Faculty Publications
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Item Utilization of Recycled Concrete Aggregates Processed Using the Ball Milling Method in Cement-Treated Bases for Pavements(Springer Science and Business Media Deutschland GmbH, 2024) Chiranjeevi, K.; Kumar, D.H.; Kumar, A.J.; Thapas, N.D.S.; Ravi Shankar, A.U.Pavement construction and maintenance have become very common worldwide as traffic volumes and vehicular axle weights continue to rise as the global population grows and technology advances. The extensive utilization of natural resources implies that their existence for long-term availability cannot be assured. Using materials from the various damaged and collapsed structures will save money and find a solution to the trash disposal issue. These materials have inferior engineering properties compared to conventional materials and cannot be used directly in pavement applications. These materials must be processed or stabilized by mechanical and chemical stabilization techniques. Processing of Recycled Concrete Aggregates (RCAs) has gained more importance in improving the physical properties. In the current investigation, construction and demolition (C&D) waste was processed in two stages successively. In the first stage, C&D waste was subjected to manual crushing and further processed through jaw crushing. The aggregates were processed through ball milling in the second stage. The natural aggregates are entirely replaced with the RCA in cement-treated bases (CTBs) at 3, 5, and 7% stabilization levels. Mechanical and durability properties were evaluated. The RCA produced from the ball milling method performs better than the unprocessed RCA. The mix having 7% cement content with processed RCA met the specifications for CTB. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.Item Optimisation of recycled concrete aggregates for cement-treated bases by response surface method(Taylor and Francis Ltd., 2023) Chiranjeevi, K.; Kumar, D.H.; Srinivasa, A.S.; Ravi Shankar, A.U.Sustainability is a primary concern that needs to be addressed since infrastructure development requires significant natural resources. Using Recycled Concrete Aggregates (RCA) for road construction has numerous benefits in saving natural resources and the environment. In the present investigation, the demolition waste is being used for road construction, partially/fully replacing natural aggregates. The Cement Treated Recycled Concrete Aggregate (CTRCA) specimens were prepared at 3%, 5%, and 7% cement with various blends of RCA and Natural Coarse Aggregates (NCA) ranging from 0 to 100%. The strength characteristics in terms of Unconfined Compressive Strength (UCS), Flexural Strength (FS), Elastic Modulus, Indirect Tensile Strength (ITS) and durability tests were conducted on cured samples. Microstructural analysis using Scanning Electronic Microscope (SEM) revealed that the pores and cracks in the old mortar have a detrimental influence on the mechanical properties of CTRCA mixes. However, Energy Dispersive Spectroscopy (EDS) and durability tests have shown positive results. The Response Surface Method (RSM) was utilised to optimise the RCA and cement content in CTRCA mixes. The research resulted in the maximum possible RCA of up to 70% with a cement content of 5.8%, which met the Indian Road Congress (IRC) specifications for Cement Treated Bases (CTB). © 2023 Informa UK Limited, trading as Taylor & Francis Group.Item Laboratory investigation on cement-treated recycled concrete aggregate bases for flexible pavements(Elsevier Ltd, 2023) Chiranjeevi, K.; Hemanth Kumar, D.; Yathish, R.G.; Ravi Shankar, A.U.India's economy is progressing fast, and many infrastructure development programs are going on. Especially the road network expansion is going on many folds. As a result, natural coarse aggregates are getting depleted, which has an impact on environmental sustainability. Utilizing the resources from the many aged and demolished structures will be cost-effective and solve the disposal problem of these wastes. India's government insists on using marginal material, demolished waste, or recycled aggregates as alternative materials for road construction. New codes developed by IRC and MoRTH recommend Cement Treated Bases (CTB) and Cement Treated Sub-Bases for pavement lower layers. In light of this, the present study attempts to utilize Recycled Concrete Aggregates (RCA) obtained from construction and demolition (C&D) waste in the CTB. The efficiency of RCA was checked at various replacement levels ranging from 0% to 100% with cement stabilization of 3%, 5%, and 7%. The strength properties like Unconfined Compressive Strength (UCS), Flexural Strength and durability were evaluated. The microstructural characteristics and elemental analysis of the cement treated recycled concrete aggregate mixtures were examined. The research yielded the highest potential RCA of up to 50% with a cement content of 5%, meeting the Indian Road Congress (IRC) criteria for CTB. © 2023Item Effect of aggregate gradation and bitumen type on mechanical properties of semi-flexible asphalt mixtures(Elsevier Ltd, 2023) Kumar, D.H.; Chinnabhandar, R.K.; Chiranjeevi, K.; Ravi Shankar, A.U.R.