a guide to sustainable concrete production

A Guide to Sustainable Concrete Production: From Cement and Aggregate

Substitutes to Sustainable Production Methods

September 9, 2010

A Guide to Sustainable Concrete Production: From Cement and Aggregate

Substitutes to Sustainable Production Methods

Alexander Lechner, Nadja Ortner, Alexander Penzias

A Guide to Sustainable Concrete Production: From Cement and Aggregate Substitutes to

Sustainable Production Methods

September 9, 2010

2

ABSTRACT

There are various substitutes for aggregates and supplementary cementitious

materials, which will be described and analyzed in this article. The geographical

concentration is on the State of Qatar and options that are evaluated have been

chosen according to their feasibility from a logistical and economical view-point as well

as on their environmental friendly properties. The goal of this paper is to provide an

overview as to what materials are being used as substitutes and where research is still

being done to provide incentives to use new materials. Also, it will be briefly discussed

as to whether lightweight concrete or concrete with a very low density and high air

content can be used in a humid desert climate as is the case for the Middle East. The

origin of the replacement materials will be described and their sustainable properties

high-lighted. This excursion in the world of concrete will then go on to sustainable

construction methods and will illustrate ways of reducing dust and carbon emissions

from cradle to batch plant. The objective of this paper that has been met is to high-

light workable solutions that respect the triple bottom line, namely economically,

socially and environmentally.



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List of Abbreviations

AAC – Autoclave Aerated Concrete

ASR – Alkali-Silica-Reaction

BFS – Blast Furnace Slag

BOS – Basic Oxygen Steel Slag

CaO –Lime or Calcium Oxide

CC – Conventional Concrete

C&D – Construction and Demolition

CO2 – Carbon Dioxide

EAFS – Electric Arc Furnace Slag

GBFS – Granulated Blast Furnace Slag

GGBFS – Ground Granulated Blas Furnace Slag

HFVA – High Volume Fly Ash

IRRI – International Rice Research Institute

LCA – Life Cycle Analysis

MaO – Magnesium Oxide

NRMCA – National Ready Mixed Concrete Association

OPC – Ordinary Portland Cement

PM – Particulate Matter

RA – Recycling Admixtures

RCA – Recycled Concrete Aggregate

RHA – Rice Husk Ash

SCM – Supplementary Cementitious Materials

SF – Silica Fume

SFS – Steel Furnace Slag

TDOT – Tennessee Department of Transportation

UN FAO – United Nations Food and Agriculture Organization

VIP – Vacuum Insulated Panels



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TABLE OF FIGURES

Figure 1: Test specimens after 56 freeze-thaw cycles as by (Branco, de Lurdes Belgas C. Reis,

& Tadeu, Experimental Evaluation of the Durability of Cork Concrete, 2008)

Figure 2: Compressive cube strength test results as by (Limbachiya, Koulouris, Roberts, &

Fried, 2004)

Figure 3: CCA stored at NRMCA Research Laboratory(red=3000 psi, black= 5000 psi,

gray=1000psi) as by (Obla, Kim, & Lobo, 2007)

Figure 4: crusher used to produce CCA at the concrete plant as by (Obla, Kim, & Lobo, 2007)

Figure 5: (a) and (b) photos of the concrete slabs prior to being crushed; (c) image of the

crushed RCA; (d) debris in the RCA as by (Cervantes, Roesler, & Bordelon, 2007)

Figure 6: Compressive Strength vs. Time - C Ash Mixtures as by (Crouch, Hewitt, & Byard,

2007)

Figure 7: Evolution of compressive strength of concretes against curing time as by (Cordeiro,

Filho, & de Moraes Rego Fairbairn, 2008)

Figure 8: Relationship between 28 day compressive strength and percentage replacement of

silica fume as by (Katkhuda, Hanayneh, & Shatarat, 2009)

Figure 9: Compressive Strength as by (Etxeberria, et al., 2010)

Figure 10: Length change as by (Etxeberria, et al., 2010)

Figure 11: Ratio Hardened Properties / Conventional Concrete as by (Etxeberria, et al.)

Figure 12: Prices are from 2004 as by (Binz, et al., 2005)

Figure 13: Comparison of standard thermal insulation and VIPs



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Table of Contents

1. Introduction .................................................................................................................7

2. Aggregate Substitutes and Supplementary Cementitious Materials ......................8

2.1. Aggregate Substitutes .............................................................................................8

2.1.1. Wood................................................................................................................8

2.1.2. Scrap Tire Rubber ............................................................................................9

2.1.3. Cork..................................................................................................................9

2.1.4. Recycled and Crushed Concrete ....................................................................10

2.2. Supplementary Cementitious Materials (SCMs) ..................................................13

2.2.1. Fly Ash...........................................................................................................13

2.2.2. Rice Husk Ash (RHA) ...................................................................................14

2.2.3. Crushed Glass ................................................................................................16

2.2.4. Silica Fume ....................................................................................................16

3. Slag..............................................................................................................................17

3.1. Blast Furnace Slag (BFS)......................................................................................18

3.1.1 Granulated Blast Furnace Slag (GBFS) ..........................................................19

3.1.2 Ground Granulated Blast Furnace Slag (GGBFS) ..........................................19

3.2 Steel Furnace Slag (SFS) .......................................................................................20

3.2.1 Basic Oxygen Steel Slag (BOS)......................................................................20

3.2.2 Electric Arc Furnace Slag (EAFS)..................................................................21



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4. Special types of concrete or other building materials ............................................25

4.1 Autoclave Aerated Concrete (AAC)......................................................................25

4.1.1 Properties ........................................................................................................26

4.1.2 Manufacturing Process....................................................................................26

4.1.3 Advantages/Disadvantages of AAC................................................................28

4.2 Vacuum Insulation Panels (VIPs) ..........................................................................28

4.3 Lightweight Concrete.............................................................................................30

4.4 Normal Concrete with increased Air Content........................................................30

5. Types of cooling plants and cooling methods..........................................................31

5.1 Common Flake Ice Plant........................................................................................32

5.2 Ecological Flake Ice Plant .....................................................................................33

5.3 Coarse Aggregate Cooling.....................................................................................33

5.4 Cement Cooling .....................................................................................................33

6. Water efficiency on the batch plant .........................................................................34

6.1 Reduce....................................................................................................................35

6.2 Reuse......................................................................................................................37

6.3 Recycle...................................................................................................................37

6.4 Long-term Retarders/Recycling Admixtures.........................................................38

7. Conclusion ..................................................................................................................40

Bibliography...................................................................................................................45



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1. Introduction

Since concrete first came into use, it has ever since remained the first choice as a

construction material. With a global population of 6 billion people and with statistics

indicating that the population is going exceed 8 billion people by the year 2025 in a

medium scenario set up by the United Nations Economic & Social Affairs (2009), the

demand for concrete in order to construct homes as well as office buildings to sustain

the economy will also be on a rise (p.509). With the current rate, at which the global

weather is changing due to the environmental impact of human activity it becomes more

and more important to look at alternative ways on how human kind is able to reduce its

ecological footprint. Unfortunately the production process of concrete - especially

cement - is associated with high energy consumption and therefore high emission levels.

