Near infrared emission spectroscopy for rapid compositional analysis of Portland cements

Near infrared emission spectroscopy (NIRES) has been investigated to yield a new analytical method for determination of CaO, SiO₂, Al₂O₃, Fe₂O₃, MgO, and SO₃ in Portland cement samples. The analyses were accomplished by correlation of the second derivative NIRES spectra with reference elemental analyses made by X-ray Fluorescence (XRF), using Partial Least Square (PLS) regression models. Four different types of cements (type II, III, IV and V) were included in the models. The results show RMSEP from 0.18 to 1.67% (m/m) (which represents 8.6 to 2.8% of the mean value parameters, respectively) and precision (repeatability) from 0.12 to 1.49% (m/m). The worse performance of prediction [RMSEP = 0.18% (m/m), r² = 0.63] was found for Fe₂O₃ determination due its low variability in the samples employed in the calibration and validation set, usual low content in cements, and high correlation with the weak emitting C₄AF phase. However, the paired t-test at 95% confidence level demonstrated that the analytical results obtained by NIRES multivariate models are equivalent to measurements performed by XRF for all oxides analyzed. The cost, speed and safety aspects are improved in comparison with the XRF method. The method based on NIRES requires no sample preparation and speed up the cement analysis (6 min) about 5 times when compared with the method based on XRF presently employed by cement industries.