Sustainable building materials
A research study by Ayers (2002, P.12) into the demand for building materials shows that the need for superior performance of construction materials has facilitated increased research, development, and innovation into sustainable building materials. The study focuses on sustainable construction materials that are used in the construction industry in the context of financial viability, thermal efficiency, occupational health and needs, minimum environmental impact and renewable materials. According to Anink, Boonstra and Mak (2004, p.23), energy efficiency and low maintenance costs have raised the compliance requirements for high quality construction materials. That forms the basis of the research into sustainable building materials. This study focuses on material properties, the environmental impact, and other issues associated with sustainable building materials.
Environmental impact
A study of the issues associated with sustainable building materials by Anink, Boonstra and Mak (2004, p.34) on the processing, manufacturing, and use of the materials shows the negative impact the processes cause on the environment. The impacts include increased carbon emissions, disturbance and destruction of natural habitats, and the loss of top soil in the construction process. Contributions by Berge (2009, p. 10), on the effect on the quality of air, and increased dust emissions during the construction process are some of the issues associated with sustainable building materials. That is addition to the environmental impact because of the embodied energy, which is the energy consumed in the mining and production process of construction materials (McDonough & Braungart 2002, p.34). That necessitates the need for materials that have minimum negative impact on the environment. Typical examples include certified wood, adobe blocks, glass, glazed bricks and ceramic bricks. In a study on the environmental impact of construction materials, it is critical to assess the impact caused by the materials for sustainable construction. One of the approaches is to focus on assessment of the impact of the input and output on the environmental and human health impact on the people.
McDonough and Braungart (2002, p.34) provide a comprehensive review of the input and output resources used to make construction materials. According to McDonough and Braungart (2002, p.34), the engineering procedures of processing construction materials leads to a complex impact on the environment. The adverse effects start from the process of mining the raw materials from the earth and returning the waste materials into the sink, which ultimately causes emissions, effluence, and solid wastes into the environment. The process causes material depletions in terms of quality, quantity, and the ecosystems leading to an adverse impact and imbalance of the natural processes of the ecosystem due to the overuse of sources and sinks. One of the effects is climate change (McGowan & Kelsey 2003, p. 23).
The connection between environmental degradation and changes in the global climate is in the context of greenhouse gas emissions in iron and steel processing, cement production, land fill processes, and the transportation of materials (McGowan & Kelsey 2003, p. 23). That is in addition to loss of biodiversity during the extraction, manufacturing and discharge of wastes, acidification due to the emission of sulfur and other exhaust gases, and emissions due to the drainage of mines. Other sources of adverse environmental effects include acid leaching, exhausts from fossil fuel combustion, ecological biodiversity, smog, and stratospheric ozone depletions (Berge 2009, p.5).
The critical issues of sustainable building is in the acquisition, processing, and transforming the inputs of construction materials into outputs. Here, inputs are in the context of the acquisition phase demanding the use of energy to drill, mine, dredge, and harvest the inputs. In that context, the environmental impact includes the destruction of natural habitats at the points of extraction of the raw materials. If the primary materials or the ore wastes are toxic such as materials which oxidize upon exposure to the air resulting in acid mine drainage, or soil erosion that causes sedimentation and blocking of waterways, the result can be disastrous.
The process of refining and refining and processing of primary materials is another element of sustainable materials (Mendler, William & Mary 2006, p.64).
Concrete
Concrete is a material that is widely used in the construction industry in the world which consuming over 1m million tons annually, because of its strength when appropriately mixed in the right proportions with water, admixtures, aggregates, cementitious and pozzolanic materials (Mendler, William & Mary 2006, p.64). In addition, 1 billion tons of water, and 10 billion tons of rock and sand are consumed annually. The cement production process requires that for each ton of cement, 1.5 tons of fossil fuels and limestone are consumed. The huge consumption and water and energy to produce concrete comes with huge environmental costs such as CO2 emissions, energy consumption in the processing and transportation of the raw materials and other costs are some of the issues associated with the production of concrete. That leads to the study of the environmental impact of concrete components discussed below.
