A. Ramachandra Murthy

Exploration on the Biotechnological Aspect of the Ureolytic Bacteria for the Production of the Cementitious Materials—a Review

Biomineralization is a process that leads to the formation of minerals using the biologically or biotechnologically mediated route. Calcium carbonate is one such biomineral that is secreted by the ureolytic bacteria which contributes for the strengthening and improvement of cementitious and sandy materials. It is a new and innovative area in the geotechnological engineering and structural engineering due to its wide range of implications in strengthening of soil, sand, stone, and cementitious materials. The shape and size of the calcium carbonate particle vary with the strain of the bacterium used, and it is species specific. This paper aims in the critical review of the mechanism of calcium carbonate precipitation by the bacterium, various bacteria involved, and the useful outputs of the technique of biomineralization. Based on the critical review, it also recommends the future development and research in the field to develop a technology that can strengthen the existing and the proposed structures.

Behaviour of reinforced concrete beams strengthened with basalt textile reinforced concrete

Experimental investigations were carried out to determine the flexural behaviour of reinforced concrete beams strengthened with basalt textile-reinforced concrete under monotonic and low-cycle fatigue load. Reinforced concrete beams strengthened with basalt textile-reinforced concrete were tested under four-point bending. The behaviour of the strengthened beam was compared with that of un-strengthened reinforced concrete beam. It is observed that there is an enhancement in energy absorption for reinforced concrete beams strengthened with basalt reinforced concrete even though there is no considerable increase in load carrying capacity. It is observed that when the strengthened beams are subjected to monotonic loading, the increase in ultimate load carrying capacity is marginal but the increase in ductility is 84.5% and the increase in energy absorption is 162% compared with un-strengthened beam. Reinforced concrete beams strengthened with basalt reinforced concrete were also tested under low-cycle fatigue load. It is observed that there is about 20% reduction in ultimate load carrying capacity and 27% reduction in ductility compared to monotonic case. But the cracking and failure patterns are similar in both the cases.

Flexural Behaviour of Damaged RC Beams Strengthened with Ultra High Performance Concrete

This paper presents the details of flexural behaviour of damaged RC beams strengthened with Ultra High Performance Concrete (UHPC) overlay. Details of UHPC including mechanical properties are described in detail. Control RC beams of size 100 × 200 × 1,500 mm with M30 grade of concrete are tested up to failure. Damage is introduced by preloading the RC beams up to 80 and 90 % of the failure load of control RC beam. UHPC overlay is added on the tension face of the beam with epoxy and tests are conducted for flexural behaviour. It is observed that there is significant increase in load carrying capacity and ductility in the case of preloaded RC beams strengthened with UHPC overlay.

Object-oriented programming paradigm for damage tolerant evaluation of engineering structural components

This paper proposes a new fracture mechanics based OOP tool for damage tolerant evaluation of cracked structural components including tubular joints subjected to constant and variable amplitude loading. To meet requirements of damage tolerant evaluation of structural components, interactive and user-friendly software, has been developed by using OOP concepts. Application of OOP concepts with class and sequence diagrams generated using unified modified language (UML) design tool has been explained with reference to the software. Graphical user interface (GUI) has been developed using VC++, which acts as a client at the front end, while the database developed using MS-ACCESS-XP acts as the server at the back-end. Database design for typical structural components with different crack configurations has been shown in the form of tables. The details of various program modules and structure of GUI have been outlined. Number of benchmark problems has been solved through GUI for verification and validation. The efficacy of the software has been illustrated through an example problem.

Estimation of fracture properties for high strength and ultra high strength concrete beams and size effect

This article presents the details of estimation of fracture parameters for high strength concrete (HSC, HSC1) and ultra high strength concrete (UHSC). Brief details about characterization of ingredients of HSC, HSC1 and UHSC have been provided. Experiments have been carried out on beams made up of HSC, HSC1 and UHSC considering various sizes and notch depths. Fracture characteristics such as size independent fracture energy (Gf), size of fracture process zone (Cf), fracture toughness (KIC) and crack tip opening displacement (CTODc) have been estimated based on the experimental observations. From the studies, it is observed that (i) UHSC has high fracture energy and ductility inspite of having a very low value of Cf; (ii) relatively much more homogeneous than other concretes, because of absence of coarse aggregates and well-graded smaller size particles; (iii) the critical SIF (KIC) values are increasing with increase of beam depth and decreasing with increase of notch depth. Generally, it can be noted that there is significant increase in fracture toughness and CTODc. They are about 7 times in HSC1 and about 10 times in UHSC compared to those in HSC; (iv) for notch-to-depth ratio 0.1, Bazant’s size effect model slightly overestimates the maximum failure loads compared to experimental observations and Karihaloo’s model slightly underestimates the maximum failure loads. For the notch-to-depth ratio ranging from 0.2 to 0.4 for the case of UHSC, it can be observed that, both the size effect models predict more or less similar maximum failure loads compared to corresponding experimental values.

