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RE: Contraction Joints in Bonded Concrete Repairs

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Generally there are no contraction joints in structural concrete unless you 
 need to mimic existing joints.  Contraction joints are an unusual topic. 
Look at almost any horizontal structure, and you do not find contraction 
joints.  You find them on slabs on grade because slabs on grade only have 
“temperature” steel.  There is a lot of rebar in a structural slab (as 
opposed to a slab on grade) and contraction joints are not commonly used. 
Expansion joints are used, but not contraction joints.

Regards, Harold Sprague

> Date: Tue, 8 Jan 2013 14:00:01 -0500
> From: brian.felker(--nospam--at)
> Subject: [SEAINT-SEAOSC] Contraction Joints in Bonded Concrete Repairs
> To: seaint-seaosc(--nospam--at)
> I am designing repairs for an existing deteriorated concrete structure
> consisting of monolithic two-way slab/beam construction. The top side of
> the structure is exhibiting corrosion-related spalling in various
> locations. My plan is to remove the deteriorated concrete, prepare the
> steel and concrete substrates, and place fresh concrete. Sizes and aspect
> ratios of the repair areas vary widely. Repair concrete will be bonded to
> the roughened existing concrete substrate and restrained by embedded
> reinforcement, meaning only the top surface of the repair can move due to
> shrinkage. Unfortunately, I have had difficulty finding definitive
> recommendations on spacings for contraction joints in such a repair. Most
> of the ACI publications address slabs that are cast on a slippery base
> material, such that the top and bottom surfaces of the slab are free from
> significant restraint. Any insights would be much appreciated!
> Thanks,

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