difference between expansion joint and isolation joint

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    Elizabeth Meyer

    I found a verbal explanation, not much by way of diagram:

    contraction joint is formed, sawed, or tooled groove in a concrete structure to create a weakened plane to regulate the location of cracking resulting from the dimensional change of different parts of the structure.

    An isolation joint is a separation between adjacent sections of a concrete structure to allow relative movement in three directions and through which all of the bonded reinforcement is interrupted.

    An expansion joint in a concrete structure is a separation provided between adjacent sections to allow movement due to dimensional increases and reductions of the adjacent sections and through which some or all of the bonded reinforcement is interrupted. In pavements slabs on ground it is a separation between slabs filled with a compressible filler material.

    construction joint is the interface between concrete placements intentionally created to facilitate construction.

    cold joint is a joint or discontinuity resulting from a delay in placement of sufficient duration to preclude intermingling and bonding of the material, or where mortar or plaster rejoin or meet.

    https://www.concrete.org/tools/frequentlyaskedquestions.aspx?faqid=864 accessed 10/6/2020

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    shay bond (Edited )

    Thanks for the feedback, I asked because there are sources like hyperfine that consider them the same and there are other sources that consider them as different

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    Elizabeth Meyer

    My understanding is they are different. I came across some more definitions in my notes (unfortunately I did not cite a source on my index card).

    Isolation joints - provide a separation between a slab on grade and columns or walls, so that each can move independently.

    Expansion joints - are designed to allow free movement of adjacent parts due to expansion or contraction of the concrete. This movement may be caused by shrinkage or changes  in temperature. Expansion joints provide complete separation through a structure, from the top of the footings to the roof. They are waterproof, weather tight, and generally filled with an elastic joint filler. The placement and  size of the building and the maximum expected temperature differential. Expansion joints are required in buildings more than 200 ft long, at joints of building wings, and at additions to existing buildings.

    They are very similar. Hope this helps; I know I am regurgitating information, but wanted to provide thorough definition.

    Best, Liz 

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    shay bond

    Thanks, so can an isolation joint be used to separate two buildings. eg an addition to an existing? I came across that question which is what got me confused in the first place. The answer was an isolation joint is the joint used to separate an existing building from an addition and I got the question wrong, because I selected expansion joint.

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    Elizabeth Meyer

    Hmm, I would have used the same logic as you. I think you had the right answer. What platform are you using for questions?

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    shay bond

    I can't remember which platform exactly but it looks like it is either Tryweare, ARE exam prep or hyperfine. My guess is the question was somewhere in the first two platforms.

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    Aleksandar Stojkovic

    The description on the American Concrete Institute website isn't that bad. I would add that: 

    Contraction joints are also referred to as "control joints" as they are intended to control where cracking occurs during concrete drying ("intentionally weakened sections created through the concrete slab where the tensile forces caused by concrete drying shrinkage are relieved")

    Fundamentals of Building Construction state that "isolation joints" are the same thing as "expansion joints." I think it's important to know that isolation joint (as opposed to control joints) is a full-depth separation. I think even a seismic joint may be referred to as an "isolation joint."

    So Shay, I think you stumbled upon a poorly worded question from these "ARE prep" platforms.

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