Portland cement
According to Calkins (2012 p.76), cement is the main component used to manufacture concrete, with the production process causing the most adverse impact on the environment. The concrete industry consumes significant amounts of energy with the global intensity being the highest per dollar value of the outputs in the manufacturing of cement. According to Calkins (2012 p.29), the critical components for making cement in a four step process that consume significant amounts of energy include clay, shale, limestone, and rock or marl in varying concentrations. During the four phases cement manufacturing process large amounts of energy are consumed releasing large amounts of CO2, kiln dusts with an industry estimate of 38.6 kg for each metric ton of cement, other wastes from the burning of coal in the energy intensive manufacturing process. Air emissions include particulate matter, carbon monoxide, sulfur oxide, nitrogen oxides, hydrogen chloride, and total hydrocarbons, with different types of concrete producing different levels of emissions. 5% of the global carbon emissions are due to the cement manufacturing process. The wet, long dry, Precalciner, and preheater cement manufacturing processes produce different levels of emissions into the environment (Calkins 2009, p. 18).
Minimizing adverse impacts
Current programs to minimize the current and future impact caused by the production and consumption of cement and concrete include efficient use innovative cement products, use of high performance cement, and building stable structures to efficiently utilize concrete and its mixtures (Calkins 2012, p. 28).
The use of coal fly ash and other innovative cement products reduce to a significant extent the embodied energy linked to concrete production. One process that has proven energy efficient is the use of blended concrete. Blended cement, which is made from fly ash, silica fumes, clinker, and natural pozzolans allows for a reduction in embodied energy. The advantages of blended cement include higher production capabilities, lower waste emissions, and reduced energy consumption. The dry processing plant with wet production facilities are other energy reduction methods used to reduce energy consumption in the production of concrete. That includes a radical shift from the use of petroleum and associated products. A shift into the use of dry processing methods introduces the problem of energy consumption in the use of preheaters (Calkins 2012, p. 18).
Concrete can be made from any of the two types of fly ash. One type is the class c fly ash. Fly ash is produced when sub bituminous coal with a 30% CaO content and silica iron, and alumina are burned to produce cementitious pozzolan which requires hydrate and water to be produced. The resulting substance is energy efficient and offers excellent performance in terms of workability, long term strength, and short term strength strain. Another category of fly ash is the Class F fly ash. Class F fly ash is contains a low amount of calcium which is sufficient enough for the hardening process. Fly ash is made from the burning of bituminous coal and anthracite and is used in amounts of 25% for the production of cementing materials.
Fly ash makes significant contributions to sustainable production of building materials because of the range benefits gained from the use of the material. Advantages include improved workability by reducing the amount of water consumption, high performance and workability because of the electrostatic effect of the cement particles, and better pumping and consolidation capabilities. Increased set time allows for more time to work on the concrete which increases the quality of the concrete. Increased set time leads to higher compressive strength of the concrete. One shortfall with this approach is the increase of the time required for concrete to set and gain its appropriate strength, above the 28 days required for the process to enter into completion. However, the procedure results in the higher cement savings, despite the 56 days required for the concrete to set.
Research has shown a number of materials that can be used as a substitute material for the production of concrete admixtures. One of the methods is to use recycled materials for virgin aggregates. The aggregates have environmental, aesthetic, and economic advantages. The critical advantages translate to reduced embodied energy by reducing the mining and processing of the raw materials, reduction in environmental impact due to mining of the raw materials, and the reduced effect of landfill problems. The table below illustrates the substitutes with the above mentioned advantages in the production of concrete, the performance benefits, drawbacks, and the percentage substitutes for each substitute.
It is critical to note that there are a variety of other recycled products that can be used to as substitutes in the economic and environmental friendly production of cement and concrete. However, the primary limitations of using recycled materials are the limitation to predict the performance, the ability to predict the performance of the resulting concrete. It is also critical to note that it could also be difficult to predict with precision the water absorption, compressive strength, and specific gravity compliance to standard requirements and accurately predict the properties of resulting concrete (Norton 1997, p. 90).
