Recycled plastic spheres replace concrete in sustainability tour de force

Make better use of plastic recylate, reduce weight and carbon emissions during shipping, and reduce the time and energy required during construction: these are some of the sustainable highlights realized by a new blowmolded application that makes use of the skills of plastics processor Meredith-Springfield. 

The processor's work is part of a project tapping into a patented building and construction technology that may help builders reduce the weight of concrete slabs by 30-40%. Making it happen are extrusion blowmolder Meredith-Springfield Associates Inc. (Ludlow, MA), which has been tasked by neighboring firm Barker Steel LLC (Milford, MA) to supply plastic blowmolded spheres, about the size of a volleyball, for use inside a Cobiax voided concrete system. Barker is the U.S. distributor of structures made using the patented Cobiax procedure, which was developed by a Swiss company. In such structures, plastic spheres are set into steel wire cages, which are then used as reinforcement for concrete structures.

The U.S. partners have a concrete project in the works. Next month, thousands of Meredith-Springfield plastics spheres, made from plastics recyclate, will be set into steel wire cages at Barker Steel for subsequent shipping in tower crane-ready bundles for use in concrete slabs in new building construction. One of those buildings will be the brand-new Miami Art Museum (MAM). For the MAM project, the spheres are sized 225mm and 270 mm. The Cobiax productline calls for 13 different sizes of spheres, depending on the thickness of the concrete slabs.

How does a blowmolder get involved in such a project? Barker let its fingers do the walking, explained Mel O'Leary Jr., president and CEO at Meredith-Springfield, in answer to our questions. As he relates it, "Barker Steel, having no plastic industry connections, basically opened the phone book and started calling people. We got to a short list of four potential vendors: us and another in Massachusetts, and one in Connecticut and one in New Jersey. After touring our facility they determined that our core competencies and geography would be the bestmatch for them and the Cobiax product line." 

With Cobiax building units, the building slabs are up to 35% lighter than solid flat concrete slabs, and present up to 15% less load on foundations, which allows for increased design freedom. "This type of building system also allows for up to 20-meter spans with no obstructing beams, which amounts to 40% less columns," says O'Leary. "By using spherical resin products, strategically encased in concrete with reinforcing steel, one can leave out as much concrete as possible while maintaining the full flexural strength of the slab and allowing a bi-axial load transfer. The result is overall weight reduction, increased seismic performance, cost reduction, and environmental sustainability." 

The new $220 million MAM, which will be three times as large as the existing building, is being designed with the goal of achieving LEED Silver (Leadership in Environment and Energy Efficient Design) certification. For the MAM spheres, the material being blowmolded for the spheres is a 100% post-industrial HDPE copolymer which has been re-pelletized, explained O'Leary. He said the plastic had to be post-industrial or post-consumer scrap to meet certain qualifications for the LEEDS certification. "One of the challenges is sourcing enough scrap having the correct properties," he added and said that, in the end, the material costs as much as virgin HDPE would have cost.