scholarly journals Effects of Recycled Fine Glass Aggregates on Alkali Silica Reaction and Thermo-Mechanical Behavior of Modified Concrete

2021 ◽  
Vol 11 (19) ◽  
pp. 9045
Author(s):  
Ibtissam Abalouch ◽  
Siham Sakami ◽  
Fatima-Ezzahra Elabbassi ◽  
Lahcen Boukhattem
Keyword(s):  
Electron Microscopy ◽  
Thermal Effusivity ◽  
Maximum Size ◽  
Pozzolanic Reaction ◽  
Alkali Silica Reaction ◽  
Natural Sand ◽  
Fine Glass ◽  
Recycled Waste ◽  
Scanning Electron ◽  
Curing Age

The objective of this work is to develop a new composite material by substituting sand with recycled waste glass (RWG). Different volume percentages of RWG varying from 0 to 50% were incorporated into concrete, with maximum size that did not exceed 1.25 mm. The microscopic characterization by scanning electron microscopy SEM-EDS and optical microscopic test, as well as the durability against alkali silica reaction (ASR) test, were performed respectively to visualize the morphology and assess the damage caused by ASR. Furthermore, the mechanical and thermophysical properties measurements were carried out. The results of microscopic characterization showed the presence of cracks inside a minority of glass particles due to ASR, and ASR test indicated that expansion activity remained well below the limit expansion value of 0.15%. The obtained results also showed that, at 28 and 90 days of curing, compressive strength increased respectively by up to 1.63% and 29% for 20% of the incorporated RWG volume rate in concrete; however, beyond this rate it diminished receptively by 30% and 3.2%. This improvement with curing age was attributed to pozzolanic reaction. Regarding density, it reduced by around 5%. Furthermore, thermal conductivity and thermal effusivity decreased respectively by 36% and 8.06% at dry state and they dropped respectively by 44% and 21.28% at saturated state, related to reference concrete RC. It is therefore feasible to substitute high amount of natural sand with RWG to obtain new composite that may be successfully used as structural material in construction building.

scholarly journals The Expansion Cracks of Dolomitic Aggregates Cured in TMAH Solution Caused by Alkali–Carbonate Reaction

Materials ◽  
2019 ◽  
Vol 12 (8) ◽  
pp. 1228 ◽  
Author(s):  
Xiaoxiao Chen ◽  
Bin Yang ◽  
Zhongyang Mao ◽  
Min Deng
Keyword(s):  
Electron Microscopy ◽  
Energy Dispersive Spectrometry ◽  
Alkali Silica Reaction ◽  
Polarizing Microscopy ◽  
Alkali Carbonate ◽  
Area Expansion ◽  
Carbonate Reaction ◽  
Tmah Solution ◽  
Scanning Electron ◽  
Curing Age

In this study, concrete microbars and rock prisms made of dolomitic aggregates were cured in a 1-mol/L tetramethylammonium hydroxide (TMAH) solution at 80 °C to avoid the effect of alkali–silica reaction (ASR) on expansion. The expansion of specimens was only caused by the alkali–carbonate reaction (ACR). The reason that self-made cement was used in this work was to ensure that the Mg2+ contained in the brucite originated only from dolomite. Expansion of concrete microbars and rock prisms was measured, the expansion cracks were systematically observed by orthogonal polarizing microscopy, and the products of ACR were analyzed by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The results showed that the dolomite crystals in the dolomitic aggregates reacted with the TMAH solution and resulted in ACR, which formed calcite and brucite and led to cracking of the specimens. The source of the expansion was the dolomite crystals of the dolomite enrichment area. Expansion cracks either extended inside the rock or into the cement phase and eventually disappeared. The alkali–carbonate reaction significantly contributed to the expansion of dolomitic aggregates cured in TMAH solution at a later curing age.

scholarly journals Effect of lithium nitrate on the reaction between opal aggregate and sodium and potassium hydroxides in concrete over a long period of time

2017 ◽  
Vol 65 (6) ◽  
pp. 773-778 ◽  
Author(s):  
J. Zapała-Sławeta ◽  
Z. Owsiak
Keyword(s):  
Electron Microscopy ◽  
Pore Solution ◽  
Alkali Silica Reaction ◽  
Lithium Nitrate ◽  
X Ray ◽  
Long Period ◽  
Chemical Admixtures ◽  
Mortar Bar ◽  
Sodium And Potassium ◽  
Scanning Electron

