Browsing by Author "Ravishankar, A.U."

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Alkali activated concrete with steel slag aggregate for concrete pavements
(Science Publishing Corporation Inc ijet@sciencepubco.com, 2018) Palankar, N.; Mithun, B.M.; Ravishankar, A.U.
In the present study, an attempt is made to investigate the usability of steel slag, which is a byproduct from the iron and steel industry, as coarse aggregates in alkali activated slag/ fly ash concrete mixes. The mix design for alkali activated slag/ fly ash concrete mixes was optimized and further steel slag coarse aggregates were incorporated in the optimized alkali activated slag/ fly ash concrete mixes mix by replacing natural coarse aggregates at different replacement levels (0%, 25%, 50%, 75% and 100% by volume). The mechanical properties were studied in detail. The flexural fatigue behavior of concrete mixes were investigated The experimental results showed that alkali activated slag/ fly ash concrete mixes with steel slag aggregates display slightly lower mechanical strength as compared to natural aggregates. The fatigue life of alkali activated slag/ fly ash concrete mixes was found to decrease with the inclusion of steel slag aggregates. The performance of steel slag aggregates in alkali activated slag/ fly ash concrete mixes was found satisfactory for use in pavement quality concrete. © 2018 Authors.
Design Consistency Evaluation of Rural Highways
(National Institute of Technology Karnataka, Surathkal, 2013) N.J, Sowmya; Ravishankar, A.U.
Rapid growth of population and increasing economic activities are the twin factors that contribute to the tremendous increase in the vehicle population which, in turn, contributes to the growing number of road accidents. Road accidents are complex events involving a variety of factors, including highway geometry, driver behaviour, weather conditions, and speed limits. Several studies have been conducted to determine the relationship between factors associated with accidents and their effect on safety. Improving highway design consistency is considered to be an important strategy for improving traffic safety. Geometric design consistency evaluation is a widely used method of determining sections of highways which require alignment improvement. Identifying and treating any inconsistency on a highway can significantly improve its safety performance. A critical factor in highway design is maintaining a good consistency with a road geometry that meets the driver’s expectations. Considerable research has been undertaken to explain this concept, including identifying potential consistency measures and developing models to estimate them. However, considerable amount of work has not been carried out to evaluate the geometric consistency in India. Rural roads constitute about 80 per cent of Indian road network. Therefore, rural road safety accounts for a considerable share of the total road safety problem. In Dakshina Kannada District, and even in Karnataka state, intermediate lane highways make more than 50 per cent of the principal road network. The majority of these intermediate lane rural highways are historical routes and many of them do not follow a specific design code. Therefore, road safety of intermediate lane roads is a very important issue in the development of the country. This study aims to enhance the safety of these existing highways based on an understanding of actual driving behaviour by means of field data measurements, and to verify their conformance to a consistency evaluation model. Both horizontal and vertical alignments are the main focus of this study. The horizontal alignment of a road consists of a straight tangent followed by horizontal curve, whereas the vertical alignment of the road consists of a level section followedvii by a vertical curve. This study deals with developing appropriate design consistency evaluation criteria of horizontal and vertical curves using geometric, speed, and accident data of eight intermediate lane rural highways. Geometric details of a road were collected from the field and CAD (Computer Aided Design) drawings were prepared using the details of surveying. A spot speed survey was conducted for passenger cars on the approach tangent and at the beginning, middle, and end points of horizontal curves and on the approach tangent, limiting point and summit point of vertical curves. The accident details were collected for six years (from 2005 to 2010) from different police stations. The operating speed prediction models were developed for both horizontal and vertical curves. The speed change experienced by the same driver from tangent to curve i.e. speed differential was also studied for horizontal curves, and the models were developed to predict this change. Consistency evaluation criteria for horizontal curves and vertical curves were also developed to enhance the safety of the alignment. Alignment indices, are the another set of quantitative measures, were used to identify the inconsistencies that exist on intermediate lane rural highways. Finally, an attempt was made to develop the relationship between safety and alignment indices.
Estimation of Willingness to Pay for Reducing Road Accident Risk Using Route Choice Model
(Springer Science and Business Media Deutschland GmbH, 2023) Sumayya Naznin, P.H.; Anandu, V.G.; Panackel, L.S.; Ravishankar, A.U.
The proportionality of road accidents with urbanization triggers road accident cost analysis, as a prime component in the planning and designing of road projects. However, proper quantification of accidents and analyzing every parameter associated with it is a tedious task and requires expert approaches. This study deals with the cost of road accidents in Thiruvananthapuram city as it houses the most critical accident spots in the state of Kerala. Essential stretches of roads to be analyzed were identified using Accident Severity Index (ASI). A Stated Preference (SP) survey was conducted to estimate the trip-wise mean willingness to pay value (WTP) of road users of the selected road stretches based on logit models. Travel time, travel costs, and accident rates were taken as the attributes. The behavior of individual users was interpreted from the coefficients estimated from the models. The mode-specific variables showed relations consistent with the expectations. The willingness to pay value to avoid a critical accident estimated from the final model was found higher for short trip setting (Rs.1.08/trip), which indicates the importance of safety of the short frequent trips among the road users compared to the longer trip setting (Rs. 0.72/trip). Â© 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG.