The critical benefits associated with the use of recycled materials, that address issues of sustainability and impact long term adverse impact on the environment include lost costs of production, reduced energy consumption and higher energy efficiencies because of reduced need to transport the aggregates because most of the recycled materials are used on site. That is in addition to the decreased investment costs in landfills processes. However, the issues and challenges associated with recycled materials include production of dirt, fluctuating quality and performance of recycled materials, and the challenges associated with making the appropriate concrete mixtures.
Design for sustainability
Engineers and architects have embarked on developing energy efficient concrete and cement processing technologies. In addition, the designers and planners should embark on the development of structures based on the principle of “design for sustainability” which is based on the principle of mutual respect or the people and the environment (IEA. 2010b, p.45). The principle stipulates that developers use locally available or indigenous materials for construction purposes, use efficient construction methods to preserve open spaces in cities, and endeavor to create designs and embark on construction processes that protect and create rich top soils (IEA 2010b, p.45).
It is critical to consider the entire lifecycle of any structure to ensure effective environmental preservation is put into practice (Minke 2006, p.23). Typical construction processes should include effective and efficient extraction methods, processing, transportation, and construction technologies and materials that are sustainable when being processed. In addition, any solid wastes that cannot be processed further should be eliminated or dealt with in accordance with toxic waste disposal methods. It is important to study the lifecycle of the material to be used before adapting the use of the material. The critical points to study include the costs associated with the mining, processing, and transporting the material to the construction site (Minke 2006, p.23).
Other elements to include in the study is the best and energy efficient method of mining, processing, transporting, blending, and converting waste materials back into the environment. It is important to make designs which use less water for construction and do not lead to environmental degradations.
Sustainable building technologies
The use of sustainable building technologies provides improved solutions to the problems associated with adverse environmental impact, with the critical issues associated with the technologies including alternative building technologies, energy, and environmental issues. That is because building practices have dynamically evolved with time, leading to new the development of new technologies. Sustainable building technologies provide the advantages which include sustainable energy consumption, reduced consumption of high energy materials, environmental energy friendly technologies, and use of local skills, decentralized production of materials, optimal production and use of building materials, and the use of renewable energy sources (Norton 1997, p.12).
One approach used in the production of energy efficient materials and sustainable technologies optimizes the use of local skills, while investing in research and development. Some of the sustainable building technologies include the use of stabilized mud blocks, fine concrete blocks, steam cured blocks, soil lime plaster, Rammed earth blocks, and Lime–Pozzolana cements. According to the research, composite mortars for masonry and improved roofing systems which use Ferrocement and ferroconcrete are some of the technologies that are in use today (Norton 1997, p.19). The critical features of the technologies and issues associated with the technologies are discussed below.
Alternative Construction Materials
Stabilized mud blocks have been in use for the construction of low cost buildings or structures with forces applied on the materials being significantly low. In this case, “machines compacted soil create dense solid blocks using sand and soils” (Norton 1997, p. 90) and the process is done using stabilizer to achieve the required mechanical properties” (Norton 1997, p. 90). The soil composition is the key determining factor of the compressive strength of the resulting block. It is possible to improve the quality and compressive strength of the block using additional stabilizers. The production process of the stabilized mud block is low embodied energy when compared to other bricks which require less heating and a low cost of production when compared with other bricks, which eliminates the need to plaster the brick, and enhanced its aesthetical appearance.
Another material is the use of filler slab roofs. Filler slabs are made from the use of filler materials which are cheap and lighter compared with materials for similar construction work. However, a “number of alternative materials can substitute the filler materials used in the construction of filler slabs” (Minke 2006, p.29). The quantity of the filler material used for substitution purposes depends on the area of application and the thickness required for the specific areas of application. Typical examples include a situation where 25% of concrete can be replaced to accommodate the substitute material in the construction of filler block measuring 60-70 mm.
