Hemp has historically been used for a wide range of applications spanning from rope production and textile manufacture, through to more modern day applications such as its usage in hemp-based plastics.
Hemp fibers are very strong, you see, and they are also very cheap.
It has also been used as a construction material named Hempcrete for quite some time (thousands of years in fact), and now Hempcrete is getting the AM treatment thanks to a team of researchers at Texas A&M University.
The researchers, funded by a $3.74 million grant from the Department of Energy, are now planning to 3d print buildings with millenia-old building material. Hempcrete consists of hemp particulate, lime and sand. The project is funded under the HESTIA program which aims to increase the total amount of carbon stored in buildings to create carbon sinks, which absorb more carbon from the atmosphere than released during construction. HESTIA stands for “Harnessing Emissions into Structures Taking Inputs from the Atmosphere” .
Let’s look at the benefits of using Hempcrete over concrete, and also at how those benefits can potentially be enhanced with additive manufacturing.
Material-wise, Hempcrete is a breathable porous material with excellent fire resistance and thermal insulation properties, the latter being beneficial in reducing heating and cooling energy demands. It is significantly lighter than concrete, and a fraction of the compressive strength, so it requires supports to carry vertical loads. You can’t just pour it high and fill it with rebar like cement. In this regard, it is not exactly a direct replacement for cement, more of a material that can be used in-lieu of cement in particular use cases. Use cases where cement would have been overkill.
In terms of other ecological benefits, production and use of Hempcrete has a net carbon-negative environmental effect. This is in stark opposition to the manufacture of traditional cement which is incredibly energy intensive and pretty bad for CO2 emissions also.
Cement is the source of about 8% of the world’s carbon dioxide emissions, to put that into perspective. Hempcrete is carbon negative because plants absorb CO2 from the atmosphere while growing, so the hemp acts as a carbon sink before the plants are even harvested. That CO2 will remain locked inside the block, and indeed the block will absorb even more carbon through its life.
The buildings have been designed with modern design codes in mind making it more likely to be adopted by the construction industry.
While there have been some forms of Hempcrete around for eons, modern Hempcrete building processes are either cast or spray forming directly on the construction site, or assembling constructions of pre-cut Hempcrete blocks, manufactured off site.
Printing Hempcrete will allow more precise distribution of materials, and can naturally be combined with various topology optimisation techniques to further reduce material usage while maintaining strength, which is required for resilient housing..
“The advancements of this project will contribute to the U.S. maintaining its worldwide leadership in advanced construction methods and infrastructure sustainability and resilient technologies,” said Dr. Petros Sideris, assistant professor in the Zachry Department of Civil and Environmental Engineering.