Journal Oct 2019

Point of View : Material Modelling of Concrete Structures Exposed to Elevated Temperature Dipti Ranjan Sahoo

The recent fire incidences in reinforced concrete (RC) structures in India warrant for the inclusion of actions of fire effects in the design. The accidental actions of fire effects need to be considered in the ultimate limit state (ULS) design, rather than the serviceability limit (SLS). However, it is not possible to include the fire effects directly in the load combinations. Further, it is necessary to understand the behaviour of materials under the influence of elevated temperature. This paper presents a summary of fire actions and their effects on the structure and the fire design principles. The influence of elevated temperature on material properties has been discussed. The guidelines to model various material parameters of concrete and steel have been presented. These parameters can be directly incorporated in the design or evaluation of fire resistance of structures.

Effect of Elevated Temperatures on Ferrochrome Ash Based Mortars Chethan Kumar B., Subhash C. Yaragal, B.B. Das

Due to boom in construction sector, large amount of Ordinary Portland Cement (OPC) is being consumed. Cement production is energy intensive and releases large amount of CO2 into atmosphere. Efforts are on to bring down cement consumption by the use of secondary cementitious materials. An attempt is made to study the influence of combined effect of various levels of ferrochrome ash (FCA) and lime, as replacement to OPC for different cement mortar mixtures at elevated temperatures. FCA replacement considered is in the range of 0% to 20% and along with 7% lime as replacement to cement. Compressive strength of cementitious materials is being an important parameter in the design of structures. The main objective of this work is to assess the residual compressive strengths at different levels of temperatures (200, 400, 600, and 800ºC) for a retention period of half an hour. Residual strengths of mortar mixtures produced, using FCA, have shown a good performance. Upto 20% FCA and 7% lime, mixture turns out to be a good elevated temperatures enduring material. This would increase the suggested application for environmental friendly materials. Important differences were seen in microstructural observations with scanning electron microscope (SEM) for various levels of FCA and lime incorporated mortars.

Effect of Elevated Temperature on Quaternary Blended Bacterial self-Compacting Concrete (QBBSCC) M. Sridevi, P. Srinivasa Rao, T. Seshadri Sekhar

Concrete is a reliable construction material in resisting fire. But, when exposed to high temperature for longer duration, it starts losing its structural performance. Nowadays, researches are being carried out on bacterial concrete. Bacteria produces CaCO3 as a result of metabolism, which seals the pores and improves strength of concrete. In this study, an attempt has been made to investigate the fire performance of Quaternary Blended Bacterial Self-Compacting Concrete (QBBSCC), a blend of 40% cement, 10% microsilica, 25% flyash and 25% ground granulated blast furnace slag (GGBFS). Bacillus Subtilis was used. For water- binder (w/b) ratios of 0.3 and 0.4, super-plasticiser of 1.8% and 1.6% by weight of binder, respectively, were used. QBBSCC cubes were subjected to temperatures of 200ºC, 400ºC, 600ºC, 800ºC, and 1000ºC for durations of 4, 8 and 12 hours. Weight loss and residual compressive strength were found. QBBSCC exhibited better temperature resistance than reference concrete without bacteria (QBSCC).

Experimental Exploration of Perlite Concrete under Elevated Temperatures K. Varun Teja, T. Meena

In past few decades, the world has witnessed the availability of several natural resources which are being wasted. Perlite Powder (PP) is one of such natural and sustainable material, which came into limelight of researchers, it has changed the way the concrete behaves at elevated temperatures with its thermal properties. The present study aims at experimentally investigating the applicability of PP in concrete at relatively high temperatures. In this direction, control concrete and four other mixes were also prepared by varying the content of PP as 1%, 3%, 5% and 7%, respectively. The specimens, after the curing, were subjected to elevated temperatures in the range of 200°C - 800°C with an interval of 200°C followed by air-drying. Mechanical tests, such as compressive strength and micro structural analysis like XRD, TG-DTA, SEM, and EDAX analysis were conducted. The results of these analyses signify that Binary Concrete (BC) with 5% replacement of PP possesses maximum strength as well as better thermal properties.

Effect of Precursor Combination and Elevated Temperatures on the Microstructure of Alkali-Activated Binder Kruthi Kiran Ramagiri, Arkamitra Kar

Alkali-activated binders (AAB) are a new class of construction materials based on polymerization chemistry and are known to offer properties comparable to Portland Cement (PC) with a lower carbon footprint. The final performance of AAB is governed by the type and chemical composition of its raw materials, which significantly influences its microstructure. Understanding of the microstructural variations provides an estimate and reasoning for the specimen-level performance of AAB. The present study evaluates the effect of varying precursor proportion and high-temperatures on the microstructure of AAB pastes. Addition of slag at an optimum proportion enhances the high-temperature performance of AAB paste.

Multi-Criteria Optimization of Fly Ash and Iron Ore tailing Based Concretes subjected to Elevated Temperatures Subhash C. Yaragal, Babu Narayan K.S., Chethan Kumar B., Jithu G. Francis

Due to the rapid increase in concrete utilization all over the world, there is increased consumption of Ordinary Portland Cement (OPC), natural fine aggregate (NFA), and natural coarse aggregates. Increased use of OPC, is posing a serious threat due to excess CO2 emissions, and its production is highly energy intensive. On the other hand, extraction and processing stone-based fine and coarse aggregates too, is energy intensive, and the virgin resources are fast depleting. Therefore, for sustainable development, efforts are on all over the world to look for alternative materials in place of conventional ones. In this study, it is attempted to partly replace OPC with fly ash (FA) and partly replace NFA by iron ore tailings (IOT) in concretes. The performance of such concretes at ambient and elevated temperatures is also presented. Full factorial design of experiments was adopted with two control factors under three levels of replacement, i.e., FA (0, 15, and 30% by weight of OPC) and IOT (0, 50, and 100% by volume of NFA). Total nine concrete mixes were prepared and tested for their compressive strengths at room temperature, and residual compressive strengths when subjected to various levels of elevated temperatures (200, 400, 600, and 800°C), and cost of these concretes has also been analyzed. Further, three traditional multi–criteria optimization methods, i.e., grey relational analysis (GRA), technique for order of preference by similarity to ideal solution (TOPSIS), and desirability function approach (DFA) were used to optimize concrete mixes. Results showed that TOPSIS based optimization method is more significant when compared to other two methods. Further, FA-based concrete mixes showed improved performance under multi-criteria optimization.

Effect of Elevated Temperatures on High Strength Concrete- A Review S.K. Singh, S.K. Kirthika

Fire poses a serious threat to the safety of concrete structures. The relative properties of concrete, after such an exposure, are of great importance in terms of the serviceability of buildings. Mechanical and Physico-chemical properties of concrete changes when exposed to fire / elevated temperatures, due to difference in thermal conductivity and coefficient of expansion of the constituents of concrete. Many researchers carried out studies on effect of elevated temperatures on high strength concrete (HSC). However, there is still need for the recognition of an adequate understanding of elevated temperatures effects on the behaviour of HSC. This review emphasises on the current research trends on the HSC subjected to elevated temperatures, and its corresponding behaviour. In addition, the efficacies of addition of fibers in HSC, subjected to elevated temperatures, are also outlined. The effect of elevated temperatures on the properties of HSC are presented, and major failure modes are discussed. Based on the observations, the needs for future research are also highlighted.

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