Concrete contraction joints for pumped concrete?

by Tom
(Central Florida)

Q. I heard hose pumped concrete shrinks more than that with large aggregate due to the use of pea gravel. I am pouring a 20x25 5 inch slab with 4/8 20 inch spaced rebar with 12x16 footers and a gravel base. I am concerned about shrinkage cracks and curling in the Florida heat should I use contraction joints?

A. Yes, you should saw contraction joints. Saw two joints on the 25' side and one on the 20 foot side giving you approximately 10 foot by 8 1/2 foot sections.

Wet cure the concrete for 7 days to minimize curling.

Smaller aggregate concrete does tend to shrink more than large aggregate concrete. The smaller the aggregate, the more cement is used to to achieve a specified psi. More cement in the mix usually means adding more mixing water to make the concrete workable, causing shrinkage cracking.

Click here to post comments

Join in and write your own page! It's easy to do. How? Simply click here to return to Concrete Floor Questions.