It has been well studied and researched that producing 1 ton of OPC also emits between

900kg to 1 ton of CO2 emissions into the atmosphere (Marlowe, 2003, p. 6),

(Sustainable Concrete, 2008).

The task of this paper is to provide an overview as to what various alternative

aggregates and supplementary cementitious materials exist. Some of them have not

come into use yet but are being considered and some of them are already being used.

This study will also show what kind of effect these substitutes have on the compressive

strengths of various types of concrete. Some of the substitutes will not be explained in

detail because out of two reasons: either they have not been studied enough or they do

not really present an option as they have too much of a negative effect on the concrete.



September 9, 2010

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2. Aggregate Substitutes and Supplementary Cementitious Materials

As for the concrete, there are many different substitutes for aggregates and

supplementary cementing materials (SCMs), which can and partly already are being

used without having a much too drastic influence on the strength of concrete. A few

studies have been conducted on various alternative ingredients, which might be

considered as substitutes for aggregates such as wood, scrap tire rubber and cork. Then

there are already a few alternatives, which are being used in the production process of

concrete, such as recycled and crushed concrete, and glass. There are a number of

SCMs, which are being studied and some are already being used. SCMs, which might

prove to be viable in the near future, or which are already being used are Fly Ash,

various types of slag (since there are many different types of slag, they will all together

be addressed and discussed in chapter 3), rice husk ash, and micro silica.

2.1 Aggregate substitutes

2.1.1 Wood

There are only very few studies on wood being used as an aggregate for the concrete

production. Excess wood (woodwaste), which is being generated by for example

manufacturers that produce furniture, could be used as an aggregate but unfortunately

no research has been conducted as to whether different types of wood could have

different influences on the concrete. Wood reduces the compressive strength of concrete

by a substantial amount: the more coarse aggregates are to be replaced with wood, the

more drastic the effect becomes (Cornachione, 1994, p. 5). It is also not sure whether it



September 9, 2010

9

makes sense from an economical point of view. Therefore using wood as an aggregate

in concrete will not be further taken into account in this paper.

2.1.2 Scrap Tire Rubber

With the constant growth of the population and the constant increase in demand for cars

also scrap tire rubber is being studied as a possible aggregate substitute in concrete.

There has not been much research on the possibility of using scrap tire rubber as

aggregate substitute in concrete for structural parts, but mainly on using it as asphalt

concrete (Updyke & Diaz, 2008) and using scrap tire rubber as lightweight aggregate in

flowable fill (Pierce & Blackwell, 1999).

2.1.3 Cork

Cork might prove to be a viable possible substitute for aggregates in the future. A very

positive aspect of cork trees is the fact that these trees not only convert CO2 into

oxygen through photosynthesis but the unique cell structure of cork allows cork trees to

absorb additional CO2 (Cork Information Bureau, 2009).To produce cork the bark of

the cork tree is removed but the tree remains unharmed and the bark will grow back

until it can be used again. The whole process of making cork is remarkably

environmental friendly and sustainable. Unfortunately cork is only being produced in

the northern part of Africa as well as in a few parts in Europe, which means that a lot of

CO2 emissions would be generated from the transportation of cork to the Middle East.

Other than that cork itself can be used as insulation material as it has an excellent

thermal behavior and on the other side cork can absorb vibrations very well. This means

that it can also be used as a noise absorbing material (Branco, Tadeu, & de Lurdes



September 9, 2010

Belgas C. Reis, 2007, p. 2). Branco et al. (2007) found out that the higher the

percentage of cork granulates in concrete, the compressive strength of concrete falls.

Concrete with cork as an aggregate still has higher properties than other lightweight

concrete types. FIGURE 1 shows a picture of how a block of concrete looks like, when

cork is used as an aggregate. This picture was taken after 56 freeze-thaw cycles by

Branco et al. (2008) in order to identify the durability of concrete with cork as an

aggregate.

10

2.1.4 Recycled and Crushed Concrete

Construction and Demolition (C&D) is one of the processes, which is a major

contributor to the waste streams in the world (OECD, 2006-2008, p. 8). Instead of using

landfills to deposit the waste concrete it is now used as an alternative aggregate.

According to Obla, Kim and Lobo (2007), in general around 20% of crushed concrete

are being used as coarse aggregates for structural concrete within the EU (p.28).

However, it is necessary in many cases to have higher cement content in the concrete

when using recycled coarse aggregates (RCA). This is the result of natural aggregates

usually being of higher quality when used for concrete the first time (Blanco-Carrasco,

Hornung, & Ortner, 2010).

Figure 1: Test specimens after 56 freeze-thaw cycles as by (Branco, de Lurdes Belgas C. Reis, & Tadeu, Experimental Evaluationof the Durability of Cork Concrete, 2008)



September 9, 2010

It is also of importance to distinguish between recycled concrete and crushed

concrete. Recycled concrete is concrete that has already been used for a building and

therefore might contain a few other substances (e.g. oils), which might contribute in a

negative way, if used for the production of new concrete. Crushed concrete is concrete,

which has never been used for construction and therefore will also contain less other

substances than recycled concrete (Limbachiya, Koulouris, Roberts, & Fried, 2004).

Limbachiya et al. (2004) even make a distinction between 4 different types of recycled

concrete, shown in TABLE 1 and all of these types of concrete were used in their study

to produce RCA.

Limbachiy

different c

RCA, the

FIGURE

the conclu

possible w

the norma

concrete b

on the com

concrete.

a et al. (2004) then showed differences in compressive strength of four

oncrete mixes: the first mix contained 0% RCA, the second contained 30%

third mix contained 50% RCA and the last mix contained 100% RCA.

2 shows their results:

sion of this study is that it is

ithout any problems to replace

l aggregates with recycled

y 30% without having any effect

pressive strength of the new

Table 1: Source of recycled concrete aggregates used in the study of (Limbachiya, Koulouris,Roberts, & Fried, 2004)

11

Figure 2: Compressive cube strength test results as by (Limbachiya, Koulouris, Roberts, & Fried, 2004)



September 9, 2010

Obla et al. (2007) estimate that the ready mix concrete industry of the USA could

save up to $300 million per year, if more concrete producing companies would use

crushed concrete as an aggregate (p.2).

