Green Concrete In Civil Construction

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Green Concrete in Civil Construction

Name

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ABSTRACT

Through the use of a survey and literature review, the paper herein investigates

various aspects of the use of green concrete in the construction industry. The study

investigates 1) the concept of green concrete and its importance in promoting

sustainability in the construction sector. 2) The status of the green concrete in the

construction industry, 3) the benefits of using green concrete as well as the barriers

from the view of the main players in the industry. Lastly, the research will provide

feedback on how the academic research materials on green concrete can be tailored to

meet the needs of the practitioners in the industry. The paper is based first on the

literature review of the previous studies of on the use of the SCM and AAs in the

production of concrete giving a special focus on how these materials affect the

properties of the concrete. The research then collects the survey results from the

concrete dealers, suppliers, manufactures, and analysis is performed based on the

current use of green materials in the production of concrete. The research also

compares the data on the use of green concrete in the United Kingdom and the United

States. Lastly, the future of the green concrete is also considered with a specific focus

on the future of the material in the next five years to come.

New Words and Abbreviations

SCM’s – Supplementary Cementing Materials

AA’s – Alternative Aggregate

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Contents

ABSTRACT ..................................................................................................................... 2

CHAPTER 1 .................................................................................................................... 5

1.1 Introduction ............................................................................................................ 5

1.2 Research Focus ..................................................................................................... 8

1.3 Aims and Objectives of the Research .................................................................... 9

1.4 Significance of the Research ................................................................................. 9

1.5 Background of the Research .................................................................................. 9

1.5.1 Sustainability in Concrete Production .............................................................. 9

1.5.2 Properties of Green Concrete ........................................................................ 10

1.5.3 Potential barriers to the use of Green Concrete ............................................. 11

CHAPTER 2 .................................................................................................................. 12

Literature Review .......................................................................................................... 12

2.1 Introduction .......................................................................................................... 12

2.2 Case studies on the Durability of Concretes with Supplementary Materials under

Various Conditions ..................................................................................................... 21

2.3 Factors that influence the durability of concrete under Various Conditions .......... 15

2.4 Carbon content of fly ash ..................................................................................... 23

2.5 Maturity method ................................................................................................... 24

2.6 Water Ingress in Concrete ................................................................................... 25

CHAPTER 3 .................................................................................................................. 28

Research Methodology ................................................................................................. 28

3.1 Introduction .......................................................................................................... 28

3.2 Research Sample Design .................................................................................... 29

CHAPTER 4 .................................................................................................................. 30

Results and Discussion ................................................................................................. 30

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4.1 Introduction .......................................................................................................... 30

4.2 Background information about survey participants .............................................. 30

4.3 The use of SCMs ................................................................................................. 31

4.4 The use of AAs .................................................................................................... 38

CHAPTER 5 .................................................................................................................. 43

Conclusions and Recommendations ............................................................................. 43

5.1 Important Conclusions from the Literature Material ............................................. 43

5.2 Conclusion from the Survey ................................................................................. 44

References .................................................................................................................... 47

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CHAPTER 1

1.1 Introduction

The construction industry has been booming for many years now, and it is still

expected to continue growing at higher rates in the coming years. Concrete is the most

common material in the construction industry due to its various characteristics. Concrete

is also the world’s most commonly used material due to its outstanding durability,

availability, and strength (Naik, 2008). Concrete is the most used material in the world,

and as the population of the world continues to increase, its use is expected to continue

increasing. However, the production of concrete has been considered as unfriendly to

the environment, and various concerns have been raised about the carbon emission

associated with the production of the material as noted by (Glavind and Munch-

Petersen, 2000).

The traditionally mixed concrete is considered as a significant contributor to the

production of the greenhouse gases and may pose a significant threat to the global

climatic change as a result of the effect of the greenhouse gases (Glavind and Munch-

Petersen, 2000). The production and use of the ready-mixed concrete contribute large

amounts of carbon footprints in the construction industry due to various reasons. One,

the production of cement and concrete involves consumption of large amounts of

energy and the transportation of the building materials also contributes significantly to

the amount of carbon emitted to the environment. The recent unfolding on the

international organizations raising concerns about the climate change as a result of

global warming has created awareness about sustainable production and practices in

many industries, and the construction industry is not an exception.

The construction industry has been forced to implement sustainable practices by

adopting various ways of reducing the amount of emission as a result of construction

activities (Johari, Zeyad, Bunnori and Ariffin, 2012). One of the ways of promoting

sustainability in the construction industry is through the adoption of the production and

use of the green concrete. The use of green concrete aims at reusing waste materials,

reducing the amount of emission of dust and reducing the amount of energy consumed

in the production of new concrete.

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Green-concrete has nothing to do with color, and it is a concept that refers to the

use of eco-friendly materials in concrete. The main aim of green concrete is to make the

system more sustainable and to reduce the effects of the construction activities on the

environment. Green concrete has various advantages regarding sustainability which

include its use of waste materials as the main source of raw materials for making the

concrete (Flower and Sanjayan, 2007). The advantages of green-concrete include being

cheap to produce, it uses waste products as a partial substitute for cement, there is a

significant reduction in the charges of waste materials disposal, the consumption of

energy is significantly reduced, and also its durability is great. The diagram below gives

a summary definition of the green technology.

Fig. 1: Definition of Green Technology (Krishnan, 2014)

The traditional production of concrete mainly relies on the use of natural

resources which are now in the danger of depletion and extinction as the world’s

construction industry continues to grow and the demand for concrete continues to rise

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exponentially (Flower and Sanjayan, 2007). To reduce the use of natural resources,

waste materials can be used to produce the new products so that the use of natural

resources is limited to specific cases and also to protect the environment against huge

waste deposits. When a demolition is done, various materials are produced which fall

into different categories; there are the inorganic materials such as stones dust, marble

waste, crushed concrete, which are then used as green aggregates in the production of

green concrete. The use of cement can also be replaced by the use of other binding

materials such as fly ash, silica to help in developing new green binding compounds

which are more sustainable than cement. Improving cement promotes the use of

materials with low energy consumption and hence offers a better solution for the

production of building materials which are highly sustainable (Hameed and Sekar,

2009). There is considerable research that has been conducted on the use of other

industrial byproducts and fillers on concrete to supplement the use of concrete. The

main concern of using these materials was not only to make the concrete cost effective

but also to improve its quality which includes improving its durability.

The demand for concrete is high across the world, and if the quest for obtaining

sustainability is pushed, business will not be as usual in the global construction industry

as the production of the traditional concrete and cement will have to be reduced to its

minimum level possible (Mehta, 2002). The move is an attempt to respond to the

pressure to improve sustainability in the construction sector. It is unlikely that there is no

any technological approach that will be able to provide the savings that would be

required in the construction industry by 2050. Therefore, the green concrete approach

was created as one of the most sustainable ways of supplying the construction industry

with the materials that are required as it promotes environmental conservation as well.

However, despite the fact that the sustainability of concrete can be increased by

recycling waste materials, the addition of other binders such as the supplementary

cementitious materials and the AAs can have a significant impact on the main

properties of the concrete such as its compressive strength and workability (Mehta,

2002). The strength properties and the workability of the concrete are important

characteristics that determine its use and application in the building industry. Also, the

production of concrete using the waste materials may not be sustainable unless the

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durability of the concrete can be confirmed. Various researchers have done a lot of work

in identifying the waste materials that can be used as potential SCMs and AAs in the

production of green concrete and they each one of them has presented different ideas

(Mehta, 2002). Also, one of the main points of concern about these findings is the

conflicting arguments that are presented by these researchers. For example, various

researchers have identified material such as fly ash, pozzolans, and blast-furnace slag

as potential materials that can be used as slag in the production of the green concrete.

Various waste materials that could be used as potential aggregates have also

been explored through experiments and research and their properties have been tested.

However, despite the presence of significant research regarding the use of waste

materials in the production of green concrete, there is still a wide gap between the

industrial practice and the academic research materials as presented by the various

researchers. For instance, in some cases the materials studied through academic

research and recommended for use may have various restrictions that affect their

application in the construction industry and also makes it difficult to rely only on the

academic findings. One of the main examples that have been cited to possess

conflicting information is the use of recycled aggregates from demolitions as raw

materials for the production of sustainable concrete. The research on recycling

aggregates seems promising, but the quality of the recycled material must be proved

before it can be considered fir for use. Low-quality materials could affect the workability

and the compressive forces of the concrete hence affecting its suitability as far as its

use is concerned.

1.2 Research Focus

The research herein focuses on the use of green concrete in the world today to

promote sustainability in the production of concrete as well as to promote environmental

conservation by reducing the number of carbon emissions into the atmosphere. The

research reviews literature related to the current state of green concrete, where they are

used and the plans of using the green concrete in the construction industry.

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1.3 Aims and Objectives of the Research

The research herein seeks to examine how the green concrete concept has been

applied in the construction industries putting special focus on the benefits of green

concrete and the barriers of using green concrete. The following are the important aims

and objectives of the research;

1. To find out the current status of green concrete in the construction industry in

UK and USA.

2. To collect data on the benefits of using green concrete in the construction

industry.

3. To find out the main barriers that affect the use of green concrete in the

concrete production industry.

4. To find out the future of green concrete in the concrete industry.

1.4 Significance of the Research

The research herein seeks to find out how the concept of the green concrete has

shaped the concrete production industry. The results of this research will be useful in

determining the role of the concrete production industry in promoting sustainability in the

construction industry as well as helping in conserving the natural resources from threats

of depletion. The results will also identify the future of green concrete as well as the role

of academic research in shaping the industry.

1.5 Background of the Research

Under this section, the potential benefits of using green concrete are discussed

as well as the barriers that can affect the use of green concrete to promote sustainability

in the construction industry. The findings are based on previous research to determine

the use of green concrete. It also involves the review of the mechanical strength of the

green concrete as well as how the forces can affect its use in various cases during the

construction works.

1.5.1 Sustainability in Concrete Production

As already mentioned in the introduction to this research, the use of concrete

around the globe has been going up raising the questions of its sustainability. It is

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estimated that about 8.4 billion cubic yards of concrete was used in 1997 twenty years

from now and the amount has been increasing over the years with the number expected

to increase about one hundred times in 2050 (Nielsen and Glavind, 2007). The United

States concrete production doubled between the early 1990s and 2004 from the initial

220 million cubic yards to 430 million yards (Nielsen and Glavind, 2007).

The production of concrete consumes large amounts of energy and also has

significant negative effects on the environment. For example, the cement industry alone

is estimated to be contributing to about 7% of the total carbon emission into the

atmosphere hence being one of the major industries that contribute to the addition of

the GHG into the atmosphere (Nielsen and Glavind, 2007). Also, based on the findings

from research, it is technically impossible to reduce the amount of energy required to

produce concrete below the current 3.79 Million Btu per ton requirement. Therefore, an

alternative approach to the production of concrete should be explored to promote the

sustainability of the concrete production.

The use of the SCMs and other identified waste materials in the production of

concrete will help save the excessive use of energy, protect the environment and also

conserve the natural resources. For instance, replacing only twenty-five percent of the

amount of cement in the production of concrete with the SCM and waste materials could

save the United States about one billion dollars every year. Also, about one percent of

the replacement of cement with fly ash resulted in about 0.7% reduction in the amount

of energy consumed during the production of cement (Naik, 2008).

1.5.2 Properties of Green Concrete

The use of green materials such as the waste materials, the SCMs and the AAs

have been studied in the United States, the United Kingdom and other parts of the world

to find out the effects of the materials on the properties of the resulting concrete. Fly

ash, furnace slag, and silica fumes are among the common SCMs that have been

studied on how they can be used in the production of concrete and their effect on the

properties of the resulting material (Hameed and Sekar, 2009). Other researchers have

also presented their works on some of the AAs such as rubber, building rubbles, waste

glass, oyster shell and other waste materials. Most of the results from the experiments

showed that the effect on the property of the concrete depended on the type of the

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material used and the percentage of replacement. The properties of the resulting

concrete may be positively impacted or negatively affected depending on the amount of

the SCMs added or used. Higher amounts of fly ash for example used in the mix

affected the compressive strength of the mix negatively, and an addition of about 30%

of the RCA reduced the concrete strength by a significant percentage (Hameed and

Sekar, 2009).

1.5.3 Potential barriers to the use of Green Concrete

Despite the numerous potential benefits that can be accrued from the use of

green concrete, many barriers are likely to affect its adoption in the construction

industry. The main barriers to using AAs and SCMs in the production of green concrete

lies the concrete properties, its cost-effectiveness and the general perception of the

industry that affects its use in the construction sector.

Cost Effectiveness

One of the major considerations in the choice of materials in any industry is its

cost-effectiveness as co pared to the other alternative materials. Therefore, the main

determining factor that is likely to affect the application of the green concrete into the

industry is its cost-effectiveness. For instance, the recycling and reuse of the waste

materials to produce the concrete require extra labor which adds cost to the whole

process (Glavind and Munch-Petersen, 2000). Additional energy is also required for the

sorting and recycling of the waste materials to incorporate them in the production of the

green concrete. For example, it is important to compare the cost involved in obtaining,

sorting and crushing the wastes to the cost of obtaining the virgin aggregates so that a

cost justification for the use of the green concrete can be made (Johari, Zeyad, Bunnori

and Ariffin, 2012). The cost of transportation of the waste materials from the demolition

sites should also be compared with the cost of transportation of the virgin aggregates to

ensure that one does not introduce an extra cost while using the green concrete.

Concrete Properties

The properties of concrete are the main reasons why the material is widely used

in the construction industry. The use of various materials as ingredients in the

production of concrete can either improve or affect its properties negatively depend on

the type of the material as well as the amount added (Johari, Zeyad, Bunnori and Ariffin,

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2012). For example, several experimental models of research have shown that using

waste streams as concrete ingredients can help in improving some types of concrete

properties while undermining others. For example, the user of oyster shell in the

production of the concrete improves its compressive strength but reduces its workability

(Johari, Zeyad, Bunnori and Ariffin, 2012). Also, when using glass in concrete, it

essential to take into account the likely chemical reaction between the silica-rich glass

and the alkali which may as well have a severe effect on the properties of the resulting

concrete product. Also using plastic aggregates also reduced the tensile and the

compressive strengths of the resulting concrete. Another critical concern is the lack of

the supporting quantitative data on the properties of using waste materials.

CHAPTER 2

Literature Review

2.1 Introduction

For the cement and the concrete industry to remain sustainable and efficiently

contribute to the reduction of carbon from the atmosphere, then alternative materials

must be incorporated in the production of concrete (Sakthivel, Ramya, and Raja, 2013).

The additional materials can include the use of waste materials, using less carbon-

intensive fuels, using materials with cementitious properties and minimizing the energy

consumption during the production of cement. The green concrete concept, therefore,

refers to the process by which waste materials and other environmentally friendly

materials are incorporated in the production of concrete (Sakthivel, Ramya, and Raja,

2013). The green concrete concept covers all the practices involved in reducing the

amount of environmental harm caused by the use and production of cement and

concrete. The green concrete concept covers things like use of carbon-reducing

cement, reducing energy consumption during the production of cement, embracing the

use of waste materials in the production of cement among other methods.

