crack in the parapet slab
crack in the parapet slab
(OP)
Cracks in the parapet slab
Please have a look on the attached photos. What can be the reason for this crack which appeared already one day after the casting. The parapet slab is supported with a permanent shutter board and has dimensions of approx 0,5m by 6m and is slightly reinforced with Y10 @ 250mm
regards
lolobau
Please have a look on the attached photos. What can be the reason for this crack which appeared already one day after the casting. The parapet slab is supported with a permanent shutter board and has dimensions of approx 0,5m by 6m and is slightly reinforced with Y10 @ 250mm
regards
lolobau






RE: crack in the parapet slab
RE: crack in the parapet slab
RE: crack in the parapet slab
RE: crack in the parapet slab
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: crack in the parapet slab
see attached sketch
or have I done a mistake that I cast such an long and narrow element? shouldn´t it be rather divided with joints? but you don´t want joints in the balustrade slab
lolobau
http://files.engineering.com/getfile.aspx?folder=8...
RE: crack in the parapet slab
could it be that it was to narrow and to long? so thats why the cracks appeared?
lolobau
RE: crack in the parapet slab
What were the weather conditions at time of placement and first 24 hours afterward? Was it windy?
RE: crack in the parapet slab
yes it was very hot, around 30degree celsius.
You think with the right curing and covering it wouldn´t appear?
how would you cure it? Just keep it wet? and cover with plastic?
but why is the crack orientation just in the one direction? how can this be explained?
lolobau
RE: crack in the parapet slab
Cracks occur either before or after hardening, and we don't know which is the case for your parapet capping. If before hardening, they are plastic shrinkage or plastic settlement cracks, and could have been repaired during finishing. If they occurred after hardening, they are drying shrinkage cracks. Drying shrinkage cracks occur not because the concrete shrinks, but because the concrete element is restrained from shrinking, thus placing it in tension.
In your case, considering the weather condition and the many cracks that appeared, I would think these are plastic cracks. Drying shrinkage cracks don't usually occur that close together.
RE: crack in the parapet slab
Drying Shrinkage cracks will normally be full depth of the concrete and the spacing is normally regular and related to the shape of the concrete. They are caused by restraint to shrinkage as Hokie explained.
Parapet walls (and any thin concrete member poured attached to a longitidinal concrete member) are highly prone to drying shrinkage cracking as the parapet is normally poured against already cured and hardend concrete which has already experienced a large degree of its own shrinkage. As well, the walls tennd to be relatively thin so experience much higher shrinkage than the concrete they are attached to. These cracks are normally regularly spaced and fairly closely spaced at half to 1 times the wall height. Much higher reinforcement ratios are required in thees walls than the minimum required for normal slabs and walls, normally about 3-4 times as much to provide good crack control.
Your Parapet slab would not appear to have the same problem but it is hard to tell without the full details of connections.
RE: crack in the parapet slab
hey guys thanks a lot for the very detailed explanation. I really appreciate it and it teached me a lot. Thanks
lolobau