Department of Civil Engineering
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Item Temperature, porosity and strength relationship for fire affected concrete(Springer, 2022-02) Barai, Sudhir KumarIn a fire incident, structural members are mostly unevenly exposed to temperatures and consequently suffer uneven damage. To rehabilitate and restore these for future usage, it is essential to correctly map the temperature field that the structural elements were subjected to during fire events. The majority of the existing relationships for temperature prediction apply to reinforced concrete beams only. In the present study, a material-porosity-based approach is proposed. Normal and high strength concrete structural elements were exposed to a range of elevated temperatures, and reserved compressive strength was evaluated. Another set of the same specimens were used to determine porosity using four techniques. Based on the observations, correlations among temperature, strength, and porosity for normal and high strength concrete are proposed. The suggested methodology and expressions may be used to predict the reserved strength and temperature field that the structural elements may have been exposed to, based on the evaluated porosity of concrete. Back-scattered electron Imaging was found to be the most fitting method for porosity evaluation.Item Methodology for Predicting the Structural Response of FRP-Concrete Composite Beams Using Abaqus/CAE Software Package(Springer, 2022-07) Singh, Shamsher BahadurA Fiber Reinforced Polymer (FRP)-Concrete composite beam system comprises of several contact interactions, sub-components with varying geometries, and complex material behavior. Evaluating the flexural response of such structures through experimental campaigns is highly expensive and time-consuming as obtaining the desired output variables requires the specimens to be heavily and precisely instrumented. A numerical simulation could provide a much better alternative in this case as it can simulate the complete mechanical response of the physical system with relatively much ease and economy. However, the complexities involved with the problem regarding contact interactions and complex material behavior, make such analysis suffer from several convergence difficulties. The chapter is an attempt to overcome these difficulties by establishing a methodology that can be followed for modeling and analyzing such structures.Item Reliability-based mix design of marble dust incorporated concrete and its assessment using the concept of performance index(Wiley, 2022-03) Srivastava, AnshumanConcrete is one of the most important and versatile construction materials and variation in its properties is inevitable. Mix design of concrete is done in such a way that the design compressive strength is typically higher than the actual values specified by the structural engineer. The concept of reliability has not been explicitly used in regard of calculation of compressive strength using mix design and demands attention. A design procedure based on the reliability-based index is presented. The design procedure is developed for the concrete mix with partial replacement of cement by marble dust. The mechanical property which is the compressive strength of the concrete mix design is considered as a random variable, assumed to be lognormally distributed. The present study makes an effort to design a concrete mix in accordance to theory of confidence level for various levels of reliability. Mix design guidelines and graphs for various levels of replacement of cement by marble dust have also been presented in the study. Also, the cost analysis of various design mix proportions used has been calculated and compared. Four different cases to illustrate the performance rating in accordance with replacement levels of Marble dust have been formulated. The concrete mixes with marble dust induced in concrete had lower partial safety factors than those without inclusion. The characteristics of Marble dust incorporated concrete have been assigned numerical performance index values. These values may constitute a reliable means for concrete producers in finding the rate of cement replacement by other cementitious materials. The compressive strength of most of mixes with marble dust had a coefficient of variation and within-test coefficient of variation value ranging between 2% and 3% and less than 1.5%, respectively. This indicates toward improvement in quality of concrete with cement partially replaced by marble dust.Item Experimental investigation on paver blocks of fly ash-based geopolymer concrete containing silica fume(Taylor & Francis, 2021-12) Srivastava, AnshumanUtilisation of geopolymer may reduce the global warming potential of concrete. This study examines geopolymer concrete as interlocking paver blocks. Three concretes are compared: conventional cement, fly ash-geopolymer and fly ash–silica fume geopolymer. Sodium hydroxide solution is used in both