Concrete Distress Resulting from Embedded Waterstop

An investigation was undertaken to determine the cause of on-going spalling concrete at the floor level construction joints of exposed exterior concrete columns in a recently constructed high-rise building on the east coast. A black substance was typically observed behind each spall location. Background research indicated that a hydrophilic waterstop strip was specified to be cast into the construction joints at the floor lines of the columns to prevent water infiltration into the building. A review of the waterstop manufacturer’s product literature did not provide information regarding water absorption characteristics, force generation of confined saturated waterstop material, or how the waterstop behaved when subjected to freezing temperatures while in a saturated condition. This investigation included a series of laboratory tests to determine physical properties and anticipated force generation of saturated water stop as well as a limited structural analysis to determine if the waterstop alone could be responsible for the observed distress. The investigation concluded that under certain conditions, expansion of embedded waterstop can exert enough pressure to cause spalling of surrounding concrete.