Effect of temperature on mechanical properties of ultra-high performance concrete

High temperature mechanical property data are needed for evaluating fire resistance of structural members. Being a relatively new construction material, there is a lack of temperature-dependent mechanical property data on ultra-high performance concrete (UHPC). To address this knowledge gap, this paper presents results from an experimental study on the effect of temperature on mechanical properties of UHPC. Specimens made of two UHPC mixes: one with only steel fibers (UHPC-S) and the other with hybrid fibers, that is, both steel and polypropylene (UHPC-H), were tested under different heating conditions in 20 to 750°C temperature range. Compressive strength, tensile strength, stress-strain response, and elastic modulus of UHPC were evaluated at various temperatures. Results generated from these property tests on UHPC were compared with property relations specified in design codes for conventional normal strength concrete (NSC) and high strength concrete (HSC). The comparisons show that UHPC experiences faster degradation in compressive strength and elastic modulus as compared to conventional concrete. However, UHPC exhibits slower degradation in tensile strength and ductility at elevated temperatures due to the presence of steel fibers. Data generated from these property tests were utilized to propose relations for expressing the mechanical properties of UHPC as a function of temperature and these relations can be used as input to numerical models for evaluating fire resistance of structures made of UHPC.     

Characteristics of polyester polymer concrete using spherical aggregates from industrial by‐products

Despite its excellent physical and mechanical properties, polymer concrete has not been widely used owing to its much higher unit price than conventional portland cement concrete. To ensure the economic efficiency of polymer concrete, it is utmost important to reduce the use of polymer binder, which occupies most of the production cost of polymer concrete. Based on the experimental investigations, replacing filler (calcium carbonate) and fine aggregate (river sand) with fly ash and rapid‐cooled steel slag (RCSS), which are spherical materials obtainable from industrial by‐products, was found to be effective for improving the strength characteristics and durability as well as the cost efficiency of polymer concrete. The product developed in this study successfully reduced the demand for polymer binder by 21.3% compared to the conventional product, which in turn saved the total material costs by 18.5%. Although the use of RCSS showed performance degradation at an elevated temperature condition, considering typical temperature ranges that actual concrete infrastructures experience, it is expected that the polymer concrete using fly ash and RCSS will provide high‐level performances as construction and repair materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermal and mechanical properties of fiber reinforced high performance self-consolidating concrete at elevated temperatures

This paper presents the effect of temperature on thermal and mechanical properties of self-consolidating concrete (SCC) and fiber reinforced SCC (FRSCC). For thermal properties specific heat, thermal conductivity, and thermal expansion were measured, whereas for mechanical properties compressive strength, tensile strength and elastic modulus were measured in the temperature range of 20–800 °C. Four SCC mixes, plain SCC, steel, polypropylene, and hybrid fiber reinforced SCC were considered in the test program. Data from mechanical property tests show that the presence of steel fibers enhances high temperature splitting tensile strength and elastic modulus of SCC. Also the thermal expansion of FRSCC is slightly higher than that of SCC in 20–1000 °C range. Data generated from these tests was utilized to develop simplified relations for expressing thermal and mechanical properties of SCC and FRSCC as a function of temperature.     

Thermal properties of lightweight‐framed construction components at elevated temperatures

Fire resistance behaviour of lightweight‐framed assemblies is determined by defining the thermal and structural performances of the assembly when exposed to fire. To adequately model thermal behaviour in a lightweight wood‐framed assembly, thermal properties of the components of the assembly at elevated temperatures must be well defined. This paper presents results of measurements of thermal properties at elevated temperatures of construction materials commonly used to build lightweight wood‐framed assemblies that were conducted at the National Research Council of Canada since 1990. The test results, in graphical form, are given as a function of temperature for thermal conductivity, specific heat, mass loss and thermal expansion/contraction for wood, gypsum and insulation. In addition, the effects of temperature on the thermal conductivity, specific heat, mass loss and thermal expansion/contraction of these materials are discussed. Finally, in addition to providing a resource of information, this paper also identifies the additional thermal property tests required to complete the matrix of information. Copyright © 2005 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.     

Effect of high temperature or fire on heavy weight concrete properties

Temperature plays an important role in the use of concrete for shielding nuclear reactors. In the present work, the effect of different durations (1, 2 and 3 h) of high temperatures (250, 500, 750 and 950 °C) on the physical, mechanical and radiation properties of heavy concrete was studied. The effect of fire fitting systems on concrete properties was investigated. Results showed that ilmenite concrete had the highest density, modulus of elasticity and lowest absorption percent, and it had also higher values of compressive, tensile, bending and bonding strengths than gravel or baryte concrete. Ilmenite concrete showed the highest attenuation of transmitted gamma rays. Firing (heating) exposure time was inversely proportional to mechanical properties of all types of concrete. Ilmenite concrete was more resistant to elevated temperature. Foam or air proved to be better than water as a cooling system in concrete structure exposed to high temperature because water leads to a big damage in concrete properties.     

