Many investigators have tried to represent the nonlinear behavior of stress-strain relation of concrete using mathematical curves. Clearly, a thorough knowledge of concrete behavior at early ages is great importance to the durability and service life of the concrete construction. However, most of empirical expressions for stress-strain relation are focused on old-age concrete, and not able to represent well concrete behavior at early ages.
In this research, compressive stress-strain responses of 5 different strengths from 12 hours to 28 days are observed. Tests were carried out on 100×200 mm concrete cylinders that were cured at 20±3℃ in water. The influence of age on stress-strain responses for 5 different strengths is represented. An analytical expression of stress-strain relations with age is developed using regression analysis of experimental data.
For the verification of the developed model, experimental data and some models that have been often referenced are compared with the proposed model. It was found that most of models for stress-strain relations do not represent particulary the descending branch of curve. The reason is that most of models do not consider an increase of slope at the descending branch of curve as the age increases. The analysis shows that the proposed model agrees well with experimental data and describes well ageing effect on stress-strain relations.
