Within the cement industry, chemical and mineralogical control is one of the principal means of guaranteeing the quality of the final product and its optimum performance in the final application.
On the other hand, pushed by environmental issues and rising customer demands in terms of quality and new functionalities, the market is imposing new challenges on cement producers, demanding the development and increasing use of more sustainable materials. Cement producers therefore have to know and examine the exact composition of each of the raw materials more deeply, as well as their effects, not only on the final product, but also on the production process.
Modern X-ray diffraction (XRD), combined with X-ray fluorescence (XRF) (Figure 1), is a powerful tool for determining the elemental composition and the mineralogy of the materials used in the production of traditional Portland cement, as well as potential new cementitious materials.
XRF provides detailed information for proportioning raw materials and controlling the main variables in the production process. It also plays a significant role in the environmental control of waste recovery, raw materials, alternative fuels, analysis of trace elements and chemical characterisation of liquids such as additives and slurries. XRD enables us to obtain a complete and accurate identification and quantification of the crystalline components of the material, providing detailed mineralogical information about them. This is very useful because the performance of cement-based products is determined more by its mineralogy than by its elemental composition. As a result of better knowledge about the science and engineering of materials, which is provided by tools such as XRF and XRD, cement plant process teams, supported by R&D departments, can monitor, control and, in some ways, predict the main parameters regarding the grindability of raw materials and clinker, the burnability of raw feed, the grindability of clinker and supplementary cementitious materials, cement setting times, strength development and the final performance of cement-based products.
Figure 1. Axios WD-XRF and X'Pert PRO-MD (PANalytical). Argos Research and Development Center.
More sustainable cement
One of the main options for producing cement with a smaller environmental impact is, without a doubt, using less clinker in the final product. In order to be able to do this, a more detailed analysis of the materials and processes has to be carried out to ensure not only adequate amounts in the final formulations, but also its performance in the final application.
More reactive clinker: using less clinker in cement requires the cement producer to guarantee to the customer that the product will have the same performance when it is used in the final product. To achieve this, R&D teams face the challenge of increasing the reactivity of clinker. One of the ways to do this is to identify the different polymorphous characteristics of the C3S and define the best conditions to reach the most reactive form. Without the use of technological tools such as XRD and XRF, this analysis would be almost impossible.
Use of more limestone: as a result of more reactive cement, the use of limestone as a mineral admixture is increasing in many countries in order to obtain a more environmentally friendly material. However, it is known that limestone is more than just a filler. Limestone, depending on its crystalline form, can react in different ways in the cement hydration process, resulting in the formation of products that have different effects on the performance of cement. These effects must be measured and XRD tools allow us to identify the different compounds that stem from the use of limestone in cement hydration products.
Figure 2. XRD analysis of cement added with sider slag and pozzolan. (Source: Argos Research and Development Center.)
Partial replacement of clinker/cement: supplementary cementitious materials (SCM), such as slags, flyash and pozzolans, are the main materials used to replace clinker in cement production or to replace cement in concrete production (Figure 2). For many years now, these materials have been used in the cement and concrete industry. However, even though there have been many studies seeking to understand their reaction mechanisms and effects on the final product, it is still not completely clear how they work or what the main phenomena are that determine their reactions with Portland cement. In addition, new technologies, such as chemical activation, have been studied over the last few decades in order to produce new types of cement and/or to increase the use of these materials in the cement industry. Technical analyses like XRF and XRD are tools that are fundamental for understanding the main reactions and products of SCMs in cement. Determining chemical species and minor elements, such as alkalis, along with their chemical structure, crystallography, and at the same time, their reactive phase (glassy, amorphous) is extremely important in understanding the role of each species and how they work during the hydration process, in more detail. Finally, in the product, after application, it is still very important to identify the main compounds that these materials formed or helped to form and how these new products influence, either positively or negatively, the performance of the final application.
Read Part 2 here.
Written by Juan Guillermo Morales, Claudia Rodriguez, Carolina Giraldo and Ruby Estela Cardona, Research and Development Department, Cementos Argos S.A.
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Read the article online at: https://www.worldcement.com/the-americas/14012014/xrd_and_xrf_analysis_cementos_argos_part_1_592/