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Concrete production accounts for approximately 5 of worldwide greenhouse gas emissions. The majority of these emissions derive from the cement binder. Although developments in cement manufacture have led to a significant reduction in CO2 emissions, further substantial reductions will require radical change. This paper summarises the findings of a study of options for 'low carbon concrete' and options for their availability in UK and opportunity to use them in construction industry on site.
An extensive desk study identified seven groups of technologies with potential to reduce the carbon footprint: secondary cementitious materials, modified Portland or non -Portland cements, low cement concrete, ultra high strength concrete changes in Portland cement (PC) manufacture, alternative binders and carbon capture. A short list was produced of three candidates with potential for high CO2 reduction and suitability for construction: (i) Asphalt concrete (a bituminous binder from the processing of heavy fuel oils); (ii) GGBS (high slag binder comprising a blend of 20% Portland cement and 80% ground granulated blastfurnace slag) and (iii) geopolymer (an alumino-silicate material formed by the reaction of alumina and silicate rich materials with an alkali activator). These three candidates were studied in detail for engineering characteristics, availability, environmental impact and construction issues. The CO2 emissions associated with manufacture and transport of the materials were calculated and recommendations made for their future development.
The completion of this research paper has been the most interesting and toughest challenge throughout my academic tenure. It would not have been possible to complete the thesis without the invaluable support and guidance of my supervisor Dr. Mukesh Limbachiya.
My sincere appreciation to the faculty of Science Engineering & Computing for their extended help.
I am indebted to my colleagues and friends who have been a moral support throughout my thesis.
Lastly, my heartfelt thanks to my family, who always stood by me and kept motivating me to give my best shot.
List of Tables
List of Figures
CO2 - Carbon dioxide
GGBS - Grounded Granulated Blast furnace Slag
OPC - Ordinary Portland cement
HVFA- High Volume Fly Ash
UHPC - Ultra High Performance Concrete
CSIRO - Commonwealth Scientific and Industrial Research Organization
ASTM - American Society for Testing and MaterialsÂ
GWP - Global Warming Potential
SWRDA - South West Regional Development Agency
Chapter 1: INTRODUCTION
Concrete is a very versatile and stable building material. For this reason, it is the second most widely used resource in the world after water. It is the most widely used building material in the world because of its beauty, strength and durability, among other benefits. Concrete is used in nearly every type of construction, including homes, buildings, roads, bridges, airports and subways, just to name a few. And in an era of increased attention on the environmental impact of construction, concrete performs well when compared to other building materials. As with any building product, production of concrete and its ingredients does require energy that in turn results in the generation of carbon dioxide, or CO2. The amount of CO2 produced during manufacturing and the net impact of using concrete as a building material is relatively small.
With the rapid climate changes in the recent times, it is important to focus on the biggest concern of our environment and make it to be a better place. As stated by Ecocem, "if an individual in their normal life reduced their emissions by 50% they might save 8 tons of CO2 annually," but "if professionals in the construction industry reduce the emissions of their projects during construction by 50% they can save up to 4,000,000 tons of CO2 annually" (Overview - National Climate Change Strategy, 2011). (ECOCEM, 2010).
The following features of concrete construction help minimize its carbon footprint (Erin Ashley, 2008):
Concrete is resource efficient and the ingredients require little processing.
Mostof the materials for concrete are acquired and manufactured locally which minimize transportation energy.
Concrete building systems combine insulation with high thermal mass and low air infiltration to make homes and buildings more energy efficient.
Concrete has a long service life for buildings and transportation infrastructure, thereby increasing the period between reconstruction, repair and maintenance and the associated environmental impact.
Concrete, when used as pavement or exterior cladding, helps minimize the urban heat island effect thus reducing the energy required to heat and cool our homes and buildings.
Concrete incorporates recycled industrial by-products such as fly ash; slag and silica fume which helps reduce embodied energy, carbon footprint and quantity of land filled materials.
Concrete absorbs CO2 throughout its lifetime through a process called carbonation, helping reduce its carbon footprint.
Concrete production accounts for approximately 5% of worldwide greenhouse gas emissions. The majority of these emissions derive from the cement binder. Although developments in cement manufacture have led to a significant reduction in CO2 emissions, further substantial reductions will require radical change. Low carbon concrete is an improvement on normal concrete.
1.1 Background and Context
Due to the high emission of carbon dioxide into atmosphere, Cement is considered as one of the most environmentally hazardous materials in the world.According to the Sustainable Development Commission, 4% of Co2 is caused by aviation. Depending on how conservatively you do the sums, cement-based building materials, including concrete and asphalt, account for between 5% and 10% of all carbon dioxide emissions (Adam, 2007). Making the 2bn tons of cement used globally every year pumps out 5% of world's CO2 emission- more than the entire aviation industry. And the long-term trends are upwards: a recent report by the French bank Credit Agricole (Dodson, 2006) (jha, 2008) estimated that, by 2020, demand for cement will increase by 50% (Erin Ashley, 2008) compared to today. Finding an alternative product to cement would, therefore, make excellent environmental sense, especially if Britain is to meet the government's ambitious target of a 60% reduction in carbon dioxide emissions by 2050. Previous attempts to make cement greener have included adding more aggregate to a concrete mixture, thereby using less cement. But this still does not tackle the problem of the carbon emissions from making the cement in the first place.
1.2 Scope and Objectives
As discussed earlier this work aims to investigate about low carbon concrete and findings of a study of options for 'low carbon concrete'. The prompt for the study was a newspaper article discussing low carbon alternatives to concrete, including use of a bituminous binder from processing heavy fuel oils, which was claimed to have negative carbon emissions. At the outset, it was decided that the study should not focus on a single proprietary material but should review other alternatives to Portland cement binder. Concrete production accounts for approximately 5% of worldwide greenhouse gas emissions. (Wimpenny, 2009)Most of the embodied CO2 emissions in concrete derive from the Portland cement (Figure 1) and the worldwide production of Portland cement accounts for approximately 3% of annual CO2 emissions.Each tonne of Portland cement produced generates approximately 1 tonne of CO2; 42% derived from the fuel required in processing and burning the constituents and grinding the cement and 58% being a by-product of de-carbonation of the limestone within the kiln.
Figure : Summary of CO2 Emissions derived from Concrete
A number of factors have acted to mitigate the potential carbon emissions associated with Portland cement use in concrete:
Changes in the production process have increased cement strength development and allowed the content to be reduced by over 25% for the same concrete strength.
