Indian Concrete Journal

Rubberized geopolymer concrete: Possibilities and challenges Divya S. Nair, T. Meena

As more concrete is needed to satisfy infrastructure demands, conventional cement production produces large amounts of CO₂, which has a negative impact on the environment. An environmentally acceptable substitute for cement is geopolymer concrete, which uses alumino-silicate ingredients and an alkaline activator. Fly ash and ground granulated blast furnace slag are examples of aluminosilicate materials that are chemically activated to form geopolymer binders. The scarcity and expense of natural sand can also be addressed by partially replacing fine aggregate with tire rubber waste crumbs. This scientific investigation looks at how the molarity of NaOH affects rubberized geopolymer concrete’s (RGPC) compressive, flexural, and split tensile strengths. Additionally, this study looks into how curing techniques like ambient and oven curing affect the mechanical characteristics of RGPC.

One of the best ways to reuse agricultural and industrial waste is through the use of geopolymer technology, which creates products with pozzolanic qualities. The construction sector has experienced long-term growth with the introduction of geopolymer concrete technology. Additionally, the natural sand is overused in the building and industrial sectors, leading to a shortage that has increased the cost of the material. The study’s conclusions will advance knowledge of and advancements in sustainable building materials. The findings of the study may encourage the use of RGPC in building projects, which would lower carbon emissions and enhance waste management.

Effect of graphene oxide on durability, microstructure, and performance characteristics of high strength fiber reinforced self compacting concrete Narendra Kumar B., Vemula Rajesh, Akula Akhil Kumar

The purpose of this study is to determine how graphene oxide (GO) affects the performance, microstructure, and durability of high-strength fiber-reinforced self-compacting concrete (HSFRSCC). Using various proportions of fly ash, ground granulated blast-furnace slag (GGBS), 50 % river sand, 50 % manufactured sand and different amounts of GO (0, 0.025, 0.05, 0.075 and 0.1 % by weight of cement) in addition to an ideal steel fibre content of 0.25 % by volume of concrete, seven different concrete mixes were developed in the current work to investigate the concrete properties. A number of tests were carried out after 7, 28 and 56 days of curing period, mechanical tests like compressive, tensile and flexural strength including water absorption and desorption, the ultrasonic pulse velocity (UPV) test, the rapid chloride penetration test (RCPT) to evaluate for durability and the microstructural features were examined using scanning electron microscopy (SEM), with an emphasis on the distribution of GO and hydration products inside the cement matrix. According to the tested results, the microstructure of the concrete was considerably enhanced by GO by producing a denser and less permeable matrix. Tests on durability revealed less penetration of chloride ions and better water resistance, while tests on mechanical strength revealed increased strength. Thus, the mix with 0.075 % graphene oxide and optimal steel fibre performed superiorly when compared to all other mixes. This study also provides a novel approach to address the brittleness and tensile limitations of conventional concrete, contributing to the development of more durable and resilient infrastructure. The reduced CO₂ emissions associated with the use of GO also highlight its potential for sustainable construction practices.

Compressive and tensile strengths of linz-donawitz slag aggregate concrete and their random forest prediction Prince Singh, Brajkishor Prasad, Virendra Kumar, Y. Rama Murthy

The purpose of this study is to investigate the effects of incorporating Linz-Donawitz slag (LD slag) as a partial replacement for natural fine and coarse aggregates on the fundamental strength of concrete. The study also aims to compare the performance of these LD slag-based concretes with conventional concrete. The research involves substituting the natural fine and coarse aggregates typically used in concrete with LD slag aggregates. This replacement is done by weight and is carried out incrementally at 20 %, reaching up to 100 %. To conduct the experiments, concrete of grade M25 is cast into standard cube, cylinder, and prism specimens using both the natural aggregates and the LD slag aggregates. These specimens are then cured underwater and subjected to testing to evaluate their compressive strength, split tensile strength, and flexural strength.

The experimental results show that the concrete made with LD slag aggregates exhibits a higher density compared to the reference concrete. Also the LD slag aggregate concrete (LDSAC) exhibited better performance under compressive, split tensile and flexural loading as compared to the conventional concrete, particularly when the replacement of aggregates fell within the range of 40-80 %. Furthermore, the study employs a machine learning technique called random forest (RF) to predict the compressive, split tensile and flexural strengths of the concrete.

Strength and ductility based seismic resistant design of RC sections in flexure Bibhas Mandal, Bijoy Kumar Jha, Santanu Bhanja

According to the Limit State Method as envisaged in IS: 456 (2000), designers can design reinforced concrete sections in flexure within the limiting conditions of balanced and maximum under-reinforced ones. No specific recommendation or guideline is available regarding the choice of section within this range. As per the limit state method, deformations are checked only at service loads, and it is expected that if the deformations are within the permissible limits, the deformation at the collapse or ultimate state will not affect the safety of the structure. However, overloading can be a routine phenomenon during earthquakes and the probability that the deformations occurring under such conditions will not endanger the safety of the structure cannot be overruled. The aim of design should be preservation of life and property up to and even beyond design levels i.e., under overloading. Failure should occur in flexure only, as all other failure modes are brittle in nature and may occur suddenly at a low value of total strain without giving ample warning to the inhabitants. However, for achieving higher levels of ductility, higher plastic rotations are necessary which might be difficult for reinforced concrete (RC) sections to mobilize especially for deeper girders. The associated plastic rotations can result in serious damage and can even cause actual collapse of the section. So, a designer should neither design a maximum under reinforced section where strength of the section is minimum, but ductility is maximum associated with huge plastic rotations, nor aim for a balanced section where strength of section is high but ductility and plastic rotations are significantly less. Thus, a balance between strength, ductility and plastic rotation is necessary for optimum design. In this connection it may be mentioned that IS: 13920 (2016) provides only some tips to improve the ductility of the sections whose strengths are designed as per IS: 456 (2000). Strength and ductility are conflicting properties as increasing strength with higher percentage of tension reinforcement leads to reduction in ductility of the sections. In the present paper an attempt has been made to propose some simple guidelines and aids, so that along with strength design, requirements of ductility which are virtually neglected, are also taken into consideration. A simple * Corresponding author: Bijoy Kumar Jha, Email: bijoyjha108@gmail.com mathematical model has been proposed to evaluate the ductility of the flexural members without going for complex, lengthy and cumbersome calculations. which will result in optimum performance of sections subjected to flexure.