Ivan Tamayo Ramos

Tierradura.mx

25 August 2020

 

Standardization of Rammed Earth Construction Methods and Soil Design

 

In order to meet the Sustainable Development Goals proposed by the United Nations, we must improve the technologies and materials of the construction industry worldwide. I am keen on participating in the effort to solve climate change via the decarbonization of our built environment. My interest in sustainable construction started in 2014 when I had the opportunity to attend a workshop for sustainable construction organized by Base Habitat, from the University of Linz in Austria, I was introduced to rammed earth as a building material and construction method by Austrian expert Martin Rauch. I decided to continue with the implementation of rammed earth construction in Mexico. Such endeavor led me to Arizona, USA where I met pioneer Quentin Branch from Rammed Earth Solar Homes who helped me build a model house for a sustainable community of agricultural workers in the Sonoran desert. 

Through intensive experimentation, I managed to build the tallest single wall in Mexico at the time (2017), 7 m high by 5 m long and 45 cm wide, for a private house in Culiacán, Mexico where I innovate by integrating a concrete structure built inside the wall.

 A gratifying experience was to build a community center for the Fairtrade Foundation in a village named Los Janos. Another milestone in my career was the design, project management and construction of Viva Organica, an agricultural complex that includes a rammed earth building. The project is published by Archdaily under my architecture studio Tierradura.

Rammed earth has been used for centuries across the globe, for foundations, floors, and walls. Nowadays it is experiencing an exponential resurgence due to its structural, thermal, and aesthetic characteristics. The material gained exposure and popularity with its appearance on the first episode of a Netflix show The World Most Amazing Houses in 2017.

Renowned architects worldwide are choosing rammed earth walls for their projects. Among them are Herzog de Meuron, Renzo Piano, Peter Zumthor, and Tatiana Bilbao. The Morocco Pavilion by Oualalou + Choi architects is designed to be a 33 m high rammed earth building for Dubai expo 2020. Norwegian architecture company Snøhetta has an ongoing research project named CLAY where it is finding applications for earth-based materials.

Among the pioneers of contemporary rammed earth construction are Anna Heringer in Germany, David Easton from Rammed Earth Works in California, Meror Krayenhoff from SIREWALL in Canada, and John Oliver from Rammed Earth Construction in Australia.

Rammed earth makes use of excavated subsoil. By using locally available materials, it reduces cost and minimizes environmental impact in the form of GHG (greenhouse gas) emissions. When implemented without industrial additives, raw earth mix is always a recyclable material.

An ideal proportion of possible granularity, with a visibly wide range of possibilities, is clay between 10 and 40%, silt between 10 and 40%, sand between 35 and 65%, gravel between 0 and 40% (Monsiuer, 2019). The size of the particles can vary from 5mm to 2.5 mm. 

The granularity will influence the aspect of the walls. Gravel and stones will be visible on the surface of the wall providing an interesting texture. Rammed earth requires the soil mix to have 16% humidity when compacting.

There is a need to research new ways to improve strength and durability using ecological additives. GHG emissions are considerably higher when stabilizing the soil mix with cement. The Global Warming Potential of modern Portland cement is close to 830 grams CO2 per kg of cement, about 40 times larger than earth. (Van Damme & Houben, 2020) Thus, even moderate incorporation of cement – say, 5 to 10% – represents a significant increase in GHG emissions.

The productivity of rammed earth construction depends on site circumstances, weather conditions, formwork system workers, and tools proficiency. Generally, the design and assembling/disassembling of formwork are one of the most time-consuming processes in rammed earth construction. Formwork can be standard or customs systems depending on the design of the structure. It can be made by plywood or steel sheets. Like concrete formwork it is required to have sufficient strength, stiffness, and stability to resist pressures it is subjected to during assembly, compacting, and dismantling. 