Blending of Portland cement with secondary cementitious materials (such as slag and fly ash) resulting in an estimated annual UK reduction in greenhouse gas emissions equivalent to 1.2million tonnes CO2.
Use of water-reducing admixtures resulting in over a 10% reduction in cement content for the same concrete strength.
Improvements in kiln efficiency and use of alternative waste fuels (such as scrap tyres, waste solvents and biofuels) have reduced fuel consumption by 50% since the 1970's.
Despite significant work in the cement and concrete industry to enhance and emphasise the sustainability of concrete, including its whole life benefits of thermal mass and longevity, further significant reductions in embodied CO2 in concrete will require fuller application of these existing technologies across the industry, as well as more radical change. This is reflected in the results of the desk study.
The Main Objective of this dissertation to study the various low carbon concrete constituents which is being experimented worldwide and finding the constituents that emits very low carbon along with considering few conditions like, to use during flood alleviation and the availability of them in UK. Also, providing the amount of CO2 emission by the Conventional concrete containing these constituents.
The study comprises three stages:
A desk study to review candidate materials and strategies being developed in different countries.
Screening the options to produce a maximum short-list of three candidate materials.
A detailed appraisal of the shortlisted materials for engineering suitability and effectiveness in reducing CO2 emissions with case studies.
An extensive desk study identified seven groups of technologies with potential to reduce the carbon footprint: secondary cementitious materials modified Portland or non-Portland cements, low cement concrete, ultra high strength concrete changes in Portland cement (PC) manufacture, alternative binders and carbon capture. A short list was produced of three candidates with potential for high CO2 reduction and suitability for construction: (i) Asphalt (a bituminous binder used for construction of roads and highways); (ii) high slag binder comprising a blend of 10% Portland cement and 90% ground granulated blast furnace slag; and (iii) geo-polymer (an alumino-silicate material formed by the reaction of alumina and silicate rich materials with an alkali activator). These three candidates were studied in detail for engineering characteristics, availability, environmental impact and construction issues. The
CO2 emissions associated with manufacture and transport of the materials were calculated and recommendations made for their future development.
The test would be selected by the judgment choice methodology where the research test on a certain criterion supported. As discussed, earlier that the building industry becomes the more elaborately in the light of the new alternatives, environmental problems and the enclosed national economy.
Compare the different seven types of concrete with their co2 emissions during the various processing.
The observations made in this process would be graphically represented and statistically analysed for reaching an outcome.
The detailed appraisal of these three low carbon concrete constituents providing their engineering characteristics and the amount of carbon emission by the conventional concrete containing them. Also interviewing the concrete experts with questionnaire of these three constituents and analyse the result based on them.
1.4 Overview of Dissertation
Concrete production accounts for approximately 5% of worldwide greenhouse gasemissions. The majority of these emissions derive from the cement binder. Although developments in cement manufacture have led to a significant reduction in CO2 emissions, further substantial reductions will require radical change. This dissertation summarises the findings of a study of options for 'low carbon concrete'. The study was based on the paper in 2007 by UK Government's Environment Agency, through its Carbon Reduction Fund, with the aim of identifying low CO2 alternatives to concrete for use on flood alleviation schemes.
An extensive desk study identified seven groups of technologies with potential to reduce the carbon footprint: secondary cementitious materials modified Portland or non -Portland cements, low cement concrete, ultra high strength concrete changes in Portland cement (PC) manufacture alternative binders and carbon capture.
A short list was produced of three candidates with potential for high CO2 reduction and suitability for construction: (i) Asphalt (a bituminous binder used for road and highway construction); (ii) high slag binder comprising a blend of 10% Portland cement and 90% ground granulated blast furnace slag; and (iii) geopolymer (an alumino-silicate material formed by the reaction of alumina and silicate rich materials with an alkali activator). These three candidates were studied in detail for engineering characteristics, availability, environmental impact and construction issues. The CO2 emissions associated with manufacture and transport of the materials were calculated and recommendations made for their future development.
Chapter 2. Literature Review
2.1 Introduction of Low-Carbon concrete and environmental impact
Concrete is one of the building materials, which are being used widely in the world. This is because of its strength, durability and also many other benefits. It is been included in almost every type of construction, which includes housing, commercial buildings, bridges and roads. In attention on the environmental impact of construction, it performs and gives more benefits compared to other building materials. During any building product, the production of concrete and its ingredients does require energy, which in turn generates carbon dioxide. Even though the amount of CO2 produced during concrete manufacturing and the net impact of using it as building material is comparatively very small, the amount of CO2 emission can be decreased to minimum by usage of Low-Carbon concrete.
2.2 CO2 emissions from concrete production
(Malhotra, 2003)The total CO2 emissions per ton of cement can range from about 1.1 tons of CO2 from the wet processing plants to about 0.8 tons from a plant with precalcinators.
About half of the CO2 emissions are due to the calcination of limestone and the other half are due to the combustion of fossil fuels. According to (Cahn, 1997) , the emissions from the calcination of limestone are fairly constant at about 0.54 tons of CO2 per ton of cement; the emissions from the combustion depend on the carbon content of the fuels being used and the fuel efficiency.
The CO2 emissions associated with the manufacturing of Portland cement can be reduced significantly by reducing the production of current clinker (Malhotra, 2003). The resulting loss in Portland cement production can be overcome by the increased use of supplementary cementing materials, especially fly ash.
(Ernst Worrell, 2010)Carbon dioxide emissions in cement manufacturing come directly from combustion of fossil fuels and from calcining the limestone in the raw mix. An indirect and significantly smaller source of CO2 is from consumption of electricity, assuming that the electricity is generated from fossil fuels. Roughly half of the emitted CO2 originates from combustion of the fuel and half originates from the conversion of the raw material.(Ernst Worrell, 2010) Not accounted for are the CO2 emissions attributable to mobile equipment used for mining of raw material, used for transport of raw material and cement, and used on the plant site. Current emission estimates for the cement industries are based solely on the assumed clinker production (derived from cement production assuming Portland cement) and exclude emissions due to energy use. Emissions from energy use are included in the estimates for emissions from energy use, and not allocated to cement making.
