environmental sciences

The environmental sciences essay below has been submitted to us by a student in order to help you with your studies.

Energy And Co2 Emissions Of Concrete Waste Environmental Sciences Essay

Abstract-A significant amount of solid wastes produced every year from construction and demolition activities, and had caused significant pollution to the environment and risen public concern. Therefore, the minimization of construction wastes has become a critical issue in construction industry Concrete is the most commonly used construction material in the world, and after water is the second most consumed product on the planet. The huge popularity of concrete also carries environmental costs, the most harmful of which is the high energy consumption and CO2 release during the production. This paper investigates the amount of energy used and CO2 emission generated during the production of concrete. Furthermore to estimate the total impact of both indicators based on concrete wasted generated on site. Data were obtained through questionnaire survey and interview within the building construction projects in U.T.M. These impact assessment were followed the life cycle assessment (LCA) methodology. The results show that the production of the raw material and the transports of the concrete are the main contributor to the total environmental load. The highest impact value was generated during the production of cement at upstream level .the amount of energy used and CO2 emission by cement production was about 70 percent of the total embodied energy and 95% of the carbon dioxide emissions of concrete production and Within the transportation operations, the transportation of concrete is the largest contributor equal to 25% to 28% the production of concrete and on the other hand 12% to 14% for CO2 emission.

Keyword; Environmental impact, Energy and CO2 emission, Construction waste

INTRODUCTION

The impact of concrete material to environmental and human health impacts are a hidden cost of our built environment. The impacts that may occur along the life cycle such as manufacturing, transportation, installation, use, and disposal of construction materials can be significant, yet often invisible. Construction materials and products can be manufactured hundreds, even thousands, of miles from a project site, affecting ecosystems at the extraction and manufacturing locations, but unseen from the project location. Likewise, extraction of raw materials for these products can occur far from the point of manufacture, affecting that local environment. Transportation throughout all phases consumes fuel and contributes pollutants to the atmosphere. Disposal of manufacturing waste and used construction materials will still another environmental impact. These impacts are “invisible” because they are likely remote from the site under construction and the designer’s locale.

Approximately 3.7 million tons of concrete were used in Sweden in buildings, roads and other construction in 2004. This makes concrete one of the most common building materials on the market. The main ingredients in concrete are aggregate (70- 80 %), cement (10-20 %) and water (7-9 %), and to enhance specific characteristics, chemical admixtures (less than 1 %) are added.

Portland cement is the key ingredient in concrete binding the aggregates together in a hard mass. However, it is also the ingredient in concrete that produces the greatest environmental burden. In 2006, more than 2 billion tons of Portland cement were consumed worldwide, with 131 million metric tons (MMT) consumed in the United States. This is a 16% increase over 2002. Ninety-nine MMT of cement were produced in the United States and 32 MMT were imported, primarily from Canada, Thailand, China, and Venezuela [17].

Cement production is an energy-intensive process using primarily fossil fuel sources. Cement composes about 10% of a typical concrete mix but accounts for 92% of its energy demand. Cement production requires the preprocessing of large quantities of raw materials in large kilns at high and sustained temperatures to produce clinker. An average of almost 5 million Btus is used per ton of clinker. In 2004, the cement sector consumed 422 trillion Btus of energy, almost 2% of total energy consumption by U.S. manufacturing [13].

Portland cement manufacturing include different emission such as carbon dioxide (CO2), particulate matter, carbon monoxide (CO), sulfur oxides (SOx), nitrogen oxides (NOx), total hydrocarbons, and hydrogen chloride (HCl). Emissions are different from type of cement, compressive strength, and blended constituents. CO2 emissions. Worldwide, the cement sector is responsible for about 5% of all man-made emissions of CO2, the primary greenhouse gas that drives global climate change [6].

The impact of aggregate production in both terms of manufacturing and CO2 emission are not significant. The considerable impact by the aggregate production refers to dust in operations of mining and blasting, quarry roads, loading and unloading, crushing, screening, and storage piles which are not the concern of this paper [9].

Parallel to rapid economic growth and urbanization in Asia, environmental impacts from construction and demolition (C&D) waste are increasingly becoming a major issue in urban waste management. C&D waste management in developing countries in the Asian region is relatively undeveloped and emerging. Environmental issues such as increase in volume and type of waste, resource depletion, shortage of landfill and illegal dumping, among others are evident in the region. Furthermore, the Asian countries have limited or no available data on C&D waste and the management aspects, particularly with regards to their C&D waste generation and composition; practices and policy, key actors and stakeholders’ participation [1].

