Shrinkage Cracks
Shrinkage Cracks
(OP)
Hi All,
We have a situation where early shrinkage cracks occured after 1-2 hours of the concrete was placed. Enclosed are the pics of these cracks. The grade of concrete is 45 Mpa (flow upto 600mm) and was pumped up 16 storeys by placing boom. Ambient temp was 41 deg centigrade max.. concrete temp 30 degrees max...Observations on-site revealed that no immediate protection was in place by burlaps, PVC sheets, no wind barrication. The surface seemed dry but the concrete was wet inside...The contractor is complaining that the concrete did not set within first 2-3 hours and thats the reason he could not make late finishing and early curing, as the masons feet were inserted into the concrete..
Please analyse the reasons and solutions to avoid such cracks..
We have a situation where early shrinkage cracks occured after 1-2 hours of the concrete was placed. Enclosed are the pics of these cracks. The grade of concrete is 45 Mpa (flow upto 600mm) and was pumped up 16 storeys by placing boom. Ambient temp was 41 deg centigrade max.. concrete temp 30 degrees max...Observations on-site revealed that no immediate protection was in place by burlaps, PVC sheets, no wind barrication. The surface seemed dry but the concrete was wet inside...The contractor is complaining that the concrete did not set within first 2-3 hours and thats the reason he could not make late finishing and early curing, as the masons feet were inserted into the concrete..
Please analyse the reasons and solutions to avoid such cracks..





RE: Shrinkage Cracks
If lightweight, was the aggregate pre-wetted?
At what location was the slump/flow measurement taken?
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: Shrinkage Cracks
There is no reasonable repair for this. Some autogenous healing will occur, but generally the discontinuous plastic shrinkage cracks will interconnect by further drying shrinkage of the concrete, thus creating meandering shrinkage cracks.
Consider wind breaks and surface fogging during the finish operation.
RE: Shrinkage Cracks
What shall be the sequence of finishing operations immediately after pouring?
When shall the water be sprinkled? When the concrete did not attain its initial setting (upto 3-4 hrs) how can the workers carry out floating operations?
Is it recommended to immediately cover the surface after initial finishing and then wait for the concrete to set (3-4 hrs) and then start late finishing? During this water has to be sprinkled?
Batching plant uses washed sand, prewetted aggregates.
Please explain in detail..
Thanks
RE: Shrinkage Cracks
RE: Shrinkage Cracks
No retarder was used...The crack is still not inspected from the bottom as shutters will be opened after 14 days... We hope it is not thru-n-thru crack.
RE: Shrinkage Cracks
Conplast SP430 does retard set, especially when used in the relatively high concentration which you described.
RE: Shrinkage Cracks
RE: Shrinkage Cracks
Results of the strength test specimens for this placement could be interesting.
The admixture supplier should be able to give major input on the proper and improper characteristics of their product.
RE: Shrinkage Cracks
So, where is the mason in the photo?
Mike McCann
MMC Engineering