Advancing Rammed Earth Construction for Sustainable Buildings in Bali
- RAMMED EARTH
- ARCHITECTURE
- SUSTAINABILITY
Rammed earth is an ancient monolithic construction method used for various purposes such as building walls, roofs/floors, foundations, furniture, embankments, and earthen bunds. The construction process typically includes compacting moistened soil in layers with a granulometry from clay to gravel within a sturdy formwork.
Rammed earth constructions can be divided into two main types: stabilized rammed earth and unstabilized rammed earth. Unstabilized rammed earth structures are primarily made using natural materials like soil and aggregates. Conversely, stabilized rammed earth construction involves the addition of inorganic stabilizers such as cement or lime alongside natural materials.
Rammed earth constructions can be divided into two main types: stabilized rammed earth and unstabilized rammed earth. Unstabilized rammed earth structures are primarily made using natural materials like soil and aggregates. Conversely, stabilized rammed earth construction involves the addition of inorganic stabilizers such as cement or lime alongside natural materials.
Physical Stabilization
Physical stabilization is achieved through the use of additives and compaction. First and
foremost, they can be mineral and organic substances, which can be divided into natural and synthetic.
Historical origins
Throughout history, rammed earth has been used by various civilizations around the world for its durability, thermal properties, and availability of materials. One of the earliest known examples of rammed earth construction is the Great Wall of China, parts of which were built using compacted soil and stone. In ancient Mesopotamia, the Sumerians and Babylonians employed rammed earth to construct ziggurats and temples, showcasing the versatility and strength of this building technique. Similarly, in Africa, structures such as the Great Mosque of Djenné in Mali stand as remarkable examples of rammed earth architecture, demonstrating the enduring legacy of this traditional building method.
Comeback as sustainable Construction Method
Contemporary rammed earth building has garnered interest from architects, engineers, and other construction experts due to its environmental benefits, including low carbon footprint and eco-friendliness. It allows for attractive finishes and versatility in design. Moreover, there’s ample opportunity to utilize local materials, industrial by products, and mining waste, minimizing environmental impact.
Properties & Characteristics
Sustainability
Clay is an exceptionally efficient building material, conserving both energy and resources. With soil being widely available across the globe and requiring minimal industrial processing, the production of construction soil consumes a mere 1% of the energy typically used for conventional building materials like reinforced concrete or bricks. Additionally, significant energy savings are achieved during transportation, depending on construction methods. Furthermore, construction soil can be created from recycled materials and waste products, such as excavated material from construction sites. However, to ensure the sustainability of construction soil, it’s crucial to avoid stabilizing it with environmentally harmful binders like cement.
Indoor health and confort
Humidity
Thanks to the capillary properties and good diffusivity, soil provides a constant, pleasant humidity. If the soil is processed correctly, the risk of mold is very low, which is why bathrooms are often made of it or finished with clay plaster.
Pollutants and Health
The solid components of an earthen house absorb the humidity of the air and pollutants. Odors, vapors, smoke, and steam leave hardly any traces, and because of its neutral pH, the soil is kind to the skin. Especially in kitchens, these favorable properties prove very useful, which is why a fume hood is usually unnecessary in rammed earth walls with a free surface. (2)
Heat Storage
Rammed earth has a high thermal mass. The thick walls of an earthen house absorb heat in warm conditions and store the energy until it can be released in colder temperatures. This mitigates daily temperature fluctuations, minimizing the need for air conditioning and/or heating. Whether this is a benefit, however, depends on the building location and climatic conditions.
Sound Insulation
Thanks to its density, the volume of the component not only has excellent advantages in heat storage, it perfectly absorbs sound and thus protects the interior of the room from noise from the outside. In terms of acoustic performance, the “reverberation time” is a parameter to consider. It defines the time required for sound to “fade” or decay in an enclosed space. Although there are not enough studies, many experts and authors point out that due to its porosity Rammed earth has excellent properties in this matter.
Fire Hazard
Soil is classified as “noncombustible” and thus does not contribute to fire. If the soil has an unusually high proportion (1 %) of organic matter, it may be classified as “severely flammable” if necessary, but this still corresponds to Rammed earth constructions can be divided into two main types: stabilized rammed earth and unstabilized rammed earth. Unstabilized rammed earth structures are primarily made using natural materials like soil and aggregates. Conversely, stabilized rammed earth construction involves the addition of inorganic stabilizers such as cement or lime alongside natural materials.
Maintenance and care
The maintenance and frequency of a rammed earth structure depends very much on the composition used for the different constructive elements as well as on the climatic conditions in which it is located. Care practices and considerations vary depending on whether a rammed earth structure is stabilized (and how) or unstabilized as well as on the humidity or drought levels of the site.
Maintenance frequency for unstabilized rammed earth structures:
Due to the higher moisture content and potential for accelerated weathering, inspections should be conducted every six months to check for signs of damage, including cracks, erosion, or moisture ingress.
Crack Repair: Cracks should be repaired quickly to avoid continuous deterioration. Depending on weather conditions, cracks should be attended to every 6 months to 1 year.
Protective Finish Application: Due to their higher vulnerability to moisture absorption and erosion, the use of protective finishes such as breathable sealants or lime washes every 2-3 years is considerable.
