scholarly journals Microscopic analysis of the alkali-silica reactivity of various origin fine aggregate

2020 ◽  
Vol 322 ◽  
pp. 01025
Author(s):  
Aneta Antolik ◽  
Daria Jóźwiak-Niedźwiedzka ◽  
Kinga Dziedzic ◽  
Karolina Bogusz ◽  
Michał A. Glinicki

Alkali silica reaction (ASR) is a harmful phenomenon occurring as a result of chemical interactions between sodium and potassium hydroxides in the pore solution and reactive minerals contained in the aggregate. Reactive minerals like microcrystalline, cryptocrystalline or strained quartz dissolve in the alkaline solution and form an expansive gel product. Proper selection of concrete constituents is necessary to ensure the durability of concrete structures. The proper recognition of the aggregate mineralogical composition is a very important element in the process of selection of concrete components due to the risk of ASR occurrence. This paper presents the results of detailed microscopic analysis of alkali-silica reactivity of domestic fine aggregates of various origins. Six siliceous sands from different locations in Poland and one limestone sand were tested. Detailed petrographic analysis was performed on thin sections. In all siliceous sands micro- and cryptocrystalline quartz was recognized as a reactive mineral. Digital image analysis was performed for quantitative assessment of the potential of reactivity of sands. It revealed, that siliceous river sands were the most susceptible to an alkali-silica reaction, which was confirmed by mortar bar expansion test performed according to the standard test method.

2018 ◽  
Vol 163 ◽  
pp. 05009
Author(s):  
Daria Jóźwiak-Niedźwiedzka ◽  
Mariusz Dąbrowski ◽  
Karolina Gibas ◽  
Aneta Antolik ◽  
Michał A. Glinicki

Salt solutions are used to ensure safe driving conditions during winter. NaCl deicer is the most often used brine in Polish climatic zone. The chemical effects of this type of chloride-based deicer in wetting and drying (WD) and temperature cycles on concrete need to be better understood. This research was focus to study the microstructure of air-entrained pavement concrete after combined chemical (10% of NaCl) and physical (WD and 60°C) exposure conditions. The adopted WD and temperature regime was designed to verify the hypothesis that regularly alternating wetting and drying cycles with external alkali supply from deicer salt will provoke the Alkali-Silica Reaction (ASR). The aggregates varied their origin and mineralogical composition. The microscopic examination was carried out on concrete specimens using SEM with EDX. The microscopic analysis has shown that main reason for concrete deterioration during cyclic chemical and physical exposure conditions was both physical influence - WD cycles and the chemical influence – ASR (primarily, the fine aggregate which lead to form of alkali-silica gel). The expansive gel was shown to be capable of destroying the test specimens. Also differences in mineralogical composition of coarse aggregates influenced on the concrete prism expansion due to ASR.


Author(s):  
Jose Leomar Fernandes ◽  
Reynaldo Roque ◽  
Mang Tia ◽  
Lorenzo Casanova

The uncompacted void content of fine aggregate, or fine aggregate angularity (FAA), was introduced in the Superpave mixture design system to screen smooth or rounded fine aggregates that may result in mixtures with low rutting resistance. The assumption is that fine aggregates with lower FAA values have lower shear strength (internal friction) and lower resistance to rutting. Continued implementation and evaluation of the Superpave system has led to numerous questions regarding the validity of this assumption and of the use of the FAA test in general. Nine fine aggregates were used to evaluate the FAA test and to determine whether it was a reliable indicator of fine aggregate shear strength. FAA tests were performed using three gradations and the three standard test methods (A, B, and C). Microscopic analysis was conducted to obtain independent visual measures of angularity and texture. Direct shear tests were performed at four confining stresses to determine shear strength parameters. Results indicated that FAA values were related to visual measures of texture and angularity. However, although FAA value contributed to shear strength, it appeared that other factors such as toughness, gradation, and packing characteristics of the fine aggregate overshadow its effect. For the fine aggregates tested, the FAA test rejected aggregates with high shear strength and accepted aggregates with low shear strength. It was concluded that FAA values alone may not be adequate to assess shear resistance of fine aggregate. Direct shear strength may be a better parameter, but additional work is required to evaluate its validity and feasibility.


