Influence of hydration reaction on engineering properties of hardening concrete

The engineering properties of hardening concrete depend on the microstructure of the cementitious material, and thus on the amount of hydration products formed. A determining measure for the amount of hydration products is the amount of reacted cement, which can be described by means of the degree of hydration. An extended experimental program was carried out in order to verify the influence of the degree of hydration on the engineering properties of hardening concrete. The instantaneous and time dependent mechanical behaviour was investigated experimentally on hardening concrete with different compositions. Portland cement as well as blast furnace slag cement were considered. Furthermore, the fracture energy of hardening concrete was investigated, using a deformation controlled three-point bending test. It was concluded that the degree of hydration is a fundamental parameter for the description of hardening concrete, including time-dependent mechanical behaviours and fracture properties. Based on the experimental results and on a phenomenological view of hydration, engineering models were developed, enabling an accurate simulation of the behaviour of early-age concrete (i.e. first 28 days).