2. Thesis and Dissertations
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Item Potential Use of Processed Lateritic Fine Aggregates in Cement Mortars and Concretes for Sustainable Development(National Institute of Technology Karnataka, Surathkal, 2020) S. N., Basavana Gowda; Rajasekaran, C.; Yaragal, Subhash C.Availability of river sand is becoming scarce, due to rapid increase in infrastructure projects in India. Acute shortage of river sand, has led to indiscriminate sand mining. Adverse effect of sand mining includes river bank erosion, river bed degradation, loss of biodiversity and deterioration of river water quality and ground water availability. To address the above issues, research efforts are on, to find substitutes for river sand to be used as fine aggregate in mortars and concretes. One among the locally available resources is laterite. Laterite is a product of tropical or sub-tropical weathering, which is an abundant soil material available in many parts of India. An attempt has been made to characterize the processing technique to obtain good quality lateritic fine aggregates (lateritic FA). Experiments were designed and conducted to study the performance of lateritic FA as replacement to river sand, in cement mortars and concretes. Processed lateritic FA in replacement levels of 0, 25, 50, 75 and 100 wt.% to river sand at all fineness levels (Zone I to Zone IV as per Indian standards) is considered. The workability and compressive strength characteristics of cement mortars and concretes are evaluated. Laterized mortars with Zone III and Zone IV fine aggregates, at all replacement levels, result in the same compressive strengths as those of control mortars. Suitable strength enhancement technique has been attempted to achieve strengths of Zone I and Zone II lateritic fine aggregates based mortars at 100 wt.% replacement, to achieve strength at least equal to or more than those of control mortars. Laterized concretes have achieved nearly the same strengths as those of control concretes, at all replacement levels and for all fineness levels (Zone I to Zone IV). Microstructure studies were also conducted to understand the arrangement of river sand and lateritic FA with cement matrix and their Interfacial Transition Zones (ITZ) using Scanning Electron Microscope (SEM). In the second phase, performance evaluation of laterized mortars blended with GGBS and fly ash at elevated temperatures was studied. The study was carried out in three stages, in the first stage effect of elevated temperatures on laterized mortar with different proportions of fly ash and GGBS were evaluated with constant retention period and varying exposure temperature. In the second stage, the best performing laterized mixes with GGBS and fly ash were examined for different retention periods of 30, 60 and 90 minutes. The effect of retention period on the physical and mechanical properties are investigated. In the third stage, the effect of different cooling regimesii on the residual properties of laterized mortar specimens when subjected to elevated temperatures are assessed. In the present study, three cooling regimes namely furnace cooling, ambient air cooling and water quenching were adopted. Microstructure analysis of specimens subjected to different exposure temperatures was done through SEM image analysis using image J software. In the third phase, usage potential of recycled concrete aggregates (RCA) along with lateritic FA in concrete was studied. Mechanical properties of RCA based laterized concretes were examined. Suitable strength enhancement methodology is adopted to overcome the decrement in strength caused by the usage of RCA in concrete. Finally, sustainability in the production of concrete is achieved by using GGBS as sole binder and lateritic FA as fine aggregates and RCA as coarse aggregates along with alkali solution as an activator. The resultant alkali activated slag concrete with lateritic FA and RCA shows almost similar results in terms of mechanical properties when compared to control concrete.Item Studies on Performance Characteristics of Hydrogen Loaded Concrete Mixes(National Institute of Technology Karnataka, Surathkal, 2016) Malkapur, Santhosh M.; Narasimhan, Mattur C.In many nuclear installations like particle accelerators and medical cyclotrons, concrete has been used as a radiation shield due to its gamma and neutron radiation shielding capabilities. The gamma radiation shielding properties of concrete mixes are found to be enhanced by using high density ingredients. It has been professed that the neutron radiation shielding properties can be enhanced by use of ingredients containing higher amounts of lighter elements like hydrogen and boron. In the present work, attempts are made to use alternative materials as additional hydrogen sources within the concrete mixes and evaluate their effectiveness in enhancing the neutron radiation shielding properties. In the first phase, commercially available Styrene Butadiene Rubber (SBR) latex was used to produce latex modified concrete mixes and their neutron shielding capabilities were evaluated. It is observed that the latex modified mixes showed enhanced neutron shielding capabilities reflected in terms of lower dose transmission values vis- à-vis a control concrete mix. In the second phase, pulverized high density polyethylene (HDPE) was used as a partial replacement (replacement in the range of 30-50% by volume) to the fine aggregate fraction of the concrete mix. It was necessary to proportion these mixes as a class of self compacting concrete mixes so as to restrict the segregation behavior of the polymeric particles, in such Polymer Incorporated Self Compacting Concretes (PISCC) mixes. The segregation characteristics of PISCC mixes are found to be within allowable limits, their fresh properties and the mechanical strength properties are satisfactory. It is found that such PISCC mixes have significantly improved neutron shielding performances. Though there are improvements in the attenuation of neutron flux, the PISCC mixes are in particular, more effective in reducing the neutron dose rates. In the final phase, efforts were made to incorporate high density aggregates (both fine and coarse) so as to enhance the shielding properties and produce highly flowing