Characteristics of Materials in Construction - Essay Example

1. Define embodied energy giving examples of specific materials. Explain why embodied energy is important in terms of assessing the environmental credentials of construction materials Embodied Energy Embodied energy is the total energy combined which are consumed by all processes associated in the construction of the building. It covers from the acquisition of raw materials, product delivery including their manufacture into a useable product, transportation at each stage, and the energy consumed on all administrative functions associated with every processing and production stages. Embodied energy is categorised into initial and recurring. The initial embodied energy are those non-renewable energy consumed in the acquisition of raw materials, their processing, manufacturing, transportation to site, and construction. This has two components namely: direct and indirect. Direct energy is the energy used to transport building products to the site, and then to construct the building while indirect energy is the energy used to acquire, process, and manufacture the building materials, including any transportation related to these activities. The recurring embodied energy are those non-renewable energy consumed to maintain, repair, restore, refurbish or replace materials, components or systems during the life of the building. Embodied Energy in Materials Different materials have different embodied energy. It is measured as a quantity of non-renewable energy per unit of building material, component or system. It may be expressed as megaJoules (MJ) or gigaJoules (GJ) per unit of weight (kg or tonne) or area (square metre). Some embodied energy of common materials are presented in the table below. MATERIAL MJ/kg MJ/m3 Aggregate, general Aluminum (recycled) Cement Cement mortar Brick Brick, glazed Concrete block Lumber Steel (recycled) Plywood Glass 0.10 8.10 7.80 2.00 2.50 7.20 0.94 2.5 8.90 10.40 15.90 150 21,870 15,210 3,200 5,170 14,760 2,350 1,380 37,210 5,720 37,550 Importance in assessing environmental credentials of construction materials Embodied energy in construction has important connection to environment since CO2 emissions are highly correlated with the energy consumption. Literatures show that on average, 0.098 tonnes of CO2 are produced per gigajoule of embodied energy. Therefore, the higher the embodied energy of a specific construction material the higher its environmental effects. In the following question you need to look at the function of a number of components of a domestic property. 1. What are the required properties of the external building envelope? The building envelope and its purpose The external envelope is the primary and critical component of a building that serves as insulator and a protective physical covering for the occupants. The envelope consists of the roof, walls, windows, and the doors. Design of a building’s external covering is based upon several performance objectives such as: structural integrity, moisture control, temperature control, and control of air pressure boundaries. Common measures of the effectiveness of a building envelope include physical protection from weather and climate (comfort), indoor air quality (hygiene and public health), durability and energy efficiency. In order to achieve these objectives, all building enclosure systems must include a solid structure, a drainage plane, an air barrier, a thermal barrier, and may include a vapor barrier. Moisture control is essential in cold climates. Properties of the external envelope Since the building enclosure is subject to different conditions of temperature and air pressure, the building designers must be aware of the importance of wetting, drying, and storage properties of the materials used in the construction. Moisture and air movements as well as all possible sources and locations must also be properly considered. Air barrier is also an essential component of building enclosures. It should be strong enough to withstand wind and air pressures across it. It must be durable to remain intact throughout construction. The major properties and performance required of building enclosure include the following: thermal performance, moisture performance, fire safety, acoustics, productivity, material durability, and maintainability. In terms of thermal performance, the thermal conductivity of the materials used must be considered. Window design and material selection must consider the appropriate type that suits the need whether to regulate heat penetration into the building’s interior or control of heat loss or both. To regulate the entry of solar radiation the use of glazing and other insulation materials can be practical for windows, wall, and roofing. The building enclosure must have better thermal performance or resistance from heat or coldness or any climate changes. Moisture performance of the material can be assessed by its capability to resist in wetting and drying and storage. Wetting can be through direct exposure of the material to the source of moisture. Drying can be by desorption or evaporation, while storage is the capacity of the material to absorb and hold water. The capability to absorb moisture and the resistance during the drying process is a point to consider also in selecting the materials. Better moisture performance of windows can be supported by better designs of flushing, jambs, and water-proofing. Another important property considered in selecting building envelope material is its safeness on fire. The fire resistance of the material if determined can be the basis if fire proofing and other processes to reduce fire hazard is necessary. Aside from these the maintainability of the material is also an important property to consider. In the overall context the above properties: resistance to changes in thermal conditions, resistance to moisture, fire safety, maintainability, and other factors contribute to the durability of the materials used as building envelope.. 