FIGURE 3 shows an example of a concrete slab, which is crushed and turned into

RCA for a research conducted by Cervantes, Roesler and Bordelon (2007), FIGURE 5

shows a crusher used to produce crushed concrete and FIGURE 4 shows different types

of crushed concrete at the NRMCA Research Laboratory.

(a) (b) (c) (d)

(Obl

12

Figure 5: (a) and (b) photos of the concrete slabs prior to being crushed; (c) image of the crushed RCA; (d) debris in the RCA as by (Cervantes,Roesler, & Bordelon, 2007)

a, Kim, & Lobo, 2007)
Figure 3: CCA stored at NRMCA Research Laboratory(red=3000 Figure 4: crusher used to produce CCA at the concrete plant as by psi, black= 5000 psi, gray=1000psi) as by (Obla, Kim, & Lobo, 2007)



September 9, 2010

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2.2 Supplementary Cementitious Materials (SCMs)

Supplementary Cementitious Materials (SCMs) replace the cement used for concrete

production by a certain amount. Most of the SCMs are by-products from other

production processes, meaning, they almost have no carbon footprint. Carbon Dioxide

emissions are associated with SCMs when they have to be crushed and ground, when

they have to be brought into a proper, usable form and when they have to be

transported. SCMs can replace the cement needed for the concrete production by up to

50%, depending on what SCM is used. If the transportation route is not very long, the

production of concrete would therefore have a low carbon footprint. This chapter lists

and discusses a few SCMs, which are already in use or studied in order to check their

properties, when used in concrete.

2.2.1 Fly Ash

Power plants that generate electricity by firing coal are able to capture the fine Fly Ash

particles, which are then used as an SCM in the production of concrete. Fly Ash is

already widely used and lately studies have been undertaken to take a look at the

benefits from using higher volumes of Fly Ash as an SCM. Crouch, Hewitt and Byard

(2007) have shown in their studies that it even is beneficial, if Fly Ash makes up about

50% of SCMs. The compressive strengths of different types of concrete studied in this

paper were dependent on various factors such as what kind of Fly Ash was used, how

much of it was used to replace cement what admixtures were used and how old the

concrete was. A distinction is made between two types of Fly Ash: type C and type F.

Due to higher free lime, type C Fly Ash is better suited for concrete production than

compared to type F Fly Ash.



September 9, 2010

Figure 6 by Crouch et al. (2007) shows the difference of compressive strengths of

a normal concrete TDOT Class A with 25% type C Fly Ash and the high volume Fly

Ash concrete HVFA with 50% type C Fly Ash as a cement replacement. One easily

notices that the compressive strengths of HVFA are in general higher than the TDOT

Class A concrete.

2.2

The hu

Interna

rough r

rice pa

1http://be

2http://ww

3http://ww

F

14

.2 Rice Husk Ash (RHA)

sks from rice might prove to be a very potential source of SCM. According to the

tional Rice Research Institute (IRRI) and the UN FAO, the global production of

ice (i.e. rice paddy) in the year 2008 was 685 million tons1. Around 20%2 of the

ddy is rice husks and when burning the rice husks, 25%3 of those 20% remain as

ta.irri.org/index.php/Online-Query.html

w.knowledgebank.irri.org/rkb/index.php/rice-milling

w.ricehuskash.com/product.htm

igure 6: Compressive Strength vs. Time - C Ash Mixtures as by (Crouch, Hewitt, & Byard, 2007)



September 9, 2010

rice husk ash. This would mean that alone in the year 2008 34.25 million tons of RHA

was or could have been produced. RHA is very interesting because it might be

generated as a byproduct when burning the rice husk in biomass power plants. As

Chungsangunsit, Gheewala and Partumsawad (2004) have demonstrated burning rice

husks in order to create electricity is already being done in Thailand and it proves to

emit less CO2 than when electricity is generated by oil or coal. If the rice husk is burned

at a sufficient temperature then the RHA will contain a large amount of silica and it can

be used as an SCM. Cordeiro, Filho and de Moraes Rego Fairbairn (2008) state that the

silica content of RHA is somewhere between 80% - 90% and in Figure 7, present their

results of compressive strength over time of various concrete mix designs that include

different RHA replacement levels.

F

15

Here one can see that replacing 20% of cement with RHA results in a higher

compressive strength of the concrete.

igure 7: Evolution of compressive strength of concretes against curing time as by (Cordeiro, Filho, & de Moraes Rego Fairbairn, 2008)



September 9, 2010

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2.2.3 Crushed Glass

Up until recently using crushed glass as fine aggregate has not been an option. Glass

proves to have a high amount of silica but on the other hand it is very possible that the

glass used as an aggregate in concrete could produce an alkali-silica (ASR) reaction

with the cement, which would render the concrete unusable for construction. Nowadays

it is possible to use admixtures, which prevent this reaction to take place or it is possible

to develop a special type of cement that is ASR resistant. Glass may either be used as a

coarse aggregate, or if ground thoroughly it can also be used as an SCM. Ansari, Maher,

Luke, Zhang and Szary (2000) tested out different concrete mixes with different

amounts of glass as coarse aggregate substitute and came to the conclusion that it is

possible with the right mix of admixtures and cementitious materials to get compressive

strengths of more than 30 MPa, but the authors found out that there was a large drop off

of compressive strength in all the concrete mixes after 56 days (p. 25). They also

recommend that it should therefore not be used in concrete for structural purposes.

2.2.4 Silica Fume

Silica Fume (also known as Microsilica) comes as a byproduct from electric arc

furnaces, where alloys are being produced, which contain silicon. It is a highly

pozzolanic material and therefore well suited to partly replace cement, if a higher

compressive strength is to be achieved. Katkhuda, Hanayneh and Shatarat (2009) tried

to find out the isolated effect of Silica Fume on the compressive strength on concrete.

Therefore they tried out different mixes with different amounts of Silica to replace

cement, as well as different w/c ratios. Their results, shown in Figure 8, point out that



September 9, 2010

in general adding silica fume to the concrete mix will result in higher compressive

strength compared to when no silica fume is added at all.

3.

Becau

variou

or as

proce

result

used

substi

produ

Ff

igure 8: Relationship between 28 day compressive strength and percentage replacement of silica

17

Slag

se there are so many different types of slag, this chapter will solely discuss its

s types and whether or not they can be used as coarse aggregates, fine aggregates,

supplementary cementitious materials.

