scholarly journals Influence of Magnetite Nanoparticles on Mechanical and Shielding Properties of Concrete

2017 ◽  
Vol 19 (3) ◽  
pp. 223 ◽  
Author(s):  
A. Lesbayev ◽  
B. Elouadi ◽  
T. Borbotko ◽  
S. Manakov ◽  
G. Smagulova ◽  
...  
Keyword(s):  
Magnetite Nanoparticles ◽  
High Performance ◽  
High Performance Concrete ◽  
Maximum Efficiency ◽  
Electromagnetic Disturbance ◽  
Protective Properties ◽  
Negative Effect ◽  
Chemical Condensation ◽  
Superparamagnetic Properties ◽  
Made In

This paper presents an experimental study on the performance of shielding concrete with additives of magnetite nanoparticles. Two concretes with magnetite additives as well as one based concrete were tested. In order to achieve the high-performance concrete, all concrete mixes had a constant water/cement ratio of 0.45. In order to measure the mechanical properties, concrete samples were made in accordance with dimension such as 40 × 40 × 160 mm. But, for measurement of protective properties the concrete was made in accordance with dimension of rotary antennas such as 400 × 400 mm with a thickness of 10 mm. The nanoparticles Fe3O4 were synthesized by chemical condensation method. XRD have shown the presence of cubic structure of Fe3O4 spinel with crystallite size is equal to 130.0 Å. The TEM microphotograph shows that the Fe3O4 nanoparticles are spherical, the range of sizes is 12‒30 nm. The magnetic retardation suggests that the magnetite nanoparticles have superparamagnetic properties. This is explained by the fact that under the influence of external magnetic field, they are single-domain, in other words, they become uniformly magnetized throughout the volume. The additives of magnetite nanoparticles at a concentration of 0.5% mass have not a negative effect on flexural strength. The samples with additives of magnetite nanoparticles showed better shielding of microwave radiation in the frequency range from 0.7 GHz to 13 GHz. The maximum efficiency of suppression of electromagnetic disturbance is equal to 19.9 dB at a frequency of 1.5 GHz with a thickness of 10 mm.

scholarly journals Effect of Elevated Temperature on the Bond Strength of Prestressing Reinforcement in UHPC

Materials ◽  
2020 ◽  
Vol 13 (21) ◽  
pp. 4990
Author(s):  
Petr Pokorný ◽  
Jiří Kolísko ◽  
David Čítek ◽  
Michaela Kostelecká
Keyword(s):  
Bond Strength ◽  
High Performance ◽  
Elevated Temperatures ◽  
High Performance Concrete ◽  
Future Research ◽  
Ultra High Performance Concrete ◽  
Negative Effect ◽  
Laboratory Investigations ◽  
Increasing Temperature ◽  
Positive Effect

The study explores the effect of elevated temperatures on the bond strength between prestressing reinforcement and ultra-high performance concrete (UHPC). Laboratory investigations reveal that the changes in bond strength correspond well with the changes in compressive strength of UHPC and their correlation can be mathematically described. Exposition of specimens to temperatures up to 200 °C does not reduce bond strength as a negative effect of increasing temperature is outweighed by the positive effect of thermal increase on the reactivity of silica fume in UHPC mixture. Above 200 °C, bond strength significantly reduces; for instance, a decrease by about 70% is observed at 800 °C. The decreases in compressive and bond strengths for temperatures above 400 °C are related to the changes of phase composition of UHPC matrix (as revealed by X-ray powder diffraction) and the changes in microstructure including the increase of porosity (verified by mercury intrusion porosimetry and observation of confocal microscopy) and development cracks detected by scanning electron microscopy. Future research should investigate the effect of relaxation of prestressing reinforcement with increasing temperature on bond strength reduction by numerical modelling.

