Use of recycled concrete as brick aggregate in Bangladesh

i
USE OF RECYCLED CONCRETE AS BRICK AGGREGATE –
BANGLADESH PERSPECTIVE
MD. SHAH ALAM KHAN SHAKIB
MD. MOSHIUR RAHMAN
NUR AHMED SOWROV
DEPERTMENT OF CIVIL ENGINEERING
AHSANULLAH UNIVERSITY OF SCIENCE AND TECHNOLOGY
141-142, LOVE ROAD, TEJGON INDUSTRIAL AREA, DHAKA-1208
JANUARY-2017

ii
APPROVED AS TO STYLE AND CONTENT
BY
Dr. S. Reza Chowdhury
Professor
Department of Civil Engineering
AHSANULLAH UNIVERSITY OF SCIENCE AND TECHNOLOGY
141-142, LOVE ROAD, TEJGON INDUSTRIAL AREA, DHAKA-1208
JANUARY-2017

iii
DECLARATION
The work performed in this thesis for the achievement of the degree of bachelor of science in Civil
Engineering is" ". The whole work is carried out by the authors under strict and friendly
supervision of Dr. S. Reza Chowdhury, professor, Department of Civil Engineering, Ahsanullah
University of Science and Technology, Dhaka, Bangladesh.
Neither this thesis nor any part of it is submitted or is being simultaneously submitted for any
degree at any other institutions.
Signature of the student:
………………………………
MD. Shah Alam Khan Shakib
Student ID: 12.02.03.069
……………………………….
MD. Moshiur Rahman
Student ID: 12.02.03.075
……………………………….
Nur Ahmed Sowrov
Student ID: 12.02.03.087

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ACKNOWLEDGEMENT
We would like to express our sincere gartitude and profound appreciation to our supervisor, Dr.
S. Reza chowdhury, professor, Department of Civil Engineering, Ahsanullah University of
Science and Technology for his constant guidance, sincere instruction, valuable suggestion,
encouragement and extra instruction through the period of this study. He helped us through our
entire project by his continuous judgment, inspiration and gave us advice in solving difficult
problems encountered during the analysis. Without his contribution, we could not fulfill this
requirement.
We dedicate the whole work and success of our project to our parents and well-wishers for their
encouragement. Finally, we thank to Almighty Allah that our project and thesis has been
completed successfully in time.

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ABSTRACT
The recycled concrete can be defined as crushed concrete composed of aggregate fragments
coated with cement paste or cement mortar from the demolition of the old structures or
pavements that has been processed to produce aggregates suitable for use in new concrete. In
Bangladesh, the volume of demolished concrete is increasing due to deterioration of concrete
structures as well as the replacement of many low-rise buildings by relatively high-rise
buildings caused by booming of real estate business. Disposal of the demolished concrete is
becoming a great concern to the developers of the buildings. If demolished concrete is used for
new construction, the disposal problem will be solved, the demand for new aggregates will
be reduced, and finally consumption of the natural resources for making aggregate will be
reduced. In most of the old buildings, brick chips were used as coarse aggregate of concrete in
Bangladesh. Regarding the results of most of the previous research that has been done so far, the
application of Recycled Aggregate is mostly currently in low quality/strength concrete, for
example, pavement base and slab rather than used in structural concrete. The most common
application of Recycled Concrete Aggregate is the use in concrete sub-base in road construction,
bank protection, noise barriers and embankments, many types of general bulk fills and fill
materials for drainage structures. This study describes the state of art of recycled concrete from
different papers available in literature. This thesis paper presents an overview of results of research
that is carried out on a concrete made with recycled clay brick as an aggregate.

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TABLE OF CONTENTS
TITLE i
DECLARATION iii
ACKNOWLEDGEMENT iv
ABSTRACT v
TABLE OF CONTENT vi
LIST OF TABLES ix
LIST OF FIGURES xii
Chapter 1 INTRODUCTION
1.1 General
2
1.2 Objective
5
1.3 Methodology
5
Chapter 2 REVIEW OF LITERATURE
7
2.1 Introduction
2.2 Properties of Recycled Concrete Aggregate 7
2.2.1 Aggregate Grading 7
2.2.2 Shape & Surface Texture of Aggregate Particles 8
2.2.3 Water Absorption 8
2.2.4 Bulk Density of Aggregate 9

vii
2.2.5 Crushing & Abrasion Resistance 9
2.2.6 Presence of Harmful Substances 10
2.2.7 Physical & Mechanical Properties 10
2.2.8 Exploitation Properties in Sense od Durability 13
2.2.9 Structure of Concrete 13
2.3 Structure of Concrete 13
2.4 Uses of Recycled Concrete 16
2.5 Advantages of Recycling 18
Chapter 3 RECYCLED AGGREGATE USED
IN BANGLADESH
3.1 Introduction 21
3.2 Causes of Deterioration of Concrete Structures
in Bangladesh 21
3.3 Problems at Construction Sites That Causes Early
Deterioration of Concrete Structure in Bangladesh 22
3.4 Properties of Concrete Made With Various Aggregate
Commonly Used in Bangladesh 23
3.5 Recycling of Demolished Concrete as Coarse
Aggregate 26
3.6 Recycling of Recycled Fine Aggregate 29
3.7 Development of Permeable Concrete for Special
Applications 31

