Anne-Mieke Poppe

Creep and shrinkage of self-compacting concrete.

Due to its advantages during placing, self-compacting concrete (SCC) seems to be a very promissing material for concrete construction. At this moment however, not much information is available concerning the fundamental background of the properties of the SCC. At the Magnel Laboratory for Concrete Research, an extended research programme is going on in order to more fundamentally understand the behaviour of this material. This research project includes the study of the fresh, hardening and hardened SCC, with due attention given to the time-dependent mechanical behaviour. In this contribution, results are reported concerning the creep and shrinkage of SCC. The measurements are carried out on sealed and unsealed specimens in order to be able to extract basic and drying creep and shrinkage. Different mix compositions are considered, studying different parameters, like cement type, filler type, c/p (cement to powder ratio). To study the deformations in more detail, the applicability of traditional creep and shrinkage models is investigated. Well-known models like the CEB-FIP Model Code 1990, the ACI-model and the model of de Larrard are evaluated. Some suggestions are made to include the influence of the addition of the fillers in the model of the Model Code.

Hydration modelling of filler rich self-compacting concrete

For the realisation of self-compacting concrete, high filler contents are generally added to the cementitious system. In order to avoid problems with excessive heat of hydration during hardening, inert filler materials can be used. Within this research two different filler types are considered: limestone filler and quartzite filler, and this in combination with different types of Portland cement. Although the mentioned filler material is considered to be inert with respect to cement hydration, experimental research shows that it is interfering with the hydration processes. On the one hand the reaction speed is influenced due to a modified nucleation possibility. On the other hand, the reaction mechanism is also altered due to the presence of the large filler content, with a new hydration peak occuring, especially in the case of limestone filler. Based on isothermal conduction calorimetry on different cement filler systems, an existing hydration model for blended cement is modified for the situation of cement filler systems. Within the degree of hydration based hydration model for the filler rich cementitious systems, the cement powder ratio is an important parameter. The model results in an accurate prediction of the heat of hydration during the hardening process. This was also verified by means of adiabatic hydration tests on concrete.