Estimated carbon emissions from cement production in 1994 were 307 MtC, 160 MtC from process carbon emissions and 147 MtC from energy use. These emissions account for 5.0% of 1994 world carbon emissions based on a total of 6199 MtC reported by the Carbon Dioxide Information and Analysis Center.
(Ernst Worrell, 2010)Provided the CO2 emissions estimate (in million metric tons of carbon) by key cement-producing countries and regions. Of the countries explained, China accounts for by far the largest share of total emissions (33.0%), followed by the United States (6.2%), India (5.1%), Japan (5.1%), and Korea (3.7%). Over- all, the top 10 cement-producing countries in 1994 accounted for 63% of global carbon emissions from cement production for that year. Regionally, after China, the largest emitting regions are Europe (11.5%), OECD-Pacific (9.3%), and Asian countries excluding China and India (9.3%), and the Middle East (8.4%). World average primary energy intensity was 4.8 GJ/t, with the most energy-intensive regions being Eastern Europe and the former Soviet Union (5.5 GJ/t), North America (5.4 GJ/t), and the Middle East (5.1 GJ/t).
(Ernst Worrell, 2010)The average world carbon intensity of carbon emissions in cement production is 222 kg of C/t of cement. Although China is the largest emitter, the most carbon- intensive cement region in terms of carbon emissions per ton of cement produced is India (253 kgC/t), followed by North America (242 kgC/t), and then China (240 kgC/t). Figure 6 shows the carbon intensity of cement production in various regions (Ernst Worrell, 2010).
2.2 Feasible Low carbon concrete constituent types:
An initial desk study of construction industry databases and web sites indicated that the strategies being adopted or developed in twelve countries around the world could be divided into seven groups. The effect upon CO2 emissions of changes in kiln technology, such as oxygen enrichment and carbon sequestration, are not known. Introduction of such technology across the industry will be a slow process and given the need for immediate measures, it has not been considered further.
2.2.1 Secondary Cementitious Materials:
It is necessary to pay much attention to use greater amount of Secondary Cementitious Materials because approximately 95% of all CO2emissionsare from cement manufacture by Ordinary Portland Cement.
Secondary Cementitious Materials are one of the most sustainable construction materials which help to reduce the carbon footprint to a great amount. This includes Fly ash, ground-granulated blast-furnace slag (GGBS).Because of the following reasons they plays major role in development of Low Carbon environment.
When they incorporate into concrete, it recovers an industrial byproduct.
Industrial byproducts can be avoided completely.
Emission of green gas and usage of natural raw materials can be decreased due to the reduced content of Portland cement in concrete.
Durability of concrete can be improved by increasing the structure service.
The compressive strength of High Volume Fly Ash (HVFA) mixtures were 8, 55, and 80 MPa at 1, 28, and 182 days, respectively. Extensive laboratory tests (V.M, 1994) concluded that the Young's modulus of elasticity, creep, drying shrinkage, and freezing and thawing characteristics of HVFA concrete is comparable to normal Portland cement concrete. The HVFA concrete also has high resistance to water permeation and chloride-ion penetration.
Another by-product that is useful for cement substitution is ground-granulated blast-furnace (GGBF) slag. According to (Mehta, 1999) the world production of this slag is approximately 100 million tons per year; only approximately 25 million tons of slags are processed into the granulated form that has the cementitious properties. Because GGBF slag is derived as a by-product from the blast furnaces manufacturing iron, its use has environmental benefits. The use of GGBF slag in concrete significantly reduces the risk of damages caused by alkali-silica reaction, provides higher resistance to chloride ingress, reduces the risk of reinforcement corrosion, and provides high resistance to attacks by sulphate and other chemicals. The use of GGB slag in concrete has increased in recent years and this trend is expected to continue.
Secondary Cementitious products comprise the glue that holds concrete together. These materials include traditional Portland cement and other cementitious materials, such as fly ash, ground granulated blast furnace slag (ggbs), limestone fines and silica fume. These materials are either combined at the cement works (to produce composite cement) or at the concrete mixer when the concrete is being produced (the cementitious product is called a combination in this case).
Fly ash and ggbs are the most commonly used of these materials in the UK. These secondary materials are useful by-products of other industrial processes, which would potentially otherwise be sent to landfill. Ggbs is a useful by-product recovered from the blast-furnaces used in the production of iron. It can be used un-ground as a coarse aggregate or as a supplementary cementitious material (where it can replace up to 70% of cement in a concrete mix). Fly ash is a useful by-product of coal-fired power stations and is environmentally beneficial. If it were not used in composite cements or as an addition at the concrete mixer then the material would be wasted and sent to landfill. Using ggbs or fly ash in concrete, either as a mixer addition or through a factory made cement, significantly reduces the overall greenhouse gas emissions associated with the production of concrete
According to (Concrete Credentials: Sustainability, 2010)Direct annual CO2emissions have reduced by nearly 40 per cent since 1990 in absolute terms. The cement industry met the UK's 2010 Climate Change Agreement target four years in advance and is continuing its commitment to improvement. This compares favourably with the UK construction industry, which overall recorded an increase in CO2 of more than 30 per cent over the same period.
Silica fume is a by-product resulting from the reduction of high-purity quartz with coal or coke and wood chips in an electric arc furnace during the production of silicon metal or ferrosilicon alloys. The condensed silica fume contains between 85 and 98 percent silicon dioxide and consists of extremely fine spherical glassy particles (the average particle size is less than 0.1Î¼m) (Tony C.Liu, 2008).
Because of its extreme fineness and high silicon dioxide content, condensed silica fume is a very efficient pozzolanic material. The worldwide production of silica fume is estimated to be about 2 million tons. Because of limited availability and the current high price relative to Portland cement and other pozzolans or slag, silica fume is being used primarily as a property enhancing material [Ref. 10]. In this role, silica fume has been used to provide concrete with very high compressive strength or with very high level of durability or both. It has been used to produce concretes with reduced permeability for applications such as parking structures and bridge decks and for repair of abrasion damaged hydraulic structures.
(Tony C.Liu, 2008)One of the major barriers against the use of large quantities of fly ash and other supplementary cementing materials in concrete is the current prescriptive-type of specifications and codes. The prescriptive-type of specifications generally place limits on the maximum percentage of the cement that can be replaced by the supplementary cementing materials. For example, ACI 318 Building Code limits the maximum percentage of fly ash or other pozzolans to not exceed 25% of the total cementitious materials by mass for concrete exposed to deucing chemicals. High performance concrete mixtures being produced with HVFA concrete prove that prescriptive specifications hinder the widespread use of fly ash and other supplementary cementing materials.
