Indian Concrete Journal

Circular concrete: Prospects and possibilities of CO₂ mineralization process for sustainable concrete systems Aswathy Rajendran, Pranav Desai

We are faced with an era where availability of raw materials for construction is discussed as an under threat point and possibilities of alternate binders and aggregates are researched extensively. Although there are a number of possibilities emerging, such as LC3 cement and composite cements with lower clinker proportions, the alternative binders used in these systems are by-products of other industries, such as ceramics, thermal power plants, steel plants, and so on. What if we are able to provide a two-level sustainability idea of utilizing the waste generated within construction industry to be utilized for a new construction? The novelty of CO₂ induced mineralization of hydrated concrete fines comes from this fact and it can be used to serve multiple utilization points such as: (i) Kiln feeder material; (ii) Alternate SCM and many more. The purpose of this paper is to review the aspect of the need for such projects, the mechanism of CO₂ mineralization in hydrated products, phase changes and micro-structural alterations, the use of the mineralized powder, and practical explorations of the venture from cement to admixture companies. The paper is intended to act as a comprehensive data provider for the researchers interested in the area, given the global interest that has aroused in this research area.

Development of interaction surfaces for RCC columns subjected to axial load and biaxial bending reinforced with Fe550 steel Shweta R. Patrekar, Popat D. Kumbhar

RCC elements subjected to axial load and biaxial bending generally come across in design practice; a corner column in an RCC-framed structure is a typical example. Failure of any column subjected to bending, for a particular axial load, can be shown by a failure surface called an interaction surface. This interaction surface is required for designing columns subjected to axial load and bending. An interaction diagram is a vertical section of the interaction surface showing a plot of the axial load a column could carry against its moment capacity. In recent years, higher grades of concrete and steel (Fe550, Fe550D) are being used in many construction projects. With the introduction of such new grades of materials, it has become necessary to develop interaction surfaces and diagrams to meet the design requirements. This paper presents the interaction surfaces developed using ETABS and MATLAB software for RCC columns of different sizes subjected to axial load and biaxial bending considering M20, M25, and M30 concrete grades and Fe415, Fe500, and Fe550 steel grades. Results indicate that for the same column size and concrete grade, the moment-carrying capacity of the column increases by 18.22 % and 29.81 % for Fe500 and Fe550 steels respectively when compared to the column with Fe415 steel. Also, for the same column size and steel grade, the moment-carrying capacity of the column increases by 7.91 % and 13.26 % for M25 and M30 concrete grades respectively when compared to the column with M20 concrete grade. As the developed interaction diagrams are not available in the SP16 code for Fe550 steel, it would be beneficial for designers to verify if the designed column is safe or unsafe.

Steel fiber based concrete in its fresh state-a comprehensive study of workability of the concrete Manzoor Ahmad Tantray

The workability of concrete is a complex phenomenon that is equally difficult to measure. Extensive workability tests performed by various researchers are purely empirical. Neither of these methods measure workability in relation to the fundamental properties of fresh concrete. This paper proposes an analytical model to measure the workability of fresh steel fiber reinforced concrete. The model is formulated from the properties of the concrete components and can be effectively used to measure the workability of fiber mixtures in terms of reasonable applicability. An extensive experimental program was established to develop the model. Four (4) non-fiber and eighty (80) fiber-reinforced concrete mixtures were prepared and intensively studied to investigate the effects of variables such as cement content, coarse-to-fine aggregate ratio, fiber content, and fiber aspect ratio on the properties of fresh fiberreinforced mixtures. It was noticed that there is a significant effect of these variables on the properties of fresh and hardened concrete. Tremendous loss in slump was observed with increased fiber-matrix index in steel fiber-based concrete. The predicted model was compared with the experimental results of this study as well with the observations of some previously researched data. The model was found in good compliance with the experimental results and previously researched published data.

Experimental and numerical study on concrete cylinders for finding optimum percentage of crimped steel fibers with different aspect ratios N. A. G. K. Manikanta Kopuri, S. Anitha Priyadharshani

Different types of fibers are added to concrete to control cracking due to shrinkage. The parameters affecting the behavior of fiber reinforced concrete are volume of fibers, aspect ratio of fibers, mixing etc. Beyond a percentage addition of fibers doesn’t contribute to reduction in cracking due to ballling of fibers. It is necessary to find the optimum percentage of fibers required to improve the characteristics of concrete. In this experimental and numerical investigation, compression behavior of concrete cylinders with M25 grade concrete of mix proportion 1:1.82:3.15 with w/c ratio of 0.50 are studied for different percentage addition of crimped steel fibers with aspect ratios 60 and 100. Concrete cylinders are cast with crimped steel fibers of aspect ratio 60 and 100 for fibers with 0, 0.5, 1, 1.5, 2, and 2.5 % by weight of cement. In these concrete cylinders ferro chrome slag is used as partial replacement of fine aggregate by 40 %. Uniaxial compression test is carried out on the concrete cylinders by using compressometer. Optimum percentage of crimped steel fibers is found to be 2 and 1.5 % for aspect ratios of 60 and 100 respectively. The experimental results are compared with numerical results obtained from ABAQUS. Experimental and numerical results are found to be in good agreement.