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1

Post-fire impact behavior and durability of steel fiber-reinforced concrete containing blended cement-zeolite and recycled nylon granules as partial aggregate replacement

Nematzadeh Mahdi, Nazari Ali, Tayebi Morteza

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 1

art. no. e5, 2022

EN

Recycling polymeric waste in concretes to replace a portion of the stone aggregate volume can improve some of the mechanical features of concrete such as impact resistance, while also helping mitigate the associated environmental problems. Thus, this research was aimed at exploring the combined effect of nylon granules (0, 10, and 20%) as a replacement for fine aggregate, steel fibers (0, 0.75, and 1.25%), and zeolite (0, 10, 15, and 20%) as a replacement for cement on the impact resistance and durability of concrete following several heating levels (20, 300, and 600 °C). For this purpose, 432 concrete samples were manufactured, and the concrete features including compressive strength, tensile strength, impact resistance, loss of weight, water absorption, porosity, density, and failure type of concrete samples after different heating levels were investigated. The results demonstrated that the impact energy at the failure level declined considerably with temperature for all the concrete samples containing nylon granules and steel fibers (by 46–94% for 600 °C). However, increasing nylon granule content to 20% in concrete improved the impact resistance at the first and ultimate crack levels following exposure to 20 and 300 °C, while significantly lowering this parameter (by up to 40%) following exposure to 600 °C. Furthermore, the inclusion of steel fibers in concrete and increasing its content led to increased impact energy of the heated and non-heated concretes.

2

Quantitative Rietveld analysis of the decomposition of hardened rapid sulphoaluminate cement after exposure to elevated temperatures

Tchekwagep Jean Jacques Kouadjo, Chen Dangui, Mukhopadhyay Anol K., Wang Shoude, Huang Shifeng, Cheng Xin

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 3

576--594

EN

Concrete made from rapid sulphoaluminate cement is widely used today, especially in China. It is likely to continue gaining popularity since its manufacture produces less CO2 than the process of manufacturing ordinary Portland cement. Elevated temperatures are among the most serious threats to the structural stability of this product. In the present study, laboratory tests were carried out, through Rietveld analysis and other systematic testing, on samples of hardened rapid sulphoaluminate cement paste exposed to six different temperatures. As the temperature increased, the content of minerals that contribute to rapid sulphoaluminate cement strength was reduced. There was also an increase in porosity. The results show that the chemical dehydration of rapid sulphoaluminate cement after exposure to elevated temperatures is great enough to increase the local pores’ absorption, a change that can be fatal to rapid sulphoaluminate cement concrete’s strength. This understanding could help us characterize strength reduction in a more effective manner, not just in laboratory samples but also in actual structures containing rapid sulphoaluminate cement that has been exposed to elevated temperatures.

3

Fire Resistance of Timber Joints with Steel Fasteners

Domański T., Kmiecik K.

Czasopismo Inżynierii Lądowej, Środowiska i Architektury / Journal of Civil Engineering, Environment and Architecture

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2018

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z. 65, nr 2

81--90

EN

Fire safety is a major concern in the design of timber construction. Wood is combustible material. The thermal response of timber connections is usually the main factor in evaluating the overall load-bearing capacity of wood structures exposed to fire. The analysis of timber joints under fire conditions is difficult and complex. Finite element model is developed to predict the thermal behavior of bolted wood-to-wood joints exposed to fire. In fire, the material characteristic depend on the temperature. The thermal model is continuous, taking into account the thermal continuity between the joint components. Also, the thermal model is used to predict the evolution of the temperature field inside the connection. The paper presents a summary of results from a numerical studies of the fire behavior of wood-to-wood timber connections with steel bolt. As a result of computer simulations the temperature distribution was obtained. During fire exposure, the timber section is reduced and steel bolt reduces strength. Loadcarrying capacity per shear plane in fire conditions was calculated using two methods: design methods according to EN 1995-1-1 [5] and reduced load method according to EN 1995-1-2 [6]. In the first approach, the timber section loss and steel strength reduction during the fire were taken into account.