Elevated temperature thermal properties of advanced materials used in LSF systems

Lightweight cold-formed steel (CFS) construction solutions are increasingly adopted in low and mid-rise buildings. Many different materials are used to construct CFS wall systems, without a full understanding of their thermal properties. For many of these materials, only ambient temperature thermal properties are available from their manufacturers. This creates difficulty in classifying the materials for use at elevated temperatures. In this study, a series of elevated temperature thermal property tests to measure specific heat, thermal conductivity, and mass loss was conducted for a range building materials from wallboards, insulation, and phase-change materials (PCMs), used in Australia and several other countries. Simultaneous Thermal Analyser and Laser Flash Apparatus were used to determine the elevated temperature thermal properties of the selected materials, gypsum plasterboard, PCM incorporated gypsum plasterboard, magnesium sulphate board, fibre cement board, cellulose insulation, vacuum insulation panel, microencapsulated paraffin PCM, and bio-based PCM. Their elevated temperature thermal properties are presented in this article, which also includes analyses of their chemical composition and associated chemical reactions at elevated temperatures. These results can be used in the selection of suitable energy-efficient and fire-resistive materials, and in heat transfer modeling to identify wall configurations with increased fire resistance and energy efficiency.     

Investigation of the damage behaviour of refractory model materials at high temperature by combined pulse echography and acoustic emission techniques

The understanding of the thermomechanical behaviour of high temperature castables is essential for their use as linings in high temperature furnaces and refining vessels in the metallurgical, cement, and petrochemical industries. The increasing use of the finite element calculations for the prediction of the behaviour in using conditions requires the knowledge of mechanical properties at high temperature and especially for model materials. This work deals with the characterisation of the damage behaviour during thermal cycling of two two-phase refractory model materials when considering thermal expansion mismatch between the constituents. The acoustic emission technique (AE) and the ultrasonic pulse echography technique, both carried out at high temperature, were applied as non-destructive characterisation methods to monitor the damage extension within the materials submitted to thermal stress and to follow the evolution of the associated elastic properties, respectively.     

Porous single-fired wall tile bodies: Influence of quartz particle size on tile properties

This study examines the effect of quartz particle size in raw material composition customarily used for the manufacture of porous single-fired wall tile bodies on the characteristics of the green tiles and on the thermal and mechanical properties of the fired tiles. Quartz particle size was varied, while the quantity and particle size of the other raw materials were kept constant. Tile compacts were formed by uniaxial pressing and fired at different peak temperatures. The resulting fired microstructure was then characterised and tile thermal and mechanical properties were determined. Microcrack formation around quartz particles leads to hysteresis of the coefficient of thermal expansion during heating and cooling. The studied mechanical and thermal properties are shown to be a function of the magnitude of the hysteresis and porosity. This relationship is independent of the operating variables (pressing pressure, operating temperature, and quartz particle size) used. The results obtained confirm that the green and fired properties of porous single-fired wall tiles may be considerably enhanced, while holding low shrinkage and high porosity, compatible with low moisture expansion, by reducing quartz particle size and appropriately adjusting the pressing pressure and peak firing temperature. This should enable thin and/or large-sized porous wall tiles to be manufactured, without (immediate or delayed) curvatures, and with a higher breaking load than that required by the standards.     

Thermal and tensile properties of polysialate composites

Polysialate, or geopolymer, composites have gained interest due to their inherent high temperature resistance, low density and ease of manufacturing. These characteristics also suggest that polysialate composites have significant potential as materials in high temperature structures, although little is known about their thermal and mechanical properties. This study aimed to determine relevant thermal and mechanical properties over a representative temperature range. The results show that polysialate composites can exhibit stable thermal properties up to 1000 °C. Tensile properties up to 760 °C highlight a significant reduction in stiffness, but a retention of strength, at these temperatures. The thermal and mechanical results achieved provide strong evidence that polysialate composites can be suitable for use in high temperature structures, whilst subsequently providing an understanding of their limitations. In addition to this, the values ascertained also provide the data required for the design and modelling of next generation high temperature structures.     

龄期和养护方式对高强混凝土力学性能的影响

实际混凝土材料的力学性能不仅取决于材料组成,还与环境因素有关.通过考察龄期和养护方式对高强混凝土力学性能影响的研究,试验结果表明:混凝土力学性能随环境条件发生变化,尤其是断裂性能,明显受时间和温湿度的影响;随龄期增长,断裂韧性、断裂能均有不同程度降低,并且高强混凝土随龄期的增长脆性增大的倾向更为明显;同时,自然养护较标准养护显著增大了混凝土的脆性.     

