Chapter 9 ALTERNATIVE TECHNOLOGIES

Transcription

1 Chapter 9 ALTERNATIVE TECHNOLOGIES 9.1 INTRODUCTION In the current scenario of pollution caused by construction Industry in India, a need arises to cater the market demand with energy efficient materials and techniques. Use of Environmental friendly techniques is one of the option been explored to minimize the use of high energy materials; Concern for environment, minimize transportation and maximize the use of local materials and resources [18]. Innovation in design can also accolade towards maximum of 5 points under LEED rating [18, 21]. Thus in this present scenario, Centre for Sustainable technologies was formed in 1974 at Indian Institute of Science (IISc), Bangalore, to cater to developing technologies for sustainable development [18]. Some of the alternate technologies which can be utilized for the components of a housing unit using RAC and TRC are studied herewith. 9.2 COMPOSITE BEAM AND PANEL ROOFS This concept is based on the efficiency of beam and slab construction. The roofing consists of partially precast or cast-in-situ ribs/beams at certain spacing covered with panels. A typical composite reinforced tile-work panel roof is shown in fig 9.1. Fig. 9.1: Composite reinforced tile-work panel roof. [17] The panels (curved, folded or flat) and beams are connected through shear connectors to achieve composite action. Beams of precast reinforced concrete, rolled steel sections, trussed steel members, timber, steel, concrete composite, etc. are available and panels of precast concrete, reinforced brickwork, stone slabs, reinforced SMB panel, etc. Use of curved shape panels results in a composite jack-arch roof. The beam cross section can also be adjusted to minimize the material consumption. The major advantages of this type of roofing system are: Possibility of prefabrication and Study of properties of concrete made using Recycled aggregate and Industrial Page 193

2 quick erection, Better quality assurance due to prefabrication, Savings in volume of materials and hence cost effectiveness, and possibility of using hollow panels to increase thermal comfort [17,18]. 9.3 FILLER SLAB ROOFS Filler slab roofs are solid reinforced concrete slabs with filler material in the tension zone. The filler material could be cheaper and/or lighter. A number of alternative materials can be thought of: (a) brick or brick panel, (b) Mangalore tile, (c) stabilized mud block, (d) Concrete Waste etc. Figure 9.2 below shows ceiling of a typical filler slab roof using SMB filler. Depending on thickness of slab the tension zone of the slab can be replaced by filler material [17,18]. Fig. 9.2: Ceiling of a typical filler slab roof using stabilized mud block filler [17] Design parameters Filler slab can be designed like a conventional RCC slab, however the dead load reduction due to the filler material and the spacing of reinforcement as per the size of the filler material should be considered [111]. The thickness of filler material should not exceed the depth of the neutral axis. e.g. for a slab thickness of 125mm, the filler material depth should not exceed 60mm.The size and shape of the filler material selected should comply to the design requirements. Shape and size of filler material governs the quantity of concrete to be replaced in tension zone. Form cost consideration, effective compaction and ease in pouring concrete at least 25% of the concrete should be replaced by filler material Construction of filler slabs Important construction steps for filler slab are as discussed below. 1. The filler material to be used must be waste materials which are available locally and lighter than concrete. Refer fig 9.3. Study of properties of concrete made using Recycled aggregate and Industrial Page 194

3 2. The shuttering for slab is erected as for a conventional RCC slab. Fig. 9.3: Laying of Mangalore tiles for filler slabs. 3. A minimum bottom cover of 15 mm is kept after erecting the shuttering which forms a grid and filler material can be placed centrally in each space of the grid. No filler material is provided in bands of concrete along the edge of the slab. The width of these concrete bands is normally minimum 300 mm. The reinforcement spacing in these bands is smaller than spacing around the filler materials. 4. After all the filler materials have been placed any concealed electrical work etc., should be placed in the spaces between the filler material and then concrete is placed between the filler materials and top of it to achieve slab thickness. 5. Concrete vibrators must be avoided in bottom portion of slab as they may disturb the placement of the filler materials. Manual tamping is advised. Fig. 9.4: Reinforcement layout for filler slab [18] Reinforcement layout for a filler slab using compressed earth blocks as filler material of size 230mm x 190mm x 50mm.(Refer fig. 9.4) [17-19]. 9.4 RAT TRAP BOND FOR WALLS A Rat-Trap Bond is a type of wall brick masonry bond in which bricks are laid on edge (i.e. the height of each course in case of a brick size 230x110x75 mm, will Study of properties of concrete made using Recycled aggregate and Industrial Page 195