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3.8Determination of Carbonation Co-efficient
of Concrete 33
3.9Applications of Recycled Aggregate & Permeable
Concrete 35
Chapter 4 RECYCLED AGGREGATE CAN BE
USE FOR MORE AREAS
4.1 Possibilities for Using RCA Concrete in Non-structural
Construction Materials 37
4.1.1 Concrete Sandwich Panels 37
4.1.2 Concrete Sound Walls 40
4.1.3 Architectural Precast Concrete Panels 46
4.1.4 Stonework 51
4.1.5 Concrete Pavements 58
Chapter 5 THE POSSIBILITY OF USING RECYCLING
AGGREGATE IN BANGLADESH
5.1 Current Situation of the Recycled Coarse Aggregate 67
in Bangladesh
5.2 Possibility in Bangladesh 68
Chapter 6 CONCLUSION & RECOMMENDATION
6.1 Conclusion 70
6.2 Recommendation 70

ix
LIST OF FIGURES
Figure 1.1 : Demolished Concrete Block & Recycled Aggregate 3
Figure 1.2 : Recycling Process 4
Figure 2.1 : Appearence of the Recycled Aggregate Grains 7
Figure 2.2 : Shape & Surface Texture of Different Fractions
of Recycled Aggregate 8
Figure 2.3 : Diagram of Relationship Between Tensile Strength &
Compressive Strength of Recycled Aggregate Concrete 12
Figure 3.1 : Workability of Concrete Made With Different Aggregates 25
Figure 3.2 : Demolished Concrete Block & Recycled Aggregate
(a) Different Aggregates (Left)
(b) Different Moisture Condition (Right) 25
Figure 3.3 : (a) Compressive Strength of Concrete With The
Variation of W/C (Left)
(b) Tensile Strength VS Compressive Strength
of Concrete (Right) 28
Figure 3.4 : (a) Compressive Strength of Concrete VS Wear (Left)
(b) Cumulative Probability Distribution of Compressive
Strength of Recycled Aggregate Concrete 28
Figure 3.5 : Compressive Strength of Recycled Mortar Block 30
Figure 3.6 : Unit Weight of Pervious Concrete Made With
Different Aggregates 33
Figure 3.7 : Pervious Concrete Made With Different Aggregates
(a) Percentage Void (Left)
(b) Permeability (Right) 33
Figure 3.8 : Pervious Concrete Made With Different Aggregates
(a) Compressive Strength (Left)
(a) Tensile Strength (Left) 34
Figure 3.9 : Relationship Between Depth of Carbonation &
Age of Structure for Indoor Exposure (Left) &
Outdoor Exposure (Right) 34
Figure 4.1 : Detail Of A Sandwich Panel 38

x
Figure 4.2 : Cross Section of A Sandwich Panel 39
Figure 4.3 : Pinkcore Insulated Concrete Sandwich Panel System 40
Figure 4.4 : Sound Wall 41
Figure 4.5 : Form Liners 41
Figure 4.6 : Minimum Length of Sound Wall 42
Figure 4.7 : The Height of The Wall Reduces The Sound 42
Figure 4.8 : Micrograph of The RCA Structure 44
Figure 4.9 : Detail Image of The RCA Microstructure 44
Figure 4.10 : How The RCA Content & The W/C Ratio Affects
The Porosity & Concrete 44
Figure 4.11 : Hydrophobic Impregnation 45
Figure 4.12 : Different Types of Curtain Facades 46
Figure 4.12(a) : Details Section Showing Bearing Support of Panel 47
Figure 4.12(b) : Steel Tube Bearing Support & Viewing From The Top 47
Figure 4.13 : Tieback Connections 48
Figure 4.14 : Metal Stud Crete 48
Figure 4.15 : Slender Wall 49
Figure 4.16 : Slender Wall Design Finishes 50
Figure 4.17 : Flexural Tensile Load on a Stonework Wall 52
Figure 4.18 : Stones Used in Stonework 52
Figure 4.19 : Solid Concrete Blocks 53
Figure 4.20 : 2000 Solid Dense Readyblock 54
Figure 4.21 : Enviroblocks Used on The RAF Maintenance
Facility in Syerston , Newark 55

xi
Figure 4.22 : Enviroblock Wall 58
Figure 4.23 : Concrete Ppavement Layers 59
Figure 4.24 : Dowel Bars & Tie Bars 59
Figure 4.25 : Types of Concrete Pavements JPCP, JRCP and CRCP 60
Figure 4.26 : RCA pavements in Shanghai 62
Figure 4.27 : RCA concrete pavement structure 63

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LIST OF TABLES
Table 3.1 : Properties of Aggrgates Investigated 25
Table 3.2 : Properties of Aggregates 27
Table 3.3 : Cases Investigated 27
Table 3.4 : Grading of Different Fine Aggregate 30
Table 3.5 : Summary of Aggregate Properties 31
Table 3.6 : Mixture Properties of Pervious Concrete 32
Table 4.1 : Suggested Possibilities for RCA Concrete in
Concrete Sandwich Panels 45
Table 4.2 : Suggested Possibilities of Using RCA Concrete in
Precast Curtain Wall 51
Table 4.3 : The Product Range of Envirblocks 56
Table 4.4 : Certified Environmental Profiles of Enviroblocks 57
Table 4.5 : Physical Characteristics of Enviroblocks 57
Table 4.6 : Suggested Possibilities for Utilization of RCA
Concrete in Concrete Pavements 64

