Experimental and statistical study on the irregularity of carbonation depth of cement mortar under supercritical condition

Abstract

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.

Time-Varying Reliability Evaluation of Concrete Based on Carbonation Depth

“…Thus, probabilistic analyses are useful to quantify these unavoidable uncertainties. Hao proposed that the probability density functions of carbonation depth agree well with the lognormal distribution [26]. Meanwhile, Hao found that the average and variance augment with the increase of time.…”

“…Due to variations associated with climatic factors (e.g., temperature and humidity), concrete materials properties and geometric configuration [24,25], it is physically impossible to evaluate carbonation depths precisely. Several studies have demonstrated that carbonation depth is characterized by significant dispersion [26,27]. Thus, probabilistic analyses are useful to quantify these unavoidable uncertainties.…”

Prediction of Concrete Failure Time Based on Statistical Properties of Compressive Strength

“…Since the presence of variations associated with climatic factors (e.g., temperature and humidity), concrete materials, and geometric configurations [18,19], the compressive strength of concrete should be regarded as a variable in order to account for these uncertainties in deterioration. In practical engineering problems, these unavoidable uncertainties are often qualified by probabilistic models [20][21][22], among which reliability analyses are widely applied in structural safety assessments [23][24][25]. In the existing time-varying reliability models, the probabilities of corrosion initiation and corrosion damage are calculated based on the change in climatic variables [26].…”

Experimental study and multi-physics modelling of concrete under supercritical carbonation

“…Naturally, the distribution of carbonation depth is irregular with distinctive minimum and maximum along the boundary of a carbonation zones under both natural [27] and supercritical [28][29][30] conditions. However, the irregularities cannot been predicted by most carbonation models that assumed all cement-based materials are homogenous [31] , resulting in uniform carbonation depth [32] .…”

“…However, the irregularities cannot been predicted by most carbonation models that assumed all cement-based materials are homogenous [31] , resulting in uniform carbonation depth [32] . In fact, the topography of carbonation depth is affected by the presence of coarse aggregate [12,33,34] , cracks [35][36][37] , porosity of cement [29,30,38] , porosity of the Interfacial Transition Zone (ITZ) [39,40] and compositions of concrete [41,42] . To statistically study the distribution of irregular carbonation depth, Alahmad, et al [43] showed that penetration and diffusion of CO2 were significantly affected by cracks in cement mortar.…”