Top-down cracking of rigid pavements constructed with fast-setting hydraulic cement concrete

Test sections of jointed plain concrete pavement were constructed with fast-setting hydraulic cement concrete (FSHCC) as part of the California Department of Transportation accelerated pavement-testing program. Many of the longer slabs cracked under environmental influences before any traffic load was applied to them. Data from field instrumentation were recorded and analyzed along with laboratory test data to determine the cause of the cracking. Cores drilled through the cracks indicated that cracking began at the top of the slabs and propagated downward. This was confirmed with the ILLI-SLAB (ILSL2) finite-element package in which high tensile stresses were predicted at the top of the slab as a result of the differential drying shrinkage between the top and base of the slab and the nonlinear nature of the negative temperature gradients through the slab. Laboratory free-shrinkage tests with the test section concrete indicated significantly higher levels of shrinkage compared with that achieved with ordinary Type II portland cement. Load plus environmental stress analysis with ILSL2 suggested that the critical failure location for the FSHCC pavements would be near the corner of the slab and not at the midslab edge.