Fatigue behavior of Lateritic soil stabilized with enzyme and effectiveness of flexible pavement with stabilized soil as sub-base
(2011) Mithanthya, I.R.; Ravishankar, A.U.; Rao, N.B.
The Lateritic soil is abundantly available in coastal Karnataka (India). To improve its properties the soil has to be stabilized either mechanically or chemically. Soil stabilization using enzyme is one of the methods developed recently. Various experimental investigations have shown that Atterberg's limit values are improved favorably and there is increase in CBR values. The unconfined compressive strength increases with the increase in curing period when treated with enzyme. These improvements mainly depend on type of soil and enzyme used. In recent past many enzymes have come to the market which can be used as a stabilizing agent. In the present investigation commercially available enzyme is used for stabilization of lateritic soil and improvement in Unconfined Compressive Strength (UCS) has been investigated. It has been observed that the enzyme treated soil shows significant improvement in terms of UCS with longer curing period. Considering this, fatigue behavior of enzyme stabilized soil samples has been studied to find relationship between UCS, fatigue life, enzyme dosage and curing period and correlation between them has been established through multiple regression analysis. Considerable amount of improvement is observed in its fatigue behavior when subjected to repeated loading. This enzyme stabilized soil is used soil as sub base layer in the design of flexible pavements. Using the results of laboratory tests on enzyme treated lateritic soil, the thickness of sub base required has been calculated with the help of "KENPAVE" software. The thickness obtained is compared with the thickness suggested by Indian Road Congress (IRC) for defined sub grade strength (CBR value). Cost comparison has been made considering conventional method of design. � 2011, Advanced Engineering Solutions.
Fatigue behavior of Lateritic soil stabilized with enzyme and effectiveness of flexible pavement with stabilized soil as sub-base
(2011) Mithanthaya, I.R.; Ravishankar, A.U.; Rao, N.B.
The Lateritic soil is abundantly available in coastal Karnataka (India). To improve its properties the soil has to be stabilized either mechanically or chemically. Soil stabilization using enzyme is one of the methods developed recently. Various experimental investigations have shown that Atterberg's limit values are improved favorably and there is increase in CBR values. The unconfined compressive strength increases with the increase in curing period when treated with enzyme. These improvements mainly depend on type of soil and enzyme used. In recent past many enzymes have come to the market which can be used as a stabilizing agent. In the present investigation commercially available enzyme is used for stabilization of lateritic soil and improvement in Unconfined Compressive Strength (UCS) has been investigated. It has been observed that the enzyme treated soil shows significant improvement in terms of UCS with longer curing period. Considering this, fatigue behavior of enzyme stabilized soil samples has been studied to find relationship between UCS, fatigue life, enzyme dosage and curing period and correlation between them has been established through multiple regression analysis. Considerable amount of improvement is observed in its fatigue behavior when subjected to repeated loading. This enzyme stabilized soil is used soil as sub base layer in the design of flexible pavements. Using the results of laboratory tests on enzyme treated lateritic soil, the thickness of sub base required has been calculated with the help of "KENPAVE" software. The thickness obtained is compared with the thickness suggested by Indian Road Congress (IRC) for defined sub grade strength (CBR value). Cost comparison has been made considering conventional method of design. Â© 2011, Advanced Engineering Solutions.
Investigations on Accelerated Consolidation of Coir Reinforced Laterite, Lithomargic Clay and Blended Soils with Vertical Sand Drains for Pavement Foundations
(National Institute of Technology Karnataka, Surathkal, 2013) Hegde, Ramakrishna; George, Varghese; Ravishankar, A.U.
