Housing and Building National Research Center, Egypt
The energy consumption in construction sector consumes a large part of the total energy produced in Egypt. The rise in energy price and its impact on the environment increase the need to study how to save the consumed energy in the construction sector. To achieve such a purpose, new building techniques are used in order to save energy in material's manufacturing process by decreasing the weight of the construction materials and reducing energy for heating and air conditioning by using materials with high thermal insulation. Moreover, the energy can be saved through using local building materials to reduce the consumed energy of manufacturing and transporting. In this paper, the light is shed on the important types of sustainable building systems that are available recently in Egypt. In addition, it provides an evaluation of these systems in terms of their advantages and disadvantages in order to attain the suitable structural systems in Egypt. It is found that reinforced concrete system is the most suitable for buildings in cities and dense populated villages in Egypt, while load-
Keywords:Sustainable, Green, Reinforced, Concrete, Buildings, Bricks
In developing countries, the construction sector constitutes more than 50% of investments which encourage the economic and social developments. On the other hand, this sector consumes a large portion of resources (raw stone, gravel and sand) and about 30 % of the total solid waste in the world. Also, it consumes about 40-
The sustainable development is defined as the development that meets the needs of the present without compromising the ability of future generations to meet their own needs. The sustainability achieves the balance between economic development, social development, and environmental protection. Sustainability in the construction sector refers to all practices that should be adopted in order to ensure that a building is environmentally friendly, economically feasible as well as healthy and comfortable to its users. Sustainable building (Green building) refers to both the structure and its processes that are environmentally responsible and resource-
2. Sustainable Building Materials
The priorities for selecting building materials are:
The evaluations of available sustainable systems, in terms of their advantages and disadvantages, are presented.
2.1 Buildings of mud bricks
Mud bricks made of a mixture of loam, mud, sand and water mixed with a binding material such as straw, bricks were generally sun-
2.1.1 Mud Buildings by architect Hassan Fathy
The architect Hassan Fathy provided an approach of poor architecture in the last century through constructing a mud village in Qurana (south of Egypt). The architecture of buildings allows retention of cool air at night to be spread during the day when heat increases. The thickness and type of the walls increase the thermal resistance of walls which makes homes cool in summer and warm in winter. On the other side, some experts believe that the application of this system at this time is not suitable due to: the scarcity of clay materials, higher labor cost, the difficulty of maintaining the quality of execution, the difficulty of providing safety and short life in this type of construction compared to other. Therefore, this approach is no longer valid for our time, as it was not successful at the time of its appearance. This kind of architecture is used for tourism and recreation (Katab, 2007). The amendments of these buildings have been made through demolishing some components and rebuilding by the burned bricks and reinforced concrete (Mohamed, 2013).
2.2 Buildings of Sandbags
A sandbag is a bag made of polypropylene or other materials that is filled with sand or soil. Sandbags are also used to make inexpensive, environmentally sustainable homes. The bags, when empty, are compacted and light-
2.3 Rammed Earth Buildings
Rammed earth is a technique for buildings using natural raw materials such as earth, lime or gravel. Rammed earth walls are executed either by a solid wall of earth or individual blocks which are stacked like regular blocks but are bonded together with a thin mud slurry. Rammed-
2.4 Masonry Buildings
Masonry structure is one of the oldest building techniques. The common materials of masonry construction are clay or shale or sand brick, stone such as limestone, and concrete block. Masonry has many attributes that make it green and sustainable. Masonry is generally a highly durable form of construction as well as is a sound attenuation. It also offers protection from fire damage and increase the thermal mass of building. Although the wood is an important construction material because of its renewability, the masonry buildings are more resistant to projectiles than wood buildings. Moreover, they consume less reinforcement steel and cement and less expensive compared to reinforced concrete buildings. The disadvantages of masonry structures are the vulnerability during earthquakes as well as inability to remove walls or modifying their places after its creation.
