scholarly journals Alkali-silica reaction (ASR) - Investigation of crystallographic parameters of natural sands by backscattered electron diffraction

2021 ◽  
Vol 14 (3) ◽  
Author(s):  
Kleber Franke Portella ◽  
Leonardo Evangelista Lagoeiro ◽  
Jeferson Luiz Bronholo ◽  
Dayane de Cristo Miranda ◽  
Mariana D’Orey Gaivão Portella Bragança ◽  
...  
Keyword(s):  
Electron Diffraction ◽  
Portland Cement ◽  
Alkali Silica Reaction ◽  
X Ray ◽  
Electron Backscattering ◽  
Electron Backscattering Diffraction ◽  
Cement Mortars ◽  
Backscattered Electron ◽  
Crystallographic Planes ◽  
Mortar Bar

abstract: This study involved analyzing several natural sands to ascertain the possible causes for distress due to ASR. The analyses were performed using the following techniques: X-ray diffractometry, accelerated mortar bar tests (AMBT), electron backscattering diffraction and elementary chemistry analyses, by FEG-SEM/EBSD/EDS. These experiments allowed identifying the presence of several mineral composites (such as microcline, anorthite, among others), as well as the microstructural-crystallographic planes of quartz (such as the Dauphiné type). From the results it could be inferred that the multiple techniques used, especially the FEG-SEM / EBSD, proved to be promising in the analysis of the ASR potential of sands for use in Portland cement mortars and concretes.

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.

scholarly journals Electron backscattering diffraction and X-ray diffraction studies of interface relationships in Sr3Ru2O7/Sr2RuO4 eutectic crystals

Micron ◽  
2011 ◽  
Vol 42 (4) ◽  
pp. 324-329 ◽  
Author(s):  
R. Ciancio ◽  
H. Pettersson ◽  
R. Fittipaldi ◽  
A. Kalabukhov ◽  
P. Orgiani ◽  
...  
Keyword(s):  
X Ray Diffraction ◽  
X Ray ◽  
Electron Backscattering ◽  
Electron Backscattering Diffraction

scholarly journals Mineralogical Characterization of Dolomitic Aggregate Concrete: The Camarasa Dam (Catalonia, Spain)

Minerals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 117
Author(s):  
Encarnación Garcia ◽  
Pura Alfonso ◽  
Esperança Tauler
Keyword(s):  
Portland Cement ◽  
Type A ◽  
Alkali Silica Reaction ◽  
Type B ◽  
Mineralogical Characterization ◽  
Group Mineral ◽  
X Ray ◽  
Concrete Type ◽  
Further Development

The Camarasa Dam was built in 1920 using dolomitic aggregate and Portland cement with two different compositions: type A (dolomite and Portland cement) and type B (dolomite and sand-cement). The sand cement was a finely powdered mixture of dolomite particles and clinker of Portland cement. The mineralogy of concrete was studied by optical microscopy, scanning electron microscopy, and x-ray powder diffraction. Reaction of dedolomitization occurred in the two types of concrete of the Camarasa Dam, as demonstrated by the occurrence of calcite, brucite, and/or absence of portlandite. In the type A concrete, calcite, brucite, and a serpentine-group mineral precipitated as a rim around the dolomite grains and in the paste. The rims, a product of the dedolomitization reaction, protected the surface of dolomite from the dissolution process. In type B concrete, in addition to dolomite and calcite, quartz and K-feldspar were present. Brucite occurred in lower amounts than in the type A concrete as fibrous crystals randomly distributed in the sand-cement paste. Although brucite content was higher in the type A concrete, type B showed more signs of loss of durability. This can be attributed to the further development of the alkali-silica reaction in this concrete type.

scholarly journals Evaluation of external sulfate attack (Na2SO4 and MgSO4): Portland cement mortars containing fillers

2020 ◽  
Vol 13 (3) ◽  
pp. 644-655 ◽  
Author(s):  
D. J. DE SOUZA ◽  
M. H. F. MEDEIROS ◽  
J. HOPPE FILHO
Keyword(s):  
Portland Cement ◽  
Linear Expansion ◽  
Sulfate Attack ◽  
Hardened Cement ◽  
X Ray Diffraction ◽  
Limestone Filler ◽  
Sulfate Ions ◽  
X Ray ◽  
Cement Mortars ◽  
Physical And Chemical

Abstract Sulfate attack is a term used to describe a series of chemical reactions between sulfate ions and hydrated compounds of the hardened cement paste. The present study aims to evaluate the physical (linear expansion, flexural and compressive strength) and mineralogical properties (X-ray diffraction) of three different mortar compositions (Portland Cement CPV-ARI with limestone filler and, with a quartz filler, in both cases with 10% replacement of the cement by weight) against sodium and magnesium sulfate attack (concentration of SO4 2- equal to 0.7 molar). The data collected indicate that the replacing the cement by the two fillers generate different results, the quartz filler presented a mitigating behaviour towards the sulfate, and the limestone filler was harmful to Portland cement mortars, in both physical and chemical characteristics.