Another substitute material used in the construction industry for sustainability purposes include unreinforced masonry vaulted roofs. Using the material yields additional benefits which include low production costs, low embodied energy, and better aesthetic values. In addition to that, the Lime–pozzolana cement, which is made from secondary grade lime and calcium hydroxide in the correct proportions provide the best substitute material for construction purposes.
It is important to use materials produced from renewable sources of energy because such materials cause minimum environmental impact. It is critical to conduct a study on the embodied energy of both alternative sources of materials based on energy sources. A typical example is aluminum which requires a significant amount of energy for production purposes. When compared with steel, aluminum consumes eight times more energy than cement. However, aluminum consumes electricity from hydroelectric power sources while cement consumes energy from the burning of coal and related materials.
Earthen materials
A survey of existing raw material used to manufacture construction materials that exists in the earth’s crust have different mechanical properties than can be exploited to for construction purposes. The earthen raw materials incorporate soil to significant extent, water, and clay. However, the properties of soil vary depending on the application and performance requirements (Norton 1997, p. 90).
The most appropriate soil for construction purposes includes silt, gravel soil, silt, and sand. Clay is a sticky material when wetted with water and its particulate nature has particles which measure 0.005 mm with strengths varying between high to medium plasticity. Some soils have mechanical properties unsuitable for construction purposes (Norton 1997, p. 90).
Other types of soils include sand with high strength and low particle porosity. In addition to that, silt is another type of soil with low plasticity and mechanical strength, making the silt unsuitable for construction purposes. Gravel, which has low particle porosity, is appropriate for earth construction, especially applied in trench construction. It is important to improve the mechanical properties of soil to make it appropriate for earth construction purposes. One of the strategies used to improve the mechanical properties of soil to make it suitable for different construction purposes is densification. Densification is achieved through compaction, reducing the capillarity of soils pores, and eliminating any air in the soil (Norton 1997, p. 90).
The mechanical properties of soil can be achieved through cementation using insoluble synthetic hair strands fly ash, and other materials already discussed in the paper. Other methods of improving the quality of soil are the use of linkages, and the use of imperviousness. Imperviousness stabilizes soil for construction by removing water and other ingredients. In addition, the water proofing is a technique that enables soil with the ability to resist the flow and penetration of water into the block (Norton 1997, p. 90).
Energy consumption
Energy is a critical component in the manufacturing and production of cement. According to research studies by Minke (2006, p.29), energy for the “construction of buildings can either be in the form of embodied” ” (Minke 2006, p.30) and “energy or in the form of energy consumed to maintain a building” (Minke 2006, p.31). Energy consumed to maintain a building depends on changes in the climate, and other variations in the weather. The following table illustrates energy embodiment for differ rent walling and roofing systems.
The critical values obtained and recoded in the table above were obtained by making actual measurements of the quantities used during the construction process. it has been established that energy consumption by multilayered buildings are the highest and energy intensive. The typical values of energy consumption for a multilayered building per square meter of built up area is 4.21 GJ per m2. However for a two storeyed building, the energy consumed is 2.92 GJ/m2, making it less costly by 30% compared with conventional methods (IEA 2010b, p.30).
However, with the use of alternative building materials, it has been shown that the energy consumed per building is 1.61 GJ/m2, using SMB filler substitutes. Based on research observations made by comparing both conventional and substitute materials in the context of energy savings resulting in a 50% reduction of energy (Easton 2000, p.3). The overall benefits are to conclude that substitute materials provide significant energy savings and environmental protection. Other benefits include simple techniques that can be understood and used by a majority of people with little technical skills, reduced energy consumption in the transportation and use of materials, provision for the use of decentralized production systems which accommodate and allows for the use of cheaper technologies, and the creation of local employment.
Future prospects
Future perspectives depend on a road map that has been built based on previous studies and research and development. The typical roadmap covers materials for constructing sustainable buildings.
