Effects Of Elevated Temperature Exposure Research Articles

Effects of elevated temperature exposure on the mechanical properties of recycled fine aggregate concrete

ABSTRACT In this work, a compound waste material was made up of raw construction waste concrete, waste tiles, and waste bricks was mixed at a weight ratio of 6:3:1. They were ground into recycled fine aggregates (RFA). RFA substituted the local river sand in proportions of 0%, 30%, 50%, 70%, and 100% for preparing recycled fine aggregate concrete (RFAC) with varied water-to-cement ratios. It intended to explore concrete’s mechanical properties and ultrasonic pulse velocity changes before and after high temperatures (300–800°C). The loss on ignition (LOI) of concrete was simultaneously determined to compare the performance in resisting elevated temperature. Test results presented that the higher the replacement ratio of RFA, the gradually higher the reduction in the concrete splitting tensile, compressive, and residual compressive strengths and ultrasonic pulse velocity after elevated temperature exposure. A rapid reduction was especially found at the heated temperature of exceeding 440°C. Furthermore, the old cement paste adhered to the surface of the raw construction waste had a relatively higher LOI. This led to the consequence that the RFAC had an increased LOI with the increment of the RFA replacement ratio, while the LOI of RFAC dropped with the increment of the originally heated temperature.

Effect of elevated temperature exposure on the flexural behavior of steel–polypropylene hybrid fiber-reinforced concrete

Effect of elevated temperature exposure on the flexural behavior of steel–polypropylene hybrid fiber-reinforced concrete

Effects of elevated temperature exposure on the residual stress state and microstructure of PVD Cr coatings on SiC investigated via in situ X-ray diffraction and transmission electron microscopy

Pure Cr coatings are being considered as corrosion-resistant layers for SiC-SiCf composite fuel cladding in light water reactors. The residual stress state and interdiffusion behavior of Cr coatings deposited on SiC substrates using bipolar high-power impulse magnetron sputtering (B-HiPIMS) and direct current impulse magnetron sputtering (DCMS) were studied using in situ X-ray diffraction experiments at 300 °C, 700 °C, and 1200 °C. After elevated temperature exposure, evolution of the coating microstructure and coating/substrate interdiffusion was characterized by transmission electron microscopy. The compressive residual stress of the dense B-HiPIMS coating at room temperature was gradually relieved at 300 °C, while the stress transitioned to a tensile state at 700 °C. Grain growth of the Cr coating and a Cr–SiC interdiffusion layer consisting of newly formed Cr–C and Cr–Si phases were observed in the B-HiPIMS coating after exposure at 700 °C. The phases in the interdiffusion layer were identified to be Cr7C3, Cr3Si, and Cr5Si3Cx experimentally and by thermodynamic predictions. For the DCMS coating, however, changes in residual stress and microstructure at the elevated temperatures were limited by the inherent porosity and inhomogeneous structure of the as-deposited coating. At 1200 °C, both coating types interacted rapidly with the underlying SiC substrate in the early stages of the experiment. The results from this study suggest that the characteristics of the Cr coatings do not significantly change at the reactor operating temperature of 300 °C, while changes in microstructure and stress state are expected in off-normal conditions of 700 °C and 1200 °C. The results from this study suggest the B-HiPIMS coating is best-suited as a protective coating for SiC fuel cladding.

Enhancing the thermal stability of alkali-activated Fe-rich fayalite slag-based mortars by incorporating ladle and blast furnace slags: Physical, mechanical and structural changes

A proper and detailed understanding of the thermal stability of Fe-rich fayalite slag-based alkali-activated materials (AAMs) is important due to their potential use in refractory and fire-resistant applications. Here, fayalite slag (FS) was used as the main precursor for AAMs. The effects of incorporating ladle slag (LS) or blast furnace slag (BFS) and different temperature exposures up to 1000 °C were investigated through visual observation, compressive strength, ultrasonic pulse velocity (UPV), thermal conductivity, x-ray diffraction (XRD), thermogravimetry and differential scanning calorimetry (TG/DSC), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope coupled with electron probe microanalyzer (SEM-EPMA). The experimental results indicated that the incorporation of LS or BFS as additional calcium and aluminum sources positively affected the high-temperature behavior of blended mortars, which exhibited a reduction in voids, cracks, and thermal shrinkage while having higher residual strength and thermal stability than solely FS-based AAMs. This was mainly due to the differences in mineralogical transformation and the phases formed. Interestingly, the joint effect of elevated temperature exposure and the addition of LS or BFS enhanced the formation of more stable crystalline phases and densified the structure of blended mortars at 1000 °C.