Pavement layers built over the sub-grades are designed to transmit loads to the soil layers below, keeping the deformations within limits even under adverse climatic and loading conditions. Sub-grades on embankments need to provide structural stability to support trafficloads. Soil obtained from borrow pits, transported, and laid on embankments for highway construction, have very low CBR values in the range of 1-2%. In the conventional practice of road construction, the consolidation of soil layers take 1-2 years to materialize after the soil is compacted. In this context, the use of natural fibers such as coir in providing vertical sand drains and in soil-reinforcement is expected to accelerate the process of consolidation by permitting pore-water pressures to be easily dissipated when subjected to overburden pressures, which will prevent further subsidence of lateritic sub-grades. The use of vertical drains, accelerate the radial drainage and enhance consolidation, by reducing the length of the drainage paths. However, it is found that more investigations need to be performed on the use of vertical drains for coir-fiber reinforced lateritic soils of the peninsular regions of India with special reference to the District of Dakshina Kannada. Research in this direction is expected to generate information on improving the efficiency of vertical drains, and will have a profound influence in the field of highway construction especially in tropical regions where coir is abundantly available. Laterite and Lithomargic (Shedi) soil samples used in this study were collected from a site close to National Institute of Technology Karnataka, located in the district of Dakshina Kannada, India. Tests for basic properties and CBR, were performed as per specifications of Bureau of Indian Standards (BIS). Investigations on consolidation were performed for samples of laterite soils, shedi soils and laterite blended with shedi (lithomargic) soils, using circular test moulds of ferrocement (of 70 cm. internal diameter, and 85 cm. internal height). Tests for consolidation were performed on the un-reinforced soil samples with and without the use of vertical sand drains. Similar tests were performed on randomly reinforced soil samples also, to assess the effect of the use of vertical drains. The randomly reinforced soil samples were prepared for optimal coir-fiber content by weight of soil, determined based on CBR studies. Each soil sample was first subjected to a preload of 50 kg (1.2x10-3 N/mm2) at the top of the cylindrical test mould, and the settlement was studied. When the settlement rate reduced to lesser than 0.02 mm per hour, the next increment of preload was applied. The procedure was repeated until the settlement readings were taken for a final preload of 500kg (11.6 x10-3 N/mm2). In the above studies, locally available river-sand passing through 4.75 mm IS sieve was used for fabricating the vertical drains. The aspect-ratio of coir fiber used was 1: 275. In this study, the use of sand randomly distributed with 1.0 % coir fiber was used. The coir reinforcement imparts lateral stability to the vertical drain, while enhancing the drainage properties. River sand of same characteristics was used in the preparation of the top and bottom layers of the cylindrical test mould to ensure uniform loading and drainage for the tests for settlement and consolidation. While analyzing the results for 100%L+0%S, it was seen that the soil attained stability at around the 121st minute after application of the pre-loads for UR (un-reinforced soil), UR-VD (un-reinforced soil with vertical drains), and RR-VD (randomly-reinforced soil with vertical drains). Using the 121st minute as the datum, it was observed that the effect ofproviding vertical drains alone was not significant when compared to the rate of settlement, for the entire range of pre-loads from 50 kg (1.2x10-3N/mm2) to 500kg (11.6x10-3N/mm2). Also, in the case of 100%L+0%S UR soils, it was observed that the maximum value of Cv of 2.0825 cm2/s was found to occur at a higher pressure range of 3.5 to 4.6 x10-3 N/mm2. In the case of UR-VD soil conditions, the maximum value of Cv of 2.2683 cm2/s was found to occur at a lower pressure range of 2.3 to 3.5 x10-3 N/mm2. Also, in the case of RR-VD soil conditions, the maximum value of Cv of 2.2882 cm2/s was found to occur at a lower pressure range of 2.3 to 3.5 x10-3 N/mm2. This indicates that the consolidation occurs at a faster rate at lower pressure ranges for reinforced soils. While analyzing the results for 0%L+100%S, it was seen that the soil attained stability at around the 225th minute after application of the pre-loads for UR, UR-VD, and RRVD soils. Using the 225th minute as the datum, it was observed that the effect of providing vertical drains was significant considering the rate of settlement for pre-loads ranging from 50kg (1.2x10-3N/mm2) to 250kg (5.8x10-3N/mm2). However, for higher pressures varying from 300kg (7x10-3 N/mm2) to 500kg (11.6x10-3N/mm2), further settlement was not found to be significant. For UR-VD soils, the relative increase in the settlement when compared to that of UR soils, ranged between 40.61% and 294.55%, with an average increase of 176.6% for the preload ranging between 50kg (1.2x10-3 N/mm2) and 250kg (5.8 x10-3 N/mm2). This is very significant from the practical point of view. But for pre-loads higher than 250kg, the effect of providing vertical sand drains alone (as in UR-VD soils) was not significant as it was found to vary between 4.01% and 13.06% only, with an average increase of 7.67%. Also the case of 0%L+100%S RR-VD soils, there was an additional increase of 32.6% in the settlement when compared to that of UR-VD soils for pre-load ranging from 50kg (1.2x10-3N/mm2) to 250kg (5.8x10-3N/mm2). For higher pre-loads, an increase of 10.76% was observed. Thus, it can be concluded that for 0%L+100%S RR-VD soils, there is a significant increase in settlement due to random reinforcement with coir fibres when coupled with the use of vertical drains. In the case of 0%L+100%S UR soils, it was observed that the maximum value of Cv of 1.0821 cm2/s was found to occur at a higher pressure range of 3.5 to 4.6 x10-3 N/mm2. In the case of UR-VD soil conditions, the maximum value of Cv of 1.3661 cm2/s was found to occur at a lower pressure range of 2.3 to 3.5 x10-3 N/mm2. Also, in the case of RR-VD soil conditions, the maximum value of Cv of 1.8277 cm2/s was found to occur at a lower pressure range of 2.3 to 3.5 x10-3 N/mm2. This indicates that the consolidation occurs at a faster rate at lower pressure ranges for reinforced soils. Similar studies were made on 75%L+25%S soils, 50%L+50%S and 25%L+75%S soils. In the above study, it was observed that in the case of lithomargic soils there was a significant increase in settlement at lower preload pressures. Reinforced soils of this category also displayed very high settlements, indicating that softer soils can be effectively consolidated using vertical drains and random reinforcements using natural fibers. In the case of pure lateritic soils, the use of vertical drains alone was not found to be effective. However, for other lateritic blends, the use of vertical drains significantly contributed to the settlement.