According to Mehta (2004), concrete refers to the mixture of coarse aggregates,

fine aggregate and cement or a binder. The coarse aggregates often consist of the

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crushed rock while the fine aggregates include sand. When the mixture is mixed with

the required quantity of water, it forms an initial fluid phase that can be modified into

shapes or cast and allowed to set to produce a strong, rigid concrete solid structure or

element (Ekins, 2002). The green concrete concept aims at replacing the ordinary

Portland cement with alternative binders as well as replacing the ordinary components

of the concrete with other materials such as waste from demolished buildings.

Therefore, in finding a suitable replacement for the cement, a thorough investigation is

required to determine the cost-effectiveness and the effect of the material on the

mechanical properties of the material.

The alternative green materials being used in the production of the concrete must

meet at least three conditions before they can be considered as potential replacements

for the conventional concrete. First, the materials must be usable and able to work well

both in long and short terms (Duxson, Provis, Lukey and Van Deventer, 2007). The

second condition that the alternative materials must meet is that there must be enough

information proving the capability of the product in meeting the engineering standards

for the specified functions. The last condition for the alternative material is that it must

be locally available in large quantities to be able to meet the large demands of the

concrete production as well as the construction industry (Bisby, Green, and Kodur,

2005). Many materials can be used for the manufacturing of cement, but the above

conditions must be met to make the materials applicable in the production of concrete.

On an engineering point of view, the materials must be selected based on their

additional functionality and their cost-effectiveness. The approach used by the above

researchers by looking at the materials in terms of their cost-effectiveness and

functionality is important as it will help in justifying why green concrete is a better option.

According to Johari, Zeyad, Bunnori, and Ariffin (2012), supplementary materials

like slag, silica fume, and fly are beneficial supplements in the production of concrete.

The supplements have known properties of improving the strength of the concrete due

to its pozzolanic reaction and increased permeability due to the reduction in porosity of

the microstructures (Johari, Zeyad, Bunnori, N.M. and Ariffin, 2012). Improved strength

and permeability reduce the ingression of water and harmful salt solutions. Additionally,

the production cost could be reduced significantly if the mentioned supplements were to

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be used to produce concrete. The pozzolanic reaction that takes place when mineral

mixtures are added to the concrete composition starts in a week’s time. The pozzolanic

reaction causes a subsequent increase in amounts of C-S-H gel that is the main

strengthening component in concrete (Bisby, Green, and Kodur, 2005). Research

shows that slag combined with fly ash improves the overall strength of concrete

throughout as well as silica fume addition. Construction industries today have

developed the culture of using supplementary materials in building concrete for

durability purposes. Plain concrete without any supplements, when used in building

infrastructures such as dams, are susceptible to thermal cracking due to the high heat

of hydration (Sata, Jaturapitakkul, and Kiattikomol, 2004). When supplementary

materials are used, risks associated with the high heat of hydration are reduced

because the subsequent rise in temperature is reduced in direct proportion to replaced

cement (Bisby, Green, and Kodur, 2005). Pore refinement caused by the use of

supplements like slag and fly ashes make the concrete more durable to chemical

attacks. Experiments conducted on cement paste comprising of low quantities of fly ash

show that pore refinement occurred within a period of twenty-eight to thirty days of the

curing period.

Despite being good supplements, slag or fly ash make the concrete gain strength

slowly in initial stages. Carbon present in fly ash is likely to provide unstable air void

systems. The above concerns are likely to affect concrete resistance to salt scaling and

freeze-thaw effects. ACI Committee 201 on concrete durability has stipulated

guidelines to help produce durable concrete that can withstand freezing conditions. The

stipulated guidelines include adequate compressive strength before freezing, a period of

air drying before freezing and adequate air entrainment (Aı

tcin, 2000). When class C fly

ash was included in concrete at a ratio of one to twenty-five, the concrete that was

produced was of low compressive strength and split as early as seven days. After seven

days, concrete containing class C fly ash was of high compressive strength when

compared to the earlier on manufactured reference concrete. Studies show that

replacing cement with thirty percent of slag or fly ash may help in attaining long-lasting

durability in frost conditions (Sata, Jaturapitakkul, and Kiattikomol, 2004). Concrete has

a higher water to binder ratio is likely to encounter more problems relating to internal

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micro-cracking and salt scaling because of the freeze and thaw reactions. High carbon

content in fly ash interferes with the air entraining agents in concrete. However,

researchers reveal that adequate spacing and sufficient air circulation in the concrete

cancels out the problems caused by high carbon content in fly ash.

Wang and Pan (2014) reports that the method used to measure air content using

pressure recorded lower volumes of air compared to that recorded using microscopic

analysis. The main reason behind the observation made was an increased amount of

internal bubble pressure that accompanied reduced bubble diameter. When an error

was calculated between the meter reading and actual air content, air bubbles that were

smaller than ten micrometers were found to be significant while air bubbles that were

greater than fifty micrometers were insignificant (Nehdi, Mindess, and Aïtcin, 1996).

Practically, air bubbles less than ten micrometers cannot occur in concrete. The main

reason behind the theory is that concrete has high internal pressures that would

automatically force air bubbles with small diameters to dissolve (Nehdi, Mindess, and

Aïtcin, 1996). However, finer cement has reduced capillary pore that is likely to improve

the durability of concrete. Cement with high alkali content has an increased scaling

resistance. Regardless of the content of lime in fly ash, a durable fly ash concrete could

be produced using specific spacing values and air void sizes. High volume fly ash

concrete containing fly ash exceeding fifty percent as a replacement is produced when

fly ash is inter-ground with cement or simultaneously incorporated in a mixer as

materials having different batches (Wang and Pan, 2014). The blended high-volume fly

ash is improved in all properties to include much durability in freeze-thaw condition

resistance and mechanical resistance. However, there was no resistance to deicing

salts in comparison to concrete that was made by separately mixing fly ash and cement.

High volume fly ash concrete has additional advantages of improving the strength and

penetration of ion chloride. Therefore, fly ash can be considered as a potential green

concrete material that can be used as a binding substance.

2.3 Factors that influence the durability of concrete under Various Conditions

Many critical factors influence the durability of concrete when exposed to various

weather conditions. The durability of the concrete refers to its ability to resist corrosion

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from various factors such as extreme weather conditions, weight, chemical and physical

conditions. The following pictures show the failure of concrete under various conditions.

Fig. 2: Bridge falling as a result of concrete failure under moist environments and

varying loads (Factors Affecting Durability of Concrete, 2016)

The factors are discussed below in understandable subsections.

Strength, slump, and cementitious material content

Many researchers have studied the nature of concrete and finally came up with

measures that are likely to make concrete more durable to freeze-thaw effects together

with salt scaling. In cases of severe exposures, the best recommendation for air-

entrained concrete was that they have the strength that ranged from 3500-4500 psi

(Gao, Sun, and Morino, 1997). Additionally, it was advisable that the water to cement

ratio does not exceed 0.45 and as well as the slump that was not to exceed 3.5 inches

(Gao, Sun, and Morino, 1997). Another recommendation was about finishing that was

considered critical because excessive laitance was most vulnerable to frost action more

so when de-icing salts were present.

