Modeling of Concrete Creep Based on Microprestress-solidification Theory

Creep of concrete is strongly affected by the evolution of pore humidity and temperature, which in turn depend on the environmental conditions and on the size and shape of the concrete member. Current codes of practice take that into account only approximately, in a very simplified way. A more realistic description can be achieved by advanced models, such as model B3 and its improved version that uses the concept of microprestress. The value of microprestress is influenced by the evolution of pore humidity and temperature. In this paper, values of parameters used by the microprestress-solidification theory (MPS) are recommended and their influence on the creep compliance function is evaluated and checked against experimental data from the literature. Certain deficiencies of MPS are pointed out, anda modified version of MPS is proposed

On modelling the influence of creep on corrosion-induced cracking in reinforced concrete

Naturally occurring corrosion rates in reinforced concrete are so low that rust accumulates often over tens of years near the surface of the reinforcement bars before sufficient pressure in the surrounding concrete is generated to induce cracking in the concrete cover. To speed up the process in laboratory tests, corrosion setups with impressed currents are used in which the corrosion rate is controlled so that cracking of the concrete cover occurs within a few days. Extrapolating the results of these accelerated tests to those of naturally occurring corrosion requires an understanding of the influence of long-term creep deformations of concrete on the corrosion induced cracking process. In mathematical models in the literature, creep deformations are often ignored for accelerated but considered for natural corrosion rates in the form of a constant creep coefficient, which is used to reduce the Young modulus of concrete. In this work, two numerical models are proposed to investigate the effect of creep on corrosion-induced cracking. The first approach is based on an elastic axisymmetric thick-walled cylindercombined with a plastic limit on the circumferential stress. The second model uses a three-dimensional lattice (network) approach to discretise the thick-walled cylinder.</div