When concrete structures are not permanently saturated with water, it begins to lose moisture and begin to shrink by the time the curing process stops.
The 7 primary structural effects of shrinkage are as follows.
The shrinkage of the concrete between the moving joints causes the joints to open up or widen. The joints must therefore be designed to accommodate the widening caused by shrinkage.
2. other material
Where other materials, such as ceramic tiles, are fixed on top of the concrete surface, shrinkage of the concrete results in relative movement between the different materials. The resulting stresses can cause failure at the interface.
If the shrinkage is stopped, the concrete is put under stress and when the tensile stress equals the tensile strength, the concrete cracks.
Structural designers may design structures to reduce restraint, press concrete to prevent tensile stress, or use reinforcement to control cracking.
4. pressure loss
Due to the shrinkage, the compressive force decreases. When calculating prestressing forces, designers take this into account to ensure that the residual stress is structurally sufficient.
If concrete is used to fill a cavity in the old concrete, the shrinkage of the new concrete is inhibited by the surrounding old concrete. Repair concrete and mortar must be specially prepared (by incorporating a polymeric material) to prevent cracking caused by this restraint.
6. bond strength
As the concrete shrinks, the reinforcing bars hold the concrete more firmly in place. This increases the friction between the concrete and the steel and therefore improves the bonding strength, especially for plain bars.
Contraction increases the deflection of the flexural members. This is because the lighter reinforced compression region is free to shrink more than the heavily reinforced tension region.