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1.1 General
Aggregate is one of the most vitally important materials in use for concrete production as
it profoundly influences concrete properties and performance. Regarding aggregate usage in
concrete, concrete consumption in the world is estimated at two and a half tons per capita per
year (equivalent to 17.5 billion tons for 7 billion population in the world) (CAMBUREAU, 2008;
Mehta, 2009). This figure is assumed to represent total aggregate production, including
usage in concrete and road base. Aggregate usage in concrete constitutes perhaps between 25
and 35 percent of the total aggregate production. The sheer bulk of global aggregate usage is
staggering.
The recycled concrete can be defined as crushed concrete composed of aggregate fragments
coated with cement paste or cement mortar from the demolition of the old structures or
pavements that has been processed to produce aggregates suitable for use in new concrete. The
processing, as with many natural aggregates, generally involves crushing, grading and washing.
This removes contaminant materials such as reinforcing steel, remnants of formwork, gypsum
board, and other foreign materials. The resulting coarse aggregate is then suitable for use in
concrete. The fine aggregate, however, generally contains a considerable amount of old
cement paste and mortar. This tends to increase the drying shrinkage and creep properties
of the new concrete, as well as leading to problems with unworkable mix and strength.
Therefore, many transportation departments have found that using 100% coarse recycled
aggregate but with only about 10% to 20% recycled fines works well.
The above inevitably impacts on the environment due to the great huge quantity of general and
construction waste materials or from building demolition sites generated in developed countries.
The research conducted for the Industry Commission Report indicated that about 3 million
tons of waste aggregate has been created in the Australia alone. The disposal of all this
waste has become a harsh social and environmental problem. This is a large burden on the
world’s natural resources and an increasingly expensive problem for solid waste management.
Therefore, a possible alternative aggregate method to overcome this issue may be using recycled
concrete aggregates instead of natural aggregate in construction tasks. This solution not only can
help to conserve and extend natural resources but also can reduce the cost of waste treatment and
the demand on landfill sites for disposing the waste.
In Bangladesh, the volume of demolished concrete is increasing due to deterioration of
concrete structures as well as the replacement of many low-rise buildings by relatively
high-rise buildings caused by booming of real estate business. Disposal of the demolished
concrete is becoming a great concern to the developers of the buildings. If demolished concrete
is used for new construction, the disposal problem will be solved, the demand for new
aggregates will be reduced, and finally consumption of the natural resources for making
aggregate will be reduced. In most of the old buildings, brick chips were used as coarse
aggregate of concrete in Bangladesh. Studies related to the recycling of demolished concrete
are generally found for stone chips made concrete .

3
Regarding the results of most of the previous research that has been done so far, the application
of Recycled Aggregate is mostly currently in low quality/strength concrete, for example,
pavement base and slab rather than used in structural concrete. The most common application of
Recycled Concrete Aggregate is the use in concrete sub-base in road construction, bank
protection, noise barriers and embankments, many types of general bulk fills and fill materials
for drainage structures.
For investigation, demolished concrete blocks were collected from demolished building
sites and broken into pieces as aggregate as shown in Fig 1.1. Before making concrete,
the aggregates were investigated for absorption capacity, unit weight, and abrasion.
Standard grading of the aggregates were controlled as per ASTM.
Figure 1.1: Demolished Concrete Block and Recycled Aggregate
Recycling is the reprocessing of old materials into the new products, prevent the waste of
potentially useful materials, reducing the consumption of raw materials. Recycling or re-using of
bricks is an environmentally friendly way of eliminating it from the waste stream. Fine recycled
brick aggregates recovered from demolished masonry structures can be utilized in the
manufacture of new concrete mixtures. At this way, it is possible to reduce the problem of
construction and demolition waste storage, and to reduce the consumption of natural materials.
The utilization of masonry waste and of crushed brick as an aggregate in mortar and concrete
would have a positive effect on the economy also. Namely, a preservation of natural materials is
significant for an ecologically responsible and sustainable building that would be cost effective
also. This kind of building implies a usage of low cost materials that can be used without any
negative impact on the environment.
This thesis presents an overview of results of available research that is carried out on a concrete
made with recycled clay brick as an aggregate. Ecologically responsible and sustainable building
implies that the material cycle will be completely closed, and the original constituents (clay brick
and tiles, gravel, sand, cement stone) are recovered in thermal process. This concept of recycling
and reuse of masonry waste is shown in Figure 1.2.

4
Figure 1.2: Recycling process
Therefore, investigations on recycling of demolished brick aggregates concrete are necessary.
With this background, this study was planned.

5
1.2 Objective
The main objectives of this thesis are:-
1. The Use of recycle concrete in Bangladesh and other countries.
2. Evaluate the engineering properties of recycle concrete aggregate.
3. Advantage of use of recycle concrete aggregate for green environment and other perspective
over virgin concrete.
4. Possibility of using Recycled Concrete as Aggregate in Bangladesh.
1.3 Methodology
This study describes the state of art of recycled concrete from different papers available in
literature. This thesis paper presents an overview of results of research that is carried out on a
concrete made with recycled clay brick as an aggregate.

6
CHAPTER 2
REVIEW OF LITERATURE

7
2.1 Introduction
This thesis study concerned with the case study of different types of journal & papers available
in literature. The major objective of most of the experiments or research on recycled aggregate is
to find out the results in the strength characteristic area and what is the best method to achieve
high strength concrete with recycled aggregate. This successful research has been achieved in
many countries, in particular in Europe; United States; Japan and China. This chapter presents
literature reviews on the effects of various factors on the recycled aggregate from
research from those countries & also in Bangladesh. In here, also discuss about the advantage
and disadvantage of recycle concrete.
2.2 Properties of Recycled Concrete Aggregate
The use of recycled aggregate obtained from the waste concrete, as a component of the new
concrete mixture, implies a thorough understanding of its basic properties, considering that some
of them may significantly differ from the properties of aggregates obtained from natural
resources. In addition, their differences primarily depend on the quantity and quality of cement
mortar, which is attached to the grains of recycled aggregate (Figure 2.1), then, on the quality of
the original concrete from which the aggregate is made by recycling and also on recycling
methods. Nonetheless, in cases where the recycled aggregate comes from many different
sources, the uneven quality, i.e. variations in the properties of recycled aggregate are much more
pronounced than as is the case with natural aggregates.
Figure 2.1: Appearance of the recycled aggregate grains.
2.2.1 Aggregate grading
Grading of recycled coarse aggregate normally satisfies the standards for natural aggregate,
while in the case of recycled fine aggregate, composition corrections are often necessary,
because, according to many practical experiences, it was found that there was often a certain
amount of grains larger than what is required by standards for natural aggregate (S. Marinković et
al. 2009).

