Cement Lifecycle Review
Life Cycle Review of Cement and Concrete Manufacturing Table of Contents Introduction3 Concrete Overview3 Life Cycle Stages4 Portland Cement4 Raw Material Extraction5 Crushing Process5 Kiln Processing6 Clinker Cooling and Storage7 Clinker Grinding7 Packaging and Shipping7 Concrete Processing8 Recycling and Landfill8 Environmental Considerations Throughout Life Stages9 Inputs: Consumption9 Outputs: Waste10 Air Quality and Pollution11 Land Quality and Biodiversity12 Alternative Suggestions in Minimizing Environmental Impact13
Solutions for Minimising Ecological Footprint13 Solutions for Improving Air Quality13 Solutions for Minimising Land Degradation14 References15 Introduction A life-cycle assessment (LCA), as described by the US Environmental Protection Agency, is “a technique to assess environmental impacts associated with all the stages of a products life from cradle-to-grave”(USPA 2010). Therefore, an assessment of a product’s life cycle endeavors to analyze its existence from raw material extraction, to manufacturing, through to disposal.
This report will not provide adequate data for the purpose of undertaking an LCA, however, it is aimed at “thinking” about the life cycle, and collecting information from past LCA studies to undertake a report on concrete production, particularly focusing on the life-cycle of cement, a critical component of concrete.
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Therefore, the following “life cycle thinking” review will endeavor to utilize previous LCA studies in order gain an insight about the major environmental impacts throughout each lifestage, chiefly centering on cement manufacturing.
Correspondingly, it will also discuss alternative strategies of delivering cement and concrete as a building material with fewer environmental impacts. Concrete Overview Concrete is a multifaceted construction material, which is assembled mainly from cement, water and aggregate (Reding et al 1977). Concrete is one of the most durable building materials, which allows it to exhibit many functions, including; precast elements, underwater construction, infrastructure formation and residential housing.
In view of the fact that the life cycle stages and environmental impacts differ between manufacturing for each function concrete withholds, this report will focus on concretes function as a building material for residential housing and apartments (Anonymous 2012). Concrete is labeled one of the most durable building materials; therefore concrete structures withhold an elongated service life (Reding et al 1977. As a result of this, concrete is the most extensively used construction material in the world and has contributed momentously to the built environment throughout history. Life Cycle Stages
In a straightforward description, as mentioned above, concrete consists of three basic components, including cement, aggregates and water. Although there are various cement blends used for different purposes, this lifecycle review will focus particularly on Portland cement manufacturing, which is frequently utilized for industrial purposes (Anonymous 2012). In observing a life cycle of concrete manufacturing, the production of cement generally takes place separately, which is then transported to the selected building location, where water and aggregates are added to bind all components into one homogenous material – concrete (Anonymous 2012).
Although there are obviously procedures in obtaining the water and aggregate for concrete production, the life-cycle discussed in this report will focus primarily on Portland Cement production (Reding et al 1977). Portland Cement The major raw materials extracted for cement production include limestone, sand, shale and clay. These feedstock ingredients provide calcium carbonate, alumina, silica and ferric oxide, which are critical elements of cement (Anonymous 2012). Figure 1: Proportion of cement components (CCAA 2010) Raw Material Extraction
The initial stage of Portland cement production is the extraction of the raw materials by either quarrying or mining (Anonymous 2012). This withholds an adverse risk to land quality, potentially effecting fauna and flora within close proximity. Quarrying and mining are undertaken by operations such as drilling, blasting, excavating, handling, loading, hauling, and crushing (Reding et al 1977). The fragmented material, which can reach meters in length, is then transported via dump trucks to the cement plant, which is generally located nearby (Anonymous 2012). Crushing Process
When transferred to the plant, the rock material is fed through a primary crusher, which breaks it down into smaller pieces up to six inches in size (Anonymous 2012). Subsequently, the rock is then transported via a conveyor to the secondary crushing stage, which accordingly, crushes the rock down to sizes of three inches or less. Following these essential crushing processes, all raw material undergoes a mixing and grinding process, where additional silica and iron may be added (Anonymous 2012). Within this stage, particulate emissions are profoundly emitted into the atmosphere.
The mixing process can either be wet or dry, depending on the plant, however, the Cement Industry Federation states in their most recent Environmental Report that wet process plants in Australia now only account for less then 15% of total production, as wet processes have momentous water consumption (CIF 2010). In the instance of a wet mixing and grinding process, large impact dryers completely dry out the materials whilst grinding is undertaken, however if a wet process is embarked on, water is added during the grinding process which turns the mix into the form of a “slurry” (Anonymous 2012).
