CIE: Cracking Induced by Environmental Processes
Minisymposium organized by
- I. Carol, UPC Barcelona, Spain
- G. Hofstetter, University of Innsbruck, Austria
- K. Willam, University of Houston, USA
In addition to mechanical actions also environmental processes may have to be taken into account for the appropriate description of the material behavior of concrete. In particular, this minisymposium is focused on cracking of concrete due to
- high temperatures,
- moisture changes,
- chemical processes.
High temperatures may induce drastic moisture movements within the hardened cement paste, and cause important structural changes in the cement microstructure, mainly due to dehydration of some of its compounds. For cement as a whole, the consequences are non-trivial volume changes (first expansion, then contraction), accompanied by changes in mechanical properties. Since aggregates typically exhibit an always-expanding thermal behavior, the resulting mismatch leads to cracking and damage, with the subsequent loss of linearity and superposition between the effects of temperature and load (the so-called LITS effect). Moisture migration and moisture transfer to the environment, caused by a decrease in ambient relative humidity, results in drying shrinkage of concrete. Since shrinkage deformations of the dryer near-surface regions are restrained by the moist inner regions, tensile stresses are generated in the near-surface regions, which may result in cracking. A variety of chemical processes can also induce dissolution, or incompatible volume changes in cement, mortar and concrete, leading to degradation of mechanical properties and cracking. The most common are sulfate attack, carbonation (or, in general, acid attacks), calcium leaching, and akali-silica reaction. In general those processes are governed by one or more diffusion-reaction processes. The first one is in general the penetration of the aggressive ions through the pore system. Then the reaction takes place within the cement or concrete depending on ion concentrations and other local conditions. The reaction product itself may crystallize or precipitate in situ and directly filling pores and perhaps produce expansions, or may lead to secondary soluble products that then may diffuse outwards and finally precipitate somewhere else.
In this minisymposium, contributions concerning numerical modeling of cracking induced by environmental processes as well as comparisons of numerical predictions of the structural behavior of concrete structures, affected by environmental processes, with measurement data are welcome.