Making concrete change: Innovation in low-carbon cement and concrete

By Ann Link of TTL with thanks to Dinah Morgan

HempIt’s not about getting stoned. Industrial hemp, which is not psychoactive, can help reduce climate damage. So why is it not more widely grown?

Industrial hemp can form part of a carbon negative building material. It is grown as a crop in many countries including China, France, the USA and Canada. Yet its cultivation here in the UK is minute at around 1% of farmed land. The National Farmers’ Union backs growing it as part of its strategy to reduce carbon emissions from farming.

Eight percent of global climate gas emissions are from concrete production, mainly because of  its essential ingredient, cement. Cement is made by heating limestone, and its emissions come from the limestone as well as the fossil fuels used for heating it. Making Concrete Change Innovation in Low-carbon Cement and Concrete

Some of the uses of concrete can be replaced by hempcrete, made from industrial hemp and lime. It is light, breathable, has insulating properties and helps regulate the moisture content of a building. It still needs a structural frame, which can be made of wood, another carbon negative material. The Yorkshire Hemp House was built in this way. There are now many other examples.

Yorkshire Hemp building

Image above & top courtesy of East Yorkshire Hemp

Hempcrete has negative net carbon emissions, locking away more CO2 in the building than are emitted during the production, processing and transportation of the material. This is because plants take up CO2 in their lifetime and this isn’t released into the atmosphere when the plant is processed and used in these materials because they remain in their original states. Embodied Carbon (EC) is the figure used to demonstrate how much (kg) of carbon is embodied in each material per m³.

Hempcrete with a hemp lime binder has an Embodied Carbon figure of -35kg CO2/m³ based on figures from the ICE Database 2008. The process of producing lime and natural cements in the hempcrete mixture requires energy and large amounts of heat to produce therefore producing more CO2 into the atmosphere and reducing the Embodied Carbon figures. For background see here…

Hemp has been grown for thousands of years and has had many different uses from food to shelter of both man and his animals, sails and ropes for ships and paper. Hemp was first grown in Asia, and is one of the oldest cultivated fibre plants. Early Chinese civilisations used hemp to make fishing nets, ropes, clothes and paper. Plants soon spread to Europe, and hemp and lime has traditionally been used as a building material in France.

So why has the UK government been so restrictive of industrial hemp? This is partly because of confusion with another subspecies of the cannabis plant, which produces psychoactive THC. Growers must apply for a licence from the Home Office as if they were growing a crop for drug production. There are licensing fees, registration and ongoing checks with police. Recently there has been a controversy when the Home Office forced a grower to plough up a crop – this was being grown for medicinal CBD oil, which was thought to be permitted. However, normal fibre uses are trouble-free.

There is much potential for further uses of hemp, which is fast growing and requires few pesticides or fertilisers. These include compostable plastics, textiles and paper.

For further information and organisations supporting hemp growing in the UK see: