Materials And Sustainable Buildings Construction Essay

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One of the oldest building materials still around in the construction industry, Bricks continue to be used on projects throughout the country. This is down to various factors:

They are cheap to make

They are durable

Little maintenance is required

They can be made from different materials, including clay, shale, soft slate, calcium silicate, concrete or shaped from quarried stone.

A) The number of bricks used in construction, is the amount increasing or decreasing?

In 2001, the brick industry sold 2.8 Billion bricks (BDA 2002). Bricks are a popular construction material throughout the industry, its place in the future of construction is secure, this however, does not secure is current rate of production.

As building methods evolve and innovative systems that speed the construction process up are introduced, the use of bricks in the structural/engineering sense decreases and the secure position of bricks in the industry is left with the variety of facing bricks available.

Brick production from the introduction of new, cheaper and quick methods has reduced. The annual production of all bricks in the UK reduced from 7,283 Million in 1960, to 4,562 Million in 1980 and 3,802 Million in 2003 (Surrey 2003)

In particular, the percentage of common bricks produced in 1960 was 64%, by 1980 this percentage had fallen to 35% and further still to 23% in 1990 (Surrey 2003), this came about mainly down to the introduction and use of concrete blocks.

However, consideration must be made of construction industry recessions throughout these years, they are also partly to blame for the decrease in common brick demand, these numbers do give us an indication of the changes that took part in the use of bricks on construction sites.

B) How Bricks are produced, what impact does production have?

Ceramic bricks, made from clay that is extruded from the ground in many parts of the UK. Clays are varied, a brick produced in one part of the country may look completely different from a brick produced in another area. The area that the clay is extruded from may very well provide the brick with different properties in performance as well as its appearance. (BSG 2009).

The production of bricks, as with many construction materials, has an impact on the environment in many ways. The extraction of materials and processing of the bricks can cause unwanted amenity. Problems such as poor quarry maintenance can create unwanted waste and cause unnecessary problems.

Extraction and production

The extraction process works on an 'open pit' method, the depth of the pit will differ in different regions and the type of clay being extruded. The rate of extraction amounts to no more than 3% of tonnage of quarried materials in the UK (BDA 2008), demonstrating that the volume of clay is low compared with other minerals. For extraction to be feasible, the ratio of brick to waste rock must be high. The rate and volume of extraction is often restricted to a limited number of weeks per year, this immediately reduces the amount of impact on the environment (BDA 2009).

Brick production is done by the 'soft mud' (handmade) method or more commonly through extrusion. Brick making factories are usually situated alongside the quarries, this will obviously minimise the energy used to transport the raw materials to the factories (BDA 2008).

Fig 1. Brick manufacturing - the extrusion process (Barton 2007)

Extrusion is a method where a column is formed by pushing the materials through a die at high pressure, this column can then be cut into bricks, and this is known as wire cutting. Bricks are then dried prior to firing in a kiln.

Kilns used energy to fire the bricks; many kilns will have to be optimised to reduce the amount of energy they use. Improvements are also enabling for efficient kilns to allow recycled heat to be used in the drying process.

This production process is prone to emissions released into the atmosphere, such as Carbon gases, hydrogen fluoride and particulates. 90% of the industries output of emissions are down to kilns that exceed 2 megawatt, these kilns are subject to statutory control of fluoride emissions (BDA 2009-B).

i) How much energy is consumed by production?

The table below (Fig 2.) shows the amount of energy used by the production of bricks over several years, it demonstrates the reduction due to implementing new legislation to meet energy reduction targets.

Year

Output (tonnes)

Energy consumed (KWh)

2001

6539688

5100130531

2002

6456265

4872262517

2003

6444972

4858304907

2004

6652605

4963269329

2005

6357704

4810757299

2006

5877820

4357362086

2007

5788880

4193104438

2008

4575741

3396100176

Fig 2. Specific energy consumption per tonne of output. Source: (BDA 2009 - B)

ii) How much CO2 is produced as a by-product?

The table below (Fig 3.) gives a measure of the CO2 emissions per square metre of brickwork per annum, these take into consideration the emissions from energy and the process. It must be noted that the rise in 2008 is due to the recession, this because Kilns cannot be used intermittently.

Year

Tonnes CO2 / Sq. metre / annum

2001

0.000189

2002

0.000186

2003

0.000186

2004

0.000185

2005

0.000186

2006

0.000183

2007

0.000180

2008

0.000183

Fig 3. CO2 emission per square metre of brickwork. Source: (BDA 2009 - B)

iii) Does the production process use any waste products from other industries?

Secondary materials and waste from different industrial process's are being used and others explored as a substitute for primary clay.

Figure 4 shows the materials currently in use and materials being explored as a substitute or that may be added to the clay mix.