Kiln Processing This process involves the slurry or the finely ground dry material to be fed into a high-temperature, cylindrical rotary kiln, heated to about 2700 degrees F (Anonymous 2012). Kilns are mounted with the axis slightly inclined from the horizontal and can reach up to 180m long, with a six meter diameter, thus it can take up to two hours for the material to travel through. The upper end of the kiln provides the entrance for the material, whereas the lower end comprises a roaring blast of flame, fueled by either coal or natural gas.
During this process, any water contained in a “slurry” mix is lost through evaporation (Reding et al 1977). Ultimately, as the mixture travels through the kiln, it transforms both physically and chemically into grey pebble-like substances called clinker (Anonymous 2012). During kiln processing, particulate and GHG emissions are released. This stage also consumes the most energy, as fossil fuels are incinerated to provide extreme heat. Clinker Cooling and Storage
The clinker is expelled from the lower end of the kiln and is then transported onto a conveyer through a cooling system where large fans and water are utilized to cool the temperature (Anonymous 2012).The United Kingdom Environmental Agency state in their Environmental Performance Evaluation, that the vast majority of cement plants around the world now transfer the heated air from the coolers back towards the kiln as a means of saving fuel (UKEA 2010).
Once the clinker is cooled, it is deposited into a storage area where it awaits until it is required for it’s final stage of grinding. Clinker Grinding The clinker is finally transported via a conveyor to its final crushing stage and is ground into a fine powder. This is carried out by steering the product through rotating tube mills with rolling crushers, which grind the cement into a fine powder. During this stage, other materials conveying analogous characteristics are added.
Gypsum is also combined with the mix, as it assists in regulating the setting time of the final concrete product (Anonymous 2012). The continuous rolling assists in distributing the materials and gypsum throughout the cement evenly, and also separates the cement particles according to size (Reding et al 1977) . The material that has not been ground to the adequate size is deflected through the system again, however the final product is guided to the final storage silo (Anonymous 2012). Packaging and Shipping
The final product is either mechanically or hydraulically hauled out from its storage silo and is either packaged in paper sacks or supplied in bulk where it is then transported via truck, rail car or ship to the location of utilization (Anonymous 2012). Transportation must still be taken into consideration in contributing to the manufacturing air emissions. Concrete Processing Once transported to the building location, the addition of water to the cementitious material forms a thick cement paste, through the method of hydration (Anonymous 2012).
Both fine and course aggregates; consisting of natural gravel, sand and soft stone are also commonly added to the cement paste, to create bulk and a strong, high resistant concrete (CCAA 2010). Aggregates are granular materials such as sand, gravel or crushed stone, which are usually dredged from a river, lake, pit or seabed (CCAA 2010). Prior to combining the aggregate in the cement, it undergoes a washing process to remove any unwanted silt, dust, clay or organic matter that could potentially interfere with the bonding reaction with the cement (Cement Industry Australia 2003).
Similarly to the cement manufacture process, the aggregate is also sorted into different granular sizes (Anonymous 2012). This is undertaken by passing the material through a screen containing different size openings. Once arranged into adequate sizing, the aggregate is transported to the building site where it congregates with the cement (CCAA 2010). Thorough combining of cement, water and aggregate is crucial for the invention of high quality, uniform concrete, therefore equipment and methods such as cement trucks and on site mixers are utilized (CCAA 2010).
Once all the constituents are thoroughly combined, it is molded or positioned as anticipated and then left to harden. Recycling and Landfill When a concrete building structure reaches the end of it’s life, either recycling or landfill is an option (CCAA 2010). The process of demolition of a concrete structure involves pulling it down either mechanically or manually through the utilization of excavators or bulldozers (Chen et al 2010). Larger buildings however, may require more powerful equipment.
Following, the shattered concrete fragments are either transported by trucks to landfills for disposal or collected from the annihilation site and transported to a crushing facility, where it is fed through a crushing machine to be broken down and used for aggregate of new concrete (Cement Australia 2003). In conjunction with quarries, landfills also hold significant environmental consequences, as it can destroy or alter species habitat. Environmental Considerations Throughout Life Stages Inputs: Consumption
The Cement Industry Federation (CIF) states in their 2003 environmental report, that the cement manufacturing process is extremely energy and resource intensive, therefore, it withholds a significant environmental footprint (CIF 2003). As displayed in the life-cycle diagram (figure 2), raw materials, energy and in some instances water, are the chief inputs associated with the manufacturing process, therefore, their consumption levels are predominantly to blame for the industries heightened environmental footprint (Anonymous 2012).
