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Qatar: Green Concrete Technologies Towards a Sustainable Concrete Industry in Qatar by Miguel Blanco-Carrasco, Fridolin Hornung, Nadja Ortner March 2010

ŠCopyright Ortner Consulting 2010. Commissioned by Mobil-Baustoffe GmbH


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

SUMMARY Traditional ready-mix concrete is a significant cause of production of GHG (Green House Gases), less in regards to GHG emissions per m3, but in particular in regards to the high quantity produced world-wide. New available technologies allow the use of different types of concrete and advanced ways of production which represent a lesser hazard to the environment. The State of Qatar is embarking in a number of major infrastructure and real estate state projects. Embracing some of the technologies discussed in this paper at either public or private level will result in a considerable reduction of greenhouse emissions and a showcase of best practices. In the life-cycle of concrete there is plenty of room for improvement towards sustainability that starts from sourcing the materials and goes as far as using innovative systems imposing fewer burdens on the environment for the concrete cooling and the usage of renewable energy sources for primary energy consumption. The method of production and extensive usage of concrete on building sites allows achieving a significant number of LEED (Leadership in Energy and Environmental Design) points, to decrease the carbon footprint and to optimize the usage of energy. Concrete remains less harmful than most other common building materials, but as the quantity of concrete used in construction is fairly higher than the quantity used of other building materials, improvement in the concrete production process and its application has a great effect on the total environment burden that arises out of building construction.

[2]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

A combination of different existing green technologies and an optimization on energy consumption hence can make a concrete batching plant an environmental friendly undertaking.

[3]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

Contents Summary .......................................................................................................................................... 2 List of Abbreviations ......................................................................................................................... 6 Introduction ....................................................................................................................................... 7 Qatar ................................................................................................................................................ 9 Country Profile .............................................................................................................................. 9 Political and Social Factors .........................................................................................................9 Economic Indicators ................................................................................................................. 10 Regulatory Frame affecting Environmental Issues .................................................................... 10 Overview of the Concrete Industry in Qatar .................................................................................... 11 Green Concrete .............................................................................................................................. 11 Traditional Concrete .................................................................................................................... 11 Green Concrete Technologies..................................................................................................... 12 Contemporary Concrete Production and Eco-friendly Enhancement Options .............................................................................................................. 12 Concrete Carbon Footprint ....................................................................................................... 12 Comparison of Primary Energy used in Traditional Building Materials ................................................................................................................................... 14 Compressive Strength .............................................................................................................. 14 Ingredient Materials and Supply Chain ........................................................................................ 15 Supply Chain and Production Process ......................................................................................15 Ingredient Materials ..................................................................................................................... 17 Cement ..................................................................................................................................... 17 Cement Substitutes .................................................................................................................. 18 Material Reuse and Recycling .................................................................................................. 19 Staff Training and Education ....................................................................................................... 24 Construction and Logistics .......................................................................................................... 24 Construction .............................................................................................................................24 Logistics ................................................................................................................................... 25 Energy Management and Reduction of the Use of Fossil Fuels ...................................................... 27 Energy Management ................................................................................................................ 27 Utilization of Renewable Energy .................................................................................................. 27 Option 1- Solar Power .............................................................................................................. 27 Option 2- Waste to Energy........................................................................................................ 30

[4]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

Green Concrete Certification ....................................................................................................... 33 Concrete Cooling ............................................................................................................................ 41 Concrete in a Desert Environment ............................................................................................41 Conventional Concrete Cooling ................................................................................................42 Case Story ................................................................................................................................45 Flake Ice Plant Systems ........................................................................................................... 47 Sustainable Cooling of Ready-Mixed Concrete ........................................................................... 48 Coarse Aggregate Cooling ........................................................................................................ 49 Coarse Aggregate Cooling versus Flake Ice Cooling ................................................................51 Dust Emission ...........................................................................................................................53 Advantages of a Coarse Aggregate Cooling System ................................................................53 Temperature Profiles using the Coarse Aggregate Cooling System ..................................................................................................................................... 53 Cement Cooling .......................................................................................................................... 54 Cooling Method Comparison ....................................................................................................... 55 Plant Layout and Equipment Utilization ....................................................................................... 56 Conclusion ...................................................................................................................................... 56

EXHIBIT A ...................................................................................................................................... 59 EXHIBIT B ...................................................................................................................................... 60 References ..................................................................................................................................... 61

[5]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

LIST OF ABBREVIATIONS

ACBFS

Air-Cooled Blast Furnace Slag

CSP

Concentrated Solar Power

C&D

Construction & Demolition

DEF

Delayed Ettringite Formation

GHG

Green House Gas

GGBS

Ground Granulated Blast Furnace Slag

GCC

Gulf Cooperation Council

HSE

Health, Safety & Environmental

LEED

Leadership in Energy and Environmental Design

LNG

Liquefied Natural Gas

LN

Liquefied Nitrogen

OPC

Ordinary Portland Cement

SRC

Sulfate Resistant Cement

QSAS

Qatar Sustainability Assessment System

[6]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

INTRODUCTION

Generally the construction industry accounts for a massive environmental impact due to its high demand of energy. The cement industry and, as more specifically discussed in this paper, the production of ready-mixed concrete stands for a significant part of carbon footprints in the construction sector, mainly due to the high energy consumption of the transportation of building materials. As a result of the awareness built during the past few years about green house effect and damage to the nature, more people and countries became conscious about their future and the future for the coming generations. This paper will analyse different options of producing green concrete by reducing dust emissions, waste materials and quantitative energy consumption and saving considerable amounts of water, but also by switching from energy production with fossil fuels in power generators or public grids to renewable energy solutions for production sites in temporary lay-down areas in remote areas with extreme climate. The study is made for the State of Qatar and reflects a combination of proven models in this and other parts of the world in relation to existing legal and supply conditions as there are extant in the territory. Increasing interest in the reduction of CO2 emissions in the United States and Europe and the heavy environmental impact due to increasing energy consumption and over-usage of fossil fuels has led the government in Qatar to focus on alternative solutions and to promote a more environmentally-friendly approach to ‘doing business’ to the country’s numerous local and foreign investors.

[7]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

The sustainable development of concrete and its design will be a milestone for the construction industry as concrete besides steel is the most common construction material in the world and counts for a significant part of environmental damage that derives from this sector. This paper will not only illustrate alternatives for energy supply such as a concentrated solar power plant (ray concentration by the means of parabolic mirrors) and a waste-to-energy solution, but will also introduce the valued reader to innovative technologies with little or no environmental impact to produce cooled concrete in a desert environment by the means of an eco-friendly cooling system, which sets itself apart from others by saving energy as no ice is used in order to reach the required temperatures and pollution through dust diminishes towards zero. Qatar’s fast industrial development, high GDP, constantly growing demand for power consumption in addition to steadily increasing environmental awareness in both, the public and the private sector, make the country ideal for innovative solutions.

[8]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

Q ATAR COUNTRY PROFILE POLITICAL AND SOCIAL FACTORS Qatar is one of the fastest growing economies in the world, driven by a buoyant hydrocarbon industry combined with high oil and gas prices during previous years. Qatar has been investing in diversifying the economy on the back of its natural resources surpluses.

The State of Qatar became independent from the UK on 3rd September 1971 and HH Sheikh Hamad bin Khalifa Al-Thani has been the ruler since June 1995. Qatar is one of the most stable countries in the region and the government has recently enhanced its efforts to raise the state’s international profile as a diplomatic mediator in foreign issues through a number of high-level sporting and cultural events and conferences. Economic growth is driven by proven oil reserves accounted to 25.7bn barrels at the end of 2007 and 902trn cu ft (tcf) gas reserves, equivalent to 162bn barrels of oil1.

1

Oxford Business Group, Qatar Report 2009 [9]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

ECONOMIC INDICATORS Qatar has experienced rapid economic growth over the last several years on the back of high oil prices, and posted its eighth consecutive budget surplus in 2008. Economic policy is focused on developing Qatar's non associated natural gas reserves and increasing private and foreign investment in non-energy sectors, but oil and gas still account for more than 50% of the GDP, roughly 85% of export earnings, and 70% of government revenues2. Oil and especially gas have made Qatar the second highest per-capita income country following Liechtenstein - and one of the world's fastest growing economies. However, Qatar’s stabile economy and massive investments in both the public and the private sector is estimated to result in a GDP growth of 9 % in 20093.

