Pure creep, maturity and MP-creep in concrete in terms of an exo-process

Abstract

Pure asymptotic creep of concrete is described as a manifestation of relaxation under low constant stress, where creep-induced damage is absent. An analytical solution for pure creep is obtained as a time-operator and is shown as an exo-function. The potential of stress loss in pure creep is found to be essentially higher than in relaxation due to steady re-elevation of the relaxed stress to the initial constant value. The duration of pure creep is described and found to be prolonged versus relaxation. Elastic maturity (the increase of the elastic modulus with time) and strength maturity (increase in concrete strength with time) are also exo-processes, described by a common time-operator. For structural concrete, they differ in the exponent – for elastic maturity, the exponent is 4·2–4·8 and for strength maturity its value is 3·8–4·2, depending on the type and content of cement. The influence of temperature up to 70°C is incorporated in the exo-operator of maturity. MP-creep – a combination of plain creep and increasing maturity – is described by equations, based on material parameters determined from tests. It is shown that elastic strain decreases under MP-creep.