Classification of crack
Classification of crack
(OP)
Hi All,
Please classify the crack shown in the uploaded pic. Other data is as below,
1. Concrete grade 45 Mpa (490 Kgs cement)
2. Pumped @ 100 meters
3. Initial water curing not done. Curing membrane was applied late.
4. Slab thickness 40cm & 70cm.
Also recommend measures to control such cracks.
Thanks
Please classify the crack shown in the uploaded pic. Other data is as below,
1. Concrete grade 45 Mpa (490 Kgs cement)
2. Pumped @ 100 meters
3. Initial water curing not done. Curing membrane was applied late.
4. Slab thickness 40cm & 70cm.
Also recommend measures to control such cracks.
Thanks





RE: Classification of crack
Assuming the concrete in the core was newly placed within the last few weeks.....
1. Since the crack occurs only from the top and does not extend through the cross section, it is likely a plastic shrinkage crack.
2. The crack is quite wide at the top, thus also indicating plastic shrinkage.
3. The crack does not show tensile failure of the coarse aggregate, so it occurred prior to the development of adequate bond strength between the paste and aggregate...another indication of plastic shrinkage; however, this can also occur in typical early-occurring drying shrinkage cracks and will occur in weak concrete mixes as well. Also occurs when coarse aggregates are contaminated.
All in all, my guess is plastic shrinkage crack.
How to stop? Use proper concrete mix, designed for the application, control the placement techniques, prevent drying at the surface....in short, use good concrete technology controls.
RE: Classification of crack
RE: Classification of crack
We recommended the contractor to immediately after intial finishing, cover the concrete with wet burlap and plastic sheets...wait for 1-2 hrs till the concrete can take some load...then remove the coverings and late finish the concrete using power float, hand trowels as required...upon late finishing re-cover the burlap...continue sprinkling cold water and cover with plastic sheets.. for a minimum of 3 days...Is that sufficient??
RE: Classification of crack
RE: Classification of crack
RE: Classification of crack
RE: Classification of crack
With as much evaporation as you describe, you're going to have to provide ancillary means of moisture protection. As I mentioned before, set up a fogging system and employ it immediately after screeding.
RE: Classification of crack
I think the additives have been overdone, so that the retarding effect is too much. Waiting 2 hours to finish is extraodinary in hot weather conditions.
Spraying aliphatic alcohol on the surface immediately behind the screeding and bullfloating will help to prevent premature surface drying.