Modelagem do mecanismo de cinética do co2 no processo de carbonatação natural do concreto

Abstract

The use of mathematical modelling for the prediction of carbonation in concrete is considered a parameter for assessing durability against the entry of aggressive agents by porous matrix. However, these formulations suffer limitations because their input data are not easily transposed to represent the phenomenon. Most common and applicable models assume that the kinetics of CO2 ingress is a function of the square root of time due to a diffusivity finding, without taking into account microstructural modifications of permeability and formation of salts in the porous matrix in which they slow down the process, causing that the existing models do not accurately represent the advance of the carbonated front. Based on an experimental program that includes carbonation depth tests on concrete specimens under conditions of natural exposure during the intervals of 14, 28, 56 and 84 days and analyzes of the terms of the equations and their boundary conditions, the objective of this work is to propose a diffusivity term model capable of being used in existing equations and that satisfactorily represents the phenomenon. Due to what was proposed, it is possible to describe that the penetration kinetics of CO2 can be written as a function of permeability, carbon dioxide pressure, contact area and amount of carbonate salts formed. The modelled term showed a maximum variation of 25% in relation to the actual data obtained, showing good representativeness for the conditions in which it was submitted.