8
It has been shown that the presence of recycled fine aggregate has a negative impact on the
physical-mechanical properties of concrete, therefore, even though through a careful mix design
and application of appropriate production technology these effects can be reduced to an
acceptable level, in practical application, a fine fraction of recycled aggregate is usually left out,
in a way that it is completely replaced by the river sand (I. Ignjatović et al. 2009 & M. Malešev
et al. 2010). Figure 2.2 shows different fractions of recycled aggregate, produced by a classical
procedure.
Figure 2.2: Shape and surface texture of different fractions of recycled aggregate
2.2.2 Shape and surface texture of aggregate particles
In terms of morphological characteristics, recycled aggregate is less favorable than natural
aggregate. The grains are irregular, mostly with angular shape, rough and with cracked surface
and porous. These grain characteristics grains significantly affect the workability of fresh
concrete, as well as the permeability of liquids and gases in the hardened state; they also
significantly depend on the properties of concrete used in recycling for production of aggregate,
especially its strength, porosity, exploitation conditions to which it was subjected, but also on the
ways and levels of recycling – the type of applied crusher and possible additional processing
procedures.
2.2.3 Water absorption
Water absorption of recycled aggregate is a characteristic by which this aggregate differs most
from the aggregate obtained from natural resources. According to all available research in this
area, it has been shown that recycled concrete aggregate has a significantly higher absorption
level compared to natural aggregates. The reason for that is that the original cement mortar,
which is an integral part of the recycled aggregate, has a significantly more porous structure in
comparison to natural aggregate, whereby its porosity primarily depends on the water cement

9
ratio of the original (old) concrete. Thus, the absorption of water of recycled aggregate is even
bigger, as the quantity of mortar, which is attached grains of the original recycled aggregate,
increases. It has been shown in practice that the stated amount of cement mortar in recycled
aggregate ranges from 25% to 65% (in volume percentage), and that it differs in certain fractions
– the smaller the fraction, the greater the amount of cement mortar, as well as the level of water
absorption (S. Marinković et al. 2009). Also, the analyses undertaken in extensive research around
the world indicate that the stated amount of old cement mortar depends on the crushing method
in the recycling process, thereby, according to some researchers, the maximum amount of mortar
layer in recycled aggregate is recommended to less than 44% for constructional concrete.
Additionally, the researchers from the University of Hong Kong recommend that the amount of
recycled aggregate in structural concrete should range from 20% to 30%, in order to ensure that
the maximum water absorption of aggregate used is less than 5% (D. Jevtić et al. 2009).
It is known that the aggregates from domestic natural resources have negligible absorption, up to
1% as maximum, while the value of the classically recycled coarse aggregate typically ranges
within the interval from 3.5% to 10%, and for the fine aggregate, within the interval from 5.5%
to 13% (C. S. Poon et al. 2008).
According to the Japanese standard for the use of recycled aggregate as a component of concrete,
there is a limit so that a coarse fraction of recycled aggregate whose absorption is not higher than
7%, and fine fractions whose absorption goes up to 13% (K. Janković 2004), i.e. 10% can be used
for the production of concrete. Accordingly, the absorption capacity of recycled aggregates
should be treated as one of the basic properties, which is to be taken into account while designing
the mixture of new concrete on the basis of this aggregate. Through the influence on the water-
cement ratio porosity and consistency, an increased water absorption of recycled aggregate also
influences a range of physical-mechanical properties of fresh, as well as hardened new concrete.
2.2.4 Bulk density of aggregate
The bulk density of the recycled aggregate, due to a higher porosity of mortar layer, has a lower
value than the bulk density of natural aggregates and their mutual difference decreases if
recycling is conducted by an advanced technology, which can remove a significant portion of the
old cement mortar. Also, the smaller the fraction, the greater the amount of cement mortar in the
total mass of aggregates, so the bulk density is accordingly lower. According to practical
experience, it was shown that the bulk density of recycled aggregate was on the average by 10%
lower compared to the bulk density of natural aggregates (D. Jevtić et al. 2009, V. Radonjanin & M.
Malešev. S 2007, Marinković et al. 2009).
2.2.5 Crushing and abrasion resistance
Mechanical properties of recycled aggregate are primarily dependent on the quality of the
original cement mortar present in the aggregate, and also, as in the case with natural aggregates,

10
depend on a number of other factors - the type of the original aggregate, structure, shape and size
of grains, aggregate grading and so on.
The resistance to crushing and abrasion of recycled aggregate is less than the respective
resistance of natural aggregate, which is a consequence of easier separation and crushing of the
mortar layer around the recycled aggregate grains. In addition, recycled aggregate, in most cases,
meets standard requirements in terms of the resistance to crushing and abrasion, which are
prescribed for aggregates from natural resources. Their differences may widely range - from 0%
up to 70%, which, as already pointed out, primarily depends on the quality, original concrete
compressive strength, as well as the methods of crushing of recycled aggregate(S. Marinković et
al.. 2009, V. Radonjanin & M. Malešev 2007).
2.2.6 Presence of harmful substances
Harmful substances, which may be present in recycled aggregate, are a consequence of harmful
substances present in the original concrete, furthermore, of exposure of the original concrete to
aggressive effects of various chemicals during the original exploitation, of inadequate levels of
treatment during the recycling process, of possible mixing of different waste materials etc. These
substances can be found in the following forms: lumps of clay, humus, gypsum, various organic
substances (bitumen, wood, paper, cardboard, plastic, coal, plant materials, and various colors),
steel and other metals, glass, lightweight concrete, brick, etc.
The presence of the stated components negatively affects the characteristics of the new concrete,
and the studies show that they can cause a reduction in compressive strength by up to 15%.
According to the Japanese standard for use of recycled aggregate in concrete, the amount of
harmful materials of density less than 1200 kg/m3 is limited to 2 kg/m3, and plastic, clay, humus
and other harmful substances of density less than 1950 kg/m3 to 10 kg/m3.
In the event of contamination of recycled aggregate by gypsum, Rilem recommendations refer to
the use of sulphate resisting cement, while the total content of sulphates should not be higher
than 1% of the dry aggregate mass (K. Janković 2004).
2.2.7 Physical-mechanical properties
Compressive strength of recycled aggregate concrete primarily depends on the quality of applied
aggregates, so that it is possible to obtain higher, identical or lower strength compared to the
natural aggregate concrete. In fact, a considerable amount of research confirms that in the case of
application of recycled aggregate produced by concrete crushing, whose compressive strength
was higher than the targeted compressive strength of new concrete, recycled aggregate concrete
of equal or greater strength in relation to comparable natural aggregate concrete are obtained.
Moreover, in case that the compressive strength values of the original concrete, of which
recycled aggregate is manufactured, and targeted compressive strength value of new aggregate,
were approximately equal, it was found that the strength values of recycled aggregate concrete