REGULATORY FRAME AFFECTING ENVIRONMENTAL ISSUES In 2005 the permanent Qatar Constitution came into effect, establishing the legal operational framework of Qatar. Art.33 of the Constitution states:

“The State shall preserve the environment and its natural balance in order to achieve comprehensive and sustainable development for all generations.”

The previous article clearly states the commitment of the Qatari Government to promote policies to protect and improve the environment in the Qatari Peninsula. The Ministry of Environment is the government body entitled with the regulation and supervision of industrial practices regarding environmental issues, and a number of initiatives are taking

2 3

CIA World Factbook th Gulf Times, 27 January 2010. [10]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

place from both public and private sector in order to minimize environmental impact, particularly in the construction industry with “Green Building” rating systems such as QSAS (Qatar Sustainability Assessment System) and LEED (Leadership in Energy and Environmental Design) becoming increasingly available4.

OVERVIEW OF THE CONCRETE INDUSTRY IN QATAR

There are above 40 ready mix operations varying in size in terms of plant capacity and fleet size. Portland cement, Sulfate Resistant Cement, GGBS (Ground Granulated Blast Furnace Slag), Fly Ash, Silica Fume are all sourced from Qatar National Cement Company (QNCC) and Gulf Cement Company (GCC). Coarse aggregate (Gabbro) in various sizes is sourced and shipped in from neighboring countries such as the United Arab Emirates. Limestone another coarse aggregate used in most parts of the world is rarely found in Qatar projects, although its use has slightly increased in 2009. Market volumes for 2008 were approximately 13 million m3, 2009 taking into consideration the global financial crisis managed approximately 10million m3. Most concrete operations use flake ice plants in Qatar to cool concrete apart from few plants that use nitrogen gas. The majority of ready mix companies have their own haulage and cement tanker trucks to transport aggregates and cement.

GREEN CONCRETE TRADITIONAL CONCRETE Traditionally, concrete is constituted by cement, sand, gravel and water. The most extended type of cement is the Portland cement, invented in 1824, which is manufactured 4

th

Gulf Times - Green building rating system to strike balance – 12 January 2010 [11]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

by processing limestone at 1450째C with a mixture of clay, sand, iron, ore, shale or bauxite. Applying intense heat to those raw materials alters their chemical composition during the production process, where raw materials are heated at sintering temperatures. The major caveats of this process are the high amount of GHG (Green House Gas) emissions released during the heating and mixing of materials and the amount of energy required5. CO2 exhaustion is a result from burning limestone calcium carbonate (CACO3) to calcium oxide and carbon dioxide (CAO+CO2) in the cement kiln and from the energy production required for the process.

GREEN CONCRETE TECHNOLOGIES CONTEMPORARY CONCRETE PRODUCTION AND ECO-FRIENDLY E NHANCEMENT OPTIONS Taking into account how much energy is required to produce the concrete components, but also to heat, mix, and transport concrete, it can easily be concluded that the use of traditional concrete in green buildings is not effective at decreasing the carbon footprint of its users.

CONCRETE CARBON FOOTPRINT The carbon footprint is a measure of the quantity of carbon dioxide emitted through fossil fuel combustion. It is often expressed as tons of carbon emitted per annum6.

Traditionally the Concrete industry has been considered a major producer of GHG emissions, mainly due to the high environmental footprint of cement. It is estimated that

5 6

P. C. Hewlett, 1998 www.nada.org [12]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

during produce 1 ton of cement approximately one ton of CO2 will be released7. The world’s total production of cement in 2008 was 2.84 billion tons, which positions cement together with fossil-fuel burning and gas-flaring as one of the top-emitter industries8. Currently the concrete industry is taking a number of steps to reduce the carbon footprint of concrete, from using less Portland cement and more fly ash or slag to enhance the mix with chemicals that allow working with less water. Further the introduction of coarse aggregate cooling systems help to find ways to more innovative solutions including carbon sequestration9. Technology is pacing the way for concrete to leave behind its image of being a polluting material to become an indispensable element in sustainable construction projects. For instance, a recent study regarding the installation of railway sleepers shows that concrete sleepers produce six times less GHG emissions than timber ones. This is of foremost relevance in Qatar and the GCC area where timber is a scarce commodity and the prospect of a joint GCC railway system will demand the installation of a considerable number of sleepers10.

7

Fountain, Henri, 2009. U.S. Geological Survey, 2010. 9 National Science Foundation, 2009. 10 Crawford et al., 2009. 8

[13]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

COMPARISON OF P RIMARY E NERGY USED IN TRADITIONAL BUILDING MATERIALS Looking at the graphs below concrete is less harmful to the environment than other building materials since the use of primary energy is comparatively low.

Source: B. V. Venkatarama Reddy, 2008

COMPRESSIVE STRENGTH The compressive strength is the ability of a material to withstand stress. It is an important property of concrete and the most common performance measure for durability and quality. Other than the compressive strength in concrete its tensile strength is relatively low at about 10% of the compressive strength. In below example an average value is used, as its properties depend on the character of the ingredient materials as well as on the method of production11.

11

NRMCA, 2003 [14]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

TABLE – PRIMARY ENERGY versus COMPRESSIVE STRENGTH Compressive Strength

E-Module

Primary Energy Consumption

N/mm²

N/mm²

kWh/to

Brick Work

5

5,000

450

Concrete

50

30,000

300

Aluminum

450

70,000

52,000

Steel

500

210,000

5,900

Material

Source: own estimation

INGREDIENT MATERIALS AND SUPPLY CHAIN SUPPLY CHAIN AND PRODUCTION PROCESS It is a long way from the raw material to the finished and installed product in the concrete industry and the reduction of carbon foot-prints can start at the very beginning of the concrete life-cycle. Areas of possible improvement are shown in the graph below:

[15]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

The following steps show in detail, where in the material acquisition, concrete production and final installation processes can be enhanced to make concrete a more sustainable building material:

[16]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

INGREDIENT MATERIALS CEMENT The world cement industry accounts for 5% of global anthropogenic CO2 emissions12. Cement, which is an integral part of all standard concrete products, is the most significant and harmful factor and environmental burden when producing concrete or concrete products. Several studies are dealing with how to produce concrete with very little or no cement, but do not show to be advanced enough to be evaluated further for specific projects at this point of time. Replacing energy-consuming Portland cement with recyclable materials and minerals offers two distinct benefits to the environment—it significantly reduces the amount of CO2 released into the atmosphere and it minimizes massive landfill disposal. In contemporary concrete production successful reduction of cement is usually done by replacing a part of the required cement content with fly ash, silica fume and GGBS13. Fly ash and GGBS can seriously be considered to replace bigger amounts of cement in order to reduce the burden on the environment as not only the product strength but also the product quality increases. These materials are by-products and therefore do not undergo a special production process in order to being generated and hence do not require additional energy sources for their production. In average the cement content of a standard mix design represents 85% of embodied energy and up to 96% of GHG14 emissions15.

12

Flower & Sanjayan, 2007 Ground Granulated Blast Furnace Slag 14 Green House Gas 15 NRMCA Sustainable Concrete Plant Guidelines 13

[17]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

As per LEED specifications by-products are considered as ‘recycled’ products as their production does not require a separate production process. CEMENT SUBSTITUTES Fly Ash: Fly ash is a promising green concrete solution being heralded for sustainability is high-volume fly ash cement. It is a by-product of coal-combustion from coalburning power plants, and in the past, almost 75% of fly ash produced made its way to landfills. A replacement of 20% of the Ordinary Portland Cement by fly ash results in concrete with high sulfate resistance. Fly ash, when mixed with CA(OH)2, a constituent of cement, and water, forms a compound similar to Portland cement and is extremely strong and durable. High-volume fly ash concrete displaces more than 25% of the cement used in traditional

concrete,

reducing

the

amount

of

emissions needed to make the concrete mix. Fly ash concrete was sometimes difficult to find in the past. Due to a significant increase in demand, nowadays

there

are

more

producers

and

distributors trying to cope with the steady increase in demand. GGBS: Similar to fly ash, blast furnace slag (GGBS) could be considered a recycled16 material and used as a cement substitute for concrete. It is produced from blast furnaces used to make iron and, like fly ash, it creates a very strong and

16

LEED Reference Guide [18]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

durable concrete. Its use is independent from the kind of aggregates used for the mix. GGBS is commonly referred to as slag, and is also similar to fly ash since the result is a concrete with increased sulfate resistance. BLAST FURNACE CEMENT: After iron has been extracted from the blast furnace the slag is quenched with water and grounded. The use of slag increases the durability and strength of the concrete, while permeability is reduced17. OPC (Ordinary Portland Cement) or SRC (Sulfate Resistant Cement) can be replaced with Blast-Furnace Cement18, which already comprises slag as an integrated additive to the cement composition. The use of recycled cement substitutes such as GGBS, Fly Ash and Slag is awarded with 1-2 LEED points19.

