INVESTIGAÇÃO & DESENVOLVIMENTO

CONSTRUÇÃO SUSTENTÁVEL

Sustainability is a concept that has monopolised a large number of the scientific debates in a wide range of spheres connected not only with architecture, urban planning and construction, but also with the product market, tourism, culture, etc. However, sustainability is indissolubly linked to vernacular architecture and the lessons this architecture of the past can teach us for the future. The concept of sustainability as it is presented is wide-reaching and encompasses not only environmental issues but also sociocultural and socioeconomic questions. The lessons we can learn from studying vernacular architecture in these three broad spheres are manifold, and can help us not only to further the conservation and retrieval of this architecture already in existence but to rethink new architecture in the light of what we have learned.

A construção sustentável implica a utilização de materiais renováveis, recicláveis e/ou reciclados (madeiras, resinas e tintas, rebocos, cortiça e outros isolamentos naturais), que não contaminam o meio ambiente, com excelente desempenho térmico e acústico e baixo consumo energético ao longo das diversas fases de uma construção (extracção / transporte / transformação / execução / utilização / reciclagem). 

Na Arq2T. Atelier projectamos com base em parâmetros técnicos quantificáveis e critérios bioclimáticos locais, integrando o construído na envolvente e utilizando todo o potencial da topografia, das orientações solares e da ventilação cruzada, potenciando as qualidades naturais dos materiais com a inércia térmica da terra crua ou a resistência estrutural da madeira.

Em paralelo desenvolvemos sistemas tecnológicos completos com a integração e aproveitamento das diversas fontes de energia renováveis, como o sol ou a geotermia, garantindo um conforto interior agradável e natural com consumos e custos mínimos de energia ao longo de todo o ano.

O Material

Silt, clay, soil are natural building materials and occur in different compositions under the top mold in every part of the world. Silt is made up of clay and sand and develops out of the destruction of other native rock. Hardly any silt is the same. The sand and clay parts are just as important as the clay kind for its building characteristics. Silt soils often show the complete spectrum of soil colors: from white to light beige, yellow to ochre, brown to gray blue and red. In its damp condition, silt is according to its composition, a more or less ductile material which becomes load-bearing through air drying. More than a third of the world's population lives in houses, which have been built completely or at least to some part in silt and rammed earth. Up to 40 different earthen building techniques have been used. Just as different the local silt and soil compositions are, so are the according earthen building techniques.

Building techniques

Rammed earth is a thousand of years old building technique and is a widely used. Crumbly, soil-damp and relatively lean silt matter is poured in layers into a mould and compressed mechanically. A certain advantage of the rammed earth technique is, that the mixture of silt, sand and gravel often appears in nature and is perfect in its characteristics for this building technique. With this in mind, 50% to 100% of the excavation material without top soil can be used for building. Rammed earth is a very solid, its density can be compared to concrete and its specific weight is, according to the mixture and its location from 1,8 to 2,2 t per cubic meter. Its best use is for load bearing earthen structures. Also for heat storing in glass houses and in the combination with heating systems can the technique be applied technically and creatively. The handling of the earth masses requires a contemporary, mechanical conditioning and a rational building site management. Silt and clay has the positive effect that it can be conserved damp in its conditioned state over weeks or years. The quality of the material can even be improved through the storage (Mauken). 

With the Pisee-technique the silt and earthen mixture is compressed periodically in horizontal layers of roughly 12cm thickness in the mould. The crumbly, soil-damp mixture is poured in layers and is compressed with air compression beaters and vibration rolls. After every third layer, a mortar layer is mounted on the mould edge and also compressed into the mixture. Alternatively stone or brick sheets can be used. A working section and mould section is 15 m to 20 m long at the maximum and not higher than 2,8 m. The vertical alignment splices to the next wall section come up in an angle of 40°. At a storey-high mould the wall thickness is usually at 60cm, as the mould has to be accessible for the compression procedure. On smaller mould sections the thickness of the load bearing walls can be reduced, according to the structural purpose, to 20 or 40 cm.

Consistency

Silt and silt bound building materials are soluble in water, in principle. If the hardened earth is worked on with enough water, the consistency reached through drying is reversed. The material becomes ductile and moldable. In this sense silt earth is the only building material that can be reused unrestrained and without quality loss. The water solubility is of course a problem for the weather and erosion proofing of earthen buildings. A lot of experiments and developments go into the direction of annihilating this quality from the silt and making it more durable for wetness. With supplementing cement this can be reached to a certain extent, however other very positive characteristics of the silt earth will be impaired. Silt earth shows a equilibrium moisture content of about 6 to 7 %, which means it is dryer than wood, but has the ability to absorb dampness out of the air very fast and releasing it at the same speed. Although this fast drying quality the rammed earth constructions need to be shielded well against moisture penetration, especially from above through constructive measures.

In order to avoid ascending moisture the walls are placed on a concrete plinths which rise 35cm out of the fastened or unfastened soil. As a horizontal isolation between the concrete and the rammed earth bitumen sheeting is spread out. For the coping of the wall crest and the outside of Parpetten, metal sheets or ceramic tiles can be used with projections of 5 to 15 cm according to the wall height. The lintels of windows and door openings will be built in during the compression of the mixture into the mould, with the load being transferred off to the side. The undersides of lintels are constructed in concrete (pre-fabricated) or done in steel. In the case of larger door openings or window series, reinforced concrete bands made of site-mixed concrete are integrated into the earthen walls.

Quality controlling

Since load bearing and bracing rammed earth wall have in only very few cases been tested for planning laws and circumstances, hardly and norms and numbers exist, an affirmation of its use will be needed in every building situation. This requires locally identified testing circumstances before and after the building process. After the excavation, the local material will be analyzed; one or two mixture recipes will be made. With this mixture cylindrical probes are fabricated, burst strength, modulus of rupture and (if needed) creep resistance will be tested. On the basis of preliminary tests, monitoring tests will be conducted during the whole building process. Special attention has to be given to the dampness in the core of the rammed earth wall. The loading of the earthen walls with roofing constructions for example can only begin at the state of complete dryness within its core.

Specific values

The following properties are based on data which were acquired in the Berlin reconciliation church in a testing procedure conducted at the technical university of Berlin, institute for design, construction, building economics and building law, department for structural engineering and building construction. The properties were accepted and accredited by the local building authority.

Nominal compression strength: 2,40 N/mm2
Bending tensile strength: 0,52 N/mm2
Shear strength: 0,62 N/mm2
Mixing in fibers, flax or hay can result in a enhancement of these characteristics.
Material shrinkage: 0,25 %
Creep resistance: 0,2 %
Dilatation: 0,005mm/m.K.
Thermal conductivity: according to Material 0,64W/mK up to 0,93W/mK

Aging process

Due to the special structure and color of the rammed earth, erosion and partial damage will not become very obvious and critical. A minimal erosion process is given in every case and will be technically and artistically accounted for. Earthen walls ideally undergo a natural aging process, especially because of the UV resistance of the earth pigments. Because of its dryness and the hygroscopic activity of the silt material, microorganisms and fungus cannot develop. The facades show in the course of decades hardly any color changes, the color intensity even becomes stronger as time passes on. With a technical flawless building process of edges and surfaces, maintenance should not be needed for decades. Even if erosion intensifies, the rammed earth walls can be retouched with the same raw material, so that the repair is hardly to be seen.