2.5 Structural Insulated Panel Buildings (SIP)
Panel systems are defined as those building components that arrive at the site either partially or fully fabricated, which are joined to other panels to create walls, floors, and roofs of a house. A structural insulated panel (SIP) is an engineered composite product composed of an insulating core sandwiched between two face materials. SIPs are most commonly made of expanded polystyrene insulation board laminated between two oriented-
SIP systems bring many benefits and some drawbacks when compared to traditional buildings. The energy efficiency of homes constructed using SIPs can be very high compared to standard framing techniques. Although SIPs have a higher initial cost than traditional framing materials cost, saving will be achieved in the long run due to reducing of energy for heating and air conditioning. In addition, SIPs provide a more airtight dwelling, which makes a house more comfortable and quieter. The structural insulated panels have a high strength-
2.6 Reinforced Concrete Buildings
Reinforced concrete is one of the most important available materials for construction in Egypt and all over the world. In addition, reinforced concrete has many positive qualities: high compressive strength, thermal mass, low maintenance material, durability, great resistance to fire, ability to be cast in a variety of shapes. Therefore, concrete conforms to the ideal sustainable building material concept. But, the key issue with concrete is carbon dioxide emitted in the cement manufacturing process. Fly ash and blast furnace slag can also be blended with cement, resulting in reduced carbon dioxide emissions, reduced energy consumption, and expanded production capacity (Chales, 2008).
3. Selecting a Suitable Structural System of Typical Buildings in Egypt
The selection of structural system for building is influenced primarily by the intended function, architectural considerations, internal traffic flow, height and aspect ratio and the intensity of loadings (Paulay & Priestly, 1990). The structural system can be considered as sustainable when all the three dimensions of sustainability (environmental, economic, social) are taken into consideration. The choice of the material of structural system which achieves all of these aspects is not easy to make, however, the most suitable design is likely to satisfy these aspects.
Two case studies were selected as typical low-
3.1 Case Study 1
For 3 stories model, the comparison between reinforced concrete, masonry and load bearing SIP systems was carried out. Beside to reinforced concrete system, the building is redesigned for masonry structure system and load bearing SIP system with the same architectural plan. The load bearing masonry building is designed according to Egyptian code for masonry structures. The width of masonry walls equals 250 mm. The floors are reinforced concrete solid slab and the foundation of building is a R.C. strip footing.
The insulating foam core sandwiched panel is considered to represent structural insulation panels. M2 is one type of insulating foam core panel products which has a section of polystyrene, steel and cement mortar used in the construction of floors, roofs and walls. M2 system applied in the Egyptian market showed flexibility to be used as independent construction system or to combine with reinforced concrete skeleton systems and act as isolated wall element (El-
The selected parameters in comparison are the total vertical loads, the initial cost, the amounts of materials (reinforcement steel, cement, masonry, gravel and sand) of three structural systems of the case study as well as the total energy consumption in construction process of the building materials. Table 1 illustrates the initial cost of different systems of "build your home" model. The cost is calculated assuming that the prices of cement and reinforcement steel equal to 500, 4300 pounds per ton, respectively. Also, table 1 illustrates the amount of reinforcement steel, cement, bricks, sand and gravel of three structural system of case study which include all items of construction, plain and reinforced concrete, brick masonry, interior and exterior plaster and Flooring. In addition, table 1 shows the total energy consumption in construction process of the building materials ( embodied energy ) which is calculated by the product of the quantity of the material and the energy needed for producing a unit weight of the material. For example, the energy consumption of R.C. system = 10.4× 45 + 57.1×6.5 + 85× 5 + 423 × 0.5 = 1475 (Giga joule).
It can be noted from table (1) that the total initial cost of SIP system is approximately the same as the cost of R.C. system, while the total weight of SIP system decreases of about 30 % compared to R.C. system. The amounts of reinforcement steel and cement of SIP system decrease of about 50 % and 32 % respectively, if compared to R.C. system. Therefore, the energy consumption of SIP system is lower than energy consumption of traditional systems by more than 50%.
