No Epansion joints 1

[Allan2000]

Future project to build 1000 ft x 300ft x 10inch thick structural slab supported on 2000 piles. ACI recommendation is to place expansion joints every 200ft - 250 ft. Can we build the slab without Expansion joints but with several Construction joints which contain shear keys and rebars across, and with controllable pour sizes and checkerboard pour system, with 14 days time delay between adjacent pours, without experiencing significant shrinkage cracks???????????

Allan

 

[ishvaaag]

Feasible to some extent should be since airports (thicker slabs) longer than that are built.

The target is to force adequate separation between cracks and their size.

Give a look to the publication + software

Design of Continuously Reinforced Concrete pavement ofr AIrports

CRC-AIRPAVE

Sold as a unit by CRSI.

(There's other for Highways CRC-Highway Pave)

In any case, the checker boarding may be is not as good idea this time since the built units could act as prefixed joints to be later apparent.

 

[emmgjld]

I would also suggest looking into details of concrete placement/sequencing for large 'superflat' industrial slabs.

My own experience is that long and narrow slabs will perform better than a 'checkerboard' placement pattern. I strongly recommend the careful reading of ACI 360R-92(97) (Guide for Design of Slabs on Grade), Note Chapter 9, Reducing the effects of Slab Shrinkage and Curling.

I tend to discourage 'rebars' crossing the joints as I have seen significant cracking (parallel to and 2' to 4' away from the joint) of the old and new slabs due to restraint of the shrinkage of the adjoining slabs. I usually prefer proper dowelling to allow shrinkage movement but, your application may not allow such. The 14 days (or more) delay between adjoining pours is good and may be sufficient to minimize craking to an acceptable amount.

 

[Ron]

Agree with ishvaag and emmgjld....
Keep in mind that concrete is rarely any larger (volumetrically) than immediately after placement. Rarely is there a need for true "expansion" joints. Total shrinkage in concrete is almost always greater than any thermal or moisture expansion potential.

You don't give your location, but there are a few area where environmental conditions coupled with placement conditions can give you a problem. An example is placement of the concrete at relatively low temperatures (40F or so), then getting high temps of greater than 100-110F on the concrete itself at some time later. This can cause problems in long, narrow strip placements.