Stabilization of lateritic soil using bio-enzyme
(2008) Mithanthaya, I.R.; Ravishankar, A.U.
Soil stabilization is a technique aimed at increasing or maintaining the stability of a soil mass, or otherwise improving its engineering properties. Various techniques are being used for stabilization of soil. Sub-base is an integral part of the road pavement structure. The main function of the sub-base is to provide a stress transmitting medium for spreading the surface wheel load in such a manner as to prevent shear and consolidated deformations. A number of researchers worked on characterizing variousus properties of the laterite soil and found that the following problems could be associated with the laterite: 1)In the majority of cases, the laterite doesn't satisfy conventional specifications for road construction materials especially road base. 2) The laterit undergoes property changes during construction; gradation being considered to be the most sensitive. To improve on the above deficiencies and consequently to improve on there field performance characteristics, laterites need to be stabilized. Bioenzyme - stabilization is a newer technique for strengthening the sub-base soil. The Bioenzyme alters the engineering properties of soil such as the capacity to bear loads. These enzymes are liquid additives, which act on the soil to reduce the voids between soil particles and minimize absorbed water in the soil for maximum compaction. The locally available laterite soil procured from the field is used to improve the strength and bearing capacity. One type of Bio-enzyme namely TerraZyme has been used for stabilization of laterite soil. In this study soil with variable enzyme dosages were tested for stabilization process and strength of the stabilized soil has been evaluated after curing period of one week, two weeks, three weeks and four weeks. The tests were carried out to determine the consistency limits, CBR, unconfined compressive strength and permeability of the soil specimens with and without enzyme for a curing period of one week to four weeks. The effect of enzyme on different percentages of sand blended laterite soil was also studied for the curing periods. The enzyme treated soil showed significant improvement in CBR (California bearing ratio) and UCS (Unconfined Compressive strength) with curing. � AES-Advanced Engineering Solutions.
Stabilization of lateritic soil using bio-enzyme
(2008) Mithanthaya, I.R.; Ravishankar, A.U.
Soil stabilization is a technique aimed at increasing or maintaining the stability of a soil mass, or otherwise improving its engineering properties. Various techniques are being used for stabilization of soil. Sub-base is an integral part of the road pavement structure. The main function of the sub-base is to provide a stress transmitting medium for spreading the surface wheel load in such a manner as to prevent shear and consolidated deformations. A number of researchers worked on characterizing variousus properties of the laterite soil and found that the following problems could be associated with the laterite: 1)In the majority of cases, the laterite doesn't satisfy conventional specifications for road construction materials especially road base. 2) The laterit undergoes property changes during construction; gradation being considered to be the most sensitive. To improve on the above deficiencies and consequently to improve on there field performance characteristics, laterites need to be stabilized. Bioenzyme - stabilization is a newer technique for strengthening the sub-base soil. The Bioenzyme alters the engineering properties of soil such as the capacity to bear loads. These enzymes are liquid additives, which act on the soil to reduce the voids between soil particles and minimize absorbed water in the soil for maximum compaction. The locally available laterite soil procured from the field is used to improve the strength and bearing capacity. One type of Bio-enzyme namely TerraZyme has been used for stabilization of laterite soil. In this study soil with variable enzyme dosages were tested for stabilization process and strength of the stabilized soil has been evaluated after curing period of one week, two weeks, three weeks and four weeks. The tests were carried out to determine the consistency limits, CBR, unconfined compressive strength and permeability of the soil specimens with and without enzyme for a curing period of one week to four weeks. The effect of enzyme on different percentages of sand blended laterite soil was also studied for the curing periods. The enzyme treated soil showed significant improvement in CBR (California bearing ratio) and UCS (Unconfined Compressive strength) with curing. Â© AES-Advanced Engineering Solutions.
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.