Applications of XRD and XRF


Construction is all about interfaces with the earth, and involves foundations, excavation and materials. X-ray diffraction (XRD) and X-ray fluorescence (XRF) analytical methods are used to describe the fundamental nature of earth materials where they are important. This may be from a descriptive standpoint where rock-type must be determined or to examine the quality of the material so that its suitability can be assessed.

Certain parameters of rock and soil masses are purely geotechnical and relate to fracturing and potential for failure, but critical characteristics include the state of weathering of the ground and the mineralogy of clays which are present. For example, clay-heave is a property of soils which include significant quantities of smectites which have a very high water-storage potential. XRD is the best method for studying clay mineralogy because it is highly applicable to very fine-grained materials, and relies upon the same responses as the clay particles in the ground. Similarly, the weathering state of hard rocks can be studied through the range of minerals present.

All forms of construction require materials in the form of aggregates, sand and cement. The quality of all those materials is determined by their actual, rather than supposed, mineral content. Standards which apply to aggregates and sands specify limits to the presence of clay, lignite, mica, pyrite and in the case of marine-dredged aggregates, shell. The abundance of clay, mica and pyrite can be determined directly by XRD. Shell can be estimated by XRD because other sources of carbonates in marine sands are rare, and the abundance of lignite affects the loss on ignition. Problems due to alkali-silica reaction in concrete can be predicted by use of XRD to analyse for potentially hazardous content.

The other principal component in construction is cement, mostly manufactured from quarried limestones and shales and small quantities of sand. XRD is the best method of assessing the qualities of those materials, and XRF is a routine analysis performed for quality control upon the milled feedstock. Both methods are important in the exploration for new reserves to extend the active life of a cement plant, where there is drilling to map in 3D where potentially advantageous or hazardous strata can be found. XRD is also valuable in the quality control of the finished cement product because the primary mineralogy of the powder and any additives can be determined directly.

Modern, environmentally sustainable practices in the use or re-use of waste materials can be underpinned by careful examination of the resource to ensure that its properties are not harmful. For example, waste streams from incinerators, recycled aggregates and tailings from mineral processing can be characterised in terms of both chemistry and mineralogy to ensure that they find appropriate markets or end-use as blended product.

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