scholarly journals Study of the alkali-silica reaction rate of Spanish aggregates. Proposal of a classification based in accelerated mortar bars tests and petrographic parameters

2021 ◽  
Vol 71 (344) ◽  
pp. e263
Author(s):  
E. Menéndez ◽  
R. García-Roves ◽  
B. Aldea ◽  
E. Puerto ◽  
H. Recino
Keyword(s):  
Environmental Factors ◽  
20Th Century ◽  
Open Porosity ◽  
Reaction Rate ◽  
Classification Method ◽  
Reactivity Index ◽  
Alkali Silica Reaction ◽  
Long Period ◽  
Accelerated Curing ◽  
Siliceous Limestone

The alkali-silica reaction has been studied in depth due to the evolution in the knowledge of the expansive phenomenon. One of its most important aspects is the reaction rate of the aggregates. In Spain, at the early 90s of the 20th century, aggregates were considered almost non-reactive. However, the use of accelerated curing and other environmental factors revealed that there were potentially reactive siliceous aggregates. Nevertheless, there are several siliceous and limestone aggregates with siliceous inclusions that show reactivity over long period. In the present work, open porosity, expansion and petrography with quartz reactivity index have been determined, in 68 siliceous, limestone and dolomitic aggregates, from quarries located in areas with diagnostic reactivity. Based on these parameters and their interrelation, a classification method is proposed to detect slow-reacting aggregates.

scholarly journals Changes in the strength and width of the Hadley Circulation since 1871

2012 ◽  
Vol 8 (4) ◽  
pp. 1169-1175 ◽  
Author(s):  
J. Liu ◽  
M. Song ◽  
Y. Hu ◽  
X. Ren
Keyword(s):  
20Th Century ◽  
Global Climate ◽  
Hadley Circulation ◽  
Recent Change ◽  
Early 20Th Century ◽  
Greenhouse Warming ◽  
Long Period ◽  
The Past ◽  
Period Oscillation

Abstract. Recent studies demonstrate that the Hadley Circulation has intensified and expanded for the past three decades, which has important implications for subtropical societies and may lead to profound changes in global climate. However, the robustness of this intensification and expansion that should be considered when interpreting long-term changes of the Hadley Circulation is still a matter of debate. It also remains largely unknown how the Hadley Circulation has evolved over longer periods. Here, we present long-term variability of the Hadley Circulation using the 20th Century Reanalysis. It shows a slight strengthening and widening of the Hadley Circulation since the late 1970s, which is not inconsistent with recent assessments. However, over centennial timescales (1871–2008), the Hadley Circulation shows a tendency towards a more intense and narrower state. More importantly, the width of the Hadley Circulation might have not yet completed a life-cycle since 1871. The strength and width of the Hadley Circulation during the late 19th to early 20th century show strong natural variability, exceeding variability that coincides with global warming in recent decades. These findings raise the question of whether the recent change in the Hadley Circulation is primarily attributed to greenhouse warming or to a long-period oscillation of the Hadley Circulation – substantially longer than that observed in previous studies.

scholarly journals Effect of LiNO3 on Expansion of Alkali–Silica Reaction in Rock Prisms and Concrete Microbars Prepared by Sandstone

Materials ◽  
2019 ◽  
Vol 12 (7) ◽  
pp. 1150 ◽  
Author(s):  
Jinxin Liu ◽  
Lanqing Yu ◽  
Min Deng
Keyword(s):  
Electron Microscope ◽  
Critical Concentration ◽  
Stress Test ◽  
Molar Ratio ◽  
Alkali Silica Reaction ◽  
X Ray Diffraction ◽  
High Concentration ◽  
X Ray ◽  
Long Period ◽  
Scanning Electron

The aim of this research is to investigate the effect of LiNO3 on the alkali–silica reaction (ASR) expansion of reactive sandstone and the mechanism through which this occurs. This paper presents the results from tests carried out on rock prisms and concrete microbars prepared by sandstone and LiNO3. The findings show that LiNO3 does not decrease the expansion of these samples unless the molar ratio of [Li]/[Na + K] exceeds 1.66, and the expansion is greatly increased when its concentration is below this critical concentration. The expansion stress test proves that Li2SiO3 is obviously expansive. X-ray diffraction (XRD) and scanning electron microscope (SEM) results indicate that LiNO3 reacts with the microcrystalline quartz inside sandstone, inhibiting the formation of ASR gel, and the formation of Li2SiO3 causes larger expansion. A high concentration of LiNO3 might inhibit the ASR reaction in the early stages, and the formation of Li2SiO3 causes expansion and cracks in concrete after a long period of time.

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.

Was Paul Klee’s scleroderma an occupational disease? A series of historical and clinical vignettes, part III

2020 ◽  
Vol 5 (2) ◽  
pp. 85-89
Author(s):  
Richard M Silver
Keyword(s):  
Heavy Metals ◽  
Systemic Sclerosis ◽  
Environmental Factors ◽  
20Th Century ◽  
Occupational Disease ◽  
Susceptible Host ◽  
Paul Klee ◽  
Clinical Vignettes ◽  
Self Tolerance ◽  
Potential Factors

Paul Klee (1879–1940), one of the most influential artists of the 20th century, died at 60 years of age from complications of systemic sclerosis (scleroderma). The precipitating event(s) of Klee’s scleroderma, as in most cases, will never be known. Among various potential factors, exposure to heavy metals, crystalline silica, and organic solvents—acting alone or in combination—can now be considered potential factors in the onset of Klee’s disease. By altering and modulating epigenetic determinants in a genetically susceptible host, these and other environmental factors may have led to perturbations of self-tolerance and inflammation culminating in Klee’s scleroderma.