Thin fly ash/ ladle furnace slag geopolymer: Effect of elevated temperature exposure on flexural properties and morphological characteristics

The flexural properties and thermal performance of 10 mm-thin geopolymers made from fly ash and ladle furnace slag were evaluated before and after exposure to elevated temperatures (300 °C, 600 °C, 900 °C, 1100 °C and 1150 °C). Class F fly ash was mixed with liquid sodium silicate (Na2SiO3) and 12 M sodium hydroxide (NaOH) solution using aluminosilicate/activator ratio of 1:2.5 and Na2SiO3/NaOH ratio of 1:4 to synthesise thin fly ash (FA) geopolymers. 40 wt% of ladle furnace slag was partially replacing fly ash to produce fly ash/slag-based (FAS) geopolymers. Thermal treatment enhanced the flexural strength of thin geopolymers. In comparison to the unexposed specimen, the flexural strength of FA geopolymers at 1150 °C and FAS geopolymers 1100 °C was increased by 161.3% to 16.2 MPa and 208.9% to 24.1 MPa, respectively. A more uniform heating was achieved in thin geopolymers which favoured the phase transformation at high temperatures and contributed to the substantial increase in flexural strength. The joint effect of elevated temperature exposure and the incorporation of ladle furnace slag further improved the flexural strength of thin geopolymers. The calcium-rich slag refined the pore structure and increased the crystallinity of thin geopolymers which aided in high strength development.

The bond strength of self-compacting concrete exposed to elevated temperature

Self-compacting concrete (SCC) is a flowable concrete that can flow, fill and pass through congested area of reinforcement without segregation. As a material used in massive constructions, understanding of the effects of elevated temperature exposure on the properties of SCC is vital. The bond between concrete and embedded steel, which degrades with an increase in temperature, influences the load-carrying capacity and thus the fire resistance of reinforced concrete elements. The objective of this study was to evaluate the bond strength of SCC specimens made with fly ash, ground granulated blast-furnace slag (GGBFS) and expanded perlite aggregate (EPA) under elevated temperature exposure. EPA was introduced to enhance the fire endurance of the SCC. Slump flow, J-ring and V-funnel tests were conducted as per EFNARC guidelines to check the rheological characteristics of SCC. Specimens were exposed to elevated temperature following the ISO 834 standard fire curve. Pull-out tests were carried out to determine the bond strength of reference SCC specimens and specimens exposed to elevated temperature. Data from the tests showed that the SCC specimens made with a combination of GGBFS and EPA exhibited improved bond strength, both at room and elevated temperatures.

Effect of elevated temperature on flexural behavior and fibers-matrix bonding of recycled PP fiber-reinforced cementitious composite

This research aims to study the effects of elevated temperature exposure on the flexural performance of recycled polypropylene (PP) fiber-reinforced cementitious composites. Four mixtures with different percentages of PP fibers (0%, 0.5%, 1%, and 1.5% by volume) were studied. For each mortar, 9 samples of 40 × 40 × 160 mm were cast and cured for 28 days. While 3 samples of each mixture were tested under standard conditions, the other 6 were exposed to high temperature (200 °C) for 2 h and cooled in two different ways before testing (3 were tested hot and 3 were let cool down completely). Flexural strength test, Differential Image Correlation (DIC) and digital microscopy techniques were employed to evaluate the effects of high-temperature exposure and cooling procedures on flexural strength, toughness and bonding. Results showed that the use of recycled PP fibers had a negligible effect on flexural strength in normal conditions. However, fibers provided mortars a residual strength and ductile behavior after peak-load. Besides, flexural strength, post-peak residual strength, secondary strength and secondary toughness were enhanced after exposure to 200 °C and slow cooling, improving the behavior of the composite under flexural stresses. These results, along with the optical microscope images, suggest an improved bonding between the mortar matrix and the PP recycled fibers after exposure to 200 °C (temperature close to the melting point of fibers).

Effects of elevated temperatures on the properties of nanomodified rapid hardening concretes

Effects of elevated temperature exposure and hardening age on mechanical properties of nanomodified concrete are presented. The mass loss, compressive strength and shrinkage of the exposed to the elevated temperatures and cooled specimens were determined. Nanomodification by ultrafine mineral additives and polycarboxylate eter superplasticizer provides direct early structure formation, higher strength at early and later ages, and improved thermal resistance in a range of 200-350 °C of cement-base materials. High specific surface area of ultrafine mineral additive particles and their “excess surface energy” determine interaction degree with powder part components of concrete and allow realizing dense packing, filler, high water-reducing, early pozzolanic reaction, high early strength effects to increasing the rigidity of the cement matrix to resist deformation at impact of elevated temperature.

