Browsing by Author "Ravi Shankar, A. U."

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Analysis and Prediction of Road Accident Cost
(National Institute of Technology Karnataka, Surathkal, 2024) P H, Sumayya Naznin; Ravi Shankar, A. U.; Mohan, Mithun
Road traffic accidents (RTAs) significantly impact a country's economic advancement by consuming a large portion of its Gross Domestic Product (GDP), especially in developing countries. The proportionality of road accidents with urbanization mandates road accident cost analysis as a prime component in the planning and designing of road projects. The quantification of accidents and their associated parameters remains challenging, as it demands a meticulous approach. Moreover, allocation towards road safety infrastructure should be based on a cost-benefit analysis to ensure the most efficient use of available resources in formulating road safety policies, reinforcing the significance of road accident cost estimation. Different countries use varying methodologies for this estimation, rendering international comparisons unreliable. Notably, the existing methodologies mainly focus on developed countries, leaving a gap in the literature for developing nations. Human Capital (HC) and Willingness to Pay (WTP) are two commonly used approaches for estimating accident costs. The HC method, using diverse data sources such as police accident databases, questionnaire surveys, private hospital records, and vehicle garage bills (considering collision types), provides a component-wise breakdown of costs. The RTA cost estimation using the HC method reveals the loss of productivity, accounting for 49% of total costs, as the most significant component. Medical costs comprised 24%, vehicle damage 10%, human costs 16%, and administrative costs accounted for a mere 1%. However, this method overlooks intangible factors like pain, grief, and suffering (PGS) along with the contribution of post-retirement victims and caregivers of RTA victims. In contrast, the WTP-stated preference methodologies, Contingent Valuation (CV), and Discrete Choice Experiments (DCE) used in this study provide insight into the intangible costs, although with varying degrees of accuracy. Notably, WTP-CV estimates tend to have a lower bound, whereas WTP-DCE estimates are substantially higher. WTP-CV payment card approach reveals that accident costs are mostly influenced by population and risk reduction, with socioeconomic factors and driving behaviour also playing a major role. Meanwhile, the WTP-DCE method indicates that travel attributes have a greater impact on WTP than socioeconomic factors. Taking into account the limitations of both HC and WTP, a Hybrid method is proposed. This approach modifies the conventional HC method by incorporating the concept of Value of Statistical Life (VSL) to account for intangibles such as PGS. It also acknowledges the contributions of post-retirement victims and caregivers of RTA victims. The VSL concept, in conjunction with the Maximum Abbreviated Injury Scale (MAIS), enables a more comprehensive cost estimation, with PGS comprising 56% of total costs in the Hybrid method. In contrast, the productivity loss is reduced to 17%, ensuring the method is not solely focussed on lost productivity. Considering the nation's economic situation, using the weighted average method, the VSI for grievous and minor injuries was determined to be 19.4% and 3.6%, respectively, which can be implemented in regions with similar socioeconomic profiles. A Python-based program is developed, making this methodology more accessible and applicable. This tool can evaluate the severity of an accident, computing the resultant loss. A similar tool is also developed for calculating court-awarded compensations. The comparison results indicate that the cost and compensation differences are substantial and that compensation is typically less than the RTA cost, as it is predominantly based on the subjective judgment of the court. Using an expert opinion survey, the Hybrid method was adjudged as the best suited method for RTA cost estimation for accidents of different severity as more than 60% of the experts chose the RTA cost estimated using the Hybrid method over the other methods across various test scenarios. In conclusion, while the Hybrid methodology provides a more holistic perspective of accident costs, it still provides an estimate with a lower bound. This study does not consider some costs, such as infrastructure damage and traffic congestion. However, the approach highlights the imperative need to comprehend and estimate the true economic and intangible effects of road accidents, particularly in developing nations.
Assessment of Impact of Roadside Frictions on Passenger Car Unit Values and Capacity of Urban Roads in Disordered Traffic Using Microscopic Simulation Model
(National Institute of Technology Karnataka, Surathkal, 2021) Raj, Pooja; Ravi Shankar, A. U.; Gowri, A.