11
was 5% to 10% lower than those of the comparable natural aggregate concrete. In case of
designing such recycled aggregate concrete the targeted strength value is greater than the one of
the original concrete (which is usually the case in practical application), lower strength class of
recycled aggregate concrete is inevitably obtained than in the comparable natural aggregate
concrete, while a decrease of strength depends on the level of application of such recycled
aggregate. Furthermore, it was observed that during the application of both - fine and coarse
recycled aggregate, the above mentioned decline in the strength of recycled aggregate concrete
of 15% to 50%, compared to the comparable concrete made entirely with natural aggregate,
occurs. The application of solely recycled coarse aggregate and natural sand leads to the
maximum decrease of strength of such concrete in relation to the comparable one, in range of 5%
to 10%, while in the case of application of recycled aggregate in the amount up to 30% of coarse
fractions (or up to 50% - differences in research) obtained concretes in which the decline of
strength is generally negligible, if the strength of original concrete is not drastically lower than
the target value of new concrete. Compressive strength values of concretes with a mixture of
aggregates made of natural coarse aggregate and recycled fine aggregate is up to 50% lower in
relation to the comparable natural aggregate concrete - which implies the exclusion of this
combination in practical application. In addition to the above, the variations of compressive
strength of recycled aggregate concrete depend on uniformity of quality of recycled aggregate, so
potential problems in the practical application could occur if concretes without proper
classification, i.e. with significant differences in compressive strength, is delivered to recycling
plants.
An increase in the compressive strength during the period up to 28 days of age is usually higher
in natural aggregate concrete in relation to concrete made entirely from the recycled aggregate,
in ages higher than 28 days the situation is reversed, which is explained by the reaction of
cement from previously un-hydrated cement paste, attached from grains of recycled aggregates.
Tensile strength, usually determined by splitting tensile test through the line pressure, and more
rarely by flexural tensile test, does not significantly depend on the type and amount of applied
recycled aggregate (especially if only recycled coarse aggregate is used in the mixture), but, its
primary function is the ratio of aggregates and cement amounts – an increase in this ratio reduces
tensile strength. In fact, studies have shown that the presence of only coarse fraction of recycled
aggregates causes a decrease in tensile strength up to the maximum 10%, whereby the level of
participation of coarse fractions of recycled aggregate of 20% to 50% usually results in about 2%
lower tensile strength in comparison to the concretes made entirely with natural aggregate.
Differences in tensile strength in relation to natural aggregate concrete are to be expected in the
range of 10% to 20% only in cases when concrete is prepared entirely with recycled aggregate.
Thus, in relation to the coarse fraction, fine fraction of recycled aggregate has a slightly higher
impact on this feature.
The tensile and compressive strength ratio in recycled aggregate concrete is lower than the ratio
defined for natural aggregate concrete according to Eurocode 2- which can be concluded by
analysis of the diagram shown in Figure 2.3, where the test results of several researchers are
summed up. In this regard, it is noted that the values in the diagram refer to different percentages
of replacement of both – coarse and fine natural aggregate with the recycled one.

12
Figure 2.3: Diagram of relationship between tensile strength and compressive strength
of recycled aggregate concrete (I. Ignjatović et al.)
The full line in the diagram shown in Figure 2.3 represents the connection between tensile and
compressive strength according to Eurocode 2.
Where: fctm [МРа] – the mean value of axial tensile strength of concrete cylinder,
fck [МРа] − characteristic compressive cylinder strength of concrete at 28 days and
fcm [МРа] – the mean value of concrete cylinder compressive strength.
Based on the above, it can be seen that tensile and compressive strength ratio of recycled
aggregate concrete is averagely by 7% lower than the ratio defined for natural aggregate concrete
according to Eurocode 2, regardless of the share of recycled aggregate in the total mass of
applied aggregate.
The elasticity modulus of recycled aggregate concrete is lower than the one of comparable
natural aggregate concrete, which is a consequence of significant amount of old cement mortar
(in grains of recycled aggregates), which has relatively low elasticity modulus. Research

13
suggests that the level of decrease of modulus significantly depends on the type of fine fraction
in the aggregate mass. In fact, in concrete with 100% content of recycled coarse aggregate and
natural fine aggregate, a decline of elasticity modulus in relation to concrete made entirely with
natural aggregate goes up to 20%, while in the case of concrete produced entirely recycled
aggregates, decline of elasticity modulus ranges from 15% to 45% in relation to natural
aggregate concrete. Also, it is interesting to note that several studies have noted that the
difference level in elasticity modulus between recycled aggregate concrete and natural aggregate
concrete depends also on the compressive strengths of observed concretes, in the sense that for
concretes with middle values of strength of up to 30 MPa the difference in the modulus values is
almost negligible, while on the other hand, with the increase in strength above the stated value,
the difference between the subjected modules increases.
2.2.8 Abrasion resistance
The use of recycled aggregate concrete influences abrasion resistance, in a way that an increase
in the quantity of this aggregate reduces resistance to abrasion, due to higher amount of cement
matrix, which is more easily abraded than the grains of natural aggregates.
Adhesion between concrete and reinforcement does not significantly depend on the presence of
recycled aggregate in the mixture, since the adhesion is achieved through the new cement matrix.
2.2.9 Exploitation properties in sense of durability
General conclusions about the characteristics essential for the durability of concrete with
recycled aggregate cannot be made due to contradictory con clusions in the existing literature.
However, the facts related to the existence of two interfacial transition zones and usually higher
permeability of concrete based on recycled aggregate in relation to the comparable natural
aggregate based concrete, indicate greater vulnerability to degrading mechanisms during
exploitation. However, as permeability largely depends on the size, distribution and continuity of
capillary pores in cement matrix and interfacial transition zones in concrete structure, by
applying the above-described specificities related to the composition, design and preparation of
these types of concrete, it is possible to produce satisfactory, even high-performance concretes,
in terms of durability (M. Malešev et al. 2006, S. Marinković et al. 2011, B. M. Berry et al. 2012).
2.3 Structure of concrete
The recycled aggregate concrete generally has much more complex structure than natural
aggregate concrete, primarily due to the existence of two different forms of interfacial transition
zones within the composition of grains. Namely, while analyzing at micro level, the so-called
“old” and “new” interfacial transition zone can be observed. Old interfacial transition zone is
located between the original grain and original cement mortar that is completely or partially
attached to it, while the new interfacial transition zone is located between the recycled aggregate