MATERIAL REUSE AND RECYCLING Water Recycling Water pollution is another environmental burden that occurs in the production of ready-mix concrete. The high pH level of wash-out water, which is normally pH 12, and the large quantities of water used in a modern batching plant pose a threat to the environment if the correct measures are not implemented20. It is common for wash-water, which derives from cleaning of the equipment, to be discharged into ponds where solids can settle out. This is both an inefficient way of processing wash-water and an environmental hazard. By installing closed-loop systems the amount of the required water, which in Qatar is a precious resource, can be reduced, which subsequently eliminates the environmental

17

NRMCA Sustainable Concrete Plant Guidelines also called Slag Cement 19 LEED Reference Guide 20 Water with a high alkaline level is toxic to fish and aquatic life in general. Environment Canada has studied the negative effects of fish exposed to Portland cement concentrations. (http://www.ec.gc.ca/) 18

[19]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

hazard of grey water. Grey water typically contains cement, other fines (fly-ash, GGBS, sand < 0.1 mm) that includes the output water from the cleaning of the concrete pumps and truck-mixers. Recycled Water in concrete production can qualify a building for 1-2 LEED points21.

Waste Concrete and Recycling of Aggregates: Waste materials from concrete production can be recycled and reused, but may increase the cement content22. By using recycled concrete, generally a higher cement content is necessary than by using good quality natural aggregates. Depending on local regulations and building codes it is possible to use up to 35kg/m3 of recycled solids in concrete production with no effect in the quality of the product. Concrete waste is not only an output of Construction and Demolition (C&D), it is created as well in new construction projects. Ready mix concrete plants have developed a number of solutions in order to avoid creating waste out of partially disposed truckloads, although new available admixtures technology allows storing the mix for later re-activation. Further it is possible to reclaim aggregates from unused fresh concrete by means of separating the cement and aggregates into reusable aggregates for concrete production23. Using crushed recycled concrete as aggregates is one possibility, but a more ecofriendly version can be aimed for. A far greener solution is to wash out the waste concrete before the hardening begins, instead of using a high amount of electrical power to crush the waste after it hardened out. Crushed recycled concrete can be used as aggregate in concrete for non structural elements such as backfills, blinding slabs, core filling,

21

LEED Reference Guide Edvardsen. C., Tollose, K., 2001 23 www.concreteclaimers.com 22

[20]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

embankments and road construction. Crushed concrete aggregate used in concrete for structural purposes need to pass the same testing requirements as natural sourced aggregates.24 Concrete rubble product of construction, demolition, reconstruction and restoration of buildings can also be treated to be used as aggregate and is normally easily available. Concrete containing recycled aggregate complies with the same standards and requirements than any concrete made using natural aggregate. Nevertheless, it is important to study each project individually since for outdoor usage it is convenient to ensure that no material with potential alkali silica reaction is used in the mix25. Resource extraction such as quarrying virgin aggregates can be reduced, if using recycled materials as aggregate replacement26. Recycled Concrete, if used as coarse aggregate substitute, qualifies a building for 12 LEED points27.

CO2 Content in Traditional Concrete The graph below illustrates the CO2 content in traditional concrete with a standard mix-design (average assumptions for numbers) and shows a break-down of the environmental burden occurring from each content material. Traditional concrete consists of Portland cement, coarse aggregate and fine aggregates, and water and chemical admixtures that enhance various properties of the finished product.

24

www.cement.org Gr端bl, Peter and R端hl, Marcus, 1998. 26 NRMCA Sustainable Concrete Plant Guidelines 27 LEED 2009 Reference Guide. 25

[21]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

CO2 EMBODIED IN TRADITIONAL CONCRETE

Material

Quantity in kg per m3 of concrete produced (mix design)

Quantity in % per m3 of concrete

kg of CO2 emitted per ton of material produced

kg of CO2 emitted for every m3 of concrete produced

Cement

320

13.34

1000

320

Coarse Aggregate

1100

45.72

135

149

Fine Aggregate

800

33.33

63

51

Admixture

2.5

0.12

0.21

~0

Water

180

7.49

0

0

TOTAL

2402.5

100

n.a.

520

The graph below illustrates the amount of CO2 produced in supplementary materials: CO2 EMBODIED IN SUPPLEMENTARY MATERIALS MATERIAL

Quantity in kg of CO2 kg of CO2 kg per m3 Quantity in emitted per emitted for of concrete available in % per m3 ton of every m3 of produced Qatar of concrete material concrete (mix produced produced design)

Cement

150

6

1000

63

y

GGBS

90

4

630

27

y

Fly Ash

70

3

0

0

y

Silica Fume

10

0

0

0

y

Coarse Natural Aggregate

770

32

135

44

y

ACBFS*Aggregate

330

13

80

10

n

Fine Natural Aggregate

560

24

63

15

y

ACBFS*Sand

240

10

80

8

n

Admixture

2.5

~0

~0

~0

y

Recycled Water

180

8

0

0

y

TOTAL

2402.5

100

n.a.

167

n.a.

*Air-Cooled Blast Furnace Slag

[22]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

The figure below illustrates all sources of environmental impact in the concrete industry and shows that the whole process is generating significant CO2 emissions. Besides that the figure also shows where possibilities of system enhancements are, especially in regards to the interfaces between the different processes such as the production of the mixing materials, material mixing, transportation and in-situ placement.

Source: Flower, D.J.M. & Sanjayan, J.G., 2007, Concrete CO2 Emissions System Diagram

CO2 emissions were found to be reduced in average by 22% for standard mixes with OPC and GGBS as additive, while mix designs using OPC and fly ash results in a reduction of CO2 emissions ranging from 13-15%28.

28

Flower, D.J.M., Sanjayan, J.G., 2007 [23]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

STAFF TRAINING AND EDUCATION All employees including, but not limited to drivers and equipment operators on a ready-mix concrete plant should undergo regular health, safety, and environmental (HSE) training sessions, which are to be repeated a) for all new staff b) every three months for everyone in order to being able to immediately and effectively react to imminent danger. The importance of HSE trainings and adhering of guidelines and policies needs to be communicated to all staff independent of their level of employment. HSE policies are not only crucial to have for licensing purpose but especially for the companyâ&#x20AC;&#x2122;s sustainability. HSE issues need to be evaluated and revised on a consistent basis to ensure the health and safety of all employees, the protection of the environment, the maintenance of regulatory compliance and the enhancement of the companyâ&#x20AC;&#x2122;s reputation within the community as well as the satisfaction of customers and the promotion of profitability. Health & Safety training shall include: hazard identification, risk assessment and control, control measures, plant safety management plan, special duties as required from plant or equipment designers, safe driving tests and assessments for drivers and operators Environmental training shall include: controlling air emissions and dust, proper storage and spill prevention of hazardous liquids, management of process water, and management of solid waste29.

CONSTRUCTION AND LOGISTICS CONSTRUCTION From the contractors side high environmental impact can be avoided by the partial use of stainless steel or coated steel as massive environmental loads are opposed to the structures for repair and maintenance works.30

29

Maryland Center for Environmental Training, 2009 [24]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

Source: Edvarsen, C., Tollose K.; 2001

However, stainless, coated or other high quality steel are not economical for use and can only be partially used for reinforcement purpose on places where long-term corrosion protection is essential or the necessary in-situ concrete coverage is not possible due to limited space or in the event that highly porous light-concrete structures are used.

LOGISTICS In the Middle East, other than in Europe or the United States, batch plant operators usually operate their own fleet, not only for the delivery of the finished product to site, but also for the transport of the ingredient materials (cement, sand, aggregates) to site. Therefore an optimization can be initiated through the ready-mix organization itself and can already be achieved during the material transportation from the cement and sand plants and the Gabbro Harbor31 to the concrete batching plant and subsequently for the finished product from the plant to the construction site. In order to avoid the usage of fossil fuels and subsequently high CO2 emissions, a batch plant operator is not only limited to environmental friendly power supply for the

30 31

Edvardsen, C.; Tollose, K.; 2001 Port where aggregates are deposited in Messaied [25]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

batching plant, but can also equip his fleet and heavy equipment, such as front-end loaders, fork-lifts and cranes with environmentally less harmful engines. Due to capacity reasons and long-recharge duration for heavy vehicles the option of electric motors is not recommended. Due to low fuel prices and less developed collection network in Qatar it also cannot be considered feasible to elaborate further on pure biodiesel engines with used oils as may be appropriate in other regions. The options evaluated further therefore are gas-driven vehicles, which are currently among the cleanest in the world32. Gas engines are proven to be appropriate for big fleets and heavy vehicles independent from climate conditions and Qatar has made its first attempts to equip airplanes and means of public transport with this technology. Major problems that come with gas engines are the availability and accessibility of gas- refueling stations, which in this case would need to be directly at the batching plant. Due to available facilities in Qatar, the usage of LNG33 shall be given priority to compressed gas options and an agreement with the governmental company WOQOD34 would need to be discussed in order to serve the batching plant with the required capacities on site. Least environmental burden arises by the use of barges, which in Qatar are generally used for the transportation of coarse aggregates, which are mostly shipped from the United Arab Emirates. Some construction sites using mobile batching plants have dedicated jetties and should be encouraged to use these for receiving coarse aggregates on site.

32

www.naturalgas.org Liquefied Natural Gas 34 QATAR FUEL www.woqod.com.qa 33

[26]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

ENERGY M ANAGEMENT AND REDUCTION OF THE USE OF FOSSIL FUELS ENERGY MANAGEMENT Traditional fossil fuels emit GHGs into the atmosphere. The consumption of energy on a batching plant using fossil fuels for production can be optimized or ideally power supply could be taken from renewable energy sources. Optimized equipment usage and internal power consumption monitoring for major equipment and components are essential basics in the process to reduce electricity consumption.

UTILIZATION OF RENEWABLE ENERGY OPTION 1- S OLAR P OWER While not directly related to the production of concrete, but tailor-made for projects in remote areas where a connection to the public grid is impossible, mobile batching plants used for mid-sized and major projects can draw their energy from renewable sources. Looking at the characteristics and geographic position of Qatar it seems useful to use solar as the main source of energy. For a production of 2000 m3 of ready-mixed concrete per day (plant capacity of 100 m3/hour) a power plant with a capacity of up to 1 MW (includes electricity consumption for the cooling process and site facilities) is needed. A suitable option would be a concentrated solar power version, a so-called CSP35 system. The necessary power is independent from the production quantity per day but depends on the size of the mixer, the output per hour and the capacity of the chillers. Example: to run plants and chillers in a Prototype batching

35

Concentrated Solar Power Plant [27]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

plant 2x 4,5 m3 plant in Ras Laffan, 1 MW electric capacity is needed independent from the number of m3 produced per day. The plant is comparatively big for Qatari standards.

To produce one cubic meter of concrete circa 2kWh are required, while cooling down one cubic meter of concrete by 10 Kelvin requires additional 6.5 kWh.

Concentrated Solar Power: A Concentrated Solar Power Plant (â&#x20AC;?CSPâ&#x20AC;?) produces electricity which is costefficient on a long-term perspective and at the same time causes no environmental damaging waste. Capital expenditure for solar is higher than the one for some traditional

technologies

while

operational expenditure is lower and the operating costs remain stable as there is no price fluctuation in the cost of resources.

Source : Philibert, C. ; International Energy Agency

The figure above shows the total irradiance every place on earth receives. The irradiance is expressed as Watt per square meter. There are two different concepts of generating electricity with solar power: ď&#x201A;§

The first concept uses so-called photovoltaic cells. This technology consists of large plates covered with cells that convert the sunshine directly into electricity. [28]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

ď&#x201A;§

The second concept, a CSP, which shall be the preferred option for this project, makes use of the warmth the sun provides. This warmth is concentrated through a set of mirrors and is used either to heat a liquid or air, both of which drive a turbine, which generates electricity36.

Picture: Parabolic Mirror as an integral part of a CSP

A

study

by

the

Prometheus

Institute37 shows, that for big scale applications, concentrated solar power is the only technology that is capable of successfully generating enough energy.

Technology The concentrated solar power plant makes use of a number of lenses and mirrors, to focus the striking sunlight into a small beam. This beam is then directed onto a large tank containing a fluid (normally water). This fluid is heated by the sunlight, and as a result evaporates and creates steam. This steam is then used to drive a turbine, which in its place creates electricity, just like it does in a regular power plant (the difference is that in a conventional power plant the heat to create steam comes from the burning of gas or other non-renewable energy sources).

36

37

Ortner, N.; 2009. Concentrating Solar Power Technology, 2008

[29]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

There are a wide variety of technologies used to concentrate sunlight in a beam. They differ in the ways in which they track the sun and focus sunlight into a beam. In order to use a CSP for the energy supply of a concrete batching plant and its utilities a removable and re-installable system shall be considered as the high system price only allows economical operations, if amortized over a 8-10 years period.

OPTION 2- W ASTE TO ENERGY

A number of technologies are currently available in order to process a wide variety of materials e.g. municipal solid waste, sewage sludge, plastics, etc. and to produce energy. This option could prove beneficial in both reducing costs in the processing of waste and generating part of the energy required. Particularities in the composition of waste and high initial cost may advice to encompass this option within the scope of a large development or a permanent plant location (stationary plant). There is no general governmental regulation to separate waste in Qatar in most of the residential and commercial areas and hence waste separation also has certain limitations on construction sites setting forth the regulations of the government bodies that apply for districts and regions. Only systems can be evaluated that allow the use of nonseparated or only partially separated waste. Landfill areas where waste is dumped are general in remote areas and in particular 70km from Doha, direction to Umm Bab. Transportation cost for dumping the waste are significantly high and high environmental standards for landfill areas have to be respected. It is manifest to use waste to energy systems for the power generation of a batching plant by incineration or heating method that allows the usage of non-separated waste from

[30]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

the construction site and residential waste from surrounding labour camps and staff accommodation.

Technology Ultra-high temperature gasification systems can convert materials such as sewage sludge, plastics and municipal solid waste to a dry and sterile powder. Toxic components in contaminated waste (such as hospital waste) are fully eliminated and no harmful emissions to the environment are released. While toxic ingredients are entirely eliminated, this only partially applies to radioactive materials. Such system recovers and utilizes the content of waste and biomass and harvests all valuable elements efficiently. In addition thereto a pulverizing system accelerates compressed air to supersonic speed in a closed cyclonic chamber, where materials are broken down from their molecular structure to an almost atomic structure. By this means not only the energy content of the waste materials can be recovered, also recycled value added materials can be created. In the pulverizing system all materials can be handled that can be crushed, dehydrated (or dried) and sterilized. The newly generated energy is divided into electrical power and thermal energy. The thermal energy, if not needed for heating can be fed into an additional energy vector and be converted into electricity for optimized utilization.

[31]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

Source: E. Koenig, 2009

Different than standard incineration systems in the gasification reactor there is no fire burning. Disadvantages of pyrolysis are dissolved by this method by operating at elevated temperatures above 1200 degrees Celsius, which ensures the creation of clean gas and clean residues. The thermal converter is operated without oxygen. The newly created clean syngas is used to produce electricity. The inorganic material (approximately 10%) converts to a non-leachable sand or basalt-like environmentally harmless residue. A gas turbine finally generates electricity38.

