New Viscoelastic Model for Early-Age Concrete Based on Measured Strains and Stresses

摘要

The heat of hydration generally induces thermal stresses; this may cause cracking problems in concrete at early ages. Therefore, it is necessary to accurately evaluate the actual stresses that occur in early-age concrete. The behavior of concrete at early ages is rather complex because the development of viscoelastic properties is so rapid due to the fast hydration process during early stages. The purpose of the present study, therefore, is to identify viscoelastic properties, including the relaxation function at early ages, from measured strains and stresses of actual concrete members. Furthermore, a compliance function for early-age concrete (called herein the Choi-Oh Model), which is necessary to predict actual stresses, is proposed. To this end, several series of full-scale test members were fabricated, from which temperatures, total strains, stress-independent strains, and stresses were directly measured for various elapsed times after concrete placement. The calculated stresses based on the proposed model agreed very well with measured stresses, whereas the stresses calculated on the basis of existing compliance models did not agree with the measured stresses and showed a large deviation from the test data for early-age concrete members. The proposed model for compliance function realistically considered the development of material properties during early ages. The proposed model allowed a more realistic and accurate evaluation of actual stresses occurring in early-age concrete structures.