14 days for underside of slab beams arches above 4 5 meter up to 6 meter span.
Roof slab curing time.
21 days for underside of beams arches above 6 meter span and up to 9 meter span.
The precast concrete items are normally immersed in curing tanks for a certain duration.
Ideally the slab could be water cured for 7 days some builders on a tight schedule water cure for 3 days as this achieves approximately 80 of the benefit of water curing for 7 days.
Are cured by spraying water.
The enclosed area is continually flooded with water.
Pavement slabs roof slab etc.
Are covered under water by making small ponds.
Water curing can be done after the slab pour by building dams with soil around the house and flooding the slab.
The removing of shuttering related with span of the roof slab.
But to answer the question of how long does concrete take to set concrete setting time is generally 24 to 48 hours.
Curing time for concrete.
In standard industrial cases full strength concrete is recognized at 28 days.
The indian standard is 456 2000 recommends that curing duration of concrete must be at least seven days in case of ordinary portland cement at least ten days for concrete with mineral admixtures or blended cements are used.
At seven days you should have concrete that is cured to 70 full strength or greater.