Replies

1. GBA Editor
   Martin Holladay | May 05, 2015 09:05am | #1

   Sural,
   This type of construction system has been around for years, but is rarely used in the U.S. because of its high cost. The 3D system uses EPS panels covered on both sides with welded-wire mesh; once erected on the job site, they are finished on both sides with concrete -- usually 1.5 to 3 inches of shotcrete or gunite (that is, a special concrete mix that is applied by a equipment that propels the concrete at a high velocity).

   The finished building is relatively airtight, and therefore can be energy-efficient. Like all concrete buildings, these buildings are durable and resist storm damage. But they are expensive.

   In India, you will need shotcrete equipment, or will have to modify the usual method of construction used in the U.S., and apply the concrete with a trowel.

   I wrote an article on the construction system for the April 2004 issue of Energy Design Update. In part, here is what I wrote:

   "Two manufacturers, 3-D Panel and Hadrian TriDi Systems, produce wall panels incorporating a polystyrene core sandwiched between two layers of welded-wire mesh. Once the panels are erected on site, they are coated inside and out with shotcrete.

   "Hadrian TriDi Systems and 3-D Panel produce similar wall panels. Both companies manufacture their panels using machinery made by Entwicklungs Verwertungs Gesellschaft (EVG), the Austrian company that developed the wall system. Located in Brunswick, Georgia, 3-D Panel was formerly known as Insteel Construction System (see EDU, January 1992 and November 1992). Although Hadrian TriDi Systems operates out of Vista, California, its production plant is in Mexicali, Mexico.

   "Most 3-D panels have a core of polystyrene with a density of 1 pound per cubic foot, although customers interested in higher R-values can order panels with polyisocyanurate cores. Panels can be manufactured with foam cores ranging in thickness from 2 to 6 inches, with 4 inches being typical. Panel width is always 4 feet, and most panels are between 8 feet and 25 feet long. (Panels as long as 40 feet can be manufactured.) Since panels are installed vertically, the desired ceiling height determines the length of the panel needed. The walls of multistory buildings are continuous; for example, a one-story house with a basement usually requires 18-foot-long panels.

   "At the factory, the polystyrene core is sandwiched between two layers of 11-gauge 2” by 2” welded-wire steel mesh. The mesh layers are connected by a series of steel or plastic connectors that pierce the polystyrene, creating a three-dimensional cage with the foam at the center; the mesh stands about 3/4 inch proud of the foam. While Hadrian TriDi Systems uses steel connectors, 3-D Panel uses plastic connectors to reduce thermal bridging.

   "The wall panels are erected on a concrete footing or slab. The manufacturer specifies that vertical #3 rebar stubs, 24 inches on center, should protrude about 16 inches out of the concrete along all of the exterior walls. The panels are relatively light, and are usually lifted by hand over the rebar stubs, which fit between the polystyrene core and one of the layers of mesh (see Figure 1). Once plumb, the panels are secured with temporary diagonal braces. Seams between panels are then covered with strips of 2” by 2” splicing mesh; when installed at inside or outside corners, the strips of splicing mesh include a 90-degree bend.

   "Window and door openings are cut on site, using bolt cutters or a reciprocating saw to cut the mesh, and a handsaw to cut the foam. Typically, pressure-treated lumber frames are set in the window rough openings before shotcrete is sprayed (see Figure 2). Window headers narrower than 6 feet usually require no rebar reinforcement.

   "Electrical conduit and electrical boxes need to be installed before the walls are coated with shotcrete. To make room for the conduit, a propane torch is used to melt channels in the polystyrene.

   "Once the panels are plumb and braced and conduit has been installed, the mesh on both sides of the panels is coated with a 1 1/2-inch to 3-inch thick layer of shotcrete or gunite, with or without plastic fiber reinforcement. (While shotcrete is pumped wet, gunite is pumped dry, with water mixed at the nozzle.) Typically a 2,500 psi concrete is specified (see Figure 3).

   "In remote areas without access to shotcrete equipment, the concrete may be hand-troweled onto the 3-D panels. Like ICFs, 3-D panels can be used below grade; like SIPs, the panels can be used for roofs, although most 3-D buildings include conventional truss roofs. The maximum pitch for a 3-D panel roof is about 4 in 12. Roof panels are temporarily supported with purlins and shoring until the underside of the roof can be coated with shotcrete, and the concrete roof deck can be poured."

2. 
   kaulsuraj | May 06, 2015 02:31am | #2

   Dear Martin
   Thank you for your valuable information. however I am still not able to fully understand why this technology is being termed as cost effective by African countries who are already using this technology.

3. GBA Editor
   Martin Holladay | May 06, 2015 04:21am | #3

   Sural,
   Cost-effectiveness depends on available alternatives. It's possible that alternatives used in the U.S. -- for example, framing lumber -- are more expensive in some African countries than in the U.S. For example, I imagine that framing lumber isn't very cheap in Mali or Sudan.

4. Expert Member
   Dana Dorsett | May 06, 2015 05:17pm | #4

   The generic term for this type of construction goes by the acronym "SCIP" , for "Structural Concrete Insulated Panels". A web search "SCIP" with the "concrete" as a second search term will find dozens of manufacturers and many industry articles in several countries.

   It is more expensive than building with cemeticious mud or concrete blocks, but is far more resilient to hurricanes / typoons or earthquake forces due to fact that it is a steel reinforced concrete monocoque, and it takes less cement than many other resilient walls. The thermal insulation characteristics of the EPS core gives it comparable or better thermal performance in tropical areas as more thermally massive mud/stone construction. The cost and availability of cement and concrete mixing equipment can make SCIP more economic than more massive poured concrete walls in some areas.

   It doesn't take expensive shot-crete equipment to build with SCIP. With small aggregate mixes it can be applied with lighter duty stucco / mortar spraying tools (see http://www.mortarsprayer.com/diy-shotcrete/ ) or it can be troweled on by hand, no power equipment necessary. Hand application is expensive in high labor-cost countries, much less so in poorer regions. In the US construction labor costs many times what it does in most of Africa, making cheaper to heavier duty concrete sprayers (though still more expensive than some other common types of construction here.)

   Buildings that are more than one story with SCIP is possible, but the specifications of the concrete & steel reinforcements and how the walls/floors/roofs tie together become more important as the amount of weight it as to support grows. In the US it is still not common enough that code officials are often uncomfortable with it unless the design specifications have been verified by an independent structural engineer, which adds to the cost of construction.

5. 
   kaulsuraj | May 07, 2015 08:29am | #5

   Dear Dana
   Thank you for your valuable information on the use of alternate tools for shotcrete. Kindly help me with other alternate tools or techniques to make it more cost effective. Also, during my research i got to know that a couple of companies that provide machines that manufacture EPS Panels namely Schnell and Emmedue, however would you know of any other company that provides EPS manufacturing machines.