Evaluating the Cause of Understrength Concrete During Construction of Multiple Tower Mat Foundations

April 29, 2014
Publication: Proceedings of the Structures Congress 2014, April 3-5, 2014, Boston, MA, ASCE
Author(s): Scott DiFiore Robert Holland

Abstract: A contractor erected multiple reinforced concrete mat foundations over the spring and summer construction season to support large tower structures. Six weeks into the construction, after nearly half of the nineteen foundations were cast, twenty-eight-day compressive strengths for the first several pours showed an alarming rate of below-strength results. The contractor, engineer, and concrete supplier scrambled to determine why the concrete was understrength. Was it the aggregate size? The withholding of trim water? The initial curing process? Testing procedures? As the team investigated and worked to remedy the problem, construction was delayed by nearly two months, which jeopardized the project delivery schedule. This paper describes the analysis of available data to determine what went wrong and how, from the submittal process through placement and cylinder testing.