4 be 110 mm plus mortar thickness) such that the shinner and rowlock are visible on the face of masonry as in fig.9.5. Fig. 9.5: Rat Trap bond for walls [156]. A cavity is formed and bridged in the wall through the rowlock. The cavity adds an added advantage as it adds a Green building feature of help maintain improved thermal comfort and keep the interiors colder than outside and vice versa. Being a modular construction care must be taken for designing the wall lengths and heights. The openings and wall dimensions to be in multiples of the module. Also the course below sill and lintel to be a solid course by placing bricks on edge. The masonry on the sides of the openings also to be solid as will help in fixing of the opening frame [17,20]. The RFCA bricks made in the project (discussed earlier) can be used for a 1 or 2 storey housing unit with Rat-trap bond for walls Materials selection as per need and design Fly ash bricks and/or RFCA bricks can be used as compared to traditional bricks. Lime mortar can be used as it is locally available in many parts of the country and helps reduce the consumption of cement Advantages of using rat trap bond technology Rat-trap bond can save approx % less bricks and 30-50% less mortar; also this reduces the cost of a 9 inch wall by % and productivity of work enhances. For 1 m 3 of Rat trap bond, 470 bricks are required compared to conventional brick wall where a total of 550 bricks are required. Rat trap bond wall is a cavity wall construction with added advantage of thermal comfort. The interiors remain cooler in summer and warmer in winters. When kept exposed, create aesthetically pleasing wall surfcace and cost of plastering and painting also may be avoided. It can be used for load bearing Study of properties of concrete made using Recycled aggregate and Industrial Page 196

5 as well as thick partition walls with other components concealed. The walls have approx. 20% less dead weight and foundations and other supporting structural members can suitably be designed, this gives an added advantage of cost saving for foundation. In case of structural safety, reinforcement bars can be inserted through the cavity till the foundation. Cost saving of approx. 20% can be achieved with Rat-Trap bond construction for walls per m 3 [17,18, 20]. 9.5 ENERGY IN ALTERNATIVE BUILDING TECHNOLOGIES Energy consumption in buildings can take place in two ways: (i) energy capital that goes into production and transportation of building materials and assembling of the building (embodied energy), and (ii) energy for the maintenance/ servicing of a building during its useful life. The second one greatly depends on the climatic variations in a particular region. The first one is a one-time investment, which can vary over wide limits depending upon choice of building materials and techniques. Energy in conventional (common) and alternative building technologies and buildings, their implications on sustainable building construction practices are discussed in the following sections. Table 9.1 below gives the details of energy content in various types of common and alternative walling and roofing systems [19]. Table 9.1: Embodied energy in various walling and roofing systems [19] The table 9.1 indicates that: (a) Alternative roofing systems like SMB filler slab, composite panel roof, ribbed slab roof, etc. can be used in place of conventional reinforced concrete roof saving about 20 40% of energy, and (c) Ferroconcrete tile roof consumes 30% less energy when compared to conventional mangalore tile roof. Thus it is clear that use of alternative building technologies results in reduction of considerable amount of embodied energy. Embodied energy was computed based on the actual measurements of quantities during constructing these buildings. Energy per 100 m 2 of Study of properties of concrete made using Recycled aggregate and Industrial Page 197

6 built-up area of the buildings is considered for the purposes of comparison. A multistoreyed reinforced concrete framed structure building is most commonly used for building flats in urban areas. Also, it is very common to find 2 3-storeyed load-bearing brick and concrete slab roof buildings. The multi-storied building consumes highest amount of energy at 4.21 GJ per m 2 of built-up area, whereas the energy consumed by the load bearing conventional 2-storeyed brickwork building is 2.92 GJ/m 2 (30% less than that used by multi-storeyed framed structure building). Two-storeyed building using alternative building materials like SMB walls, SMB filler slab roof, etc. is highly energy efficient. The energy consumed by this building is 1.61 GJ/m 2, which is about 40% and 55% of that consumed by multi-storeyed building and conventional brick wall building respectively. This clearly indicates that use of alternative building technologies results in considerable amount of reduction (50%) in embodied energy, thus paving the way for efficient utilization of energy resources and simultaneously reducing GHG emissions, thereby protecting the environment. Major features/impacts of the alternative building technologies discussed in the previous sections can be highlighted as follows: 1. Energy efficient, consuming less than half of the energy required for conventional building methods leading to energy conservation. 2. Techniques are simple and employ maximum local resources and skills 3. Reduce cost and energy involved in transportation of building products. Recycled aggregate brick was the concept taken and tested in the current project. 9.6 CLOSURE Study of Filler roof pattern, unreinforced masonry vaulted roofs and Rat trap bond can help in using these techniques in components of a housing unit using RAC and TRC. Housing unit along with concrete made using RA and SR and CR and these alternative techniques can be adopted for saving in energy and cost. Study of properties of concrete made using Recycled aggregate and Industrial Page 198