Replacing the prescriptive-type of specifications and codes with performance-based specifications and codes will accelerate the rate of utilization of fly ash and other supplementary cementing materials and can provide economic and environmental benefits.
2.2.2 Non-Portland cements binders:
Non-Portland cements binders are the constituents which act as binders without involving Portland cement. Geopolymer is one of the best examples of this type of cement. Apart from geopolymer there are few other materials, which are made of calcium sulphate based and magnetite based cements. Also the materials that are made of calcium sulfoaluminate are also included in this category. Geopolymer is made of aluminosilicate materials with potential use in a number of areas, essentially as a replacement for Portland cement and for advanced high-tech composites, ceramic applications or as a form of cast stone. Geoploymers are example of the broader class of alkali-activated binders, which also includes alkali-activated metallurgical slags and other materials (Cajin shi, 2006)
The use of fly ash-based Geopolymer Concrete contributes to the potential for reduced global warming. A recent life cycle assessment of geopolymer concretes indicates that the global warming potential (GWP) of geopolymer concretes is between 26 and 45% lower compared to ordinary Portland cement concrete (Stengel, 2009). However, when other ecological impact factors are considered, geopolymer concrete does not rate as favourably as Portland cement concrete. This is largely ascribed to the sodium silicate and sodium hydroxide production (Stengel, 2009). The impact of each depends upon the processing employed. The use of alkaline solutions form waste streams of other processes, such as aluminium processing, may provide potential reduction in the environmental impact of geopolymer concrete.
According to (Mcleod, 2005)Geopolymeric cements are the only products reviewed that are clearly capable of achieving low carbon footprints.
2.2.3 Low cement concrete:
These are the concrete mixtures with low cement content used for blinding off and typically of low compressive strength. They are also known as Lean Mix Concrete.
2.2.4 Ultra high strength concrete:
The term Ultra High Performance Concrete (UHPC) has been used to describe a fibre-reinforced, super plasticized, silica fume-cement mixture with very low water-cement ratio (w/c) characterized by the presence of very fine quartz sand (0.15-0.40 mm) instead of ordinary aggregate (A.R.Lubbers, 2003). The absence of coarse aggregate was considered by the inventors to be a key-aspect for the microstructure and the performance of the UHPC in order to reduce heterogeneity between the cement matrix and the aggregate. However, due to the use of very fine sand instead of ordinary aggregate, the cement density of UHPC is as high as (900-1000 kg/m3) (S. Collepardi, 1996). One of the primary benefits of this class of concrete is that it can exhibit significant tensile strength and toughness. Much of such properties enhancement is imparted to the concrete by the addition of short, discontinuous fibres during the mixing procedure (P.E.Hartman, 2000)
2.2.5 Changes in Portland cement Manufacture:
Changes in Portland cement Manufacture can be obtained by either adding few materials in the manufacturing stage else replacing the Ordinary Portland cement. It is reduced CO2 cement. They are energy efficient production and follows environmental management system and it sustains fuel.
Oxygen enrichment of kiln atmosphere to enhance burning Belite cements, Alinite and Fluoralinite cement and Portland limestone cement are few examples of cements which are manufactured by making changes in Ordinary Portland cement.
2.2.6 Alternative Binder Type:
To reduce the production of greenhouse gas (CO2), people should attempt to use less cement in concrete. To achieve this, usage of cement in concrete has to be minimized to the least and at the same time; the strength and durability of the concrete should not be collapsed. There are bituminous-based binders which acts helps to reduce the CO2 emission from the concrete to the maximum.
Asphalt is one of the bitumen that is mainly used for the road construction to replace the cement concrete. Asphalt concrete, commonly known as asphalt, is used in the construction of highways and roads. It is produced in a variety of mixtures, including hot mix, warm mix, cold mix, cutback, mastic, and natural, each with distinct material and energy inputs. A highway or road is built in several layers, including pavement, base, and sub-base. (Levis, 2008)
2.2.7 Carbon Capture:
Limecrete is the method of carbon capture that helps to reduce the CO2 emission from concrete. Ty- Mawr Ltd designed this innovative flooring system in 1998 as an alternative to cement-based concrete for use in old and historic properties. Hempcrete is a combination of chopped hemp shiv and binder comprising of natural hydraulic lime and a small amount of cement. It is firm and self-insulating. Hempcrete is suitable for uses such as timber frame infill, insulation and, with the addition of aggregate, floor slabs. Hemp is a renewable biomaterial and lime is an abundant quarried material. Hempcrete is carbon negative and the obvious choice for buildings aiming to achieve a low carbon footprint and the highest sustainable building code levels.
According to (Ty- Mawr Ltd, n.d.)Hempcrete is carbon negative. A 300mm hemcrete wall absorbs in its construction 40kg per m2 CO2. A typical brick and block wall emits 100kg giving a net benefit of 140kg. We use British hemp. Hempcrete is also recyclable at the eventual end of the life of the building.
2.3 CO2 Emissions relative to Portland cement Concrete:
CO2 Emissions from various low carbon concrete constituents can be compared relatively with the Ordinary Portland cement concrete CO2 Emission respective to the percentage.
Based on the various experiments which is carried out to find the CO2 emission from the different type of concrete which is explained before are compared to the CO2 emission from the Portland cement concrete.
According to (Wimpenny, 2009), they are classified into five different categories as mentioned in the table below:
CO2 emissions relative to Portland cement concrete
Table : CO2 Emission relative to Portland cement concrete
Long- term effects such as carbon capture by carbonation or extended service life were not considered in the screening process. A very approximate assessment of CO2 emission was undertaken based on the potential reduction in the cement content or concrete volume or the embodied CO2 of the binder relative to Portland cement. The CO2 emissions for the options were categorised as shown above.
CO2 emissions less than 0% indicate that the material 'captures' CO2 by incorporating a component that could release CO2 into the atmosphere if used or disposed of in an alternative way.