38

E.Koenig, 2009 [32]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

GREEN CONCRETE CERTIFICATION

Concrete is a key element in Green Buildings and the right use of concrete can play a considerable role in obtaining a â&#x20AC;&#x153;Green Buildingâ&#x20AC;? certification.

System

DGNB

BREEAM

LEED

Green Star

CASBEE

Minergie

QSAS

Country of Origin

Germany

UK

USA

Australia

Japan

Switzerland

Qatar

For illustrative purposes the advantages of concrete when applying for LEED 2009 certification will be detailed in this section. Leadership in Energy and Environmental Design (LEED) is a rating system created by the United States Green Building Council (USGBC) and one of the most widespread certifications worldwide.

Non-Certified Certified

LEED 2009

Silver Gold Platinum 0

20

40

60

80

100

LEED uses a system of points to determine the different certification level. Platinum level is the most rigorous and marks the industry best practices with 80 or more points. Gold level requires 60 points while Silver needs 50 points. The minimum level of certification is achieved with 40 points.

LEED Certification Level Certified Silver Gold Platinum

[33]

Points Required 40-49 50-59 60-79 80+


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

The totality of available points in LEED 2009 NC (New Construction) is 110, distributed in 5 main credit categories and 2 additional credit categories as per the following table: Points Available

Credit Category Sustainable Sites (SS)

26

Water Efficiency (WE)

10

Energy & Atmosphere (EA)

35

Materials & Resources (MR)

14

Indoor Environmental Quality (EQ)

15

Innovation & Design Process (ID)

6

Regional Priority Credits (RP)

4 110

Total Points Available

The use of concrete can contribute to a maximum of 62 points in the LEED 2009 NC certification. We will summarize the different credits where concrete could play a role.39

Development Density & Community Connectivity (Sustainable Sites Credit 2) 5 points

Concrete can be used to develop urban zones through different strategies. For this particular credit the use of multi-storey building, for which concrete is a material of choice, and its energy efficient capabilities contribute to gain LEED points.

Brownfield Redevelopment (Sustainable Sites Credit 3) 1 point

Contaminated soils can be stabilized by the use of concrete, amongst other options.

39

For additional details on how to implement the right strategies to obtain the point please refer to the USGBC website or to a LEED accredited practitioner. [34]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

Site Development: Protect or Restore Habitat (Sustainable Sites Credit 5.1) 1 point

This credit aims to protect existing natural areas which could be achieved, for instance, by building underground concrete parking garages instead of utilizing further terrain for a surface parking.

Site Development: Maximize Open Space (Sustainable Sites Credit 5.2) 1 point

Concrete can be used to maximize the ration between open space and developed area by building and underground garage or using pervious concrete to avoid retention ponds.

Storm-water Design: Quantity Control (Sustainable Sites Credit 6.1) 1 point

Pervious concrete contributes to minimize the disruption of natural hydrologic features. Vegetated roofs would also be considered for this credit and often would require concrete for structural support.

Storm-water Design: Quality Control (Sustainable Sites Credit 6.2) 1 point

Related to the previous section, the intent of this credit is to optimize the management of storm water. Both pervious concrete and vegetated roofs would contribute towards obtaining this point.

Heat Island Effect: Non-Roof (Sustainable Sites Credit 7.1) 1 point

Heat islands consist of thermal differences between developed and undeveloped areas. Concrete could be used to minimize that difference by providing shade or building surfaces with a high solar reflectance index (SRI) instead of asphalt. [35]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

Heat Island Effect: Roof (Sustainable Sites Credit 7.2) 1 point

The use of concrete for its high reflective properties and/or the used of vegetated roofs contributes towards obtaining this point.

Water Efficient Landscaping: Reduce by 50% (Water Efficiency Credit 1.1) 2 points

Pervious concrete, concrete cisterns for the collection of rainwater, and concrete waste water and grey water management systems would contribute to the water efficiency of the projects.

Water Efficient Landscaping: No Potable Water Use or No Irrigation (Water Efficiency Credit 1.2) 2 points

Using only recycled rainwater, wastewater and grey water could bring an extra 2 points. Concrete is traditionally used in water management systems for its durability and reliability.

Innovative Wastewater Technologies (Water Efficiency Credit 2) 2 points

The use of concrete cisterns and treatment plants for grey and brown water and its further use for irrigation or the sewage conveyance would contribute to obtaining this credit.

Water Use Reuse Reduction (Water Efficiency Credit 3) 2, 3 or 4 points (30%, 35%, 40% reduction of water use)

By reducing the amount of municipal water used by the building in a percentage higher than 30% from a typical building it is possible to gain a considerable number of

[36]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

points. Pervious concrete and concrete cisterns could be used as a strategy to achieve this reduction.

Minimum Energy Performance (Energy & Atmosphere Prerequisite 2) No points

It is a prerequisite for LEED 2009 certification that there has to be an improvement in energy efficiency of at least 10% compared to a typical building (5% in existing building renovations). The insulation and heat-storage properties of concrete contribute to moderate the temperature fluctuations in many climates and hence require less energy consumption. The benchmark for energy efficiency is ANSI/ASHRAE/IESNA 90.1-2007.

Optimize Energy Performance (Energy & Atmosphere Credit 1) 1-19 points

The thermal mass properties of concrete will increase performance when considered as a part of a whole building projects simulation.

Building Reuse (Materials & Resources Credit 1.1) 1, 2 or 3 points (55%, 75% or 95% of the previous structure left in place)

The longevity and durability characteristics of concrete contribute to the renovation of buildings through a concrete frame and/or a concrete skin.

Construction Waste Management: Divert 50% From Disposal (Materials & Resources Credit 2.1) 1 point & Construction Waste Management: Divert 75% From Disposal (Materials & Resources Credit 2.2) 1 point

This credit aims to recycle or salvage at least 50% of the construction, demolition, and land clearing waste. This credit is easily obtainable when concrete buildings are demolished since that concrete debris can be recycled into aggregate, or used to make

[37]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

landscaping blocks. If the percentage of disposal materials is least 75% the project would be eligible for an extra point.

Recycled Content: 10% (post-consumer + ½ pre-consumer) (Materials & Resources Credit 4.1) 1 point & Recycled Content: 20% (post-consumer + ½ preconsumer) Materials & Resources Credit 4.2) 1 point

Cementitious materials like fly ash and slag cement are considered pre-consumer recycled content and recycled concrete aggregate is considered a post-consumer recycled content. Furthermore, reinforced bars used in conjunction with concrete are manufactured in many occasions from recycled steel. All these factors contribute to obtaining these points.

Regional Materials, 10% Extracted, Processed & Manufactured Regionally (Materials & Resources Credit 5.1) 1 point & Regional Materials, 20% Extracted, Processed & Manufactured Regionally (Materials & Resources Credit 5.2) 1 point

‘Regional Material’ is understood as material being extracted, harvested, recovered or manufactured within 500 miles of the project. Ready mixed concrete would contribute towards this credit almost automatically since it is rare to transport the mixed concrete for more than 500 miles, and traditionally the harvesting of materials occurs within the 500 mile range.

Daylight & Views: Daylight 75% of Spaces (Indoor Environmental Quality Credit 8.1) 1 point

Concrete allows building large floors with none or few columns and shallow floor plates which contribute providing daylight to the building occupants.

[38]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

Daylight & Views: Views for 90% of Spaces (Indoor Environmental Quality Credit 8.2) 1 point

By building large concrete floors with column free spaces and shallow floor plates it would be easier to qualify for this credit.

Innovation in Design (Innovation & Design Process Credit 1) 1 â&#x20AC;&#x201C; 5 points

Innovative design and technologies can lead to obtaining 1 to 5 additional points which are not represented in any of the previous categories or that raise the benchmark beyond the level currently considered in LEED certification.

LEED Accredited Professional (Innovation & Design Process Credit 2) 1 point

Having at least one LEED accredited professional as member of the project team will qualify the project for this credit.

Regional Priority Credit (Regional Priority Credit 1) 4 points The USGBC regional authority can identify some environmental priorities in its area and assign a number of extra points to different categories depending of its regional requirements.

