SUPERVALU concluded the site that was once occupied by a depression era poor farm and a county maintenance facility in Hopkins, Minnesota was the preferred location for their new 579,000 square foot grocery warehouse and distribution center.

The new facility would be a mostly automated, state-of-the-art distribution center designed with maximum efficiency, safety, and utilization. Braun Intertec partnered with SUPERVALU, Planmark and Ryan Companies to develop an environmental evaluation program, a geotechnical evaluation program and a construction testing program that would define and evaluate concerns and solutions related to the past use of the site, preparation of the site for construction and finally specific construction concerns of SUPERVALU.

Challenges

The site presented many challenging, but not insurmountable, environmental issues that needed to be addressed as part of this redevelopment project. Clearly, the effects of having a county maintenance facility on site for many years presented the normal issues related to use of petroleum type products. Building demolition needed to address issues associated with construction of the 1960’s and ’70’s. In addition, concerns related to any remnants of when the site was used as the area pour farm had to be addressed because records indicated that a cemetery had been located on the property.

The new construction generally consisted of a large box building with delivery building docks on one side and distribution loading docks on the other. The geotechnical evaluation indicated the removal and replacement of zones of unsuitable fill and other unsuitable areas needed to be addressed as part of the grading operation. In addition, new fill needed to be placed to support the elevated floor slab. This part of the construction was pretty typical.

Inside the warehouse, high stack shelving and the use of automated forklift traffic were planned. To achieve this plan, the floor slab needed to be super flat to keep the shelves plumb and the slab poured in larger than normal sections so that construction joints, control joints and after placement cracking could be minimized. A reduced number of construction or control joins was desired because of issues associated with erosion distress caused by the hard tired fork lifts as they crossed the joints and the great expense of maintaining the joints.

Solutions

To address the environmental issues, Braun Intertec conducted a Phase I Environmental Site Assessment (ESA) to identify areas of possible concern and also a Phase II ESA to further evaluate issues that were identified as part of the Phase I ESA. A detailed construction response action plan was prepared as a follow up to the Phase II ESA. The overall time frame for Phase I and II studies and the recommended remediation was a very fast five months, with most of the remediation occurring simultaneously with the first three months of demolition and grading activities at the site.

Braun Intertec was also asked to develop and implement a plan to minimize joints, cracking and curling of the ground-supported slab concrete. After reviewing many options, the use of a highly compacted granular subgrade, a highly compacted Class 5 aggregate base and a shrinkage compensating concrete to serve as the floor slab system was recommended and selected for design and construction. This was done knowing the use of shrinkage compensation concrete would present challenges of its own.

The granular subgrade and Class 5 aggregate base provided the stability needed below the floor slab to allow for the fine grading needed to install the concrete and the stability needed to allow for the laser-guided concrete placement machines to successful place the desired super flat slab.

For the shrinkage compensating concrete to meet the expectations of the design and construction team, the properties of the cement needed to be defined and monitored, and the performance criteria of the concrete mixture needed to be defined and monitored so that the expansion occurred within the defined limits or the benefits of using this mixture would be negated. To establish the required parameters and to monitor the performance, Braun Intertec engineers developed and implemented an innovative and aggressive quality control and quality assurance plan. This plan consisted of:

• Testing of each load of cement delivered to the batch plant for use on the project
• Periodically testing of the fine and coarse aggregates
• Extensive trial batching of the proposed mixes
• Expansion jar testing in the field to monitor the short-term expansive potential
• Conducting the normal testing on the fresh concrete
• Casting expansion bars for long-term expansive potential
• Monitoring each slab placement for flatness, curing procedures and post placement shrinkage

The performance of the concrete slab exceeded the expectations of the owner and design team. The field-testing procedures developed for the project and the results were submitted to the American Concrete Institute committee developing standards for testing shrinkage compensating concrete, as none were available at the time of this project. With the success of the project, the American Consulting Engineers Council of Minnesota (ACEC/MN) awarded this project a "Grand Award" for the use of a non-typical floor slab concrete and an innovative testing program.