Introduction
The use of rammed earth in construction dates back to centuries in different parts of the world and it is commonly known by the French name ‘Pise’. According to Ciancio and Becket (2014), there are many thousands of historic rammed earth structures around the world, some of them dating from 1500 BC such as the great wall of China. These constructions which are usually known to be cheap and affordable can still be visible to present which buttresses their sustainability.
According to Carnivell et al (2020), heritage values, bioconstruction, and sustainability are three interrelated factors that make rammed earth construction advantageous in modern times. Besides these, interest in the use of rammed earth as a viable wall system was drawn from its characterization as a sustainable material (Cautius, 2011). Below its sustainable reputation is its ability to function in nearly all climatic zones. Just as it is in different parts of the world, building walls constructed with rammed earth still exist in different parts of Nigeria.
With the advent of modern means of construction which have generally been accepted, Nigerians have found it difficult to revert back to earth construction with its attendant benefits probably due to ignorance (Okoronkwo et al, 2013) and partly due to a lack of knowledge on how to make earthen material durable and appealing aesthetically (Walker and McGregor, 1996; Daniel et al, 2018).
The urgent search for sustainable means of construction which began many decades ago was born out of the fact that buildings consume 30 – 40% of the world’s energy consumption, generate 30 – 40% of waste, and 30 – 40% of greenhouse gases released annually (UNEP, Umar and Khamidi, 2012; Nduka and Sotunbo, 2014). The buildings that contribute to this menace were made with one or a combination of cement, steel, aluminum, and glass as these have largely been produced over many decades and used as building materials.
The effect of climate change is everywhere and there is an urgent need to reduce them. In developing countries especially in Nigeria, cement which is among the largest contributor to greenhouse gases is largely produced and used in building construction. Rammed earth has many benefits with regard to durability, reusability, thermal insulation (Daniel et al, 2018), and cost-effectiveness. With these benefits, Nigeria needs to adopt rammed earth to provide housing to the poor mass population within the country and reduce greenhouse emissions.
How to achieve rammed earth construction
Rammed earth construction can be achieved in three stages:
- Design the Structure
- Carry out Soil Tests to determine suitable soil
- Erect the Structure
Design the Structure
The designs necessary for rammed earth construction are similar to that used in conventional construction. It is necessary to produce a suitable architectural drawing according to the client’s brief. Since the rammed earth walls are structural load bearing walls, elaborate structural designs for single or multi-storey buildings as specified in EC 2, BS 8110, or IS 456, etc are not usually necessary. It may be necessary to consult some specialized code (countries like Australia, Newzealand, Zimbabwe, etc have codes for the design of rammed earth walls) or advice from specialists on rammed earth construction. The mechanical and electrical installation designs are also done.
Carry out Soil Tests
Not all soils are suitable for rammed earth walls. Soil tests such as particle size analysis are necessary to determine suitable grading. Generally, the minimum percentage of clay and silt content in the soils should be 20-25% while the maximum percentage should be 30-35%. The minimum percentage of sand and gravel should be 50 – 55% while the maximum percentage should be 70 – 75%. The next important test is the linear shrinkage test. If the soil that has high linear shrinkage is used for rammed earth construction, undesirable cracks could be expected on the walls. A soil with linear shrinkage ≤ 7% is preferable. A compaction test is done to determine the maximum dry density (MDD) and optimum moisture content (OMC). Compressive strength is what enables rammed earth walls to bear loads. To improve the compressive strength of rammed earth walls, a small amount of cement and/or lime is usually added. The necessity to determine the optimum content of lime and cement calls for the need to carry out compressive strength tests on the soils proposed to be used for the rammed earth construction in question.
A test carried out on lateritic soil from the south eastern region of Nigeria shows the percentage of lime and cement added and the compressive strength obtained in the Table below. We can observe how the compressive strength was improving and can possibly get within the range of the compressive strength of concrete. With little consumption of cement and lime, it is possible to achieve high strength walls with a natural material: soil. This is the reason rammed earth walls are adjudged eco-friendly walls. Recommended range of cement for rammed earth walls is 5 – 10%. However, it is always better to carry out compressive strength tests to get the quantity suitable for each soil. A complete test would require curing the specimens and soaking them in water for 7, 14, 21, and 28 days and then checking their compressive strength.
| Lime added (%) | Cement added (%) | Duration of curing (days) | Average Compressive strength (N/mm2) |
| 2 | 2 | 7 | 1.44 |
| 2 | 4 | 7 | 5.78 |
| 2 | 6 | 7 | 9.68 |
| 2 | 8 | 7 | 19.38 |
The best colour for materials used in rammed earth construction is red. Lateritic soils which are abundant in Nigeria and usually possess reddish or reddish-brown colour show suitable properties for rammed earth walls. This reddish colour is invariably affected by the addition of cement and lime. Besides these, other colours and wall decoration features can be added to rammed earth walls to improve their appearance. This can be a form of seal to provide both water proofing and gloss appearance to the walls. In this situation, it is usually not necessary to plaster the walls (See Figure 2).
