scholarly journals Oxidation Behavior of Matrix Graphite and Its Effect on Compressive Strength

2017 ◽  
Vol 2017 ◽  
pp. 1-6 ◽  
Author(s):  
Xiangwen Zhou ◽  
Cristian I. Contescu ◽  
Xi Zhao ◽  
Zhenming Lu ◽  
Jie Zhang ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Pore Formation ◽  
Oxidation Behavior ◽  
Mercury Porosimetry ◽  
Strength Loss ◽  
Nuclear Graphite ◽  
Matrix Graphite ◽  
Oxidation Performance ◽  
Lower Oxidation ◽  
High Temperature Gas

Matrix graphite (MG) with incompletely graphitized binder used in high-temperature gas-cooled reactors (HTGRs) is commonly suspected to exhibit lower oxidation resistance in air. In order to reveal the oxidation performance, the oxidation behavior of newly developed A3-3 MG at the temperature range from 500 to 950°C in air was studied and the effect of oxidation on the compressive strength of oxidized MG specimens was characterized. Results show that temperature has a significant influence on the oxidation behavior of MG. The transition temperature between Regimes I and II is ~700°C and the activation energy (Ea) in Regime I is around 185 kJ/mol, a little lower than that of nuclear graphite, which indicates MG is more vulnerable to oxidation. Oxidation at 550°C causes more damage to compressive strength of MG than oxidation at 900°C. Comparing with the strength of pristine MG specimens, the rate of compressive strength loss is 77.3% after oxidation at 550°C and only 12.5% for oxidation at 900°C. Microstructure images of SEM and porosity measurement by Mercury Porosimetry indicate that the significant compressive strength loss of MG oxidized at 550°C may be attributed to both the uniform pore formation throughout the bulk and the preferential oxidation of the binder.

Study on the Mechanical Properties and Frost Resistance of Recycled Concrete Prepared by Village Construction Wastes

2011 ◽  
Vol 418-420 ◽  
pp. 406-410
Author(s):  
Jun Liu ◽  
Yao Li ◽  
Dan Dan Hong ◽  
Yu Liu
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Frost Resistance ◽  
Cement Mortar ◽  
Strength Loss ◽  
Recycled Concrete ◽  
Recycled Aggregate ◽  
Replacement Rate ◽  
Concrete Mechanical Properties ◽  
Better Than

Abstract. Recycled aggregate—rural building material wastes pretreated by cement mortar—are applied into concrete with different replacement rates: 0, 25%, 50%, 75%, and 100%. Results from measurements of compressive strength, cleavage tensile strength, mass loss after fast freeze-thaw cycles, and compressive strength loss indicate that a different recycled aggregate replacement rate certainly influences concrete mechanical properties and frost resistance. Recycled aggregate replacement rates less than 75% performs better than common concrete. Data from the 100% replacement rate is worse than that of rates less than 75% but still satisfy the general demands of GB standard on C30 concrete.

scholarly journals Study on High Energy Propellant Waste in the Processing of Fired Clay Bricks

2020 ◽  
Vol 70 (6) ◽  
pp. 596-602
Author(s):  
P.K. Mehta ◽  
A. Kumaraswamy ◽  
V. K. Saraswat ◽  
Praveen Kumar B.
Keyword(s):  
Compressive Strength ◽  
Water Absorption ◽  
Pore Formation ◽  
High Energy ◽  
X Ray Diffraction ◽  
X Ray ◽  
Clay Bricks ◽  
Baking Process ◽  
Fired Bricks ◽  
Xrd Studies

Utilisation of propellant waste in fabrication of bricks is not only used as efficient waste disposal method but also to get better functional properties. In the present study, high energy propellant (HEP) waste additive mixed with soil and fly ash in different proportions during manufacturing of bricks has been investigated experimentally. X-ray diffraction (XRD) studies were carried out to confirm the brick formation and the effect of HEP waste. Ceramic bricks were fabricated with HEP waste additive in proper proportions i.e. 0.5 wt %, 1.0 wt %, 1.5 wt %, 2.0 wt %, 2.5 wt %, 3 wt %, 3.5 wt %, and 4 wt % and then evaluated for water absorption capability and compressive strength. Compressive strength of 6.7 N/mm2, and Water absorption of 22 % have been observed from modified fired bricks impregnated with HEM waste additive. Scanning electron microscopy (SEM) studies were carried out to analyze the effect of HEP waste additive on pore formation and distribution in the bricks. Further, the heat resulting from decomposition of propellants can cause a decrease in the energy required of baking process. The process of manufacturing of bricks with HEP waste additive is first of its kind till date.