Recycled material

Progress

Comment

Clay off cuts

In use

Recycled internally

Grog

In use

Recycled internally

Scrubber waste

In use in one plant

Waste from own scrubber

Pulverised fly ash

In use

Traditional alternative material for brick making

Town ash

In use

Traditional alternative material for brick making

Coke breeze

In use

Traditional alternative material for brick making

Coal fines

In use

Traditional alternative material for brick making

Slag

In use in one plant

Blast furnace slag from the steel manufacture

Sugar starch

In use in a couple of plants

Saw dust

In use in one plant

Quarry fines

In use

ISSA

In use in one plant

WTR

In use in one plant

Pottery glaze

In use

Foundry sand

In use / trials

A small amount of primary sand is recycled internally. Trials were undertaken for the use of foundry sand in the bricks

Bone ash

Lab / work trials

Bottom ash

Lab trials

Container glass

Lab / work trials

R&D work was undertaken via WRAP funded projects

CRT glass

Lab trials

Some work was undertaken via WRAP funded projects

Dredged harbour sediment

Lab trials

Fine steel sludge

Lab and work trials

Ti oxide rich waste

Lab trials

Plastic residues

Lab trials

Pottery clay

Lab trials

Paper sludge

Lab trials

Paper ash

Lab trials

Figure 4. List of waste / alternative materials with the potential to be used in bricks and the progress made so far by the industry in UK. Source: (Barton 2007)

Colliery waste with waste burnt oil are an important secondary source of brick clay in Scotland. The content of CO2 in colliery waste can vary dramatically and it can range between 5 and 30%, this is creates a problem, in that the brick product can not guarantee constant quality, this product also gives off high levels of CO2 when being fired (BGA 2008).

A by-product of coal incineration, pulverised fly ash is becoming a more commonly used product for production of soft mud bricks, replacing nearly 20% of clay in the production of them.

Glass trials have proven that when used as a fine grounded material, it provides instability when firing, this in tern reduces the temperature and therefore saves energy on the firing process.

The main alternative for bricks, however, is the use of concrete blocks, these have very much taken over the use of common bricks and prove substantially cheaper to produce and build with.

C) Environmentally damaging emissions from the production of bricks

As earlier discussed, the process of producing bricks involves the release of emissions such as Carbon gases and hydrogen fluoride. The EU Emissions trading scheme came into effect 2005, this scheme's aim is to reduce the amount of carbon dioxide released into the atmosphere. The brick industry is part of this scheme, and as such, an allowance of CO2 emission have been allocated to all brickworks throughout the UK.

Carbon dioxide is produced from two areas in the production process, the fuel used to manufacture the bricks and also from the body itself, depend on the carbonate mineral content of the clay, the emission from the body maybe as high as the fuel used to fire them (Scottish Executive 2007).

The steps made to reduce the amount of carbon dioxide that is released, i.e. reducing the amount clay used, therefore, using less fuel to fire the brick, may have effects in other areas, such as the aesthetics of the bricks and also the technical properties of the end product.

With the reduction of carbon dioxide emissions in the manufacturing process affecting the properties of the final brick produced, it is a concern that the consumer may look elsewhere for the brick that they desire. This may involve the increase of importing brick from various places; an issue that this highlights is transportation of the bricks. Bricks are generally transported on road and this is unlikely to change, however, the volume of bricks transported on road compared with other materials are relatively low (Scottish Executive 2007).

Hydrogen fluoride is released into the air from heating clay at high temperatures, this is just one of the industrial process that

releases Hydrogen fluoride into air, figure 5 shows the percentage of Hydrogen Fluoride released into the atmosphere in Victoria, Australia, notably the production of clay bricks is the largest cause.

In the UK, Kilns are now subject to the monitoring and controls of the amount of Hydrogen Fluoride released.

Fig 5. Australian Fluoride emissions into atmosphere

(Source: Victoria 2007)

D) The durability of bricks

A highly durable construction material, bricks are however, not without there problems. Over time various defects can occur with bricks, most aesthetically, some more serious.

An initial problem is simply caused by the bricks getting wet, causing soluble salts are deposited on the face the brickwork. This is called Efflorescence and generally is a harmless process. Usually the process happens when new bricks are hit with rain for the first time.

Efflorescence is down to poor building design and can be avoided by incorporating overhangs and such like to avoid excessive rain on the bricks. This defect will usually disappear after the bricks have dried out a few times but can be encouraged to disappear by brushing the bricks with clean water.

Bricks can also be prone to frost attack, this is where a very wet spell is followed by extremely cold weather causing ice to form and crack the bricks.

Clay bricks have 3 classifications - (F) Frost resistant, (M) Moderately frost resistant, (N) Not frost resistant. Brickwork should be designed incorporating the correct brick classification for the area, noting the amount of saturation the area of proposed construction receives.

