Estimation models for creep and shrinkage of concrete made with natural, recycled and secondary aggregates

Besides strength and elastic modulus properties of concrete, creep and shrinkage are also important in designing structures as they can affect seriously their integrity in the long term. It is shown that design codes internationally, as well as researchers in general, have omitted to consider the influence of aggregate, in particular its stiffness, in the models developed for estimating creep and shrinkage of concrete. This paper shows that the American ACI, Australian AS 3600, European Eurocode 2, Japanese JSCE and B4 models are mostly found to estimate creep coefficient and shrinkage strain of concrete inaccurately, irrespective of the type of aggregate used - natural, recycled or secondary. It is proposed that the stiffness of aggregate can be represented reasonably by its pore structure and in turn, for ease of measurement, by its water absorption. Two empirical models are proposed for estimating creep coefficient and shrinkage strain of concrete covering a wide range of natural, recycled and secondary aggregates alone or in any combination of these, as well as the cement effect and its proportion effect in the form of aggregate/cement ratio.