Modelling of autogenous shrinkage of concrete based on paste measurements

In order to be able to improve concrete modelling based on its constituent, more knowledge is needed about the material behaviour of these constituents. In this research the focus is on the behaviour of hardening concrete, therefore the properties of hardening cement are of most relevance. Information about cement paste behaviour can be used as input for computer models that are able to represent concrete as a heterogeneous material. During the development of these models the output has to be verified with data from actual concrete. In order to be able to perform measurements on autogenous deformation of cement paste a new test setup was developed. The design is based on the Temperature Stress Testing Machine (TSTM), a setup used for experiments on autogenous deformation in concrete. A device available at the Microlab, called the mini tensile testing machine served as a basis to create the mini-TSTM. The device can either measure the free deformations of cement paste or it can measure the build up of stress in the paste if these deformations are restrained. This part of the research is described in [2]. For the modelling of the heterogeneous material the Delft Lattice Model is used. This is based on a lattice of beams to which different material properties can be assigned. The measured paste deformations from the mini-TSTM are imposed on this lattice as a load. The development of the stiffness (Young’s modulus) of the cement paste is taken from Hymostruc, a computer model that determines properties of hardening cement. The material properties of the other concrete constituents, in this case the aggregates, are based on assumptions. The properties and the displacements of the cement develop over time, therefore this model runs a calculation for every time step. With the model simulations of free shrinkage and restrained shrinkage tests on concrete are simulated and the results are compared with the experimental outcome. Qualitatively the results look promising. More tests and simulations are needed to exactly define all the relevant parameters in the mode