Dependence of Basic Creep on the Relative Humidity

Abstract

The prediction of delayed strains is particularly important for prestressed structures. In modern codes like the fib MC2010, the delayed strains are split into four components: autogenous shrinkage, drying shrinkage, basic creep, and drying creep. Basic creep is the creep of a concrete sample in a test where drying is avoided. When drying is allowed, drying creep is the difference between the total strain minus the total shrinkage and the basic creep. However, in the drying creep test, the relative humidity (RH) is lower than the RH of the test performed to measure the basic creep. And there are several experimental pieces of evidence showing that, when the RH is lower, basic creep is reduced: micro-indentation tests and creep tests on large samples with an initial drying to lower the internal RH. In the first part of the paper, we analyze these tests and propose a relation for RH-dependent basic creep. In the second part of the paper, the consequences of this dependence on the evaluation of drying creep are discussed by using FEM simulations for the modelling of the total creep test and considering the drying phenomenon.