Another defect is called Lime Saturation; this is when calcium hydroxide is left on the bricks. This occurs when brickwork is saturated as Portland cement is setting, causing it to release lime, once this lime dries, it leaves a coating of Calcium Hydroxide. Calcium Hydroxide when exposed reacts to the Carbon Dioxide in the air and this causes Calcium Carbonate. Once Calcium Carbonate is set on the bricks, it requires specialist treatment to be removed.

In order to avoid lime staining, it is advised to protect the brickwork for a week while the mort sets.

Sulphate attack is the most serious defect, however, it effects the mortar and through the cements defect, causes problems with the brickwork. A chemical reaction causes the cement to expand, this happens when excessive amounts of water are in contact with the mortar and brickwork.

It can be avoided by protecting the bricks from excessive rainwater such as the building design, by using clay bricks with low soluble salts or high cement content mortars.

These defects stated are mainly down to the amount of rainwater that the brickwork is exposed to and will differ in each area, the defects are also encouraged due to the Portland cement that is being used. Improving the actual brick used in construction to overcome these problems may not provide a great advantage. To overcome the saturation of rain, the amount of soluble salts in the bricks material is a part solution, but this will involve the careful selection of brick manufacturer chosen throughout the country, where the brick manufacturer is a fair distance away from the construction site will intern cause excessive transport emissions.

E) Can bricks be easily re-used or recycled

More than 60% of the UK's demolition waste is recycled in one way or another (BDA 2007). As brick structure reach the end of there life cycle, depending on the quality of the brick, they can be demolished and broken up in to small, easily handled pieces, these can easily be placed in trucks and transported to be reused / recycled.

Uses of the waste material are as follows:

Concrete aggregate

Road building

Pipe trench filling

Substitute for primary quarried materials

Reusing bricks is also possible; bricks are commonly reused in practice to match building on projects in conservation areas, where, the planning restrictions detail the colour of the brick to match the existing buildings. This practice, however, is restricted to buildings that are 60+years old; this is down to the fact that these buildings were constructed using lime mortars. Lime mortars have a low strength and as such, can be easily separated from the brick.

The process of selecting, cleaning, transporting and storing the bricks for re-use does however have economic and environmental costs implications. Problems also occur where the design of building uses metric unit of measure and this bricks, due to their age are obviously to imperial measurements. It may also not be possible to guarantee the properties of the re-used bricks, for example, when selection a brick that require high frost resistance (BGS 2008).

Considering that only bricks from buildings over 60 years old and more can be easily used to rebuild new buildings, it raises a concern that this will no longer possible, by the assumption that eventually all brick buildings will have been built using Portland cement and those still standing are here to stay or are in the minority. It is therefore fair to say that, other than using old bricks for the above alternative uses (of which must be limited to the required supply of old bricks), old bricks bonded to cement will eventually become useless. This requires the improvement of technology and innovation to create a system where Portland cement can be used and then removed when the brick is to be re-used, or, an alternative bonding material that like lime is easily removable, yet, like Portland cement, creates a strong bong - a contradiction in terms but an aim none the less.

F) What effect will future developments in the construction industry have

Bricks see an uncertain future in the ever-changing construction industry. New technology and building systems are being developed in order to meet new government targets in both the planning process and building regulations.

From an aesthetics point of view, bricks won't disappear from our building facades, whether they are the bricks we know and work with today is another question.

Compared with new construction methods and materials, bricks have a relatively low insulation property (Green Spec 2010), in order to effectively insulate new dwellings when using brick construction, a method of building a cavity wall comprising off single skin brick outer leaf, a cavity and a single skin block work inner leaf, the cavity is then filled with insulation in order to achieve suitable insulation properties.

The introduction of brick cladding panels provides and alternative solution to construction dwellings in bricks and achieving a good thermal performance. The system uses thinner sections of brick which immediately indicates energy savings, this is down to the fact that by manufacturing smaller sections of brick will cut the amount of energy required to make them and will therefore require less raw materials to excavate, produce and transport.

The cladding panels are backed with insulation, the type of insulation will depend upon the amount of energy saved in the dwelling, using a highly thermal insulation will mean that heating bills are lower and the amount of energy used in the home is reduced.

The concept of brick cladding panels has been around for some time, however, its development is only minor, as emission targets become more difficult to achieve using traditional brickwork, systems such as brick cladding panels will become more popular and will appear more in common practice of construction.

G) How much fuel does the production process consume

The use of oil to produce is predominantly from the consumption of energy required to quarry the materials and the fire the bricks. The amount of energy used by the production of an individual brick ranges between 1.840 and 2.800KJ/kg (Moedinger 2005).