Graham 2003 described that construction activity is one of the major contributors of CO2 emissions and other greenhouse gases to the atmosphere. Steel manufacture, for example, is estimated to cause emission of approximately two tons of CO2 for every one ton of steel produced, while cement manufacture causes approximately one ton of CO2 per ton of cement. Cited in Kulatanga et al. (2006) stated that approximately 40% of the generated waste portion globally originates from construction and demolition of buildings. In Malaysia, the construction industry generates a lot of construction waste which cause significant impacts on the environment and increasing public concern. Thus, the minimization of construction waste has become a pressing issue. The source of construction waste at the project site includes materials such as soil and sand, brick and blocks, concrete and aggregate, wood, metal products, roofing materials, plastic materials and packaging of products. Concrete and aggregate is the largest component with 65.8% [2]. CO2 production has been directly linked to climate change and global warming and Malaysian governments have set specific targets to reduce national emissions. Production of concrete on sites is of direct importance both in terms of the contribution to CO2 and energy. Environmental and human health impacts of materials are a hidden impact of our built environment. Impacts during manufacture, transport, installation, use, and disposal of construction materials can be significant, yet often invisible.

AIM AND OBJECTIVE

The aim of this research is investigate the impact of concrete waste in construction sites in term of energy consumption and CO2 emission:

To determine the amount of concrete waste in construction sites.

To estimate the amount of energy used and CO2 emission for production of concrete.

To estimate the total energy and CO2 emission based on the different weight of concrete waste on sites.

To evaluate the disposal option of concrete waste.

LITRETURE REVIEW

Concrete is the most commonly used construction material in the world, while water is the second most consumed product on the planet. Each year the concrete industry uses 1.6 billion tons of cement, 10 billion tons of rock and sand and 1 billion tons of water worldwide. Every ton of cement produced requires 1.5 tons of limestone and fossil fuel energy inputs [8]. And its use is expected to double in the next 30 years (Eco Smart Concrete).The huge popularity of concrete also carries environmental costs, the most harmful of which is the high energy consumption and CO2 release during the production of Portland cement. While the resources for aggregate and cement are considered abundant, they are limited in some areas, and more importantly, mining and extraction of the raw materials results in habitat destruction, and air and water pollution [8].

Cement is a hydraulic binder, which hardens when it is mixed with water. The main constituents of cement are limestone and clay. However. In 2006, more than 2 billion tons of Portland cement were consumed worldwide, with 131 million metric tons (MMT) consumed in the United States. This is a 16% increase over 2002. Ninety-nine MMT of cement were produced in the United States and 32 MMT were imported, primarily from Canada, Thailand, China, and Venezuela [17].The production of cement is an energy-intensive process using primarily fossil fuel sources. Cement composes about 10% of a typical concrete mix but accounts for 92% of its energy demand. [9].CO2 emissions. Worldwide, the cement sector is responsible for about 5% of all man-made emissions of CO2, the primary greenhouse gas that drives global climate change [6].Coarse and fine aggregates in concrete make up between 60% and 75% of the concrete volume. Aggregates are either mined or manufactured. Energy to produce coarse and fine aggregates from crushed rock is estimated by the PCA’s Life Cycle Inventory to be 35,440 kJ/metric ton. The energy to produce coarse and fine aggregate from uncrushed aggregate is 23,190 kJ/metric ton [9].

C&D waste is a major component of the solid waste stream, which should be recognized as a valuable resource as large quantities of it could either be reused or recycled. C&D waste has been mostly overlooked in the efforts to reduce waste sent to landfill, with the emphasis being placed on domestic reuse and recycling. With this view, Asian countries have a problem of disposal sites of which C&D waste largely account to it[4].Reduce, Reuse, and Recycle (“3Rs”) Action Plan and the Progress of Implementation on Science and Technology for Sustainable Development were adopted during the G8 Sea Island Summit in USA in 2004. In 2005, the 3Rs Initiative was formally launched at a Ministerial Conference in Tokyo, Japan [1]. In Hong Kong SAR, Poon et al. (2004) reported that the waste generated by the building construction projects assumes a large proportion of environmental waste.

C&D waste generation in million metric tons in Asian countries. PR China has the highest waste generation in Asia, followed by Japan and South Korea. Vietnam estimated C&D waste generation includes part of sewage waste which is quite minimal part of the total municipal solid waste. According to Central Pollution Control Board India, the total generation of waste from construction industry is estimated to be 14.7 million tons per year [12]. Construction regulation in most of the Asian countries is practiced formally. Some countries consider only large size construction projects and middle end size projects with construction regulations. While regulation to demolished buildings is still not yet recognize in most of the countries. Some of them like countries from Indonesia, India, Malaysia and Thailand practiced demolition permit in an informal way, meaning some cities and/or states (e.g. India) of these countries practiced it. No regulations are present on demolition activities at the moment in some countries in Asia.