Author(s):  
Steve A. Tomka ◽  
Lori B. Love ◽  
Timothy K. Perttula

Characterizing the mineralogical composition of ceramic vessels and sherds from Caddo sites in East Texas by means of petrographic analysis provides a unique opportunity to gather and investigate empirical evidence from ceramic vessels on: (1) technological and manufacturing practices, and (2) their trade and exchange at varying scales conducted by ancestral Caddo people with their neighbors, both near and far (i.e., other ancestral Caddo groups as well as non-Caddo communities). This evidence in turn can be used to explore changes in the nature of social and economic relationships between particular Caddo groups and other prehistoric populations. Identified compositional and paste differences that have been recognized between the different wares made by Caddo groups (i.e., plain wares, utility wares, and fine wares) can also be employed to explore functional and technological differences in vessel function and form. It is important to build on existing petrographic studies of Caddo vessels and vessel sherds by examining unstudied assemblages to (1) better clarify the compositional nature of these ceramic wares across the Caddo temporal and geographic landscape; (2) to help pinpoint other ceramic manufacturing locales and mineralogical compositional groups, but also to assess their apparent technological complexity; and (3) lead to better evaluations of the regional character of prehistoric and historic Caddo trade and interaction networks that existed, and more definitively establish whether there were changes through time in the direction and intensity of local and long distance trade and interaction. The disparate pieces of information contained within the sherds and vessel fragments of Caddo ceramics found on many prehistoric and early historic sites throughout the region have the potential to address these questions and research issues, and can contribute unique information concerning those relationships that existed in the distant (and not-so-distant) past between Caddo farmers. Twenty decorated sherds from the Musgano ceramic assemblage curated at the Texas Archeological Research Laboratory at The University of Texas at Austin (TARL) were selected for petrographic analysis. The sherds were split and one of the remaining fragments of each pair was used for the production of thin sections. Originally, the other half of each sherd was to be submitted for instrumental neutron activation analysis, but such analyses were not done; the remaining sherd fragment was returned for continued curation at TARL. Upon the receipt of the thin sections, they underwent petrographic analysis as reported on herein. The 20 sherds include sherds from engraved fine wares (n=8, 40 percent)—bottles and carinated bowls— as well as sherds from utility wares (n=12, 60 percent). The utility wares have brushed-appliqued, incised, incised-punctated (from Maydelle Incised, Weches Fingernail Impressed, and Washington Square Paneled vessels), and punctated decorative elements. Ten percent of the sherds are from bone-tempered vessels, based on macroscopic examination, while the others are from grog-tempered vessels.


2018 ◽  
Vol 23 (1) ◽  
pp. 163-177 ◽  
Author(s):  
Anna Rauba-Bukowska

Abstract For microscopic examination, 22 pottery fragments from sites 11, 15 and 20 in Święte, Jarosław District were selected. The pottery types included beakers (N=19) and amphorae (N=3). The goal of the petrographic analysis was to identify mineralogical composition of ceramic fabric, sources of raw materials, and intentional additives to the clay. The analysis yielded data that helped determine ceramic fabrics types and preparation methods, as well as pottery firing conditions and approximate firing temperature. In all samples analysed, ceramic fabrics were prepared in a similar way, using heavy clay poor in muscovite, with grog deliberately added. Crystalline material present in some of the samples is most likely a natural component of raw materials used in the production process. No sand is added to the clay. No other method for preparing pastes was identified for the amphorae type. Previous observations on amphorae firing are confirmed: amphorae are fired in oxidizing conditions. The ceramic fabrics of two vessels have a deliberate admixture of bones in addition to grog and argillaceous rock intraclasts. Vessels decorated with cord impressions and vessels with herringbone or other incised patterns are more often made from paste type A (inclusion and grog) and paste type B (grog), respectively.


Author(s):  
Jose F. Muñoz ◽  
Chandni Balachandran ◽  
Terence S. Arnold

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.


2021 ◽  
Author(s):  
Noura Sinno

Many preventive measures showed improved performance of concrete against alkali-silica reaction (ASR) based on the concrete prism test (CPT) described in the Canadian and American Standards, CSA A23.2-14A and ASTM C1293. However, research has shown that preventive measures that limited the 2-year expansion in the concrete prism test produced late expansion after 7-15 years when tested in the field. The objective of this research is to understand the possible reasons for this late expansion under field conditions and to come up with modified approach to determine the level of supplementary cementing materials (SCM) needed to mitigate the long-term expansion. The research mainly focuses on studying two possible reasons to explain the late expansion. The first reason is the rate and ultimate hydration of SCM, where their capacity to bind alkalis under CPT could be higher than those under field conditions. The other reason for the late expansion could be the geometry and size of the CPT samples which might reduce the expansion due to the excessive alkali leaching. Larger samples showed less leaching compared to standard prisms. 100-mm cylinders showed higher expansion than 75-mm standard prisms; however, both sample shapes showed similar expansions for one tested aggregate when used with SCM. In addition, the capacity of SCM to bind alkalis was shown to be higher at 38ºC compared to the other two tested temperatures investigated in this study: 23ºC and 60ºC. Samples with SCM at high replacement levels expanded more at 60ºC compared to 38ºC. Due to their reduced leaching compared to prisms, testing cylinders at 60ºC showed accelerated results reducing the testing duration to one year compared to the standard test duration of two years. Moreover, a new way to predict the minimum levels of SCM required to mitigate expansion due to alkali-silica reaction is presented showing better correlation with the field. Finally, a fast and reliable test method is suggested to evaluate the reactivity of mineral fillers by adapting and adopting the current test methods available for ASR testing.