Representation of traffic in terms of its car equivalences (Passenger Car Unit) is more appropriate to estimate capacity in disordered traffic due to the presence of several vehicle types with varying static and dynamic characteristics following poor lane discipline. Many attempts have been made to overcome the complexities involved in accurate estimation of Passenger Car Unit (PCU) in disordered traffic. The widely used method for PCU estimation considers the relative speed and projected area (length × width) of vehicles. However, as a vehicle will be influenced by a larger area than its projected area, which is proportionate to the surrounding vehicle types (effective area of a vehicle); this study aims to deal with the influence of surrounding vehicles while estimating its PCU value under disordered traffic condition. PCU values are influenced by various factors such as traffic conditions, geometric conditions, road side frictions, etc. Among these factors, roadside frictions (e.g., curbside bus stops, undesignated pedestrian crossings, roadside parking) cause significant deterioration in the quality of urban traffic flow and thus, considerably influence road capacity which in turn affects the PCU values. Many research works have been carried out to investigate the impacts of some of the influencing factors (e.g., vehicular composition, traffic volume, road width) on traffic characteristics as well as PCU values. However, the sensitivity of PCU values and capacity due to the presence of roadside frictions are not adequately studied. Furthermore, PCU values and capacity for urban roads recommended by the existing manuals (e.g., IRC 106 1990) are applicable only for the ideal/base sections i.e., the section devoid of any side frictions. The recently published highway capacity manual (Indo-HCM 2017) suggests adjustment factors for capacity estimation of roads with the presence of a few side frictions (e.g., parking, access points, bus stops), however, the adjustment factors for estimating PCU values are not suggested. To address these gaps, this research study aims to estimate PCU values for vehicles under the influence of curbside bus stop and undesignated pedestrian crossings which are the most common roadside frictions being observed in developing countries. As the change in PCU values will have an influence on capacity as well, it is essential to study the impact of curbside bus stop and undesignated pedestrian crossings on capacity. Lack of space for providing ii exclusive bus bays and higher demand for public transport buses in urban roads justify the need for investigating the influence of curbside bus stop. The non-compliant behaviour of pedestrians at undesignated pedestrian crossings creates complex vehicle-pedestrian interactions which affect the capacity of roads and thus, this justifies the need for studying the influence of pedestrians. Furthermore, the influence of side frictions on PCU values and capacity are not considered in the existing studies which used simulation tools. Hence, this study mainly aims at development of a simulation model to examine the influence of these side frictions on PCU values as well as capacity. Methodology of this study involves development and validation of a microscopic simulation model for ideal section (base model) using the data collected from Bangalore city, India. To study the impact of side frictions on PCU values and capacity, two different urban divided arterials are selected; one with the presence of curbside bus stop and an ideal section near it (Ideal_bus), and another with undesignated pedestrian crossings and an ideal section near it (Ideal_ped). Logics involved in base model development are formulated and implemented in MATLAB using object-oriented programming concepts. To estimate the PCU values for different vehicles, a new methodology considering the influence of surrounding vehicles is proposed and incorporated in the validated model. The base validated model is then modified to simulate the traffic manoeuvers on urban roads in the presence of curbside bus stop (bus stop model). To study the vehicle-pedestrian interactions in disordered traffic, the base model is modified in such a way that the movement logics of vehicles and pedestrians consider vehicle-pedestrian interactions (vehicle-pedestrian interaction model). The relative influences of various parameters such as traffic volume, vehicular composition, bus proportion (applicable only for bus stop section), proportion of stopping buses (applicable only for bus stop section), and pedestrian volume (applicable only for pedestrian section) in the presence of side frictions are investigated by carrying out sensitivity analysis. With simulated results from sensitivity analysis, regression models are developed to predict PCU values for different types of vehicles and capacity of road sections, with and without curbside bus stop, and with and without undesignated pedestrian crossings. iii The simulated results of sensitivity analysis indicate the significant differences in PCU values due to the presence of curbside bus stops when vehicular composition, bus proportion, proportion of stopping buses, and traffic volume are varied. For observed vehicular composition and traffic volume, simulated PCU values for bus showed a drastic increment of 28% in bus stop section when compared to that of ideal section. As curbside bus stops create temporal pseudo bottlenecks, capacity of bus stop section significantly gets reduced by 18% from that of ideal section for observed vehicular composition. Due to the impact of undesignated pedestrian crossings, the capacity reduction in pedestrian section when compared to that of ideal section is found to be 19.1% for observed vehicular composition and pedestrian volume. PCU values for vehicles are also found to have significant variations with change in vehicular composition, traffic volume and pedestrian volume. The study findings and results can be used by traffic engineers and planners to predict realistic PCU and capacity values for planning and designing of new facilities with side frictions instead of directly adopting the values available in the existing manuals. The study results find interesting implications in updating standards related to PCU and capacity estimation considering the influence of curbside bus stops and undesignated pedestrian crossings. In future, this research can be extended to study the impact of curbside bus stops, undesignated pedestrian crossings and other roadside frictions (e.g., parking, encroachments) on PCU values and capacity of different facility types (e.g., urban undivided roads, rural roads, intersections) by modifying the logics in the simulation model. The bus stop model can be further modified to simulate the traffic manoeuvers in sections with bus bays and exclusive bus lanes. The model describing the vehicle-pedestrian interactions can be modified to determine surrogate safety measures (e.g., time-to-collision between vehicles and pedestrians) that reflect the safety of urban roads (where the presence of pedestrians is significant).
