Residual mechanical strength of concrete exposed to high temperatures – international standardization and influence of coarse aggregates

Considering the constant technological developments in the aeronautical, space, automotive, shipbuilding, nuclear and petrochemical fields, among others, the use of materials with high strength mechanical capabilities at high temperatures has been increasingly used. Among the materials that meet the mechanical strength and corrosion properties at temperatures around 815 °C one can find the nickel base alloy Pyromet® 31V (SAE HEV8). This alloy is commonly applied in the manufacturing of high power diesel engines exhaust valves where it is required high resistance to sulphide, corrosion and good resistance to creep. However, due to its high mechanical strength and low thermal conductivity its machinability is made difficult, creating major challenges in the analysis of the best combinations among machining parameters and cutting tools to be used. Its low thermal conductivity results in a concentration of heat at high temperatures in the interfaces of workpiece-tool and tool-chip, consequently accelerating the tools wearing and increasing production costs. This work aimed to study the machinability, using the carbide coated and uncoated tools, of the hot-rolled Pyromet® 31V alloy with hardness between 41.5 and 42.5 HRC. The nickel base alloy used consists essentially of the following components: 56.5% Ni, 22.5% Cr, 2,2% Ti, 0,04% C, 1,2% Al, 0.85% Nb and the rest of iron. Through the turning of this alloy we able to analyze the working mechanisms of wear on tools and evaluate the roughness provided on the cutting parameters used. The tests were performed on a CNC lathe machine using the coated carbide tool TNMG 160408-23 Class 1005 (ISO S15) and uncoated tools TNMG 160408-23 Class H13A (ISO S15). Cutting fluid was used so abundantly and cutting speeds were fixed in 75 and 90 m/min. to feed rates that ranged from 0.12, 0.15, 0.18 and 0.21 mm/rev. and cutting depth of 0.8mm. The results of the comparison between uncoated tools and coated ones presented a machined length of just 30% to the first in relation to the performance of the second. The coated tools has obtained its best result for both 75 and 90 m/min. with feed rate of 0.15 mm/rev. unlike the uncoated tool which obtained its better results to 0.12 mm/rev.

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Properties of Ambient-Cured Normal and Heavyweight Geopolymer Concrete Exposed to High Temperatures

Materials ◽

10.3390/ma12050740 ◽

2019 ◽

Vol 12 (5) ◽

pp. 740 ◽

Cited By ~ 13

Author(s):

Farhad Aslani ◽

Zohaib Asif

Keyword(s):

Mass Loss ◽

High Temperatures ◽

Offshore Structures ◽

Normal Weight ◽

Geopolymer Concrete ◽

Coarse Aggregates ◽

Residual Properties ◽

New Type ◽

Heavyweight Concrete ◽

Underwater Structures

Ambient-cured heavyweight geopolymer concrete (HWGC) is a new type of concrete that combines the benefits of both heavyweight concrete (HWC) and geopolymer concrete (GC). HWGC provides proper protection from the sources that emit harmful radiations in medical and nuclear industries. Furthermore, HWGC may also be used in offshore structures for pipeline ballasting and similar underwater structures. In this study, heavyweight aggregates (magnetite) have been used and replaced by normal-weight coarse aggregates in GC at volume ratios of 50, 75, and 100% to attain heavyweight classification according to British standards. This study investigates the impacts of high temperatures on standard ambient-cured geopolymer concrete and ambient-cured HWGC through its residual properties regarding compressive and tensile strengths, mass loss, spalling intensity, and flexural strength. The residual properties were examined by heating 100 × 200 mm cylinder specimens to 100, 300, 600, and 900 °C. The results indicated that the maximum compressive strengths of 40.1 and 39.0 MPa were achieved by HWGC at 300 and 100 °C, respectively. The overall result shows that the strength of HWGC increases by increasing magnetite aggregate proportion, while the mass loss, intensity of spalling, and loss of strengths is proportional to temperature after a certain point. Minor spalling with holes and cracking was observed only at 900 °C in HWGC.

