Concrete question? 2

[11echo]

...I work in the oil fields of Calif., and I've noticed a trend when pouring concrete for equipment foundation to use a pumper rig to pump the concrete into the frames. It's easy to see this is an easier operation, but as I understand things, the aggregate in pumped concrete can't be any bigger then PEE Gravel! I also remember years back that when you design foundation for larger equip. that you wanted larger aggregate in the concrete mix to make a stronger foundation! Now I've just witnessed a pour of a 24 ft.Sq.x 2 ft. high foundation for a API 650 tank. 15'-6" dia.x 30'-0"tall tank with 30 anchor chairs spaced around the base ...this is in seismic zone 4.
My question, have I missed something new in foundation design, or should I be jumping up and down waving my arms about this? ...As you probably guess civil/structural is NOT my discipline. ...Mark

 

[Ron]

No reason to wave your arms at this point.

Pumping concrete is common. With available equipment now, concrete with large aggregate can be easily and successfully pumped. The size of the aggregate pumping capability is governed by the mix design and by the pump/line size. For instance, a 6-inch concrete pump can easily pump 1" nominal size aggregate, if the mix is designed for that.

Larger aggregate does not equate to stronger concrete. The strength of the concrete is primarily governed by the water-cement ratio. Larger aggregate can actually lower the strength of concrete if you have lower strength aggregate to begin with.

I would; however, request that the contractor provide a mix design for review and that you hold the field activities strictly to that mix design (slump, air content, water addition, etc.).

 

[StephenA]

Just to add to Ron's explanation. Larger aggregate is used as this gives a smaller surface area to coat with cement. This is then cheaper and also gives off lower heat of hydration (important in large volume casting to prevent cracking).