2.4Carbon dioxide emission in UK through concrete manufacturing:
(Sustainable Concrete Forum, 2010)Approximately half of the carbon emissions in the UK's Carbon Budget are covered by the European Union Emission Trading Scheme (EU ETS). In the case of concrete, the majority of emissions are from cement, which is covered by the EU ETS and is actively managed in order to meet the EU carbon reduction targets. The continuing investment in new technology and use of biomass fuels has enabled further reductions in the CO2 emissions from the production of cement. In most of the other sectors slight increases in the CO2 emissions per tonne have been observed. (Sustainable Concrete Forum, 2010) Consistent with the energy efficiency indicator, whilst the industry has continued to invest in energy and carbon efficiency measures, the fixed energy requirement of the manufacturing assets being allocated over a reduced volume of production during the market downturn has largely off-set the gains made. (Sustainable Concrete Forum, 2010) The inclusion of the UK average reinforcement content to the concrete has increased the CO2 emissions by around 9%.
The emissions associated with the production and fabrication of steel reinforcement indicates a slight reduction in 2010 compared to 2009. (Sustainable Concrete Forum, 2010)All of the steel produced by BAR members is produced using Electric Arc Furnace which uses scrap material as its main raw material. As a consequence steel reinforcement bar has approximately a third of the embodied energy and a fifth of the carbon impact of primary steel production.
2.5Geo Polymer Concrete and its Carbon footprint:
Geopolymer is a term used to describe a family of alumino-silicate materials formed by the reaction of alumina and silicate rich materials with a metal alkali activator. A key parameter in determining the characteristics and use of the geopolymer is the silica: alumina ratio, as indicated in Table 2. For civil engineering silica: alumina ratio of approximately 2 is required.
Silica: alumina Ratio
Rigid crystalline structure
Bricks, ceramics and fire protection
Low CO2 cement and concrete waste encapsulation
Ductile polymeric structure
Foundry equipment Heat resistant composite (200-1000Â°C)
Fire and heat resistant fibre competes
Source: Report on Low Carbon Concrete-Options for the Next Generation of Infrastructure by Don Wimpenny in 2009
Table : Influence of silica: alumina ratio
The alumino-silicate component of geopolymer can be derived from materials such as metakaolin, slag or fly ash. The accelerator would typically be a potassium or sodium hydroxide or silicate. The calcium and carbon content of the binder have to be controlled to avoid variable properties. Fly ash should have a loss on ignition less than 7% and derive from a sub-bituminous coal with calcium content less than 10%.
The Commonwealth Scientific and Industrial Research Organization (CSIRO) has investigated the use of the material in construction, including marine structures, fluid containment and conduits, although it admits that the transition from a well-established, material such as cement to a novel one is difficult. Trials undertaken by Curtin University of Technology, Perth, Australia on reinforced beams and columns have proved promising and concrete is being produced commercially using geopolymer binder. However, no published examples have been obtained of the material being used in reinforced structural elements in the field.
By virtue of their stable alumino-silicate structure, it would be expected that geopolymers would have good durability and they have been considered for stabilisation and encapsulation of the nuclear waste. Fire resistance should be superior to conventional concrete because of the negligible water in the mix and the sulphate and acid resistance should be enhanced because of the lack of calcium bearing material in the binder. The alkalinity of the constituents should provide a sufficiently high pH to passivate steel reinforcement to corrosion.
The short setting time of these materials and the need with some combinations for heat treatment is a major drawback, which is likely to restrict its use in the first instance to precast items, specialist fast-setting repair materials and sprayed concrete.
There are no standards and codes covering the use of geopolymer in construction and this would most likely be facilitated by testing against a performance specification.
With the current cement production growth ranges from 5% to 16% and suggest an average growth rate in favour of the 5% increase scenario. In 25years from now, world cement CO2 emission could equal the 3,500 million tonnes total CO2 production of Europe (EC); industry+energy+transportation, or 18% of present world CO2 emission (Davidovits, 1994). This addresses the need for a drastic change in the cementitious systems involved in the utilization of concrete, through the manufacture of new type of cement which doesn't involve the calcination of limestone which release CO2.
To produce concrete, instead of cement paste, geopolymer is used as the binder. Then this geopolymer paste helps to bind the fine and coarse aggregates along with other unreacted materials together to form the geopolymer concrete. Using the usual concrete technology methods, the geopolymer concrete can be manufactured. As in the Portland cement concrete, the aggregates occupy the largest volume, that is, approximately 75 to 80% by mass, in geopolymer concrete (Djwantoro Hardjito, 2004). The silicon and the aluminium in the fly ash are activated by a combination of sodium hydroxide and sodium silicate solutions to form the geopolymer paste that binds the aggregates and other unreacted materials (Djwantoro Hardjito, 2004).
Geopolymer is a type of amorphous alumino-silicate cementitious material. Geopolymer cement is also acid-resistant, because unlike the Portland cement, geopolymer cements do not rely on lime and are not dissolved by acidic solutions. Geopolymer can be synthesized by polycondensation reaction of geopolymeric precursor, and alkali polysilicates. Comparing to Portland cement, the production of geopolymers consume less energy and almost no CO2 emission. (Djwantoro Hardjito, 2004) Geopolymers are not only energy efficient and environment friendly, but also have a relative higher strength, excellent volume stability, better durability, good fire resistance, and easy manufacture process. Thus geopolymer will become one of the perspective sustainable cementitious materials in 21st century.
Geopolymer concrete is seen as a potential alternative to standard concrete, and an opportunity to convert a variety of waste streams into useful by-products. One key driver in geopolymer development is the desire to reduce greenhouse gas emissions from the production of concrete products.
2.6Ground Granulated Blast furnace Slag (GGBS) in Concrete:
Another by-product that is useful for cement substitution is ground-granulated blast-furnace (GGBF) slag. Although the world production of this slag is approximately 100 million tons per year, only approximately 25 million tons of slags are processed into the granulated form that has the cementitious properties (Mehta, 1999). Because GGBF slag is derived as a by-product from the blast-furnaces manufacturing iron, its use has environmental benefits. The use of GGBF slag in concrete significantly reduces the risk of damages caused by alkali-silica reaction, provides higher resistance to chloride ingress, reduces the risk of reinforcement corrosion, and provides high resistance to attacks by sulphate and other chemicals. The use of GGBF slag in concrete has increased in recent years and this trend is expected to continue.
Laboratory work by Lang and Geiseler (Lang, 1996) on a German blast furnace slag cement (405 m2/kg specific surface area) containing 77.8 per cent slag showed that excellent mechanical and durability characteristics were achieved in super-plasticized concrete mixtures with 455 kg/m3 cement content and 0.28 w/cm. The compressive strengths at ages 1, 2, 7, and 28 days were 13, 37, 58, and 91 MPa, respectively. The concrete also showed good resistance to carbonation, penetration of organic liquids, freezing and thawing cycles (without air entrainment), and salt scaling.