Slag is a non-metallic secondary product of the steel and iron manufacturing

ss. Slag has less density than melted metal and therefore it floats on top. As a

it can easily be removed during the manufacturing process. The Slag that is being

or considered being used as a supplementary product for cement or aggregate

tute is separated into Blast Furnace Slag and Steel Furnace Slag. As Slag is a by-

ct in a manufacturing process it is initially CO2 neutral.

ume as by (Katkhuda, Hanayneh, & Shatarat, 2009)



September 9, 2010

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Furthermore slag emits less PM, because it is a by-product of the steel

manufacturing process. It only needs to be crushed to be used as an aggregate substitute

or as SCM, whereas all virgin aggregates need to be blasted out of mountains prior to

being crushed. All of the virgin coarse aggregates are being supplied by one of the 69

quarries in Fujairah or one of the 33 quarries in Ras Al Khaimah, UAE. These quarries

are strictly controlled and some of them have been closed down for certain periods as

they were emitting too much PM when dust was whirled up from the ground during

extraction, as well as during the quarry operations itself (Landais, 2010).

3.1 Blast Furnace Slag (BFS)

Blast Furnace Slag accrues when smelting iron ore and adding slag formers at a

temperature of around 1500 Degrees Celsius. The slag will then be separated from the

molten iron and further processed into a usable form for concrete production. If the Slag

is been poured into slag yards to slowly cool down by air it will form blast furnace slag.

3. Slag

3.1 Blast FurnaceSlag (BFS)

3.1.1 GranulatedBlast Furnace Slag

(GBFS)

3.1.2 GroundGranulated Blast

Furnace Slag(GGBFS)

3.2 Steel FurnaceSlag (SFS)

3.2.1 Basic OxygenSteel Slag (BOS)

3.2.2 Electric ArcFurnace Slag

(EAFS)



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This BFS can further be processed by crushing it into the specific sizes to be used as

substitute coarse aggregates.

3.1.1 Granulated Blast Furnace Slag (GBFS)

If the molten slag is separated and rapidly cooled down with high pressure and a high

volume of water the molten slag will explode and form Granulated Blast Furnace Slag.

Granulated Blast Furnace Slag has a maximum size of 6mm and a density of 60%-70%

compared to natural sand (Australasian (iron & steel) Slag Association, 2004). It can be

used as a substitute for fine aggregates but is mostly used to produce GGBFS.

3.1.2 Ground Granulated Blast Furnace Slag (GGBFS)

Granulated Blast Furnace Slag can be dried and ground to a powder, which then is

called Ground Granulated Blast Furnace Slag. GGBFS has cementitious properties,

which are enhanced when used with ordinary Portland cement. If used as supplementary

cementitious material it can replace up to 70% of the cement used in the mix design

(National Ready Mixed Concrete Association, 2006). Its use is independent from the

kind of aggregates used for the mix. There are various sources within Qatar, which

distribute GGBFS as the demand for it is high.



September 9, 2010

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3.2 Steel Furnace Slag (SFS)

Steel Furnace Slag is created when row iron or scrap metal with a temperature of

approximately 1650 Degrees Celsius is melted, whilst adding lime and other slag

forming substances (FEhS - Institut für Baustoff-Forschung e.V.). Due to the lower

density of the slag it will float on top of the molten iron and will be separated into slag

yards. After cooling down the slag can be crushed into aggregate sizes and shows

similar properties when compared to Blast Furnace Slag. As lime and dolomite have

been added as slag formers, untreated SFS contains chemically unbound lime (CaO-

free) and magnesium oxide (MaO-free), which can cause a negative impact on the

overall volume stability. Steel plants use different methods to reduce the amount of

CaO-free and MaO-free (Lang & Tabani, 2003).

3.2.1 Basic Oxygen Steel Slag (BOS)

In a Basic Oxygen Furnace, hot metal from the Blast Furnace will be refined into raw

liquid steel by decarburization and removal of phosphorus. Scrap metal is added to

regulate the large amounts of heat generated by this process, as the heat generated

during the process is extremely high and can be regulated through the addition of scrap.

Furthermore lime and dolomitic lime are the main ingredients to help form the slag. The

slag then will be poured out of the vessel after the steel and cools down in slag yards.

Around 60 kg - 100 kg of slag are produced per ton of steel (World Steel Association,

2010). BOS should not be used as an aggregate substitute due to possible expansion of



September 9, 2010

21

free lime (Cement Concrete & Aggregates Australia, 2008, p. 17). Lang and Tabani

(2003) have tested BOS and found the properties to be not suitable in concrete.

3.2.2 Electric Arc Furnace Slag (EAFS)

3.2.2.1 Production

Within the Electric Arc Furnace, scrap metal of different types is added and then melted

by heating up the mixture with electrodes. By adding oxygen and carbon powder a slag

will foam to increase thermal efficiency in the vessel. During the slag foaming, slag will

constantly exit through a slag door (World Steel Association, 2010). Slag, which has not

been reused will be dumped at the slag yard. With 88.3% of the crude steel production,

the Middle East produced 14,521,000 metric tons of steel with Electric Arc Furnaces in

2007 (World Steel Association, 2009, pp. 31-33).

3.2.2.2 Use as Aggregate Substitute

A way to reduce the expansive behaviour of concrete containing EAFS as aggregates is

to expose the EAFS aggregates to weather for at least 90 days and continuously

spraying them with water before using EAFS aggregates for concrete production

(Tomasiello & Felitti, 2010, p. 2).

According to Etxeberria, Pacheco, Meneses and Berridi (2010), who have been testing

EAFS as an aggregate substitute over 56 weeks in substitute ratios for the aggregate of



September 9, 2010

25%, 50% and 100%, EAFS can be used in concrete and it shows similar, if not better

properties compared to conventional mixes. Table 2 below shows one of the mix

designs used for the 56 weeks test. The mix design containing EAFS is a mix design

considered as having a medium water/cement ratio (the abbreviation CC stands for

Conventional Cement). C-EAFS25/50/100 refers to the above mentioned substitute

ratios of Electric Arc Furnace Slag.According to the test results of Etxeberria, et al.

(2010), concrete mixes made with EAFS as aggregate substitute obtain higher

compressive strengths (illustrated in Figure 9) than conventional concrete, similar

T
able 2: Mix design by (Etxeberria, et al.. 2010)
F
igure 9: Compressive Strength as by (Etxeberria, et al., 2010)
22



September 9, 2010

tensile strength and m

Figure 11). Furtherm

exposure to a temp

conventional concrete

identical with the con

substitute considerabl

(2010), however, leav

F

F

igure 10: Length change as by (Etxeberria, et al., 2010)

odules of elasticity like a conventional concrete mix (illustrated in

ore it showed that the residual compressive strength after a 4 hour

erature of 800 Degrees Celsius remained higher than the

mix. Figure 10 shows that the concrete mix C-EAFS50 is almost

ventional mix. Using a high amount of slag as coarse aggregate

y reduces the workability of the concrete mix. Etxeberria et al.

e it unclear what kind of Electric Arc Furnace Slag they have used

igure 11: Ratio Hardened Properties / Conventional Concrete as by (Etxeberria, et al.)