Residual Properties of TMT Steel Bars after Exposure to Elevated Temperatures

AbstractMany reinforced concrete (RC) structures use thermomechanically treated (TMT) bars as reinforcement and are designed to withstand fire loads. Though the properties of mild steel at elevated temperatures have been extensively studied, there is little information available about how TMT bars are affected. An attempt is made here to study the effect of elevated temperature exposure on the metallographic characteristics and mechanical properties of TMT bars. Fe500 high-strength deformed TMT bars were exposed to peak temperatures up to 950°C for durations up to 240 min. The samples were then allowed to cool to room temperature in air before a microstructure examination and other tests (tensile behavior and hardness) were carried out. A temperature of approximately 500°C was found to be a “threshold” for the TMT bars, beyond which substantial damage was found to occur. It was found that in addition to temperature, the soaking period could also bring about 6–8% additional loss in strength. Exposure to el...

Fatigue behavior of a thin gage Ni alloy after exposure to elevated temperature

Thin gage Ni-base superalloy materials are being targeted for hypersonic applications up to 1100°C. To achieve an optimized system design, standard mechanical behavior data on these materials are needed under a range of loading conditions such as tensile, creep and fatigue at representative temperatures. In order to meet this need, a unique test system developed in-house for determining materials properties of very thin materials was used to determine the fatigue response of a high temperature Ni alloy, both with and without prior exposure to elevated temperatures. This paper examines the effects of elevated temperature exposure on the ductility and fatigue resistance of Haynes 230 with a thickness of 0.127mm.

The effect of elevated temperature exposure on the fracture toughness of solid wood and structural wood composites

Fracture toughness of wood and wood composites has traditionally been characterized by a stress intensity factor, an initiation strain energy release rate (G init) or a total energy to fracture (G f). These parameters provide incomplete fracture characterization for these materials because the toughness changes as the crack propagates. Thus, for materials such as wood, oriented strand board (OSB), plywood and laminated veneer lumber (LVL), it is essential to characterize the fracture properties during crack propagation by measuring a full crack resistant or R curve. This study used energy methods during crack propagation to measure full R curves and then compared the fracture properties of wood and various wood-based composites such as, OSB, LVL and plywood. The effect of exposure to elevated temperature on fracture properties of these materials was also studied. The steady-state energy release rate (G SS) of wood was lower than that of wood composites such as LVL, plywood and OSB. The resin in wood composites provides them with a higher fracture toughness compared to solid lumber. Depending upon the internal structure of the material, the mode of failure also varied. With exposure to elevated temperatures, G SS for all materials decreased while the failure mode remained the same. The scatter associated with conventional bond strength tests, such as internal bond and bond classification tests, renders any statistical comparison using those tests difficult. In contrast, fracture tests with R curve analysis may provide an improved tool for characterization of bond quality in wood composites.

Performance of high strength concretes at elevated temperatures

In this study, the effect of temperature on compressive strength, spalling and mass loss of High Strength Concretes (HSCs) by fc′>65 MPa is discussed. Average compressive strength of the HSCs was from 65 to 93 MPa, which was optimized by Taguchi’s method as a powerful tool for optimizing the performance characteristic of a product/process. This paper presents results of an experimental program on the effects of elevated temperature exposure on the mechanical properties and potential for explosive spalling of HSCs. Effects of four parameters; water to cement ratio (w/c), sand ratio, silica fume ratio and amount of silica fume (sf) addition are considered in tests. Mechanical properties of HSCs were measured by heating 150×300 mm cylinders at 20∘ C/min to temperatures of up to 800∘ C. The tests include sixteen mixtures; twelve contain sf and four are without sf that are selected by Taguchi’s method. The paper presents results of measurement that indicate the effect of sf, cement, fine aggregate, coarse aggregate and water on residual strength, spalling and mass loss of the HSCs. The presence of silica fume had no statistically significant effect on the relative compressive strength while it had an overall statistically significant effect on increasing spalling. The type of aggregate had a significant influence on the thermal properties of HSCs at elevated temperatures. In most cases, by increasing sand ratio, residual compressive strength increased while this trend is inversed for coarse aggregate.

Effects of elevated temperature exposure on heating characteristics, spalling, and residual properties of high performance concrete

Effects of elevated temperature exposure on heating characteristics, spalling, and residual properties of high performance concrete

Effects of elevated temperature exposure on heating characteristics, spalling, and residual properties of high performance concrete

This paper describes results of NIST's experimental program that focuses on effects of elevated temperature exposure on residual mechanical properties of HPC. Residual mechanical properties were measured by heating the 102×204 mm cylinders to steady state thermal conditions at a target temperature, and loading them to failure after the specimens had cooled to room temperature. The test specimens were made of four HPC mixtures with water-to-cementitious material ratio (w/cm) ranging from 0.22 to 0.57, and room-temperature compressive strength at testing ranges from 51 MPa to 93 MPa. Two of the four HPC mixtures contained silica fume. The specimens were heated to a maximum core temperature of 450°C, at a heating rate of 5°C/min. Experimental results indicate that HPCs with higher original strength (lowerw/cm) and with silica fume retain more residual strength after elevated temperature exposure than those with lower original strength (higherw/cm) and without silica fume. The differences in modulus of elasticity are less significant. However, the potential for explosive spalling increased in HPC specimens with lowerw/cm and silica fume. An examination of the specimens' heating characteristics indicate that the HPC mixtures which experienced explosive spalling had a more restrictive process of capillary pore and chemically bound water loss than those which did not experience spalling.

