Hemp Cinder Block Under Development at U Nebraska

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By Jean Lotus

A structural engineering study is in a third round of testing by a professor at the University of Nebraska-Lincoln to develop a hemp-based load-bearing masonry block. The new product has the potential to “greenify” the construction industry while also promoting a new agricultural crop for US farmers.

Marc McGuire, an assistant professor of civil engineering at U Nebraska-Lincoln’s Durham School of Architectural Engineering & Construction, has completed work on a prototype block, which will be manufactured by a local cement company in a trial run to undergo testing at the university before commercial manufacturing.
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Funding McGuire is Nebraska-based hemp processing company Global Fiber Processing, which is sponsoring the research along with the Nebraska Department of Economic Development. The private-public project plans to commercially license the blocks to concrete block manufacturers, utilizing US-grown industrial hemp.

The finished block will be the equivalent of a concrete masonry unit (CMU), commonly known as a cinder block, McGuire told HempBuild Mag.

The current laboratory version of the block meets strength, density, and water absorption criteria for standard CMUs required by ASTM C90. The strength of the developed material is 2500 psi, while coming in at half the weight of normal weight concrete (150 pcf vs 75 pcf). The team also subjected the laboratory specimens to simulated fire conditions and outperformed a portland cement control mixture. The material was shown to absorb considerable additional atmospheric carbon over its lifetime, gaining additional strength.

“Ultimately we’re making something that you’ll be able to buy on a pallet at Lowe’s,” he said. “Our goal is to make this a one-to-one swap. If an architect or engineer wants to build with concrete masonry units and wants a greener solution that has less of an impact on the environment, he or she can take our block and not even have to think about the engineering.”

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The blocks are made from “hurd” or “shives” derived from the woody core of processed industrial hemp stalks mixed with a cementitious proprietary binder. The block is more than 50% hemp, developers told HempBuild Mag and weighs about half of a traditional cinder block.

Builders in Europe have been using hemp hurd with lime for a natural wall infill insulation product for 30 years. The new hemp CMU products are not being developed for insulation value but for load-bearing properties, McGuire said.

Unfortunately, the decades-old nickname “hempcrete” for the insulation is a misnomer, since the material hardens into a fibrous limestone, but is not load-bearing.

No hemp-based load-bearing substance has been sold yet as a commodity building material. Some in the developing hemp building industry consider a load-bearing product to be a “holy grail.”

McGuire rejected that characterization. “I don’t know if ‘holy grail’ is the right way to talk about it,” he said. “As an academic, I try not to use too grandiose of language. When you talk about anything in the realm of [construction] sustainability, you talk about a suite of solutions,” he said. He called the hemp-based cinder block “one piece of the puzzle.”

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The revenue for the US concrete pipe and block manufacturing industry is projected to be $7.8bn in 2023, according to Ibisworld industry reports.

“We’re not really supplanting concrete with this. We’re taking a portion of the market that wants a sustainable solution,” McGuire said.

A local concrete block manufacturer will produce a trial run of around 500 blocks for research and development, and then the blocks will be tested for ASTM standards for compression strength and durability at the U Nebraska labs.

“The building and engineering industry is very conservative. Our number one goal is safety, right? We don’t want structures to fall down, and we don’t care about anything else. We don’t care what the structure looks like. We don’t really care about thermal performance. We want people to be safe,” McGuire said.

Graduate construction engineering and management Ph.D. student Zina Ebrahim is building computer models to determine the structural tests needed for the blocks. She said the project to create sustainable building materials attracted her to guide her future career path.

“I actually got excited because when you start reading about hemp, you’ll feel amazed because it has different properties that can improve the construction materials and can make an impact in the construction industry,” she told HempBuild Mag.

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Ultimately, the plan is for the formula for the blocks to be licensed to localized concrete manufacturers across the United States and internationally. Concrete is usually regionally manufactured because of the shipping costs of moving cinder blocks.

The price of the blocks will be “competitive” with concrete cinder blocks, the team said.

Concrete is becoming more expensive because of the worldwide shortage of Portland cement, an ingredient in traditional concrete CMU blocks. To make Portland cement, limestone is extracted from quarries and burned at high temperatures, releasing large amounts of carbon dioxide. As much as 8% of the world’s human-derived greenhouse gasses come from the production of concrete.

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As prices for Portland cement rise, at the same time, the price of industrial hemp agricultural products is expected to drop as the supply chain develops in the United States.

“We’re looking forward to trying to find a product that will be beneficial to the farmers in Nebraska,” said Alliance, NE farm owner Jeff Manion, part-owner of Global Fiber Processing. The company partners with two farm machinery companies, Colorado’s Formation Ag and Giltner, NE-based Hemp Harvest Works.
Last year, in 2022, only 250 acres of industrial hemp was grown and harvested in Nebraska, according to the US Department of Agriculture’s National Agricultural Statistics Service.

“With this structural block, the volume of hemp crop grown that would get a small segment, maybe 1% of the block market, is a substantial amount of acres,” said Corbett Hefner of Formation Ag. That acreage could compete for farm acreage with traditional crops such as corn and soy and make farming hemp as a rotational crop financially attractive for farmers, Hefner said.

Many companies looking to develop products using hemp for construction materials are “looking for prefabrication instead of onsite mixing,” Ray Kaderli, president of the US Hemp Building Association told HempBuild Mag in an email. “A load bearing block would be an important stride in the right direction,” he added.