Cement production is responsible for approximately six to eight percent of global carbon emissions. Much of this occurs in countries that make more of it, and/or less sustainably. Differences are substantial. For example, the #1 producer, China, releases six times more CO2 than #2 India. By comparison, cement accounts for 1.25% of carbon emissions in the United States.

Nonetheless, the U.S. concrete industry embraces myriad ways to seek carbon neutrality throughout its value chain. Toward that end, the Portland Cement Association (PCA) and its members embrace its Roadmap to Carbon Neutrality. Substantial progress is to occur by 2030, with full carbon neutrality the goal by 2050.

The five links in this chain are clinker, cement, concrete, construction, and carbonation. There are many opportunities to reduce emissions at every stage.

McKinsey estimates that an optimized “Cement Plant of 2050” could operate with 75% lower emissions. The consulting firm estimates that a fifth of the gains will come from increased energy-efficiency and clinker substitution. Alternative fuels (AF) will contribute another 10%. Carbon capture tech is another piece of the puzzle.

What is XRD?

Another important step is to optimize the use of tools already at the industry’s disposal. XRD is one example. XRD is the acronym for x-ray diffraction. The process involves irradiating a material with incident X-rays. The intensities and angles of the X-rays are analyzed, yielding vital information about cement composition and quality.

In materials science, XRD is used to analyze the degree to which crystallographic structures deviate from the norm. It looks at a variety of structural properties. Examples include grain size, internal stresses, defects, lattice parameters, and epitaxy. Solid-phase epitaxy is the transition between amorphous and crystalline phases of a material.

XRD is a quick, non-destructive analytical process. It is very accurate, and it is done in-situ. XRD evaluates single crystal, poly, and amorphous materials. Standards are pre-established for thousands of material systems. It is a valuable tool in making cement plants more efficient.

History of XRD

Bragg’s Law (n λ =2dsinθ) represents the work of a father-son team more than a century ago. In 1913, the Braggs identified how crystal phases reflect X-rays at specific angles. This form of x-ray wave interference became known as x-ray diffraction. The work of the English physicists provided direct evidence of the periodic atomic structure of crystals. In 1915, the Braggs won the Nobel Prize in Physics for their work in crystallography.

XRD in the Cement Industry

To tailor XRD to the cement industry, it was necessary to account for the handling and presentation of a dry sample. It was also necessary to develop an analytical method suitable for the complex suite of phases contained within Portland cement.

In a cement plant, a continuous flow of samples passes through the diffractometer. Data collection occurs via a wide-range, position-sensitive detector. Rapid detection of the full diffraction pattern is the goal. Rietveld-style data analysis delivers a quantitative estimate of each of the phases present.

A purpose-built interface links the diffractometer to a PC. Phase abundance information goes to the plant’s central computer where it establishes mill parameters. Examples include temperature, retention times, and gypsum feed rates.

XRD measures Portland cement’s crystalline phases. Together, scanning electron microscopy, X-ray microanalysis, and image processing deliver refined microstructure analysis. Ultimately, XRD mineralogical analysis aids the cement industry’s transition to a low-carbon economy. It is the one proven industrial technology capable of quantifying the amorphous content of SCMs. It verifies that the composition of complex cements meet required standards.

Toward Greener Cement With XRD

XRD promotes greener cement by quantifying minerals and crystalline phases. Importantly, it is the one way to quantify the amorphous content of SCMs. It is also efficient. XRD identifies a sample’s mineral composition in minutes. Ultimately, XRD improves clinker quality while enhancing the functionality of entire cement plants.

In cement plants, XRD allows for::

• Controlled blending and maximizing of SCMs

• The selection of the proper raw materials and SCMs

• Optimized pyroprocessing

Optimize SCMs from waste streams

XRD reduces emissions by optimizing the use of supplementary cementitious materials (SCMs). Such substances enhance hardened concrete via hydraulic or pozzolanic activity, or both. Some are waste products from major industrial processes. Fly ash, blast furnace slag, and silica fume are common examples. There are also natural pozzolans like calcined clay (metakaolin). It is obtained by heating kaolinite to approximately 700° C. Industrial sources of calcined clay include paper sludge waste and oil sands tailings.

Interest in recycling waste streams into construction materials is greater than ever. SCMs replace some of the Portland cement used in concrete mixes. Unfortunately, SCMs exhibit lower reactivity than clinker, limiting replacement percentages. XRD adds precision to the process. It allows plants to maximize the use of emissions-reducing SCMs. XRD identifies different forms of calcium sulfate like gypsum, bassanite, and anhydrite. More SCM means less Portland cement in a mix. The end result is greener cement.

More efficient cement plant operations

XRD ensures product quality in cement plants. It promotes efficient operations while reducing environmental impacts.

Overall, the use of X-ray diffraction: :

• Improves clinker quality

• Confirms that the cement composition meets required standards

• Contributes to the formulation of new green cements

• Streamlines plant operations

About PACA

The Pennsylvania Aggregates and Concrete Association (PACA) reports on recent industry developments. Our team welcomes questions about your current or upcoming concrete project. Please contact us today!