concrete mixes. The maximum polymer replacement was retained; high density fine and coarse aggregates and a small amount of borax were added. Based on the detailed experimental investigations, recommendations are made to design such class of mixes so as to have good slump flows (> 400mm) and better segregation resistance characteristics. The studies on neutron radiation shielding characteristics indicated greater improvements in the shielding properties with a maximum of 12.7% reduction in half value layer (HVL) thickness for neutron radiation. The gamma radiation shielding studies of these mixes have also indicated significant improvements with a maximum of 13.7% reduction in HVL thickness.Item Performance Appraisal of Eco-Friendly Mortars and Concretes(National Institute of Technology Karnataka, Surathkal, 2018) Prabhu, K. Rajendra; Yaragal, Subhash C; Venkataramana, KattaCement concrete is the major construction material largely used throughout the world for infrastructures like buildings, pavements, irrigation structures and so on. Concrete is prepared by using locally available materials. One of the important concern facing construction industry today is, the scarcity of virgin materials due to their exponential depletion and continued increase in demand. This is due to rapid growth in construction industry and stringent environmental policies to check and control harmful effects on environment, caused by production or processing methods for construction materials and chemicals. As the natural resources are fast depleting and also the production of cement and aggregates consume energy (energy intensive) which also indirectly produce carbon dioxide posing threat to the environment. Due to the above pressing needs, it is most warranted to search for alternative or promising eco-friendly materials. Huge amount of wastes generated in various fields is not utilized other than for land filling, incineration etc. These wastes can be utilized as ingredients partially or fully by embedding these wastes in either mortars or concretes without being detrimental. Experiments with Broken Mangalore Tiles (BMT) wastes in the form of Secondary Cementitious Material (SCM), Fine Aggregates (FA), and Coarse Aggregates (CA) were planned and executed to replace cement, river sand and granite CA respectively, to study the performance of both BMT based mortars and BMT based concretes. Further experiments have also been conducted to ascertain performance of BMT based mortars and BMT based concretes at elevated temperatures. Usage potential of BMT CA, in pervious concretes is studied. The scope for utilizing Iron Ore Tailings (IOT) and / or Copper Slag (CS) as replacement to River Sand (RS) is also assessed. Further Melt Processed Plastic (MPP) pellets as filler in mortar and concrete is attempted. Use of EPS packaging material as FA (as filler) and CA (as filler) is also undertaken in this investigation. Results show, with BMT waste material as fine aggregate or coarse aggregate to the extent of 100% replacement is possible without compromise on concrete strength,with 90 days of curing. It is interesting to note also that 100% FA and 100% CA could be replaced by 100% BMT FA and 100% BMT CA without loss in concrete strength with 90 days of curing. Even in the case of mortar, there is no loss in strength for mortar with 100% BMT FA, with 90 days curing. 80% addition of BMT powder or 20% replacement of cement by BMT powder with 90 days curing is possible without loss in mortar strength. 100% BMT CA, based concrete has given higher endurance to elevated temperatures as regards to strength. Loss in weight increases with both rise in temperature as well as increase in the BMT CA content. Higher BMT CA increases porosity and assists better elevated temperature endurance. Up to 600°C, the performance of concrete with BMT FA (either half or full replacement) is superior when compared to concrete with 0% BMT FA. Higher BMT FA increases porosity indirectly favouring better elevated temperature endurance up to 600°C. For BMT FA and BMT CA based concrete at elevated temperatures, residual compressive strength remains nearly constant up to 400°C. Further increase in temperature up to 800°C, strength decreases. However, the differences in strengths between various combinations reduce after 400°C. Residual strength of mortar mix BMT FA100, monotonically decreases with increase in temperature. However its performance appears to be better than mortar mix BMT FA50 for temperature levels of 600°C and 800°C. It is observed that mortar with BMT powder as addition to OPC possesses more strength than replacement to OPC at all levels of temperatures. For a given porosity, the density of pervious concrete with BMT CA is always lower than that of granite CA by around 300 kg/cu.m. BMT CA in full replacement to granite CA, performs well in pervious concretes. Compressive strength of concrete reduces by about 26% when sand is replaced from 0 to 100% by IOT. Strength values almost remain constant up to 75% replacement of sand by IOT. Copper slag replacing sand to the extent of 100% does not result in strength reduction of concrete. From mortar strength studies with IOT and CS in place of sand, it is to be noted that for both cases replacement level of 50%, result in no loss in strength with two months of curing period. MPP pellets are added as filler by volume of concrete. It isobserved that the concrete strength drops by 50% for approximately 25% filler. Strength variation of mortars containing river sand, IOT and CS as FA with MPP pellets as filler at different blending dosages is studied. For all the three cases strength drops with increase in filler content, however the rate of drop is lower for mortar containing IOT as FA and higher for CS as FA, when compared to mortar with RS as FA. For concrete, with increase in EPS CA (as filler) content, all the three strengths (compression, split tensile and flexural) decrease by about 70-80% for 100% replacement. For mortar, as EPS FA (as filler) content increase, there is decrease in strength. At 100% replacement, the strength is approximately 15% of the reference mortar strength. This study is a step towards sustainable construction practices and recommends use of these eco-friendly unconventional materials to the extent possible.