Seal Slab Concrete Compressive Test

[JackBolt]

The general notes issued with a project called for a "seal slab" to be used on any foundation excavation left open more than 24hrs. The material callout is simply 2,000psi lean concrete. The onsite QA/QC rep for the project is requiring concrete cylinder breaks to prove the seal slab material strength prior to acceptance and continuation of the structural concrete pour for the foundations.

Has anyone heard of requiring compressive tests for seal slab concrete?

 

[civilperson]

Does the contractor want to be paid for the seal slab? If tests are required to be paid, then test the lean mix.

 

[JAE]

Sounds pretty stupid to require compression tests for a non-structural slab like that.

 

[DRC1]

Why is this requirement here in the first place? If you could pour on soil, then you should be able to pour on very weak concrete, and it will still be better than the soil. Even in trenches that weap we have almost always poured on virgin gound. We have poured mud slabs on contaminated or soft soils to provide a seperation to the underlying soils, but not for structural reasons. We have poured tremie seals in cofferdams, but that was to allow inital dewatering. I have never heard of your situatioon and am trying to imaginre the reason. Please provide more details

 

[JackBolt]

DRC1...We typically have wording for the contractor to pour foundations within the day of excavation. Many times this is not possible, so as a option, we ask the contractors to pour a mud slab/seal slab. This slab will reduce effects of moisture intrusion into the excavation or excessive evaporation of the soil moisture prior to the structural concrete pour. This can reduce initial settlements. Also, this seal slab provides a good working surface to set the steel and foundation formwork.

The situation of requiring the testing is coming from a third-party quality control/field inspection service company. I do not believe they are specialists in Civil inspection and testing. This work is being performed in the petrochem field.

JAE - I agree

 

[DRC1]

If it is just to seal the surface, I would not require testing as it will be better than the soil it is resting on. As for requiring a seal pour if you can't excavate and pour the same day - wow. I have never seen that. We have left excavations open for several days at a time with no ill effects. Heavy rains can be a problem in soft clays or silts. Typically if we are in such a condition, we will put down 3/4 inch stone under the footing. I think the slabs really add cost for little benefit.