Rammed earth walls are usually constructed in layers so colours can be added after each layer or every third or fourth layer at the edge of the wall.
Erect the Structure
Rammed earth walls could be constructed in thicknesses ranging from 200 mm to 300 mm or 450 mm for internal and external walls respectively depending on the number of storey and the purpose of the structure.
Moisture control is very important in rammed earth walls. Prior to construction, it is necessary to ensure that the soils to be used are kept dry.
To erect rammed earth walls, first, build the foundation. The foundation is usually made of concrete and a strip footing. Dig the foundation to a suitable depth and width depending on the stability of the ground. It is necessary to use a penetrometer during digging to determine a stable ground. After digging, erect formwork and cast concrete up to 300 – 450mm above the ground surface. Because rammed earth walls are usually heavy it is not often necessary to dig the foundation too deep like when using block walls. The strength of concrete in the foundation should not be less than 30 N/mm2. The foundation concrete should be reinforced at the top and bottom as shown below (Figure 3).
Next erect formwork for the walls. Before placing the soils and compacting, ensure that DPM is introduced along the wall length because water from the foundation can weaken the compacted walls if not prevented.
Place the soils stabilized with suitable quantities of lime and/or cement and moistened at OMC based on laboratory soil tests in the mould in layers of 150 mm and ram down to 100 mm using manual or electronic ramming (see Figures 4 and 5). Note that desirable additives such as colour or sealants can be added before compaction.
A layer is considered properly rammed when an echoing sound is heard from the rammer as an indication of the compactness of the layer. Continue to adjust the formwork and ram until you get to the required height. In a storey building, assuming a headroom of 3000mm, ram up to 2700mm, tie the walls with reinforcement bars with 300mm depth concrete to flush level to the required headroom. Then continue to ram for the second floor. While ramming, endeavour to provide movement/expansion joints at specified intervals.
Conclusion
Even though rammed earth walls cannot be used to replace all buildings in a society, they can be used instead for residential buildings especially ones that are not high-rised buildings. This would go a long way to reduce the cement and energy consumption in buildings. It is also known to perform better under earthquake conditions than walls made of conventional bricks and blocks.
Watch a live video: How to build Rammed Earth Walls
References
Canivell, J. J., Martín-del-Río, J.J.,Falcón, R.M. and Rubio-Bellido, C. (2020). Rammed Earth Construction: A Proposal for a Statistical Quality Control in the Execution Process. Sustainability (MDPI). 12, 2830; doi:10.3390/su12072830.
Cautius, C.E. (2014) Rammed Earth: Adaptations to Urban Toronto. A thesis presented to the University of Waterloo in fulfilment of the thesis requirement for the degree of Master of Architecture.
Ciancio, D. D. and Beckett, C. (2014). Rammed earth: an overview of a sustainable construction Material. University of Western Australia, 6009 Australia. School of Civil and Resource Engineering M051, University of Western Australia, 35 Stirling Highway, Crawley 6009 Western Australia.
Daniel, A.A., Benjamin, G.K. and Tali, J.O. (2018). Adopting Stabilized Earth Construction to Address Urban Low-cost Housing Crisis in Jos, Nigeria. J Ergonomics Stud Res 1: 101.
Nduka and Sotunbo (2014). Stakeholders Perception on the Awareness of Green Building Rating Systems and Accruable Benefits in Construction Projects in Nigeria. Journal of Sustainable Development in Africa. Volume 16, No 17 pp 118 -130.
Okoronkwo, D.C., Khatib, J.M., Emekwuru, N. and Hall, R.F. (2013). The Rammed Earth House in Nigeria X CIATTI 2013. Congreso Internacional de Arquitectura de Tierra Cuenca de Campos, Valladolid. PP 27 – 36
Umar, U.A. and Khamidi, M.F. (2012). Determination of the Level of Green Building Public Awareness: Application and Strategies. International Conference on Civil, Offshore and Environmental Engineering, Kuala Lumpur Malaysia.
Walker, B. and McGregor, C. (1996). Building with Earth in Scotland: Innovative Design and Sustainability. Edinburgh: Scottish Executive Central Research Unit.
2 Comments
Does the rammed earth wall just sit or stand on the footing? What is there attaching the wall to the footing?
Rammed earth is a very heavy mass. Thus, they are made of load bearing walls. They can probably sit on a roughened concrete surface and strongly bond under compaction on the surface. Some length of reinforcement from the concrete foundation can possibly be taken into the rammed earth to provide proper anchorage.