2. Thesis and Dissertations
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Item Influence of Aging Condition on Performance of Fine Aggregate Asphaltic Matrix(National Institute of Technology Karnataka, Surathkal, 2021) Akhandappagol, Ningappa.; N, Suresha S.The major distresses in the flexible pavement are fatigue cracking, rutting, and moisture induced damage. There is lack of consideration of ideal test methods to evaluate the distresses present in the asphaltic pavement. By knowing the majority of the distresses appear within the mortar or Fine Aggregate Matrix (FAM) of the asphalt mixture, researchers have started to use this FAM phase in place of full asphalt mixtures to characterise the performance properties. Additionally, one can also attain higher precision in test results from Dynamic Shear Rheometer (DSR) by maintaining the uniformity in the prepared FAM specimens. The thesis report presents the research study performed on FAM mixtures focusing on its test methodology, rheological investigation results, and conclusions of the study. The main objectives of the present research is (i) to investigate the effect of different long-term oven aging (LTOA) levels on performance properties of FAM mixtures to mitigate the fatigue cracking in asphalt pavement, (ii) to assess and analyse the effect of binder types, different loads, and temperatures on creep and recovery performance of the FAM mixtures, (iii) to assess and analyse the impact of moisture on creep recovery response of FAM mixtures. To achieve this objective, a detailed test plan was prepared based on exhaustive review of research findings related to FAM mixtures and the latest practices for FAM characterisation were adopted by various agencies across the world. Major differences were observed in these practices, particularly with respect to the different aging methods, gradations used/considerations, specimen preparation method, and considerations of air voids, binder content, binder grade, and binder types. In light of the above, the rheological investigation was carried out on FAM mixtures in three stages, i) Cracking susceptibility of FAM mixtures prepared with three different asphalt binders VG-30, VG-40, and PMB(S) is evaluated through the experimental testing and numerical modeling on FAM mixtures produced at design (laboratory) stage. Various criteria and approaches for the prediction of cracking in FAM mixtures are assessed and their correlation is discussed. Different levels of aging in laboratory are simulated, and the effects of long term oven aging (LTOA) on linear viscoelastic parameters, and fatigue characteristics of FAM mixtures are explored. ii) Creep recovery behavior of FAM mixtures were evaluated by vii determining the percent recovery (%R) and non-recoverable creep compliance (Jnr) parameters from the Multiple Stress Creep Recovery (MSCR) test at different stress levels and temperatures. Additionally, strain response from the Burgers four element model was also modelled and compared with the observed experimental results, iii) Resistance to moisture-induced damage of FAM mixtures was evaluated by determining the ratios of %R and Jnr in dry and wet conditions from the Static Creep Recovery (SCR) test at 40°C for different stress levels. Results of the study indicated that irrespective of the aging level applied to the FAM specimens, there is a small difference in the LVE limit was found for all FAM mixtures. Viscoelastic properties (|G*| and δ) for FAM specimen aged for 24 hrs at 135°C, and 12 days at 95°C aged FAM specimens showed similar results from the master curve plots. The fatigue life of FAM mixtures decreased as the aging level increases as expected. Despite of the similar viscoelastic properties, the trend observed between FAM mixtures aged 12 days at 95°C and 24 hrs at 135°C were not found to have similar fatigue life. Among FAM mixtures considered, the F2 mixture prepared with asphalt binder (VG-40) showed good resistance against permanent deformation for all the considered temperatures and corresponding stress levels. An important finding of this study also reported that Burgers model can be successfully applied for creep-recovery response of FAM mixtures under different temperatures and stress levels considered in this research. Further, the F3 mixture shows the highest %Rratio and lowest Jnr_ratio values compared to the other two FAM mixtures, indicating a lower sensitivity to moisture damage which could be possibly due to the use of polymer modifier in F3 mixture. Overall, based on the findings observed from the above rheological investigations, the FAM phase of full asphalt mixtures can be successfully used to characterise the effect of long-term aging on viscoelastic and fatigue properties of FAM mixtures. Similarly, FAM phase can also be used successfully to describe the permanent deformation, and moisture induced damage characteristics of FAM mixtures.Item Grain Refinement and Surface Modification Technique by Equal Channel Angular Pressing and Laser Shock Peening on Magnesium Alloy(National Institute of Technology Karnataka, Surathkal, 2020) R, Praveen T.; Nayaka, H Shivananda.Design and development of any part in mechanical design consists of three elemental parameters. Such as, selection of material, geometrical constrains (dimensioning) and loading or boundary conditions. Boundary conditions are the functional requirements of design which need to be satisfied from the geometry of the component by allowing optimal material to execute the function. Hence, selection of materials is the primary building block of any component in mechanical system. Selection of material is very crucial and based on type of loading, environment