4

Bainitic reaction and microstructure evolution in two normalized and tempered steels designed for service at elevated temperatures

Ławrynowicz Z.

Advances in Materials Science

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2017

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Vol. 17, nr 4(54)

22--36

EN

In the present work conventional heat treatment like normalizing (bainitic microstructure) and tempering of the alloys has been performed. The materials used in this study were two steels, one the laboratory prepared experimental low alloy Cr-Mo steel in comparison to typical commercial 10CrMo9-10 steel. The determined carbon concentrations of the residual austenite at the different temperatures of bainite transformation supports the hypothesis that the growth of bainitic ferrite occurs without any diffusion with carbon being partitioned subsequently into the residual austenite. It was found that bainitic reaction has stopped when average carbon concentration of the untransformed austenite is close to the T0 line and supports formation of bainitic ferrite by a shear mechanism, since diffusionless transformation is not possible beyond the T0 curve. Normalized samples were air cooled down to room temperature before tempering at various temperatures in the range of 500-750°C. Samples have been austenitized at 980°C for 0.5 hour air cooled and tempered at 500, 550, 600, 650, 700 and 750°C for 1 hour. After heat treatment, the assessment in the microstructure and phase precipitation was made using the samples prepared for metallographic and transmission electron microscope (TEM) on thin foils analysis. Quantitative X-ray analysis was used to determine the retained austenite content after heat treatment like normalizing and tempering and the total volume fraction of the retained austenite was measured from the integral intensity of the (111)γ and (011)α peaks. The changes observed in the microstructure of the steel tempered at the higher temperature, i.e. 750°C were more advanced than those observed at the temperature of 500°C. Performed microstructural investigations have shown that the degradation of the microstructure of the examined steel was mostly connected with the processes of recovery and polygonization of the matrix, disappearance of lath bainitic microstructure, the growth of the size of M23C6 carbides, and precipitation of the secondary M2C precipitates. The magnitude of these changes depended on the temperature of tempering.

5

Research progress on the flexural behaviour of externally bonded RC beams

Qeshta I. M. I., Shafigh P., Jumaat M. Z.

Archives of Civil and Mechanical Engineering

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2016

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Vol. 16, no. 4

982--1003

EN

The flexural behaviour of strengthened reinforced concrete (RC) beams is more complicated compared to the normal beams due to the different bond conditions and properties of the externally bonded material. A significant number of research studies have been reported on the use of different types of material for flexural strengthening of RC beams using the external bonding (EB) technique. Although most research has focused on the conventional strengthening materials, namely, steel plates, FRP and ferrocement; unconventional materials, such as sprayed FRP and cement-based composites, have shown that they also have a significant effect on the behaviour of bonded beams. This paper presents a comprehensive state-of-the-art review of the different materials used for strengthening RC beams using the EB technique and their evaluation criteria. The behaviour of the strengthened beams is discussed in terms of load carrying capacity, stiffness under service loads, and ductility and failure modes. In addition, the effect of elevated temperatures on the externally bonded materials is also discussed. The critical review of the existing data can help for a better utilization and usage of the different materials for strengthening projects, which contributes significantly to the current efforts of developing optimum and feasible strengthening systems.

6

Utilization of acoustic emission at study of mechanical properties and structure of magnesium-aluminium alloy AZ61 under elevated temperatures

Cizek L., Hanus A., Lichy P., Tański T., Kraus M., Rusz S., Borek W.

