Early Age Concrete

One of the most important aspects of concrete behavior at early age is volume change due to shrink-age and thermal deformations. Considering that volume reduction in hardening concrete is always re-strained, shrinkage and thermal contraction lead to buildup of stresses that often cause micro- or macroscopic cracking. In order to avoid reduction of durability of concrete, understanding volume changes at early age is of key importance. This is a very challenging task due to a number of coupled dynamic processes that take place in early age concrete, caused both by cement hydration and by complex interactions of the concrete with the surrounding environment. Depending on the mechanisms involved and the time at which they play a major role, one can distinguish the following types of concrete deformations at early age: plastic shrinkage, autogenous shrinkage, drying shrinkage and thermal deformations. Our research activities in the field of early-age are aimed at reducing cracking in concrete and improving the durability. - Plastic shrinkage - Autogenous shrinkage and internal curing - Thermal dilation coefficient - Mechanisms and modelling of autogenous and drying shrinkage.
Plastic shrinkage cracking appears in elements exposed to evaporation (in particular due to high ambient temperature and wind) in the first few hours after casting, while the concrete is still in the plastic state or shortly after setting.
Drying shrinkage takes place due to the development of pore fluid pressure caused by desaturation of pores in hardened concrete exposed to drying.
Autogenous shrinkage is the bulk deformation caused by the development of pore fluid pressure due to the emptying of the fine capillary pores by the ongoing hydration of cement (chemical shrinkage and self-desiccation). Autogenous shrinkage is of particular importance in high-performance concrete with low water-to-binder ratio and addition of fine supplementary cementitious materials (SCM).
Concrete elements at early age experience temperature increase due to the exothermic nature of ce-ment hydration. Further cooling leads to contraction of hardened concrete and buildup of thermal stresses. Prediction of thermal deformation requires precise measurements of the coefficient of ther-mal expansion (CTE).