scholarly journals Effect of Nano-SiO2 on the Microstructure and Mechanical Properties of Concrete under High Temperature Conditions

Materials ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 166
Author(s):  
Piotr Brzozowski ◽  
Jarosław Strzałkowski ◽  
Piotr Rychtowski ◽  
Rafał Wróbel ◽  
Beata Tryba ◽  
...  
Keyword(s):  
High Temperature ◽  
High Temperatures ◽  
Coarse Aggregate ◽  
Mechanical Performance ◽  
Mercury Porosimetry ◽  
Thermal Characteristics ◽  
Total Porosity ◽  
Cement Matrix ◽  
Cement Concrete ◽  
Structural Tests

The aim of the research was to determine how the admixture of nanosilica affects the structure and mechanical performance of cement concrete exposed to high temperatures (200, 400, 600, and 800 °C). The structural tests were carried out on the cement paste and concrete using the methods of thermogravimetric analysis, mercury porosimetry, and scanning electron microscopy. The results show that despite the growth of the cement matrix’s total porosity with an increasing amount of nanosilica, the resistance to high temperature improves. Such behavior is the result of not only the thermal characteristics of nanosilica itself but also of the porosity structure in the cement matrix and using the effective method of dispersing the nanostructures in concrete. The nanosilica densifies the structure of the concrete, limiting the number of the pores with diameters from 0.3 to 300 μm, which leads to limitation of the microcracks, particularly in the coarse aggregate-cement matrix contact zone. This phenomenon, in turn, diminishes the cracking of the specimens containing nanosilica at high temperatures and improves the mechanical strength.

scholarly journals Insight into the Mechanical Performance of the UHPC Repaired Cementitious Composite System after Exposure to High Temperatures

Materials ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4095
Author(s):  
Qing Chen ◽  
Zhiyuan Zhu ◽  
Rui Ma ◽  
Zhengwu Jiang ◽  
Yao Zhang ◽  
...  
Keyword(s):  
Compressive Strength ◽  
High Temperature ◽  
High Temperatures ◽  
Bonding Strength ◽  
Composite System ◽  
Mechanical Performance ◽  
High Performance Concrete ◽  
Interfacial Structure ◽  
Cementitious Composite ◽  
Average Percentage

In this paper, the mechanical performance of an ultra-high-performance concrete (UHPC) repaired cementitious composite system, including the old matrix and the new reinforcement (UHPC), under various high temperature levels (20 °C, 100 °C, 300 °C, and 500 °C) was studied. In this system, UHPC reinforced with different contents of steel fibers and polypropylene (PP) fibers was utilized. Moreover, the physical, compressive, bonding, and flexural behaviors of the UHPC repaired system after being exposed to different high temperatures were investigated. Meanwhile, X-ray diffraction (XRD), baseline evaluation test (BET), and scanning electron microscope (SEM) tests were conducted to analyze the effect of high temperature on the microstructural changes in a UHPC repaired cementitious composite system. Results indicate that the appearance of the bonded system changed, and its mass decreased slightly. The average percentage of residual mass of the system was 99.5%, 96%, and 94–95% at 100 °C, 300 °C, and 500 °C, respectively. The residual compressive strength, bonding strength, and flexural performance improved first and then deteriorated with the increase of temperature. When the temperature reached 500 °C, the compressive strength, bonding strength, and flexural strength decreased by about 20%, 30%, and 15% for the UHPC bonded system, respectively. Under high temperature, the original components of UHPC decreased and the pore structure deteriorated. The cumulative pore volume at 500 °C could reach more than three times that at room temperature (about 20 °C). The bonding showed obvious deterioration, and the interfacial structure became looser after exposure to high temperature.

Effect of High Temperatures on Microstructure of Repair Mortars Containing Artificial Aggregate Based on Sintered Ash

2015 ◽  
Vol 1100 ◽  
pp. 147-151
Author(s):  
Jiří Bydžovský ◽  
Tomáš Melichar ◽  
Ámos Dufka ◽  
Michaela Fiedlerová
Keyword(s):  
High Temperature ◽  
High Temperatures ◽  
Analytical Methods ◽  
Maximum Temperature ◽  
Cement Matrix ◽  
Lightweight Aggregates ◽  
Temperature Influence ◽  
Repair Materials ◽  
Repair Mortars

The research presented in this article is focused on analyzing of high temperature influence on behaviour and microstructure of polymeric-cement matrix based repair materials containing lightweight aggregates on the basis of sintered ash. Also admixtures and polymeric fibres were applied to obtain the required parameters. The study of microstructure and its changes was realized using SEM, XRD and DTA analytical methods. Maximum temperature of exposure environment of the tested mortars was 1000°C, while cooling of specimens was gradual.

scholarly journals Uniaxial Tensile Behavior, Flexural Properties, Empirical Calculation and Microstructure of Multi-Scale Fiber Reinforced Cement-Based Material at Elevated Temperature

Materials ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 1827
Author(s):  
Li Li ◽  
Mehran Khan ◽  
Chengying Bai ◽  
Ke Shi
Keyword(s):  
Tensile Strength ◽  
High Temperature ◽  
Tensile Properties ◽  
High Temperatures ◽  
Cement Matrix ◽  
Uniaxial Tensile ◽  
Flexural Properties ◽  
Fiber Reinforced ◽  
Multi Scale ◽  
Reinforced Cement

