Bonded cement-based material overlays and their substrates constitute a
hybrid or composite structural system
. The interaction of these two material layers (with different ages), with each other, with the external boundary conditions (foundations, supports) and possible joints, and under loading, defines the
of this composite system. The main
governing this structural behaviour are (1) the differential deformations of the two layers due to autogenous shrinkage, thermo-mechanical effects due to cement hydration and/or external climatic influences and drying shrinkage, (2) settlements, and/or (3) imposed forces (dead loads, traffic loads). These actions give rise to stresses which depend on the stiffness of the substrate with respect to the new layer, and that eventually may result in failure either by transverse crack propagation, by debonding or both. Composite structures formed of building materials of different kinds and ages are very common: slabs on grade, steel-concrete, wood-concrete, concrete-concrete, concrete repairs, cement-based overlays, etc. However, until now, the causes of distress in these composite structures and their design were mostly addressed by empirical approaches. This document shows howa common approach might treat all these applications on the unique basis of the mechanical description of the behaviour of composite structural members under restrained shrinkage.