23



September 9, 2010

24

and how high the percentage of free lime and free magnesium oxide is within the slag.

First researches have been conducted by Tomasiello et al. (2010) that EAFS can

be used in self-compacting concrete, if partly being used as a substitue for 4-8mm

gravel. The conclusion was that adding EAFS to the mix reduces the amount of

superplasticizers needed . Furthermore there is a slight increase of the compressive

strength when some of the aggregates are subsituted with EAFS. Also, if EAFS is added

as a substitute and Fly Ash is used as substitute for limestone filler, a slight decrease in

compressive strength has been observed. Here the question arises, which may be an

opportunity for further research, by how much Fly Ash reduces the compressive

strength and, whether EAFS then again reduces or balances the resulting decrease.

Further research from Lang and Tabani (2003) was especially aimed at

determining the constancy of volume of concrete mixes containing Electric Arc Furnace

Slag. If crushed sand made out of SFS is used the compressive strength will increase as

a result. As by 2003 aggregates >5mm made out of SFS have only been used in asphalt

mixtures and are subject to some corrective actions in the traditional mix designs.

However due to the higher density of EAFS compared to natural coarse aggregates, the

gross density of fresh and hardened concrete will increase. They reckon that the

workability of concrete with EAFS aggregates is only given, if a higher volume of

cement paste, flows to the water/cement ratio, while the amount of liquid added in

forms of agent and water should not change. Compressive strength, flexural strength,

tensile splitting strength, dynamic and static E-module are higher than with natural

coarse aggregates. EAFS in concrete mixes has the same properties as concrete



September 9, 2010

25

containing Fly Ash and is ecologically harmless. Lang and Tabani (2003) conclude that

most EAFS can be used in concrete as aggregate substitute.

3.2.2.3 Sourcing of Electric Arc Furnace Slag

According to Qatar Steels’ annual report 2008 a limited amount of crushed slag is

brought to the market. Sourcing from Iran is presents a possibility. According to the

World Steel Association (2009), Iran is the largest steel manufacturing country in the

Middle East, followed by Saudi Arabia. India as third largest steel manufacturer of Asia

is another source, which has acceptable distance as the CO2 emissions for the

transportation have to be considered.

4. Special types of concrete or other building materials

There are various other types of building materials next to concrete that have special

positive attributes such as providing better thermal or acoustic insulation. As it is the

goal of this paper to show that water and energy can be saved during the concrete

production process and therefore reducing costs, it might be of interest to take a look at

other building materials, which help reducing energy consumption in the building and

therefore, again, reducing costs.

4.1 Autoclave Aerated Concrete (AAC)

As looking for alternative concrete where the aggregate rate is low autoclaved aerated

concrete should be considered. AAC was first used in the mid-1920s in Sweden. Further



September 9, 2010

26

processing and manufacturing technologies have been invented in Germany and

development of AAC still continues through to today (Bundesverband Porenbeton,

2008). It has been used in the Middle East for the past 40 years (Schnitzler, 2006, p. 2).

AAC is been used in the Precast construction only as it requires factory production.

4.1.1 Properties

The density of AAC is in between 300kg/m3 and 1000kg/m3, giving it the ability

to float on water

Strength of normal AAC blocks are between 2.5MPa and 10MPa

AAC contains approximately 80% air4

AAC uses 50% less energy than normal concrete in production

End product has up to 5 times the volume of the raw material

Due to its porous structure an exceptional acoustic insulation is given

No toxic ingredients

4.1.2 Manufacturing process

Differing from conventional concrete, which in general contains cement, water,

sometimes slag or Fly Ash, fine aggregates, coarse aggregates and admixtures, AAC

contains a mix of 3 components. The largest amount in a sample mix is silica, which

can be sand or Fly Ash. Depending on the choice of sand or Fly Ash, the colour will be

either white (sand) or grey (Fly Ash). If sand is chosen, it has to be free of any

4(Schnitzler, 2006, p. 3)



September 9, 2010

27

impurities and will be ground to powder. Any type of cement and/or lime will then be

added as binding agent. Thereafter, aluminium powder or paste is added as porous

additive. Water will then be added to initiate the chemical reaction. As an example it

would need 270 kg/m3 of sand, 120 kg/m3 of cement and/or lime, 0.5 kg/m3 aluminum

powder or paste and 225 liters of water to get one m3 of raw material, which will

expand to up to 5m3 of autoclaved aerated concrete.

If reinforcement is going to be used it has to be pretreated as the cellular concrete

does not provide any protection for embedded reinforcement (Neville, 2008, p. 710).

Therefore, a common method is to paint or coat the reinforcement with rust prevention.

Rust prevention could be cement slurries, bituminous emulsions or water based coatings

(Bundesverband Porenbeton, 2008).

The mix will be poured into moulds, which are either equipped with

reinforcement or empty for standard blocks. The moulds will only be filled by half of

their volume and during the pre-curing stage the mixture will gain volume until the

mould is filled. Within the pre-curing stage the added aluminum reacts with slaked lime

and hydrates. The hydrogen expands the raw mixture, reacts with oxygen and dissolves

to water, while the created pores still remain in the AAC. The so called cakes are being

taken out of the mold to be cut to their final size and then will be placed in the autoclave

to cure under pressure of 12 bar saturated steam under a temperature of 190 Degrees

Celsius. The curing time takes approximately between 6 and 12 hours. The autoclave

usually is a steel tube, which has a diameter of 3 meters and is about 45meters long

(Winter, 2010).



September 9, 2010

28

Chemically, the cement and the silica will almost completely hydrate and form 1.1 nm

tobermorite5. If parts of the sand or Fly Ash haven’t reacted in the autoclave there might

be some residual calcium hydroxide. After the curing stage the blocks will be taken out

of the autoclave to cool down and then can be used directly after the cooling process.

4.1.3 Advantages/Disadvantages of AAC

Unfortunately, because of its lightness and very low density, autoclave aerated concrete

has to be protected from weather, especially moisture. It can be used to construct

buildings with up to nine levels (Baumarkt + Bauwirtschaft).