Spectral Investigations Concerning the Degradation Degree of Romanian Historical Leather

2009 ◽  
Vol 415 ◽  
pp. 45-48 ◽  
Author(s):  
Maria Giurginca ◽  
Lucretia Miu
Keyword(s):  
Environmental Factors ◽  
Chemical Characteristics ◽  
Comprehensive Investigation ◽  
Spectral Techniques ◽  
Long Period ◽  
Physical And Chemical Characteristics ◽  
Historical Leather ◽  
Degradation Degree ◽  
Physical And Chemical

A comprehensive investigation has been made of a set of historical leather samples from the 17th – 20th centuries. For the investigation of the degradation degree spectral techniques in IR (MID and NIR) and UV-VIS have been used, and collateral Micro Hot Table (MHT) determination as well. Changes in the physical and chemical characteristics values of the leather issues due to the interaction with the environmental factors during a long period of time were used in order to identify the possible deterioration ways.

Lichens and ultramafic rocks: a review

2004 ◽  
Vol 36 (6) ◽  
pp. 391-404 ◽  
Author(s):  
Sergio E. FAVERO-LONGO ◽  
Deborah ISOCRONO ◽  
Rosanna PIERVITTORI
Keyword(s):  
Environmental Factors ◽  
20Th Century ◽  
Distribution Patterns ◽  
Disjunct Distribution ◽  
Ultramafic Rocks ◽  
Chemical Interactions ◽  
Ecological Features ◽  
Physico Chemical ◽  
Wide Range ◽  
Occurrence Of Species

Floristic, vegetational and ecological features of lichens in ultramafic environments are reviewed using a wide range of literature dating from the beginning of the 20th century. Co-presence of acidophytic (silicicolous) and basiphytic (calcicolous) species and the occurrence of species characterized by particular (disjunct) distribution patterns are features of lichens in ultramafic environments. It is not possible to detect consistent trends in data on other broadly accepted features, such as paucity of species, low cover and the occurrence of particular ecotypes because of the influence of several environmental factors in addition to the substratum. Some recent data about physico-chemical interactions between saxicolous lichens and ultramafic rocks are also reported.

scholarly journals Characteristics of development of Tajik jewelry art at the turn of the 21st century

2018 ◽  
Vol 50 ◽  
pp. 01226
Author(s):  
Zarrina Umarova
Keyword(s):  
Natural Resources ◽  
20Th Century ◽  
21St Century ◽  
Transitional Period ◽  
Early 20Th Century ◽  
Long Period ◽  
Folk Traditions ◽  
History Of ◽  
The Republic ◽  
Characteristic Features

The paper identifies and analyzes the characteristic features of the development of Tajikjewelry art in the late 20th - early 21st centuries. The author believes that at this time, after a long period of oblivion, there is a marked way to restoration of many lost and nearly forgotten folk traditions in Tajik jewelry art. This period of time can be distinguished as a transitional period in the history of Tajik jewelry art development. This issue carries a significant value in the history of Tajikistan because the jewelry art in the period from the 80ies ofthe 20th century to the early 20th century was previously not subjected to a dedicated study, which results in certain gaps in the research of modern Tajik jewelry art. Studying the characteristics of the development of jewelry art at the turn of the 21st century and of the problems faced by master jewelers (zargars) at that time will aid in the future to identify the most efficient ways of developing this industry and facilitate its becoming one of the export-oriented areas, taking into account that the Republic of Tajikistan possesses all the necessary natural resources.

New Turner-Fairbank Alkali-Silica Reaction Susceptibility Test for Aggregate Evaluation

2021 ◽  
pp. 036119812110045
Author(s):  
Jose F. Muñoz ◽  
Chandni Balachandran ◽  
Terence S. Arnold
Keyword(s):  
False Negative ◽  
Field Performance ◽  
Outdoor Exposure ◽  
Test Method ◽  
Susceptibility Test ◽  
Reactivity Index ◽  
Alkali Silica Reaction ◽  
River Sand ◽  
Negative Results ◽  
Alkali Silica Reactivity

The ASTM C1260 and ASTM C1293 are generally accepted as being the best available accelerated tests to evaluate the alkali-silica reactivity of aggregates used in concrete. Unfortunately, these tests have limitations, such as the significant amount of false-positive and false-negative results in ASTM C1260 and the alkali leaching in ASTM C1293, that reduce their accuracy. This paper introduces an alternative test method, the Turner-Fairbank alkali-silica reaction (ASR) susceptibility test (T-FAST) that overcomes traditional limitations of both ASTM standards. In the new test, the ASR was accelerated by exposing the aggregates to a 1 N NaOH solution, three different amounts of CaO, and two temperatures for 21 days. The reactivity index (RI), calculated based on the 21-day concentrations of aluminum, calcium, and silicon in liquid phase, was used to assess the alkali-silica reactivity of 24 well-known aggregates—17 coarse and 7 fine. The results agreed with the classification of the same based on ASTM C1293 and historic field performance available in the literature. The alkali levels at which the ASR reaction was triggered in a selection of aggregates were measured using the T-FAST experimental set up. The threshold alkali values obtained matched those previously reported using accelerated concrete expansion tests as well as with concrete blocks in outdoor exposure sites. The alkali threshold determined for a river sand from Arkansas helped to understand the unexpected ASR distress observed in the field for an aggregate traditionally categorized as nonreactive. This case is a good example of mismatch between the information obtained from accelerated-ASR standard tests and field performance.

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