62 Damage to concrete structures
3.7.5 Demoulding problems
Problems can occur when striking the formworks is done too early. The concrete element should have enough strength to be self-supporting before
formworks can be safely removed. As shown in Figure 3.14, premature
demoulding of concrete floor slabs could lead to cracking near the beams.
Even without cracking, the risk of higher deflections of the slab increases
due to premature demoulding and thus mechanical loading of the slab.
The earlier the slab is loaded, the higher creep effects will become.
The surface of formworks should also be well prepared before casting the
concrete. This typically includes the application of demoulding oils, making
Accumulation of water
Water drainage point
Figure 3.13 Wrong positioning of formwork (wrong inclination, not enough negative
deflection during casting).
Formwork
Column
Slab
Reduced shear
capacity due to
penetrating formwork
Figure 3.12 Wrong positioning of formwork at connection between column and rib floor.
3.7.5 Demoulding problems
Problems can occur when striking the formworks is done too early. The concrete element should have enough strength to be self-supporting before
formworks can be safely removed. As shown in Figure 3.14, premature
demoulding of concrete floor slabs could lead to cracking near the beams.
Even without cracking, the risk of higher deflections of the slab increases
due to premature demoulding and thus mechanical loading of the slab.
The earlier the slab is loaded, the higher creep effects will become.
The surface of formworks should also be well prepared before casting the
concrete. This typically includes the application of demoulding oils, making
Accumulation of water
Water drainage point
Figure 3.13 Wrong positioning of formwork (wrong inclination, not enough negative
deflection during casting).
Formwork
Column
Slab
Reduced shear
capacity due to
penetrating formwork
Figure 3.12 Wrong positioning of formwork at connection between column and rib floor.