LOW COST BUILDING MATERIAL AND TECHNIQUES

 1. RAT TRAP BOND

The rat trap bond is a masonry technique, where the bricks are used in a way which creates a cavity within the wall, while maintaining the same wall thickness as for a conventional brick masonry wall. While in a conventional English bond or Flemish bond, bricks are laid flat, in a Rat trap bond, they are placed on edge forming the inner and outer face of the wall, with cross bricks bridging the two faces. The main advantage of Rat-trap bond is reduction in the number of bricks and mortar required as compared to English/ Flemish bond because of the cavity formed in the wall. The cavity also makes the wall more thermally efficient. This also reduces the embodied energy of brick masonry by saving number of bricks and the cement-sand mortar. It is suitable for use, wherever one-brick thick wall is required. Since its original dissemination in Kerala in the 1970sby architect Laurie Baker, rat trap bond has been extensively used in every category of building from large institutional complexes, community buildings. Government offices/village panchayats, individual homes both for high income and middle income and also in government supported EWS housing programmes.

2. FILLER SLAB

Filler slab is a variation of conventional reinforced cement concrete slab in which part of the concrete is replaced with a filler material which can be a waste material to ensure economical advantage over an RCC slab. The basic principle in a filler slab is that, considering an RCC slab of a given thickness, the concrete in the bottom half of the slab is simply dead weight and does not play a role in taking up compressive load, which is normally taken up by concrete in an RCC slab. So, this concrete can be replaced by a suitable lightweight filler material which can be accommodated in the bottom half of the slab. Since it reduces the weight of the slab by replacing concrete, savings can also be achieved in quantity of steel reinforcement without any compromise on the quality and strength of the slab.  The filler materials commonly used are burnt clay tiles (such as Managalore tiles), bricks, coconut shells, terracotta pots etc. The filler slab was first popularized by architect Laurie Baker in India in the late 70s and subsequently promoted by HUDCO through its national network of building centres. It has been successfully tested for structural performance by the Research and Development laboratory by the Civil engineering department of Anna University , Chennai

3. MICRO CONCRETE ROOFING TILES

Micro-concrete roofing (MCR) tiles are used as a cladding material for construction of sloping roofs. They are 10mm thick and basically made up of a plain cement concrete which uses stone aggregate of less than 6 mm size. The concrete mix is well compacted through optimum vibration provided by an electric vibrator. These tiles derive their strength primarily from their shape and a very low water cement ratio used during production. When the tile is produced on a vibrating table top, it is flat. The tiles are moulded to their standardized profile after they are transferred to a plastic mould. The profile of the tiles is such that it enables overalp between adjacent tiles to prevent water leakage. The effective dimensions of the tiles (after overlap) are 400mm x 200mm, with 13 tiles needed for 1 m2 of roof area. The production package available for the tiles has been specially designed to provide a compact work-station with an integrated vibrating table to compact the tiles. MCR tiles can be laid over a variety of under-structures like trusses, rafters and purlins, made with steel, timber or even bamboo. Tiles of two profile types- Pan (curved) and Roman (flat) can be made using the production equipment.

4. FUNICULAR SHELL ROOF 

Masonry arches, vaults and domes have a long history of use in India over centuries and many of them have stood the test of time. Following the same principle, funicular shells can also be constructed as roofs or even intermediate floors. Funicular Shell Roof is a system comprising of two components – a doubly curved (curved in both directions, like a dome) shell and a reinforced concrete supporting beam around the perimeter of the shell.  The curvature of the roof is such that the rise of the roof at its centre is shallow – generally 150-200mm -  which can easily be filled up to create a flat surface, if needed in case of an intermediate floor. Generally, this system is advantageous for roofs which can be sub-divided into smaller sections using a grid of RCC beams, like a coffer slab. Each of these smaller sections can then be spanned by a separate funicular shells. Each of the beams can be partially cast before the shells are constructed and fully cast together with the shell. This roof is a very good option for areas where waste stone pieces can be accessed from stone polishing & cutting units and used in constructing the shell. The significant reduction in steel for slab construction and the creation of beautiful patterns using stone waste of different colours and bricks are special features of this technology. Anangpur Building Centre in the NCR region developed a funicular shell based roofing system and used it extensively in various projects.

5. PRECAST CONCRETE BLOCK MASONRY 

Concrete has a wide application in construction across various parts of a building – from foundation to columns to roof, because it can be formed into various shapes. Concrete blocks are precast masonry units which are rectangular in shape and made with plain cement concrete of a lean mix-proportion that ranges from 1:9 to 1:13 (1 part of cement: 13 parts of sand and stone aggregates). In addition to the basic components, the concrete for making blocks may also contain additives like admixtures to increase compressive strength, or improve workability. They have also been produced with improved textures for better durability and appearance using stone ships or glazed surfaces. Concrete blocks have been in use in India for nearly three decades and are commonly found in all parts of the country- both rural and urban. They also owe their popularity to the fact that speed of construction is enhanced since the blocks could be 5-10 times bigger than burnt bricks. Commonly available dimensions are length 200-400mm, width 100 or 200mm and height 150-200 mm. Both solid and hollow blocks are made – generally hollow blocks are used for partition walls. Various machines are available in the country for concrete block production

6. PRECAST RCC PLANK AND JOIST

This is a system which uses precast concete elements to construct a roof which can also be used as an intermediate floor. It consists of two main elements – 1. the plank which represents smaller sections of the slab and therefore of reduced thickness and reinforcement, and 2.Joist which is a beam spanning across the room to provide bearing for the planks. The joist is partially precast, with the remaining portion being cast in-situ after the planks are installed. The planks can be made in standard sizes of 0.3m x 1.5m and the joists can be 0.15m x 0.15m in size for a roof span upto 4 metres. The planks are supported over partially precast RC joists side by side and then joined together with in-situ concrete poured over the entire roofing area. Monolithic action of the slab elements is enhanced by leaving reinforcement hooks projecting out of joists and providing nominal reinforcement over the planks, before the in-situ concrete is poured. The technique has been developed by the Central Building Research Institute (CBRI) and validated by the BMTPC (Building Materials and Technology Promotion Council). The technique can be easily adapted by masons who are familiar with the similar technique of placing stone slabs over girders to construct roofs. Both elements of the roof – planks and joists can be manually produced at site using a wooden moulds. Alternatively, given the context of a large scale use such as housing project, they can be produced in a small enterprise mode using steel moulds mounted on vibrating tables. The technique has successfully been used in many rural housing projects and EWS housing developments.

7. STABILIZED EARTH BLOCK

Earth is one of the oldest and the most abundantly available building material and there are many examples all over the world which prove the durability of well constructed earthern buildings. There are many techniques of building with earth such as making masonry blocks out of earth, or making monolith earth walls by ramming. Stabilized Compressed Earth Blocks (SCEB), are an improved version of earth based masonry units. These masonry blocks are made by compressing earth/ soil by simple mechanical means. Although block production is feasible using a wide variety of soils, understanding type of soil available for SCEB is one of the most important aspects – generally sandy clay is the most appropriate. A small percentage of stabilizer – most commonly 5-7% cement is added to the soil mix to increase strength of blocks and their resistance to water. Several block presses, both manual and mechanized types, have been developed by various institutions and are available to produce blocks of various sizes. The thickness of walls made with SCEB are generally close to 230mm conventional burnt clay masonry. The distinct advantage of these blocks are their uniform sizes and good finish which should be left unplastered externally, provided the building design takes into account basic features of protection from water. This technology is also very amenable to local employment generation through a block production enterprise.