Contech2011
Civil/Environmental
Do you have any other name other than surface blemishes? And possible reasons please...
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Surface Blemishes
- Thread starter Contech2011
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I also agree with @Ron. It is poorly compacted.I am not sure whether it is a honey comb or not as far as I know honeycomb defects shows a hard surface with exposed aggregate.
Basic things to remember
1. pour the concrete within 1.5 hrs if you use admixtures.
2. place the concrete in layers not more than 50 cm and compact it properly using needle vibrators.Then place the next life within 1.5 hrs -2 hrs so that there is proper bond between the layers and compact it again. If you take too much time you will see cold joints later.
3. The slump at site should be atleast 100 mm for workability.
4. Curing is very very important in the strength gain of concrete and for the surface finish.
5. For finish use long clean smooth finished battens.Most of the masons sprinkle the water over the surface to make it more workable and easier to finish.
If you keep these things in mind then you shouldn't have any problem. If you are practicing this and you have problems then maybe you can disclose us your mix proportions of the concrete.
Basic things to remember
1. pour the concrete within 1.5 hrs if you use admixtures.
2. place the concrete in layers not more than 50 cm and compact it properly using needle vibrators.Then place the next life within 1.5 hrs -2 hrs so that there is proper bond between the layers and compact it again. If you take too much time you will see cold joints later.
3. The slump at site should be atleast 100 mm for workability.
4. Curing is very very important in the strength gain of concrete and for the surface finish.
5. For finish use long clean smooth finished battens.Most of the masons sprinkle the water over the surface to make it more workable and easier to finish.
If you keep these things in mind then you shouldn't have any problem. If you are practicing this and you have problems then maybe you can disclose us your mix proportions of the concrete.
It is a core wall. Slump on-site not less than 180mm. proven mix design, poured many adjacent structures without such surface defects. We observed surface missing cement paste...probably absorbed by rough and reused formwork. Schmidt hammer shows low readings.. may be excessive water added on-site to the mix
Slump at site @180 mm is too much since the concrete in this slump is in flow able condition vibrating it too much may cause bleeding and segregation. If you are pouring with pump maximum slump at site should be 140 mm and if you are using shoots 120 mm would be enough.
Go back to the lab and try the mix with reduced w/c ratio and fix the admixture dosage as per the requirement.
Schmidt rebound test only gives you a rough idea about the strength of the concrete at the surface. Also you should calibrate it with the concrete of the same grade in your lab and then compare the results at the site.This is what I would do instead of relying on the manufacturers reference graph.
Go back to the lab and try the mix with reduced w/c ratio and fix the admixture dosage as per the requirement.
Schmidt rebound test only gives you a rough idea about the strength of the concrete at the surface. Also you should calibrate it with the concrete of the same grade in your lab and then compare the results at the site.This is what I would do instead of relying on the manufacturers reference graph.
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