Effect of Warm Mix Asphalt Additives and Marginal Aggregates on Mechanical Properties of Semiflexible Asphalt Mixtures
(National Institute of Technology Karnataka, Surathkal, 2024) Doma, Hemanth Kumar; Ravi Shankar, A. U.; Mohan, Mithun
Semi-Flexible Asphalt (SFA) mixture is a wearing course in which Open-Graded Asphalt (OGA) mixes having air voids of 20-35% are grouted with cement mortar. In the present work, an effort was made to assess the effect of the Sand-Cement (S/C) ratio in determining the optimal grout proportions. Taguchi technique combined with Grey Relational Analysis (GRA) was used to obtain the optimal grout proportion. The optimum grout was obtained for an S/C ratio of 0.6, a water-to-cement (W/C) ratio of 0.40, and a polycarboxylic ether-based superplasticizer (SP) content of 0.75% by weight of cement. The SP content was identified as the most influencing factor, along with the S/C ratio. To investigate the effect of aggregate gradation and bitumen type on the mechanical properties of SFA mixtures, a new aggregate gradation with neat and modified bitumen was used to prepare OGA mixtures and later grouted with optimal grout proportion. The Marshall Stability, compressive strength, Indirect Tensile Strength, Cantabro loss, fatigue resistance, moisture and Oil spillage resistance tests were conducted. The results showed that the SFA mixtures prepared with Polymer- Modified Bitumen (PMB) and the new aggregate gradation have better mechanical properties, implying the significance of bitumen type and aggregate gradation. Due to the enormous generation of construction and demolition waste, processing and utilising recycled aggregates in pavement layers, particularly in asphalt layers, is deemed necessary to reduce the disposal problem and depletion of natural resources. Evaluating the performance of asphalt mixtures with recycled aggregates is complex due to the heterogeneity of materials. Therefore, the potential of utilizing the recycled aggregates in semi-flexible asphalt mixtures was explored along with the ferrochrome slag (FCS) aggregate. Though the FCS aggregates exhibited good mechanical and engineering properties, studies on the utilization of ferrochrome slag aggregate are limited. Therefore, in the next phase of this research, the Natural Coarse Aggregates (NCA) in OGA were replaced by Recycled Concrete Aggregates (RCA) (50% and 100%) and Ferrochrome Slag aggregate (FCS) (100%), and the effect on the mechanical properties of SFA mixtures were evaluated. The RCA was obtained by crushing the laboratory-prepared concrete specimens and passing them through the jaw crusher, followed by the ball-milling. SFA with 100% FCS exhibited higher stability, compressive strength, moisture resistance, fatigue life and rutting resistance due to strong aggregate having good impact value. At the same time, SFA with marginal aggregates (RCA and FCS) met the requirements of IRC SP 125. With the objective to reduce working temperatures of OGA mixtures, three Warm Mix Asphalt (WMA) additives, Sasobit (3%), Rediset (0.8%) and Zycotherm (0.1%), were added to PMB 40. The SFA mixtures prepared using WMA-modified binders were evaluated, and concluded that the SFA with Sasobit exhibited better mechanical properties than other mixtures, while the SFA with Rediset exhibited lower mechanical properties; however, all the SFA mixtures satisfied the specifications of IRC SP 125 2019. In the present study, a new approach, based on percentage coating, was adopted to determine working temperatures. The WMA additives reduced mixing and compaction temperatures by 30 oC and 28 - 33 oC. In the final phase, Semi-Flexible Asphalt (SFA) mixtures were prepared using marginal aggregates (50% RCA, 100% RCA, and 100% FCS) combined with WMAmodified binders. The incorporation of WMA additives allowed for a reduction in mixing and compaction temperatures by 25–35°C and 28–33°C, respectively. However, the mixtures 50RCA-R, 100RCA-S, 100RCA-R, and 100RCA-Z showed higher Cantabro weight loss, indicating lower durability, and were therefore excluded from further evaluation. The 100FCS-S mixture exhibited the highest fatigue life across all stress levels. The rut depth and DS results for SFA mixtures with FCS displayed similar values, emphasizing the significant influence of the aggregate quality or type. Only the mixtures 50RCA-S, 50%RCA-Z, 100FCS-S, 100FCS-R, and 100FCS-Z met the IRC requirements. Among these mixtures, SFA mixtures prepared with Sasobit additive and FCS aggregate performed better than other additives and marginal aggregates.
