10979: Chloride penetration in cracked and uncracked concrete structures

1.1 Research summary

In recent years, there is a clear trend towards design for durability of concrete structures. This requires the development and subsequent introduction of performance criteria as a design tool for practice. Corrosion of steel reinforcement induced by chlorides penetrating from the ex-posed concrete surface is considered as the major threat to durability of concrete structures. In the current project, a significant number of chloride profiles will be retrieved and thereupon evaluated taking into account the prevailing exposure condition. For existing concrete structures, the chloride profiles obtained reflect the real exposure conditions prevailing during the preceding period. This information forms the basis for the quantification of key parameters (apparent surface concentration, diffusion coefficient and aging factor), featuring in models that describe combined moisture (in surface zone) and chloride transport. Furthermore, a thorough evaluation of the laboratory accelerated migration test is performed, eventually re-sulting in a straightforward test procedure. This includes the comparison between the migra-tion coefficients determined on labcrete (potential quality) as opposed to the migration coeffi-cient on realcrete (using iodide as migrating ion).

In addition, the effect of cracks on the migration is examined in detail as well, using an inno-vative set-up and deploying the moisture and chloride migration models developed in the cur-rent project. It is expected that the project results in an improved quantification of residual service life times, and provides high quality information on the actual performance of existing structures, especially after a prolonged period of exposure.

1.2 Utilization summary

About 50% of the expenditure in the construction industry is spent on repair, maintenance and remediation. It is evident that even modest savings will result in the reduction of substantial costs. An increasing proportion of these costs is related to concrete structures and their (resid-ual) service life. Current prediction models of the residual service life are still in their infancy and based on arbitrary choices, and a considerable improvement in approach is the main ob-jective of the current project. The proposed research will result in suitable engineering models for a reliable (residual) service life prediction. In order to allow for sound service life predictions of a complete structure, sufficient amounts of quality data are collected (e.g. the chloride profiles of existing structures), are obtained by accelerated lab tests, and combined with advanced numerical simulation. From a stakeholder point of view: the present research leads to a robust tool which can be used to assess the service life of new structures and to compute the remaining economic value of existing structures. Key parameters, such as the apparent diffusion coefficient, the time de-pendent surface chloride concentration, the aging factor, and the effect of cracks, will become known more accurately, enabling a reliable prediction. The background of the applicants and the composition of the participating organisations (Appendix) will assure the utilization of the project results and the implementation in design codes, and in new maintenance and repair strategies of infrastructure.