1.18, 0.6 and 0.3mm), laying patterns of two types [stretcher and basket weave), concrete mixes with four variations (cement, cement with 20% fly ash, cement with steel fibre (0.5%) and cement with both fly ash and steel fibre] were tested. The test section consisted of 100 mm x 200 mm x 100mm blocks fixed over a 20 mm thick bed of 4.75 mm sand. A wet mix macadam layer over the sub grade supported the blocks. The study revealed that the joint filling with 0.6 mm sand gave a higher LTE than the other two sizes. The basket weave resulted in a higher average LTE than the stretcher bond and incorporating steel fibre and fly ash in concrete also showed an increase in the LTE.Item Investigations on Alkali-Activated Slag/Fly Ash Concrete with steel slag coarse aggregate for pavement structures(Taylor and Francis Ltd. michael.wagreich@univie.ac.at, 2017) Palankar, N.; Ravi Shankar, A.U.; Mithun, B.M.The present investigation is conducted to evaluate the effect of steel slag coarse aggregates on mechanical properties and fatigue behaviour of Alkali-Activated Slag Fly Ash Concrete (AASFC) mixes. AASFC mixes were prepared with steel slag coarse aggregates by replacing natural coarse aggregates at various replacement levels (0, 25, 50, 75 and 100% by volume). Various mechanical properties and fatigue performance were tested and compared with conventional Portland concrete. The incorporation of steel slag aggregates resulted in decrease in mechanical strength of AASFC mixes. The fatigue lives of AASFC mixes containing steel slag were found to be lower than AASFC with natural coarse aggregates. Two-parameter Weibull distribution was used for statistical analysis of fatigue data and it was observed that the fatigue data of concrete mixes can be approximately modelled using Weibull distribution. Steel slag aggregates reported acceptable performance in AASFC mixes for its use in pavement quality concrete. © 2015 Informa UK Limited, trading as Taylor & Francis Group.Item A Study on Elastic Deformation Behavior of Steel Fiber-Reinforced Concrete for Pavements(Springer, 2019) Chandrashekar, A.; Palankar, N.; Durga Prashanth, L.; Mithun, B.M.; Ravi Shankar, A.U.The present study discusses the experimental investigation of steel fiber-reinforced concrete slabs on ground under wheel load with the objective of understanding the stress behavior when subjected to central and edge wheel loading. The steel fiber-reinforced fly ash concrete slabs of 900 mm × 900 mm, 150 mm thickness were investigated in this study. Strain gauges and data acquisition system were used to measure the strains at the center and the edge of the slab under the action of the load. The load versus strain relationship under central and edge loading for reference concrete and steel fiber fly ash concrete showed a linear variation even up to the pressure of 2.5 MPa, which is much beyond the conventional tyre inflation pressure of 0.8 MPa. The load versus strain graphs clearly signify the higher modulus of elasticity of fly ash steel fiber-reinforced concrete. The stresses were calculated using IITRIGID software and ANSYS software and were found matching significantly. The value of modulus of elasticity of fly ash steel fiber-reinforced concrete (FS) using ANSYS model for experimental values of load and strains measured was approximated to 34,000 N/mm2 and was found to closely match with the experimentally obtained modulus of elasticity. No significant effect of Poisson’s ratio of concrete on load–strain characteristics was observed within the range 0.15–0.2 of concrete. © 2019, The Institution of Engineers (India).Item Use of Stabilized Lateritic and Black Cotton Soils as a Base Course Replacing Conventional Granular Layer in Flexible Pavement(Springer, 2020) Amulya, S.; Ravi Shankar, A.U.The present work investigates the improved properties of lateritic and black cotton soils stabilized with ground granulated blast furnace slag (GGBFS) and alkali solutions. The alkali solution includes a mixture of sodium hydroxide and sodium silicate. The lateritic and black soils are treated with 30% GGBFS and the alkali solutions consisting of 6% Na2O having silica modulus (Ms) of 0.5, 1.0 and 1.5 at a constant water binder ratio of 0.25. The treated samples were air-cured for 0 (immediately after casting), 3, 7 and 28 days at ambient temperature. The treated lateritic soil with 0.5 and 1.0 Ms is found durable after 3, 7, and 28 days curing. Whereas, the treated BC soil found durable with Ms 0.5 at modified Proctor density after 28 days curing. The formation of calcium silicate hydrate and calcium aluminosilicate hydrate structures resulted in a remarkable improvement of compressive strength, flexure and fatigue life of treated soils due to dissolved calcium ions from GGBFS, silicate and aluminium ions from alkali solutions. The microstructure image of the durable soil sample shows the crystal orientation of particles. The design of high and low volume roads is proposed by replacing the conventional granular layer with the durable stabilized soil and stress–strain analysis is carried out using pavement analysis software. © 2020, Springer Nature Switzerland AG.