Full Program »

Modeling drying shrinkage of concrete at the meso-level

Creep and shrinkage are complicated time-dependent processes taking place in cementitious materials. Creep refers to a stress-induced increasing deformation at constant stress while shrinkage is stress-independent. It is generally accepted that creep, unlike shrinkage, is unbounded, even though it grows at a gradually decreasing rate.
In typical concretes, the most significant part of shrinkage is represented by drying shrinkage, but autogenous shrinkage (salient for modern and high-performance concretes) can become important, too. Decrease in relative humidity of pores causes increase in capillary tension of pore water and in the solid surface tension at pore walls, which leads to shrinkage.
Experimental data indicate that the ultimate value of concrete/mortar shrinkage is a nonlinear function of the ambient relative humidity. The nonlinear behavior is partially caused by microcracking, which has its origin in combination of internal (mesostructure) and external (specimen geometry, humidity gradients) restraints preventing the cement paste to shrink freely. On the other hand, drying shrinkage of hardened cement paste measured at gradually decreasing relative humidity is found to be a linear function of relative humidity, at least in the typical range of relative humidity.
A question arises what would be the nature of the macroscopic shrinkage computed using the meso-scale model in which the drying cement paste is described by the viscoelastic model based on the Microprestress-solidification theory with tensile cracking and with a constant shrinkage coefficient. To answer this question and to compare the results with the typical experimental data is the aim of this contribution.

Author(s):

Petr Havlasek    
Department of Mechanics, Faculty of Civil Engineering, Czech Technical University in Prague
Czech Republic

Milan Jirasek    
Department of Mechanics, Faculty of Civil Engineering, Czech Technical University in Prague
Czech Republic