Fire is one of the most unfavorable conditions that cement-based composites can face during their service lives. The uniaxial tensile and flexural tensile properties of the steel-polyvinyl alcohol fiber-calcium carbonate whisker (CW) multi-scale fiber reinforced cement matrix composites (MSFRCs) under high temperatures are studied, including strength, deformation capacity, energy dissipation capacity, and its ability to be assessed through the empirical calculation method. The study showed that with the increase of the treatment temperature, the MSFRC residual bending strength, bending toughness, and tensile strength decreased overall, but the decline was slow at 600 °C. The peak flexural deflection and peak tensile strain of MSFRC first reduced and then increased with the increase of the temperature. As the temperature increased, the nominal stiffness of MSFRC bending and straight gradually reduced, and the rate of decline was faster than that of its strength. However, the uniaxial tensile properties were more sensitive to the temperature and degraded more rapidly. A quantitative relationship was established between MSFRC residual bending, tensile strength, and temperature. A comparison with existing research results shows that MSFRC has achieved an ideal effect of high temperature resistance. The multi-scale hybrid fiber system significantly alleviates the deterioration of cement-based composite’s mechanical properties under high temperatures. With the help of an optical microscope and scanning electron microscope (SEM), the high temperature influence mechanism on the uniaxial tensile and flexural properties of MSFRC was revealed.

scholarly journals Influence of Urena lobata Fibre Treatment on Mechanical Performance Development in Hybrid Urena lobata: Fibre/Gypsum Plaster Composites

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Jerum Biepinwoh Kengoh ◽  
Ekane Peter Etape ◽  
Beckley Victorine Namondo ◽  
Josepha Foba-Tendo ◽  
Yakum Renata Nafu ◽  
...  
Keyword(s):  
Moisture Transfer ◽  
Mechanical Performance ◽  
Autogenous Shrinkage ◽  
Nucleation Site ◽  
Lower Percentage ◽  
Cement Matrix ◽  
Hardened Cement ◽  
Cement Composites ◽  
Cement Concrete ◽  
Performance Development

Autogenous shrinkage is related to the chemistry and changes in the internal structure of the cement concrete paste on drying. This problem of drying shrinkage in early stages that occur without any moisture transfer to the surrounding environment has triggered the incorporation of fibres in the cement concrete matrix to fill the micropores and control cracking (autogenous shrinkage). This study aimed at investigating the potential use of Urena lobata (UL) fibre as microreinforcement in enhancing mechanical properties of hybrid UL-fibre/gypsum cement composites used for plasters. The fibre was harvested from the coastal region of Cameroon and treated with 0.06 M NaOH over different periods. Dispersion of treated fibre bundles in the composite (at Wt. % UL-fibre dosages of 0, 1.5, 2.5, and 3.5) was facilitated by blending with the cement paste which also helped to improve interfacial bonding between the fibre and the cement matrix. The moisture/water absorption and flexural properties within the hardened cement matrix were quantitatively assessed, and it was observed that the incorporation of treated fibre accelerated the hydration process. The test results showed an increment in compressive strength and reduction in autogenous shrinkage for the hybrid UL fibre/gypsum cement composites, while lower percentage additions (less than 2.5%) of untreated fibre appeared to have adverse effects on specimens. It was observed that properly dispersed (blended) treated UL fibres filled the fine pores in the cement matrix by providing an additional nucleation site that resulted in a denser microstructure, which in turn enhanced the strengths and limited the autogenous shrinkage.

scholarly journals Lightweight concrete with coarse aggregate from ceramic waste at high temperatures

2020 ◽  
Vol 13 (2) ◽  
pp. 433-454
Author(s):  
L. PASSOS ◽  
A. L. MORENO Jr. ◽  
A. A. A. SOUZA
Keyword(s):  
Mechanical Strength ◽  
High Temperatures ◽  
Coarse Aggregate ◽  
Lightweight Concrete ◽  
Mechanical Performance ◽  
National Standard ◽  
Ceramic Block ◽  
Ceramic Waste ◽  
Concrete Mixtures ◽  
Concrete Production

Abstract With the increasing use of recycled materials from civil construction, mainly as substitute for some aggregates in concrete mixtures, it is necessary to obtain technical information on the performance of these new mixtures. National and international research on the use of ceramic waste in concrete production highlight good results of this new material’s mechanical performance in environmental situations. However, little is known about its behavior at high temperatures. In this context, we sought to verify the performance of concrete mixtures produced with aggregates from ceramic block waste at high temperatures, with evaluation of their residual mechanical strength, axial compressive strength and elastic modulus, and also their tendency to spalling in fire situations. The RILEM-129 MHT method [1] was used for the assessment of residual mechanical strength, and the tendency to spalling was evaluated according to the procedure suggested by Souza and Moreno [2]. In both these evaluations, there is no national standard, and, in the case of spalling, not even an international standard. Three concrete mixtures were used, one prepared with natural coarse basalt aggregate (reference) and the other two by replacing part of this natural aggregate with aggregate from ceramic block waste (40% and 100% of substitution in volume). In the end, it is concluded that the substitution of natural coarse aggregate for lightweight aggregate from ceramic block waste can be an excellent alternative to increase the resistance of concrete to fire. Thus, the results of mechanical strength and spalling in a fire situation, unprecedented in our country, can greatly support the decision-making about the use of this alternative material in the national construction industry.

