Decalcification of cement mortars: Characterisation and modelling

This paper presents the results of a thorough microstructural characterisation of a set of cement mortars (made with three w/b ratios and five different cement types), degraded by the ammonium nitrate method. Both destructive and ultrasonic non-destructive techniques were used to characterise the samples. The initial calcium content of the samples plays a dominant role in both the advance of the degradation process and the degradation grade of the samples. In addition, the decalcification process kinetics and the degradation grade are modelled, using Fick’s second law of diffusion and the shrinking unreacted-core model. Two parametric equations are presented and used to estimate the decalcification process kinetics and the degradation grade using accessible microstructural parameters of the native mortars, such as the initial CaO content, the open porosity, and the cementitious matrix volume fraction. Furthermore, the degraded depth in the samples is measured using ultrasonic testing with an average error of about 10%.