huangyhg

definition of expansion joint
i was arguing with my fellow engineers (all novices) about the definition and function of expansion joint.he was suggesting that the prime function of the expansion joint is it acts as a temporary separator between two concrete surfaces during construction. to me he was implying that even if there is no filler but an initial gap say 25mm (one inch) is left behind it can still be called an expansion joint . is this correct?
we both agree that expansion joint is provided to allow some movement (expansion of the structure) . i think this is quite obvious.
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essentially, yes this is true. the purpose of the filler is to keep the expansion joint clean and working as deigned.
the problem with leaving out the compressible filler in the joint is that this gap could rapidly fill with non-compressible detritus. this will then prevent the joint from moving and doing the work it was designed to do.
joints termed "expansion joints", in reality, act as contraction joints. they are provided to account for drying-shrinkage in the concrete. rarely does a structure expand due to temperature differential more than it contracts due to drying-shrinkage.
here is my two cent contribution:
in general, an "expansion joint" is just that, it allows movement due to expansion and contraction between adjacent building elements. the joint can be between the same material or different materials, in one structure or the interface between two different structures. since it is designed to move both ways, an expansion joint must be kept clean to allow the movement. if foreign material gets into the joint, it can prevent the intended movement, which can result in cracks appearing in unwanted areas.
for concrete, i generally see two types of joints; a "construction joint" and a "crack control joint". a construction joint is the joint between two pours. a crack control joint is install purposly, in specific locations to make the concrete structure crack at that point.
as an aside, concrete does expand thermally, just look at buckling of a highway pavement! also, there are special, expansive cements that expand during hydration, to counteract the effects of schrinkage.

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