Cement Australia (2010) states that on average, water utilization of a modern dry cement plant is between one hundred to two hundred litres per tonne of clinker produced (Cement Australia 2010). This water consumption is primarily used for cooling heavy equipment and exhaust gas. Although this appears quite high, Chen et al (2010) mentions that it is a dramatic improvement from earlier, yet still subsisting wet process cement plants (Chen et al 2010). The addition of water in cement to create the final product of concrete also consumes a large quantity of water.
Similarly, the cement industry is highly energy intensive, especially during the kiln life stage (CIF 2003). Generally, cement plants today use natural gas, heavy oil and coal for fuel (Chen et al 2010). However, as coal accounts for almost 40 per cent of manufacturing costs, the utilization of fossil fuels in cement production has decreased since 1990 and has been partly substituted by alternative fuels (CIF 2003). The impact the high consumption of fossil fuels possesses on the environment is accelerated greenhouse releasement into the atmosphere, thus contributing to global warming (Chen et al 2010).
Therefore, environmental consideration of adequate selection of alternative fuels is crucial in minimizing the environmental footprint. Outputs: Waste Furthermore, the outputs within each life stage also exhibit environmental issues throughout the entire cycle, from resource extraction through to landfill (Chen et al 2010). The outputs fluctuate and vary between atmospheric emissions, waterbourne wastes, solid wastes and other co-product releases (CIF 2003).
These outputs, in conjunction with the reasonably high input consumption, are the causes of the evident impacts the industry posses on the environment. Lemay & Leed (2011), mention in a broad perspective that air emissions leading to climate change, resource depletion, water consumption, ecotoxicity, eutrophocation, human health criteria, habitat alteration, smog formation and acidification are the main documented impacts that occur throughout the cement manufacturing process, whether it be instant or over time (Lemay & Leed 2011).
Although there is clearly a vast array of impacts associated with cement manufacturing and concrete assembly, the impact on air quality and land quality appear to be considered by numerous LCAs to be a vital issue associated with manufacture, therefore they will be analyzed in more thorough detail. Air Quality and Pollution Air pollution is highly likely to occur throughout each life stage of cement production, whether it is a result of fuel combustion or particulates from raw and finished materials (CIF 2003).
Eco Tech (2011) mentions in its Cement Industry Report, that the uttermost crucial impacts associated with air pollution include; hydrocarbons and particulates which posses a threat to human health and environmental quality, and greenhouse gas emissions accelerating climate change (EcoTech 2011). In relation to Greenhouse gas emissions, Chen et al (2010) scrutinized in his Cement Plant Evaluation, that different Portland cement plants around the world is under close inspection these days because of the large volumes of CO2 emitted (Chen et al 2010).
The report also continues to address that almost one tonne of CO2 is released for every one tonne of cement produced in the industry, which appears to be momentous considering in the year 2010, the world produced approximately 3. 6 billion tonnes of cement (Rosenwald 2011). Contrary to greenhouse gas emissions, dust emissions are at their highest peak at the initial quarrying stage and the final building demolition stage, as a result of forceful blasting and obliterating (Chen et al 2010).
Other sources of dust emissions, however, are raw mills, kilns/ clinker coolers and cement mills. The Cement Industry Federation (2003) states that transportation of raw materials from the quarry to the site and stockpiles of raw materials contribute significantly to dust emissions (CIF 2003). Overall, the dust emissions released throughout the different life stages impact momentously on air quality, thus it threatens human health and overall environmental quality. Dust is the most common and extensive air pollutant from a quarry (CIF 2010).
It has different origins in a quarry site such as mechanical handling operations that include crushing and grading process; haulage with which is related to the vehicle, and the nature and condition of the way; blasting; additional manufacturing operations and wind blow from paved areas, stockpiles (Chen et al 2010) . Land Quality and Biodiversity The central issue of cement production upon land quality comes from quarrying, atmospheric deposition, disposal of wastes and storage of raw material (CIF 2003).
These issues, predominantly atmospheric deposition, arise from merely every life stage of cement manufacturing; therefore it is an issue that must be taken into great consideration (Chen et al 2010). Quarrying and landfill have both direct and indirect environmental impacts on land and its surrounding biodiversity (Chen et al 2010). The direct impacts include habitat destruction thus biodiversity loss, dust inhalation and noise from rock drilling and blasting (CIF 2010). Subsequently, the effects of cement works on habitats are difficult to quantify, however the potential harm is much greater in vulnerable areas.
