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concrete slab on grade expansion joint questions
i am in the process of designing the joint pattern for a manufacturing building.
i have located the control joints and construction joints and i am now considering whether to include an expansion joint. right now the reinforcing (heavy mesh for the 6" slab) in the slab stop at the construction joints.
generally, the slab is 6" thick, 80 feet wide, and 800 feet long. i say generally, because there is a 8" thick slab strip that is 450 feet long and 15 feet wide also.
there are the usual traffic aisles, manufacturing aisles, platforms, racks, crane columns, utility trenches scattered throughout the structure.
the building will be heated in the winter with no cooling in the summer.
the slab will be poured in the summer when the building is enclosed. possible temperature at time of pour could be in the range of 80-100 degrees fahrenheit.
questions
1. is there a way to estimate the drying shrinkage of a slab?
2. would you include an expansion joint(s)?
expansion joints are common in outdoor slabs, but are not so common in interior slabs. the temerature range is not that wide.
for most concretes, shrinkage after two years is between 500 and 700 millionths. the commonly accepted values are "low shrinkage" 0.0005 inches per inch; "medium shrinkage" 0.0006 inches per inch; "high shrinkage" .0007 inches per inch.
many factors affect the degree of shrinkage, such as slump, temperature, time period of haul in mixer, number of revolutions at mixing speed, cement type used, aggregate size, aggregate quality and the use of admixtures.
pca recommendation for joint spacing of a 6" slab is between 12 and 15 feet for a slump ranging between 4-6 inches respectively, and 18 feet for a slump less than 4 inches.
thank you for the shrinkage information.
i am okay with the joint spacing.
my main question is whether to include an expansion joint or not.
some additional information concerning possible temperature swings. project is located in the central plains of the us. building will be heated during the coldest months. building will not be cooled. high temperatures in the summer can get to 100 degrees fahrenheit and range from 80-100.
will building have an expansion joint? if so, then i would recommend a slab ej at that location.
building is a pre-engineered metal building with 3 expansion joints.
the location of the building expansion joints is not really condusive for the slab expansnion joints because of equipemnt and factory operations.
if you building has expansion joints i would consider them in the slab. however, i don't think they are required.
building expansion joints and slab expansion joints are not going to be at the same location.
not anyway possible because of factory operations and equipment lay-out.
is your slab directly attached to your building? i don't think it will be of any importance to match your expansion joints. in my opinion building expansion joints and slab expansion joints address different issues. you will find that there is not much good documented information on slab-on-grade construction. it is much more of an art than a science.
we always include an ample amount of construction joints/control joints so that we don't need an expansion joint. unless they plan on pouring the entire slab at once (which won't happen) you will have quasi-expansion joints everywhere.
hopefully this document will help you decide.

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