Experimental Study on Anti-Frozen Durability of Concrete in Saline Soil Region

2011 ◽  
Vol 368-373 ◽  
pp. 1555-1560
Author(s):  
Wei Feng Jin ◽  
Yi Hong Wang ◽  
Gang Zhou ◽  
Kun Fan
Keyword(s):  
Experimental Study ◽  
High Performance ◽  
High Performance Concrete ◽  
Saline Soil ◽  
Single Factor ◽  
Qinghai Province ◽  
Chemical Attack ◽  
Salt Corrosion ◽  
Made In ◽  
Durability Of Concrete

Aiming at the problem of salt corrosion of concrete used in bridge and foundation in the salted areas of Qinghai province in our country,we study the performance of the prevention of salts corrosion and anti-freeze durability of concrete itself and concrete daubed waterproof materials outside or mixed the materials inside.The high-performance concrete made in this article used waterproof materials to prevent brine penetration and set multi-channel protection. The high-performance concrete specimens for comparison,the specimens daubed waterproof material, and rhe specimens mixed waterproof material inside are made to study the changing regularity under single factor and double factors(freeze and melt + chemical attack, carbonize + freeze and melt). The research results show the high-performance concrete made in this article has good anti-freeze durability and the protective covering of waterproof material can form multi-channel protection and effectively slow frozen corrosion of the concrete.

Advances in Research on Influence of Raw Materials on Workability of Fresh Concrete: A Review

2009 ◽  
Vol 405-406 ◽  
pp. 83-88 ◽  
Author(s):  
Gai Fei Peng ◽  
Zhan Qi Guo ◽  
Piet Stroeven ◽  
Ri Gao ◽  
Jiu Feng Zhang
Keyword(s):  
High Performance ◽  
High Performance Concrete ◽  
Fresh Concrete ◽  
Raw Materials ◽  
Experimental Tests ◽  
Solid Particles ◽  
Future Research ◽  
Negative Effect ◽  
The Relationship ◽  
Positive Effect

A literature review was carried out to identify advances in research on workability of fresh concrete via both experimental tests and modeling, especially high performance concrete and self-compacting concrete. As to the relationship between fluidity of concrete and that of paste, future research can be conducted in two aspects, i.e. one is the influence of the quantity of paste in concrete, and another is the influence of fluidity of paste affected by a couple of factors. Most literature proved that the flow of concrete depends both on positive effect and negative effect, the former promote fluidity, such as dispersing, filling and lubricating, and the latter restricts fluidity, such as formation of particle coagulation, an increase of wettable surface of solid particles and mechanical interlock.

UHPC Railing Panels for a Bridge Renovation in Sázava Municipality

2018 ◽  
Vol 272 ◽  
pp. 299-304
Author(s):  
Jan Tichý ◽  
Pavel Ryjáček ◽  
Vit Šmilauer ◽  
Bohuslav Slánský ◽  
Stanislav Ševčík
Keyword(s):  
High Performance ◽  
High Performance Concrete ◽  
Bridge Engineering ◽  
Ultra High Performance Concrete ◽  
Aggressive Environment ◽  
High Durability ◽  
Strong Material ◽  
Thin Walled ◽  
Made In

UHPC (ultra high performance concrete) is used mainly within bridge engineering, due to the demand for subtle but strong material, with high durability against aggressive environment. During the last two years, a series of thin-walled railing panels were made in premises of Skanska a.s. company. They were used for a footbridge in Čeperka village, and this year also for a renovation of a bridge SZ-001 in Sázava municipality. The renovation of a bridge, manufacturing of the railing panels, development of its shape and results of conducted test will be presented.

scholarly journals Optimization of selection process of constituent materials for high performance concrete and mortars

2015 ◽  
Vol 14 (1) ◽  
pp. 053-064 ◽  
Author(s):  
Nataliya Lushnikova
Keyword(s):  
High Performance ◽  
High Performance Concrete ◽  
Selection Process ◽  
Stochastic Equations ◽  
Maximum Efficiency ◽  
Mathematical Treatment ◽  
Chemical Admixtures ◽  
Determination Of Activity ◽  
Selection Of

The paper gives coverage on approach to the optimization of selection process of constituents for high performance concrete (HPC) and mortars. There is shown the example selection of cement, mineral and chemical admixtures, as the most costly and influential on concrete, from the point of their maximum efficiency, measured by flowability and compressive strength increasing indexes. Method combines models for determination of activity indexes with simple stochastic equations obtained at mathematical treatment of experimental results.

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