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Steel and concrete have been the dominant materials for structural uses for the last hundred years, with the addition in multistory construction over the last 30 years of glulam and cross-laminated timber. But as ongoing labor shortages and volatile markets for both structural steel and concrete continue to hamper estimators’ attempts to keep costs down, a Florida-based company is putting together an alternative building system, block by glass fiber-reinforced block.

Renco USA is manufacturing a patented mineral composite, fiber-reinforced (MCFR) building system that uses blocks that interlock like Lego bricks to create everything from structural walls to floors and roofs. The construction materials—which are a combination of recycled glass fibers, resin and naturally occurring calcium compounds—are manufactured in Renco’s Jupiter, Fla., manufacturing facility using a process similar to injection molding. This approach lets the company form the material into any shape necessary, from building blocks for walls that lock together, to roof beams, joists and floor decking that connect in similar ways. What fuses the MCFR pieces together is a methyl methacrylate bonding agent, similar to that already used for aerospace, marine and large truck connections. No heavy cutting, welding or masonry work is needed, and trade contractors installing mechanical, electrical and plumbing equipment can use the same methods as in conventional concrete or steel construction to hang conduit and install ducts, piping, wiring or junction boxes.

The 3D model of Renco USA’s Lakewood Road project shows each MCRF brick, deck piece and roofing joist, and is color coded to show the construction sequence and which piece goes where.
3D Model courtesy of Renco USA Inc.

Photo courtesy of Renco USA Inc

Importantly, once it has been molded into blocks or other shapes, MCFR performs well. Extensive testing of the relatively lightweight material has shown it to be exceptionally strong, while also exhibiting other properties indicative of long-term durability.

Renco has further tested its product by constructing a variety of prototype structures in other countries, including Turkey, where the material was initially fabricated. Now, Renco is putting its product to the test in the U.S. via a $21-million, four-building multifamily project now nearing completion in Palm Springs, Fla., near West Palm Beach. Construction of the 96-unit development is being managed by Coastal Construction. Renco co-founder Tom Murphy, Jr., is also founder, chairman and CEO of Coastal Construction Group, which ranked 169th on ENR’s 2023 Top 400 Contractors list. Miami-based architectural firm Arquitectonica designed the project.

The project’s construction—or, to be more precise, its assembly—has required a crew of only about 11 workers with varying levels of skill and experience to erect the three-story buildings using only the manufactured materials and its proprietary adhesive.

Glue guns to apply the adhesive and rubber mallets to hammer in the interlocking blocks are the only tools necessary, and with no need for heavy equipment such as cranes and lifts, the site was quiet compared to typical jobsites, Murphy told ENR during a visit to the nearly complete project in early August.

Placement of the buildings’ floor slabs—which are bolted to the wall system—by concrete supplier Cemex via concrete contractor Woodland Tilt-up, provided the most noticeable noise levels during the erection of the buildings, the project team says. All of the excess building materials were taken back to Renco’s manufacturing facility to be remelted and reused on future projects.

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Renco USA’s mineral composite, fiber-reinforced wall, floor and roof sections (below) are manufactured in a process similar to injection molding in the company’s facility in Jupiter, Fla. These steel molds form the blocks and decks from raw materials such as recycled crushed glass. Connections (above) were seismically tested to failure and revealed elastic but strong bonds within the overall building system.
Photos courtesy Renco USA Inc.

All-New Building Material

“We worked on this [system] for more than 10 years,” Murphy tells ENR. “We had to keep changing it to make it better and easier to work with,” he says. “As we did that, making a building with it got faster and easier, and … the building got stronger each time.”

Murphy adds that because workers don’t require any specialized training—the MCFR system uses color-coded plans and 3D models of the interlocking system that new workers can easily follow—the system is an economical choice for the contractor from a labor perspective as well as in terms of tools and materials.

To determine the product’s flexural strength under wind, a test lab shot a wood 2x4 going 55 mph at a Renco wall. After surviving the missile test, the design load was estimated to be able to withstand winds of up to 275 mph.
Photo courtesy Renco USA Inc.

Renco USA’s MCFR system qualifies for LEED points for its recycled content, is rated to withstand winds up to approximately 275 mph, and its blocks, joists, decking and adhesives have passed tests in ANSI-certified laboratories for structural performance, physical characteristics and fire resistance. Because of the resin in its composition, the MCFR material wicks moisture away rather than absorbs it. When the material was tested for insect infestation, a terrarium filled with one of Renco’s components along with one queen termite and 99 males turned into an untouched block and 100 dead termites a month later.

On Aug. 8, Renco closed a first round of financing by issuing $18 million in convertible notes, valuing the company at $318 million. That milestone, along with the Palm Springs project and the company’s Jupiter manufacturing facility, was only possible due to work that began over a decade ago.

The starting point in the firm’s development came about 13 years ago, when Renco co-founder Engin Yesil—whom Murphy knew as a Miami social acquaintance for several years—approached the contractor with his idea for an interlocking block system for construction. Within months of the two men discussing the idea, Yesil had provided Murphy with digital and physical models of a potential interlocking block system.

One of Murphy’s first hires was Renco USA president Kenneth Smuts, a former Coastal Construction executive and real estate executive with the Related Group in Miami prior to that. With multiple engineering degrees, Smuts immediately got to work on what would eventually become a barrage of more than 400 tests to get the product accepted into the International Building Code.

“[Pursuing the testing and certification] was a throwback to my education and training as an engineer,” Smuts said. More than a decade of testing and refinement of the system had Smuts “traveling around the country and working through all these different organizations,” he says.