scholarly journals Evaluation of Oxidation Performance of TRISO Fuel Particles for Postulated Air-Ingress Accident of HTGR

2020 ◽  
Vol 2020 ◽  
pp. 1-8
Author(s):  
Fangcheng Cao ◽  
De Zhang ◽  
Qingjie Chen ◽  
Hao Li ◽  
Hongqing Wang
Keyword(s):  
Reaction Rates ◽  
Good Oxidation Resistance ◽  
Triso Fuel ◽  
Rate Determining Step ◽  
Parabolic Law ◽  
Oxidation Performance ◽  
Triso Particles ◽  
Fuel Particles ◽  
Air Ingress ◽  
High Temperature Gas

In a high-temperature gas-cooled reactor, the integrity of tristructural-isotropic-(TRISO-) coated fuel particles ensures the safety of the reactor, especially in case of an air-ingress accident. The oxidation of TRISO particles with the outer layers of silicon carbide (SiC) was performed at temperatures of 900°C–1400°C in air environment. Both the microstructure and phase composition of the SiC layers were studied. The results showed that the SiC layers had a good oxidation resistance below 1100°C. However, the amorphous silica on the SiC layers formed at 1200°C and gradually crystallized at 1400°C with the presence of microcracks. The reaction rates of the SiC layers were determined by measuring the silica thickness. It was proposed that the oxidation of the SiC layers followed the linear-parabolic law with the activation energy of 146 ± 5 kJ/mol. The rate-determining step of the oxidation was the diffusion of oxygen in silica.

scholarly journals Design of alkali-activated materials for a modular green wall and green roof system

2019 ◽  
Vol 274 ◽  
pp. 04001
Author(s):  
Maria Manso ◽  
João Castro-Gomes
Keyword(s):  
Compressive Strength ◽  
Mine Waste ◽  
Green Roof ◽  
Strength Loss ◽  
Capillary Absorption ◽  
Green Wall ◽  
Roof System ◽  
Density Reduction ◽  
Alkali Activated ◽  
Reference Mixture

This study presents the work developed with alkali activated mixtures to be used as component of a new modular green wall and green roof system (GEOGREEN). The aim is to find the most appropriate composition of alkali-activated mixture to maximize water absorption and porosity and also find a good mechanical strength with reduced density. Alkali-activated mixtures were produced using two precursors, mine waste mud from Panasqueira mine (W) and ground waste glass (G) and two alkaline activators, sodium silicate (SS) and sodium hydroxide (SH). A ventilated oven was used to speed up the curing process. Variables as percentage substitution of W per G, molar concentration of SH, cure length and temperature, were tested to identify the reference mixture. After these tests different percentages of aggregates as sand (S), expanded cork granules (C) and expanded clay (A) were added to reference mixture (REF). Results indicate that S25 obtained the maximum compressive strength of 35 MPa after 7 curing days. However, about 30% compressive strength loss is observed after immersion of this mixture in water for 24h. Capillary absorption coefficient can reach to 4,77 kg/m2.h0,5 with C25 and to 4,11 kg/m2.h0,5 with S25. Also C50 enables a 20% density reduction compared to REF.

Researches on Fractal Features of Graphite Porous Materials

2012 ◽  
Vol 507 ◽  
pp. 25-29 ◽  
Author(s):  
Qi Liu ◽  
Ya Fei Hu ◽  
Qi Li Wang
Keyword(s):  
Fractal Dimension ◽  
Pore Formation ◽  
Inflection Point ◽  
Pore Diameter ◽  
Mercury Porosimetry ◽  
Microscopic Structure ◽  
Fractal Characteristics ◽  
The One ◽  
Main Factor

The mercury porosimetry experiment has tested three different kinds of porosity graphite and the microscopic structure of impregnation antimony materials, and has calculated the corresponding fractal dimension by using the Menger model. The results show that: the main pore diameter of the graphite materials is in the interval of , most of which can be filled by impregnation antimony, and graphite and impregnation antimony materials both have the fractal characteristics. Graphite materials also have the dual fractal characteristics. Its fractal inflection point aperture is about 1μm, and the fractal dimension (3.05 ~ 3.25) of the small pores (φ≤1μm) is less than the one (3.71 ~ 3.95) of the large pores (φ>1μm). The reason why existing the dual fractal characteristics is that the size of the pore formation mechanism is different. Impregnation occurs mainly in the range of large pores, characteristics of which is an important factor to influence the quality of impregnation materials. The material formula is the main factor to influence the large pores and an important guarantee to improve the quality of impregnation products.