Micro-structural investigations of concrete, when subjected to salt scaling,

indicate higher porosity in surface areas when compared to the bulky part of the

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concrete. When the slump is high, it may lead to high amounts of bleed water on upper

surfaces hence rendering the top surface vulnerable to damage because of the deicer

salts (Nilson and Martinez, 1986). Higher compressive strength is fundamental in

enhancing scaling resistance of concrete. Average compressive strengths for concrete

mixtures that contained Class C fly ash, Class F fly ash, and plain cement was recorded

as 4460 psi, 3500 psi and 4910 respectively when cured at a temperature of 4.4

degrees Celsius (Aslam, Shafigh and Jumaat, 2017). With increasing compressive

strengths, resistance to deicer scaling also improves entirely. Cementitious material

present in Class F and Class C mixtures were more compared to the cementitious

material that was present in plain cement mixtures. Recommendations are made that

when the minimum cementitious material is used together with maximum water, then a

ratio of 0.45 should be used to attain satisfying performances in case concrete was to

be subjected to the deicer salts (Aslam, Shafigh, and Jumaat, 2017). For example, the

diagram below shows a picture of a chemically eroded concrete structure.

Fig. 3: Concrete decay under Chemical conditions (The Constructor, n.d)

The rate of freezing and Concrete Strength

The freezing rate is an important factor used to specify the durability of concrete

to freeze-thaw conditions. The higher the freezing rate, the lower the spacing factor

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used in building concrete. When preparing concrete, the ratio of water to cement should

be between 0.5 and 0.6 according to the universal spacing factor of 250 micrometers,

for specified freezing rates which are 11 degrees Celsius per hour (Korolev and

Inozemtcev, 2013). Different mixtures of concrete have a constant water to cement ratio

of 0.5 if subjected to various spacing factors during the curing periods. Critical spacing

factors depending on the freezing rate of the concrete were originated from changes in

length measurements that were conducted once three hundred cycles were completed

(Moreno, Zunino, Paul and Lopez, 2014). The critical spacing factors were observed to

reduce whenever freezing rates were increased from two to six degrees Celsius per

hour. Concretes that had spacing factors of 250 to 300 micrometers was likely to resist

300 cycles of freeze-thaw conditions in water when the rate of freezing was 8 degrees

Celsius per hour (Korolev and Inozemtcev, 2013). The test results indicated that the

obtained test results from ASTM C666 procedure B where there was thawing in water

and freezing in the air were similar to the test results obtained from procedure A where

freezing and thawing occurred in water. However, the concrete that froze in water

underwent surface scaling after undergoing three hundred cycles, but those that froze in

the air did not undergo surface scaling.

Stable air-void system

Research shows that a proper air void spacing is the most valuable factor used

to determine the resistance of concrete to freeze-thaw conditions. When the air voids

are packed close to one another, the surrounding paste of cement does not expand

when freezing occurs hence preventing the formation of cracks in the concrete (Korolev

and Inozemtcev, 2013). The critical spacing factor of a given concrete is defined as the

value of which concrete cannot be damaged due to internal cracking in case it is

subjected to freeze-thaw cycle test. When the concrete has water to cement ratio of 0.3

and is exposed to freeze-thaw actions, then the observation made is that the critical

spacing factor is 300 micrometers for the condensed silica and 400 micrometers for the

plain cement concrete (Korolev and Inozemtcev, 2013). Fly ash has organic matter

content that significantly affects how fresh concrete retains air voids.

Loss on ignition of fly ash and the total amount of carbon in the fly ash show little

correlation to how fresh concrete retains air in comparison to organic matter content.

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Class C fly ash has greater retention power of entrained air compared to Class F fly

ash. Concretes that were air entrained in the presence or absence of fly ash were good

resistors when freezing, and thawing occurred in moist conditions during curing under

temperatures of 23 degrees Celsius (Korolev and Inozemtcev, 2013). Concrete made

with Class F fly ash, however, shows low resistance in comparison to concrete made

with class C fly ash when the concrete is curing under low temperatures. Apart from the

200 micrometers that are the spacing factor used to measure durability, field concrete is

believed to be durable too as it has an air content of 5-8 percent. Assumptions are

always made that concrete that contains air content of six percent has the spacing

factor as 200 micrometers. Consequently, concrete that has the air content as high as

nine percent and low as four percent has a spacing factor of 200 micrometers (Moreno,

Zunino, Paul and Lopez, 2014). Thus, it is advisable that one specifies the critical

spacing factor value of concrete when it is being produced under cold weather

conditions as proposed by Moreno, Zunino, Paul, and Lopez, (2014). It is therefore

important that one specifies the critical spacing factor value instead of entirely relying on

the value of air content the way it is always done in field constructions. The following

graphs shows the effects of calcium salts on air-void structure in air-entrained concrete.

Fig. 4: The effect of calcium salts on air-void structure in air-entrained concrete (Ge, Li

& Zhang, 2015)

Curing

The main purpose of the curing process is to reduce the permeability of concrete.

Concrete that contains supplementary materials depends on the curing process

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because of the increased levels of cement replacement. Experiments conducted to

determine the resistance of frost to none air entrained high strength concrete that

contains silica fumes showcase various shortcomings of ASTM C666 thus

recommending a curing process that only lasts for fourteen days when exposed to

freeze-thaw cycles (Moreno, Zunino, Paul and Lopez, 2014). Silica fumes together with

other pozzolanic materials require much time to hydrate and desiccate so that the

amount of freezable water is reduced. Concrete that contained fifty percent fly ash had

little compressive strength and therefore has to undergo intense curing process. The fly

ash concretes permitted less oxygen in comparison to OPC concretes with similar

strength levels irrespective of the type of curing method applied. Researchers

suggested that the durability of concrete could best be extended by increasing the

amount of time used for moist curing as opposed to increasing the amount of cement in

the concrete (Moreno, Zunino, Paul and Lopez, 2014). Amounts of scaling residues

reduced significantly when moist curing was replaced with membrane curing. When

curing compounds were used, it resulted in a scaling resistance that was similar to that

experienced when concrete was moist cured for fourteen days (Wang, Yu, LI, and

WANG, 2014). The results obtained however varied depending on the type of

compound that was used for curing. Curing of the specimen using accelerated heat

negatively influenced scaling resistance.

Degree of hydration

The degree of hydration is an essential factor that should be considered when

determining the amount of internal water that is present in a paste mixture. The

information obtained could be important in predicting the performance in same concrete

mixtures in various areas. In binary systems that contain both fly ash and cement, it is

essential that one determines the reaction of fly ash products besides that of hydration

products. Fly ash reaction is determined using selective dissolution procedures (Wang,

Yu, LI, and WANG, 2014). HVFA pastes that contain forty-five to fifty-five percent fly

ashes have a remainder of eighty percent fly ash that did not react. Non- evaporable

contents of water in fly ash paste should be lower than that of plain cement paste at that

particular water to binder ratio (Wang, Yu, LI, and WANG, 2014). Hydration rates are

always greater in silica fume pastes, the second one being OPC pastes then the third is

Page 21 of 50

fly ash paste. The degree of reaction of silica fumes is greater than that of fly ash paste

because the fumes have higher specific area and its reaction with Class C fly ash is

greater compared to that of Class F fly ash after some days. XRD patterns show the

similarities between OPC hydration products with fly ash and slag. However, slag has

the best pozzolanic activity compared to fly ash. When fly ash is hydrated, it causes

densification of microstructures as shown in SEM studies (Korolev and Inozemtcev,

2013). SEM studies show glassy materials etching around ash after twenty-eight days.

The deposits on the fractured surface comprise of toroidal, round plates that has same

compositions as C-S-H. The readings considered under this section covered the

specific factors that affect the durability of concrete under various weather conditions.

The section also offers important information for this research that will form the

background in which the usage of green concrete can be justified.

2.2 Case studies on the Durability of Concretes with Supplementary Materials

under Various Conditions

Concrete is likely to undergo two forms of damages when exposed to cold

weather conditions. The damages include internal cracking experienced as a result of

freeze-thaw actions and secondly, surface scaling caused due to the presence of deicer

salts (Chen and Liu, 2008). Under this section, we are going to discuss the results

obtained from other selected case studies. Various ternary and binary blends as tested

in studies conducted in Virginia Department of Transportation show that when the

components were combined, durability was achieved after exposure to three hundred

cycles of freeze-thaw action. However, only one binary blend showed a mass loss that

exceeded seven percent (Chen and Liu, 2008). Findings showed that concrete mixtures

that were properly air entrained and constituted of forty percent Class F fly ash and fifty

percent Class C fly ash were the best in resisting freeze-thaw conditions. The class F fly

ash showed less scaling than Class C when exposed to the fifty cycles of freeze-thaw

conditions. It would, therefore, be more effective if Class F fly ash was used to improve

resistance to the penetration of chloride instead of Class C ash (Li, Yao, and Wang,

2009). Strength and water to binder ratio cannot be used to determine if concrete that

contains fly ash is resistant to scaling effects. During the curing process under a specific

temperature, the concrete that exhibited the best scaling resistance was the one that

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was not combined with Fly ash. Poor resistance to scaling was observed in concrete

that had fifty percent of fly ash.

The four fly ash mixtures that were used in testing showed the worst ratings

about scaling resistance after five or ten cycles of exposure to freeze-thaw conditions.

An observation was also made that, when superplasticizer was added to the concrete, it

resulted to increased spacing between the concrete hence reducing its durability (Zhang

and Gjvorv, 1991). Additionally, increasing the period of curing does not guarantee that

the concrete will be more resistant to the frosting. When thirty-five to fifty percent of fly

ash were incorporated in concrete, resistance to frost was not significant despite being

subjected to a curing period that lasted for eighty days. However, twenty percent of fly

ash when incorporated into concrete would lead to higher performance levels regarding

durability that in most cases exceeded sixty percent (Zhang and Gjvorv, 1991). Thirty

percent fly ash incorporated into concrete resulted in fewer performance levels with a

durability factor that was ranging from forty to sixty percent. Authors found SEM

micrographs that showed how the decrease in freeze and thaw resistance was as a

result of slow microcrystalline displacement and fibrous hydrates originating from the

dense C-S-H region. Blended silica fume cement concrete formed a curing compound

with scaled off particles weighing two kilograms per square meter (Zhang and Gjvorv,

1991). Adding slag or fly ash to concrete leads to poor scaling resistance in comparison

to a blend of silica fume cement. Test results indicate that the surface layer of concrete

normally has high porosity levels hence resulting in the reduction of scaling resistance

to deicer salt (Zhang and Gjvorv, 1991).

Microstructural investigations show that higher porosity levels experienced at the

top layers are opposed to the bulk nature of concrete. Despite having slow reaction

rates, forty percent of fly ash mixtures show good resistance to scaling. The scaled

particles for the mixture weighed 0.02 kilograms per square meter after being

introduced to ten cycles of freeze-thaw conditions. The above research was primarily

based on the maximum limit of scaling that was one kilogram per square meter

according to the Swedish standards. During the first ten cycles, it is believed that the

mass of scaled particles also increases depending on the amount of fly ash added.

During the ten cycles, the duration of bleeding and amount of bleed water on the

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surface of the concrete also increased hence leading to increased porosity on the

surface. Increasing the ratio of water to binder simultaneously increases the amount of

scaling. A lot of variabilities were observed in the scaling test results conducted on fly

ash concrete. When fly ash was used to replace cement in the production of concrete,

an increased amount was scaling. Majority of the tested mixtures exhibited good scaling

resistance when observed after three days of the moist curing process. Various factors

including environmental factors affect the strength of concrete. The case studies gives

an account of how these factors affect the properties of the various green concrete

elements. The researchers give an important analysis that is helpful for this research in

identifying some of the factors that may affect the usage of green concrete in the

construction industry.

2.4 Carbon content of fly ash

Concrete that contains fly ash is likely to be durable to freeze-thaw effects when

the system is stable and air void. The carbon that is present in fly ash is reported to be

the main reason entraining air agent has reduced its effectiveness. For the carbon

content to be doubled, the air entraining mixture also had to be doubled. In the findings,

it was revealed that as long as the air contents required were obtained then the amount

of carbon in the fly ash was not going to affect the performance of fly ash concrete when

subjected to freeze-thaw effects. The carbon content in the fly ash also contributes on

its ability to withstand extreme temperatures. The figure below shows the effect of fly

ash on the rate of temperature rise.

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Fig. 5: Optimizing the use of fly ash in concrete (Thomas, n.d)

2.5 Maturity method

In production of concrete, it is important to know the in-place strength of concrete

so that construction schedules can be planned in advance and later on executed so that

maximum benefits can be plowed. The maturity technique uses the collected history of

temperature during a particular curing period to find the equivalent age that is required

to attain desired levels of strength under different temperature conditions. Maturity

techniques have been used in many areas, and an example is in pavement construction

where a specific tool is used to determine the strength of the concrete (Wang, Rhee,

Wang, Y. and Xi, 2014). When the tests have been conducted it becomes a useful

source of information that is used in making decisions about the time required for curing

before a pavement is opened for use after construction.

Some of the devices that are used to measure the temperature of concrete

include sensors like thermistors or thermocouples that are inserted to constructed

concrete to desired depths. An instrument called the data logger that stores temperature

data is used to collect temperature measurements (Wang, Rhee, Wang, Y. and Xi,

2014). After that, the instructions are transferred using a software code that transmits

the instructions in intervals like those recorded when collecting temperature readings.

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Under isothermal curing conditions, the amount of strength gained by concrete can be

described through a hyperbolic curve that has three parameters. The three parameters

include the long-term limiting strength, the rate constant and the age when the rapid

development of strength begins.

Another important parameter that should not be forgotten is the activation

energy. Activation energy is the energy that is required for initiating a reaction (Wang,

Rhee, Wang, Y. and Xi, 2014). Activation energy can also be described as the minimum

energy that is required to form an active complex when reactants collude. Activation

energy is related to Arrhenius function through the rate constant which accounts for the

influence of temperature differences on gained strength (Sata, Jaturapitakkul, and

Kiattikomol, 2004). The maturity method has been accurately used to monitor and

predict gained strength of rapid concrete pavements repairs during curing periods.

Predictions using maturity methods, however, are likely to underestimate strength

gained at early stages. The initial and final set time for any mixture can be predicted

provided activation energy is acquired. The temperatures used in early stages of curing

greatly influences the ultimate strength of produced concrete (Sata, Jaturapitakkul, and

Kiattikomol, 2004). To acquire equal levels of maturity, specimens that were exposed to

low temperatures at an early age were weaker during early maturities but became

stronger later on in the maturity process. Researchers also highlighted the crossover

effect whereby low curing temperatures at early stages resulted to high ultimate

strengths. The authors highlight the effect of cooling temperature during curing and how

it can affect the properties of the concrete. The maturity method gives a perfect

description of how the cooling temperature must be considered when developing green

concrete. The concept is important in the development of green concrete as it may be

used as one of the key tests to determine how environmental factors can affect the

properties of concrete.

2.6 Water Ingress in Concrete

The resistance of concrete to ingress by water or corrosive salts depends on the

permeability of the system. Denser microstructures of concrete also reduce the

absorption of water apart from only ensuring that there is less ingress of harmful salts.