Archives of Materials Science and Engineering

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2014

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Vol. 68, nr 2

66--74

EN

Purpose: This work present experimental determination of the elastic-plastic condition of the magnesium alloy depending on the temperature and pace of the sample tensile stress. Design/methodology/approach: At the acoustic emission (next denoted the „AE”) use, tensile tests at high temperatures may, among other things, be used for analysis of the AE signal sources and set, in more detail, the temperature limit of elastic-plastic deformations existence in the material under examination. The AE is, during tensile tests at high temperatures, based on the scanning of released elastic waves generated by sharp tension changes in the body as a result of the subsequent physical-metallurgical processes such as plastic deformation, tension redistributing, creation of microcracks and their spreading in macroscopic scale. Findings: The aim of the acoustic emission monitoring at tensile tests at higher temperatures is therefore the specification of the critical heat barrier of the elastic-plastic condition of materials and provision of information concerning the dynamics of deformation processes at tension including influences of surface layers for which acoustic emission, as confirmed by measurement results is a very suitable method. Research limitations/implications: The results of testing above mentioned magnesium alloys will serve for evaluation of possibility those magnesium alloys for application of SPD methods. Presented work was further focused on determination of structure characteristics including investigation of fracture characteristics with use of light microscopy and SEM analysis. Originality/value: Knowledge of the relaxation properties of metal materials at high temperatures is necessary for the verification of susceptibility of castings to the creation of defects during the production process. Generated tensions in the castings are the cause of creation and development of defects.

7

Computation of the effect of pH on spur chemistry in water radiolysis at elevated temperatures

Swiatla-Wojcik D.

Nukleonika

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2008

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Vol. 53, suppl. 1

31-37

EN

Diffusion-kinetic model has been employed to calculate the effect of pH and associated ionic strength on the primary yields in the radiolysis of water from ambient temperature to 200°C. Account has been taken of the effect of ionic strength, I, up to 0.1 molźdm-3 in both acidic and alkaline solutions resulting from the addition of H+ and OH-,assuming the counter ions have unit charge. The primary yields are essentially independent of pH for I ? 10-4. AboveI = 10-4 molźdm-3 the primary yields of e-aq and H2 in acidic solutions decrease whereas the primary yields of the H atom, hydroxyl radical and hydrogen peroxide increase. At I >10-3 molźdm-3 in alkaline solutions, the OH radical and hydrogen peroxide are partially converted into Oo- and HO-2 , respectively. Increases in the total yields GoOH + GOo- and Ge-aq + GHo and a decrease in GH2O2 + GHO-2 have been found with increasing pH. At elevated temperatures the effect of pH is diminished. The temperature effect on the primary yields in acidic and alkaline solutions is nearly the same as in neutral water.

8

Mechanical properties and structure of magnesium alloys with graduate content of aluminium at elevated temperatures

Čížek L., Hanus A., Greger M., Juřička I., Rusz S., Prażmowski M., Tański T., Hernas A.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2007

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Vol. 321, z. 89

91-92

EN

At the contemporary stage of the development of the engineering thought, and the product technology itself, material engineering has entered the period of new possibilities of designing and manufacturing of elements, introducing new methods of melting, casting, forming, and heat treatment of the casting materials, finding wider and wider applications in many industry branches. Therefore the development of engineering aims at designs optimizing, reducing dimensions, weight, and extending the life of devices as well as improving their reliability [1-3]. Contemporary materials should possess high mechanical properties, physical and chemical, as well as technological ones, to ensure long and reliable use. The above mentioned requirements and expectations regarding the contemporary materials are met by the non-ferrous metals alloys used nowadays, including the magnesium alloys. Magnesium alloys and their derivatives, characterize of low density (1.5-1.8 g/cm3) and high strength in relation to their weight [1,3]. Knowledge of the relaxation properties of metal materials at elevated temperatures is necessary for the verification of susceptibility of castings to the creation of defects during the production and forming processes [1,4]. Temperature limits of materials where highest tension values are generated may be detected with tensile tests under high temperatures. Experimental investigation was made on magnesium alloy AZ91 - samples A and AZ61 - samples B (after ASTM Standard) in initial state as cast. The purpose of the measurement was the study of deformation and tension changing with temperature at the tensile test and in time with simultaneous acoustic emission (AE) measurement (in the case of alloy AZ61). These dependencies were also monitored at various temperatures of sample heating from 15°C to 400°C with crosspiece shift of 6mm/min. The measurement included material sample stress at the given temperature by tension at the INOVA electro hydraulic loading machine with a loading force of 20 kN with possibility of the acoustic emission (AE) monitoring. The test bar with 0 4 mm was warmed up in a graphite furnace in inert atmosphere (argon). The AE scanner records released elastic waves (overshoots) in a frequency band between 30 kHz and 400 kHz. The output from the scanner is carried to the AE preamplifier where it is amplified and impedance-adjusted so it is possible to be transferred to more far-reaching places. The signal is further carried to the EMIS 01 system and to the PC's hard disk and they are processed in the EXCEL. Microstructure of the alloys in initial state is formed by solid solution and by minority phases Mgn(Al,Zn)i2 in massive and dispersion form and showed dendritic segregation. During heating magnesium alloy AZ91 at chosen temperatures there occurs partial dissolution of minority phases. Homogenisation of microstructure is, however, accompanied by simultaneous forming of inter-granular non-integrities, which is unfavourable from the viewpoint of strength and plastic properties, especially at higher temperatures. Failure occurs practically at all temperatures basically by inter-crystalline splitting along the boundaries of original dendrites. Trans-crystalline plastic character of fracture in small areas at 300°C was occurred. Similar temperature dependence was occurred in the case of alloy AZ61. In this case the plasticity properties were at high level. An acoustic emission method was used for a better analysis of the course of the deformation action at the tensile test. The AE method especially enables a study of dynamics of these processes at various temperatures. The opportunity to study deformation processes preceding initiation of cracks and monitoring of initiation and crack growth as up to the macroscopic scale is a big advantage of the AE. The method is therefore used in the technical diagnostics and at a check of technological operations in the production process.