This is energy is produced by the consumption of fossil fuels. The forming, drying and firing stages can use natural gas and fuel oil, other solid fuels are used, also electricity and so can gas from landfills.

Development of the Percentage of Various Fuels Used (Thermal Energy)

Clay Brick & Roof-tile Industry

COAL

OIL

NATURAL GAS

1960

1975

1990

1995

2001

1960

1975

1990

1995

2001

1960

1975

1990

1995

2001

AUT

2

0

0*

20

19

15*

78

81

85*

BEL

83

4

10

4

2**

17

40

7

6

2**

0

56

83

90

96**

GER

77

5

3

3

20

76

17

15

3

19

80

82

DEN

68

11

5

4

32

89

9

9

0

0

86

87

FRA

4

15

0

56

9

5

40

76

95

ITA

0

2

0*

49

19

10*

51

79

90*

NED

49

2

2

1

51

1

1

0

0

97

97

99

ESP

30

10

0

0

50

65

71

67

20

25

29

33

UK

50

11

4

3

14

4

2

1

36

85

94

96

HUN

94

60

26

15

6

8

0

0

0

32

74

85

CH

1

0

0

63

51

47

36

49

53

Figure 6. Development of the Percentage of Various Fuels Used (Thermal Energy) Clay Brick & Roof-tile Industry. Source: (Stay with clay 2005)

Natural gas is commonly used in factories, this fuel produces less CO2 than oil when used in Kilns.

H) Are bricks renewable?

The initial material is not a renewable mineral, once out of the ground and the brick has been produced, the process to reduce it back to clay is not possible. It is therefore, important to consider other options, we have discussed the reusable possibilities of bricks and recyclable uses, and these however, don't seem to way up as potentially positive long term solution. The only way bricks will become renewable is if a economical method to take used bricks, remove the attached mortar and clean them up is implemented, this allows the initially use that bricks are created for to be continued. A concern that will rise if this is ever possible is, will the bricks lose their structural properties after each use? This is another important factor to consider and therefore another solution to be found in order to implement the renewable property of a brick.

I) Are the reserves of bricks limited?

The amount of clay brick reserves in the UK relates to the spread of the mineral throughout the country. The brick industry has and still is undergoing changes, such that companies are merging, factories have been closed due exhausting clay reserves. This however is not to say that we are 'running out'.

A survey has never been conducted to ascertain the amount of 'permitted' tonnage of reserves within the UK. "In mineral planning terms 'reserves' 'mineral reserves' or 'permitted reserves' refer to the tonnage of mineral that has a valid planning permission for mineral extraction.' (BGS 2008) Without this, no amount of material can be released and no operation may take place.

The exact amount of clay resources in the UK is actually near enough confidential due to the commercial restraints attached to the data. However, a report produced by Survey of land for mineral workings in England 2000 produced information that the land area of clay / shale was 8430ha. From this information we can assume that the reserves of clay in the UK are very high, this unfortunately does not give us an indication on the clay type or quality and therefore can be misleading.

J) Conclusion

Arguably, bricks are one of the most popular building materials available, they are common, and it is with is in mind that we can take into consideration the worldwide use of bricks, the amount of bricks produced and the amount wasted.

From the research provided, it is clear that every attempt to make this ever so popular construction material more energy efficient, by lowering its carbon emissions in extraction, production and usage means that industry want it to stick around, as shown in fig. 3, the production of Carbon dioxide has reduced from 0.000189 to 0.000180t/sq.m per year (BDA 2009 - B) over 8 years, this is a transparent example of how efforts to reduce the impact on the environment from using bricks for construction are working.

The brick itself, as discussed, requires the extraction of clay, in order for it to be produced, this raises many concerns and from the information given in fig 4, we can confirm that those issues are being addressed. New materials are being explored to mix with the clay in order to reduce the amount extracted, these findings are also proving benefits in other areas of brick production that are helpful to reducing carbon emissions, energy savings and green targets.

Bricks are here to stay, or it would initially appear, the amount of reserves can not be accurately documented but, they are still 'reserves' and this means that there is no infinite amount, so the statement of bricks are here to stay is not actually accurate, as we have explored efforts to provide solutions to re-use bricks are somewhat limited, this has an effect on the amount of bricks that are produced and the clay extracted to produce them.

In order to keep bricks around, systems to economically re-use old bricks need to be set in place, this will dramatically reduce the amount of bricks required to be produced by factories. This solution can be coupled with other attempts as explained in section f, those efforts are that to reduce the size of the brick that is required to construct a building; this will also reduce the overall production of bricks. Through these reductions, emissions will lower and so will the overall carbon footprint - in order to do this though, brick companies will take a hit as the mass productions of bricks will lower, closing factories across the country.

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