(Cementitious Slag Makers Association (CSMA), 2012)With the same content of cementitious material (the total weight of Portland cement plus GGBS), similar 28-day strengths to Portland cement will normally be achieved when using up to 50 per cent GGBS. At higher GGBS percentages the cementitious content may need to be increased to achieve equivalent 28-day strength. GGBS concrete gains strength more steadily than equivalent concrete made with Portland cement. For the same 28-day strength, a GGBS concrete will have lower strength at early ages but its long-term strength will be greater. The reduction in early-strength will be most noticeable at high GGBS levels and low temperatures.(Cementitious Slag Makers Association (CSMA), 2012) Typically a Portland cement concrete will achieve about 75 per cent of its 28-day strength at seven days, with a small increase of five to 10 per cent between 28 and 90 days. By comparison, a 50 per cent GGBS concrete will typically achieve about 45 to 55 per cent of its 28-day strength at seven days, with a gain of between 10 and 20 per cent from 28 to 90 days.(Cementitious Slag Makers Association (CSMA), 2012) At 70 per cent GGBS, the seven-day strength would be typically around 40 to 50 per cent of the 28-day strength, with a continued strength gain of 15 to 30 per cent from 28 to 90 days. Under normal circumstances, the striking times for concretes containing up to 50% GGBS, do not increase sufficiently to significantly affect the construction program (Cementitious Slag Makers Association (CSMA), 2012). However, concretes with higher levels of GGBS will not always achieve sufficient strength after one day to allow removal of vertical formwork, particularly at lower temperatures, lower cementitious contents and in thinner sections (Cementitious Slag Makers Association (CSMA), 2012)
(Tony C.Liu, 2008)Approximately 5 million tons of GGBF slags were used in concrete mixtures annually in Taiwan and also Up to 55% of the Portland cement (ASTM Type V) had been replaced by GGBF slag in concrete mixtures where high sulphate resistance is required and in the moderate sulphate resistance applications, 45% of Portland cement (ASTM Type II) can be replaced by GGBF slag with excellent performance. Concrete containing 45-50% of GGBF slag was commonly used for concrete slurry wall constructions in Taiwan (Tony C.Liu, 2008).
(Hanson Heidelberg Cement Group, 2009)The use of cement replacements with lower environmental burdens offers opportunities for significant reductions in energy use and carbon dioxide emissions. The most effective alternative to Portland cement is ground granulated blast furnace slag (GGBS), which typically replaces 50 per cent of the Portland cement in a concrete mix. Greater proportions of up to 70 or even 80 per cent can be used with advantage in suitable situations (Hanson Heidelberg Cement Group, 2009).
The uses of GGBS in concrete are to reduce emission of carbon dioxide, conserve natural resources and also it saves energy.
As a result of its low environmental impacts, using GGBS can reduce significantly many of the environmental burdens associated with concrete.
The following table 3 shows the environmental benefits of replacing 50 per cent of the Portland cement with GGBS in a typical concrete mix.
Effect of using GGBS
Emission of Carbon dioxide
Primary energy requirement
Source: Higgins D, Parrott L & Sear L, Effects of GGBS and PFA upon the environmental impacts of concrete, CIA/DETR Partners in Technology Project, 2000.
Table : Effect of GGBS on various Environmental issues
(Hanson Heidelberg Cement Group, 2009)To allow comparison of products, the Building Research Establishment has produced a scoring system that allocates Eco points to materials - the more Eco points, the larger the impact on the environment. Under this method GGBS scores 0.47 Eco points, while Portland cement scores 4.6 Eco points.(Hanson Heidelberg Cement Group, 2009) This classes GGBS as having only one tenth of the environmental impact of Portland cement.(Hanson Heidelberg Cement Group, 2009) BRE has also released Green Guide to Specification ratings for use with the government's Code for Sustainable Homes. This guide includes examples of 50 per cent GGBS concrete, which consistently achieves improved sustainability ratings relative both to normal concrete and concrete made with fly ash (Hanson Heidelberg Cement Group, 2009).
2.7Asphalt Concrete and its carbon dioxide emission:
The construction of highways and roads are commonly made with Asphalt concrete, which is also known as Asphalt. It comprises various mixtures, including hot mix, warm mix, cold mix, cut-back, mastic, and natural, each with distinct material and energy inputs. Road construction involves different layers namely pavement, base and sub-base. Asphalt concretecan be used for the construction of pavement layer and surface layer instead of Portland cement concrete.
(Yuta Iwatani, 2012)CO2 emissions from the production of the surface layer and base course material, as well as from its transportation activities, were responsible for about 70-80% of the total amount of CO2 emissions from each pavement. The amount of CO2 emissions per 100 m2 of pavement for the cement concrete pavement was the highest with all traffic loads. Especially, there were large differences in the production of surface materials (Yuta Iwatani, 2012). The proportion of CO2 emissions caused by the production of materials in asphaltic pavement was smaller than that in other types of pavement. The use of cement as the raw material for concrete was responsible for this difference in the amount of CO2 emissions. For mending activities, the amount of CO2 emissions from asphaltic and interlocking block pavements was 50-60% lower, compared to that for the new pavement construction. It is because these pavements were reusable from recycled pavement materials. (Yuta Iwatani, 2012) In cement concrete pavement, however, the amount of CO2 emissions only decreased by 20%. The difficulty of reusing cement concrete was the reason why the emissions were still high from this type of pavement. In addition, in interlocking blocks and cement concrete pavements, the amount of CO2 emissions generated from the surface material production accounted for about 80% of total CO2 emissions. On the other hand, in asphaltic pavement, the amount of CO2 emissions generated from the production of base course pavement only accounted for about 40% (Yuta Iwatani, 2012). This was due to the use of recycled asphalt mixture which emitted low amounts of CO2 for mending the surface layer in asphaltic pavement.
Considering the amount of CO2 emissions from new pavement construction, the emissions generated from the production of the surface layer and the base course materials, as well as from its transportation, were responsible for about 70-80% of the total CO2 emissions (Yuta Iwatani, 2012).