4.2 Vacuum Insulation Panels (VIPs)

To reduce the amount of CO2 when a building goes operational a sophisticated thermal

insulation is required. Especially in a desert climate, where air conditioning units,

respectively chilled water district cooling plants are being used to regulate the

temperature within the building. The consideration of shaded facades during the

planning and design stage of a building improves the indoor climate but choosing the

right insulation is one of the core factors to energy saving within a building. There are

several types of thermal insulations as glass wool, rock wool, foam glass or polystyrene,

which are commonly used in the construction industry.

5Tobermorite is a calcium silicate hydrate mineral that occurs in hydrated cement paste



September 9, 2010

Howe

for ex

comm

The R

mater

keep

insula

centu

build

autho

Figure 12: Prices are from 2004 as by (Binz, et al., 2005)

29

ver as seen in FIGURE 12, there are more efficient thermal insulation material as

ample Vacuum Insulated Panels, which have a very high R-Value compared to

on insulation materials and have a very thin architecture as seen in FIGURE 13.

-value measures the thermal resistance of construction

ials and therefore shows material’s ability to hold back or

heat of cold. High values indicate a high suitability as

tion material.

The development of VIPs started at the end of the 19th

ry but has recently become of greater importance to the

ing sector as energy prices undergo a steady increase. In Germ

rized by the building authorities in July 2007 for the first time

Figure 13: Comparison of standardthermal insulation and VIPs

any VIPs have been

(VIP-bau.de).



September 9, 2010

30

Due to the excellent thermal insulation capabilities and complicated

manufacturing process of VIPs they are significantly more expensive in the initial

purchase stage but due to the tremendously higher thermal insulation and thinner

architecture, a Life Cycle Analysis (LCA) for Qatar should be conducted where VIPs

are taken into account.

These panels have to be handled with great care as they are very sensitive to

external impact. Furthermore thermal bridges can especially reduce the efficient use of

the VIPs.

4.3 Lightweight concrete

Using expanded slate aggregates in a concrete mix will decrease the weight due to less

density of the aggregates compared to gabbro. The density of aggregates in normal

concrete is usually between 2.6 kg/dm3 and 2.9 kg/dm3 (Weber, 2007, p. 21), whereas

expanded slate aggregates have a density of 0.6 kg/dm3 to 1.4 kg/dm3.

4.4 Normal Concrete with increased Air Content

Considering that Autoclaved Aerated Concrete has no coarse aggregates in it the

questions arises, if increasing the air content in a standard concrete mix will reduce the

overall percentage of other ingredients, which are contain embodied carbon dioxides.

Depending, on which aggregates have been used in a concrete mix the air content varies

from 1% to 2% in normal concrete and up to 6% in fine-grained concrete (Weber, 2007,



September 9, 2010

31

p. 37). In colder climate, air entraining admixtures are added to create microscopic

bubbles in the concrete, which improve the durability of the concrete mix in the

freeze/thaw process. Furthermore increased air content will increase workability and

reduce the amount of water need for the mix.

Generally aerated concrete can be used for C20 and C 25. 1% of air results in a

reduction of 2N/mm3. The question remains, if a higher cement content in concrete

allows for an increase of air in concrete without risk. Usually a higher cement content in

concrete reduces the amount of air within the concrete (Portland Cement Association,

1998). This question might be of importance as in Qatar the cement content is high (by

industry standards). However, as stated already above, for every 1% of air content a

decrease of 5% of its compressive strength is observed (Portland Cement Association,

2010), (Neville, 2008, p. 559).

5. Types of cooling plants and cooling methods

Due to the hot desert climate in Qatar it is necessary to cool down the concrete in the

stage of mixing in order to reach the required fresh and hardened concrete temperatures.

Without cooling of the heated coarse and fine aggregates, the fresh concrete temperature

would be high above 40 Degrees Celsius, which would result in serious cracking and

damages within the concrete during the process of hardening. In general, flake ice is

used to replace a certain amount of the water used to mix the concrete in order to lower

the temperature. This chapter discusses different flake ice cooling plants and explains a

few methods on how to keep the temperature during the process of mixing as low as

possible.



September 9, 2010

32

5.1 Common Flake Ice Plant

Most of the concrete mixing batch plants in Qatar use conventional flake ice plant

systems to regulate the temperature of the fresh and hardened concrete, especially in the

months of summer when temperatures can rise to over 50 Degrees Celsius and the

ingredients heat up even more. The flake ice is added during the mixing process and it

will decrease the concrete temperature by 1 Kelvin per 7,5kg ice added. Although it is

possible to replace all the liquid water in the mix with ice there are limits to the water

usage in the concrete mix.

A commonly applied method of the region to add more ice to the concrete mix without

exceeding the maximum water level is spreading the fine aggregates (washed sand) over

large area to let them dry. As a result the washed sand contains less humidity and

therefore more water and/or ice can be added in the mixing process. A reduction from

8% humidity to 2% humidity in the sand would lead to an additional 44kg of ice in a

given MPa40 mix design (Lechner, Ortner, & Amato, 2010), which therefore means a

reduction 5.87K.

However to produce 1 tonne of additional ice a common flake ice plant will

consume an additional 2.9kW of power on average. If a concrete batch plant is to

produce 1500m3 of concrete per day, the additional kW consumption will rise by

191kW on average.



September 9, 2010

33

5.2 Ecological Flake Ice Plant

Whilst using different technologies than drum ice generators some manufacturers

managed to bring down the average kW per tonne to 1.53kW, which is almost 50% in

energy savings compared to a common flake ice plant.

5.3 Coarse Aggregate Cooling

Another, new technology, is the coarse aggregate cooling plant, which runs completely

without ice. Instead of cooling down the concrete in the mixing process, the coarse

aggregate cooling system chills the aggregates prior to the mixing process. The coarse

aggregates will be chilled down to a temperature of 6 Degrees Celsius effectively.

Cooling the coarse aggregates to 6 degrees has the advantage that their core temperature

is 6 degrees as well, whilst working with ice only cools down the surface. As the

aggregates are being washed there is less dust emissions when transporting the coarse

aggregates to the mixer.

5.4 Cement cooling

Apart from what cooling method is used one of the most important ingredients in

concrete is cement. It can easily reach 90 Degrees Celsius, which will affect the fresh

and hardened concrete temperatures. When adding cement to the mixer it can be cooled

down by up to 50 degrees Kelvin using nitrogen or carbon dioxide gas. This does not

affect the mixing period or the quality of concrete. Before the cement is being added to



September 9, 2010

34

the mix from the bulker it can be cooled by an external cold air compressor to reduce

the temperature in the silo at the beginning. Using an external compressor for blowing

in the cement has a positive side effect: the vibrations will not be transferred to the

bulker and therefore dust emissions will be reduced.