The US Environmental Protection Agency (2002), states in their report that two large operating cement plants in England are located on the edge of National Parks, therefore site selection must be considered in depth prior to implementation (USEA 2002). On the other hand, indirect impacts can potentially cause different catastrophes such as landslides and flashfloods in and around quarry sites (Chen et al 2010) . Furthermore, dust particulate has physical effects on plants, such as damage and blockage to the leaf surface, which may lead to death if photosynthesis is unable to occur (Chen et al 2010).
Chemical effects on the other hand, can potentially produce changes in soil chemistry, which ultimately leads to changes in the long term associated with plant chemistry alterations, species competition and community structure (CIF 2010). Dust particulates from quarrying and wastes also affect waterways, as supplementary sedimentation may cause nearby reservoirs to dry out or flood (Chen et al 2010) . Alternative Suggestions in Minimizing Environmental Impact Solutions for Minimising Ecological Footprint
Due to the significant amount of energy consumed in cement manufacturing, the cement industry has considerably focused over a long period on escalating plant efficiency and decreasing energy consumption. Cement Australia (2010) affirms that the Australia Cement Industry has seen a 23% decrease in CO2 emissions in the period between 1990-2009 (Cement Australia 2010). Although this is a significant decrease, further methods could potentially be utilized to further cutback consumption. Firstly, energy could be more efficiently recycled and transferred within the plant system.
For example, excess heat from the clinker cooler being transferred back to the kiln stage to prevent energy waste should be implemented in all modern cement plants (Lemay & Leed 2011). Secondly, alternative fuels should be enhanced, especially in clinker manufacture. Alternative fuels may include items such as tyres, oils and tarrow. Solutions for Improving Air Quality As mentioned earlier, air emissions for GHG release has improved over the last decade as a result of utilization of alternative fuels.
This however, has the potential to be further improved, therefore complete replacement of fossil fuels to alternative fuels could potentially take place to completely eradicate GHG releasement (Lemay & Leed 2011). In addition, the Cement Industry Federation (2010) asserts that improvement techniques for dust collection such as baghouse dust collectors has also been implemented over the past century (CIF 2010). Although there have been improvements, likewise, the potential for further development still remains. Perhaps aspects of the layout design could be improved, as a means of stockpile design and transportation throughout the system.
Containment of conveyors could be implemented and perhaps pipelines, which substitute transport to and from the quarry to the plant, could be considered to prevent particulate emissions being released (Lemay & Leed 2011). In addition, the moistening of the raw material throughout the crushing stages via sprays could also potentially to instigated to minimize dust release (CIF 2010). Filters and collectors could also be applied within each stage so the dust gathered can be sent through to the kiln for clinker production Solutions for Minimising Land Degradation
Unfortunately quarrying and landfill in any form will impact on land quality, however methods such as buffer zones between workings and alternative habitats for defined species could be considered in an attempt to conserve biodiversity within or around the sites (Lemay & Leed 2011). Rehabilitation programs to restore once existing biodiversity on site could also be considered when the quarry material is completely exploited. Additionally, as displayed in the life cycle review, recycling of the final concrete material is an option as opposed to landfill.
Perhaps the promotion of further cement and concrete recycling could be considered to avoid the amount of quarrying required. This would also minimize the amount of product discarded into landfill, thus retaining natural habitat. References Abdul-Wahab S. 2006. “Impact of fugitive dust emissions from cement plants on nearby communities”. Ecological Modelling. Vol: 195. Issue: 3-4. Page 338-348. Anonymous. 2012. “How Portland Cement is Made”. Portland Cement Association. Available: www. cement. org/basics/howmade. asp. (Last Accessed 7/10/12) Cement Australia. 2010. Environmental Performance”. Cement Australia. Available: www. cementaustralia. com. au/wps/wcm/connect/website/cement/home/sustainable-development/environmental-performance (Last Accessed 10/10/12) Cement Concrete and Aggregates Australia (CCAA). 2010. “Sustainable Concrete Materials”. CCAA. Available: www. concrete. net. au/sustainability/documents/documents2. pdf. (Last Accessed 7/10/12) Chen C, Habert G, Bouzidi Y, Jullie A. 2010. “Environmental impact of cement production: detail of the different processes nd cement plant variability evaluation”. Journal of Cleaner Production.
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