TRIAXIAL COMPOSITE MODEL FOR BASIC CREEP OF CONCRETE

This paper shows how the mechanics of elastic composite materials can be adapted to predict the basic creep of concrete with aging due to hy dration. The prediction is made on the basis of the given composition of concrete, the elastic constants of the aggregate, and the aging vis coelastic properties of the portland cement mortar. The triaxial actio n of the composite is approximated by Dvorak's transformation field an alysis. To convert the aging creep problem to an elastic problem of a composite material with inelastic strains, Granger and Bazant's approa ch is used. This approach relies on Bazant's age-adjusted effective mo dulus method that reduces the integral-type stress-strain relation for linear aging creep with nonconvolution kernel to a quasi-elastic incr emental stress-strain relation with inelastic incremental strain. Expl icit expressions for the aging creep properties of concrete as a compo site are deduced. The model is calibrated and verified by Ward et al.' s and Counto's test data. The predictions obtained are almost as close as those recently obtained by Granger and Bazant's model. While the p resent model has the advantage of describing the triaxial composite ac tion in a rational manner, it does not yet capture the effect of the d eviation of the aggregate configuration from the case of a contiguous aggregate skeleton of maximum possible compactness. Further refinement s in this respect are needed. Another refinement might be needed to ta ke into account possible enhancement of creep in the interface layers between the mortar and the aggregate.