Effect of Hydrate Failure in ITZs on the Initiation of Prepeak Nonlinearities of Concrete under Multiaxial Compression

Abstract

Significant nonlinear material behavior of concrete subjected to compression is to be avoided in reinforced concrete structures subjected to regular service loads. Herein, initiation of prepeak nonlinearities under multiaxial compression is predicted using a multiscale model. The latter is based on a microscopic criterion for pressure-sensitive shear failure of micron-sized hydrate-gel needles that are part of the microstructure of the thin interfacial transition zones surrounding the aggregates. Model predictions agree well with starting points of significant nonlinearities in macroscopic stress-strain curves from several multiaxial compression tests. Corresponding limit stress surfaces are illustrated in a principal stress space, for general stress paths of multiaxial compression. Sensitivity analyses with respect to the initial composition of concrete and its maturity are described. The study confirms that the microstructural mechanism governing failure of concrete under uniaxial compression triggers initiation of prepeak nonlinearities under multiaxial compression.