Compressive Strength of High Volume Slag Cement Concrete in High Temperature Curing

2011 ◽  
Vol 287-290 ◽  
pp. 793-796 ◽  
Author(s):  
Sasan Parniani ◽  
Mohd Warid Hussin ◽  
Farnoud Rahimi Mansour
Keyword(s):  
Compressive Strength ◽  
Working Conditions ◽  
High Volume ◽  
Strength Loss ◽  
Cementitious Material ◽  
Cement Concrete ◽  
Slag Cement ◽  
Hot Weather ◽  
Rate Of Evaporation ◽  
Compressive Tests

Recent consideration has been given to use of GGBFS as separate cementitious material mixed along with Portland cement in production of concrete. Problems are frequently encountered in producing good-quality concrete specially slag cement concrete in hot climates.Curing problems are exaggerated when concreting in hot weather, as a result of both higher concrete temperatures and increased rate of evaporation from the fresh mix. The disadvantage of GGBFS concretes is that they proved to be more sensitive to poor curing than OPC Therefore, special care must be taken when using this type of concrete, especially on site, where the working conditions and the application of curing are not as easy to control as in the laboratory concrete. The purpose of this paper is investigation and evaluation strength loss in slag cement concrete in poor curing situation. To carry out this aim, 72 cube specimens with three different proportion of slag are made and cured in two different conditions. And result of compressive tests compared together to determine susceptibility of GGBFS concrete in hot-dry condition.

scholarly journals Deterioration and Microstructural Evolution of the Fly Ash Geopolymer Concrete against MgSO4Solution

2017 ◽  
Vol 2017 ◽  
pp. 1-11 ◽  
Author(s):  
Tao Long ◽  
Qingyuan Wang ◽  
Zhongwei Guan ◽  
Yu Chen ◽  
Xiaoshuang Shi
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Magnesium Sulfate ◽  
Strength Loss ◽  
Sulfate Attack ◽  
Aluminum Silicate ◽  
Geopolymer Concrete ◽  
Portland Cement Concrete ◽  
Sodium Aluminum Silicate ◽  
Magnesium Aluminum Silicate

Fly ash geopolymer concrete (FAGC) and ordinary Portland cement concrete (OPCC) specimens were immersed in 5% MgSO4solution undergoing 32 wetting-drying and heating-cooling cycles. Their compressive behavior was investigated after every 8 cycles. Several microstructure analysis techniques were applied on the samples to identify the materials formed due to magnesium sulfate attack, including XRD, FTIR, SEM, and EDS. Experimental results elucidated that the compressive strength loss ratio in the heating group of FAGC was 12.7%, while that of OPCC was 17.8%, which means that FAGC had better magnesium sulfate resistance than OPCC. The compressive strength loss of OPCC was due to the formation of gypsum under the magnesium sulfate attack exposed to wetting-drying and heating-cooling cycles. The deterioration mechanisms of FAGC against MgSO4solution were discovered to be that sodium aluminum silicate hydrate (N-A-S-H) gels reacted with MgSO4, leading to the creation of low strength magnesium aluminum silicate hydrate (M-A-S-H) gels.

Durability of Sugar Cane Bagasse Ash (SCBA) Concrete towards Chloride Ion Penetration

2014 ◽  
Vol 567 ◽  
pp. 369-374 ◽  
Author(s):  
Nasir Shafiq ◽  
Asma Abd Elhsameed ◽  
Muhd Fadhil Nuruddin
Keyword(s):  
Weight Loss ◽  
Compressive Strength ◽  
Penetration Depth ◽  
Sugar Cane ◽  
Fine Particles ◽  
Strength Loss ◽  
Sugar Cane Bagasse ◽  
Chloride Penetration ◽  
Chloride Ingress ◽  
Sugar Cane Bagasse Ash

In this study, the effect of sugar cane bagasse ash (SCBA) on chloride penetration resistance of concrete was investigated. 100-mm side cubes were cast and cured in water for 28 days followed by six months curing in 4% NaCl solution. The resistance to chloride penetration was assessed by measuring the chloride penetration depth, weight loss, compressive strength loss and bond strength loss. Chloride penetration depth was measured using AgNO3–based method. It was obtained that inclusion of SCBA in concrete significantly reduced the chloride penetration depth, weight loss, compressive strength loss and bond loss that was attributed to the fine particles of SCBA that filled up the pores and prevented the chloride ingress in the concrete.

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