Background

Background

September 07, 2016

Concrete is the most widely used building material. Its good performance in service, including durability, is the second important characteristic after the usual required mechanical properties. However, the last decades the problems of unsatisfactory durability of structures, especially reinforced concrete ones, are in a dramatic increase.Deterioration of concrete in service may be the result of a variety of mechanical, physical, chemical or biological processes. Corrosion of steel reinforcement is the most serious durability problem of reinforced concrete structures. It impairs not only the appearance of the structure, but also its strength and safety, due to the reduction in the cross-sectional area of the reinforcement and to the deterioration of bond with the surrounding concrete. This causes not only economic impacts, because the repairing expenses of deteriorated structures are almost equal to the cost of construction of new ones, but also industrial, environmental and social problems due to decrease of reliability and safety.

 

 

Over the past 50 years, an enormous amount of energy has been expended in laboratory and field studies on concrete durability. The results of this research are still either widely scattered in the journal literature or mentioned briefly in the standard textbooks. Moreover, the theoretical approaches of deterioration mechanisms with a predictive character are limited to some complicated mathematical models not widely applicable in practice.

A significant step forward could be the development of appropriate software for computer estimation, including the reliable mathematical models and strengthened by adequate experimental data.

The European Standard ΕΝ 206 development as well as the corresponding parts of Eurocode 2, such as on concrete cover to reinforcement, provide for the first time serious technical  specifications for concrete durability. Durability is specified either through the traditional practice of limiting values of concrete composition or by performance-related methods. The requirements shall take into account the intended service life of the concrete structure.

The performance-related method should consider each relevant deterioration mechanism, the service life of the element or structure, and the criteria which define the end of this service life, in a quantitative way. It may be based:

  • on satisfactory experience with local practices in local environments,
  • on data from an established performance test method, or
  • on the use of proven predictive models.


The orientation of the present work is towards the development of performance-related methods based on proven predictive models. The basic logical diagram of a generalized method for estimation of concrete durability, includes:

  • Initial approach of the concrete composition in order to satisfy the structural requirements, such as the strength class.
  • Definition of the environmental conditions where the structure will be exposed
  • Use of proven theoretical, mathematical models that simulate reliably the mechanism and rate of deterioration.
  • Estimation of structure service life and improvement of the initial mix design, if required
  • Technical and economical optimization.


In the present work, a mix design strategy to fulfill any requirements on strength and service life is presented. The chemical and volumetric characteristics of concrete are first estimated and the service life of the concrete structure is then predicted, based on fundamental models developed earlier mostly by the present author. The prediction is focused on the basic deterioration phenomena of the reinforced concrete, carbonation and chloride penetration. Aspects on concrete strength and production cost are also considered. The proposed models enable mixture proportions to be accurately specified and concrete performance reliably predicted. This work is the source book for the development of the software for estimation of concrete service life, EUCON®. In general, this work concerns Construction Engineers and Building Material Manufacturers towards fundamental comprehension of materials behavior. Basic principles of Chemical Engineering are applied to simulate the physicochemical processes, yielding simple and accurate mathematical models for design and prediction. The work structure presented herein is in full compliance with the new European Standards for cement: EN 197 and concrete: EN 206.