It can be concluded that SIP systems are suitable for additional stories above existing buildings due to light weight and the buildings required saving energy, after the checking the precautions required for this type of construction
Table (1) illustrates that the initial cost of masonry system is lower than the R.C building system by 11 % , while the total weight of masonry system is greater than the weight of R.C. system of about 32 %, the increase is due to the wall thickness equals 250 mm in masonry system while the wall thickness equals 120 mm in R.C. system. The amounts of reinforcement steel and cement of masonry system decrease of about 57 % and 12 % respectively, when compared to R.C. system. The total energy consumed of masonry system is higher than energy consumed of R.C system of about 14 % due to the amount of bricks increase more than double.
The initial cost of one story masonry system of case study 1 is lower than the R.C. system by about 20 %. With increasing the number of stories, the difference of cost between the masonry and R.C. systems decreases. The cost of 5 stories masonry system is approximately the same as the cost of R.C. system (El-
It can be concluded that load-
3.2 Case Study 2
Based on the results of case 1 study, reinforced concrete system is suitable for residential buildings (for 5 stories or more). The masonry wall width is equal to 120 mm which is frequently used to infill reinforced concrete buildings. But, it is recommended to use the partitions walls from materials with light weight and high thermal resistance. To illustrate this objective, the comparison was conducted between different types of partition walls in the selected typical residential building (case study 2). In addition to ordinary bricks (hollow shale), several types of bricks were studied. The types of bricks are light sand lime bricks, shale bricks and cement bricks with thickness equals 120 mm and 250 mm. Also, SIPs were used as partition walls. The insulating foam core sandwiched panel was selected to represent structural insulation panels, 120 mm thickness with a 60 mm thick polystyrene core, as mentioned in Figure 8.
3.2.1 Weight of Walls
Table 2 illustrates the weight of walls per square meter and the total weight of floor per square meter for the case study 2 model for different types of partition walls. The total weight includes the walls weight, the own weight of structural members, floorings and the live loads. It is evident from table (2) that the weight of walls (120 mm thickness) is equal to 30-
3.2.2 Thermal Resistance of Walls
Some studies indicate that the leaked heat ratio of walls and floors attained 60-
Table 3 presents the thermal resistance of different types of walls. The thermal resistance of the walls is calculated by summation of R of bricks, plaster and exterior and interior surface thermal resistance according to the Egyptian Code.
R = Rso + L1/k1 + L2/k2 + Rsi
Where, Rso and Rsi are the values of exterior and interior surface thermal resistance. L1 and L2 are the thickness of plaster and brick layers. K1 and K2 are the thermal conductivity of layers. For example, R for hollow shale bricks wall = 0.055 + 0.05 / 1 + 0.12/ 0.6 + 0.123 = 0.428 (m2 oC /W), where 0.055, 0.123 are the values of exterior and interior surface thermal resistance, 0.05 and 0.12 are the thickness of plaster for both sides and bricks, in meters. K1 and K2 are equal to 1 and 0.6 for plaster and shale bricks, respectively.
Table 3 illustrates that the panel of core foam is perfect material for insulation, the thermal resistance of a SIP (120 mm thickness with a 60mm thickness of polystyrene core) is 4 times greater than thermal resistance of the ordinary (hollow shale brick) wall. The thermal resistance of walls with Light weight sand lime bricks increases by about twice over than the ordinary walls, while the use of solid cement bricks reduces the thermal resistance of the walls compared to ordinary bricks.
It can be concluded that the use of partition walls with lightweight bricks or SIPs decreases the weight of building and increases the thermal resistance of building that are recommended in hot regions. Although SIPs and light weight bricks have a higher initial cost than traditional materials, saving will be achieved in the long run due to reducing of energy for heating and air conditioning. In addition, the houses become more comfortable. On the other hand, the use of solid cement bricks reduces the thermal resistance of the walls and increase the building weight compared to ordinary bricks. In addition to the negative effect of the cement industry on the environment, it is recommended to reduce using the cement bricks.
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