Journal Jul 2021

Development of natural based foaming agent for the potential use in foam concrete Selija Khwairakpam, Indu Siva Ranjani Gandhi

The feasibility of the use of locally available sesame seeds (SS) as an alternate to synthetic foaming agents for foamed concrete production has been assessed in this study. The use of such ecofriendly and abundantly available material as foaming agent can facilitate wider use of foamed concrete. The various parameters involved in the extraction of surfactant from SS, such as SS concentration, duration of heating, heating temperature, sodium hydroxide concentration (alkali for hydrolysis), ammonium chloride concentration (for neutralization) and sodium fluoride concentration (antiseptic) are considered in the present study. Also, the foam generated at the chosen surfactant production parameters is observed to result in foam concrete with acceptable properties as per ASTM standards.

Roller compacted concrete used in pavement S. Kar, S. K. Deb, B. Bhattacharjee

The use of fly ash in roller compacted concrete (RCC) is an avenue for fly ash utilization. This study focuses on investigating the possibility of achieving higher strength, investigating the use of fly ash in RCC, and economic analysis of RCC in the Indian scenario. In this study, cementitious material contents are varied from 15% to 25%, and fly ash contents are used as the replacement of cement in a proportion of 25% and 30%. It is found that the compressive strength of RCC increases with the increase of cementitious material content and fly ash content within the limits of investigations. It is also found that the flexural strength of RCC increases with the increase of cementitious material content. But, the fly ash does not affect flexural strength uniformly.

An experimental investigation on the mechanical properties of glass fibre reinforced geopolymer concrete Kallempudi Murali, T. Meena

This article focuses on an experimental study of the mechanical properties of fly ash (FA) and ground granular blast furnace slag (GGBFS) based geo polymer concrete (GPC) using glass fibres. In this study, an 8-molarity concentration of NaOH with an alkaline liquid ratio of 2.5 was used. Mechanical properties like compressive strength, split Tensile strength and flexural strength of GPC20, GPC40 and GPC60 grades of concrete with FA and GGBFS have been found out. Five different volume fractions, viz., 0.1, 0.2, 0.3, 0.4 and 0.5% of 13 mm length glass fibres were considered in this study. The parameters considered in this research work were different proportions of fly ash and GGBFS, i.e., 70:30, 60:40 and 50:50, at ambient curing conditions. Based on the test results, it is observed that gradual addition of glass fibres improved both split tensile strength and flexural strength of fibre-based geopolymer concrete. The optimum dosage of glass fibre was found tobe 0.3% by volume of concrete.

An experimental study on bio-composites by the methods of bacterial immersion and injection Girish S., Soumya T., Ananya Girish

The recent researches have shown that micro-organisms can be helpful material to self-repair of cracks in concrete by using bacteria, generally of Bacillus species as a novel approach of "Bacterial Concrete". The method of application of healer bacteria to the cracks in concrete structures also needs a focus on whether the location of crack is on horizontal concrete surfaces like slabs and floors or vertical as columns and walls. Immersion method suits horizontal concrete surfaces and the injection method suits vertical concrete surfaces. The present study concentrates on the effectiveness of using bacteria on crack healing and the effective methods such as immersion method and injection method of application of bacteria into the concrete. The experimental study on Bacillus species under different methods of application through compressive strength and UPV tests reveals that Bacillus sphaericus in combination with phosphate buffer solution suits through immersion method for horizontal cracked surfaces and with calcium lactate through injection method for vertical cracked surfaces is a best-suited combination.

Studies on P-M interaction curves for uniaxial bending of high strength concrete rectangular sections P. S. Rao, M. N. Shariff, N. Harsha

High-strength concretes (of grades higher than M55) are now commonly used in the construction of high-rise buildings, industrial structures and long span bridges. However, IS: 456 (2000) restricts the applicability of the concrete design parameters given in the code only to concretes of grades up to M55. The IRC: 112 (2019) (also its 2011 version) and EN 1992 - 1 - 1 : 2004 + A1 : 2014 give grade-specific design parameters for concrete grades between M65 and M90 or M110. Expressions necessary for evaluating the P-M interaction curves have been developed in this paper using concrete stress block parameters given in IRC: 112 (2019) for high strength concretes. Results obtained for two numerical examples using the expressions derived have been presented. Closed form expressions proposed by the authors for the magnitude and line of action of the concrete compressive force, as per IRC: 112 guidelines, when the neutral axis lies outside the cross-section should enable the designers to develop their own design charts for uniaxial bending of rectangular sections.

Bimodular damage-elastoplasticity constitutive model for concrete R. Raveendra Babu, Arbind K. Singh, Gurmail S. Benipal

The available constitutive models proposed for concrete generally aim at investigating its nonlinear inelastic mechanical behavior in all the aspects. Authors have recently proposed a new analytical bimodular elastic damage model with a restricted scope, viz., the identification of peculiar nonlinearity of damaged concrete. Isotropically-damaged bimodular concrete has been shown to belong to the class of homogeneous mechanical systems. Also, a new damage potential governing damage evolution is formulated. Authors have earlier proposed a standard stress-based purely elasto-plastic constitutive model based upon a new empirical unified loading function. In the present paper, a coupled damage-elastoplasticity constitutive model is proposed by coupling the authors’ bimodular damage and elastoplastic constitutive models. Salient aspects of the predicted mechanical behavior of concrete are discussed. The contribution made by the proposed model to concrete mechanics is critically evaluated.

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