Reducing water absorption means that the durability of concrete is improved in freeze-

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thaw conditions (Du Plooy, Villain, Lopes, Ihamouten, Dérobert and Thauvin, 2015). A

lot of money is spent yearly towards the rehabilitation of bridge decks that often

deteriorate over some time when the steel used for reinforcing is corroded. When air

voids are filled up with water, scaling of virgin concrete dramatically increases. When a

system is unsaturated, water flows within porous media under capillary action then

becomes dependent on the material’s pore structure. Capillary action is, therefore, the

strongest force that can be used when the material that is being used is dehydrated and

reduces under saturated conditions (Du Plooy, Villain, Lopes, Ihamouten, Dérobert and

Thauvin, 2015). In concrete, the absorption of water can be influenced by how porous

the aggregate is, the porosity of the cement gel matrix, the packing measurements of

constituent elements like course aggregate, sand and rarely due to the inclusion of air

entraining added mixtures (Ho et al., 2015). Concrete becomes highly permeable due to

poor compaction practices or when the ratio of water to cement is higher.

The high permeability of concrete could also occur when supplementary

materials are not included in the mixture. When supplementary materials are added in

the concrete mixture porosity is refined and reduced. Cumulative absorptions and the

rate of ingress of water in concrete is determined by the sorptivity test that uses the

theory of capillary action. In the sorptivity test, the depth of water penetration is usually

proportional to the square root of time hence making it an important test that can be

used to further study on the quality of concrete surfaces when subjected to dry and wet

cycling phases (Ho et al., 2015). Researchers found that when concrete containing a

mixture of forty percent fly ash was adequately cured, and then sorptivity was likely to

reduce by thirty-seven percent. Under fog cured conditions, the sorptivity of concrete

mixed with fly ash was lower than the sorptivity of OPC concrete. Studies have also

been conducted to highlight the effects of surface finishes on the sorptivity rates of

concrete (Ho et al., 2015). It is believed that cut sections are not the best samples to be

used in testing because cutting is likely to introduce small cracks on the concrete. When

the top, bottom, and cut surfaces were cut to test for sorptivity the results found were

that the top surfaces had higher sorptivity rates then followed by the bottom surfaces

and the cut surfaces emerge last in the list (Valipour, Shekarchi, and Arezoumandi,

2017).

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Most researchers who have worked on the topic of green concrete have only

focused on the applicability of the concept but have not researched on the specific

aspects such as areas of application, barriers and benefits. Therefore, there is a

research gap on the specific applications of green concrete and how it can be

incorporated in the construction industry to help the in improving sustainability and

green construction. Therefore, this research focuses on identifying the specific areas in

which green construction can be applied and how it can be used as a sustainable

approach in the construction industry. Green construction is the future of construction

and researchers should focus more on identifying ways in which the concept can be

used on the practical scale rather than only on the academic scale.

2.7 Summary

The literature review covers the previous works done by other researchers on

concrete and green concrete. Most of the literature reviewed mainly focused on

experiments about green concrete and their applicability in the construction industry.

The literature review also focused on the various types of AAs and other cementitous

materials that can be used as alternatives for the ordinary cement-based concrete.

Since concrete is the main building material in the entire world, it is important to look at

the effects of various factors on its durability, strength and how these factors can affect

its load-bearing capacity. Therefore, the literature review also focused on the

researches conducted to determine the effects of factors such as moisture, wind, heat

and other natural forces on green concrete. The studies showed how various

environmental factors can affect the durability and strength of green concrete which is a

good subject to this research paper. However, most of the researchers did not cover the

practicability of using green concrete in the construction industry. The latter created a

research gap which forms the basis on which this research paper is based. Therefore,

the research herein focuses on the applicability of green concrete and how the industry

is trying to embrace the concept. The research focuses on the extent of use, the

benefits and the barriers of using green concrete in the construction industries in the

United Kingdom and United States. The next chapter of this research is the research

methodology which gives a description of how the research was carried out. The

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research methodology covers the steps used in data collection, data analysis and in the

presentation of the results.

CHAPTER 3

Research Methodology

3.1 Introduction

The section herein gives a summary of the research methods used in this

research. The section highlights the ways which were used in the collection, reviewing

and the analysis of the data. Also, the section gives a brief definition of the target group

as well as the main sources of information that was used in this research. This chapter

describes the research approach used in the paper. The chapter mainly highlights how

the information meant to answer the research question were collected and analyzed to

come up with useful conclusions. The data collected for this research were obtained

from secondary sources and through a survey to collect the information necessary for

the answering of the research questions.

The research herein aims to investigate the use of green concrete in the

construction industry and its contribution to the conservation of the environment. The

research also aims at investigating the current state of the use of green concrete in the

United Kingdom and the United States identifying some of the barriers that affects its

use in these two countries. The feedback from the industry would be important for

analyzing the use of green concrete in the construction sector and also identifying some

of the industry concerns on the use of the materials.

To collect the information required answering these questions, this research used a

questionnaire survey approach to interview the main players in the construction industry

to include concrete trade associations, public organizations as well as concrete

suppliers in both the United States and the United Kingdom.

The survey approach was used in this research due to its high

representativeness and hence it offered the best method to represent the state of the

construction industry as a whole (Brinkmann, 2014). The survey method is also low in

cost and would make the whole process affordable since it will be based on online

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survey without any physical interaction with the participants. The survey was conducted

through an online approach by sending emails to the respective companies to get their

feedback on the various issues of concern as far as this research was concerned. The

survey questions were designed to enquire on the specific issue which include finding

out the types of green concrete materials currently used in the construction industry, the

benefits of using the green concrete, the barriers of using the green concrete and what

are other potential materials that could be used in the production of the green concrete.

The questions used in the survey were structured, some having multiple-choices while

the others being open-ended. The questions were divided into three parts which

included the company background, the usage of the SCMs within the companies and

the usage of other waste materials in their construction needs.

3.2 Research Sample Design

The participants in the survey were identified and recruited based on their

relevance to the topic and they active roles in the construction industry. The potential

participants were identified by looking if they were members of the main construction

associations in their local areas, for example, some participants were selected since

they were members of the Ohio Ready Mixed Concrete Association which is an

association of companies dealing with concrete business in Ohio.

The participants were contacted through emails and they given an explanation of

the importance of this study and a request for their contribution in the study was made.

The research also assured them of the confidentiality of their responses as well as their

identity during the whole process of data collection to data presentation. Several emails

were sent to the previously identified participants where some of them replied

confirming their commitment to the project while others failed to reply the email. The

number of people who replied was enough to guarantee the quality of the results

required to validate the findings of this research and hence the data collection went on

with the participants who had earlier committed themselves to the research. After

obtaining the commitment of the participating companies and organizations, one person

who was recommended by the companies was interviewed to give a brief overview of

the use of green concrete in their daily activities. The companies for interviewing were

found through the National Ready Mixed Concrete Association and other trade

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organizations of the concrete producing and supplying companies in the United States

and the United Kingdom.

From the analysis of the available literature about green concrete, most of the

scholars did not tackle the extent of usage of green concrete in the construction

industry. Most researchers looked only at the applicability of green concrete but did not

go to the specific matters that include looking at the factors that affect the use of green

concrete, the extent of usage and how the green concrete can be incorporated in the

entire construction industry to improve sustainable development. Therefore

CHAPTER 4

Results and Discussion

4.1 Introduction

In the study, local concrete suppliers, popular organizations in the concrete

industry were interviewed on their opinion and experiences with green concrete

production collected for analysis. One organization in the concrete industry that

participated in the interview was ORMCA, and the state agency was the Ohio

Department of Transportation. Out of the two hundred and twenty-three companies that

participated in the online survey, only thirty-four companies completed the online

questionnaires. The response rate was fifteen percent representing low turnout. The

results that were obtained through the online questionnaires and interviews were later

combined in an analysis. The research findings are therefore discussed below in three

sections.