Smuts adds that dozens of product tests were performed, in four directions, in order to find any possible weak spots. “The material tests alone were a little over 100,” he estimates.

The Renco floor-ceiling assembly containing an MCFR load-bearing floor system met the conditions of acceptance outlined in ASTM E119 for a total of 60 minutes. The test took place at Intertek in Texas.
Photos courtesy Renco USA Inc.

Looking Beyond Construction

Finding an adhesive that would sufficiently connect the system’s various components proved vexing.“It took us 20 different adhesives,” Smuts says. One suggestion offered to Smuts and Murphy was to use an acceptance criteria-approved adhesive such as those in structural insulated panels, but that wasn’t what eventually worked. Looking beyond construction, Murphy read up on marine, trucking and aviation connection adhesives. “We ended up working through the aviation, marine and truck-building industries, and came up with this methyl methacrylate adhesive that works exceedingly well,” Smuts adds.

William O’Donnell, managing principal for DeSimone Consulting Engineers’ Miami and San Francisco offices, helped Smuts and Murphy come to the decision to use the methyl methacrylate adhesive. O’Donnell served as engineer of record as the Renco team took the product’s development—including the more than 400 tests and numerous adjustments—to its final design and production.

Crews can assemble walls using Renco USA blocks that are installed with mallets and a two-part adhesive that fuses the blocks together. This project in Palm Springs, Fla., will provide affordable housing stock for the area.
Photos courtesy of Renco USA

The engineer says the exercise in designing a building material and an all-new building system “was intellectually very interesting.” O’Donnell wondered, for example, “‘What’s this building going to be like? What is this going to feel like when you’re in the building? Does it feel like you’re in a plastic building?’”

Once inside one of the completed Palm Springs buildings, O’Donnell says the structure “is solid as the day is long,” and described it as “a chemically welded exterior bearing wall system that is incredibly strong. And the pultruded Renco joists and the pultruded deck also are incredibly strong.”

O’Donnell notes that the team discovered during testing that the system’s use of the methyl methacrylate adhesive to connect the building’s structural elements actually makes the walls essentially monolithic. Smuts said that while the walls are strong, because of the building system’s positive connections, they still passed tests for Seismic Design Categories A and B and are currently being tested for certification in categories C and D.

O’Donnell—who previously served on a National Institute of Standards and Technology team studying the adoption of composite materials in sustainable infrastructure—says that, in and of itself, the use of this two-part adhesive to chemically weld blocks together is “a remarkable advancement in construction technology.”

At the job site, all walls are bolted to the slab, says Brett Perry, Coastal Construction superintendent for the Palm Springs buildings. “The floors are slab-on-grade, and depressed 12 inches down to support the bearing and shear walls. Those sill pieces come about 6 feet long depending where you’re building. What the wind load is determines the amount of anchors. We run that through the whole base, the doorways, everything.”

Photo courtesy Renco USA Inc.

To figure out a manufacturing process that would make the blocks, decking, joists and other building materials strong enough for construction, Renco developed proprietary bulk molding and pultrusion processes that suspend continuous filament-reinforcing elements within the block, decking and joists. This combines to make the bottom as strong as the top, Smuts explains.

The molds that make the material are manufactured in Turkey. Smuts was looking at shop drawings of molds while speaking to ENR: “Each mold is massive; they weigh several tons apiece and the machines themselves [of which the molds are just one part] are massive, too,” he says.

The company is sourcing the machinery and equipment needed to manufacture the building product from Turkey as well as the U.S., Smuts says.

Part of the process of standing up the factory was figuring out a way to produce the building products with less intense labor. Renco’s Turkish supplier can produce 400 machines a year. There are only 12 in Jupiter today. “We just ordered 57 molds for the Jupiter plant,” Smuts said.

The manufacturing facility has created 100 jobs in Jupiter, and Smuts said it’s the tip of what they’ll need to supply a strong Southeast multifamily sector and possibly other markets.

Bernardo Fort-Brescia, principal at Miami-based Arquitectonica, says his firm’s involvement with the project amounted to another test for the product.

“They wanted to know how they could design something that was aesthetically acceptable in the marketplace,” says Fort-Brescia. Sometimes, with prefabricated systems, he adds, “people wonder whether they are adaptable to architecture as we know it.”

At the start, says Fort-Brescia, “Like every architect, we were suspicious.” But concerns soon fell away.

Photo courtesy Renco USA Inc.

“It was like dealing with any other system except it was more suitable and faster to build,” he says. “Everything we tried to do, frankly, was no different than what we would do with regular construction, except that it was a different material.”

With building codes and other factors making concrete structures ubiquitous throughout South Florida, the fact that the project would be constructed from material that would help the residential buildings remain cooler than if built from concrete block also appealed to Fort-Brescia, the architect said.

For the town of Palm Springs, the project means much-needed housing.

“We were excited to hear about a project that was more affordable that could be put up more quickly than standard construction,” said Palm Springs vice mayor Kimberly Glas-Castro. When city officials toured the completed buildings, “they said, ‘you wouldn’t know what’s underneath.’”

Smuts and Murphy acknowledge that new materials or manufacturing processes alone won’t solve the nation’s housing shortage.

“Jupiter will be able to produce 6,000 apartment units’ worth of material per year,” Smuts said. “There’s 1.5 million housing starts in the U.S. on an annualized basis. There’s roughly a 5-million housing-start backlog that I don’t think anyone’s ever going to catch up with.”