Abstract
This paper deals with an experimental study on the creep and stress relaxation of concrete for the purpose of preventing cracking caused by thermal stress. In the experiment, the concrete was made using normal Portland cement, fly-ash cement and blast-furnace slag cement. Using compressive creep test machines, the concrete specimens were loaded at 3 or 7 or twenty-eight days.
The results may be summarized as follows.
(1) The relation between the creep strain of concrete and the time was expressed in the following equation:
f=αtβ;
where f: creep strain, t: time since application of load, α and β: experimental constants.
(2) The relation between the relaxation stress of concrete and the time was expressed as the following equation:
f=αtβ
where δ: relaxation stress, A and B: experimental constants, U: ultimate residual stress.
(3) The strong correlation was observed between the measured values of stress in relaxation test and values of relaxation stress calculated by using effective modulus of elasticity in creep test. The other side, Wittmann's method which could calculate the relaxation stress by using the creep function was examined.
(4) The influence of the kind of concrete and the age of concrete at application of load and stress/ strength ratio on the creep and the stress relaxation of concrete was examined.