LITOSFERA ◽  
2019 ◽  
pp. 228-241
Author(s):  
A. K. Vishnyakov ◽  
M. S. Vafina ◽  
V. I. Poklonov

Research subject. In this research, we set out to investigate polyhalite-containing rocks of the Southern Urals. The purpose of this study was to characterize the patterns of formation and transformation of polyhalite-containing rocks, as well as to identify conditions leading to their destruction. Materials and methods. We studied available literature and archive materials on the southern Urals, as well as core samples. Samples for thin sections were taken from the core of polyhalite-containing rocks. The sections were manufactured (where possible) in 2 mutually perpendicular cuts relative to the axis of the monolithic core sample. Considering a high solubility of salt minerals (halite) and the possibility of converting other minerals in aqueous media (e.g., polyhalite into gypsum due to the leaching of K and Mg cations herefrom), thin sections were manufactured in anhydrous liquids (kerosene, transformer oil). In order to determine the mineralogical composition, as well as the structural and textural features of the polyhalite-containing rocks under study, a petrographic analysis of the thin sections was carried out optically using a Polam-213 microscope. Geological sections were built using Corel Draw 13. To this end, geophysical data (gamma-ray logging) and lithological composition were studied.Results. It is found that pelitomorphic sulphate clusters transform into polyhalites followed by their further recrystallization into crystalline accretions. The diagenetic nature of this process is presumed. The location of polyhalite mineralization in the rocks under study confirms the effect of the basin bottom paleorelief on the intensity of polyhalite material accumulation. Conditions determining further destruction of these rocks were formed in local areas under the influence of various geological processes. Conclusion. The results of our research can be used for predicting zones rich in polyhalites in the southern Cis-Urals.


Author(s):  
Karl F. Hanson ◽  
Thomas John Van Dam ◽  
Karl R. Peterson ◽  
Larry L. Sutter

The chemical composition and morphology of alkali–silica reaction (ASR) products is of great importance in studying the reaction mechanism and assessing the effectiveness of mitigation techniques. Epoxy-impregnated, polished thin sections were prepared from an in-service concrete pavement to examine ASR products that originate from chert particles in the fine aggregate. Both hydrous and anhydrous thin-section preparation techniques were used to investigate the influence of sample preparation on the results. Two distinct morphologies of ASR products were observed in the voids adjacent to the chert particles: a bladed crystalline type and a glassy amorphous type. The chemical compositions of the reaction products were determined with a scanning electron microscope via quantitative X-ray energy dispersive spectrometry. Both the chemical composition and morphology were influenced by sample preparation, with hydrous preparation resulting in leaching and degradation. It is recommended that, when conducting studies to assess the ASR mechanism and the effectiveness of mitigation techniques, anhydrous sample preparation be used.


2021 ◽  
Author(s):  
Noura Sinno

Many preventive measures showed improved performance of concrete against alkali-silica reaction (ASR) based on the concrete prism test (CPT) described in the Canadian and American Standards, CSA A23.2-14A and ASTM C1293. However, research has shown that preventive measures that limited the 2-year expansion in the concrete prism test produced late expansion after 7-15 years when tested in the field. The objective of this research is to understand the possible reasons for this late expansion under field conditions and to come up with modified approach to determine the level of supplementary cementing materials (SCM) needed to mitigate the long-term expansion. The research mainly focuses on studying two possible reasons to explain the late expansion. The first reason is the rate and ultimate hydration of SCM, where their capacity to bind alkalis under CPT could be higher than those under field conditions. The other reason for the late expansion could be the geometry and size of the CPT samples which might reduce the expansion due to the excessive alkali leaching. Larger samples showed less leaching compared to standard prisms. 100-mm cylinders showed higher expansion than 75-mm standard prisms; however, both sample shapes showed similar expansions for one tested aggregate when used with SCM. In addition, the capacity of SCM to bind alkalis was shown to be higher at 38ºC compared to the other two tested temperatures investigated in this study: 23ºC and 60ºC. Samples with SCM at high replacement levels expanded more at 60ºC compared to 38ºC. Due to their reduced leaching compared to prisms, testing cylinders at 60ºC showed accelerated results reducing the testing duration to one year compared to the standard test duration of two years. Moreover, a new way to predict the minimum levels of SCM required to mitigate expansion due to alkali-silica reaction is presented showing better correlation with the field. Finally, a fast and reliable test method is suggested to evaluate the reactivity of mineral fillers by adapting and adopting the current test methods available for ASR testing.


2011 ◽  
Vol 201-203 ◽  
pp. 2887-2890
Author(s):  
Shun Bo Zhao ◽  
Na Liang ◽  
Xiao Lu Ma ◽  
Su Yang

The research in this paper is part of wet-sieving concrete technique for building thermal insulated reinforced concrete composite wall. The carbonized depths of fine aggregate concrete and ordinary concrete were measured by the carbonization test method. Based on the test, in standard test environmental conditions, the carbonization changes of fine aggregate concrete rely on its inherent combination changes. The lower carbonized depth takes place in fine aggregate concrete comparing with ordinary concrete, which is resulted from the increasing cement content and the reduction of grain size of coarse aggregate in fine aggregate concrete. Finally, the carbonization of fine aggregate concrete is evaluated according to the relative specification, and the reasonable service life of fine aggregate concrete is precast.


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