Deformation properties and crack sensitivity in young concrete: Experience and guidelines from a 4-year Norwegian R&D project

Early age cracking is complicated to control by structural design and rather insufficiently treated in standards. An important reason is that it is a great challenge to determine the properties involved, the volume changes in particular, for input to calculation programs, as it is in the nature of early age concrete that it changes from a liquid to a solid and that the temperature changes considerably due to heat of hydration. The volume changes are autogenous deformation (AD) and thermal dilation (TD). AD is extremely temperature dependent, and, importantly, isothermal data can not be used to predict the behavior during realistic temperature histories. Hence, AD must be measured at the realistic temperature histories. Several calculation programs have been developed world wide. A Norwegian program is presented, including a special procedure to determine AD at any temperature development, and used to assess the crack risk of a 700 mm thick wall cast on an old strip foundation. It demonstrates that the increased AD at high temperatures contributes considerably to increased cracking risk.