geopolymer concretes, and sodium silicate solution is used in fly ash-based geopolymer concrete only. Rectangle and uni shape blocks are tested for compressive strength, flexural strength, abrasion resistance and freeze–thaw resistance. Dynamic drop loading test is conducted on block pavement with herringbone laying pattern . Results revealed that resistance to abrasion and water absorption of geopolymeris improved by adding silica fume . Freeze–thaw resistance is the lowest for cement concrete paver blocks. Lowest deflection occurred in block pavement of uni shape. Geopolymer concrete provides uniform load distribution than cement concrete. Cement concrete is slightly costlier than geopolymer concrete. This study concluded the geopolymer as suitable option for paver block applicationsItem Bioconcrete-Enabled Resilient Construction: a Review(Springer, 2023-03) Lahoti, Mukund; Srivastava, AnshumanConcrete, the ubiquitous cementitious composite though immensely versatile, is crack-susceptible. Cracks let in deleterious substances causing durability issues. Superseding conventional crack-repair methods, the innovative application of microbially induced calcium carbonate precipitation (MICCP) stands prominent, being based on the natural phenomenon of carbonate precipitation. It is eco-friendly, self-activated, economical, and simplistic. Bacteria inside concrete get activated by contacting the environment upon the crack opening and filling the cracks with calcium carbonate—their metabolic waste. This work systematizes MICCP’s intricacies and reviews state-of-the-art literature on practical technicalities in its materialization and testing. Explored are the latest advances in various aspects of MICCP, such as bacteria species, calcium sources, encapsulations, aggregates, and the techniques of bio-calcification and curing. Furthermore, methodologies for crack formation, crack observation, property analysis of healed test subject, and present techno-economic limitations are examined. The work serves as a succinct, implementation-ready, and latest review for MICCP’s application, giving tailorable control over the enormous variations in this bio-mimetic technique.Item Design and Performance Criteria for Fire-Resistant Design of Structures – An Overview(Springer, 2020-09) Muthukumar, G.Concrete, despite being inherently fire resistant, cannot be considered as a fire-proof material. It undergoes substantial variation in its characteristics during exposure to elevated temperatures. These variations may become hazardous for structural stability and serviceability depending upon the type and extent of exposure. Moreover, high-strength concrete, which is commonly used in tall buildings, may perform poorly against fire due to its high binder content and very low permeability. Despite all the aforementioned factors, fire resistance design of structural members has been given very restricted consideration in the current Indian practice. Although several standards provide guidelines to achieve fire safety in structures, the provisions for high-strength concrete and spalling prevention are not specifically available in the major international and national standards. This paper attempts to compare the provisions corresponding to fire-resistant design in Indian standard with the respective provisions of other country standards, e.g., ACI 216 [3], NZS 3101 [4], EN 1992–2 [8], etc. Comparison parameters primarily include the design requirements for various structural members to improve their fire resistance. Furthermore, suitable recommendations for Indian Codal provisions are attempted in the latter part of the paper to achieve superior performance under elevated temperatures.Item Use of machine learning based technique to X-ray microtomographic images of concrete for phase segmentation at meso-scale(Elsevier, 2020-07) Barai, Sudhir Kumar; Pradhan, SubhasisThe paper discusses the technical limitation of the gray value thresholding technique to detect the voids, aggregate and mortar phases. A two-stage image processing methodology is proposed for the segmentation of the three phases of concrete using the X-ray microtomographic images. In the first stage, the gray value thresholding technique is used to detect the voids. A machine learning based technique is proposed in the second stage for the segmentation of aggregate and mortar. The training data is used to model a planar decision boundary using the logistic regression method. For this, the radial distance from the centre of the image, gray value, and gray value of the filtered embossed image features are considered. The accuracy of the model to quantify the voids is validated with the commercial software. The machine learning model based on logistic regression method exhibits very good accuracy () in detecting the aggregate.Item Environmental impact assessment of fly ash and silica fume based geopolymer concrete(Elsevier, 2020-05) Srivastava, Anshuman; Sangwan, Kuldip SinghAlkali activated