High Temperature n- and p-type Doped Microcrystalline Silicon Layers Grown by VHF PECVD Layer-by-Layer Deposition

2003 ◽  
Vol 762 ◽  
Author(s):  
A. Gordijn ◽  
J.K. Rath ◽  
R.E.I. Schropp
Keyword(s):  
Activation Energy ◽  
High Temperature ◽  
High Temperatures ◽  
Continuous Wave ◽  
Hydrogen Plasma ◽  
Silicon Layer ◽  
Dark Conductivity ◽  
High Deposition Rate ◽  
Layer By Layer ◽  
Microcrystalline Silicon

AbstractDue to the high temperatures used for high deposition rate microcrystalline (μc-Si:H) and polycrystalline silicon, there is a need for compact and temperature-stable doped layers. In this study we report on films grown by the layer-by-layer method (LbL) using VHF PECVD. Growth of an amorphous silicon layer is alternated by a hydrogen plasma treatment. In LbL, the surface reactions are separated time-wise from the nucleation in the bulk. We observed that it is possible to incorporate dopant atoms in the layer, without disturbing the nucleation. Even at high substrate temperatures (up to 400°C) doped layers can be made microcrystalline. At these temperatures, in the continuous wave case, crystallinity is hindered, which is generally attributed to the out-diffusion of hydrogen from the surface and the presence of impurities (dopants).We observe that the parameter window for the treatment time for p-layers is smaller compared to n-layers. Moreover we observe that for high temperatures, the nucleation of p-layers is more adversely affected than for n-layers. Thin, doped layers have been structurally, optically and electrically characterized. The best n-layer made at 400°C, with a thickness of only 31 nm, had an activation energy of 0.056 eV and a dark conductivity of 2.7 S/cm, while the best p-layer made at 350°C, with a thickness of 29 nm, had an activation energy of 0.11 V and a dark conductivity of 0.1 S/cm. The suitability of these high temperature n-layers has been demonstrated in an n-i-p microcrystalline silicon solar cell with an unoptimized μc-Si:H i-layer deposited at 250°C and without buffer. The Voc of the cell is 0.48 V and the fill factor is 70 %.

NICROFER 5520 Co

Alloy Digest ◽  
1995 ◽  
Vol 44 (3) ◽  
Keyword(s):  
High Temperature ◽  
Chemical Composition ◽  
Physical Properties ◽  
Tensile Properties ◽  
High Temperatures ◽  
Heat Treating ◽  
High Temperature Corrosion ◽  
Creep Properties ◽  
Nickel Chromium ◽  
Temperature Performance

Abstract NICROFER 5520 Co is a nickel-chromium-cobalt-molybdenum alloy with excellent strength and creep properties up to high temperatures. Due to its balanced chemical composition the alloy shows outstanding resistance to high temperature corrosion in the form of oxidation and carburization. This datasheet provides information on composition, physical properties, elasticity, and tensile properties. It also includes information on high temperature performance as well as forming, heat treating, machining, and joining. Filing Code: Ni-480. Producer or source: VDM Technologies Corporation.

CARLSON ALLOY C601

Alloy Digest ◽  
1994 ◽  
Vol 43 (7) ◽  
Keyword(s):  
High Temperature ◽  
Physical Properties ◽  
Stress Corrosion ◽  
Tensile Properties ◽  
High Temperatures ◽  
Stress Corrosion Cracking ◽  
Heat Treating ◽  
Resistance To Stress ◽  
Extended Exposure ◽  
Sulfur Containing

Abstract Carlson Alloy C601 is characterized by high tensile, yield and creep-rupture strengths for high temperature service. The alloy is not embrittled by extended exposure to high temperatures and has excellent resistance to stress-corrosion cracking, to carburizing, nitriding and sulfur containing environments. This datasheet provides information on composition, physical properties, elasticity, and tensile properties as well as creep. It also includes information on forming, heat treating, machining, and joining. Filing Code: Ni-458. Producer or source: G.O. Carlson Inc.

INCOTHERM TD

Alloy Digest ◽  
2005 ◽  
Vol 54 (11) ◽  
Keyword(s):  
Corrosion Resistance ◽  
High Temperature ◽  
Physical Properties ◽  
Tensile Properties ◽  
Oxidation Resistance ◽  
High Temperatures ◽  
Rare Earths ◽  
Temperature Performance

Abstract Incotherm TD is a thermocouple-sheathing alloy with elements of silicon and rare earths to enhance oxidation resistance at high temperatures. This datasheet provides information on composition, physical properties, and tensile properties as well as deformation. It also includes information on high temperature performance and corrosion resistance as well as forming. Filing Code: Ni-628. Producer or source: Special Metals Corporation.

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