Scanning electron microscopy (SEM) is a technique widely used for analysis in various industries. The latest research published in the International Journal of Innovative Research in Science, Engineering and Technology focuses on its utilization for a thorough study of sustainable concrete. This article details the basics of SEM and sustainable concrete as well as the results of the latest research.
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What is Scanning Electron Microscopy?
The scanning electron microscope (SEM) is among the most flexible tools for studying and analyzing microstructure topography as well as for elemental analysis. The capturing of signals generated by field emission and sample interactions is an essential factor for image generation during the SEM analysis.
SEM involves the bombardment of fast-moving high-energy particles in the form of a focused beam on the surface of the substrate material.
The interaction between the material surface and the emitted beam reveals critical properties such as material surface topography, chemical properties, crystalline nature, and homogeneity of the constituents.
Advantages and Limitations of SEM
There is likely no other equipment that matches the SEM in terms of the variety of applicability in the investigation of solid objects.
SEM is essential in all sectors that require the characterization of bulk objects. Furthermore, current SEMs output data in easily transferable electronic files. However, certain limitations also exist with the utilization of SEM.
Materials must be stable and fit inside the optical frame. The maximum length in horizontal dimensions is typically around 10 cm, whereas vertically oriented dimensions are much more constrained and seldom surpass 40 mm.
Furthermore, most equipment requires specimens to remain stable in a vacuum. EDS sensors on SEMs are unable to detect extremely light atoms (hydrogen, helium, and lithium), and many types of equipment are incapable of detecting atoms of substances with atomic numbers of fewer than 11. When studying electrically insulated materials in typical SEMs, an electrically conductive layer must be added, unless the equipment is capable of functioning in a fully sealed condition.
Utilization of SEM in Concrete Industry
Scanning electron microscopy has been readily utilized in concrete studies in the past few years. The SEM has aided in the advancement of ‘inner narrative’ concrete understanding. Integration of the SEM technique with a widely utilized energy dispersive X-ray spectrometer (EDS) may be particularly beneficial in identifying concrete issues such as alkali-aggregate action in concrete.
For sustainable concrete, SEM is an instrumental analysis technique for the study of microstructural behavior and performance. In addition to this, SEM can be used in conjunction with particle size distribution (PSD) and X-ray fluorescence (XRF) for material characterizations in sustainable concrete with recycled glass in its composition.
Sustainability Issues with Concrete
Concrete is made up of various substances, including binder, aggregate, and water.
Traditional Portland cement is the primary adhesive in concrete (OPC). However, its manufacture generates a large amount of carbon dioxide emissions. The environmental variables involved with OPC can be decreased or avoided through partial to whole replacement of OPC, clinker substitution, and manufacturing using alternative energy.
The use of recovered effluent from both domestic and industrial operations as a replacement for freshwater for concrete is an option.
Aggregates account for around 50–70% of the concrete volume. To address aggregate sustainability issues, discovering ways to utilize debris created by various businesses would aid in the discovery of these assets and ensure that the business can fulfill the market expectations for aggregate for concrete production.
Researchers from India have focused their latest research on the analysis of sustainable concrete. Alternative materials were used as replacements for traditional constituent substances. Cement was partially replaced with fly ash (30% and 35%, respectively) and silica fume (7.5% and 10%), while fine aggregate was replaced with manufactured sand. Based on the hydrated products generated after 28 days, the morphology and strength attributes of all seven combinations were analyzed.
For typical concrete, it was discovered that C-S-H gel was widely distributed over the hydrated cement paste combination, which was the primary reason for the practical toughness. The development of Portlandite Ca (OH)2 and Calcite (CaCO3) on the outer surface of wet cement paste was observed. The mixture with the addition of 7.5% S.F, 30% F.A, and 40% RCA termed as mixture number 4 resulted in a considerable increment in compressive strength due to the interaction of silica fume and fly ash.
The rate of hydration in Mix-4 was similar to that of a standard concrete mix, but the presence of minerals components was noticeably different from that of Mix-1, which manipulates the strength of the concrete mix.
It is reasonable to deduce that the morphological characteristics of concrete impacted the mix's tensile and compressive properties. The inclusion of low-cost ingredients such as silica fume, fly ash, recycled coarse aggregate, and M-sand altered the performance of the concrete matrix and modified the compressive strength of concrete mixtures.
Future of Sustainable Concrete
The future of the sustainable concrete industry is dependent on the ability to reduce the severe ecological consequences of ‘cement’-based materials by following a thorough approach focusing on the ‘3-R Strategy’.
The approach must consider the opportunity to decrease power consumption, emission levels, as well as a strenuous and widespread use of waste products directed at significantly lowering the amount of non-renewable environmental assets.
A few strategies to ensure efficient processing of sustainable concrete include reducing the total amount of binders by pozzolanic and filler powders, utilization of agricultural wastes, aquaculture farming as SCM (palm oil fuel ash, corn cob ash, and leaf ashes), and utilization of geopolymers. All these approaches being extensively researched will ensure a safe future for sustainable concrete.
SEM analysis has been a core technique utilized in the concrete industry. A reliable autofocus mechanism that can adjust imaging factors might be highly valuable in providing properly focused SEM pictures of concrete substances with excellent quality independent of a user's degree of skill. A lot of research is being focused on reducing the imaging time, making the sample preparation easy and simple, as well as enhancing the image resolution. In short, SEM analysis has been fundamental for the concrete industry and with further advancements, its efficiency will improve.
References and Further Reading
Saran, AS Adithya, and P. Magudeswaran. 2017. SEM analysis on sustainable high performance concrete. Int J Innov Res Sci Eng Technol 6(6). 10237-10246. http://www.ijirset.com/upload/2017/june/16_SEM.pdf
Adesina, Adeyemi Damilare. 2018. Concrete sustainability issues. 24-26. Available at: https://spectrum.library.concordia.ca/id/eprint/984818/
de Brito, Jorge, and Rawaz Kurda. 2021. The past and future of sustainable concrete: A critical review and new strategies on cement-based materials. Journal of Cleaner Production 281. 123558. Available at: https://doi.org/10.1016/j.jclepro.2020.123558
Balendran, R. V., H. W. Pang, and H. X. Wen. 1998. Use of scanning electron microscopy in concrete studies. Structural Survey. 16(3). 146-153. Available at: https://doi.org/10.1108/02630809810232718
Coppola, Luigi, Denny Coffetti, and Elena Crotti. 2018. An holistic approach to a sustainable future in concrete construction. IOP Conference Series: Materials Science and Engineering. Vol. 442(1). 012024. IOP Publishing, 2018. Available at: https://doi.org/10.1088/1757-899X/442/1/012024
Nano Science Instruments, 2022. Scanning Electron Microscopy. [Online] Available at: https://www.nanoscience.com/techniques/scanning-electron-microscopy/
Swapp, S., n.d. Scanning Electron Microscopy (SEM). [Online] Available at: https://serc.carleton.edu/research_education/geochemsheets/techniques/SEM.html
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