Parametric modelling of shrinkage effects on industrial floors

Abstract

Drying shrinkage can cause structural damage to concrete industrial floors. Shrinkage is caused by evaporation of moisture from the drying material. In the design- and construction-standards, this complex process is not described on a fundamental level. Using finite element modelling to simulate the flow of Moisture through the concrete, it is possible to simulate drying shrinkage. The research question of this thesis is: ‘How can a parametric FEM model efficiently simulate drying shrinkage in industrial concrete floors?’. Verification of the produced model is performed. The outcome is compared to shrinkage
measurements of concrete prisms. The theoretical framework presented in this thesis is based on the fact that the relative pore humidity is changing during drying. In a finite element model, the changing relative pore humidity (pore-RH) over time is calculated. Drying is caused by internal diffusion of moisture, which is driven by differences in concentration. The moisture flow is modelled using the transient heat equation. The resulting pore-RH values are used to determine the hydrostatic capillary pressure based on the equations of Kelvin and Laplace. The material response of cement paste subjected to the capillary pressure is calculated using Bentz law. At last, the models of Pickett and Neville are used to include the restraining effect of aggregates and determine the absolute deformation of concrete subjected to drying. The initial conditions of the material are determined based on HYMOSTRUC cement simulation and Powers’ volumetric model. The results of the presented theoretical framework are reasonable. Usage of the framework and the heat equation for modelling drying in FEM, proved to be successful. A significant uncertainty is found in the restraining effect of aggregates. The theoretical model is based on material modelling of drying cement paste. However, the deformation of concrete is only
16%~23% of the total deformation of cement paste. Recommended is to further research the (local) effect of aggregates on drying shrinkage. Drying shrinkage has been calculated according to the construction standards and compared to the measured drying shrinkage of the concrete prisms. From this, it can be concluded that calculations by structural engineers on drying shrinkage are preferably done according to the ‘Model code 2010’.