[39]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

Source: Ready Mixed Concrete Industry LEED Reference Guide Update, February 2009, RMC-Foundation

[40]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

CONCRETE COOLING CONCRETE IN A DESERT ENVIRONMENT Temperatures above 40°C – as usual in a desert environment – in combination with hot gravel and sand caused by the sunlight lead to an increase of fresh concrete temperature way above 40°C. Without an appropriate process to decrease the fresh concrete

temperature,

a

high

quality

production is barely possible. Especially in large and thick structures a high fresh concrete

temperature

causes

serious

cracking and damages to the building.

Consequences of high fresh concrete temperatures: 

short time of workability due to a faster setting process

extreme high concrete temperatures caused by heat of hydration at the setting process

uncontrollable cracking

high costs for intensive curing

extension of construction periods due to a production stop caused by high temperatures

[41]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

To produce high quality concrete in large quantities at extreme high outdoortemperatures is challenging. Hardening of concrete occurs due to a chemical reaction of cement and water. Depending on the kind and quantity of cement the temperature of concrete rises considerably.

As shown in the diagram above, the increase of heat is affected by the basis temperature of fresh concrete. The higher the basis temperature, the faster and heavier is the curing process and the development of heat. A high temperature difference between the centre and the exterior surface of a structure leads to uncontrollable cracking and therefore to defective buildings.

CONVENTIONAL CONCRETE COOLING At the moment ready mix producers in Qatar are using flake ice to reduce the concrete temperature. In the Middle Eastern desert climate temperature in summer months reaches up to 50oC. Precautions need to be taken when concrete temperature reaches above 32oC causing the following threats:

[42]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

Lower ultimate compress strength in comparison to concrete produced at a lower temperature.→ In many cases extra cement is added to counteract a decrease in compressive strength. The use of more cement results in a higher amount of hydration heat and therefore a higher core temperature in the concrete element which results in a reduction of quality and subsequent danger of cracking.

Thermal cracking during the hydration process leads to a high probability of undermining the structural integrity of the finished element arises. If a too high temperature between the core and the shell of the element appears, shell cracks accrue as due to the cooling down of the shell exposed to the air (or water respectively) at the place the concrete element is positioned the hydration of the cement is still ongoing, while the core is distending.

If the temperature in a concrete element during the hardening phase exceeds 65°C, the danger of expansion due to secondary ettringite formation (a swelling agent) increases dramatically, which leads- in the event of moisturefeeding – to the appearance of material expansion and subsequent surface cracking.

Generally water is added to the concrete (above the mix design requirements) to keep the concrete workable; the more water used the more reduction in compressive strength.

If the temperature of fresh concrete gets too high, this can prove hazardous to the construction of concrete structures. The main risks are: 

Problems with mixing, correct placing and curing

Thermal / differential thermal cracking of concrete

[43]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

Decreased 28-days and later strengths

Delayed Ettringite Formation (DEF) in concrete when exceeding a

temperature of about 65°C during hydration, which can cause cracking many years after the concrete was produced. In most of the existing technical rules and standards there are limitations for the fresh concrete temperature and/or the peak temperature of the core zone of the concrete structure. In Austria, for example, for watertight concrete in a so called “white tank”, the maximum fresh concrete temperature is limited to 22°C and the core temperature of the concrete structure is limited to 45°C (in exceptional cases 50°C). There are numerous ways to reduce the temperature of fresh concrete by reducing the temperature of the raw materials. The aggregates have the largest effect on the temperature of fresh concrete due to the sheer volume needed and their specific heat capacity. Reducing the temperature of the aggregates has the largest effect on the concrete temperature. 65% of the concrete temperature is controlled by the aggregate while the added water only influences the concrete temperature by 15% and the cement by about 20%. The introduction of flaked ice instead of water into the concrete mix can – due to the melting of ice – increase the effect of the water on the concrete temperature from 15% (water) to about 22% (ice).

[44]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

A summary of the most common measures of cooling concrete are illustrated in the graph below: Cooling of Fresh Concrete Operation

Effect

Investment

Running Costs

North Orientation of Storage

low

low

low

-

Shading

low

low

low

Easy

Spraying with Water

low

low

low

Easy

Short Process Time for Extraction

high

low

low

-

Passive Measures for Aggregates

Active Measures Chilled Mixing Water

low

medium

low

Easy

medium

high

medium

Difficult

Cooling Cement by LN *) in Storage Silo

high

low

high

Easy

Cooling Cement by LN in Heat Exchanger

high

high

high

Easy

medium

low

very high

Difficult

high

high

low

Medium

Crushed Ice Instead of Mixing Water

Cooling Concrete by LN in Mixer Trucks Cooling Aggregates in Water Bath *) LN: Liquefied Nitrogen

The fresh concrete temperature can also be reduced by introducing a liquid gas (e.g. nitrogen) directly into the mixer in the batching plant or into the truck mixer. This method has the disadvantages of having a limited effect and a high demand in staff. In reality a combination of processes is often needed to achieve an economical result for the required reduction of the concrete temperature.

CASE STORY Within the Austrian PPP Eastern Region (A5-S1-S2) construction project, just north of Vienna, the concrete temperature for all “white tank” constructions was limited to a maximum of 22°C. The measurement took place after the pumping of the concrete. To be sure to maintain this temperature several processes had to be used. The temperature of fresh concrete leaving the mixing plants had to be limited to 18°C to make

[45]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

sure to fulfill the required temperature of 22°C after the transportation and pumping of the concrete. The following processes were used to cool the concrete: 

Cooling of the cement to –10°C during the pneumatic conveyance of cement into the cement silo of the batching plants by adding liquid nitrogen.

The additional use of flaked ice was introduced when there was a high demand for cooled concrete (used only in one of the batching plants).

Additionally, liquid nitrogen cooling in the truck mixer was used when the previous methods proved insufficient. With this combination of processes it was possible to deliver an average of 160 m³/h of concrete with a temperature reduction of about 10K.

Cooling of concrete through electrical energy is much more cost effective than through liquid gases. For larger concrete volumes it is therefore common to use flaked ice. But these installations are susceptible to disruptions and need 1 to 2 workers for the entire working period.

[46]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

FLAKE ICE PLANT SYSTEMS

The most effective way to ensure a reasonable fresh concrete temperature is to lower the temperature of the base material. One of the most common techniques is to add flaked ice to the batch. Flaked ice needs to be produced just in time on site. Storing flaked ice over a long period of time is not possible.

Disadvantages: â&#x20AC;˘

At high temperatures further activities are needed; such as shading the aggregates or the production of concrete during the cooler night time period

â&#x20AC;˘

Lower production capacity due to a limited ice production and a long mixing process.

Technology Water is delivered to the ready mix plant and pumped into a storage container. Water from the storage container is cooled down to approximately 3oC and stored Cooled down water is subsequently transferred to the ice making plant whereby flakes of ice are produced. [47]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

All the water added in the mixing process can be replaced by ice. To decrease concrete temperature for 10 Kelvin about 7.5 kg of ice are needed. *EXHIBIT A* shows an example of the typical overall concrete temperature profile of concrete produced during the hot summer season in a desert environment.

SUSTAINABLE COOLING OF READY-MIXED CONCRETE Producers in Central Europe have developed an effective, economic and reliable system to regulate the concrete temperature of large concrete quantities. The system was initially used in Qatar, where it continues to be operated successfully. In the process the aggregates are cooled by using cold (4째C) water flowing through the storing silos. The system can be used for aggregates with a grain size over 4mm. For each fraction of aggregate two silos must be used. In one silo the hot aggregates are cooled while the other silo is used for the concrete production. The time needed to cool the aggregates is dependent on the water chiller output and the available cold water volume. It is necessary that the silos are waterproof. A crucial point is therefore the metering valves of the silos dosing the aggregates. In the first installation of the aggregate cooling system prototype in Qatar 200 tons of aggregates per hour can be cooled down by 35 K. Using the cooled aggregate and cool water for the concrete production the concrete temperature can be reduced by 20 K. For high quality concrete using a low water/cement ratio it must be taken into consideration that the use of flaked ice in the concrete mixture is very limited. Using 70kg of ice the concrete temperature can be reduced by about 10 K. Using flaked ice will cool mainly the cement mortar while the aggregates in the mixture will still have a higher temperature. Due to the temperature adjustments between

[48]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

the mortar and the aggregate during transport of the concrete the overall concrete temperature rises considerably between the batching plant and the site. The new system of aggregate cooling has the important effect that no rise in temperature takes place before the cement hydration. This is a major advantage compared to cooling with flaked ice. Due to the water saturation of the coarse aggregates a better consistency and workability of the concrete has been observed.