9

Wpływ podwyższonej temperatury na właściwości mechaniczne skał

Pinińska J.

Prace Naukowe Instytutu Geotechniki i Hydrotechniki Politechniki Wrocławskiej. Konferencje

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2007

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Vol. 76, nr 42

527-534

PL

Wskutek uszkodzenia struktury skały pod działaniem naprężeń termicznych obniża się jej wytrzymałość. Proces ten może przebiegać dwojako. Obniżenie wytrzymałości następuje bądź wstępnym wzmocnieniu na skutek rozszerzania się mocnych ziaren skalnych i powiększeniu ich powierzchni kontaktowych (typ I) lub od początku nagrzewania następuje spadek wytrzymałości (typ II). Końcowa utrata wytrzymałości jest w obu wypadkach wywołana przekroczeniem wytrzymałość ziaren skały na ich kontaktach. Ponieważ odporność skały na zmiany termiczne zależy od składu mineralnego, charakteru kontaktów ziaren składowych oraz ich lokalnej wytrzymałości to im bardziej złożony jest materiał skalny i jego struktura tym bardziej złożony jest przebieg tego procesu. Charakter wytrzymałościowych przemian termicznych zbadano na przykładzie paleogeńskich i kredowych piaskowców fliszu karpackiego, wapieni kredowych osadowej pokrywy Platform! Wschodnio-Europejskiej oraz granitognejsów Platformy waryscyjskiej. Badania wskazują, że skali węglanowe należą do skał II typu i tracą wytrzymałość od początku nagrzewania, podczas gal w skałach krystalicznych i ziarnistych okruchowych (granitognejsy, piaskowce) o znacznej zawartości mocnych ziaren kwarcowych dochodzi w pierwszym etapie nagrzewania do ich wzmocnienia (typ 1).

EN

The thermal strain damages structure and diminishes strength of rock sample. According to its type, the rock subjected to heating either is strengthening till the certain temperature, and beyond is weakening (type I) or looses continually its strength with rise of temperature (type II).The temperature versus strength changes depend on the strength, thermal expansion rate of mineral components and, their contacts type. The processes of thermal differentiation of rock strength were investigated on rock samples of the Carpathian flysch Cretaceous and Paleogene sandstones, the Cretaceous limestones from sedimentary cover of the East-European Precambrian Craton, and the granitic gneisses from the Variscan Platform. It has been discovered that strength of the crystalline and sedimentary rocks with the strong quartz grains, increase at the first part of the heating (type I). The strength of the carbonate rocks drops continually according to the type II.