United States Department of Transportation
i
Dimensional stability of concrete slabs on grade.
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2012-10-01
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[PDF-11.38 MB]
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Abstract:Drying shrinkage is one of the major causes of cracking in concrete slabs on grade. The moisture
difference between the top and bottom surface of the slabs causes a dimensional or “shrinkage” gradient
to develop through the depth of the slabs. This can cause cracks and warping which result in
serviceability and performance problems for concrete slabs on grade. There have been numerous
analytical and experimental investigations to characterize drying shrinkage as a material property.
However, there have not been significant improvements in terms of validation and calibration to provide
engineers with a reliable evaluation of the strains and stresses within a concrete element subjected to
moisture gradients and restrained shrinkage.
This test program characterizes the dimensional properties of selected concrete materials,
evaluating their performance as real slabs-on-grade in that they are exposed to ground moisture on the
bottom surface and drying conditions on the top surface. The concrete mix designs examined included
low and high strength concrete (PCC and HPC), typical Portland concrete using two common types of
shrinkage reducing admixtures (PCC+SRA), and type K, shrinkage compensated concrete which uses
Calcium sulfoaluminate cement (CSA). The data includes standard concrete material characterization
tests, joint opening measurements, internal relative humidity and temperature in ½ in. increments through
the depth of the slab, prism tests and compression test results. It was found that type K, shrinkage
compensated concrete is very stable, with no long term shrinkage, cracking or warping while typical PCC
and HPC continue to show crack growth at over 600 days of age. Shrinkage Reducing Admixtures have a
minor impact at early age but do not impact long term sectional stability. The SRA concrete exhibited
shrinkage, cracking and warping nearly similar to typical PCC but slightly better than HPC.
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