Vegetation Control: Due to its humidity, vegetation trimming or pruning should be planned at least twice a year.
Maintenance frequency for chemically stabilized rammed earth structures:
Chemically stabilized rammed earth structures may require less frequent maintenance due to their enhanced resistance to moisture and weathering. However, regular maintenance is still essential to ensure the long-term durability and performance of the structure. Stabilized rammed earth structures should be inspected once a year for signs of damage, moisture, erosion, or moisture ingress.
Crack Repair: While chemically stabilized rammed earth is more resistant to cracking than unstabilized rammed earth, address any cracks promptly to prevent water infiltration and further deterioration. Cracks may need attention every one to two years, depending on their size and severity.
Protective Finish Reapplication: Depending on the type of protective finish applied to the rammed earth walls, plan to reapply coatings or sealants every three to five years, or as recommended by the manufacturer. This helps maintain the protective barrier against moisture and weathering.
Damage & Vulnerability
Mechanical damages
Rammed earth structures, known for their dense and thick composition, have both strengths and weaknesses. Their high density gives them strong resistance to compression but also makes them heavier. This heaviness can make them more susceptible to damage from uneven settling of the ground beneath them. Additionally, the material’s brittleness and low ability to withstand pulling forces mean cracks can easily form, especially if supporting elements like beams or trusses are directly connected to walls without proper intermediary support. However, it’s important to note that our understanding of how rammed earth structures behave under different conditions is still limited, particularly in terms of their more complex behaviors like nonlinear responses. This lack of knowledge isn’t just because of a shortage of research but also because the subject is quite challenging and hasn’t been fully explored yet.
Mechanical behaviour: The essential characteristics of natural earthen materials without stabilization are governed by the soil’s cohesion and plasticity. These properties primarily rely on factors such as the clay content and type, which dictate the soil’s texture in relation to aggregates. Additionally, the degree of compaction influences the amount of water and air present in the mixture, further shaping its qualities.
Vulnerability: Vulnerability is mainly related to the presence of water, erosion, and cracking under low compressive and tensile stresses, as well as low resistance to dynamic actions, which are worsened by the high dead-load of the structure.
Vulnerability against water: Clay minerals are hydrophilic, therefore the durability of earthen structures is mainly related to the action of water on the walls. All damages —with the exception of specific kind of cracks— can be directly or indirectly linked to the effects of water, which may be present from various sources, mainly rainwater.
How to avoid: Preventing water infiltration and mitigating associated damage in unstabilized rammed earth structures poses a persistent challenge. Employing sound construction practices and suitable architectural designs whenever feasible often proves to be an effective solution. For example, implementing proper rendering on external walls, ensuring adequate slopes and wide eaves to divert rainwater away from the wall, and constructing footings that minimize capillary rise and shield the wall from rain splash can all contribute to this effort.
Biological actions: Soil is susceptible to biological processes that can result in significant structural deterioration. Its high moistur content promotes the growth of vegetation, whose roots can cause cracks in the walls. Excessive moisture can also lead to the decomposition of straw, reducing strength and increasing acidity. This acidity can alter clay minerals and degrade lime, if present, further contributing to deterioration.
Composition
Clay: Clay provides cohesion to the soil mixture, helping it stick together and form a solid structure.
Silt: Silt particles are finer than sand but coarser than clay. They help to fill in gaps between clay particles, improving the overall density and stability of the soil mixture.
Sand: Sand adds grit and stability to the soil mixture. It improves drainage and reduces shrinkage during drying.
Gravel: Gravel provides additional stability and strength to the soil mixture. It helps to prevent cracking and enhances the load-bearing capacity of the wall.
Cement: Cement is often used as a stabilizer to enhance the strength and durability of the rammed earth wall. It chemically binds the soil particles together, increasing cohesion and reducing susceptibility to weathering. Cement is usually added in small proportions, typically around 5% to 10% by volume of the soil mixture.
Lime: Lime is another common stabilizer used in rammed-earth construction. It reacts with clay particles to form stable compounds, improving the plasticity and workability of the soil mixture. Lime is added in varying proportions, depending on soil characteristics and project requirements.
Asphalt Emulsion: Asphalt emulsion can be used as a stabilizer in regions with high moisture or where additional water resistance is desired. It forms a waterproof barrier within the soil mixture, reducing water infiltration and improving the overall durability of the wall.
Water: Water is essential for preparing the soil mixture and achieving proper compaction during construction. It acts as a binder, allowing the soil particles to adhere to each other and form a cohesive mass. The amount of water added to the soil mixture is carefully controlled to ensure optimal compaction and strength.
Reinforcement (Optional): In some cases, reinforcement materials such as steel mesh, rebar, or bamboo can be added to the rammed earth wall to improve its tensile strength and resistance to cracking. Reinforcement is typically incorporated within the wall during construction, providing additional structural support where needed.
Construction Process
The rammed earth construction needs a dismountable rigid formwork. The molds consist of two leaves linked by lengthy bolts.
The rammed earth casting process involves the following steps.
1. Setting the mold
2. Processing the soil Mixing the soil, gravel/aggregates, and stabiliser in dry state
3. Mixing the materials with water
4. Pouring the partially saturated soil-aggregate-stabilizer mixture into the mold
5. Compacting the processed material into a desired density
6. Dismantling the formwork
7. Curing