Experimental Investigation of Stone Matrix Asphalt Mixtures
(National Institute of Technology Karnataka, Surathkal, 2016) Sarang, Goutham; Ravi Shankar, A. U.
Stone Matrix Asphalt (SMA) is gap graded bituminous mixture, having higher proportions of coarse aggregates and bituminous binder, yielding better rut resistance and durability than conventional dense graded mixes. The skeleton of coarse aggregates has stone on stone contact between them, which is a major requirement for this mixture. The gap graded aggregate structure and higher binder and filler content may lead to drain down in loose SMA at elevated temperatures, and it is controlled generally by using a suitable stabilizing additive in the mixture. In the current study, SMA mixtures were prepared with two aggregate gradations having two nominal maximum aggregate sizes, 16mm and 13.2mm, and are named as SMA 1 and SMA 2. Viscosity Graded (VG) 30 bitumen, Crumb Rubber Modified Bitumen (CRMB) and Polymer Modified Bitumen (PMB) of two grades, 40 and 70, were used as binders, and three types of fibers, pelletized Cellulose Fiber (CF), Coconut Coir (CC) and Sisal Fiber (SF), and Shredded Waste Plastics (SWP) were used in mixtures with VG 30 bitumen to control drain down. Fiber content was limited as 0.3% by weight of mixture, based on drain down test results, whereas SWP content was selected 4, 8, 12 and 16 % by weight of bitumen. Drain down was within specified limits for all mixtures and decreased with increase in fiber and SWP content. The specimens were prepared as per Marshall mix design and were compacted in Superpave Gyratory Compactor (SGC). The performance of these mixtures were assessed in laboratory through Volumetric and Marshall properties, Indirect Tensile (IDT) strength, rutting and fatigue behaviour and moisture susceptibly characteristics. In general, mixes with PMB 40 and CF, showed better properties among mixes with modified binder and fiber additives respectively. In case SWP mixtures, 8 and 12% plastic content produced better mixtures. For all mixture types, SMA 1 gradation showed better results than SMA 2, except for moisture susceptibility, where both gradations performed almost same. Cost analysis of all prepared mixtures was carried out based on the standard rates, and cost for one cubic meter mixture was determined.
Experimental Investigation of Superpave and Cement Treated Aggregate Base Mixtures for Long Life Asphalt Pavements
(National Institute of Technology Karnataka, Surathkal, 2020) Priyanka, B. A.; 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 Long Life Asphalt Pavement (LLAP) technology. The fatigue and rutting distresses in the pavements can be minimized to some extent by utilizing Superpave and cement treated aggregate base mixtures with LLAP concept. The LLAPs are designed in such a manner that the response of the pavements to loads (particularly strains) is kept below certain threshold levels. In the current study two types of Superpave mixtures were prepared, one with Optimum Binder Content (OBC) designed at 4% air voids (Optimum mixtures) and the other with extra binder content of +0.5% over the OBC (Rich mixtures), for asphalt intermediate and base layers of LLAP respectively. The optimum mixtures were prepared with two aggregate gradations having two Nominal Maximum Aggregate Sizes (NMAS), 25mm and 19mm named as SP1 and SP2 respectively, for intermediate layers to enhance the rutting resistance. Rich mixtures were prepared with the same aggregate gradations for asphalt base layer to improve the fatigue resistance. Viscosity Graded (VG) 30 asphalt, Crumb Rubber Modified Binder (CRMB) of grade 60 and Polymer Modified Binder (PMB) of grade 40 were used as binders. The specimens were prepared as per Superpave mix design and were compacted in Superpave Gyratory Compactor (SGC). The performance of these mixtures was assessed in the laboratory through volumetric properties, Indirect Tensile (IDT) strength, rutting resistance, fatigue behavior, resilient modulus, and moisture susceptibility characteristics. In general, mixes with PMB 40, showed better properties. In case of IDT strength, rutting resistance, resilient modulus and ITS tests, optimum mixtures performed better compared to rich binder mixtures. However, in case of fatigue behaviour and moisture susceptibility tests, rich binder mixtures performed better compared to optimum mixtures. For all mixture types, SP1 gradationshowed better results than SP2, except for moisture susceptibility, in which both gradations performed almost the same. Cement