Six different concretes are characterized during material ages between 1 and 28 days. Standard tests regarding strength and stiffness are performed 1, 3, 7, 14, and 28 days after production. Innovative three-minute-long creep tests are repeated hourly during material ages between one and seven days. The results from the standard tests are used to assess and to improve formulas of the fib Model Code 2010: the correlation formula between the 28-day values of the strength and the stiffness, and the evolution formulas describing the early-age evolution of the strength and the stiffness during the first four weeks after production. The results from the innovative tests are used to develop a correlation formula between the 28-day values of Young's modulus and the creep modulus, and an evolution formula describing the early-age evolution of the creep modulus during the first four weeks after production. Particularly, the analyzed CEM I concretes develop stiffness and strength significantly faster than described by the formulas of the Model Code. The creep modulus of the investigated concretes evolves significantly slower than their strength and stiffness. Thus, concrete loaded at early ages is surprisingly creep active, even if the material appears to be quite mature in terms of its strength and stiffness.
Keywords: creep modulus; fib Model Code 2010; hardening of concrete; stiffness; strength.