14
grain and the new cement mortar. Furthermore, the complexity of the form is even more
pronounced when the recycled aggregate concrete is produced with a certain share of recycled
aggregates, as it is often the case in practice, for which stated concretes are made (especially
structural concretes). Then there will be two forms of new transition zones, which differ in terms
of structure (first – an interfacial transition zone between cement mortar and natural aggregate
and second - between cement mortar and recycled aggregates).
According to all results, whether our own, or from the research of the cited authors, it is not
possible to influence the characteristics of the „old” interfacial transition zone during the mix
design of the new concrete, but the appropriate principles and methods of preparing can affect
the properties of the “new” interfacial transition zone.
Researches conducted by S. C. Poon, H. Z. Shui and L. Lam, from the University of Hong Kong
(2003), point out that the new interfacial transition zone, within the recycled aggregate grain, to a
large extent has the properties of interfacial transition zone between the grains of the lightweight
aggregates and the mortar - in the case of lightweight concretes, where due to the porosity of the
grain, it begins below the grain surface and spreads to the cement mortar, whilst being dependent
on various possible processes, such as:
− Water absorption from cement paste, when the aggregate is dry,
− Release of water in the interfacial transition zone when the aggregate is moist,
− Penetration of the cement material into the pores and
− Possible chemical reaction with the aggregate.
Researchers from the University of Science and Technology in Norway - M. H. Zhang and O. E.
Gjorv (1990), have found that the structure of the interfacial transition zone has a lower density
if the aggregate grain has a higher density in the surface layer. In fact, this is because there are
more calcium hydroxide (Ca(OH)2) crystals in the interfacial transition zone, similar to the
interfacial transition zone at the contact of natural nonporous aggregates, so that the water that
accumulates in the vicinity of grains cannot be absorbed into the pore structure of aggregates, to
the extent at which it would have been absorbed if the grain was more porous. The cited
researchers also suggest that a thicker interfacial transition zone implies better adhesion between
aggregate grain and cement matrix, and finally better physical-mechanical properties. The stated
conclusions were confirmed several years later by researchers from the Technical University in
Israel - R. Wasserman and A. Bentur (1996), who examined the rapidity of water absorption in
the aggregate grains. By heating aggregates at high temperatures, the properties of the surface
layer of aggregate changed in a way that the porosity was reduced, density increased, and thus
the rate of water absorption decreased, but also, the width of the interfacial transition zone
increased. Thus they concluded that the absorption of water from the cement paste, into the
aggregate pore system, prevents the accumulation of water in that zone, which is generally
considered to be the main cause of the formation of its porous structure.

15
By applying “SEM” (scanning electron microscope, which achieves up to 300.000 times
magnification) for interfacial transition zone recording, researcher M. Radeka from the
University of Novi Sad (2008), found that the interfacial transition zone in the concrete based on
aggregates obtained by recycling old concrete could be seen as a zone that has properties
somewhere in between the properties of the interfacial transition zone in the „ordinary” concrete
(made from natural aggregates, assuming that the natural aggregate is non-porous) and the
properties of the interfacial transition zone in lightweight aggregate concrete (lightweight
aggregate is porous). Also, the mentioned researcher believes that the recycled concrete
aggregates with high mechanical properties can be expected to have the characteristics of the
interfacial transition zone which are closer to the „ordinary” concrete (natural aggregate
concrete), and also that the situation is reversed in the case of aggregates obtained by recycled
lower strength concretes.
Based on the above, it is clear that the porosity of recycled aggregate grains can, to a certain
extent, have a certain advantage over natural aggregate, because the present pores can absorb
water from the cement paste, so that the interfacial transition zone of greater compactness is
formed, but, on the other hand, at the same time its significant disadvantage is in the fact that the
water absorption from the cement paste may cause a deficiency of water needed for the process
of cement hydration, within the newly-made concrete. In this regard, the conclusion arises that
for the modeling of the microstructure of recycled aggregates concrete it is necessary to know
the precise value of the actual characteristics of recycled aggregates, primarily its capacity in
terms of absorption.
In 2004 the Spanish researcher E. M. Larranga published his research on recycled aggregate
concrete, in which he, according to a comprehensive analysis of experimental tests of physical
mechanical properties and the structure of transit zones, using the SEM, found that the best
characteristics of concrete were obtained when recycled aggregate from waste concretes was
previously saturated with water, up to the value of 80% of the total water that it can absorb.
Chinese researchers L. Gengying, X. Huicai and X. Guangjing (2001), in their work related to
finding possibilities for modeling the microstructure of recycled aggregate concrete, have
estimated the quality of the connection between the recycled aggregate and the new cement
matrix on the basis of morphology, mineralogy and microstructure formed in the interfacial
transition zone. They used „SEM”, supplied with “EDS” analysis (energy dispersive spectrum),
to compare concretes made from different cements, such as: pure portland cement, expansive
cement, cement with the addition of polymers - epoxy resin, and pozzolanic cement.
Based on the determination of strength during movement on the part of the transiting zone which
represents the zone between the original mortar (which is an integral part of the recycled
aggregate) and the new mortar, it was found that the best connection is established by use of
pozzolanic cement, then expansive cement, while the worst connection was established in
concretes made with cement with an addition of polymers. In their explanation, the authors point
out at hydrophilic properties of concrete which are the reason for a significant flow of water from
the new cement paste towards the surface of the original mortar. The flow of water leads to local
increase of water-cement ratio. Due to chemical reaction of the amorphous silicon from the