COARSE AGGREGATE COOLING As shown in the example mix design above the coarse aggregate makes up for the bulk of the concrete which has the greatest effect on the overall concrete temperature. The Coarse Aggregate Cooling System Process: Water is delivered to the ready mix plant and pumped into a storage container. Water from the storage container is then cooled down to approximately 4oC and stored in insulated water tanks and kept at 4oC.

*EXHIBIT

B*

shows

a

detailed

calculation example that implies the use of a Coarse Aggregate Cooling System. Firstly coarse aggregates will be cooled to a

[49]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

temperature below 10째C by adding cold water. Silos filled with aggregates are being flooded with cold water continuously. This is an effective method of cooling fresh concrete, since aggregates are the largest component (fraction) and therefore import most energy.

TECHNOLOGY Cooled down water is used to fill water in tight insulted aggregate silos to cool down the aggregates from the ambient summer temperatures to 3oC to 6oC which will take up to 0.5 to 1.0 hours. The cooling water is circulated through the aggregates and the chillers until the necessary temperature of the aggregates (usually 8째C to 10째C) is reached.

Source: Coarse Aggregate Cooling System, 2009, M. Keckeis

Once the aggregates are cooled down (and ready to use) water is pumped back into the insulated water tanks ready to use to cool down the second adjoining tight insulted

[50]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

aggregate silo full of aggregate. Water from the insulated tanks will be used for batching concrete.

COARSE A GGREGATE COOLING VERSUS FLAKE ICE COOLING Extra running cost occur due to more power needed and in the event of the usage of power generation using fossil fuels the additional power consumption subsequently results in an additional burden on the environment. Further the coarse aggregate cooling system has less movable parts and other complex machinery components compared to the flake-ice system, which reduces the risk of a plant break-down and decreases additional cost for maintenance and repair. Flake ice plants additionally require 1-2 full time operators to run the plant, while the coarse aggregate cooling system is controlled directly from the batching plant control room and does not require dedicated personnel. The initial concrete temperatures are not low enough to reduce the risk of rejecting concrete from site due to high temperature. The temperature measured immediately after adding flake ice does not reflect the real temperature of the concrete, but only measures the temperature of the cooler mortar, while inside the coarse aggregates high temperatures remain extant. Therefore the measured temperature of the concrete has increased by the time the concrete is placed at its final position, because of the temperature balancing within the concrete element. Such increase of temperature is generally far higher than the one that can be caused by the surrounding air temperature. Producing with flake ice plants leads to a reduced potential revenue during day light hours in hot summer months and a standard plants capacity is 45 m3/ hour only, which require the usage of two or more flake ice plants to run a single batching plant effectively.

[51]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

Dried concrete build up in the truck mixers will occur rapidly when returning back to the plant from site, hence increased maintenance work is required.

Above graph illustrates that the use of the coarse aggregate cooling system results in a reduction of the annual operating energy compared to other cooling methods.

[52]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

DUST E MISSION In regards of dust emissions the coarse aggregate cooling system provides another notable advantage on the environmental side as dust is almost eliminated due the washing of the aggregates. ADVANTAGES OF A COARSE AGGREGATE COOLING S YSTEM 

Achieving concrete temperatures as low as 24 Degree Celsius.

Reduces the risk of rejected concrete due to temperatures out of specification

No extra personnel required to run the aggregate cooling system. Enhanced concrete quality allows transporting the concrete on longer distances and provides more time to place and finish concrete works on site

A coarse aggregate cooling system does not produce ice and does not have the capacity to freeze any water in comparison to a flake ice plant

Uninterrupted production, even in case of system failure thanks to backup systems.

Reduces the admixture usage in summer

Cement savings

High quality concrete with a low water/cement ratio.

TEMPERATURE PROFILES USING THE COARSE AGGREGATE COOLING SYSTEM

Illustrated below is a simplified example of the typical overall concrete temperature profile of concrete produced in Qatar in summer using the Coarse Aggregate Cooling method:

[53]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

Standard Mix Design

CONCRETE TEMPERATURE PROFILEAGGREGATE COOLING Quantity in kg

%

Average Degree Celsius

Cement

320

13

75

Coarse Aggregate

1100

46

45

Fine Aggregate

800

33

10

Water

60

2

3 18

Measured Temperature at Plant

Measured Temperature after 1 hour

18

The graph above shows the adiabatic temperature which is balanced even an hour after installation, which is one of the main differences between the conventional concrete cooling with ice and a coarse aggregate cooling system. See *EXHIBIT A and B* showing a detailed sample calculation and comparison of the systems.

CEMENT COOLING As a third alternative cement can be cooled. Large differences in temperatures lead to a high efficiency of this technique. Cement produced just in time measures a temperature of 90째C. By using nitrogen or carbon dioxide gas the temperature can be taken down to 50째C. This does not affect the mixing period or the quality of concrete.

[54]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

COOLING METHOD COMPARISON CONSISTENCY OF CONCRETE Temperature Quantity

Without cooling

Flake-ice cooling

Aggregates cooling

Aggregates & cement cooling

Cement

350 kg/m3

90°C

90°C

90°C

30°C

Aggregates 0/10

900 kg/m3

40°C

40°C

40°C

40°C

Aggregates 10/20

1100 kg/m3

40°C

40°C

10°C

10°C

Water

150 kg/m3

30°C

-2°C

8°C

8°C

Fresh Concrete Temperature

43°C

35°C

27°C

21°C

Site Concrete Temperature

85°C

78°C

69°C

63°C

CHART- TEMPERATURE PROFILE in Degree Celsius 90 80 70 60 50 40 30 20 10 0

Without cooling Flake-ice cooling Aggregates cooling Aggregates & cement cooling Fresh Concrete Temperature

Site Concrete Temperature

[55]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

PLANT LAYOUT AND EQUIPMENT UTILIZATION

Currently in Qatar most of all concrete plants use the above ground storage bins which require the use of a front end loader continuously to load the storage bins. To reduce the use of the front end loader is to construct drive over in ground aggregate storage bins whereby trucks drive over the designated bin and tip the material through a grid to the storage bin below. By using a coarse aggregate cooling system the use of a front end loader will no longer be required, although the initial capital cost are higher to construct the drive over in ground bins in comparison to above ground storage bins. Therefore the use of the front end loaders is no longer required to load bins, which sustainably reduces the overall carbon emissions of the concrete plant.

CONCLUSION This paper shows the different areas in the concrete life-cycle, where improvements can be achieved. A major environmental burden that can be reduced by the concrete producing company itself is the use of fossil fuels on the fleet and on the plants. Another important room for enhancement is given as most of the waste materials can be reused or recycled, which is not only cost-saving but environmentally friendly. The introduction to different ways of cooling is essential to increase the quality and durability of concrete structures, to reduce the danger of cooling-plant malfunction or breakdown and to additionally reduce carbon footprints on the finished product. Conventional flake-ice plants also have the disadvantage of being inefficient during the hot summer months and concrete pouring therefore usually starts in the evening hours only, which requires project schedules to be adjusted accordingly. However, it remains important for a

[56]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

building owner to ensure that innovations besides being ecologically friendly need to be feasible from the financial point of view, meaning that an increase in the cost of concrete production may increase the time of amortization for a project and of course the amount of initial capital invested. Hence, only options have been evaluated, which do not or only marginally increase the rate of concrete under certain criteria when considering relevant project sizes. Another considerable point is the replacement of the cement with cement substitutes that are by-products from other production processes such as fly ash GGBS or slag cement. This does not only have a positive effect on the characteristics of the concrete, but also allows a reduction of the environmentally most harmful building material. As concrete accounts for the greatest part in most construction projects the sustainable production of concrete has a high effect on green building ratings. This paper is taking the concrete production process even a bit further and introduces methods of running concrete batching plants entirely carbon free with the use of alternative energy that can be generated out of solid waste or solar. Waste-to-energy solutions are of considerable importance on project in remote areas or other projects, which are far away from waste dumping sites, as transportation cost often account for a significant environmental and financial burden during construction and operations. By using waste-toenergy solutions the waste is not only removed, but powers a big part, if not even all, of the operations. Both options, solar power and waste-to-energy, amortize even though initial investment is higher, quickly as the resource needed to deed the systems are free of charge (sun rays) or may be even paid for by a to be removed (waste). All over the world initiatives are ongoing to make concrete a greener product and a lot can be learned from experiences in other countries and the efficiency of innovations in this field. [57]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

While overall concrete remains less ecologically harmful than other building materials, it can reduce the environmental burden on construction site significantly due to the high quantities used for building projects worldwide.