EXPERIMENTAL AND NUMERICAL STUDY ON IN-PLANE BEHAVIOR OF BRICK MASONRY WALL PANELS

This paper presents the details of studies conducted on brick masonry units and wall panels. The investigation includes, compressive strength of brick unit, prisms, flexural strength evaluation, and testing of reinforced brick wall panels with and without opening. Nonlinear finite element analysis (FEA) of brick wall panels with and without opening has been carried out by simulating the actual test conditions. Constant vertical load is applied on the top of the wall panel and lateral load is applied in an incremental manner. The in-plane deformation is recorded under each incremental lateral load. Displacement ductility factors and response-reduction factors have been evaluated based on experimental results. From the experimental study, it is observed that fully reinforced wall panel without opening performed well compared to other types of wall panels in lateral load resistance and displacement ductility. In all the wall panels, shear cracks originated at loading point and moved toward the compression toe of the wall. The force-reduction factors of a wall panel with opening are much less when compared with fully reinforced wall panel with no opening. The displacement values obtained by nonlinear FEA were found to be in good agreement with the corresponding experimental values. The difference in the computed and experimental values is attributed to the influence of mortar joint which was not considered in FEA. The derived response-reduction factors will be useful for adopting elastoplastic design procedures for lateral forces generated due to earthquakes.

Optimised mix design for normal strength and high performance concrete using particle packing method

Abstract This paper presents the details of optimized mix design for normal strength and high performance concrete using particle packing method. A critical review of mix design methods have been carried out for normal strength concrete using American Concrete Institute (ACI) and Bureau of Indian Standards (BIS) methods highlighting the similarities and differences towards attaining a particular design compressive strength. Mix design for M30 and M40 grades of concrete have been carried out using ACI, BIS and particle packing methods. Optimization of concrete mix has been carried out by means of particle packing method using EMMA software, which employs modified Anderson curve to adjust the main proportions. Compressive strength is evaluated for the adjusted proportions and it is observed that the mixes designed by particle packing method estimates compressive strength closer to design compressive strength. Further, particle packing method has been employed to optimize the ingredients of high performance concrete and experiments have been carried out to check the design adequacy of the desired concrete compressive strength.

Prediction of fracture characteristics of high strength and ultra high strength concrete beams based on relevance vector machine

This paper examines the applicability of relevance vector machine-based regression to predict fracture characteristics and failure load (Pmax) of high strength and ultra high strength concrete beams. Fracture characteristics include fracture energy (GF), critical stress intensity factor (KIC) and critical crack tip opening displacement. Characterization of mix and testing of beams of high strength and ultra high strength concrete have been described briefly. The procedure to compute GF , KIC and CTODC has been outlined. Relevance vector machine is a machine learning technique that uses Bayesian inference to obtain parsimonious solutions for regression and classification. The relevance vector machine has an identical functional form to the support vector machine, but provides probabilistic classification and regression. Relevance vector machine is based on a Bayesian formulation of a linear model with an appropriate prior that results in a sparse representation. Four relevance vector machine models have been developed using MATLAB software for training and prediction of Pmax, KIC, GF and CTODC. Relevance vector machine models have been trained with about 70% of the total 87 datasets and tested with about 30% of the total datasets. It is observed that the predicted values from the relevance vector machine models are in good agreement with those of the experimental values.

Nutritional Behavior, Morphogenesis Cycle and Sediment Consolidation Capabilities of the Calcareous Bacteria Derived from Coastal Marine Sediments

ABSTRACT Samples from stones and sediments of a coastal site in the Bay of Bengal (Indian Ocean) yielded as many as 39 new bacterial isolates capable of precipitating calcium carbonate (CaCO3). Molecular identification revealed that these bacteria belonged predominantly to the phyla Firmicutes and Proteobacteria. Culture studies showed that nitrogen sources controlled the metabolic pathway of crystal precipitation, which was restricted to three reaction pathways, namely the deamination of amino acids, ureolytic nitrate reduction and dissimilatory nitrate reduction. The sequence of crystal morphogenesis clearly showed that bacterial precipitation of CaCO3 led to predominantly spherical structures with time. The present investigation provides the first demonstration of the bacterial contribution and mechanisms involved in the calcareous consolidation of stones and sediments by bacteria in the marine environment.

Determination of the back boundary effect on self-compacting concrete beams: bilinear and trilinear approaches

In order to understand the fracture processes in concrete, size-dependant (