The proposed energy perspective covers the reduction of CO2 emissions, based on the use and integration of low carbon technologies into the mainstream cement and concrete manufacturing processes. Estimated show a carbon reduction strategy includes a carbon capture and storage of 19% of the carbon outputs, investment in renewable sources of energy, improving the power production efficiencies, implementing the end use fuel-switching method which results in a 15% energy reduction and in the investment in safe nuclear energy (IEA. 2010b, p.5). Most of the current buildings were designed to last several years and are projected to be in use by 2050. Most of the developed nations rely on retrofitting the buildings, but the developing world will have to purchase energy efficient technologies.
Cement and concrete Technology
Cement accounts for the emission of large quantities of CO2 because of the energy embodiment. According to the Cement Sustainability Initiative (CSI), integrating efficient engineering methods and cement manufacturing technologies, it is possible to reduce the emission of CO2 by half the current value by 2050. The critical path methods for the reduction of CO2 by 2050 include employing energy efficient state of the art technologies, improving thermal and electric efficiencies, and using other energy efficient technologies.
Another approach is to use alternative fuels which are less carbon intensive, less energy intensive, and the use of biomass fuels as alternative sources of energy, and the use of substitute clinker with alternative cementitious alternatives.
Norton (1997,p.17) shows that it is possible for a reduction of emissions from the manufacture of cement as outlined in the general report by the United Nations World Commission on Environment and Development. The report urges all nations to set predetermined goals for the integration and use of energy efficient technologies and other economic development goals based on the use of sustainable technologies. In each case, any economic model adopted by any country should reflect a sustainability approach to the use of and expansion of existing sources of energy. In addition, the exploitation of virgin raw materials and other secondary materials for the manufacture of cement and concrete should be based on sustainable methods and technologies. It is critical to understand that environmental sustainability is core survival of mankind.
Other approaches that put the future into perspective are the use of nuclear powered sources of energy. Despite the vulnerabilities such as environmental radiation and other forms of threats associated with nuclear power, nuclear sources of power are worth contemplating on (Norton 1997, p. 5).
On the other hand, the future perspective holds that an assessment of the current concrete production methods and future energy efficient methods which consume minimum resources to produce structurally efficient concrete be conducted to develop better technologies. It is important to perform continuous monitoring and to collect accurate data on the progressive reduction of CO2 emissions into the environment to assess the quality of technology in use and create methods to improve the efficiency if the technology. It is also critical to develop standards and specifications that integrate the aspects of the environment for the processing and production of concrete and concrete structures (Minke 2006, p.198).
In addition, other strategies include investing in the development of technologies that promote reduced energy consumption and in other resources that consume low amounts of energy and less energy consuming substitute technologies (Minke 2006, p.198).
Structural Stability
Minke (2006, p.98) shows that the intended service life of a building should be completed without any structural weaknesses detected before the completion period of the service life of the structure. It is important to note that the structural design methods have significantly improved in the recent past. The limit state design method is the most recent and widely accepted construction method. It is possible to determine the quality of materials used in the construction of such structures using the state limit design method. However, a new approach that is becoming increasingly popular is the performance based design. Performance based design relies on compliance requirements for safety (Minke 2006, p.198).
According to IEA (2010a, p.45), facts show the need for increased degree of safety in the design and development of structures. Increased safety leads to a decrease in the burden on the environment. In addition, the current and future trend is to improve the quality of materials used in the development of structures and to decrease the burden previous materials have caused on the environment. By investing in research, development, and innovation, better construction methods, materials, and improved structural and mechanical efficiencies lead to improved environmental safety (IEA. 2010b, p.23).
Energy issues
Research by Spiegel and Meadows (1999, 45) shows that energy related issues accounts for the most critical components of sustainable processing and production of building materials. Here, environmental safety and suitability are critical issues of consideration (IEA-WBCS 2009, p.11). Examples include nuclear energy which accounts for 13.5% of the world energy production radioactive. Nuclear reactors are vulnerable to terrorist attacks and radioactive leakages that produce radioactive contamination because of nuclear disasters because of the meltdown of nuclear reactors. Some of the issues arising because of the use of nuclear power are radioactive contaminations and attacks from terrorists (IEA-WBCS 2009, p.12).
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