AbstractAlkali-silica reaction (ASR) is a reaction between amorphous or poorly crystallized siliceous phase, present in aggregates, and sodium and potassium hydroxides in the pore solution of concrete. Chemical admixtures such as lithium compounds are known to have high potential of inhibiting ASR. The aim of this study was to determine the effect of lithium nitrate on ASR in mortars containing high reactive opal aggregate over a long period of time. Mortar bar expansion tests were performed and microstructures of mortar bars were observed by scanning electron microscopy coupled with an energy dispersive X-ray microanalyser. Results from this study showed that effectiveness of lithium nitrate in mitigating ASR was limited over a long period of time. A larger amount of ASR gel which was formed in the presence of lithium nitrate indicated that the deterioration processes intensify within longer periods of time, which so far has not been observed in literature. Microscopic observation confirmed the presence of alkali-silica gel and delayed ettringite in mortars with lithium nitrate.

Use of Nanosilica and Cement in Improving the Mechanical Behavior of Disintegrated Carbonaceous Mudstone

2020 ◽  
Vol 20 (8) ◽  
pp. 4807-4814 ◽  
Author(s):  
Ling Zeng ◽  
Xiaofei Yao ◽  
Qian-Feng Gao ◽  
Hanbing Bian ◽  
Dianhua Fan
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Mechanical Behavior ◽  
Pozzolanic Reaction ◽  
Deviatoric Stress ◽  
Triaxial Tests ◽  
X Ray Diffraction ◽  
X Ray ◽  
Angle Of Internal Friction ◽  
Scanning Electron

This study aims to examine the mechanical behavior of disintegrated carbonaceous mudstone modified with nanosilica and cement (DCMNC). Many DCMNC specimens with various nanosilica contents were prepared. The X-ray diffraction (XRD) analyses and scanning electron microscopy (SEM) observations were performed on some of the specimens. Afterwards, triaxial tests were carried out on the remaining specimens to determine the mechanical behavior of DCMNC. The results showed that the cohesion exhibited a positive correlation with nanosilica content while the angle of internal friction presented a negative correlation with nanosilica content. The peak deviatoric stress, residual deviatoric stress and brittle modulus of DCMNC showed an increase followed by a decrease as nanosilica content varied from 0 to 8%, and all of them reached corresponding maximums at a nanosilica content of 2%. Thus, 2% was considered to be the optimum nanosilica content. The modification mechanism of DCMNC could be explained by the pozzolanic reaction related to nanosilica and the filling effect of nanosilica.

scholarly journals Microstructural Analysis of Concrete Using Cow Bone Ash for Alkali-Silica Reaction (ASR) Suppression

2020 ◽  
Vol 4 (2) ◽  
pp. 34-40
Author(s):  
Adanikin Ariyo ◽  
Funsho Falade ◽  
Adewale Olutaiwo
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Microstructural Analysis ◽  
Cementitious Materials ◽  
Sem Analysis ◽  
Supplementary Cementitious Materials ◽  
Alkali Silica Reaction ◽  
Bone Ash ◽  
Cow Bone ◽  
Scanning Electron

Concrete pavements are prone to microstructural changes and deterioration when exposed to Alkali-Silica Reaction (ASR). ASR results in strength reduction, cracking, spalling and other defects in the concrete if left unchecked. Supplementary Cementitious Materials (SCMs) such as Cow Bone Ash (CBA) however can be used to improve concrete performance, hence its use in this study. Concrete samples were prepared at replacement levels of 0%, 5%, 10%, 15%, 20% and 30% of cement with Cow Bone Ash. The concrete samples were then subjected to petrographic and Scanning Electron Microscopy (SEM) analysis. Petrographic examination shows that the minimal and least amount of ASR gels and micro cracking were observed at 15% CBA replacement of cement in the concrete samples. Scanning Electron Microscopy (SEM) analysis shows that changes in the elemental composition of the concrete samples is related to the effect of CBA which enhances adhesion in the concrete. SEM analysis show that, in general, the change in microstructure in the concrete was mainly due to the change in the arrangement of the C-H-S compounds. The microstructure analysis indicates that CBA in concrete influences the densification of the concrete at the transition zone, resulting in a much lower porosity. This results in the concrete having a tightly bound layer that repels ingress of water and thereby inhibiting cracks and gel formation as water is a contributing factor to the ASR in concrete.