The environmental situation resulted from construction has become a pressing issue. According to the Environment Protection Department (EPD) the construction industry generated about 32,710 tons of construction wastes per year in 1998, nearly 15% above the figure in 1997 [3]. To manage such a huge quantity of construction wastes, must adopts a policy of disposing the waste to either land reclamation or landfills. For decades, landfill has provided a convenient and cost-effective solution to the wasteful practices of the industry [10]. 29% of the solid-wastes in the USA are construction wastes. The landfills, originally expected to last 40 to 50 years, would be filled up by 2010, even if there are adequate outlets for construction materials [15]. All these investigations demonstrate that construction business is a large contributor to waste generation and that there is significant potential for protecting the environment through managing construction wastes properly. When structures are demolished, the waste concrete can be crushed and reused in place of virgin aggregate. Doing so reduces the GHG emissions associated with producing concrete using virgin aggregate material. Virgin aggregates, which include crushed stone, gravel, and sand, are used in a wide variety of construction applications, such as road base, fill, and as an ingredient in concrete and asphalt pavement. Over 2 billion tons of aggregates are consumed each year in the US, with an estimated 5 percent coming from recycled sources such as asphalt pavement and concrete [18]. Unlike many of the other materials for which EPA has developed GHG emission factors (e.g., aluminum cans, glass bottles), concrete is assumed to be recycled in an “open loop” – i.e., concrete is recycled into a product other than itself, namely aggregate. Therefore, the GHG benefit of concrete recycling results from the avoided emissions associated with mining and processing aggregate that concrete is replacing. The GHG benefits of recycling are calculated by comparing the difference in emissions associated with producing and transporting a ton of virgin aggregate versus producing and transporting a comparable amount of recycled inputs.

In the case of Malaysia, few regulating bodies’ in some municipalities or cities which deal with construction waste management, namely Local Authorities Ordinance (LAO), Local Authorities Cleanliness by law (LAC), Natural Resources and Environment Ordinance (NREO). Existing regulations are concerned with waste flow generation, transportation and disposal.

Case Study

Data for the study was collected by questionnaire survey and interview. The questionnaire was structured into three sections.

Section A: To obtain information about the respondent’s background

Section B: To survey the level of wastage in construction sites

Section C: To survey the different mixing design

Section D: To survey disposal option

Subsequently, data being analyzed and their results and inference will be presented.

The environmental assessment follows the standard LCA methodology, (ISO 14040-14043). The results are presented both per kg material for each raw material and per functional unit which is equivalent to 1 m3 of concrete. The data reported included, energy, and CO2 emissions to air for each stage in he manufacturing. The ready mixed concrete for three super structure building represents in this study with the strength levels 20 MPa (3,000 psi).

The goal of the inventory phase is to determine quantities of all materials, energy, and CO2 pollutants that contribute to the product or system being investigated.

The data for production of cement and other ingredient of concrete collected from the last research by Jeannette Sjunnesson [6], which collected from various ingredients utilized in cement production in Cement AB’s report. Data for aggregate production is taken from an existing LCA report [16] .Data for admixtures were taken from an EPD by the European Federation of Concrete Admixture Associations (EFCA). Data on transportation modes, Transportation of cement, aggregates, and other constituent materials to ready-mix plant and distances for raw materials are primarily from NTM [11].

Comparison of disposal options i.e. Land filling and recycling was also conducted by using data sources of emission factors developed by the U.S. Environmental Protection Agency (EPA) such as greenhouse gas (GHG) emission factors for recycled concrete, and land filling. To calculate the benefit of recycling concrete to displace virgin aggregate the following steps were done: Step 1: Calculate the emissions for virgin production of aggregate, Step 2: Calculate the emissions associated with processing and delivering a comparable amount of recycled concrete to be used in place of virgin aggregate, Step 3: Calculate the difference in emissions between recycled and virgin scenarios.

The analysis cement replacement material like Fly ash and Slag was also conducted. The data for Slag manufacture are obtained from LCI data and the Emission by EPA U.S.

A. System boundaries

The phases of the life cycle of concrete included in this study are shown in Figure 3.1. The use of water as a raw material is excluded since water is not regarded as a limited resource. To get a fair picture of the environmental impact of concrete, the time-frame must be sufficiently long. However, the carbonization of concrete will not be taken into consideration since the duration of this process is too long for this study. Distances to the concrete plant are assumed 100 km (60 miles) for Portland.

Figure 1. General flow chart of concrete life cycle (Jeannette Sjunnesson, 2005)

B. Data analysis

Upon the collection of questionnaire, every type of the data received under different question will be separated to answer different study objectives. The data will be analyzed manually by using the tables which mentioned in this chapter. For calculation the wastage of concrete level, there is formula [3].

