Communication and concrete slabs

Curing environment
A freezer structure including a reinforced concrete slab placed on rigid insulation was constructed within a warehouse. The slab was scheduled to be placed after completion of the surrounding freezer structure, which incorporated insulated prefabricated walls and roof. The concrete floor was cast during the summer, prior to the refrigeration system being operational. Within the enclosed, insulated space, temperatures became elevated during the concrete curing process, creating improper curing conditions that caused widespread, excessive cracking.

Had the construction team engaged in pre-installation discussions to ensure the installation procedure was understood by all, the unusual curing environment would likely have been identified. Adjustments—such as use of high-temperature concreting practices—could have been implemented to prevent rapid drying and development of plastic shrinkage cracking. 
The distressed slab was removed and a new 
slab installed after the refrigeration system 
was operational and could provide moderated temperatures within the freezer during concrete placement and curing.

This article’s authors have encountered many disputes that arose from unanticipated elevated slab deflections. These problems could likely have been avoided had the construction team communicated more effectively before construction, addressing owner expectations and the limitations of predicting slab deflections. These disputes often involve the construction team’s failure to address the potential differences between the requirements of MasterFormat Division 03–Concrete and Division 09–Finishes for floor flatness and levelness. In some cases, the project documents include provisions to address this potential difference, such as drawing general notes similar to the following:

Slabs have been designed in accordance with ACI deflection limitations. Provide leveling material as necessary prior to finish installation to account for allowable deflection.

While such information is helpful and appears to be all-encompassing, experience shows it may not provide adequate detail to prevent disputes over the scope of remedial floor slab surface treatments. The accuracy of floor slab deflection predictions can vary depending on the type of cast-in-place 
slab used, environmental conditions at the 
time of concrete placement, and numerous 
other variables within the construction process. The entire construction team should engage in discussion of elevated floor deflection issues prior to construction. Acknowledgement by all parties of the difficulties in accurately predicting slab deflections provides a basis for development of reasonable remediation provisions.

Conclusion
Communication amongst the construction team 
is critical to the success of a concrete slab project. As an owner, it is important to retain experienced design professionals and contractors that have previously performed the intended scope of work and understand the local material andconstruction limitations. Although means and methods are ultimately the responsibility of the contractor and typically the main topic of discussion during pre-installation conferences, input from the owner and design professionals is crucial to avoid common pitfalls and ensure the design intent remains intact.

George R. Mulholland, PE, SE, is a senior consulting engineer at Raths, Raths & Johnson, a national engineering, architecture, and forensic consulting practice. He has almost 30 years of experience specializing in the evaluation, investigation, and repair of distressed façades, buildings, and structures. Mulholland’s portfolio has encompassed cast-in-place, precast, and post-tensioned concrete, as well as masonry, steel, and timber structures, with a specialization in parking garages. He can be reached via e-mail at grmulholland@rrj.com.

Joseph Macicak, PE, SE, is a consulting engineer at Raths, Raths & Johnson, and has specialized in the investigation and analysis of structures, materials, and construction components for 16 years. He has applied his skills to field investigation, repair design, management and administration of repair programs, and forensic support services for dispute resolution and development of expert technical opinions. Macicak’s background includes evaluation of stucco, wood framing, and concrete distress, along with the collection and assessment of destructive and nondestructive test data. He can be reached via e-mail at wjmacicak@rrj.com.

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