geopolymer is an attractive solution to limit the adverse consequences of cement manufacturing. In this paper, an evaluation of environmental impacts of geopolymer containing fly ash and silica fume is conducted. Life cycle assessment is performed by benchmarking the environmental impacts of three geopolymer concrete mixes against the conventional cement concrete, namely: fly ash geopolymer (with hydroxide and silicate of sodium); fly ash–silica fume blend geopolymer (with hydroxide and silicate of sodium); and fly ash–silica fume blend geopolymer (with sodium hydroxide). Impact analysis is performed by using ReCiPe midpoint and endpoint methods in life cycle assessment software UMBERTO NXT using database of Ecoinvent 3.0. Sensitivity analysis is performed to determine the effect of transportation. One mix design for each concrete of equal water to binder ratio and 28-days compressive strength of more than 35 MPa is analysed. Results of life cycle assessment indicate that alkaline activators and cement are the major sources of negative environmental impacts for geopolymer and cement concrete, respectively. Global warming potential of geopolymer concretes is lower than conventional cement concrete. Fly ash–silica fume geopolymer concrete activated without sodium silicate has lowest environmental impacts. Transportation of raw materials is found to increase the overall negative of all four concrete mixes. Cost reduction of 10.87%–17.77% per unit volume is achieved with the use of fly ash – silica fume based geopolymer concrete. Sustainability in terms of cost and environmental benefits of geopolymer concrete can be further increased by using silica fume. It can be concluded that the use of fly ash – silica fume blended geopolymer in the construction industry has huge possibility to improve its sustainability. Furthermore, waste management can be effectively done by utilization of industrial by-products in concrete.Item Application of Novel Radial Thresholding Method for the Segmentation of Different Phases from X-Ray Microtomographic Images of Concrete(Springer, 2020-11-14) Barai, Sudhir KumarConcrete is a composite material, which can be segmented into three major phases, namely voids, aggregates and mortar. This paper presents the digital image processing techniques based on grey value thresholding and a novel radial thresholding approach to segregate the three phases of concrete. In this context, the 8-bit images of concrete specimen obtained from X-ray microtomography (XRT) scanning of cylindrical specimen are operated. The non-local means denoising filter is used to remove the unwanted noise from the original images and enhance their clarity without losing any details. There is a clear distinction in the grey values of air voids from that of aggregates and mortar. The threshold grey value of air voids is determined by observing the variation in grey value profile near the edges of the air voids, and using this threshold grey value, air voids are segmented assuredly. However, the segmentation of phases using this thresholding technique doesn’t suffice to isolate the aggregates from mortar because of the overlap of their grey values. Hence, a radial thresholding method is proposed for the detection and determination of the phases, which works similar to our eyes. The grey value vs radius graph exhibits sudden jumps, which represent the change in contrast, that is, phase. The change in phases is evaluated by using a simple function, ∥GV(n)−GV(n−1)|−L|>0 which is considered the radial variation for every degree rotation. The estimated air voids and aggregates content are 0.91 and 49.19%, respectively. The error in the detection of aggregates content is only 0.6%.Item Thermal and mechanical properties of concrete and its constituents at elevated temperatures: A review(Elsiever, 2021-02-08) Barai, Sudhir KumarTo retrofit a fire damaged structural element, it is important to understand the extent of thermal exposure of such structural element. It is presumed that the extent of damage of fire affected structural elements may be assessed with the knowledge of the properties of their constituent materials at elevated temperatures. The fire resistance of concrete and temperature propagation inside the structural element depends on the thermal and mechanical properties of the ingredients and also on concrete heterogeneity and its compactness. Different crystallographic arrangements of materials result in differential thermal expansion of cement-sand matrix and coarse aggregates. Since concrete consists of a major proportion of coarse aggregates, special focus has been given on the thermal and mechanical properties of different types of coarse aggregate at elevated temperatures. The objective of this paper is to present a brief critical review of the thermal and mechanical properties of different types of concrete and its constituents at elevated temperatures and highlight certain areas that may be explored further by researchers.