The Effect of MgO-Al2O3 Spinel on Refractory Bricks Made from Al2O3-Cr2O3 Slag

2011 ◽  
Vol 291-294 ◽  
pp. 1795-1799 ◽  
Author(s):  
Li Jun Zheng ◽  
Guo Dong Zhang ◽  
Dian Li Qu ◽  
Feng Liu
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Thermal Shock Resistance ◽  
Maximum Size ◽  
Raw Material ◽  
Crushing Strength ◽  
Cold Crushing Strength ◽  
Shock Resistance ◽  
Refractory Bricks ◽  
Scanning Electron

The Al2O3-Cr2O3 slag as raw material was analyzed by scanning electron microscopy (SEM). The effects of different size distribution of MgO-Al2O3 spinel grain on physical properties of refractory bricks made from Al2O3-Cr2O3 slag was studied according to YB/T376.1-1995（water quenching）, GB/T 5072－1985, GB/T 2997-1982 criterion. The results show that the main crystal phase of the refractory bricks were chromium corundum, corundum. The refractory bricks containing 10 wt% of the maximum size of 3.0 mm of MgO-Al2O3 spinel grain can significantly improve the thermal shock resistance of this refractory bricks. At the meanwhile, This kind of refractory bricks can be absolutely satisfied with the requirements about cold crushing strength, bulk density and apparent porosity.

scholarly journals Physicochemical and microscopic characterization of implant-abutment joints

2018 ◽  
Vol 12 (01) ◽  
pp. 100-104 ◽  
Author(s):  
Patricia A. Lopes ◽  
Adriana F. P. Carreiro ◽  
Rubens M. Nascimento ◽  
Brendan R. Vahey ◽  
Bruno Henriques ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Surface Defects ◽  
Microscopic Analysis ◽  
Maximum Size ◽  
Significance Level ◽  
Commercially Pure ◽  
Implant Abutment ◽  
Pure Grade ◽  
Scanning Electron

ABSTRACTObjective: The purpose of this study was to investigate Morse taper implant-abutment joints by chemical, mechanical, and microscopic analysis.Materials and Methods: Surfaces of 10 Morse taper implants and the correlated abutments were inspected by field emission gun-scanning electron microscopy (FEG-SEM) before connection. The implant-abutment connections were tightened at 32 Ncm. For microgap evaluation by FEG-SEM, the systems were embedded in epoxy resin and cross-sectioned at a perpendicular plane of the implant-abutment joint. Furthermore, nanoindentation tests and chemical analysis were performed at the implant-abutment joints.Statistics: Results were statistically analyzed via one-way analysis of variance, with a significance level of P < 0.05.Results: Defects were noticed on different areas of the abutment surfaces. The minimum and maximum size of microgaps ranged from 0.5 μm up to 5.6 μm. Furthermore, defects were detected throughout the implant-abutment joint that can, ultimately, affect the microgap size after connection. Nanoindentation tests revealed a higher hardness (4.2 ± 0.4 GPa) for abutment composed of Ti6Al4V alloy when compared to implant composed of commercially pure Grade 4 titanium (3.2 ± 0.4 GPa).Conclusions: Surface defects produced during the machining of both implants and abutments can increase the size of microgaps and promote a misfit of implant-abutment joints. In addition, the mismatch in mechanical properties between abutment and implant can promote the wear of surfaces, affecting the size of microgaps and consequently the performance of the joints during mastication.

scholarly journals Microstructure and Degradation of Mortar Containing Waste Glass Aggregate as Evaluated by Various Microscopic Techniques

Materials ◽  
2020 ◽  
Vol 13 (9) ◽  
pp. 2186 ◽  
Author(s):  
Przemysław Czapik
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Microscopic Examination ◽  
Energy Dispersive Spectroscopy ◽  
Test Procedure ◽  
Waste Glass ◽  
Alkali Silica Reaction ◽  
Glass Aggregate ◽  
Microscopic Techniques ◽  
Scanning Electron

The primary aim of this article is to focus on the alkali-silica reaction (ASR) in mortar specimens containing coloured waste glass used as an aggregate. Mortar expansion was measured using the ASTM C 1260 accelerated test procedure until the specimens disintegrated. Special attention was paid to the microscopic examination of the damaged mortar. Various methods were used for this purpose, including optical microscopy in reflected and transmitted light with one and two crossed polarizers. The specimens were also subjected to the scanning electron microscopy observations with energy dispersive spectroscopy (SEM-EDS). The data obtained from these techniques provided information on the mechanism of glass-containing mortar degradation due to ASR and also allowed the comparison of different microscopic techniques in terms of the information they can provide on ASR occurrence.

