The usefulness of calcined clay as an additive to cement has prompted the revisiting of clay for brickmaking in Africa. A number of African cement makers have shown their interest.
In March 2022, a Limestone Calcined Clay Cement (LC3) factory was commissioned in Malawi. This was a cooperative project between the Malawi government, Terrastone (a brick manufacturer) and LaFarge Cement of Malawi. Similarly, CBI Ghana proposed to set up the world's largest gas suspension calciner system near Accra, Ghana.
The clay calciner system is expected to substitute between 30 and 40 percent of the clinker in the final product. Thus, the production process of calcined clay-blended cement should show an improvement over Ordinary Portland Cement. Firstly, by reducing carbon dioxide emissions by up to 40 percent per tonne. Secondly, it should lower costs of energy, fuel consumption and overheads from clinker imports.
The Malawi project is the first calcined clay cement project in the cement industry within East Africa. However, such clay cement projects were already commissioned in West Africa. For instance, two of such projects were set up in West Africa by Turkey-based Oyak Çimento (and its subsidiary Cimpor) - in Côte d'Ivoire and Cameroon.
With these developments, Sub-saharan Africa competes favorably with Europe on existing blended cements projects. In Europe and the USA, a notable increase in the usage of blended cements is noticeable. The variety of blended cements produced in each location (and plant) also depend on whichever supplementary cementitious material (SCM) is available in the vicinity.
The Advantages of Clay in Modern Building Architecture
Clay has been used for centuries in building houses, silos, and walls in Africa. This is in addition to other abundantly available and sustainable building materials. Such materials include adobe, laterite, stone, sand, bamboo, timber, and dry vegetation. Clay bricks are equally a highly popular and preferred construction material in many parts of the world. They are known for their resilience, high tensile strength, thermal and sound insulation, as well as fire and weather resistance. Furthermore, brick making contributes to the economic growth of countries such as South Africa, Bangladesh, India and Ghana.
It is on record that Africa's climate is experiencing increased temperatures. This especially raises concern, as the frequency of natural disasters worldwide has tripled in the past 30 years - according to UNHabitat. Many African regions (excluding North Africa) are largely overcrowded settlements. Again, Sub-Saharan Africa has nearly three-quarters of the global population of children living in countries prone to natural disasters. This is an estimated population of 393 million children.
Climate experts have emphasized that sustainable materials are particularly useful in slowing down the already-manifesting effects of climate change. Additionally, they are cheaper to obtain and maintain. Combining them with modern sustainable design and building practices will be of exemplary benefit to Africans. Such modern building projects are already existing - including rural primary school buildings.
Carbon Emissions from Limestone Cement in Africa
Rapid urbanization and a high population growth rate across Africa, has increased the demand for shelter and civil engineering infrastructure. The Nigerian government for instance, is involved in a number of public-private partnerships. Such partnerships have birthed huge projects: Abuja World Trade Center, Eko Atlantic, and Lekki Free Trade Zone are typical examples. These projects consume large quantities of cement on a yearly basis.
But the production of cement presents some major problems. Firstly, the production and grinding of cement consumes a large amount of energy, thus making cement more expensive (especially in developing countries). Secondly, the increased urbanization drive across Africa means a higher demand for cement in building construction. This has led to an increase in carbon emissions.
The global threshold for limiting global warming to below 2 degrees Celsius by 2050 is 2.7 kilotonnes. As at 2018, the total per capita carbon emissions in Sub-Saharan Africa alone was just 0.81 kilotonnes. However, carbon dioxide emissions from cement production in Africa have steadily increased. From 653 tonnes in 1940, it hit the peak in 2019 at 80.36 million tonnes. Then it slightly declined between 2020 and 2021. See chart for reference.
In Nigeria alone, total carbon emissions from cement production in 2015 was an estimated 11 Million tonnes. It increased to 15 Million tonnes in 2020, and is projected to hit 28 Million tonnes in 2040.
The need to limit the environmental impact of cement as the main construction material has become necessary. To achieve this, a reduction in the amount of clinker used per cubic meter of concrete is important. Clearly the partial replacement of cement with supplementary cementitious materials (SCMs) would require less energy for production. It would also lessen carbon dioxide emissions, thus mitigating global warming.
Recommendations for the Production of Clay/Cement Hybrid Concrete and Bricks
Clinker is notably the most essential component of cement, as it contributes to the strength formation of concrete. Since clinker is a big factor in carbon emission, the move to decarbonize concrete without affecting its desirable properties (strength, workability and durability) is essential.
Blending common clays with limestone powder (as a substitute for clinker) is known to be highly beneficial. The combination enhances the mechanical and durability properties of concrete. In fact, experimental blends of Nigerian Calcined Clays, limestone powder, and Ordinary Portland Cement achieved at least a “Level 1” reduction in greenhouse gas emissions.Thus the use of common and calcinied clays could help in solving the housing deficit in Africa - especially the sub-Saharan region.