16
pozzolan with calcium hydroxide occurs the formation of a compound of CSH, and the pores get
filled in. Pozzolan particles effectively fill in the pores in the interfacial transition zone, which
results in an interfacial higher density transition zone. When expansive cement is used, ettringite
dominantly forms, and when portland cement is used, both calcium hydroxide and ettringite
form. In the case of cement modified with polymers, only a film based on polymers is observed
in the transition area (M. Radeka 2009 & V. Radonjanin et al. 2014).
2.4 Use of Recycled Concrete
Many countries are trying to use Recycled concrete for many years. Since the use of RCA still
isn’t very much popular, those who are using RCA hove some restrictions. There may be some
rules for using RCA. From the research of Mr. Tushar R Sonawane & Prof. Dr. Sunil S.
Pimplikar, Selected international experience has been outlined here which may be relevance for
the Bangladeshi situation:
A) Scotland– About 63% material has been recycled in 2000, remaining 37% material
being disposed in landfill and exempt sites.
a) The Government is working out on specifications of recycling and code of practice.
b) Attempts are being made for establishing links with the planning system, computerizing
transfer note system to facilitate data analysis and facilitating dialogue between agencies for
adoption of secondary aggregates by consultants and contractors.
B) Denmark – According to the Danish Environmental Protection Agency (DEPA), in 2003,
30% of the total waste generated was Construction & Demolition waste.
a) According to DEPA around 70-75% waste is generated from demolition activity, 20-25%
from renovation and the remaining 5-10% from new building developments.
b) Because of constraints of landfill site, recycling is a key issue for the country.
c) Statutory orders, action plan and voluntary agreements have been carried out, e.g., reuse of
asphalt (1985), sorting of Construction & Demolition waste (1995) etc.
C) Netherlands – More than 40 million Construction & Demolition waste is being generated out
of which 80% is brick and concrete.
a) A number of initiatives taken about recycling material since 1993, such as prevention of
waste, stimulate recycling, promoting building materials which have a longer life, products
which can be easily disassembled, separation at source and prohibition of Construction &
Demolition waste at landfills.
D) USA– Construction & Demolition waste accounts for about 22% of the total waste generated
in the USA.

17
a) Reuse and recycling of Construction & Demolition waste is one component of larger holistic
practices called sustainable or green building practice.
b) Green building construction practices may include salvaging dimensional number, using
reclaimed aggregates from crushed concrete, grinding drywall scraps, to use as soil amendment
at the site.
c) Promoting “deconstruction” in place of „demolition‟.
d) Deconstruction means planned breaking of a building with reuse being the main motive.
E) Japan– Much of the R&D in Japan is focused on materials which can withstand
earthquake and prefabrication.
a) 85 million tons of Construction & Demolition waste has been generated in 2000, out
of which 95% of concrete is crushed and reused as road bed and backfilling material, 98% of
asphalt + concrete and 35% sludge is recycled.
F) Singapore– Construction & Demolition waste is separately collected and recycled. A private
company has built an automated facility with 3, 00,000 ton per annum capacity.
G) Hong Kong– Concrete bricks and paving blocks have been successfully produced
impregnation of photo catalyst for controlling Nox in ambient air.
H) India– Use for embankment purpose in bridges, roads etc. up to 3% to 4% of total
production.
I) Bangladesh- In Bangladesh application of recycle concrete aggregate without any processing
include:
1. Many types of general bulk,
2. Bank protection,
3. Base or fill for drainage structures,
4. Road construction,
5. Noise barriers and embankments.
After removal of contaminants through selecting demolition, screening, or air separation and size
reduction in a crusher to aggregate sizes crushed concrete can be used as:
1. New concrete for pavements, shoulders, median barriers, sidewalks, curbs, gutters, and
bridge foundation,
2. Structural grade concrete,
3. Soil cement pavement base,
4. Lean- concrete bases, and
5. Bituminous concrete.

18
Every year many countries wasted so many construction and demolished waste which may be
used by recycling. But recycling isn’t much easy. According to Akmal, Sami (2011) the
available resources should be used appropriately & whenever recycled it should be done at the
national level with the help of GULF COOPERATION COUNCIL (GCC) &
ENVIRONMENT PROTECTION INDUSTRIAL CO (EPIC). They observe that GCC countries
produce more than 120 million tons of waste every year out of which 18.5 % is related to solid
construction waste. Results from Dubai municipality indicate that out of 75% of 10,000 tons of
general waste produced, 70% is of concrete demolition waste.
The effect of the cleanliness and percentage of the replacement of RCA that the degree of
cleanliness of aggregate has significantly affected on the results of the properties of both the
plastic and hardened concrete. The workability and compressive strengths both were lower than
the quarried aggregate from 17% to 78% depending on the percentage of replacement of RCA.
The results also indicated recycled aggregate has very high air content.
The author strongly advocates that a strong commitment & investment by government bodies as
well as private bodies make this necessary for sustainability. Some materials are reused for
recycling such as plastic, glass etc. In the same way concrete can also be used continuously as
long as the specification is right. Recycling solid waste materials for construction purposes
becomes an increasingly important waste management option, as it can lead to environmental
and economic benefits. Conservation of natural resources, saving of energy in production and
transportation, and reduction of pollution are also the advantages of recycling. In particular,
concrete is a perfect construction material for recycling. In gulf countries natural resources are
imported from different locations for fulfilling the need of construction. Small sources available
in gulf countries in Arabian Peninsula are limited. For construction work, demand of desalinated
water & sand locally available exits. Conservation of natural sources, saving natural resources,
energy transportation & reduction of pollution are advantage.
2.5 Advantage of recycling
Environmental considerations:
In this time of increasing attention to the environmental impact of construction and sustainable
development, portland cement concrete has much to offer:
(1) It has resource efficient-minimizing depletion of our natural resources;
(2) It has iner-marking is an ideal medium in which to recycle waste or industrial byproducts,
such as fly ash;
(3) It has energy efficient-in a cradle to-grave study on the impact of energy expended in all
phases of production, concrete was superior to wood and steel;
(4) It is durable-continuing to gain strength with ~ time; and finally