conditions and reliability to withstand for long duration. Magnesium and its alloys have drawn great interest from the past decade due to its superior strength to weight ratio, bio-compatibility, effective manufacturing process and other positive attributes, but there are some limitation, such as effective strength, low fatigue life, low wear resistance and high corrosion rate. These properties can be altered by grain boundary characteristics, hence reformation of grain boundary to change the grain behaviour is of significant interest. In most of the methods, one principle technique (controlling cooling rate while solidification, alloying, severe plastic deformation) is used to alter the grain size of a material, which affects the grains in whole material or at near surface. Hence, there is a research gap while combining two different techniques to achieve combination of grains for better application. Severe plastic deformation (SPD) is a top down approach to form fine grains from coarse grain, and equal channel angular pressing (ECAP) is one of the simple procedures in SPD to achieve fine grains effectively. Samples during the ECAP process experience severe shear strain followed by deformation of grains, which rupture the coarse grains into new grains with redistributed grain boundaries. Formation of fine grains and grain boundary redistribution by ECAP enhances the strength and other mechanical properties in accordance with Hall-Petch relation. Conversion of coarse grains into fine grains occurs throughout the sample and resultant grain size depends on number of passes and route of the pass. But the original shape of the sample doesn’t get altered after processing. Laser shock peening (LSP) is a surface treatment process, to induce compressive residual stresses at the surface. This technique involves creating permanent deformation at the surface, which causes grain refinementat near surface. Grain refinement of bulk sample is obtained by ECAP process, whereas grain refinement at the surface of already deformed ECAP processed sample, is obtained by laser shock peening process. Present work describes the combined effect of ECAP and LSP on AM80 magnesium alloy. As-received (cast) AM80 (Wt. 8% of Al, Wt. 1 % of Mn, balance Mg) material is homogenized and processed by ECAP upto 4 passes under route BC. The samples were tested for mechanical properties, which showed enhancement of strength and ductility in ECAP processed samples. Microscopic investigation revealed the formation of fine grains, due to applied shear strain. By increasing the number of ECAP passes, more fine grains are reported. 2–pass ECAP processed sample shows heterogeneous grains, where the large grains were surrounded by small grains, and possess maximum tensile strength of 310 MPa compared to 1, 3 and 4-pass samples. Therefore, 2-pass ECAP processed sample is considered for further processing by LSP. LSP is carried out with a power density of 8 GWcm-2 and repeatedly to achieve different percentage of coverages, LSP processed samples are analysed for mechanical properties and microstructural characterization. Microscopic examination revealed the formation of fine grains in the range of few nanometers after peening near the surface. Scanning electron microscope revealed the formation of flower petal like structures, and transmission electron microscope revealed elongated grains in the form of bands, and these bands overlapped as the percentage of coverage increases. There was a slight increase in tensile strength in LSP processed samples, due to strain hardening at surface. Dimples of various sizes were observed on fracture surface of ECAP+LSP processed region. Mg17Al12, Mg2Al3, MnAl6 with Mg phases were identified by X-ray diffraction. Wear studies of LSP processed region showed an increase in wear resistance, and microscopic image of wear surface reveals the wear mechanisms due to oxidation and ploughing of hard particles. Roughness measurement was carried out on ECAP+LSP processed samples and there was significant influence of peening in increasing roughness of the surface. Nano indentation experiments help to understand the hardness behaviour of processed material at nano scale. An increase in surface hardness is observed with LSP processed samples compared to as-cast and ECAP processed samples. Further, there was anincrease in toughness and yield strength in peened region. D-space measurements were done by X-ray diffraction to measure the lattice space before and after peening, and relative strains were converted into stresses and residual stresses were identified. Tensile residual stress profile is identified in as-cast sample due to solidification of molten metal, and homogenized sample showed decrease in tensile residual stress value due to kinetic grain growth. ECAP processed sample shows compressive residual stresses due to strains induced in between the lattice. But ECAP+LSP processed sample shows higher compressive stress at near surface (peened region). Fatigue experiments played crucial role to characterize the material in cyclic loads for reliability. Experiments were conducted at maximum stress of 120 MPa, with a stress ratio of 0.125. ECAP+LSP processed sample with 100 % coverage took 85268 cycles of load compared to homogenized sample (1 cycle of load). Investigation of fractured surface of fatigue samples showed crack initiation and propagation region followed by rupture. ECAP+LSP processed sample with 100 % of coverage shows, significant gap between crack initiation and rupture region. Hence delay in crack initiation and propagation was observed.Item 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.Item 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.