6. Water efficiency on the batch plant

Water is a very important natural resource and with the growth of the population

attention has to be paid to the availability and scarcity of this precious resource.

Especially in a humid desert climate it is important to pay attention to the water demand

and usage. Reducing water consumption in Qatar means reducing the amount of water,

which needs to be desalinated in one of the nation's wide spread desalination plants. To

produce 1 cubic meter of water, 3 kg of CO2 are being emitted (Core Economics, 2009).

However, these figures refer on reverse osmosis plants and in Qatar mainly combined

cycle plants are installed, which produce more CO2.

As concrete always requires a specific amount of water, which cannot be lessened

(admixtures might only be able to reduce the amount of water needed for concrete by a

very small amount) it is important to look at the water consumption around the batch

plant to find out, where water consumption can be reduced and where water can be used

more efficiently, thus saving operating costs at the batch plant.

To run a batch plant in an economical friendly way the guiding principles are:

“Reduce, Reuse & Recycle”. This does account not only for water but for general waste

and waste concrete as well.



September 9, 2010

35

6.1 Reduce

The most significant wastage of water on a concrete batch plant is the cleaning of drum

mixers after they delivered their load. In the following section some actions are being

listed, which can be taken to reduce the amount of water used in the batch plant:

Starting from the very beginning of the delivery process: by pouring the ready

mix into the truck mixer. Depending on the specific concrete mix, which has to

be loaded a correct speed of opening the flaps of the mixer should be maintained

as otherwise the drum of the truck mixer and the surroundings get dashes of

concrete. E.g. pouring flow concrete into the truck mixer shall be done gently: if

the flaps are opened straight to their maximum level the concrete mix will shoot

out of the drum. Whereas, if the drum contains stiff concrete, the flaps cannot be

opened straight to the maximum level as the concrete would block the hole on

top of the drum and would run off on both sides. Being careful while pouring the

concrete will reduce the amount of water needed to clean up the dashes.

Usually hoses with a large diameter are being used to clean trucks at the mixer

platforms. These should be equipped with flow control nozzles. In general the

hoses should have a smaller diameter to reduce water flow but at the same time

keep water pressure high enough to have the same cleaning effect.

The mixer itself has to be cleaned after changing the mix design from e.g. stiff

concrete to flow concrete. This is often done with large amounts of water by

washing out the mixer manually. Several manufacturers produce high-pressure

nozzles, which can be installed in a circular arrangement on top of the mixer.

While cleaning, several pre-settings for different kinds of concrete could be



September 9, 2010

36

memorized and an optimum amount of water could then be used to clean in

order to not waste water unnecessarily.

During intense cleaning before parking the mixers overnight high pressure water

blasters should be used as they will use less water due to very high pressure

while maintaining or increasing the effectiveness of the cleaning process.

The largest amount of water is used when the truck mixer drivers have to clean

the drum before loading a new batch of concrete. Therefore the most important

action is to educate the truck drivers and raise their environmental awareness.

Not only will this reduce the consumption of water, several other benefits like

reduction of fossil fuels due to more eco-friendly driving, etc. will come along

with educating the drivers. After delivering the concrete batch to the customer

approx. 100 litres of water will be added to the drum for the return trip to the

batching plant so the concrete leftovers don’t harden out. Not more than 100

litres should be added and when the water is poured out of the truck at the batch

plant it can be collected in recycling collection tanks to make it usable for

further cleaning purposes.

Maintaining all pumps, hoses and water connections to prevent loss through

leakage

There are recycling admixtures (RA) for the cleaning of the truck mixers, which

are been used in widely parts of Europe and America, however there are some

issues with the temperature in Qatar and the competency of the staff, as the RA

have to be dosed very carefully (these recycling admixtures will be briefly

discussed in chapter 6.4).



September 9, 2010

37

6.2 Reuse

If it is not possible to reduce the amount of water needed following actions can be taken

to reuse the water and save the amount of potable water.

Collect water runoff from mixing platforms and cleaning areas to reuse it for

cleaning purposes. Possible treatment through settlement traps can be done to

allow water reutilization.

Using water from washing in settlement pit and reuse for washing for one to two

times

6.3 Recycle

Installation of recycling plants where water will be treated in settlement traps

and then can be reused for cleaning

Water out of the recycling systems could be used in the batching process for the

concrete mix, if it fulfils certain requirements such as:

o PH 6-9 is ideal for concrete batching

o Total suspended soils of 50-200 parts-per-million

o No oils or lubricants within the water

Principally all water from the plant goes to the recycling plant. This means the water

from the mixer will be washed into the shovel of the wheel-loader and the wheel-loader

will take it to the recycling plant. Alternatively the water from washing the mixer can go

directly in to the recycling plant. The water from the truck-mixers will be washed in

directly. All water that goes into the recycling plant will be separated in aggregates

(everything above 0.2-0.25mm), which will then be added to the respective grain size



September 9, 2010

38

for the next mix) and water with fines will go into a basin (usually high basin) and will

be equally distributed with agitators to reach a constant mass of the fine particles. This

recycled water can then be added for mixing when being less than 0.1kg/l. Where this is

not allowed as per code, like in Qatar, recycling plants can be acquired that convert

contaminated water into usable/potable water.

It is recommended to use recycled water in concrete of lower compressive

strength.

6.4 Long-Term Retarders/Recycling Admixtures

As for the concrete that has not been used in construction yet, there is a more

environmental friendly way of reusing it, by not letting it harden out and then crushing

it. A few admixtures have been invented, so called long-term retarders and recycling

admixtures. Long-term retarders (e.g. Delvo Crete Stabilizer 10, SikaTard-930) can be

added to the concrete. These admixtures simply delay the cement hydration process thus

making the concrete reusable for up to 3 days after the concrete has been mixed.

If a truck mixer returns to the batching plant after delivery, there are usually some

concrete or cement and aggregate leftovers in the drum. These concrete ingredients are

then usually rinsed out by using a lot of water and cannot be used anymore afterwards,

forming waste. Recycling admixtures, like Delvo Easy Stabilizer or Delvo System

Application: Stabilization of concrete wash water, prevent the cement hydration within

the truck mixers. This means that on the one side, less water needs to be used to clean

out truck mixers and on the other side it is possible, because of the inhibition of cement

hydration, to reuse the leftover concrete or concrete ingredients for the next batch.



September 9, 2010

39

There have been some reports about the fact that these kinds of admixtures cannot

be used in the Middle East due to the humid desert climate. BASF was so kind as to

explain to us why these admixtures haven't been marketed to the Middle Eastern

countries yet:

"There were a number of issues relating to the use of the Delvo system, some of

which I've listed below:

1) Control of dosage - Delvo is a powerful retarder and hence requires

careful and accurate dosing. The ready-mix companies were not confident about

the competence of their staff to correctly handle the system.