2. Compare and contrast a traditional brick construction with a wood frame/ wood clad building envelope. a. Look at the sources or manufacturing processes for each material. Bricks are structural materials produced from clay with forming qualities that are capable of producing blocks to the desired strength to bear loads or compressive strengths without breaking. The clay pass through the process of kneading refining and addition of other materials such as sand or other aggregates as needed. It is then formed into sizes then air dried to reduce initial moisture content. The air dried products are subjected to kiln cooking to melt minerals within the mass which holds the materials and provide strength to the final bricks. In the other hand wood materials used as frames or envelopes of buildings come from selected trees of desired age and sizes. The trees as logged and cut into desired sizes at saw mills. It is then subjected to kiln drying for better performance. Other processes such as sap displacement and other wood treatments are employed to improved resistance of the materials to termites, moisture, thermal, fire, and other hazards. b. Consider the suitability of each building type for off-site or in-situ construction and how this may affect the overall build time and quality. Bricks are more suited for construction of structures in-situ. The brick construction process requires skilled masonry work which should be delicately performed on the actual construction site. This limits the possibility of constructing building parts with bricks off-site. However, specialised pre-cast ceramic based building components like tiles, mouldings, and others are manufactured off-site. Generally brick laying is a slow process when quality is ensured. In the other hand, wood materials and panels can be used for construction in situ as well as off-site fabrication of panel boards, windows, walls, etc without extremely endangering quality of the construction. This makes wood based construction faster compared to brick structures. c. Assess how each material type compares in terms of embodied energy. As reported above, the embodied energy of lumber and plywood is a little greater than that of the brick materials. This can be associated to a more complex process of producing the lumber up to a level where it is suited for building construction. In some cases, however, as reported other categories of wood materials have lower embodied energy than bricks. But as further processing is involved embodied energy of wood materials become higher than bricks as in the case of plywood, parquet, and other wood particle boards. d. Consider how effective each of these envelopes would be at controlling the seasonal variations in temperature. Since a building is subject to climate changes as a result of different seasons. The changing temperature, humidity, air pressures, precipitations, and others direct effects on the walling and other building envelope components. For wood, moisture control is necessary to avoid moisture-related problems with building energy performance, building maintenance, durability, human comfort and health (Moody and TenWolde, 16-12). Excessive moisture in wall cavities can have several detrimental effects such as decreasing the effectiveness of the cavity insulation (Sherwood, 1). Sherwood (1) further noted that if the cavity remains wet for extended periods coincident with warm temperatures in the wall, wood structural components may decay. Condensations on the wood materials may occur in various conditions and locations. Sherwood (1) stated that outdoor temperature and indoor humidity are the critical variables since indoor moisture is moving toward the drier outdoors and will condense if sheathing or siding are below dewpoint temperature especially during winter. In summer, indoor temperature and outdoor humidity are the critical variables since outdoor moisture is moving toward the drier air-conditioned space. This show the vulnerability of wood materials as temperature changes with climate. However the use of insulation technology can help in the performance of wood structure is some limited conditions based on the study of Sherwood (28) but it would entail additional cost. Bricks in the other hand are versatile and durable building material with high thermal mass and potential low energy impact. It can resist both higher and lower temperatures without the danger of cracking if the initial material is of fine quality. Reports show that bricks structures were some of the few materials that resisted the atomic bomb in Japan. It is the main components of ancient large structures that stood through time such as The Great Wall of China, the Pyramids, and other ancient wonders. Overall, bricks are a good example of a sustainable building practice and are currently gaining in popularity around the world. e. If the building envelopes in question 2 are inadequately maintained, discuss what changes may occur over time. Wood based structures which are maintained poorly may