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Enhancing the mechanical strength and air permeability of corundum porous materials using shape-modified coarse aggregates

Ceramics International ◽

10.1016/j.ceramint.2019.02.186 ◽

2019 ◽

Vol 45 (8) ◽

pp. 11027-11031 ◽

Cited By ~ 2

Author(s):

Xin Xiong ◽

Zhoufu Wang ◽

Xitang Wang ◽

Hao Liu ◽

Yan Ma

Keyword(s):

Mechanical Strength ◽

Porous Materials ◽

Air Permeability ◽

Coarse Aggregates

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Effect of high temperatures on the mechanical behaviour of hybrid cement

Materiales de Construcción ◽

10.3989/mc.2020.13318 ◽

2020 ◽

Vol 70 (337) ◽

pp. 213 ◽

Cited By ~ 1

Author(s):

B. Qu ◽

A. Fernández Jiménez ◽

A. Palomo ◽

A. Martin ◽

J. Y. Pastor

Keyword(s):

Fracture Toughness ◽

Mechanical Strength ◽

High Temperatures ◽

Mechanical Behaviour ◽

Ordinary Portland Cement ◽

Bending Strength ◽

Hydrated Cement ◽

Hydrated Cement Paste ◽

Physical Chemical ◽

Innovative Methodology

The high-temperature mechanical behaviour of a pre-industrial hybrid alkaline cement (HYC) was studied. The HYC in question contained 30 % Portland clinker and 70 % of a blend of slag, fly ash and a solid activator (mix of alkaline salts with a predominance of Na2SO4). The material was tested during exposure to high temperatures to establish its compressive and bending strength and elastic modulus, as well as fracture toughness, analysed using an innovative methodology to notch the hydrated cement paste specimens. Post-thermal treatment tests were also run to assess residual mechanical strength after 2 h of exposure to temperatures ranging from 400 °C to 1000 °C. TG/DTA, MIP and SEM were deployed to ascertain heat-induced physical-chemical changes in the structure. The higher mechanical strength during and after treatment exhibited by the hardened hybrid alkaline cement than the CEM I 42.5R ordinary portland cement (OPC) paste used as a reference was associated with the lower water and portlandite content found in HYC. Pseudo-plastic behaviour was observed at high temperatures in the loaded HYC in the tests conducted during exposure.

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The Role of Chemical Bonding in the Adhesion of Elastomers

Rubber Chemistry and Technology ◽

10.5254/1.3535896 ◽

1982 ◽

Vol 55 (2) ◽

pp. 525-535 ◽

Cited By ~ 8

Author(s):

A. N. Gent

Keyword(s):

Mechanical Strength ◽

High Temperatures ◽

Chemical Bonding ◽

Surface Oxidation ◽

Peel Strength ◽

Oxidation Reactions ◽

Glass Substrates ◽

Vinyl Silane ◽

Bonding Systems ◽

Strength Of Adhesion

Abstract A review is given of several studies of the effect of interfacial bonding upon the mechanical strength of an adhesive joint. In the first, polybutadiene layers were crosslinked by a free radical process while in contact with silane-treated glass. A direct proportionality was found between the minimum peel strength of the joint, at high temperatures and low rates of peeling, and the vinyl content of the silane treatment liquid. Covalent bonding between the diene polymer and vinyl groups on the treated glass was inferred. When radioactively tagged silanes were employed, extensive combination with the glass substrates was demonstrated. Again, the greater the amount of vinyl silane found on the treated glass surface, the greater the mechanical strength of adhesion between the treated glass and a polybutadiene overlayer. In another series of experiments, two partially crosslinked sheets of polybutadiene were pressed together before the crosslinking was taken to completion. The additional crosslinking was determined from measurements of the elastic properties and of the degree of equilibrium swelling by a compatible liquid. Again, the mechanical strength of adhesion between the two sheets under threshold conditions was found to be directly proportional to the inferred degree of interfacial interlinking. Thus, at least at high temperatures and low rates of peel, there is substantial evidence for a direct correlation between the mechanical strength of a joint and the degree of interfacial chemical bonding. Moreover, the relationships established in these studies allow other bonding systems to be diagnosed as chemical or physical in nature. For example, a dramatic increase in the strength of adhesion between two crosslinked polybutadiene layers was observed if they were exposed to air or oxygen for periods of an hour or two before being pressed into contact. It is inferred that interfacial chemical bonds are formed as a consequence of rapid surface oxidation reactions.