Treated Aggregate (CTA) mixtures were also prepared with two aggregate gradations having two NMAS, 37.5mm and 45mm named as CTA1 and CTA2 respectively, for base course of LLAP to enhance the structural capacity with increased stiffness. Cement contents of 3, 5 and 7 % were used in the mixtures, and the modified compaction test was carried out to prepare specimens at their respective Optimum Moisture Content (OMC) and Maximum Dry Density (MDD). The performance of these mixtures was evaluated in laboratory through compressive strength, flexural strength, split tensile strength, modulus of elasticity and flexural fatigue behavior. The experimental investigations indicate that all the mixtures satisfied the 7-day compressive strength and 28-day flexural strength requirements as specified by Indian Roads Congress (IRC) for flexible pavement design. For all mixture types, CTA1 gradation showed better results than CTA2. The fatigue and rutting criteria of pavement sections proposed in the study were evaluated using KENPAVE software. In the analysis mainly eight pavement sections (denoted as S1, S2, S3, S4, S5, S6, S7, and S8) with different combinations of layers and materials were considered. The thickness of the layers in these sections was decided to obtain critical strains within permissible limits (tensile strain < 70 micro strain and compressive strain < 200 micro strain) and were chosen using trial and error method. The sections were divided on the basis of the mixtures used in asphalt intermediate and base layer and base course. From the results it was observed that, in case of SASW load, the critical strains were found to be within limits for pavement sections S2, S3, S7 and S8. The experimental results and analysis on pavement sections with proposed mixtures for intermediate and base asphalt layers and base course show that they can be considered as a better alternative for conventional pavements.
Experimental Study on Alkali Activated Slag Concrete Mixes by Incorporating PS Ball as Fine Aggregate
(National Institute of Technology Karnataka, Surathkal, 2020) Talkeri, Avinash H.; Ravi Shankar, A. U.
Improved road connectivity is essential for any country to progress. Well designed and constructed concrete pavements are essential for the development of sustainable highway infrastructure. The increase in infrastructure and urban development activities desire to discover sustainable materials, replacing the natural raw materials required for concrete production. The higher demand for concrete roads and other construction projects has increased Ordinary Portland Cement (OPC) production. However, cement production is associated with environmental issues such as a higher carbon footprint, highly energy-intensive, and exploitation of natural resources. Cement production uses a significant amount of natural resources. Nearly 2tonnes of raw material required to produce 1ton of cement, which emits 850kg of carbon-di-oxide into the atmosphere. The present research community is focusing on developing alternative binders to minimize the production of OPC. Alkali Activated Binders (AABs) such as Alkali Activated Slag (AAS), Alkali Activated Slag Fly Ash (AASF), Geopolymers, etc., can be considered as potential alternatives to OPC. Precious Slag (PS) ball is an industrial by-product obtained from Ecomaister steel beads. PS ball has been identified as an alternative to fine aggregates for concrete production. In the present study, PS ball was considered fine aggregates to evaluate the performance of in Alkali Activated Slag Concrete (AASC) and Alkali Activated Slag Fly Ash Concrete (AASFC). The AASC and AASFC mixes are designed to attain a minimum strength of M40 grade and compared with conventional concrete. Sodium Silicate (SS) and Sodium Hydroxide (SH) are used as the alkaline activators. The alkaline liquid to binder ratio of 0.35 was kept constant for all the mixes. The influence of SH (i.e., 8, 10, 12, and 14M) and SS to SH ratios (i.e., 1, 1.5, 2, and 2.5) on the properties of fresh and hardened concrete were analyzed. AASC mixes are prepared with 100% GGBFS as a sole binder, while AASFC mixes are prepared by mixing GGBFS and Fly ash (FA) in different proportions, i.e., 90:10, 80:20, 70:30, and 60:40. Preliminary tests were carried out to identify the optimal NaOH concentration and dosage of alkaline activators for AASC and AASFC mixes.x The fresh and hardened properties such as workability, setting time, compressive strength, split tensile strength, modulus of elasticity, flexural strength, and abrasion resistance