4.2 Background information about survey participants

The participants in the survey include the companies that had responded to the

online questionnaires. Therefore, background information will include information about

the size of the company, the years the company has been in the concrete business and

the years that the respondents of the survey had worked in the concrete industry. Of the

companies that participated in the survey, the maximum year recorded was one

hundred and thirty while the minimum was six, making it a mean of fifty years. Survey

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respondents, on the other hand, recorded a maximum of forty-four and a minimum of

three making the mean twenty-three years.

The services offered by sixty-four percent of the surveyed companies included

ready to mix concrete. Forty-four percent of the surveyed members provided services

for prefabricated concrete while the rest of the members that constituted about twenty-

two percent provided services in quarry mining or manufacturing of the construction

aggregates and concrete. However, in the survey, there are some companies that

provide more than one service, for example, they both ready-mix aggregates and

concrete. The same case can be applied to the question including the kind of industrial

sectors that the companies’ concrete serves and the method that they use to design the

concrete. Eighty-nine percent of companies have their concrete used by other

companies in the building sector, eighty-four percent used in roadways or bridges, and

the remaining thirty-nine percent is used in other sectors like industries and agricultural

sectors.

When the companies were asked about the methods that they use in mixing the

concrete, they responded by indicating that they used industry standards and guidelines

as set by the American Concrete Institute, the State Department of Transportation and

the American Society for Testing and Materials. Sixty-eight percent of the companies,

however, decide to use their historical data and nineteen percent of the companies

clarified that they used other methods more so the trial batches. The results from the

survey also showed that seventy-three percent of companies maximized the utility of

green raw materials. Seventy-four percent of the companies also clarified that they had

received numerous inquiries from their customers that they manufacture green

concrete. The companies that participated in the online questionnaire mentioned that

the driving factor towards the use of green concrete was the Leadership in Energy and

Environmental Design project requirements.

4.3 The use of SCMs

The second part of the survey focused on the kind of SMCs that they were using

to manufacture concrete in a multiple choice format. Other open-ended questions were

also used to ask participants what other kinds of SMCs could be used, the most

common type of SMCs that were used and the advantages and barriers that were being

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encountered whenever they were used. The percentage of companies that had used

specific kinds of SMCs is shown in the table below. The survey also investigated the

three topmost SMCs that were commonly used based on the experiences of their

industries. The results on how the participants responded are shown in the second

graph below. The pictures below illustrate the physical differences between Class C and

Class F fly ashes.

Fig. 6: Fly Ash Class F and Fly Ash Class C (Kansas City Fly Ash, n.d)

Table 7: The percentage of companies that used each of the specified SCM

Material

Percentage of Companies that used

the material

Fly Ash Class F

Fly Ash Class C

GGBFS

Page 33 of 50

Silica fume

PLC

Others

Fig. 7: The percentage of companies that used each of the specified SCM

Table 8: Topmost SCMs as used by various companies

Material

Percentage of Companies that used

the material

Fly Ash Class F

Fly Ash Class C

GGBFS

Page 34 of 50

Silica fume

PLC

Fly ash

Fig. 8: Topmost SCMs as used by various companies

The first diagram shows that fly ash, ground granulated blast furnace slag, and silica

fumes are the most commonly used SMCs in the concrete industry today. Participants

in the survey also listed other kinds of SMCs that they used in concrete making such as

metakaolin as mentioned by two participants and rice hush that was mentioned by one

participant. Some of the participants represented in the second diagram above just

mentioned that they used fly ash but did not specify whether it was class C fly ash or

class F fly ash hence the separate listing of fly ash. The frequency at which fly ash is

used is, therefore, greater than that at which ground granulated blast furnace slag is

used. When the participants were asked the kind of SMCS that could be used in

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concrete industries, few participants gave their response because many companies did

not have adequate knowledge about other SMCs. Additionally, the mentioned SMCs

included rice husk ash by two participants, grounded limestone by one participant and

leachates from petroleum waste by one participant. A physical appearance of the

granulated blast furnace slag is shown below.

Fig. 9: Granulated Blast Furnace Slag (Granulated Slag, n.d.)

Other SCMs mentioned also include natural pozzolan that was mentioned by one

participant, bottom ash by one participant, metakaolin by one participant, ultra fine fly

ash by one participant and the last being slag that was mentioned by one participant.

The data above only show that companies have different levels of understanding when

it comes to SMCs. Some materials like metakaolin and rice husk ash that have been

successfully used by other companies can also be considered by other companies as

potential SMCs. Lack of information about SMCs could be due to lack of adequate

information sharing by other companies simply because companies normally want to

maintain their competitive prowess in the business world (Ho et al., 2015). Participants

were asked about the benefits and barriers that they were likely to encounter by using

the three most commonly used SMCs as shown in the second diagram above. The

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answers of the participants about the frequency of each item such as cost saving are

summed up in the diagrams below.

Table 10: Benefits of Using the SCMs

Benefit of Using the SCM

Percentage of companies that cited the

benefit

Aids in production of concrete

Improved concrete properties

Others

Cost saving

Local availability

Fig. 10: Benefits of Using the SCMs

Table 11: Barriers of Using the SCMs

Barriers

Percentage of companies that cited the

Page 37 of 50

barrier

Local availability

Restriction from authorities due to lack

of specification

Lower qualities

Slowing the rate of production

Increased cost

Others

Fig. 11: Barriers of Using the SCMs

The three most commonly mentioned concerns and benefits gained from using

SCMs were similar. The first one is the impact that they have on concrete properties,

the second being impact on cost then the last one being the local availability of the

SCMs. The properties of concrete were the most valuable factors used in determining

the type of SCMs to use. Manufacturers should be aware that the advantage viewed by

one concrete company in using particular SCMs could be a disadvantage to another

concrete supplier, for example, the local availability of the SCMs (Duxson, Provis, Lukey

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and Van Deventer, 2007). Depending on the properties of a particular concrete, it

should be noted that one type of SCMs may have advantages as well as disadvantages

according to the properties of the concrete. For instance, an SCM could improve the

workability of concrete but also reduce the strength that the concrete possessed earlier.

It is surprising that most suppliers and manufacturers did not know about the green

materials that were used in producing concrete. Only two percent of the suppliers and

manufacturers mentioned that reusing the waste materials was significant. Besides the

top three items that were earlier on mentioned, SCMs prove to have various

disadvantages when put into use. The disadvantages included slowing and hindering

the rates of productions and lack of restrictions or specifications from professionals like

engineers (Glavind and Munch-Petersen, 2000).

4.4 The use of AAs

The third part of the questionnaire consisted of the questions about the usage of

AAs covering its benefits and barriers. The two major types of AAs that are being used

in the concrete industry include the lightweight aggregates and the RCAs. The feedback

from the participants in this research showed that they had serious concerns about the

use of the RCAs in the production of concrete. There were a lot of uncertainties in

finding the exact sources of the old concrete making it difficult to determine the original

properties of the concrete. Various barriers were cited by the participants on the use of

RCA. The main problems that were mentioned include the inferior engineering

properties, it higher affinity and water absorption, difficult in making the specifications of

the RCA and difficulty in controlling the quality of the concrete from the side of the

supplier (Johari, Zeyad, Bunnori and Ariffin, 2012).

The use of RCA in the real construction industry was limited by these concerns

making it one of the less green materials used in both the United States and the United

Kingdom. Most of the AAs that had been recommended for use by Academic research

such as tire rubber, brick rubble, and crushed glass were not being used in the industry.

Most of the participants were not aware of the usability of most of the AAs as had been

suggested by the academic research papers. Some of the most common AAs

mentioned by the participants were cullet pumicite and natural zeolite sludge. The table

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below gives a summary of the most common AAs in the construction industry according

to the data collected.