Effect of elevated temperatures on mechanical properties of high‐strength concrete containing varying proportions of hematite

Aggregates typically constitute 70 to 80 wt% of concrete, and therefore their type, size, and structure play an essential role in modifying the properties of concrete. When concrete is used for shielding nuclear applications, temperature is also a key factor. This study investigates the effects of elevated temperatures (25 °C, 200 °C, 400 °C, 600 °C, and 800 °C), heating durations (1, 2, and 3 h), and cooling regimes (air, and water cooling) on mechanical properties of concrete containing different proportions of hematite. A sample of plain concrete was produced for comparison purposes by using river sand, crushed sand, and crushed aggregates. Replacement ratios of 15%, 30%, 45%, and 60% were used for hematite aggregates. The cement content and water–cement ratio were 450 kg/m³ and 0.38, respectively. Slump values of fresh concretes as well as unit weight, compressive strength, flexural strength, splitting tensile strength, and elasticity modulus values of hardened concrete were determined. The addition of hematite into concrete seems to improve its mechanical properties, and hematite concretes have better thermal stability at elevated temperatures than plain concrete does. Copyright © 2011 John Wiley & Sons, Ltd.     

Mechanical and thermal properties of hot pressed B4C-Cr3C2-hBN materials

In the present study, boron carbide matrix composites were manufactured by hot-pressing method. In order to reduce the boron carbide sintering temperature and to improve the mechanical properties, such as bending strength, critical stress intensity factor and hardness, chromium carbide, because of its low melting point and high thermal expansion coefficient, was added in various volume quantities. In order to prepare the material for cutting tool or ceramics sealing applications hexagonal boron nitride in quantities ranging from 2 and 8 vol.% was added to reduce the friction coefficient. The sinters were subjected to the abrasive test and to elastic properties examinations. Computer simulations of thermal stresses were prepared. The measured mechanical properties were supported by phase analysis and microstructural observations. Because the carrying out of heat is very important for mechanical properties of materials the influence of additives on thermal conductivity was also presented.     

Thermal and residual mechanical profile of recycled aggregate concrete prepared with carbonated concrete aggregates after exposure to elevated temperatures

Thermal and residual mechanical performance of recycled aggregate concrete (RAC) prepared with recycled concrete aggregates (RCAs) after exposure to high temperatures has so far received less attention than that of conventional concrete prepared with natural aggregates (NAs). This study experimentally investigated thermal and residual mechanical performance of RAC prepared with different replacement percentages of non‐carbonated and carbonated RCAs after exposure to high temperatures. The residual mechanical properties, including compressive strength, modulus of elasticity, and peak strain at the maximum strength, were measured for evaluating the fire resistance of RAC. The experimental results showed that although the fire‐resistant ability of natural granite aggregates was high, thermal deterioration of the conventional concrete after exposure to 600°C, presented by thermal induced mesocracks, was more serious than that of RAC due to thermal incompatibility between NAs and mortar. Using the carbonated RCAs can reduce the width of thermal mesocrack in RAC. The residual mechanical properties of RAC after exposure to 600°C can be obviously improved by incorporating 20% to 40% of the carbonated RCAs. For the RAC made with the 100% carbonated RCAs, the ratio of residual to initial compressive strength after exposure to above 500°C was even higher than that of the conventional concrete.     

Influence of metakaolin on the properties of mortar and concrete: A review

Supplementary cementing materials (SCM) have become an integral part of high strength and high performance concrete mix design. These may be naturally occurring materials, industrial wastes, or byproducts or the ones requiring less energy to manufacture. Some of the commonly used supplementary cementing materials are fly ash, silica fume (SF), granulated blast furnace slag (GGBS), rice husk ash (RHA) and metakaolin (MK), etc. Metakaolin is obtained by the calcination of kaolinite. It is being used very commonly as pozzolanic material in mortar and concrete, and has exhibited considerable influence in enhancing the mechanical and durability properties of mortar and concrete. This paper presents an overview of the work carried out on the use of MK as partial replacement of cement in mortar and concrete. Properties reported in this paper are the fresh mortar/concrete properties, mechanical and durability properties.     