of different concretes were evaluated as per the standard test procedure. The durability of concrete mixes was evaluated by conducting resistance to sorptivity, hydrochloric acid, sulphuric acid, nitric acid. The water absorption and Volume of Permeable Voids (VPV) were evaluated. The flexural fatigue performance of various concrete mixes was evaluated by carrying out repeated load test on beam specimens. The fatigue life data obtained were represented and analyzed using S-N curves. Probabilistic analysis of fatigue data was carried out using Weibull distribution. Survival probability analysis to predict the fatigue lives of concrete mixes with required probability of failure was carried out. The laboratory test results indicate that the incorporation of PS ball as fine aggregates in AASC and AASFC mixes improved mechanical strength. The fatigue life improved in AASC and AASFC mixes. The fatigue data of concrete mixes can be modeled by using Weibull distribution. Improved durability performance of AASC and AAFC mixes were observed. The higher water absorption and subsequent increase inVolume of Permeable Voids (VPV) was observed at the low NaOH concentration and silicate content, due to lower hydroxyl ion concentration in the activator solution. It was observed that the activator concentration has a larger influence on the mechanical properties of AASC and AASFC mixes. High sorptivity was reported for the mixes with 8M NaOH with a gradual drop in compressive strength. The permeability property of alkali activated material was dependent on total Na2O content in the activator solution. The alkali activated mix showed good resistance towards sulphate, nitrate, and chloride attacks. The AASC and AASFC mix with PS ball as fine aggregates proved to be a good concrete for pavement.
Laboratory Investigation on Lateritic and Black Cotton Soils Stabilised With GGBS and Alkali Solutions
(National Institute of Technology Karnataka, Surathkal, 2020) Amulya S.; Ravi Shankar, A. U.
The natural aggregates are depleting in developing countries due to the excessive usage in road and building construction. The present work investigates the improved properties of lateritic and Black cotton (BC) soils stabilized with Ground Granulated Blast Furnace Slag (GGBS) and alkali solutions such as sodium hydroxide and sodium silicate. The lateritic and BC soils are stabilized with 15, 20, 25 and 30% of GGBS and the alkali solutions consisting of 4, 5 and 6% of Sodium Oxide (Na2O) having Silica Modulus (Ms) of 0.5, 1.0 and 1.5 at a constant water binder ratio of 0.25. The Optimum Moisture Content (OMC) and Maximum Dry Density (MDD) are obtained for both untreated and stabilized soils from standard and modified Proctor tests. The stabilized samples were air-cured for 0 (immediately after casting), 3, 7 and 28 days at ambient temperature. In case of stabilized lateritic soil, the maximum strength is achieved at 30% of GGBS and alkali solution consisting of 6% Na2O and 1.0 Ms whereas, in case of stabilized BC soil, the maximum strength is achieved at 30% GGBS and alkali solution consisting of 6% Na2O and 0.5 Ms at both standard and modified Proctor densities. The stabilizedlateritic soil with 25 and 30% of GGBS and alkali solution consisting of 5 and 6% of Na2O having 0.5 and 1.0 Ms is found to be durable after 28 days curing at both densities. Whereas, the stabilized BC sample having 25 and 30% of GGBS and alkali solution consisting of 5 and 6% of Na2O with Ms of 0.5 only at modified Proctor density have passed durability. The stabilized lateritic soil with 30% of GGBS and alkali solution consisting of 6% of Na2O having Ms of 1.0 at both densities and the stabilized BC soil with 25% of GGBS and alkali solution consisting of 5% of Na2O having Ms of 0.5 only at modified Proctor density achieved the highest flexural strength, fatigue life and the densified structure. Thex formation of calciumsilicate hydrate and calcium aluminosilicate hydrate structures resulted in a remarkable improvement of compressive strength, flexural and fatigue life of the stabilized soils due to the dissolved calcium ions from GGBS, silicate and aluminium ions from alkali solutions. 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. The comparison of the cost of the conventional material with the proposed stabilized soils are carried out.
Laboratory investigation on the effect of rejuvenator in Reclaimed Asphalt Pavement based Stone Mastic Asphalt Mixes
(National Institute of Technology Karnataka, Surathkal, 2020) Prashanth, L Durga.; Ravi Shankar, A. U.