suffer long term problems. Among the primary effects of improper maintenance and protection are the visible signs of (a) mold and mildew, (b) decay, (c) damage caused by expansion of materials from moisture such as buckling of wood, (d) termite attacks, and other degradations. These in turn if allowed further may cause severe structural failures. Structural failures caused by decay of wood maybe rare but have actually happened. Decay generally requires wood moisture content equal to or greater than fiber saturation, usually about 30%. Rusting and corrosion of nails and other metal components in wood structures is also a potential cause of structural failure. It can occur as a result of high moisture and humidity. (Woody and TenWolde, 16-12). For bricks, the severity of the environmental conditions, such as the amount of moisture and the availability of soluble salts, determines the durability grade requirements. Using improper grade and improper maintenance of brick walls may also lead to deterioration. One form of bricks degradation is fretting. It is related to the exposure environment in which they are placed. The fretting (flaking or crumbling) of bricks is caused by the presence of salt brought by water that penetrates the brick as water evaporates salt crystals accumulate thereby weakening the structure.. It has been estimated that a significant proportion of materials are wasted during the construction process. Discuss ways in which materials wastage can be minimised. (20 marks) Although wastage is common problems in construction and other projects there are ways to reduce materials being wasted. McDonald (1) stated that wastage is one issue in efficiency and that reduction of waste means improving efficiency. Control or reduction of waste contributes to saving the environment. Before identifying some common ways in material control it is important to consider common causes of wastage. Among those causes are improper planning and improper material handling Different agencies, authors, and companies recommend different steps in waste minimisation. In the general context the following can be done to control waste in construction sites in response to the most common causes: 1) better planning, and 2) good and effective material handling. Better planning as mentioned by Waitakere City Council in their website article “Avoiding Construction Waste” are integrated in all aspect of building construction stages such as before designing, during designing, and upon construction. The document recommended examining all aspects of the design to identify accurate measurements of materials, reviewing them during design and on actual construction. Simplicity is a good point to save materials. Cuttings due to irregular shapes and extra architectural effects with less functionality should be minimised. In materials handling several steps can be effective. Prefabrication of component parts in building is one best way to reduce waste on site (McDonald, 16). Reuse or recycling of materials that are of value is another means. Bulk buying of materials can be of great help to limit the bulk of packaging waste by eliminating individual packaging for limited supply delivery. Standardisation and modernization of the construction process is effective by using advanced reusable framing support scaffoldings, and other materials for construction. References: “Avoiding Construction Waste.” Waitakere City Council. 10 Janaury 2008. “Brick Manual 2.” Austral Bricks National. Austral Bricks Pty Ltd. 14 January 2008. Dama, A. “Solar and external heat gains at the building envelope.” Keep Cool. Austrian Energy Agency. Vienna. 44p “Embodied Energy.” Measure of Sustainability. Canadian Architect. 9 January 2008. “Embodied Energy.” CSIRO Material Science and Engineering. 10 January 2008. “Embodied Energy Coefficients.” Publications. 9 November 2007. Center for Building Performance Research. Victoria University of Wellington, New Zealand. 9 January 2008. “Building Envelope.” Building Technologies Program. 8 July 2004. US. Department of Energy. 10 January 2008. < http://www.eere.energy.gov/buildings/info/design/ integratedbuilding/buildingenvelope.html> “Building Envelope.” Wikepedia: The Free Encyclopedia. 17 Dec. 2007. 10 January 2008. < http://en.wikipedia.org/wiki/Building_envelope> “Building Envelope Design Guide.” WBDG Whole Building DesignGuide. National Institute of Building Sciences. 10 January 2008. < http://www.wbdg.org/design/ envelope.php> Bomberg, M. T and W.C. Brown. “Building Envelope and Environmental Control: Part 3, Issues of System Integration.” 1 September 1993. National Research Council, Canada. 10 January 2008. < http://irc.nrc-cnrc.gc.ca/pubs/cp/wal10_e.html> “The Brick Manufacturing Process.” Glen-Gery Brick. Glen-Gery Corporation. 14 January 2008. ”Lumber.” Forest Products Management Development Institute. University of Minnesota. 14 January 2008. Sherwood, Gerald E. “Condensation potential In high thermal performance walls-hot, humid summer climate”. Res. Pap. FPL 455. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory; 1985. 29 p. 14 January 2008. Moody, R. C and TenWolde, A. “Use of Wood in Buildings and Bridges” Forest Products Laboratory. 1999. Wood handbook—Wood as an engineering material. Gen. Tech. Rep. FPL–GTR–113. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 463 p 14 January 2008 McDonald, B. “Building Construction Waste Minimisation and Recycling Project. “ Sept 1994. Fletcher Construction (Australia) Pty Ltd. 14 January 2008. Read More