The first time J.B. Sack saw Greencraft insulated tilt-up panels was when his crew arrived at the jobsite to cast them. Sack is manager of business development for family-owned T&T Construction based in Casselberry, Fla. The contractor, which specializes in tilt-up, concrete, and masonry, was hired to enclose an emergency generator at a Sprint call center in Altamonte Springs, Fla., north of Orlando.
To meet the local noise ordinance, a noise transmission consultant recommended installing a 23-foot-tall, 4-inch-thick concrete barrier around the generator. The open structure also had to withstand a 125-mph wind load to meet the Florida Building Code requirement for hurricane-resistant design.
Sprint investigated different wall systems, including reinforced concrete block, which was too thick and heavy, and highway sound barriers, which could only be built up to 16 feet high. Unable to find a cost-effective option, Sprint’s project manager contacted Greencraft LLC, an Atlanta-based manufacturer of composite insulated concrete forms for tilt-up and precast walls.
Greencraft’s patented iCast tilt-up panels offered a thinner, lightweight option that could meet both the structural and acoustic requirements. iCast tilt-up panels are cast on a composite foam insulation panel, either as a flat slab or with reinforcing elements. When cured, the concrete slab is mechanically and adhesively attached to the composite insulated foam iBoard, eliminating thermal bridges.
The insulating panel and reinforcing mesh is secured to the panel’s exterior surface by anchors that double as rebar chairs for the concrete slab. For the Sprint job, the mesh was embedded in an elastomeric sound membrane.
Greencraft designed a reinforced iCast panel with a 4-inch concrete slab cast on 4-inch continuous insulation. Three-inch-deep channels in the insulation form 7-inch reinforcing concrete ribs. The ribs effectively distribute the panels’ weight and structural stresses while using minimal materials. Reinforced iCast panels use up to 40% less concrete and 30% less steel reinforcement than flat slab tilt-up panels.
Sack expected to begin construction by framing and pouring a concrete casting bed for the three tilt-up panels: two 23 feet tall by 22 feet wide, and one 23 feet tall by 24 feet wide. However, the iBoard’s 4-inch layer of foam provided a forgiving surface to help keep concrete level when the panel was poured.
The contractor made level wooden frames in the facility’s asphalt parking lot and filled them with sand. The sand was manually compacted and topped with plywood to create a flat casting surface.
Workers placed the iBoard in 4- by 12-foot sections, with its insulating foam aligned to form the reinforcing concrete channels, 8 feet apart within each wall panel. Although the iCast design differs from insulated sandwich panels, it did not require extensive jobsite training. “There was some attention to detail in placing the insulation material correctly, but the system was user-friendly,” says Sack.
The crew placed a #4 gauge steel rebar cage in the panel’s interior ribs and #3 rebar on top of the insulating foam, 12 inches on center each way, to reinforce the 4-inch continuous concrete slab.
With less concrete and lighter rebar, the finished iCast panel was 30% lighter than an 8-inch conventional panel of the same size. T&T often produces larger, much heavier tilt-up panels that require crawler cranes on tracks, costing up to $25,000. For the Sprint job, they used a mobile hydraulic crane for about $3,000.