Mechanical properties of solid oxide fuel cell glass-ceramic sealants in the system BaO/SrO-MgO-B2O3-SiO2

Planar solid oxide fuel cells (p-SOFCs) require materials that can satisfy the high mechanical demands related to their utilization in stationary and, especially, in mobile applications. Two suitable glass-ceramic sealants based on the system BaO/SrO-MgO-B₂O₃-SiO₂ have been characterized with respect to their mechanical properties such as hardness, Young’s modulus, flexural strength at room and elevated temperature, fracture toughness as well as creep behavior at relevant operation temperatures (800 °C). Fracture toughness was calculated from crack opening displacements (COD) and the results were compared with fracture toughness measured by bending tests of notched bar samples. The mechanical behavior has been discussed regarding different thermal aging times of the glass-ceramics and their microstructural evolution. The glass-ceramics containing SrO revealed a better mechanical behavior than glass-ceramics with BaO. In particular, several superior properties were found in comparison to previously reported materials for this application.     

可控低强度材料(CLSM)性能评价方法分析

可控低强度材料(CLSM)是一种高流动性、可控低强的新型充填材料,被广泛应用于工程回填、道路基层、管道垫层等工程。目前,我国尚无CLSM性能测试标准,主要借鉴国外标准与混凝土、砂浆等材料相关评价方法,亟待制定合理、统一、系统的性能测试方法与标准,规范和促进CLSM大规模推广应用。本文综述了现有CLSM相关工作性能、力学性能、环境影响、耐久性等方面的测试方法,从测试原理、实验参数、优缺点等方面进行了对比分析,为CLSM性能测试提供依据,也为我国制定和完善CLSM标准体系提供参考。     

Mechanical properties and microstructure of high strength concrete containing polypropylene fibres exposed to temperatures up to 200 °C

High strength concrete has been used in situations where it may be exposed to elevated temperatures. Numerous authors have shown the significant contribution of polypropylene fibre to the spalling resistance of high strength concrete. This investigation develops some important data on the mechanical properties and microstructure of high strength concrete incorporating polypropylene fibre exposed to elevated temperature up to 200 °C. When polypropylene fibre high strength concrete is heated up to 170 °C, fibres readily melt and volatilise, creating additional porosity and small channels in the concrete. DSC and TG analysis showed the temperature ranges of the decomposition reactions in the high strength concrete. SEM analysis showed supplementary pores and small channels created in the concrete due to fibre melting. Mechanical tests showed small changes in compressive strength, modulus of elasticity and splitting tensile strength that could be due to polypropylene fibre melting.     

Influence of fine ceramic aggregates on the residual properties of concrete subjected to elevated temperature

The residual properties of concrete subjected to elevated temperature are of importance to assess the stability of the structure. This paper investigates the performance of concrete containing white ware ceramic sand exposed to elevated temperature. Concrete mixes containing 0%, 50%, and 100% ceramic sand were prepared. The specimen were exposed to elevated temperatures of 200°C, 500°C, and 800°C for a duration of 60 minutes. Their residual mechanical properties (compressive strength, split tensile strength), ultra sonic pulse velocity, and mass change for different cooling regimes were investigated and compared among specimen. The results showed that incorporation of ceramic sand in concrete mixes improved the resistance against elevated temperature of hardened concrete.     

聚氯乙烯热稳定性测试方法的研究

热稳定性是影响聚氯乙烯(PVC)加工和使用的重要性能之一,PVC热稳定测试方法的研究对PVC热稳定剂的研发起到至关重要的作用.从介绍PVC的降解机理入手,系统介绍和论述了白度法、变色法、刚果红法和电导法等聚氯乙烯稳定性能的测试方法,指出了不同测试方法的优缺点与适用范围.这些方法都以高温下聚氯乙烯降解释放HC l并生成共轭双键导致其颜色变化这一降解机理为依据来测试其稳定性.     

Influence of PFA on cracking of concrete and cement paste after exposure to high temperatures

Cracking is a visible type of damage to concrete that has significant adverse effects on the mechanical and durability properties of concrete. An experimental study on the identification and quantification of cracking in postheated concrete was conducted to provide a better understanding of the mechanisms of damages to concrete after exposure to high temperatures. In addition to the quantification of the residual compressive and tensile strengths of concrete after high temperature exposure, both macroscale and microscopic cracks were observed and measured. The crack patterns in different concretes, including concrete made with different water to binder (w/b) ratios and PFA dosages, were classified. Also examined was the cracking in the corresponding hardened cement pastes (hcp's) prepared without adding aggregates. The relation of cracking with deterioration of the durability properties of concrete, with respect to the chloride diffusion test results, was discussed. Crack density, a quantitative term, which had been introduced to study the microcrack properties in concrete, was adopted for measuring the severity of cracking. Severe cracking of concrete was observed after exposure to 450 °C and higher temperatures. The presence of PFA reduced the extent of these thermal cracks.