Quantifying Amorphous Cementitious Materials with Benchtop XRD

Amorphous substances influence the durability, strength, and sustainability of concrete in cementitious products, and they are an essential aspect of cementitious materials. Supplementary cementitious materials (SCMs), including slag, fly ash, calcined clay, and pozzolans, often contain non-crystalline components and contribute to the unique properties of cements.

The identification and quantification of amorphous phases are vital when it comes to understanding cement's properties and performance. X-Ray Diffraction (XRD) is a crucial investigative method that is ideal for this purpose.

XRD produces vital data on the mineralogical structure of a material by examining the diffraction patterns generated from X-Rays interacting with the sample. Utilizing this data, XRD facilitates the quantification of both crystalline and amorphous phases in cementitious materials.

For quantitative analysis of crystalline materials, the top XRD technique currently utilizes Rietveld refinements. To quantify amorphous content, appropriate techniques that are based on internal and external standards are used.

A newer approach without strict standards, referred to as PONKCS^1–3 (partially or not known crystal structures method), has been introduced in recent literature. It relies on a calibrated peak list to analyze crystal structures. Profex Rietveld software also adopts a similar strategy, utilizing a calibrated peaks list (CPL) derived from known mixtures to quantify unknown materials and assess amorphous content accordingly.⁴

As the cement industry increasingly focuses on sustainability, the ability to comprehend and regulate amorphous content via XRD analysis will play a crucial role in advancing eco-friendly cement production. This capability enables the industry to align with worldwide efforts promoting greener construction practices.

In the realm of decarbonized cement, which prioritizes minimizing environmental impact, the utilization of supplementary cementitious materials (SCMs) abundant in amorphous content is widespread. Conventional slag and pozzolan cements capitalize on this characteristic by incorporating materials such as blast furnace slag and volcanic ash.

Instrument and Software

The Thermo Scientific^™ ARL^™ X’TRA Companion X-Ray Diffractometer (Figure 1) is a user-friendly benchtop XRD system designed for both process control and advanced applications. Featuring a θ/θ goniometer with a 160 mm radius in Bragg-Brentano geometry, it is equipped with a 600 W X-Ray source (Cu or Co).

Figure 1. ARL X’TRA Companion diffraction system. Image Credit: Thermo Fisher Scientific - Elemental and Phase Analysis

Beam collimation, both radial and axial, is managed by divergence and Soller slits, while air scattering is minimized using a variable beam knife. An integrated water chiller is optionally available.

With its cutting-edge solid-state pixel detector (55 x 55 μm pitch), the ARL X’TRA Companion ensures rapid data collection and includes one-click Rietveld quantification capabilities, along with automated result transmission to a Laboratory Information Management System (LIMS).

Experimental

Powdered mixtures containing clinker and amorphous slag at various weight percentages (20, 30, 50, 70, and 80 %) were analyzed via reflection using an ARL X’TRA Companion equipped with Cu Kα radiation (10 minutes) (refer to Figure 2).

Figure 2. The rietveld fit of 48.5% amorphous content clinker mixture (center; black) and additional mixtures below and above; green 19.4%, turquoise 29.1%, blue 67.9%, and purple 77.6% amorphous content. Image Credit: Thermo Fisher Scientific - Elemental and Phase Analysis

Analysis of the slag revealed an amorphousness of 97 %, and the amorphous content levels of the mixtures were subsequently calculated based on this finding. Phase quantification was conducted using Profex software (utilizing the BGMN algorithm)⁴ employing a fundamental parameters approach.

Amorphous content quantification was achieved using a calibrated peaks list (CPL), with the mixture containing 48.5 % amorphous content (50 % slag) serving as the reference sample.

Results

Using CPL to quantify the amorphous content in specific slag mixtures demonstrates results with a deviation of no more than 1 % absolute error (refer to Figure 3), along with a linear correlation coefficient of 0.999.

Figure 3. Nominal vs. refined amorphous content with trend line; reference sample in orange. Image Credit: Thermo Fisher Scientific - Elemental and Phase Analysis

Conclusion

In this study, using CPL in Profex on data measured with the ARL X’TRA Companion allowed for the quantification of the amorphous content within 1 % absolute error without needing an internal standard. Therefore, the ARL X’TRA Companion is ideal for any routine analysis task, especially decarbonized cements.

Acknowledgments

Based on materials originally authored by Dr. Simon Welzmiller, Application Specialist XRD, and Raphael Yerly, Product Manager XRD.

References and Further Reading

1. S. Adu-Amankwah, L. Black, M. Zajac, Adv. Civ. Eng. 2022, 11, 555–568.
2. X. Li, R. Snellings, K. L. Scrivener, J. Appl. Cryst. 2019, 52, 1358–1370.
3. P.R. de Matos, J.S. Andrade Neto, R.D. Sakata, A.P. Kirchheim, E.D. Rodríguez, C.E.M. Campos, Cem. Concr. Compos. 2022, 131, 104571.
4. N. Döbelin, R. Kleeberg, J. Appl. Crystallogr. 2015, 48, 1573–1580.

This information has been sourced, reviewed and adapted from materials provided by Thermo Fisher Scientific - Elemental and Phase Analysis.

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