Quantitative invalidation characterization of Portland cement based on BSE and EDS analysis

The degradation of mechanical properties of Portland cement caused by the invalidation of Portland cement is a serious problem that affects the quality of concrete nowadays. However, an effective invalidation characterization method of Portland cement has not been set up. Back scattering electron (BSE) and energy-dispersive spectrometry (EDS) were adopted to quantitatively characterize the invalidation of Portland cement in this study. The EDS results demonstrated that the acicular crystals generated near cement particles in BSE images are ettringites. Therefore the invalidation of Portland cement is mainly caused by the expansive ettringite generated from the hydration of oxides containing Aluminium, and crystallisation corrosion is the main invalidation mechanism. When the microstructure of acicular morphology with a length longer than 3.0 μm is observed from BSE images of Portland cement samples, the cement can be quantified as exhibiting complete invalidation. Meanwhile, the content changing of element in the area of ettringite formation acquired with EDS analysis can also be used to characterize the invalidation of Portland cement. When the content of oxide containing aluminium is not more than 5.0%, the cement is not judged as invalidated; the invalidation of cement will occur once the content of oxide containing aluminium exceeded 5.0%; when the content of oxide containing aluminium exceeded 10.0%, the cement is considered completely invalidated.