LOW COST CONSTRUCTION TECHNIQUES

Low cost construction is not always low cost housing for poor but it is cost effective construction techniques.

Cost effectivenessEconomics are dependent on very diverse factors, some of which are not within local control. But certain factors can be controlled by the local area for the enhancement of the local economy.•Less outflow of money and other resources by the adoption of certain technologies and materials •Creation of employment by up-gradation of local skills •Innovative use of the available building materials •Direct market and supply connection - elimination of the middleman •Labour intensive approaches

Sustainable technologies, use of renewable energy sources is also very much part of low cost construction.

It includes-Traditional construction technologies like-Earth construction-compressed earth blocks-Rammed earth technology-Rat trap bond wall-Filler slabs-Brick arches and vaulted structures.

Advanced technologies include-Ferro cement technology.

Earth construction-Raw earth for building has been used worldwide for millennia but during the 20th century most of the skills of earth builders were lost and building with earth became marginal.Most of the projects are built with compressed stabilised earth blocks (CSEB), as this technology benefits of more than half a century of research and development worldwide. Stabilised rammed earth is also usedextensively for foundations and to a lesser extent for walls. In Auroville, CSEB present several advantages compared to the local country fired bricks:• Walls made of CSEB and stabilised rammed earth are always cheaper than fired bricks.• The initial embodied energy of CSEB produced on site with 5 % cement is ~ 4 times less than the local country fired bricks.• The strength of these blocks is most of the time higher than the local country fired bricks.There are also three other earth techniques used in Auroville. These techniques are very marginally used as only about 10 buildings have been built with them:• Raw rammed earth• Adobe blocks, the traditional sun dried mud brick• Wattle and daub which is mud plastered on a wattle made of split bamboo or palmyra tree

APPROPRIATE BUILDING TECHNOLOGIES BASED ON EARTHThe main research and development is focussed on minimising the use of steel, cement and reinforced cement concrete (RCC). Most of the technologies developed have now been mastered and the presentThe building is constructed entirely with stabilised earth, from the foundations to the waterproofing:• Stabilised rammed earth foundations (with 5 % cement)• Stabilised rammed earth walls (with 5 % cement and a “homeopathic” milk of lime and alum)• Composite columns (round and hollow CSEB with reinforced concrete)• Composite beams (U shape CSEB with reinforced concrete)• Stabilized earth mortars and plasters• Wide variety of compressed stabilised earth blocks (17 moulds are presently available for producing about 75 different types of blocks)• Various vaults with compressed stabilised earth blocks• Alternative stabilizers to cement (“homeopathic” milk of lime and alum)• Alternative waterproofing with stabilized earth (various mixes of soil, sand, cement, lime, alum and juice of a local seed)

COMPRESSED STABILISED EARTH BLOCKSCSEB is nowadays the earth technology, which is the most used worldwide, as well as in Auroville, because it represents a synthesis between traditional practices and a modern technology.In Auroville, CSEB are stabilised with 5% cement and have an average dry compressive crushing strength of 50 kg/cm2 (5 Mpa) and a wet compressive crushing strength of 25 kg/cm2. The water absorption is around 10%. Country fired bricks have resist at around 35 kg/cm² for the dry compressive strength and have a 12% water absorption rate.The Auroville Earth Institute has designed manual presses for CSEB

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Building constructed using compressed earth block.

STABILISED RAMMED EARTHIn Auroville, the earth is rammed by hand. Until 1994, Auroville had only one house made of raw rammed earth. Stabilised rammed earth was promoted since 1995, after the construction of Mirramukhi School(presently named Deepanam). Stabilised rammed earth presents the advantage of being cheaper than compressed stabilised earth blocks.

Stabilized rammed earth foundations-The soil is excavated from the trench foundation. It is sieved and then measured at the same time on the side ofthe trench. Sand always needs to be added. In Auroville, we use always 5 % by weight of cement and the mix is as follow: 500 litres soil + 200 litres sand = 1 bag cement (50 Kg).

Stabilized rammed earth foundations-

Stabilized rammed earth walls-A slipping type formwork has been designed and developed. The panels are lifted up and the walls are built like piers walls. Our process is similar to the modern rammed earth system practiced in USA or Australia, but adapted to the local context of a developingcountry. We ram by hand and we have developed also some peripheral equipment.Some sand is always added: 25 to 30 % according to the soil quality, so as to reduce shrinkage. Cement percentage will vary with the soil quality, but in Auroville, we always use 5 % by weight of cement.

VALUTED STRUCTURESThis R&D seeks to increase the span of the roof, decrease its thickness, and create new shapes. Note that all vaults and domes are built with compressed stabilised earth blocks which are laid in “Free spanning”mode, meaning without formwork. This was previously called the Nubian technique, from Egypt, but the Auroville Earth Institute developed it and found new ways to build arches and vaults.

