A 7.5 in. thick concrete slab is placed on the ground. The maximum aggregate size of coarse aggregate in the concrete mix is 1.5 in. Concrete slump is 5 in. What is the maximum spacing of control/contraction joint recommended for this slab? If concrete slump is measured as 3 inches, what spacing would you suggest for the control joints?

Considering the given data with the parameters stated, the spacing of contraction joint with 5 in slump can be 15 ft.

Considering the given data with the parameters given, the spacing of contraction joint with 3 in slump can be 20 ft.

Explanation:

Ideally, the typical spacing of the contraction/control joints are based on the follolwing parameters listed below:

a)Slab thickness

The recommended spacing is 24 to 36 times the slab thickness

b)Aggregate size

Given slab thickness above,the spacing of the control joint is decided based on the the aggregate size in the concrete. For the aggregate which is greater/larger than 3/4 inch, the spacing of the control/contraction joints ranges from 3.75ft to 7.5 ft for the slab thickness which varies from 5 inches to 10 inches respectively

c)Slump

Lastly, the slump of the concrete should also be considered to fix the spacing of the control/contraction Joint. The greater the slump , the lesser the spacing between the control/contraction joints.This is due to the fact that shrinkage will be more ,if the slump is more.

-Recommended spacing of control/contraction joints with 5 in slump.

Therefore, considering the given data with the above parameters the spacing of contraction joint with 5 in slump can be 15 ft.

-Recommended spacing of control/contraction joints with 3 in slump.

Considering the given data with the above parameters the spacing of contraction joint with 3 in slump can be 20 ft.