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In construction, the analysis of materials for safety and quality control purposes critical. Non-destructive methods are particularly suited for this need as they can be carried out on the materials in question owing to the possibility of real-time observation and characterization.
One technique commonly used for this application is spectroscopy, which covers a broad church of methodologies. This article will provide an overview of spectroscopy and its use in characterizing cement-based materials.
Spectroscopy – An Overview
Spectroscopy covers a suite of analytical methods. The technique involves splitting light (more precisely, electromagnetic radiation) into its constituent wavelengths, otherwise known as a spectrum. The technique is analogous to a prism splitting light into a rainbow, but the spectrum produced is generally more than a simple ‘rainbow’ of colors. It is the study of the interactions between matter and electromagnetic radiation.
The spectra produced by spectroscopic methods are not smooth. They are comprised of punctuated ‘lines’ of absorption/emission. This is due to the absorption and emission of electromagnetic radiation only occurring at specific wavelengths due to the energy levels of electrons in target molecules and atoms being quantized.
Originally, spectroscopy was done using a prism and photographic plates, whereas modern-day spectroscopic methods use diffraction gratings to disperse the light. This is then projected onto Charged Coupled Devices (CCDs) which are similar to those used in digital cameras. Here, 2D spectra can be extracted from the digital format to produce a one-dimensional spectrum that provides relevant information about the molecule or atom under analysis.
There are several modern-day spectroscopic techniques that are applied to a multitude of scientific studies across several industries and scientific disciplines. These include atomic spectroscopy, X-ray spectroscopy, and X-ray fluorescence, Raman spectroscopy, nuclear resonance spectroscopy (NMR), electron energy loss spectroscopy, scanning tunneling spectroscopy, spectrophotometry, and many others.
Uses of Spectroscopic Methods for Cement-Based Material Analysis
Analysis of the composition of cement is important for the manufacture of the material and quality control purposes. Over the past few decades, spectroscopic methods have been applied with more frequency for these purposes.
One of the important challenges which face the cement industry is the quantitative analysis of clinker phases (the nodular material produced by heating clay and limestone which is then ground to produce cement.) Over the past few years, X-ray diffraction spectroscopy (XRD) has emerged as a technique especially suited for the analysis of the clinker phase.
By analyzing the free lime and limestone additions in clinkers, XRD provides information on the atomic structure which is useful for controlling the kiln process and quality of the end product. This technique has been used extensively to substitute wet chemical analysis and other methods in laboratories.
XRD is also an attractive substitute for microscopy as an indirect method of calculation. Through analysis of the clinker phase with XRD, relevant information on particle size and distribution (which affects the quality of the final product) can be obtained.
AC impedance spectroscopy, which has advantages due to real-time monitoring, has been the focus of recent research and has been useful in determining hydration properties, chloride-induced corrosion, and microstructural changes in cement.
Raman and FT-IR spectroscopies have also been explored in recent studies on clinkers, polisher concrete, concrete after demolding, and coated concrete, which is all commonly used in the construction industry.
Raman spectroscopy was found to characterize the mineral/hydrated phases of post-treated concrete whilst FT-IR was found to be useful for identifying the main organic groups at the surface of the concrete. The study proposed using these two spectroscopic techniques in a complementary way to provide a range of information about these concretes and their surfaces.
Spectroscopic techniques are providing an in-depth study of concrete-based materials at the molecular level, which is advantageous for the construction industry compared to contemporary analysis methods. Different spectroscopic methods can be applied in tandem with each other for a complete study of these materials, whilst also being used alongside other scientific techniques to produce a range of results which improve the quality of concrete, a construction material which is ubiquitous with the modern age.
As these techniques continue to improve and new spectroscopic methods are developed, spectroscopic techniques will likely continue to provide a central role in the analysis of these materials and others within the construction industry.
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