Concrete Paving

[martin888888]

Have a generic question on the basic design of concrete pavement. I have seen large concrete slabs designed with just call outs for the boundary of the slab, and then I have seen slabs designed showing 20'x20' construction joints. I dont think they would ever pour a 200'x200' slab and every applicaton would have construction joints. Anyone have any imput into what the proper way to show this would be or the application of construcion joints in concrete pavement construction.

The application I am talking about in this case is an industrial yard.

Thanks

 

[fel3]

If CJs were not shown on the plans, they should have been convered in the details, with a note, and/or in the specs.

==========
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[Ron]

In general, a rule of thumb for control joint spacing is 24 to 36 times the slab thickness. In my opinion, the spacing should not exceed 15 feet in any direction and the ratio of length to width should not exceed 1.2:1.

 

[cvg]

http://www.pavementinteractive.org/category/pavement/pavement-types/rigid-pavement-types/

 

[GoldDredger]

In Texas it is fairly common to have Portland Cement Concrete (PCC) for roadway and parking lot pavement. For an industrial yard I would guess your concrete pavement will be about 6 or 7 inches thick with #4 spaced 12 or 18 inches on center.

We typically specify two types of joints, one is a sawed joint and the other an expansion joint. The sawed joints are both longitudinal and transverse directions on the slab, and we generally require a spacing no greater than 15-feet. A saw joint is is 1/8 to 1/4 inch thick, to a depth of D/4 of slab thickness.

An expansion joint is where two separate slabs of concrete meet, and are separated by a 1-inch redwood expansion board, with the top 1/2 inch filled with a joint sealant. We prefer a cold application silicon over a hot poured seal. The two slabs are connected by a smooth #6 dowel at 12" on center. They have a 6-8inch overlap with the slab reinforcement. The maximum spacing between expansion we use is 45-feet.

Nothing wrong with requiring the contractor to submit a joint spacing plan for your review either.

 

[dik]

Concrete slump and timing of sawcut is also critical...

Dik

 

[cnstengineer]

Dik is right. The timing of the sawcuts is critical so that you don't get any cracking as the concrete hardens.

 

[dik]

Golddredger... 45' between joints is a tad too much... as Ron noted, the 45' should be cut into 3 equal spaces...

Your use of wood strips brings back some history... one of my first SOG's I used plywood joints... and reasoned that the concrete would shrink away and you would be able to easily pull the plywood strips out after all the shrinkage had taken place... if the buildings are in existance still... the plywood strips are likely still there!

Dik

 

[cvg]

45 between exp jts on fully reinforced pavement is not unusual, the sawed jts are at 15.

 

[dik]

Thanks for the clarification...

Dik

 

[martin888888]

What is the downside of going bigger, say 25' between construction joints?

 

[dicksewerrat]

more cracks

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[cvg]

I don't think we were discussing construction joints. sawcuts for shrinkage crack control and expansion joints for control of expansion. construction joints should only be constructed as necessary. suggest going back on pavement interactive and you can get a better understanding of the types of joints and why they are necessary.

types of joints

http://www.pavementinteractive.org/article/joints/

 

[martin888888]

The term construction joint and contraction joint are used interchangeably. Same thing

 

[cvg]

nope, definitely not the same thing

 

[emmgjld]

"The term construction joint and contraction joint are used interchangeably. Same thing"
Only the same when the construction sequence produces (by accident or possibly purposeful) the same spacing. Don't count on it and the terminology MUST be clarified.

"What is the downside of going bigger, say 25' between construction joints?" Depends upon the reinforcement. Usually UGLY cracking.

 

[bank]

Construction joints and contraction joints are definitely not the same thing. Construction joints are placed at starting and stopping points where the concrete pour is interrupted for some reason (e.g., end of shift, equipment breakdown, etc). They are are formed using a bulkhead made of steel, wood, or more recently, plastic. Construction joints are NOT used to control cracking.

ACI 330r recommends contraction joint spacing at 25 to 30 times the pavement thickness, up to a maximum of 15 feet. In my office we usually provide a paving plan for parking lots that includes contraction and expansion joints with dimensions. Expansion joints are placed at a maximum spacing of 60 feet, with contraction joints evenly spaced between them. We don't usually show construction joints, since starting and stopping of the concrete pour is usually governed by field conditions or schedule.

 

[martin888888]

thanks. One basic question....if you had something like a concrete loading dock with a width of 42' is it best to evenly space the joints or put them at 15' apart?

 

[GoldDredger]

You'd want to space them evenly at increments equal to or lesser than 15-feet. In the loading dock case of 42-foot width, you would space them at 14-feet. Edge, 14-ft, joint, 14-ft, joint, 14-ft, edge.

 

[martin888888]

Stupid question but, what is the main reasoning for having loading docks concrete? Is it just the durability of ridgid pavment as when trucks sit there they will tend to rut an asphalt surface