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. The grout consists of cement, sand, superplasticizer, and water. 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 was used to obtain the optimal grout proportion. The optimum grout was found to be the mixture prepared with 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 the most influencing factor, while the S/C ratio was the second most influencing factor. 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 and the new aggregate gradation have better mechanical properties, implying the significance of bitumen type and aggregate gradation. © 2023Item Utilization of recycled concrete aggregates for pavement base courses – A detailed laboratory study(Elsevier Ltd, 2024) Chiranjeevi, K.; R G, Y.; Kumar, D.H.; Mulangi, R.H.; Ravi Shankar, A.U.R.Pavement construction and maintenance have become prevalent globally due to increasing traffic volumes and higher vehicular axle weights, driven by population growth and technological advancements. However, the extensive reliance on natural resources raises concerns about their long-term availability and sustainability. An emerging trend in construction involves the application of alternative materials, such as demolished waste and industrial by-products, as substitutes for natural materials like aggregates. This study examined strength properties, including unconfined compressive strength (UCS), flexural strength, elastic modulus, indirect tensile strength (ITS) and the performance aspects of durability, shrinkage, and fatigue. Cement stabilized recycled concrete aggregate (CSRCA) mixes were prepared by varying the percentage of natural coarse aggregate (NCA) and recycled concrete aggregate (RCA) from 0% to 100% and cement content from 3% to 7%. The experimental findings demonstrated that the cement content had a more significant impact on the strength and performance characteristics of CSRCA mixes than RCA content. The mixes with RCA replacement up to 50% and a cement content of 5% satisfy the strength and durability criteria recommended by IRC 37. A higher proportion of RCA was found to have a detrimental effect on mechanical properties and fatigue characteristics. It was found that the CSRCA mixes with 50% RCA replacement to NCA can be used as a base layer instead of a conventional cement-treated base (CTB) for flexible pavement. © 2023 Elsevier LtdItem Optimizing Ball Milling for High-Quality Recycled Aggregates: Examining the Mechanical Processing and Performance of Cement-Treated Bases(American Society of Civil Engineers (ASCE), 2025) Chiranjeevi, K.; Ramagiri Girish, Y.; Hemanth Kumar, D.; Mulangi, R.H.; Ravi Shankar, A.U.Producing superior-quality recycled aggregates from demolition waste is challenging. Over the years, mec hanical treatment methods for removing attached mortar from aggregates have evolved significantly. The studies on effective recycled coarse aggregate (RCA) processing with optimized processing parameters using ball milling and characterization of processed RCA (RCA) are limited. In this study, central composite design in the response surface method was employed to optimize control process factors (charge, revolution time, and aggregate weight) with aggregate properties as responses (percentage mortar removal, water absorption WA, specific gravity Sg, impact value IV, and abrasion value AV). The aggregate processed with optimized processing parameters exhibited superior quality with enhanced physical properties. The effect of the processing of RCA on the mechanical properties of cement-treated bases was studied by utilizing processed RCA in cement-treated recycled concrete aggregate mixes. The microstructural analysis was performed using 3D-surface topography, scanning electron microscopy, and energy dispersive spectroscopy. The test results demonstrated a 63% reduction in water absorption and an improvement in Sg, IV, and AV by 12.3%, 38%, and 23.7%, respectively. It is also found that the unconfined compressive strength and flexural strength with processed RCA are improved by 31.5% and 45.7%, respectively. Natural coarse aggregate can be completely replaced with processed RCA in cement-treated bases with the optimized processing method. © 2025 American Society of Civil Engineers.