As a result of mending the surface layer of pavement, the amount of CO2 emissions generated from the production of pavement materials in asphaltic pavement accounted for a high proportion in total CO2 emissions while in interlocking pavement and cement concrete pavements, the amount of CO2 emissions generated from the production of surface materials accounted for a high proportion in total CO2 emissions (Yuta Iwatani, 2012).
(Yuta Iwatani, 2012)By comparing the amount of CO2 emissions per 100 m2 from each pavement for the next 100 years after new construction, it was found that the smallest amount of CO2 emissions from asphaltic pavement were produced with pavement under 250 traffic loads. In the case of interlocking block pavement, however, the smallest one was generated from pavement with more than 250 traffic loads.
2.8 Availability of Low Carbon constituents in UK:
According to (Cementitious Slag Makers Association (CSMA), 2012)GGBS concrete is not available for smaller-scale concrete production because it can only be economically supplied in bulk. GGBS is not only used in concrete and other applications include the in-situ stabilization of soil.
IN spite of Geopolymer's major production and usage in Australia, UK also produces optimum amount of geopolymer concrete. Banah UK Ltd which is located in Northern Ireland is the only company that supplies geopolymer concrete in UK. This clearly shows that availability of this concrete makes less possible compare to the other two major constituents. According to (banah UK Limited, 2012) If banahCEM replaced OPC in the UK there would be an emissions reduction of between 10,200,000 and 10,800,000 tonnes of CO2 annually.
2.9 Comparison of Low carbon constituents and Ordinary Portland cement Concrete:
The carbon impacts of Ordinary Portland Cement (OPC) and geopolymers in an Australian context, with an identification of some key challenges for geopolymer development. The results of the examination show that there is wide variation in the calculated financial and environmental "cost" of geopolymers, which can be beneficial or detrimental depending on the source location, the energy source and the mode of transport. (Djwantoro Hardjito, 2004) Some case study geopolymer concrete mixes based on typical Australian feed stocks indicate potential for a 44-64% reduction in greenhouse gas emissions while the financial costs are 7% lower to 39% higher compared with OPC. Geopolymer, with properties such as abundant raw resource, little CO2 emission, less energy consumption, low production cost, high early strength, fast setting, these properties make geopolymer find great applications in many fields of industry such as civil engineering, automotive and aerospace industries, non-ferrous foundries and metallurgy, plastics industries, waste management, art and decoration, and retrofit of buildings. Global warming and energy saves (Djwantoro Hardjito, 2004). It is well known that a great amount of CO2 is emitted during the production of Portland cement, which is one of the main reasons for the global warming (Djwantoro Hardjito, 2004). Studies have shown that one ton of carbon dioxide gas is released into the atmosphere for every ton of Portland cement which is made anywhere in the world (Djwantoro Hardjito, 2004).
The 'greenest' of all the construction materials is Ground granulated blast furnace slag 'GGBS'. The by-product which can be extracted during the iron production is the only raw material for manufacturing this very specific slag. It utilizes all of the slag during the manufacturing stage and hence it produces almost zero waste during this process.
(Cementitious Slag Makers Association (CSMA), 2012)By comparison with Portland cement, manufacture of GGBS requires less than a fifth the energy and produces less than a fifteenth of the carbon dioxide emissions. Further 'green' benefits are that manufacture of GGBS does not require the quarrying of virgin materials, and if the slag was not used as cement it might have to be disposed of to tip (Cementitious Slag Makers Association (CSMA), 2012).
In contrast, geopolymer cement is manufactured in a different way than that of Portland cement. (Djwantoro Hardjito, 2004)It does not require extreme high temperature treatment of limestone. Only low temperature processing of naturally occurring or directly man-made alumino-silicates (kaoline or fly ash) provides suitable geopolymeric raw materials. These lead to the significant reduce in the energy consumption and the CO2 emission. It is reported by (Davidovits, 1994) that about less 3/5 energy was required and 80%-90% less CO2 is generated for the production of geopolymer than that of Portland cement. Thus it is of great significance in environmental protection for the development and application of geopolymer cement.
According to (Obla, 2009)Focusing solely on CO2 emissions from cementand concrete production does not encourage the use of recycled or crushed returned concrete aggregates; use of water from ready mixed concrete operations; use of sustainable practices such as energy savings at a ready mixed concrete plant and use of sustainable transport practices. This is because only 5% of CO2 emissions from a cubic yard of concrete are due to use of virgin aggregates, water, plant operations and material transport to the plant (Obla, 2009).
2.10 Carbon footprints of Low carbon concrete comparison with conventional concrete:
Portland cement is the most important ingredient of conventional concrete. Theproduction of one ton of cement emits approximately one ton of carbon dioxide to the atmosphere.Moreover, cement production is not only highly energy-intensive, next to steel and aluminium, but also consumes significant amount of natural resources. For sustainable development, the concrete industry needs to explore alternative binders to Portland cement. (Rangan.B.V, 2010)Such an alternative is offered by the fly ash-based geopolymer concrete, as this concrete uses no Portland cement; instead, utilises the fly ash from coal-burning power stations to make the binder necessary to manufacture concrete.(Rangan.B.V, 2010)The use of fly ash-based Geopolymer Concrete contributes to the potential for reduced global warming. A recent life cycle assessment of geopolymer concretes indicates that the global warming potential (GWP) of geopolymer concretes is between 26 and 45% lower compared to ordinary Portland cement concrete (Stengel, 2009). However, when other ecological impact factors are considered, geopolymerconcrete does not rate as favourably as Portland cement concrete. This is largely ascribed to the sodium silicate and sodium hydroxide production (Stengel, 2009). The impact of each depends upon the processing employed. The use of alkaline solutions form waste streams of other processes, such as aluminiumprocessing, may provide potential reduction in the environmental impact of geopolymer concrete.
According to (Wimpenny, 2009)CO2 emissions were calculated for conventional concrete and the candidate materials allowing for production of the primary materials, secondary processing and transport Table 4. These calculations include the energy for heating Agent-C, heated mix water for high slag and steam-curing the geopolymer. The EA carbon converter was used, which prescribes the CO2 emissions arising from different fuel types, e.g. 2.63 kg of CO2 for 1 litre of diesel.
