huangyhg

movement joint
hi,
question about movement joints:
what should be the minimal distance between movement joints for the reinforced concrete slab on the ground (thickness-150mm)
thanks
150%-200% of the thermal expansion/contraction distance.
please, what is the thermal expansion/contraction distance of a 150mm-thick reinforced concrete slab?

the thickness is irrelevant,(the joint goes through it), the length and width of the slab are the important dimensions and expansion is roughly 5/8" per 100 degrees f of temperature change per 100 feet of length.
my answer was for width of expansion joint. the spacing can be whatever is convenient.
control joints and construction joints are normally 20-25 times the thickness of the slab, (10 feet to 12.5 feet).
mammut,
i do not agree with the advice given by civilperson to place control or construction joints 10 to 12.5 ft apart. more normal practice is to use in the order of 20 ft or 6 metre spacings. joints are the main problem area for slabs on ground, so more joints is not necessarily better.
expansion joints are not usually required, as natural shrinkage of the concrete provides plenty of space for the concrete to expand into when hot.
i agree that joints are the main problem for gound bearing slabs. the number of construction joints will depend on the casting method, which may also depend on the flatness requirement.
what is your slab for? how do you intend to cast it?
i have previously worked on a 150m x 50m factory floor slab that we cast in 3nr 50 x 50m bays, no expansion joints just 2 construction joints. we achieved a good finish.
==>zambo
i have similar situation: factory floor - 120x40m.
it will be casted in 4 bays -40*30m
mammut,
by what method will you cast the slab? your bay width of 30m means that you cannot span a levelling beam between the side forms. tis means that you will need to use a lazer level and then spot check the concrete level as you proceed.
zambo:
i assume you have reinforcing accross the construction joints. what was your casting sequence - in series, or skip the middle (cast earliest or the last)? did you have saw cut control joints after curing?

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