Hemp Concrete with Mineral Additives as a Durable and Fire-Resistant Material in Green Construction

In this work, to enhance the compressive strength and evaluate the fire resistance of hemp concrete, we incorporated mineral additives such as FBC fly ash and metakaolin. This paper investigates the thermal conductivity, compressive strength, flammability, and fire resistance of hempcrete and the influence of mineral additives in the form of fly ash from fluidized bed combustion (FBC) and metakaolin on these properties. A fly ash content of 20% by weight of the binder resulted in an increase of 26% in compressive strength and about 6% in thermal conductivity compared to hemp concrete without mineral additives. The use of metakaolin in the amount of 15% by weight of the binder resulted in a 21% increase in compressive strength values with an increase in the thermal conductivity coefficient of only 0.5%. Flammability tests by direct application of a gas torch flame to the specimen surface proved the lack of flammability and spontaneous fire extinguishing ability of hempcrete. In turn, fire resistance tests showed much higher resistance to high temperatures for hempcrete modified with metakaolin, where the recorded mass loss during a 15 min test at 500 °C was ca. 58% less than in hempcrete without mineral additives, and when FBC fly ash was used, the mass loss was ca. 37% less. The obtained results are satisfactory in terms of the physico-mechanical properties of hempcrete. They also enable the replacement of traditional construction materials with waste-derived materials from other sectors of the economy, which, in the long term, will contribute to the development of green construction and support the principles of the circular economy.