Quantitative Energy-Dispersive X-Ray Microanalysis of Chlorine in Cement Paste

Energy dispersive X-ray spectroscopy (EDS) is a microanalysis technique for material characterization that can provide accurate quantification of elemental composition while maintaining high spatial resolution. EDS microanalysis studies on cementitious materials can face several challenges essentially due to the complex chemical and mineralogical characteristics of cement hydration products. Furthermore, EDS microanalysis is widely carried out in "standardless analysis" mode, which relies on the internal standards of the microanalysis software. This can lead to highly erroneous analysis results because standardless analysis typically normalizes total to 100% without taking chemically bound water into account. In the case of quantifying chlorine content of a cement paste, such normalization is unacceptable because it can lead to overestimation. For accurate determination of elemental concentrations, X-ray spectra collected from minerals or glasses with known chemical compositions are necessary as references. This paper examines the performance of six different minerals containing a wide range of chlorine concentrations as standards for quantitative EDS microanalysis. Also, the influence of experimental conditions such as beam current, accelerating voltage, dwell time, and scanning mode on the obtained results is discussed. It was found that among the minerals investigated, scapolite [(Na,Ca)4(Al3Si9O24)Cl] stands out as the most favorable microanalysis standard for quantifying chlorine content in cement paste. (C) 2015 American Society of Civil Engineers.