[58]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

*EXHIBIT A*

Example for Calculation of Concrete Temperature with Flake Ice W/C

Content

c

Temp.

m*c*T

0.5

kg/m³

kJ/kg*K

°C

kJ/m³

Cement

320

0.8

75

19,200

Fly Ash

0

0.8

45

0

GBBS

0

0.9

45

0

800

0.9

45

32,400

1.5%

1,155

0.9

45

46,778

0.5%

12

4.2

45

Fine Aggregates Coarse Aggregate Water Bond to Fine Aggregate Water Bond to Coarse Aggregate Ice

6

4.2

45

120

335

-1

Chilled Water

22

4.2

2,435

1.1

Concrete

f aggr.

Ccem 0,72 … 0,92

Caggr 0,71 … 1,05

335 kJ/kg incl. effect of melt water

3

40,200 280

22

58,458

after adiabatic temperature balance measurement immediate after mixing

~17

Maximum Temperature Reduction in Fresh Concrete by adding Crushed Ice (K) (Rough Estimation) Water / Cement - Ratio Cement Content 0.4 0.35 0.3 (kg/m³) 270 -8 -6 -5 300 -6 -8 -10 330 -12 -10 -7 360 -9 -11 -14 400 -16 -13 -10 Specific Weight of Aggregates Water Content of Aggregates

2.8 2

Ice for 1K

7.5

[59]

kg/m³

0.45

0.5

-10 -12 -14 -16 -19

-12 -14 -17 -19 -22

kg/dm³ % in weight


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

*EXHIBIT B*

Example for Calculation of Concrete Temperature with Aggregate Cooling W/C 0.5

Content kg/m³

c kJ/kg*K

Temp. °C

m*c*T kJ/m³

Cement Fly-ash GBFS Fine Aggregates Coarse Aggregate Water Bond to Fine A. Water Bond to Coarse A. Ice Chilled Water

320 0 0 800 1,155 80 35

0.8 0.8 0.9 0.9 0.9 4.2 4.2

75 45 45 15 10 15 10

19,200 0 0 10,800 10,395 5,040 1,455

0 45

335 4.2

-1 3

0 571

Concrete

2,435

1.1

18

47,462

[60]

f aggr.

Ccem 0,72 … 0,92

10.0% 3.0%

dewatered after cooling Caggr 0,71 … 1,05


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

REFERENCES •

Argeles, C.; Intrator, M.; Twitty, W.& Armor, M., 2010, Sustainable Concrete Plant Guidelines, 100% draft, NRMCA

B. V. Venkatarama Reddy, 2006. Embodied Energy in Buildings, Department of Civil Engineering, Indian Institute of Science, Bangalore.

Crawford et al. Greenhouse Gas Emissions Embodied in Reinforced Concrete and Timber Railway Sleepers. Environmental

Science

&

Technology, 2009; 090417083833050

DOI: 10.1021/es8023836 •

Deutscher Ausschuss fuer Stahlbeton, DAfStb, 1998, Richtlinie "Beton mit rezykliertem Zuschlag". Entwurf Stand Juli 1998; German Committee for Reinforced Concrete; DAfStb: Guideline "Concrete with Recycled Aggregates", Draft Status: July 1998

Edvardsen, C. & Tollose, K., Environmentally “Green” Concrete Structures, FIB symposium “Concrete and Environment”. 2001

Flower, D.J.M. & Sanjayan, J.G., 2007, Green House Gas Emissions due to Concrete Manufacture, Department of Civil Engineering, Monash University, Australia

Fountain, Henri – Concrete is remixed with environment in mind – NY Times, 30th March 2009;http://www.nytimes.com/2009/03/31/science/earth/31conc.html?_r=1

Grama, S.; Wayman, E. & Bradford, T.; 2008, Concentrating Solar Power- Technology, Cost and Markets, Prometheus Institute; Greentech Media

Gruebl, P.; 1997, Die Erstellung von Bauwerken unter Verwendung von industriell gefertigten Betons mit rezykliertem Zuschlag (Creation of Buildings with Industrial made Concrete Containing Recycled Aggregate), 18. Darmstädter Massivbau.Seminar, Vol. 18

Grübl, Peter and Rühl, Marcus, German Committee for Reinforced Concrete (DAfStb) - Code: Concrete with Recycled Aggregates, 1998, University of Dundee, Concrete Technology Unit, London, UK.

http://www.cement.org/tech/cct_aggregates_recycled.asp; accessed 24th January 2010.

[61]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

Jan R. Prunsinski, Medgar L Marceau and Martha G Van Geem, Life Cycle Inventory of Slag Cement Concrete.

Koenig, E., 2009, Processing and Recycling Technologies for the exploitation of energy and natural resources, Balteq GmbH

Kreislaufwirtschafts- und Abfallgesetz, 1994, Gesetz zur Förderung der Kreislaufwirtschaft und Sicherung der umweltverträglichen Beseitigung von Abfällen. Stand: 27. September 1994; Law to avoid waste in the producing industry: Law to advance recycling management and guarantee an unhesitating elimination of waste. Status: September 27, 1994

Marlowe, I. & Mansfield D., 2002, Toward a Sustainable Cement Industry: Environment, health & safety performance improvement, World Business Council for Sustainable Development WBCSD.

Ministry of Business & Trade, 2008, Business in Qatar, Doha.

N. Spiratos, M. Page, N.P. Mailvaganam, V.M. Malhotra, C. Jolicoeur. Superplasticizer for Concrete.

National

Science

Foundation

Footprint?Science

Daily.

(2009,

May

24).

Retrieved

How

Solid

February

Is

Concrete's

28,

Carbon

2010,

from

http://www.sciencedaily.com/releases/2009/05/090518121000.htm •

NaturalGas.org,

2004,

Natural

Gas

in

the

Transportation

Sector,

retrieved

from

http://www.naturalgas.org/overview/uses_transportation.asp accessed on January 25th, 2009 •

NRMCA, June 2008, Concrete CO2 Fact Sheet NRMCA Publication Number 2PCO2

NRMCA, 2003, CIP 35- Testing Compressive Strength in Concrete

Ortner, N. 2009, A Marketing Plan for a Solar Power Project in Brazil, University of Wales

Oxford Business Group, 2009, The Report Qatar, London.

P. C. Hewlett, 1998, Lea's Chemistry of Cement and Concrete: 4th Ed, Arnold.

PCA, 2008, Report on Sustainable Manufacturing.

Philibert, C., 2009, The present and future use of Solar Thermal Energy as a Primary Source of Energy, International Energy Agency, Paris

[62]


Qatar: Green Concrete Technologies - Towards a Sustainable Concrete Industry in Qatar

RMC Research and Education Foundation, 2009, Ready Mixed Concrete Industry LEED Reference Guide Update February 2009

Ruehl, M.; 1997, Beton unter Verwendung rezyklierten Zuschlags (Concrete Containing Recycled Aggregate), 18. Darmstädter Massivbau-Seminar, Vol. 18

U.S. Geological Survey, Mineral Commodity Summaries, January 2010.

V.M. Malhotra and P.K. Mehta, August 2002, High- Performance, High-Volume Fly Ash Concrete.

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Towards a Sustainable Concrete Industry in Qatar