Analysis of natural pozzolan in cement (CEM IV)

Significance of the topic

Natural pozzolans are widely used as supplementary cementitious materials in CEM IV cements to lower clinker content, improve durability and reduce CO2 emissions from cement production. Reliable determination of both crystalline and amorphous constituents of pozzolanic materials is essential for quality control, formulation and performance prediction. X-ray diffraction (XRD) combined with Rietveld refinement and calibrated internal standards provides a robust route to quantify phase composition including the otherwise difficult-to-measure amorphous fraction, enabling consistent production and regulatory compliance.

Objectives and overview of the application note

The application note demonstrates the use of the Thermo Scientific ARL X’TRA Companion benchtop XRD system to: assess the phase composition of a natural pozzolan; quantify its amorphous fraction using ZnO as an internal standard and a calibrated peak; and determine total pozzolan content when blended into a CEM IV cement. Emphasis is placed on one-click Rietveld workflows that streamline routine QC analyses.

Methodology

Sample preparation and measurement

- Natural pozzolan was mixed with approximately 20 wt% ZnO internal standard to enable calibrated quantification of amorphous content. Blended CEM IV samples containing the pozzolan were also prepared.
- Samples were loaded into top-loading sample cups and measured with spinning during acquisition.
- Measurements were performed in reflection mode using Cu Kα radiation (λ = 1.541874 Å) with a 10-minute acquisition time per sample.

Data analysis and calibration

- Rietveld refinement was used for phase identification and quantification. The calibrated peak approach, anchored by the ZnO internal standard, provided an absolute estimate of the amorphous fraction and allowed conversion to a standardless quantification for blended samples.

Used instrumentation

- Thermo Scientific ARL X’TRA Companion XRD System (benchtop) with θ/θ Bragg–Brentano goniometer (160 mm radius).
- 600 W X-ray source configured for Cu (or Co) radiation.
- Beam conditioning via divergence and Soller slits and a variable beam knife to reduce air scatter; optional integrated water chiller.
- Solid-state pixel detector (55 × 55 μm pixel pitch) enabling fast data collection.
- Software with one-click Rietveld quantification and automated result transmission to a LIMS.

Main results and discussion

Pozzolan (with ZnO standard)

- Rietveld results indicate the pozzolan contains a significant crystalline fraction dominated by augite (~25 wt%) and a substantial amorphous component determined at 22.87 wt% through the calibrated-peak approach.
- Other minor crystalline phases identified include nepheline, leucite, diopside, tridymite, hematite and goethite among others; several clay/serpentine-type phyllosilicates were also detected in low amounts.

CEM IV blend (with pozzolan)

- The blended CEM IV sample was quantified by combined refinement and reported a total pozzolan content of 40.70 wt% (this value includes the amorphous contribution derived from the calibrated peak).
- Clinker-derived phases were quantified: dominant alite (C3S, reported as C3SM1/C3SM3 combined ~25.64 wt% and 11.92 wt% components), belite (C2S ~6.37 wt%), aluminates (C3A components ~3.68 and 2.78 wt%) and ferrite (C4AF ~1.87 wt%).
- Sulfate phases (gypsum, bassanite, anhydrite) and minor accessory phases (lime, periclase, portlandite, calcite) were also identified and quantified. All reported values are consistent with expected ranges for CEM IV-type cements containing natural pozzolan.

Discussion points

- Using an internal standard (ZnO) and a calibrated amorphous peak increases confidence in the amorphous fraction estimate, which is critical because the reactive (amorphous) portion of pozzolans governs much of their performance in cementitious systems.
- The adopted workflow—short acquisition time, spinning samples, and automated Rietveld—supports high-throughput QC while preserving quantitative reliability for both crystalline and amorphous phases.

Benefits and practical applications

- Enables accurate batch-to-batch control of pozzolan content and reactivity-related metrics in CEM IV cements, supporting consistent mechanical and durability performance.
- Facilitates regulatory reporting and materials certification by providing quantitative phase composition including amorphous content.
- Reduces lab turnaround time due to compact benchtop footprint, fast detector, and one-click analysis; integration with LIMS supports automated data handling in industrial settings.
- Supports sustainability goals by verifying clinker replacement levels and thus the reduction of embodied CO2 in cement products.

Future trends and possible applications

- Greater automation: integration of sample changers, automated sample prep and closed-loop process control for inline or near-line XRD monitoring in cement plants.
- Detector and software advances will further reduce acquisition times while improving sensitivity to minor phases and low-content amorphous components.
- Improved amorphous quantification: combination of calibrated-peak XRD with complementary techniques (thermal analysis, solid-state NMR, quantitative SEM/EDS) to better characterize reactive silica and alumina species.
- Machine-learning-assisted phase identification and refinement workflows to increase robustness across diverse natural pozzolan chemistries and enable predictive quality control.
- Broader adoption of standardized protocols for internal-standard-based amorphous quantification to harmonize results across laboratories.

Conclusion

The ARL X’TRA Companion XRD System, using a calibrated-peak Rietveld approach with a ZnO internal standard, provides a rapid and reliable method to quantify both crystalline phases and the amorphous fraction of natural pozzolans and to determine total pozzolan content in CEM IV cements. The demonstrated workflow balances analytical rigor with the ease-of-use required for routine QC, supporting sustainable cement production through validated clinker replacement.

References

1. Welzmiller S., Application note AN41509, Thermo Fisher Scientific, 2024 — Analysis of natural pozzolan in cement (CEM IV) using the ARL X’TRA Companion XRD System.