Hemp waste, a new cement replacement and biofuel

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Hemp is a cannabis sativa plant that contains only trace amounts of THC, the psychoactive ingredient typically associated with marijuana.

The market for industrial hemp, which can be used to make a wide variety of products, was estimated to be US$5 billion in 2019 and is forecast to grow to US$36 billion by 2026.

More hemp being turned into more products means more hemp waste, which is the stalk after the leaves, flower and seeds have been removed.

The problem of what to do with all the hemp waste that is expected to be produced caught the attention of Sudip Talukdar, an instructor in the department of civil engineering at the British Columbia Institute of Technology (BCIT), and his wife, Krupal Pal, engineering manager at Nextleaf Solutions, a Vancouver cannabis extractor.

At the same time that Talukdar and Pal were thinking about hemp, concrete and cement producers were wondering if they could reduce their environmental impact by partly replacing cement with more sustainable materials.

Cement makes up approximately15 to 20 per cent of concrete by volume, the rest being water and aggregate.

Among the challenges facing the cement industry is how to reduce the embodied energy and carbon dioxide (CO2) emissions of manufacturing the material.

Cement production is reportedly responsible for two to three per cent of global primary energy use and approximately five per cent of man-made CO2 emissions.

In addition to looking for ways to reduce the size of their environmental footprint, cement producers were also searching for a new fuel to replace fly ash from burning coal for firing their kilns.

Fly ash is one of a number of recycled ashes and mineral powders that are byproducts of other manufacturing process and that can be used as partial cement replacement.

Substituting these materials for cement can reduce costs, lessen the environmental impact of cement production, and adjust some of concrete’s properties.

Ash from other types of local and plentiful organic materials, such as rice husks and bamboo and banana leaves, have also been used as supplementary cementing materials in some parts of the world.

Compared to other forms of biomass, hemp has a higher net calorific value, so it releases more heat when a unit quantity of the hemp is burned. All of which means that hemp waste is a potentially effective biomass and energy-yielding crop for biofuel applications.

With much to consider, Talukdar and Pal got together with two other scientists, Farhad Pargar and Cristina Zanotti at the University of British Columbia (UBC), to investigate the potential of hemp waste for environmentally friendly double-duty – as biofuel and a cement replacement in the making of concrete.

The research at BCIT and UBC entailed incinerating hemp waste at high temperatures and analyzing the residual hemp ash before adding it to concrete mixes.

Concrete mixes with different hemp ash replacements, between five and 25 per cent by weight, were tested for several attributes.

Results of the experiments showed the ash content of the concrete mixtures had no effect on their density.

In addition, there was only a little reduction in compressive strength (resistance to being pushed together) for mixtures with five per cent hemp ash, indicating hemp ash is viable filler in concrete when applied at low percentages.

Similar to the results for compressive strength, water absorption and concrete porosity were affected by the proportion of hemp ash in the mixture.

Test results suggested while 15 to 25 per cent hemp ash replacement is not recommended, the use of five per cent hemp ash as supplementary cementing material has only a minimal side-effect on water absorption.

Taken together, say the researchers, lower replacements of hemp ash (five per cent by weight of cement) had minimal adverse effects on the mechanical and durability properties of concrete, which suggests it can be used as a filler in concrete with positive economic and environmental benefits.

With regards to the use of hemp ash to fire cement kilns, the researchers say their experimental results are not conclusive. The effectiveness of hemp ash depends on such variables as hemp yield, the efficiency of the cement kiln and the type of fuel used to power the kiln in absence of hemp.

Results to date, however, seem to suggest the concept has merit and is worth more investigation.

In the end, the research team got a peer-reviewed, published paper from its investigations and Nextleaf has filed for a patent.

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