Sreenath Sreekumaran

The key objective in developing sustainable concrete is enhancing performance by mitigating adverse environmental effects simultaneously. Using short and discrete steel fibers to reinforce the concrete matrices is a widely accepted approach to improve the ductility of concrete. Although the utilization of traditional steel fibers enhances the strength of the concrete, it simultaneously leads to an increase in its weight. Also, the production of steel fibers is an energy‐intensive and carbon‐emitting process. To attain sustainability, it is imperative to reduce the use of steel fibers by including a suitable alternative through the hybridization of fiber reinforcements. The concrete developed in this study was composed of a ternary blended binder containing Ordinary Portland Cement, Ground Granulated Blast furnace Slag and Microsilica. Fibers were hybridized by partially replacing 25%, 50%, and 75% of steel fibers with natural sisal fibers. Mixes reinforced with 100% steel fibers and 100% sisal fibers were also assessed for better understanding. Basic properties such as workability, compressive strength, and splitting tensile strength were assessed. Fracture performance of the prepared mixes under pure and mixed, opening, and tearing modes of loading was also assessed by conducting disc bending tests. It can be observed from the results that, steel fibers can be replaced with sisal fibers up to 25% of the total fiber volume without greatly compromising the workability, strength and fracture performance of concrete. Hence, hybridizing steel fibers with sisal fibers can be considered a viable option to reduce the overall weight of the structural components, which can further help reduce the environmental impacts and overall cost of concrete production.

Low-density concretes made with lightweight aggregates are known for their enhanced thermal insulation properties. Though the temperature resistance is better than normal concretes, lightweight aggregate concrete (LWAC) experiences significant structural degradation when subjected to extreme conditions, especially those exceeding temperatures of 400°C. Encompassing the safety and durability of structures, auditing the strength of LWAC subject to elevated temperatures is crucial. The present research aims to analyse the density, strength, and microstructural morphology of expanded clay aggregate concrete when subjected to elevated temperatures, particularly 100°C, 200°C, 400°C, and 800°C. Concrete mixes were prepared with crushed stone aggregates replaced with ECA at 0%, 50%, and 100% by volume. The mixes were then further modified by reinforcing the matrix with hybrid fibres at 1.5% (1% steel and 0.5% polypropylene) by volume. The cured specimens were exposed to elevated temperatures and then tested for their mass and strength properties. Notable mass loss was observed for all the mixes post-thermal exposure, and improvement in strength was observed for the mixes when exposed up to 200°C. Further exposure led to a strength degradation. The observed degradation is potentially connected to the complete disintegration of the microstructure, as seen in the Scanning Electron Microscopy (SEM) images.

Reactive Powder Concretes (RPC) are well known for their exceptional strength properties and durability properties. The use of Supplementary Cementitious Materials (SCM) is the best way to enhance the strength and durability characteristics of RPCs further. Among various SCMs, the potential of Ground Granulated Blast-furnace Slag (GGBS) is proven by many researchers. However, the effect of GGBS on the fracture toughness of RPCs, especially under the tearing mode, is not explored. This study investigates the effect of partial replacement of OPC with GGBS in non-fibrous and fibrous RPCs, on its mode I (pure opening), mode III (pure tearing), and mixed-mode I/III fracture behaviour. A significant improvement in mode I, mode III, and mixed-mode I/III fracture toughness was observed due to incorporating GGBS and fibres in RPCs. The fibrous mix with 30% OPC, replaced with GGBS, exhibited the highest values of mode I and mode III fracture toughnesses, which were 2.35 MPa·m^0.5 and 0.98 MPa·m^0.5, respectively, and significantly high compared to the control non-fibrous and fibrous RPC mixes. The study reveals the ability of GGBS as an SCM to improve the fracture toughness of RPC mixes, thereby delaying the failure of the process of structural components.

In this study, observations were made on the effect of blending cement with fly ash and Alccofine on the fresh and hardened properties of micro steel fibre reinforced self-consolidating concrete (SCC). SCC mixes were prepared based on EFNARC guidelines. Blending has been done by replacing 5%, 10% and 15% of cement with Alccofine. Slump flow, L-box and V-funnel tests were conducted to study the flow characteristics of SCC. Compressive strength, split tensile strength, and flexural strength tests were performed to assess the strength characteristics. It was observed that the SCC with 10% replacement of cement with Alccofine showed better results than the other mixes. Further, the modification of the optimum blend with 10% Alccofine was made by adding variable percentages (0.5%, 1% and 1.5% by volume) of micro steel fibres and strength tests were conducted to optimise the fibre content. The strength degradation of the SCC with optimum Alccofine and fibre content exposed to alkaline, chloride and sulphate solutions was also studied.

The use of Cold Formed Steel (CFS) sections as structural members is widely accepted because of its light nature. However, the load carrying capacity of these sections will be less compared to hot rolled sections. This study is meant to analyze the possibility of strengthening cold formed members by wrapping it with Glass Fiber Reinforced Polymer (GFRP) laminates. Light gauge steel columns of cross sectional dimensions 100mm x 50mm x 3.15mm were taken for this study. The effective length of the section is about 750mm. A total of 8 specimens including the control specimen is tested under axial and eccentric loading. The columns were tested keeping both ends hinged. For both loading cases the buckling behaviour, ultimate load carrying capacity and load-deflection characteristics of the CFS columns were analyzed. The GFRP laminates were wrapped on columns in three different ways such that wrapping the outer surface of web and flange throughout the length of specimen, wrapping the outer surface of web alone throughout the length of specimen and wrapping the outer surface of web and flange for the upper half length of the specimen where the buckling is expected. For both loading cases, the results indicated that the column with wrapping at the outer surface of web and flange throughout the length of specimen provides better strength for it.