A Consideration about Tensile Stress Relaxation of Concrete

A study on protection against thermal cracks within mass concrete structures (III)

Abstract

This paper describes tensile stress relaxation of concrete and its application.
First, the long-term stress relaxation properties at an early age were mainly examined in one stress level and in a mix proportion.
The results were as follows.
(i) The test results have some random nature and differ from the short-term results by Kiyama-Nishibayashi et al.
(ii) The best experimental equation is Nishibayashi-Kiyama's which has physical meanings.
(iii) The mean 1/2 relaxation times A are 4-9 hours for water curing test pieces and 3-6 hours for air curing.
(iv) The final relaxation coefficients C' are under about 70%, but scatter due to the loaded ages.
(v) The influence due to the loaded ages is not apparent in A and C'.
Secondly, a thermal stress analysis were carried out, in which the previous results ware applied. From the results, it is recognized that tensile stress relaxation is important.