COST EFFECTIVENESS OF EARTHEN BUILDINGSEarthen buildings have the advantage of using local resources and being labor intensive. Therefore, most of the time, they cost less than conventional materials and technologies. The final cost of a building will depend mainly on the design, the type of finishes and the project management. In all cases, the technologies implemented are cost effective.

In Auroville, a finished m3 of CSEB masonry is always cheaper than fired bricks: 15 to 20 % cheaper than country fired bricks. Walls made of compressed stabilized earth blocks are already cheaper than fired bricks

but stabilized rammed earth walls are even cheaper than CSEB masonry. The material for CSEB or stabilized rammed earth is the same, but the difference comes from the fact that the blocks have to be cured on the ground, lifted and built by masons later on.

In the case of stabilized rammed earth, the walls are made by semi skilled labor and they stand in place at the end of the day. Therefore, a finished m3 of rammedearth wall is 20 to 30 % cheaper than CSEB wall and 30 to 50 % cheaper than fired bricks.

Rat-trap bond in wall construction: There are several types of bonds developed in different countries from time to time. They are called as stretcher bond ,English bond, Flemish bond and rat-trap bond. The rat-trap bond is laid by placing the bricks on their sides having a cavity of 4″ (100 mm), with alternate course of stretchers and headers. The headers and stretchers are staggerd in subsequent layers to give more strength to the walls. The main advantage of this bond is the economy in use of bricks, giving a wall of one brick thickness with fewer bricks than a solid bond. Rat-trap bond was commonly used in England for building houses of fewer than three stories

The main features of rat-trap bond wall are:• Strength is equal to the standard 10″ (250 mm) brick wall, but consumes 20% less bricks.• The overall saving on cost of materials used for construction compared to the traditional 10″ wall is about 26%.

The air medium created between the brick layers helps in maintaining a good thermal comfort inside the building. This phenomenon is particularly helpful for the tropical climate of South Asian and other countries.• As construction is done by aligning the bricks from both sides with the plain surface facing outwards, plastering is not necessary except in a few places. The finished surface is appealing to the eye.• Buildings up to two stories can easily be constructed with this technique (Figure 2). Baker has pioneered this type of construction and had built such houses more than 40 years ago, without showing any signs of distress till now.• In RCC framed structures, the filler walls can be made of rat-trap bond.

FILLER SLAB IN ROOF: This is a normal RCC slab where the bottom half (tension) concrete portions are replaced by filler materials such as bricks, tiles, cellular concrete blocks, etc. These filler materials are so placed as not to compromise the structural strength, result in replacing unwanted and non-functional tension concrete, thus resulting in economy. These are safe, sound and provide aesthetically pleasing pattern ceilings and also need no plaster

The main features of the filler slab are:• Consumes less concrete and steel due to reduced weight of slab by the introduction of a less heavy, lowcost filler material like two layers of burnt clay tiles. Slab thickness minimum 112.5 mm

• Enhances thermal comfort inside the building due to heat-resistant qualities of filler materials and the gap between two burnt clay tiles.

• Makes saving on cost of this slab compared to the traditional slab by about 23%.

• Reduces use of concrete and saves cement and steel by about 40%.

FERRO CEMENT TECHNOLOGYAlthough ferrocement is not strictly a 'sustainable' technology as it uses cement and steel, it nevertheless employs them in a highly efficient and cost-effective manner. Ferrocement is a thin cement mortar laid over wire mesh, which acts as a reinforcement. It is relatively cheap, strong and durable, and the basic technique is easily acquired. Ferrocement in Auroville is used, among other things, in the construction of roof channels, doors, water tanks, latrines, slabs, various form works and biogas plants

FERRO CEMENT TECHNOLOGY•A ferrocement is a thin wall of reinforced cement, where layers of continuous mesh are covered on both sides with mortar n•Ferrocement elements are durable, versatile, light and waterproof n •A ferrocement channel (FC) is a longitudinal element of a curved section (often semi-cylindrical). It is precast using moulds •A ferrocement channel uses less cement and steel while having the same strength as the same RCC •FC are used for floors or roofs, but are bad thermal insulators •A major cost reduction is achieved compared to RCC •A simple and cheap manufacturing set up is needed but the areas for prefabricating and curing need to be quite large It is easy to acquire the skill and easy to manufacture•A constant quality control is needed during the manufacturing process and a proper curing is needed for one month•If the channels are not manufactured on site, transportation has tobe organized while taking care against damage•Ferrocement channels are lifted into place and can immediately bejoined together in order to provide a shelter•No need of scaffoldings, shuttering, concrete mixer or vibrator