2) Temperature control - Most ready-mix concrete requires chilled water and

crushed ice to achieve the specified maximum temperature; particularly in the

summer. The Delvo wash-water system requires that 200 liters of water remain

in the ready-mix truck after cleaning. This water will reach ambient temperature

(or above) and hence it will be difficult to reduce sufficiently the concrete

temperature overall for the next delivery.

3) Re-use of returned concrete - Most concrete specifications limit the time of

placing to 2 hours after the addition of water to the mix. This time is recorded on

the delivery ticket. Using Delvo it is possible to extend the use of the concrete by

hours or even days hence this will comply with the specification. There was also

some opposition to selling "second-hand" concrete.



September 9, 2010

40

4) Batching problems - The reduction in added water (because some is already in

the truck) made discharging the concrete from the plant mixer difficult.

In terms of strength and durability there are no adverse effects of adding Delvo

to concrete. The main objections were practical or related to temperature control.

Chemically, the system works very well, particularly in re-use of returned

concrete."6

7. Conclusion

Outcome:

Various researchers have picked up the topic of increasing the air content or replacing

ingredient materials of concrete with green alternatives, which in building construction

does not prove to be a good solution. While replacing coarse aggregates with rapidly

renewable materials such as bamboo or cork, or reused steel as fibers or shredded tires

the problem that becomes apparent is the obvious reduction in compressive strength,

which limits the usage significantly.

As already mentioned in Chapter 4.4, aerated concrete can be used for C20 and

C25. Although with a good observation and control from the laboratory it is possible to

reach strengths of up to eventually C37. The question still remains, if it is possible to

increase the air content and the amount of cement used.

Hence it may be best off from an economical perspective to use aerated concrete

for up to 5% for the possible classes and not to replace with a material; while for the

6 (Bowerman, 2010)



September 9, 2010

41

amount exceeding 5% aggregate substitutes is a proper choice to increase slightly over

the 5%. Replacement levels have to be calculated for each mix. Entraining the air

instead of using green coarse aggregate replacements may however, may not be better

from an environmental perspective when looking at cork, as cork is CO2 absorbent and

therefore produces negative CO2 emissions, which could positively influence the

overall CO2 emissions as the negative rate from the cork, will reduce or balance the

overall rate.

The quintessence here is that replacing aggregates with any material of lower density

(other than e.g. stones or granulated slag) one can experience a reduction in the

compressive strength.

This is why it has become more common to produce by- products from steel furnaces or

coal combustion such as GGBS and Fly Ash, which are not used to replace the coarse

aggregate content in the mix, but to replace parts of the cement. Replacement levels

vary and for Fly Ash are depending on the required strength and application between

32% and 50% in building construction, while GGBS contents are recommended

between 36% and 70%. Being by-products there is no CO2 emission counted towards

their production and only the processing and transportation are taken into account. This

drastically lowers carbon emission of the concrete as cement, the main contributor,

emits something between 900 kg to 1 ton per ton of cement. While these products are

certainly green this study was also dealing with other types of slag.

In this correlation EAFS, another by-product from the electric arc furnace used for iron

production, has been evaluated, which, different than GGBS, is not used as a cement

supplement, but as a replacement for natural coarse aggregates in a granulated form. Its



September 9, 2010

42

positive attributes are not only interesting from an economical perspective, but also

from a social and environmental one. Basically EAFS does not only increase the

compressive strength and reduces CO2 emissions. It also lowers PM10 emissions

drastically and therefore reduces the burden on the human health through dust

emissions.

Finally it was looked a step further in the material life-cycle and the different cooling

methods that can be used were found to be contributing to high energy consumption

during the batching process itself. The less movable parts batching cooling plants have

the less power they need. In the cases that were evaluated here this is applicable for a

coarse aggregate cooling system with chilled ice and for an energy-efficient flake-ice

cooling plant. The problem with ice, however is, that due to the normally high moisture

content in the sand the ice that can be added to a mix is very limited as the w/c ratio

otherwise would increase beyond the limit as per specification or code. Reducing the

water content in the sand by pre-drying it allows the addition of more ice, but then the

energy and water usage for the ice production increases simultaneously and this will go

on the account of the environment and the cost. These problems do not occur with

cooling systems that do not require ice, but chilled water.

Recommendation:

From an economic and ecological point of view it becomes apparent that the usage of

various types of slag, more precisely EAFS, can be recommended. Slag is produced in

large quantities around the globe as the iron and steel industries are one of the biggest

on global scale. Additionally, the key steel producing corporations are all located in and



September 9, 2010

43

closely around the Middle East, which lowers the transportation costs and, speaking in

ecological terms, also results in lower CO2 emissions. A further benefit of slag is that it

comes in various shapes and sizes: slag can either be used as coarse aggregate, fine

aggregate and even as supplementary cementitious material. This does not only

contribute to a reduction of CO2 emissions, but because of the fact that slag does not

need to be blasted out of mountains as is the case with virgin aggregates, it also leads to

a significant reduction in particulate matter emissions.

Opportunities for further research

Yet the opportunity for further research on various topics on concrete is still very high:

as already mentioned above, vacuum insulated panels are, compared to other insulating

materials, much more efficient in retaining or keeping out heat or cold but are very

expensive. The possibility would present itself here to show whether there is a point

from an economical view by comparing the costs of producing and using VIPs in Qatar

with the cost savings that arise by needing less energy for cooling. It should be shown

as well whether or not it makes sense from an ecological point of view: if the

production of VIPs compared to the reduced energy consumption (and therefore less

CO2 will be emitted) is low enough and it is feasible from an economical point of view

it would make sense to introduce VIPs to the Middle Eastern Markets.

As discussed in Chapter 4 further research could be undertaken to find out, if the

mass of concrete is lower (by for example using admixtures, which raise the air content

within the concrete) that less reinforcement needs to be used, provided that the concrete

still has enough compressive strength to be used for structural parts in the construction.



September 9, 2010

44

Furthermore, it would be interesting to evaluate the usability of long-term

retarders or recycling admixtures in a hot, arid climate such as is the case in Qatar.

There is no doubt that admixtures like these could save the environment through waste

reduction and potentially reduce costs by improving the water consumption, as well as

giving the ability to reuse concrete leftovers.

To achieve the most precise results a real life scenario testing still could be

undertaken in order to obtain more information on these topics and to find possibilities

to further enhance these ingredient materials and the applications thereof to make them

most suitable for the Middle Eastern region.



September 9, 2010

45

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a guide to sustainable concrete production

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