Evaluation of different mechanical recycling methods of EVA foam waste

2021 ◽  
pp. 009524432199040
Author(s):  
Vanessa Biondo Rosa ◽  
Ademir José Zattera ◽  
Matheus Poletto
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Ethylene Vinyl Acetate ◽  
Mechanical Analysis ◽  
Mechanical Recycling ◽  
Physical Tests ◽  
Recycled Waste ◽  
Scanning Electron ◽  
Recycled Material ◽  
Eva Foam

In the present work, a proposal for the recycling of ethylene vinyl acetate (EVA) foam waste from the footwear industry using twin-screw extruder was evaluated. Parameters such as antioxidant addition, number of reprocessing, temperature, rotation speed were evaluated. The recycled material was evaluated by means of gel content, scanning electron microscopy (SEM), thermogravimetry (TG) and parallel plate rheometry. From this, the 4 samples were chosen, from the 16 extruded, with a higher probability of forming homogeneous foams to be used in the manufacture of new EVA foams. The foams were evaluated using scanning electron microscopy (SEM), dynamic mechanical analysis (DMA) and physical tests of density, abrasion and permanent compression deformation (PCD). The results showed a decrease in the content of crosslinked gel by up to 13 percentage points for the recycled material with antioxidant. However, there was a possible residual crosslinking, as the crosslinking of all recycled foams was greater than reference (foam). The greatest recycled material homogeneity, observed in the SEM, occurred in the samples processed for five repetitions without antioxidant. Some foams manufactured with recycled waste presented very similar morphological aspects to the reference foam. Foam manufactures with G1 recycled waste (extruded once, at 180°C, 450 rpm, without antioxidant), presented the most uniform and spherical cells. This foam also presented the best responses for the physical tests of PCD and abrasion, even compared to foam without recycle. As well as the lower viscosities for these same samples compared to the previous processing. It was understood that the viscosity of the recycled waste directly interferes with the formation of new EVA foam. Rheometry made it possible to identify the recycling process that resulted in an ideal viscosity material for incorporation in the manufacture of new EVA foams.

Pathogenesis of Human Hair Defects

1974 ◽  
Vol 32 ◽  
pp. 12-13
Author(s):  
P.S. Porter ◽  
T. Aoyagi ◽  
R. Matta
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Human Hair ◽  
Standard Techniques ◽  
Scanning Electron

Using standard techniques of scanning electron microscopy (SEM), over 1000 human hair defects have been studied. In several of the defects, the pathogenesis of the abnormality has been clarified using these techniques. It is the purpose of this paper to present several distinct morphologic abnormalities of hair and to discuss their pathogenesis as elucidated through techniques of scanning electron microscopy.

The Critical Point Drying Method Applied to Scanning Electron Microscopy of L-929 Cells

1970 ◽  
Vol 28 ◽  
pp. 278-279
Author(s):  
Charles TurnbiLL ◽  
Delbert E. Philpott
Keyword(s):  
Electron Microscopy ◽  
Carbon Dioxide ◽  
Surface Tension ◽  
Critical Point ◽  
Freeze Drying ◽  
Attractive Alternative ◽  
Crystal Formation ◽  
Critical Point Drying ◽  
Time Required ◽  
Scanning Electron

The advent of the scanning electron microscope (SCEM) has renewed interest in preparing specimens by avoiding the forces of surface tension. The present method of freeze drying by Boyde and Barger (1969) and Small and Marszalek (1969) does prevent surface tension but ice crystal formation and time required for pumping out the specimen to dryness has discouraged us. We believe an attractive alternative to freeze drying is the critical point method originated by Anderson (1951; for electron microscopy. He avoided surface tension effects during drying by first exchanging the specimen water with alcohol, amy L acetate and then with carbon dioxide. He then selected a specific temperature (36.5°C) and pressure (72 Atm.) at which carbon dioxide would pass from the liquid to the gaseous phase without the effect of surface tension This combination of temperature and, pressure is known as the "critical point" of the Liquid.

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