The conventional concrete was assumed to have a 350kg/m3 binder content comprising 40% slag. The notional use was at a construction site in St Ives, Cornwall, UK.
kg CO2 per cubic metre of concrete
Primary processing and Constituents
Source: Report on Low Carbon Concrete-Options for the Next Generation of Infrastructure by Don Wimpenny in 2009
Table : Summary of CO2 calculation
(Wimpenny, 2009)The potential CO2 reduction associated with the three materials has been calculated based on the availability of the binder constituents in the UK and for the potential for use in place of conventional concrete based on the notional site and three other infrastructure schemes in the same locality Table 5. The average amount of concrete used at the three schemes was approximately 970m3 representing 237 tonnes of CO2 when using conventional concrete.
It can be observed that high slag has the greatest availability and potential for CO2 reduction (40%). The limited opportunity to use Agent-C to replace concrete in infrastructure schemes restricts its impact to a 2% reduction in CO2. This value would be expected to be higher for schemes requiring armour blocks. (Wimpenny, 2009)Geopolymer is unlikely to be widely available in the next 10 years, until there is confidence in the material and sources of supply are established. Its potential use in the table is conservatively restricted to precast items and acid-resistant sewer linings, giving a modest 7% CO2 reduction.
Estimated CO2 reduction per annum
CO2 reduction (thousand tonnes) in UK Based on availability of constituents
CO2reduction (tonnes) for typical
Future availability may limit use
Source:Report on Low Carbon Concrete-Options for the Next Generation of Infrastructure by Don Wimpenny in 2009
Table : Estimated CO2 reduction per annum
Chapter 3: Methodology
3.1 Screening of Low Carbon Constituents:
An extensive desk study identified seven groups of technologies with potential to reduce the carbon footprint: secondary cementitious materials modified Portland or non-Portland cements, low cement concrete, ultra high strength concrete changes in Portland cement (PC) manufacture, alternative binders and carbon capture. A short list was produced of three constituents with potential for high CO2 reduction and suitability for construction in UK.
With the help of literature reading and previous works on this low carbon concrete constituents, Asphalt, GGBS and Geopolymer are screened and taken for further detailed study for their CO2 emission and availability in the UK.
These three candidates were studied in detail for their carbon dioxide emission, availability, environmental impact and construction issues. The CO2 emissions associated with manufacture and transport of the materials were calculated and recommendations made for their future development.
The sample was selected through judgment selection methodology where the research sample based on a certain criterion. As discussed earlier that the construction industry becomes all the more complicated in light of the new alternatives, environmental issues and the economics involved.
Compare the different seven types of concrete with their co2 emissions during the various processing.
The observations made in this process are tabulated and statistically analysed for reaching an outcome.
Comparison of CO2 emission from Low carbon concrete constituents with conventional concrete to find the percentage of carbon dioxide reduction.
The case studies about the projects in UK where low carbon concrete constituents used are helped to analysis the availability and their opportunity to use in current construction industry.
Chapter 4: Case Studies
4.1 Usage of ground granulated blast-furnace slag (GGBS) in White River Place, St Austell, UK:
The White River Place Development scheme aimed to renovate a brownfield site into a stimulating town centre for St Austell and was proposed to account for £75 million. The town centre is a seven storey building featuring a blend of uses involving offices, food and catering, cinema theatre, retail and a car park for about 550 cars.
The South West Regional Development Agency (SWRDA) partly sponsored this development scheme in St Austell and as per the contract; the objective of the program was to achieve BREEAM Very Good. BREEAM is the world's foremost environmental assessment method and rating system for buildings, with 200,000 buildings with certified BREEAM assessment ratings and over a million registered for assessment since it was first launched in 1990 (BREEAM, 2012). But SWRDA and the joint venture client White River Developments dreamt big and aspired to achieve BREEAM Excellent, and Sir Robert McAlpine then shared the contract.
4.1.2 Overview of Environmental Features
The team and the client worked very wise with the available credits. Instead of implementing elements that could incur more expenses, they put efforts in attaining all the available credits. They,
Maximised the materials credits with effective procurement and awareness of issues,
Used local labour and materials,
Harvested the rainwater and very efficiently used the water,
Implemented effective ecological input on a brownfield site,
Made the Parkmark compliance for the car parking compulsory,
Implemented environmental policies and management.
4.1.3 The BREEAM Assessment
All the required information was provided to the team by the BREEAM Assessors who collected and coordinated the information from the outset. By opting for this way, the project scored considerably high in Land Use and Ecology, Materials and Waste, Transport and Water. The Management section was accessed full score by using exemplar construction processes, commissioning and environmental procedures.Â
The BREEAM Assessment was a paramount part of project meetings and continued to be one throughout the project, allowing the principles of the guidance to be reviewed and implemented at very early stages so that they could not impact the cost or programme in any negative possible manner.
4.1.4 Building Services
The mechanical and electrical strategy was designed from the outset with economy and sustainability in mind, but not at the expense of functionality or comfort. One of the biggest challenges was the use of passive technologies in a busy town centre like this. The technologies were employed wherever possible, but were augmented by low carbon products with higher efficiencies such as heat pumps. On one hand, where the large expanse of roofing implied that the water accumulated on the roof during rain was to be attenuated to control the flow into the drains, on the other hand, it was an opportunity to provide a large rainwater harvesting system, which would provide free water for use, both in the landlord areas and for irrigation, for washing-cleaning and to individual tenant premises. Carbon monoxide sensors were linked to pulse fans in the car park which would run at low speed when required to provide fresh air. These fans were also linked to the smoke control system and when the fire alarms were activated, could be used to create safe fire brigade access.Â Â
4.1.5 CO2 footprint
The main contractor had ISO 14001 EMS systems and very high ISO standards set for environmental management on site. A dedicated environmental manager was also deployed on site throughout the contract tenure.
As major town centre site, liaison and community interaction and involvement were important and considerate contractor scores were very high. It was essential to make sure of the responsible sourcing. For this reason, the sub-contractors and suppliers were interrogated about the environmental credentials of materials used. It was proposed that, during construction, sustainably sourced materials (including a high content of recycled material) will be used wherever possible and all major building elements having a Green Guide 'A' rating will be used.
Along with Concrete, ground granulated blast-furnace slag (GGBS) was used which meant that the slabs were not required to be major load bearing. Thus there was a reduction in the CO2 emissions associated with concrete. The stones used were locally available, bricks came from neighbouring Devon and concrete blocks were sourced from St Austell. Slightly damaged blocks were used for areas of the building where finishes allowed saving some 60 skips worth of constru