Modelování difuze chloridů pro analýzu trvanlivosti železobetonu

Abstract

The aim of the submitted work is modeling of the durability of reinforced concrete structures with respect to the corrosion of reinforcement caused by the diffusion of chlorides, which can occur by the presence of deicing salts. The main goal and benefit of the work is the presentation of several improvements to the numerical diffusion model based on the finite element method, which will be used for faster and more accurate estimation of durability. The original model presented in the author's diploma thesis and the supervisor's habilitation thesis was extended by the following parts: new computational core with the four-node isoparametric element, time step optimization, more accurate and faster interpolation of computational core results, heterogeneity of material characteristics of concrete using random field, delayed exposure to chlorides in several possible variants. All these improvements and options can be combined appropriately. Part of the work is a general description of the process of preparation, production, testing, modeling and evaluation of concrete samples of self-compacting concrete reinforced with steel fibre with regard to verification of prepared models. The mechanical properties and parameters describing the diffusion of chlorides obtained from three test methods are compared: rapid chloride permeability test, accelerated chloride penetration and measurement of surface electrical resistance. Thanks to long-term curing and high-quality self-compacting concrete, better durability expressed by resistance to chloride penetration are observed. The influence of electrical conductivity of steel fibres on the results of test methods and numerical models is also observed and evaluated. The work also includes an analysis of data obtained from an extensive study of laboratory tests of high-performance concrete prepared at California State University, Fullerton. The first part examines the diffusion coefficient, even in terms of changes in its scattering over time. The analysis shows for which mixtures it is appropriate to describe the variance bythe average value of the coefficient of variation, and when it is appropriate to use a linear approximation to describe the time-dependent coefficient of variation. The next part of the research describes the use of a newly modified numerical model to determine the durability in terms of corrosion initiation time for all analyzed concretes. Work includes a parametric study based on the diffusion coefficient and the maturation coefficient. From the calculated durability results for the individual, high-value concretes, it was determined that there are groups with some cement replacement, which show values of time to corrosion initiation several orders of magnitude higher than the standard mixtures. The results show that the optimization steps led to the acceleration and refinement of calculations. The presented examples confirm the universality of the prepared numerical models and their possible application to a wide range of concrete mixtures and examples.