Effects of Various Amounts of Natural Pozzolans from Volcanic Scoria on Performance of Portland Cement Mortars

2017 ◽  
Vol 32 ◽  
pp. 36-52 ◽  
Author(s):  
Willy Hermann Juimo Tchamdjou ◽  
Sophie Grigoletto ◽  
Frédéric Michel ◽  
Luc Courard ◽  
Toufik Cherradi ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Portland Cement ◽  
Mechanical Strength ◽  
Calcium Hydroxide ◽  
Supplementary Cementitious Materials ◽  
Strength Development ◽  
Natural Pozzolan ◽  
X Ray ◽  
Natural Pozzolans ◽  
Cement Mortars

The aim of this paper is to assess the possibility of using natural pozzolans (NPs) from Cameroonian volcanic scoria as supplementary cementitious materials (SCMs) in the production of Portland cement mortars. Four natural pozzolans (Black Natural Pozzolan: BNP, Dark-Red Natural Pozzolan: DRNP, Red Natural Pozzolan: RNP and Yellow Natural Pozzolan: YNP) with 3600, 4500, 4700 and 5200 cm2/g Blaine fineness respectively were produced from different colors (Black, Dark red, Red and Yellow) volcanic scoria in a laboratory mill. Natural pozzolans were characterized with regard to particle size distribution, particle shape, electrical conductivity, X-ray fluorescence (XRF) and X-ray diffraction (XRD). The calcium hydroxide consumption by NPs was assessed firstly by electrical conductivity measurements of calcium hydroxide/NPs suspensions with calcium hydroxide excess. Evidence of pozzolanic reactivity of NPs is revealed in hydrated lime pastes, and low reactivity was observed in aqueous suspensions. The effects of 15, 25, and 35 wt.% of NPs as cement substitution on the properties of Portland cement mortars were investigated. Different properties were studied such as setting time, consistency, mechanical strength, pozzolanic activity, absorption by capillarity and resistance to carbonation. The reactivity of NPs was also assessed by means of the mechanical strength development of mortars. The results obtained show that pozzolanic and hydraulic reactions take place in OPC systems. The correlation between mechanical strengths and physical properties of NPs has been established. The study concludes that using DRNP and RNP at 15 wt. % cement replacement can ameliorate globally the performance of mortar. Using all NPs at 35 wt. % has negative effect on the fundamental properties of cementitious mortars.

Effect of Electron Beam and Heat Treatment on the Reactivity of Aggregates and Mineral Additives towards Alkali-Silica Reaction in Portland Cement Compositions

2020 ◽  
Vol 992 ◽  
pp. 3-8
Author(s):  
Aleksei B. Brykov ◽  
S.V. Mjakin ◽  
M.M. Sychov
Keyword(s):  
Heat Treatment ◽  
Electron Beam ◽  
Portland Cement ◽  
Absorbed Dose ◽  
Alkali Silica Reaction ◽  
Hydroxyl Groups ◽  
Treatment Results ◽  
Cement Mortars ◽  
Mineral Additives ◽  
Similar Processing

Electron beam (EB) and heat treatment of silica-containing aggregates and mineral additives for Portland cement mortars is shown to affect their activity in alkali-silica reaction (ASR) damaging concrete structures. In the case of ordinary mortar based on the sand free of alkali-reactive inclusions, both heating to 900°C and EB processing result in a significant increase of reactivity growing with the absorbed dose in the range from 100 to 600 kGy and correlating with the increase in the content of acidic hydroxyl groups on the surface. For sand with reactive chalcedony inclusions, EB treatment results in the growth of their reactivity while heating provides its significant decrease. In case of mineral additives such as silica fume and metakaolin known as very effective ASR-inhibitors, similar processing leads to the increase of their activity in mitigation of ASR. The observed effect is promising for simulation of expansion processes caused by ASR and enhancement of concrete structure resistance to alkali destruction during exploration.

Effectiveness and Mechanism of Fly Ash in Inhibiting Alkali-Silica Reaction of Sandstone

2011 ◽  
Vol 250-253 ◽  
pp. 40-45 ◽  
Author(s):  
Bei Xing Li ◽  
Jian Feng Zhang ◽  
Da Ke
Keyword(s):  
Fly Ash ◽  
Frost Resistance ◽  
Concrete Strength ◽  
Alkali Silica Reaction ◽  
Strong Reaction ◽  
X Ray ◽  
Accelerated Mortar Bar Test ◽  
Bar Test ◽  
Mortar Bar ◽  
Concrete Prism Test

The effectiveness of fly ash in suppressing expansion due to alkali-silica reaction (ASR) of sandstone are studied respectively based on accelerated mortar bar test and concrete prism test. The mechanism of fly ash in inhibiting the ASR of sandstone is examined by scanning electron microscope (SEM) and energy dispersive analysis of x-ray (EDAX). Moreover, the reliability of fly ash in inhibiting ASR of sandstone was discussed through concrete strength and frost resistance tests. Results indicate that the replacement amount of fly ash is 20%, the expansion due to ASR can be decreased to the critical value of a non-reactive aggregate. The reason why fly ash can inhibit the alkali reactivity for the sandstone is that the strong reaction between alkali and fly ash dissipates the alkali, and the products of alkali-silica-aluminate gels are non-expansible. For the concrete specimens suffered from accelerated ASR tests, their strength and frost resistance are decreased with the increment of fly ash replacement.

scholarly journals Choosing an Electron Backscattering System

2000 ◽  
Vol 8 (2) ◽  
pp. 22-25
Author(s):  
Alwyn Eades
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
World Wide ◽  
Energy Dispersive ◽  
X Ray ◽  
Electron Backscattering ◽  
Electron Backscattering Diffraction ◽  
Routine Basis ◽  
Biomedical Field ◽  
Scanning Electron

Recent advances in cameras and computers have made it possible to build electron backscattering diffraction (EBSD) cameras which can give crystallographic information from specimens in the scanning electron microscope (SEM) on a routine basis. There are a few hundred such systems world wide and the number is growing fast. In the case of crystalline samples (nearly all applications of SEM outside the biomedical field), it will surely soon be considered essential to fit an SEM with an EBSD system, just as it is now considered essential to have the SEM equipped with an energy-dispersive x-ray spectroscopy (EDS) system. There are at feast four commercial manufacturers of EBSD systems.

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