{(1) Cumulative order quantity

(2) Cumulative work done

(3) = (1) - (2) = wastage}

C. Stages of the study

Three stages of the action were formulated for the approach of the study. In stage 1, in depth literature reviews were conducted related to the interest of the study. This stage involve of a search on the ‘review of the current concrete wastage issues in construction industry sites. Stage 2 comprises of interview and questionnaire survey involving the key personnel of stakeholders. The target respondents were identified by their qualification. In the questionnaire there are three sections which start by finding the amount of concrete wasted in construction sites by asking for quantity of ordering and cumulative of work done for the concrete for super structures.

The second part consists of amount of ingredient for making of concrete in 1 m3 from aggregate, water, cement and admixtures. The third part would ask about the disposal of concrete in different situation such as Recycling or Land filling and Incineration

FINDING

Result of the amount of concrete used at superstructure from three different construction sites were, 1728m3, 370m3, 500m3, and the amount of concrete wastes generated were 84 m3, 20 m3, and 20 m3 respectively. The amount of concrete waste indicated that the wastage level is about 5%, 5.5 %, and 4% which are considered more than the norm for the concreting trade which is 4 % [3].The goal of the inventory phase is to determine quantities of all materials, energy, and pollutants that contribute to the product or system being investigated. Portland cement manufacturing, aggregate production, transporting materials to plant, concrete plant operations, and admixture production are investigated in order to find out the energy wasted in production term and environmental impact by CO2 emission by this wastage.

Based on the following figures, it can be observed that 4.84%, 4.33% and 4% are extra percentage of the energy used to produce these amounts wastage. 7 %, 5.5 %, and 4 % are the extra percentage of CO2 emission produced by the amount of concrete wasted in construction sites.

Figure 2. Energy input of total concrete production

Figure 3. Energy input for total waste production

Figure 4. CO2 emissions by total concrete production

Based on the following figures, it can be concluded that transportation of concrete to the site is one of the important and critical factor in both energy consumption and CO2 emission in which in this study found out that transportation the concrete to the site is equal 25% to 28% the production of concrete and on the other hand 12% to 14% also equal for CO2 emission. So that by reduction the distance between concrete production and delivering on site, it can useful in both terms of CO2 emission and energy consumption.

Figure 5. Energy comparison of total energy for concrete production and transportation to site

Figure 6. CO2 comparison of total energy for concrete production and transportation to site

A. End of life

Based on the finding, and as it shows it illustrative that Recycling of wasted concrete can be useful by 1.5 to 2 times more saving energy and CO2 emission than producing virgin aggregate.

Figure 7. Energy Comparison between virgin and Recycled Aggregate

Figure8. CO2 emission between Virgin and Recycled aggregate

B. Land filling

As a result, the emission factor for land filling represents the CO2 emissions associated with combusting diesel fuel to collect the waste and operate the landfill equipment. 1932 kg, 460 kg, 460 kg are the CO2 emission by land filling the wasted concrete.

DISCUSION

The data presented, documents the LCI for different concrete mixtures utilizing slag cement and fly ash. The mixtures include ready mixed concrete. Slag cement mixtures assumed 35 percent slag cement and 20% fly substitution for Portland cement. Energy, CO2 emissions to air, is significantly reduced when slag cement and fly ash used as a partial replacement for Portland cement in concrete. The slag cement mixtures produced an energy savings ranging from 29 to 30 percent; a savings in carbon dioxide emissions of 31 to 33 percent; and on the other hand 20% fly ash can save energy for 19 to 20 percent and CO2 emission for 16 to 17 percent.

Figure 9. Effect of Slag and Fly ash in embodied energy

Figure 10. Effect of Slag and Fly ash in CO2 emission

CONCLUSION

This study shows that it is the raw material production (concerning GWP) together with the transportation operations and concrete plant operations that are the main contributors to the environmental impact of concrete .In concrete; cement is the most energy intensive of all the materials used. Even though it only makes up about 10 to 20 percent of an entire concrete mixture, it is responsible for up to 70 percent of the total embodied energy and 95% of the carbon dioxide emissions of concrete. Cement is the most energy intensive, and therefore has the greatest environmental impact, of the constituent materials of concrete. However, cement only represents 10% to 15% of the total mass of concrete.

Based on the finding in recycling and producing virgin aggregate, it shows that Recycling of wasted concrete can be useful by 1.5 to 2 times more saving energy and CO2 emission than producing virgin aggregate

Using Fly ash and Slag cement as a replacement of cement can be useful in both energy saving in production and CO2 emission by an energy savings ranging from 29 to 30 percent; a savings in carbon dioxide emissions of 31 to 33 percent; and on the other hand 20% fly ash can save energy for 19 to 20 percent and CO2 emission for 16 to 17 percent.


Request Removal

If you are the original writer of this essay and no longer wish to have the essay published on the UK Essays website then please click on the link below to request removal:

Request the removal of this essay


More from UK Essays