Table 12: The Data on the Usage of AAs in the Concrete Industry

Type of Material

Percentage of Companies Used the

Materials

Lightweight aggregate

RCA

Crushed glass

Tire rubber

Brick rubber

Plastics

Slag

Crushed ceramic

Waste polysterene

Foundry sand

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Fig. 12: The Data on the Usage of AAs in the Concrete Industry

Fig. 13: Concrete with Recycled Lightweight Aggregates (Concrete with Recycled

Aggregates, n.d.)

Page 41 of 50

The research obtained fewer responses for the use of AAs as compared to the

disadvantages and the advantages of the SCMs mentioned by the participants. The

table below shows the summary of the results of using the SCM and the AAs as

reported by the survey results. The results show that the total frequency of the items is

40 and 41 for the disadvantages and the advantages of using the AAs in the concrete

production industry. The less response on the use of the AAs which include their

advantages and disadvantages can be attributed to the less knowledge that the main

players in the construction industry have about the use of AAs (Johari, Zeyad, Bunnori

and Ariffin, 2012). The results did not show any specifications for the use of the AAs

apart from the lightweight aggregates. The lightweight aggregates were the most

commonly used AAs in the construction industry. The results also showed

nonconsistency on the benefits and the barriers of using the AAs. However, most

participants recognized the structural benefits of the materials as well as the cost saving

aspect of using the AAs.

Most of the participants acknowledged that the industry was supposed to

embrace the use of the green materials in the production of concrete to promote

environmental conservation as well as to promote sustainability in the construction

sector. The green concrete would help in saving the natural resources and promote

reusing of the waste materials to meet the needs of the construction industry (Flower

and Sanjayan, 2007). One of the major disadvantages of using the AAs was the

technical barriers which include difficulty in the specification, high water absorption, and

the associated mechanical properties. Another important disadvantage of using the AAs

is the less availability of the information regarding the use of the materials and how they

affect the long-term properties of the concrete (Flower and Sanjayan, 2007).

Table 14: Advantages of Using the AAs in Green Concrete Production

Advantage

Percentage of Companies that

acknowledged

Local Availability

Improved mechanical properties of

concrete

Environmental conservation

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Cost Savings

Usability

Structural Advantage

Fig. 14: Advantages of Using the AAs in Green Concrete Production

Table 15: Disadvantages of Using AAs as Acknowledged by various Companies

Disadvantage

Percentage of Companies that

Mentioned the Disadvantage

Slow production of concrete

Technical issues

Local availability

Low quality of concrete

Increased production cost

Other disadvantages

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Fig. 15: Disadvantages of Using AAs as Acknowledged by various Companies

CHAPTER 5

Conclusions and Recommendations

5.1 Important Conclusions from the Literature Material

The use of green concrete has been facilitated by the push for sustainable

construction as well as environmental conservation issues both in the United States and

in the United Kingdom. The construction industry is struggling to get alternative ways of

building other than using the usual concrete whose production is characterized by high

emissions and high energy consumption making it unsustainable (Garg and Jain, 2014).

The high need for concrete also makes it a commodity that may face extinction in the

future if its use is not controlled through the introduction of alternative materials or

through the use of more sustainable concrete types. The green concrete, just like in the

US means the use of alternative materials in the production of cement in the United

Kingdom. The use of recycled material and other locally available materials are the

main form in which green concrete in created in most countries (Sheen, Wang and Sun,

Page 44 of 50

2014). In the United States, several materials have been used for green concrete

production. For example, crushed glass has been used for architectural concrete,

recycled tires have been used in concrete to act as proofing materials. Finally, the slag

aggregates has been used in structural lightweight concrete. Most of the materials used

in the production of the green concrete in the use consist of the unwanted concrete

which has been reclaimed. The unwanted concrete is usually crushed into usable

aggregates and use to produce new usable concrete (Sheen, Wang and Sun, 2014).

The recycled materials used as cementitious substitutes are those that can be easily

obtained and do not have negative effects on the properties of the concrete including its

compressive and tensile strengths.

The commonly used SCM include the Fly Ash, granulated blast-furnace slag and

silica fumes. The latter are obtained as waste products from other industries and used

in the production of concrete which helps the industries in their waste disposal policies.

The SCMs are then used to improve the properties of the concrete depending on the

type used and the amount of the materials added to the concrete. The materials can be

used to increase the compressive strength of the concrete as well as protect the

concrete from the effects of some factors from the environment. According to the

findings of this research, the granulated blast-furnace slag can often be use at up to 50

percent replacement of the cementitious materials. The fly ash can often be used to

make a three-way mix and can also be used as a pure replacement of the Portland

cement.

5.2 Conclusion from the Survey

The research herein presented the results of the survey on the current status of

the use of green concrete materials in the United States. Despite suggestions by many

academic materials on the potential SCMs and AAs, their current use across the United

States and the United Kingdom remained to cover only few types of the materials. The

usage included the top three SCMs, the lightweight aggregates and the RCA for the

AAs. Also, various companies presented varying results on their recognition of the use

of the SCMs and the AAs. For example, some companies may have adopted the use on

one green concrete material while the other companies may find it new. The application

Page 45 of 50

and use of the green concrete materials depended mainly on the size of the company

as the large companies used the materials more as compared to small companies.

According to the results from the survey, the benefits and the barriers of using

the SCMs were related to the properties, cost and the local availability of the substitute

materials. The results of the survey showed that there are many advantages of using

green concreter than the disadvantages as mentioned by the participants. The AAs

were less used in the construction industry in both UK and the US and the survey

participants had little knowledge about the materials. SCMs were the most commonly

used green concrete materials in US and UK construction industries. Most of the

participants had little or no knowledge of the potential benefits or barriers of using the

AAs as alternative concrete materials or supplements. Also, some participants in the

survey had recognized the concept of being green through using the waste materials

while others did not know the application of the concept.

Taking into consideration the current status of green concrete usage in the

construction industry as well as its benefits and barriers as perceived by the

practitioners in the industry, the academic researchers should focus their studies on

specific issues. The academic researchers should focus their studies on how the

selected green materials affect the properties of the concrete, their cost effectiveness as

compared to that of the conventional materials and their availability in the locality. The

research herein gives a direction on how the academic field can help the industry to

incorporate the use of green concrete as well as help it solving the problems associated

with the use of these materials. For instance, there are no accepted industry standards

on the use of most AAs and other SCMs and hence this has affected their application in

the construction industry. Also, less data exists regarding the long term durability of

concretes made from using the RCA.

Most companies in the United Kingdom are using blended cement as a way of

encouraging green construction and reducing the amount of cement used during

construction. The blended cement consists of cement replacements such as PFA and

other waste materials or by products. According to the results obtained through the

survey, the use of blended cement is responsible for a substantial reduction of the

carbon footprint. Currently, most concrete manufactures produce concrete which is

Page 46 of 50

about 85 percent blended which is way above the recommended standard of 50

percent.

Most companies in the UK also use recycled secondary aggregates to reduce the

use of virgin cement in bid to control the amount of carbon footprint. For example,

Hanson Cement produced the concrete incorporating aggregate which is a by-product

of Cornish China clay production process.

Despite the results obtained from this research, there were several limitations

that might have affected the credibility of the results. First, the survey pool was

geographically limited since and also the survey approach used may have resulted to

inaccurate results. Some companies that were contacted failed to respond to the emails

and hence the research had to use the few companies that responded to the emails as

the only source of information hence reducing the sample size for the research.

However, the sample size did not affect the results greatly but might have introduced a

little percentage of error. Future research should consider covering a larger

geographical area and focus on countries where the construction industry is flourishing

such as in China and Canada to get a real reflection of how the green concrete concept

is shaping the construction industry. Expanding the geographical pool of the research

would help in improving the quality of the results obtained as well as getting a better

understanding of the usage of the concrete across the world.

Page 47 of 50

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