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Mechanical and Microstructural Analysis of an Ultra-Flexible Nano-Silver Paste Sintered Joint

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.865.25 ◽

2020 ◽

Vol 865 ◽

pp. 25-30

Author(s):

Lahouari Benabou ◽

Quang Bang Tao ◽

Thien An Nguyen-Van ◽

Xu Dong Wang ◽

Luc Chassagne

Keyword(s):

Elastic Modulus ◽

Mechanical Strength ◽

High Temperatures ◽

Microstructural Analysis ◽

Processing Parameters ◽

Mechanical And Thermal Properties ◽

Bonding Pressure ◽

Silver Paste ◽

Nano Silver ◽

Low Elastic Modulus

Soldering using common lead-free solder alloys is still one of the main die attach technology, in particular for applications in power electronics where high temperatures have to be met. However, some newly developed attach technologies promise to offer more interesting features in terms of both mechanical and thermal properties. Among these new methods, sintering of nano-silver particles allows to obtain a high thermal conductivity needed in the assemblies of electronic or optical components, as well as a relatively low elastic modulus for better stress accommodation and enhanced thermo-mechanical reliability. The sintering processing parameters, mainly the bonding pressure, the sintering temperature profile, and the sintering atmosphere, are known to have a critical effect on the properties of the sintered layer, such as its mechanical strength and electrical/thermal performances.In this study, copper substrates are fabricated and assembled by sintering using a nano-silver paste. The objective is to obtain a bonding joint with high mechanical flexbility, capable of addressing the thermomechanical stresses for systems operating under high temperatures. The measured mechanical properties of the sintered material show on the one hand low elastic modulus of the joint which is appropriate for strong difference in thermal expansion between components, and on the other hand sufficient mechanical strength for the assembly. Microstructure analyses reveal a highly porous silver network structure of the joint, with submicrometric silver grains and large micrometric porosities homogeneously distributed.

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THE AGGREGATE CRUSHING TEST FOR EVALUATING THE MECHANICAL STRENGTH OF COARSE AGGREGATES.

Journal of the Institution of Civil Engineers ◽

10.1680/ijoti.1945.12252 ◽

1945 ◽

Vol 24 (6) ◽

pp. 125-133 ◽

Cited By ~ 7

Author(s):

A H D MARKWICK ◽

F A SHERGOLD

Keyword(s):

Mechanical Strength ◽

Coarse Aggregates ◽

Aggregate Crushing

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Phase transformations and mechanical strength of OPC/Slag pastes submitted to high temperatures

Materials and Structures ◽

10.1617/s11527-007-9247-8 ◽

2007 ◽

Vol 41 (2) ◽

pp. 345-350 ◽

Cited By ~ 60

Author(s):

Alessandra Mendes ◽

Jay Sanjayan ◽

Frank Collins

Keyword(s):

Mechanical Strength ◽

Phase Transformations ◽

High Temperatures

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SANDVIK 8R30, 8R30H

Alloy Digest ◽

10.31399/asm.ad.ss0622 ◽

1995 ◽

Vol 44 (11) ◽

Keyword(s):

Corrosion Resistance ◽

Mechanical Strength ◽

Physical Properties ◽

Tensile Properties ◽

High Temperatures ◽

Creep Strength ◽

Heat Treating ◽

Nickel Steel ◽

Stainless Chromium

Abstract Sandvik 8R30 is an austenitic, titanium-stabilized stainless chromium-nickel steel. It is suitable for wet-corrosive service, but also has good mechanical strength at high temperatures. For applications requiring enhanced creep strength, it is recommended that the variant Sandvik 8R30H be used. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties as well as creep. It also includes information on corrosion resistance as well as forming, heat treating, and joining. Filing Code: SS-622. Producer or source: Sandvik.

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