Indian Concrete Journal

Comparison of multi criterion decision making approaches (MCDM) on produced fly ash based pelletized geopolymer coarse aggregates integrated with iron ore tailings B. P. Sharath, A. R. Akhilesh Kumar, B. B. Das

This research paper explores the implementation of multicriteria decision-making approaches (MCDM) in the produced fly ash (FA) based pelletized geopolymer coarse aggregates integrated with iron ore tailings (IOT). Despite the fact that many techniques are available to aid the decision-making process, the decision makers (here the authors) are forced to go through the laborious task of selecting the appropriate MCDM method. It is because of the fact that each approach/method results in the attainment of different outcomes when applied to such specific scenario (in this case, the produced FA-based aggregates integrated with IOT). This research paper assesses three varied MCDM approaches, that are grey relation analysis (GRA), technique for order preference by similarity to ideal solution (TOPSIS) and desirability function approach (DFA), for the sixteen mixes involved in the production of FA-based aggregates integrated with IOT. These sixteen mixes were designed by taking into consideration of four experimental parameters that were Na₂O and water content dosages, blend proportion of IOT and FA and SiO₂/Na₂O ratio, with the aid of Taguchi’s experimental methodology. The characteristics of the produced FA-based aggregates like aggregate impact value, aggregate crushing value, individual crushing strength of aggregates and water absorption served as inputs in the implementation of MCDM approaches on the produced FAbased aggregates integrated with IOT. The concluding remarks obtained by the implemented MCDM approaches proved to be effective in understanding the order of influence of experimental parameters taken under consideration for producing FA-based aggregates and among all, GRA stood as a relatively better approach in comparison with the other two approaches.

The behavior of rc concrete specimen wrapped by ferrocement composites A. V. Ghogare, B. Kondraivendhan

Strengthening present structures has become an important segment of the construction industry due to various considerations such as alteration in the corrosion of reinforcement, bad quality of construction, and change in loading conditions. Also, the structures required to improve to new design requirements. So, strengthening existing systems has gained the serious focus of researchers worldwide during past some decades. An experimental study was conducted on reinforced concrete specimens to investigate the comparative performance of reinforced concrete specimens wrapped with ferro cement (Ferro-CM) and Ferro-Geopolymer (Ferro-GPM) composites under axial loading. Parameters such as column cross-sectional shape, L/d ratio (4.33 and 2), no. of ferrocement layers, and wrap thickness were taken as variables for this investigation. Experimental results revealed that the loadcarrying performance reduces as the aspect ratio increases. Furthermore, short column exhibits more load-carrying capability than slender columns for the same cross-sectional area. Similarly, wrap thickness, i.e., the number of layers of ferro mesh, enhances the load-carrying capacity compared to unwrapped column specimens. From the experimental results, it can be stated that the columns specimen wrapped with ferro-geopolymer considerably gain strength compared to the wrapped conventional ferrocement composites. The first crack come into sight near the top corner and travel vertically, disconnecting the wire mesh from the mortar layer, later failure happened of the core concrete specimen.

Feasibility of using egg shell powder as supplementary cementitious material in self compacting concrete Ujwal M. S., Bharathi Ganesh, Darshan M., Jyothi T. K., Nagendra R., Kowshika V. R. Jois

In the present study on SCC, 30 % of cement content of SCC is replaced with fly ash and 15 % with micro sized CaCO₃ by weight. The rheology, compressive strength and durability in terms of resistance to water and chloride ion penetration are assessed as per the relevant codes of practice. With the increase in cementitious content, mixes with CaCO₃ exhibited better rheological properties and increase of around 17 % in strength and nearly 70 % in water permeability of mixes in comparison with that of the control mix. The enhanced packing density and reduced porosity of SCC mixes due to the presence of finer CaCO₃ particles might have resulted in improved strength and durability, hence reduces the earth’s carbon footprint.

Microstructural analysis of recycled aggregate concrete subjected to sustained elevated temperature Vadiraj Rao N. R., Naveen B. O., Akshatha K. K., Mahalaxmi S. Sunagar

In recent years, most of the countries are promoting regulations on waste minimisation, recycling and reuse, due to its environmental impact and imminent exhaustion of available landfill capacity for the safe disposal of wastes. Hence, reuse and recycling of demolished concrete has drawn larger attention in the area of research. Currently, the demolition sites produce an oversized quantity of wastes, so that there is a greater scope to recycle the demolition waste and to use as a construction material for structural concrete. In the present study, an experimental investigation has been performed to assess the mechanical properties and to study the microstructural changes of recycled aggregate concrete (RAC) exposed to elevated temperatures of 200^o C and 400^o C. Further, RAC along with hybrid fibres (Steel + Polypropylene) for different mixes were also studied. To evaluate the performance of RAC at ambient and elevated temperatures, 72 cubes and cylinders and 30 beams were tested to study the mechanical properties at sustained elevated temperature for 2 hours of duration. Further, microstructural analysis of the samples was carried out by two methods i.e., by energy dispersive X-ray spectroscopy (EDX) and scanning electron microscope (SEM). From the results, it can be inferred that, among different percentage replacements of recycled aggregates, the mix having 50 % RAC shows better performance in compressive strength as well as improved microstructure at ambient and elevated temperatures and RAC with low water-cement ratio had a better fire resistance than natural aggregate concrete.