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The heterogeneity of a cement-based material results in a random spatial distribution of carbonation depth. Currently, there is a lack of both experimental and numerical investigations aiming at a statistical understanding of this important phenomenon. This paper presents both experimental and numerical supercritical carbonation test results of cement mortar blocks. The carbonation depths are measured along the carbonation boundary by the proposed rapid image processing technique, which are then statistically studied by calculating, e.g., their probability density and power spectral density (PSD). The results indicate that the distribution of the carbonation depth can be approximately represented by a lognormal distribution function and the PSD has quantitative correlation with some of the statistic parameters used in the simulations. In particular, the effects of the autocorrelation lengths and the coefficient of variation of porosity, which are used to define the random porosity field, on the irregularity of carbonation depth are analyzed numerically in details and validated by experimental results. The study has shown that using a random field of porosity with due consideration of spatial correlation and variance, the irregularity of carbonation depth can be realistically captured by the numerical model. The numerical results confirm that lognormal distributions represent the random nature of carbonation depth well and the average and variance of the irregular carbonation depth increase with the increase of carbonation time, autocorrelation length and coefficient of variation of porosity. The study also offers a potential method to numerically calibrate some of the statistic parameters required by a numerical carbonation model through comparing the PSD with that from experimental tests. Overall the methodology adopted in the paper can provide a foundation for future investigations on probability analysis of carbonation depth and other similar work based on multi-scale and -physics modelling. [ABSTRACT FROM AUTHOR]

In this paper, the supercritical carbonation process of cement-based materials is modelled by introducing a random porosity field to simulate the heterogeneous geometry of the carbonation profile. The suitability of two different random fields of porosity, based on the probability density function (PDF) and the ellipsoidal autocorrelation function (EAF) methods, are investigated, respectively, in simulating the distribution of porosity in cement mortar. After incorporating the above random fields into an established supercritical carbonation model, it is found that with some modifications, the EAF method with consideration of spatial correlation produces better simulation of the irregularities of the carbonation zones that have been observed from experimental results. It is also found that for given average porosity and coefficient of variation, the predicted average and maximum carbonation depths have much smaller coefficients of variation. The validated EAF supercritical carbonation model is then used in parametric studies that are conducted to assess the effect of various factors on the carbonation depth of the chemical process. [ABSTRACT FROM AUTHOR]

• We proposed a method for the preparation of mixed solution of aggressive CO 2 and H+. • We experimentally studied corrosion depth of cement-based materials in the mixed solution. • We proposed a carbonation model with moving boundary to predict the corrosion depth. • We studied the effects of corrosion condition on the deterioration of cement-based materials. The deterioration mechanism of cement-based materials in mixed solution of corrosive CO 2 and H+ was experimentally investigated. A carbonation model with the moving boundary was proposed to predict the corrosion depth of cement paste in the mixed solution of aggressive CO 2 and H+ in this paper. A test apparatus and method for the preparation of mixed solution of aggressive CO 2 and H+ was designed and manufactured. The corrosion tests of cement paste and concrete under different corrosion condition were implemented and the corrosion depth were obtained. The microscopic test methods were also applied to study the corrosion mechanism of cement-based materials. In addition, a carbonation model with the moving boundary was proposed to simulate the corrosion process. Results indicate that both the single and dual corrosion of aggressive CO 2 and H+ solution have an obvious damage on the quality of cement paste and concrete. The damage of dual corrosion of aggressive CO 2 and H+ on the specimens are greater than that of single aggressive CO 2 solution or the strong acidity. The corrosion region can be divided into gel layer, carbonated layer and transition layer. The carbonation model with a moving boundary can be used satisfactorily to predict the corrosion process of cement paste. This paper provides experimental and numerical methods for the future investigations on the durability of underground structures in acid water containing aggressive carbon dioxide. [ABSTRACT FROM AUTHOR]

• We experimentally and numerically studied irregularity of carbonation depth of concrete. • We proposed novel method to randomly distribute aggregates. • We included both aggregates and cement porosity in the numerical model. • We investigated the effects of volume ratios and gradation of aggregate on the carbonation depth. This paper presents both experimental study and multi-physics modelling of supercritical carbonation of concrete. A novel mathematical model is proposed to simulate random distribution of coarse aggregates in concrete. Supercritical carbonation tests of concrete are carried out and the measured carbonation depth is compared with the simulation results. On the basis of previous research on random field of porosity and supercritical carbonation of cement mortar, a new supercritical carbonation model is developed to study the effect of randomly distributed coarse aggregates and porosity on the irregularities of carbonation depth of concrete. The effect of the type, volume fraction and gradation of coarse aggregates and the porosity of ITZ on the distribution of irregular carbonation depth are also studied. The results demonstrate that the proposed two-dimensional random coarse aggregates model can be used satisfactorily to generate different types, volume fraction and gradation of coarse aggregates with the designed mix proportion within a confined space. The method provides a better and more realistic predictive model for simulating carbonation depth of concrete due to random distribution of coarse aggregates and porosity. [ABSTRACT FROM AUTHOR]