Meaning
Deformations occurring across different depths of a structural member generate internal stress distributions when moisture loss occurs unequally. The phenomenon of differential shrinkage strain describes the variation in volume change per unit length between top and bottom surfaces of concrete slabs. Evaporation from the exposed upper face creates higher drying rates than the sealed or damp lower face.
Structural restraint converts these strain gradients into internal moments and surface cracking.
Gradient Mechanism
Moisture loss proceeds faster near exposed slab boundaries than in deep internal zones. This localized desiccation causes differential shrinkage strain to reach peak magnitudes near the top surface during early drying phases. Internal tensile stresses develop in the drying zone while compressive stresses form in the moist interior.
Unrestrained members warp while restrained members crack.
Curvature Inductance
Bending moments develop across the cross section as upper layers shrink against lower layers. Calculating differential shrinkage strain allows structural engineers to predict long-term slab deflections and curling behavior. Linear strain profiles across depth produce uniform curvature.
Non-linear moisture distribution creates self-equilibrating internal stresses.
Restraint Stress
External foundations and internal reinforcement hinder free slab movement. Heavy restraint converts differential shrinkage strain into severe tensile stresses that breach concrete tensile strength. Microcracks coalesce into structural fractures.