The effect of elevated temperature exposure on fracture resistance and fracture path in a precipitation strengthened aluminum alloy

The combination of TEM and quantitative electron fractography shows that increased incidence of ductile intergranular fracture is associated with coarsening of grain boundary precipitates. Changes in the PFZ width, grain boundary precipitate number density and grain boundary precipitate size, coupled with matrix strength changes, govern the fracture resistance and crack path of the test alloy as a function of time and temperature of exposure. The triaxial stress state extant at crack initiation results in lower area fraction of IG failure than does fracture in less constrained stress states, as after 2 mm of crack growth.

The Effect of Elevated Temperature Exposure of Composites on the Strength Distribution of the Reinforcing Fibers

AbstractUnidirectionally-reinforced Timetal® 21S composite specimens were subjected to elevated temperature heat treatments. The SiC fibers were then chemically extracted from the matrix, and their tensile strengths were measured at room temperature. A Weibull statistical analysis of fiber strength distribution was performed to compare the Weibull parameters of fibers from the as-consolidated and heat-treated composites. Fractographic analysis of the tested fibers was used to identify the flaws which caused failure in each condition. Surface flaws were found to initiate low strength failures in all conditions, and the number of surface initiated failures increased with an increase in severity of heat-treatment. A relationship between the fiber/matrix chemical reaction and surface flaw development is demonstrated. A fracture mechanics analysis that explains the relationship between surface flaw size, fiber fracture toughness, and the measured tensile strengths is suggested.

The Effects of High Temperature Exposure on the Fracture of Thin Tantalum Nitride Films

ABSTRACTContinuous microscratch testing was used in this study to determine the effects of elevated temperature exposure on the adhesion and toughness of thin tantalum nitride films. These films were sputter-deposited at room temperature on sapphire substrates to a nominal thickness of 600 nm with some films heated to 600°C in vacuum while others were heated to 600°C in air. The films heated in vacuum exhibited no changes in composition or structure while the films heated in air completely transformed to tantalum pentoxide. Comparison of the results shows that the interfacial fracture toughness increases from 0.5 MPa-m1/2 for as-sputtered films to 0.8 MPa-m1/2 for films heated in air. However, the toughness increases to more than 3.0 MPa-m1/2 when the films are heated in vacuum. The increase in toughness values follows the reduction in deposition defect content where formation of an oxygen deficient tantalum oxide layer in air from the as-sputtered film increases interfacial toughness slightly while full densification of the tantalum nitride films in vacuum increases toughness to very high levels.

The effect of elevated temperature exposure on fatigue crack growth retardation: Bray, G. H. and Starke, E. A. Jr Scr. Metall. Mater. 1 Sept. 1992 27 (5) 593–598

Environmental and health friendly technologies with economic justification have nowadays an increasing importance in global industrial trends. Idea of global sustainable development dictates cleaner and less health hazardous machining processes. With these limitations in mind, the main issue is now to change the way mechanical components are being machined and move to alternative technologies that could moreover increase the machining performance. Cryogenic machining is one possibility to reach this goal. It consists of a system for cutting (turning, milling, etc.) assisted by liquid nitrogen, which enables a clean process with possible lower production costs and higher productivity. This article presents the results of turning hardened and normalized bearing steel AISI 52100 (DIN 100Cr6), comparing conventional flood and dry with cryogenic machining. Turning results show drastic improvements in tool lifetime (up to 370%) for cryogenic machining of normalized bearing steel 100Cr6 and reduction of thermal residual stress inducements in case of hardened bearing steel 100Cr6, while tool life is also extended.

The effect of elevated temperature exposure on fatigue crack growth retardation

The effect of elevated temperature exposure on fatigue crack growth retardation

Corrosion Commentary

Corrosion and antifreeze in solar collectors. We thought that the last word — of several million — had been said on corrosion problems and antifreeze solutions. But to prove us wrong the International Copper Development Association has just issued a report on a project they carried out (Project No.294A) on The Effects of Elevated Temperature Exposure on the Compatibility of Glycol Solutions with Metals Used in Solar Absorbers.