To compact with rammed earth it is necessary to have a pneumatic tamper powered with a medium-size air compressor, a bobcat for mixing large quantities, a hand/ manual tamper for leveling the layers of earth before compacting, a water tank and a hose with a pump. 

A large part of the job can be done by unskilled labor, but it is necessary to have an expert on-site to make sure the design of the soil mix is adequate and uniform. The mixed moist soil is poured in the formwork creating a uniform level of 15-20 cm, which after ramming is compressed to 10-15 cm hence compacting the total volume by one third. 

Productivity rates for rammed earth construction vary between 5hrs/m3 to over 25hrs/m3 depending on the high or low technology as well as the thickness of the walls which are usually 45 cm thick for load-bearing and 17 cm thick for non-bearing.

External walls of our rammed earth buildings are a minimum of 30 cm thick, to provide slow thermal exchange from extremes in climate. Remaining cool inside when it's hot outside and keeping warm interiors when cold outside.

Thermal Storage is a measure of the specific heat capacity expressed in volume terms and has units of J/m3. Houben and Guillaud (1994) claim that for rammed earth the thermal storage is around 1830 J/m3 (Dabaieh, 2019). The R-value is a measure of resistance to heat flow through a given thickness of a wall and is measured in m2 K/W. A 30 cm thick rammed earth wall has an R-value between 0.35-0.70 m2 K/W (Berge, 2009). 

Rammed earth is hygroscopic, cladding systems, and finishes must be vapor-permeable to allow evaporation. This is important for unstabilized walls, but less-so for stabilized walls where the cement will impair breathing. Nonetheless, it might be wise to consider vapor-permeable solutions for both instances to reduce the chance of condensation.

The future of earthen construction depends on the regulation of the industry. New soil standards and building codes will help escalate the use of rammed earth making it a trustworthy option for homeowners. The New Mexico Building Code states that the minimum compressive strength of a rammed earth wall is of 2.07 N/mm² or 300 psi while according to the Code Enforcement of Rammed Earth Structures of Zimbabwe, the minimum values of compressive strength is of 1.5 N/mm²  or 217 psi for one-story buildings and thick wall of minimum 400 mm and compressive strength of 2.0 N/mm² for two-level buildings (Maniaditis & Walker, 2003). Rammed earth weighs approximately 1950 kg per cubic meter.

Research and innovation of rammed earth and its variants have the potential to supply a large demand for future construction needs both in developed and developing countries. New strategies have been developed combining traditional techniques with modern construction systems and additives. A low tech variant is CEB, compressed earth blocks. CEB is a sustainable alternative to cinder blocks or fire bricks. A CEB producer is Watershed Materials by Rammed Earth Works in California.

Either ramming complete walls or producing compressed earth blocks by standardizing and automating processes we can speed up construction while lowering costs and risks. Reducing GHG emissions, helping the planet, and providing a sustainable habitat for people. 

 

Works Cited

VAN DAMME, Henri, and Hugo HOUBEN. “SHOULD RAW EARTH BE IMPROVED? AN ENVIRONMENTAL ASSESSMENT.” Amaco.org, Apr. 2020.

Dabaieh, Marwa. (2014). Building with Rammed Earth. 10.13140/2.1.4198.3048. 

Berge, Bjørn (2009). The Ecology of Building Materials. Architectural Press

Maniatidis , Vasilios, and Peter Walker. Review of A Review of Rammed Earth Construction for DTi Partners in Innovation Project ‘Developing Rammed Earth for UK Housing,’ May 2003, people.bath.ac.uk/abspw/rammedearth/review.pdf.

Monsiuer, Y. (2019). [online] Desertcreekhouse.com.au. Available at: http://www.desertcreekhouse.com.au/building2/rammedearth.pdf [Accessed 1 Apr. 2019].

Rammedearthconsulting.com. (2019). [online] Available at: http://www.rammedearthconsulting.com/library/african-rammed-earth-harmonised-standard-en.p df [Accessed 1 Apr. 2019].

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