1. Ph.D Theses
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Item 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.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.