Africa is home to approximately 33 million smallholder farmers who generate 90 per cent of the continent’s food, according to the Food and Agricultural Organisation (FAO). With every season, a trail of a farm waste is left behind. These materials are in the form of cereal husks, maize cobs, animal waste, fruit and crop peels, wheat straws and sugarcane bagasse among others.
Some of this waste is used as organic manure, and some fed to animals, but most of it is discarded. Different industries have come up with innovative ideas on how to make agricultural waste useful. Animal waste, for instance, is now a popular source of biogas and organic fertilisers.
Groundbreaking innovations
The construction industry, which is ranked among high polluters, is also embracing the idea of incorporating agri-waste or bio-waste into concrete. These innovative and progressive ideas are, on the backdrop of an evolving construction industry.
Manufacturers around the world making construction materials are embracing sustainable practices and coming up with groundbreaking alternatives. In 2023, a California-based startup introduced cement-free concrete, a revolutionary product that could change construction as we know it. In Kenya and in Africa, there is a beehive of activities in the research realm as cement stakeholders work toward easing the cost of concrete and reducing carbon emissions.
On July 19, stakeholders in the construction industry converged in Nairobi to explore circularity in construction. The event, dubbed Circular B/I-O, brought together stakeholders in academia, research, construction, government, and community based organisations.
Speaking during the event, Dr Wolfram Schmidt, from the Federal Institute for Materials Research and Testing (BAM), introduced the Circular B/I-O project, funded by the Volkswagen Foundation. The 1.2 million Euros project will be running in Kenya for the next four years and will involve three partners: BAM, SRH Hochschule Berlin and the Institute of Cement and Concrete at Meru University.
Understanding concrete and admixtures
The goal of this project is to explore alternative ways to improve the concrete used, through cheaper, locally available organic materials. A pilot construction project using alternative concrete will also be put up during the course of the project. If successful, the project will introduce a new, decentralised way of making concrete that redistributes revenues, to smallholder farmers.
Importantly, it will lead to an environmentally-friendly concrete alternative with lower carbon emissions. Before delving into how rice husks or dried and burned cassava peels can possibly be used in making concrete, it is important to understand how concrete is made in a typical construction site, here in Kenya.
Ordinarily, when mixing concrete for, there is use of cement, aggregates and water. Cement is the “glue” or binder that holds everything together, while aggregates such as sand and gravel provide strength. Beyond these three main ingredients, there are additives or admixtures to improve performance.
Admixtures are made from chemicals or minerals and enhance the workability of concrete in a number of ways (depending on the type used). Some reduce the setting time required for concrete, thus speeding up the construction process.
Water-reducing admixtures improve the flow of concrete, making it easy to work with without increasing the volumes of water used in mixing the concrete. Admixtures can be in powder or in liquid form and play an important role in construction. They could lower the cost of concrete - by reducing the quantity of cement or volumes water used.
They also play a crucial role in improving the quality of construction. For instance, if one wants easy flowing concrete adding an admixture can increase the slump of your concrete mix without using excessive water or hiring extra labour or leasing equipment to work on levelling the concrete.
In a scenario where mixing has gone wrong and perhaps the labourers put in too much water into the concrete, admixtures could also help reduce the concrete’s slump and bring it to the right consistency without adding extra cement or aggregates. But if admixtures work so well, the big question is, why do we need organic alternatives?
We had a chat with Dr Schmidt. “In Africa, where rapid urbanisation is taking place, concrete is inevitable. However, this important construction material is bound to available elements in the earth and thus, it is prone to resource depletion. In addition, the production process of concrete is associated with high concrete emissions and with increasing demand for construction, the emissions are bound to escalate. To make construction sustainable, we need to explore alternative greener and renewable properties. In addition, we need to reduce the amount of water we use in concrete without affecting the quality of construction.”
Today, chemical admixtures are made from crude oil, which is not renewable. These admixtures are also scarce and not available for all construction projects. Elements found in agricultural waste and other plants such as starch, cellulose and gum can be used to make admixtures.
Several types of agricultural waste have been considered as worthy replacements for chemical elements used in admixtures. Rice husks, cassava peels’ ash and sugarcane bagasse are some of the popular options. These agricultural waste materials contain important elements that can be extracted to make admixtures.
A good example is cassava peels. Cassava is one of the most abundant crops in Africa. Nigeria alone produces about 20 per cent of the global cassava. Cassava peels, which are often thrown away to rot, have an abundant levels of starch which can be extracted to make admixtures. When burned, the ash can also be used to partly replace portland cement (a key component in the cement we use). Replacing it is crucial in reducing the cost of cement. Ordinarily, cement is made from clinker as the key ingredient, combined with portland. By adding reactive ash from agricultural waste, we lower the amount of clinker needed in cement production, thus cutting the cost of clinker imports.
The cassava ash and starch used to make admixtures result in a cost effective, stronger materials with lower carbon emissions. In addition, the supply chain is shortened as cassava peels are sourced locally. The beauty about cassava waste is that it is not used elsewhere. Unlike other agricultural waste materials which are fed to animals, cassava peels are not digestible and, therefore, are simply dumped.
In a Circular B/I-O project done in Nigeria, researchers involved built the “Cassava Centre” a building made from cassava-based concrete. Dr Schmidt, who was involved in the project, says there was a lot to learn from the cassava centre as well as an additional project in Ghana. For starters, they were able to replace imported materials normally used in concrete. The cassava-based concrete was strong enough to outperform what is already in the market. There is however, a need for more research to figure out the technical bits such as how the ash interacts with elements in factory cement, in the long-term.
One of the challenges in using bio-waste in concrete is the seasonality of crops and differences in the variety of breeds planted in different regions. Some of these crops are clustered regionally, meaning some countries will be advantaged more than others. As such, there are efforts to explore alternative agricultural waste materials to make bio-concrete a reality for the entire continent. In the Kenyan context, plants such as hyacinth, found in Lake Victoria, and gum Arabica, found in acacia trees (common in North Eastern Kenya) are great alternatives.
The other challenge discussed during the workshop is the resistance that professionals in the built environment face when they suggest alternative materials. Project owners prefer traditional materials which are tried and tested. Complex regulatory processes can also be challenging when it comes to transitioning great research projects, from lab to site. With more collaboration and information flow, however, the construction industry can benefit from various groundbreaking research projects.
Other participants in the workshop revealed that there is a lot of innovation and research taking place in Kenya’s construction industry, calling for more synergy. The Kenya Industrial Research and Development Institute (KIRDI) has also been involved in a research project which explored the use of industrial waste in concrete and other uses. The goal was to establish whether waste from one company can be used as raw materials for another.
“We identified so many opportunities, and several of them are applicable in construction,” said Dr Kelvin Khisa, the principal research scientist at KIRDI.
These include waste ash which can be used in cement, to waste sand with potential for making construction glass, and agricultural waste that needs to be explored for additional opportunities.
Conclusively, with fewer cement factories in Africa, and growing demand for concrete, there is a need to explore alternative models for producing concrete. Dr Schimdt compares this to home cooking versus buying packaged dry foods. Buying ingredients from the market and making a nice meal at home will always produce the best and most affordable option. On the contrary, buying packaged ready food from the supermarket results in extra costs.
Similarly, builders should have alternatives. Instead of buying cement and additives from the shop, they should be able to source supplementary materials (such as ash) and admixtures locally and have a chance to mix them on site for cheaper, renewable and low-carbon concrete. A decentralised model, where admixtures are made from agricultural waste sourced locally from smallholder farmers and processed in a local factory also distributes revenues to more people in the value chain. The local production of admixture also creates employment locally, while handing extra income to farmers.