The present study discusses the characteristics of Reclaimed Asphalt Pavement (RAP) materials in bituminous mixtures. RAP is a material extracted from worn out or distressed pavement. These materials possess a valuable component such as aggregates and aged bituminous binder which has a potential to be reused or recycled. At present the field engineers are facing lot of problems to get quality aggregate for road construction. Due to the scarcity of this material, the cost is escalating. The government of India is insisting to use marginal or reclaimed materials in road construction based on investigations in the laboratory. These materials are incorporated as a replacement to conventional bitumen binder and also the aggregates in both coarse and fine fractions. The mix design for conventional and RAP based Stone Matrix Asphalt (SMA) mixes are optimised to obtain sufficient strength, durability based on the standards suggested by relevant codes to be used as a bituminous layer in flexible pavement. The RAP materials are incorporated at different replacement levels (0%, 30%, 50%, and 70% by weight of total aggregate gradation content in the mix). Various mechanical, durability and performance properties are studied in detail and compared to conventional SMA mix. It was found that the RAP based SMA Mix displayed better strength when compared to that of conventional mixes. Whereas, the durability and fatigue performance was found to decrease with the increase in RAP content. To overcome the problems of durability and fatigue performance of RAP materials, rejuvenators were used. The rejuvenators used in the present study are bio based and another petroleum based viz., Waste Cooking Oil (WCO) and Waste Engine Oil (WEO). The rejuvenators are added to reduce the stiffness and viscosity with improved workability. The test results of rejuvenated RAP based SMA Mix exhibited better strength than the conventional mix. The durability and fatigue performance of the rejuvenated mix also improved even at higher levels of replacement of RAP, indicating the significance of rejuvenation and utilization of higher RAP content in the mix.vi The use of rejuvenated RAP in bituminous mixes would lead to lower production cost of bituminous mixes as compared to the conventional type.
Performance of Alkali Activated Concrete Mixes with Steel Slag as Coarse Aggregate for Rigid pavements
(National Institute of Technology Karnataka, Surathkal, 2016) Palankar, Nitendra; Ravi Shankar, A. U.
Improved road connectivity is very essential for any countries progress. Well designed and constructed concrete pavements have been identified component for the development of a sustainable highway infrastructure. The higher demand for concrete roads and other construction purposes has resulted in the increased production of Ordinary Portland Cement (OPC), which is one of the basic constituents required for concrete production. However, the production of OPC is associated with emissions of large amounts of CO2, with the cement industry accounting for about 5-8% of worldwide CO2 emissions. In addition to CO2 emissions, the production of OPC requires considerable amounts of natural raw materials and energy. The present research community is focused on the development of alternative binders, with the aim of minimization of production of OPC. Alkali Activated Binders (AABs) such as Alkali Activated Slag (AAS), Alkali Activated Slag Fly Ash (AASF), Geopolymers, etc. can be considered as potential alternatives to OPC. Steel slag, an industrial by-product obtained from manufacture of steel can be identified as an alternative to natural aggregates for concrete production, since there is a possibility of acute shortage of natural aggregates for concrete in future. The present study is conducted to evaluate the performance of steel slag as coarse aggregates in Alkali Activated Slag Concrete (AASC) and Alkali Activated Slag Fly Ash Concrete (AASFC) by replacing natural granite aggregates. AASC and AASFC mixes are designed to attain a minimum strength of M40 grade and compared with conventional OPC concrete mix of similar grade. AASC mixes are prepared with 100% GGBFS as sole binder, while AASFC mixes are prepared by mixing GGBFS and FA in different proportions, i.e. 75:25, 50:50 and 25:75. Preliminary tests are carried out to identify the optimal activator modulus and dosage of alkaline activators for each of the AASC and AASFC mixes. Steel slag as coarse aggregates are incorporated in the AASC and AASFC mixes by replacing the natural coarse aggregates by volume replacement method at different levels of replacement, i.e. 0%, 25%, 50%, 75% and 100%. The fresh and hardened properties such as workability, compressive strength, split tensile strength,flexural strength, and modulus of elasticity of different concretes are evaluated as per standard test procedures. The durability of concrete mixes, in terms of resistance to sulphuric acid, magnesium sulphate, water absorption and Volume of Permeable Voids (VPV) are investigated. Flexural fatigue performance of various concrete mixes is evaluated by carrying out repeated load tests on beam specimens using repeated load testing equipment. The fatigue life data obtained are represented and analyzed using S-N curves to establish fatigue equations. Probabilistic analysis of fatigue data is carried out using two parameter Weibull distribution method. Further, the goodness-of-fit test is done to ascertain the statistical relevance of the fatigue data using Weibull distribution model. Survival probability analysis to predict the fatigue lives of concrete mixes with required probability of failure is carried out. The impact of the properties of AASC and AASFC mixes on the rigid concrete design is analyzed by carrying out standard pavement design. The ecological and economical benefits of AASC and AASFC mixes in comparison with conventional OPC concrete are analyzed and discussed. The results indicated that incorporation of steel slag in AASC and AASFC mixes resulted in slight reduction in mechanical strength. Reduction in number of cycles for fatigue failure was observed in AASC and AASFC mixes containing steel slag as compared to granite 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. The inclusion of steel slag aggregates slightly reduced the durability performance of AASC and AAFC mixes. The higher water absorption and subsequent VPV increase, with inclusion of steel slag in both AASC and AASFC mixes, due to higher water absorption of steel slag as compared to normal aggregates. Alkali activated concrete mixes with natural aggregates exhibited better resistance to sulphuric acid and magnesium sulphate environments as compared to OPCC, which may be attributed to properties/structure of binders. The acid and sulphate resistance of alkali activated concrete mixes decreased with replacement of natural aggregates with steel slag. The Embodied Energy (EE), Embodied Carbon Dioxide Emission (ECO2e) and cost of alkali activated concrete with natural aggregates are foundto be quite lower as compared to OPCC. Incorporation of steel slag in alkali activated concrete mixes led to further reduction in EE, ECO2e and cost as compared to OPCC. Steel slag aggregates reported acceptable performance in AASC and AASFC mixes for its use in pavement quality concrete.
Performance Studies on Pavements Using Chemically Stabilized Soils
(National Institute of Technology Karnataka, Surathkal, 2016) B. M, Lekha; Ravi Shankar, A. U.
Pavements constructed on weak soils can cause significant distress due to moisture-induced volume changes and low strength, thereby reducing the pavement life. Soil stabilization is the alteration of one or more soil properties, by mechanical or chemical means, to obtain an improved soil material possessing the desired engineering properties. Subgrade soils may be stabilized to increase the strength and durability or to prevent erosion and dust generation. In the present study two types of soils, Lateritic Soils (LS1 and LS2) and Black cotton soil and were stabilized with five different stabilizers viz. Terrasil, Terrabind, Cement, Road Building International grade 81, and marginal materials like Fly ash, Arecanut coir and aggregates. These additives can be used with a variety of soils to improve their native engineering properties, but their effectiveness depends on the amount of additive and the nature of soil. The laboratory investigations were conducted for different curing days to determine the basic and engineering properties of soil such as Atterberg’s limits, grain-size distribution, Maximum Dry Density (MDD), Optimum Moisture Content (OMC), California Bearing Ratio (CBR), Unconfined Compressive Strength (UCS), Indirect Tensile (IDT) Strength, Durability, Fatigue and Resilient Modulus (E). The investigations are also carried out to study the effect of addition of 12.5 mm down aggregates to the soil with optimum content of Cement and RBI 81 to evaluate the extent of modification in the Compaction, CBR, IDT strength and resilient modulus tests. The experimental investigations indicate that there is a good improvement in the engineering properties of the soils treated with different stabilizers. KENPAVE software was used for stress strain and damage analyses of both natural and stabilized soils and also to prepare pavement design sections for low and high volume pavements. For low volume pavements, CBR 3% and traffic T4 to T7 conditions were considered as per IRC-SP-72:2007. For high volume pavements, analyses were carried out for CBR 8% and traffic 2 to 150 million standard axles, using the standard design thickness as per IRC-37:2012 guidelines. Trial and error method was adopted to determine the thickness for treated soil aggregate mixture, by keeping the strain value within permissible limits. For stabilized soil, rutting and fatigue lives and damage ratio were also observed to be significantly improved. From the results of theexperimental research and KENPAVE analysis, it has been observed that modified soil can be effectively used as a modified subgrade and base layers. Analysis was also performed in IITPAVE for high volume roads under dual wheel loading. Cost analysis was carried out as per the Schedule of Rates (SOR) 2014-2015 for stabilized and unstabilized materials.