19
(5) It is recyclable-fresh concrete which is used on an as-needed basis (whatever is left over can
be reused or reclaimed as aggregate), and old hardened concrete can be recycled and used as
aggregate in new concrete or as fill and pavement base material.
Economic factors:
Recycling concrete is an attractive option for governmental agencies and contractors alike. Most
municipalities impose tight environmental controls over opening of new aggregate sources. In
many areas, zoning requirements and public rancor - not in my backyard sensibilities-limit the
possibility or, increase the cost of starting new quarries. For demolition contractors landfill space
is scarce especially in urban areas. Some landfills may not accept construction materials, and
disposal of old concrete and masonry is costly. Also, dumping fees will most likely rise as
construction debris increases and the number of accessible landfills decreases. Furthermore, the
cost and transport distances of conventional aggregates could continue to increase as sources
grow scarce. With recycled aggregates there is potential for cost savings in hauling. It is not
unusual for contractors to haul conventional aggregates 50 to 70 miles on projects, and also
distances greater than 200 miles are not uncommon.

20
CHAPTER 3
RECYCLED AGGREGATE USED IN
BANGLADESH

21
3.1 Introduction
Due to the large demand of housing and infrastructures, a huge number of construction works
can be seen in the capital city as well as other cities in Bangladesh. Therefore, it is essential to
take necessary steps for the sustainable development of concrete construction works in
Bangladesh. At the beginning of thinking of sustainable concrete construction works, it is
necessary to understand the causes of deterioration of concrete structures; it is also necessary to
understand the general construction practices at site that accelerate the deterioration process of
concrete structures. Therefore, these issues are included in the scope of this topic.
Due to high humidity and temperature in Bangladesh, concrete structures are damaged by
carbonation induced corrosion of steel in concrete. A detailed study is necessary to determine the
carbonation coefficient of concrete in natural exposures of different cities. Applications of
recycled aggregate and permeable concrete are necessary to make examples of utilization of
these useful and environmentally friendly materials. Also, long-term exposure tests (100 years or
more) are necessary to understand deterioration rate of concrete structures in Bangladesh. In this
case study project for sustainable development of concrete construction works in Bangladesh is:
1. Causes of deterioration of concrete structures,
2. Problems at construction sites that causes early deterioration of concrete structures,
3. Properties of concrete made with various aggregates,
4. Recycling of demolished concrete as coarse and fine aggregate for new construction,
5. Recycling of Recycled Fine Aggregate
6. Development of permeable concrete for special application,
7. Determination of carbonation coefficient in natural exposure conditions, and
8. Application of recycled concrete.
3.2 Causes of Deterioration of Concrete Structures in Bangladesh
To understand the possible causes of deterioration of concrete structures in Bangladesh, a
detailed survey of some buildings in several districts were carried out. Based on the survey
results, the main causes of deterioration of concrete structures in Bangladesh are:
1. Carbonation induced corrosion of
steel bars,
9. Thermal expansion,
2. Chloride induced corrosion of steel
bars,
10. Differential settlement,
3. Drying shrinkage, 11. Lack of reinforcement in structural
members,
4. Mud in aggregate, 12. Lack of cover thickness of
structural members,
5. Efflorescence in bricks, 13. Leakage of water through roof,
6. Sulphate attack/ Chemical attack, 14. Leakage of water from plumbing
pipes embedded in walls, and

22
7. Leakage through joints, 15. Lack of maintenance.
8. Heat of hydration,
Due to the high humidity (60% ~95%) and high temperature (40°C in summer), a high rate of
carbonation is found in concrete structures of Bangladesh. The use of low strength concrete (less
than 20.7 MPa) as well as poor quality concrete works at the construction site also accelerates
the process of carbonation. Concrete floors, beams, and columns are severely damaged due to the
carbonation induced corrosion of steel bars after 10 ~ 15 years of construction. It is found as the
most common cause of deterioration of concrete structures in Bangladesh. Investigations were
also conducted to determine carbonation coefficient of concrete in Dhaka city. These results are
summarized in this report.
In the coastal areas, the concrete structures are damaged due to the combined action of chloride
and carbonation-induced corrosion of steel bars in concrete. Investigations related to the chloride
ingress into concrete at the coastal areas of Bangladesh are necessary.
Cracks on the walls are found due to the drying shrinkage at the early age of the structure. A lime
concrete coat on the roof of the buildings is applied to reduce the heat flow in summer.
Unfortunately, the lime concrete soaks water in rainy seasons for long time and it accelerate the
deterioration of the roof slab. Storage of the materials on the roofs as well as water logging on
the roof is also found to be the causes of deterioration of roof slab. Efflorescence is found in the
partition wall due to the presence of salts in the brick. Leakage of water through the plumbing
pipes embedded in walls is also found. Soaking of water and quick damage of paints on wall are
found. Generally, patch type repair is carried out but it is found to be ineffective after a short
time of repair.
3.3 Problems at Construction Sites that Causes Early Deterioration
of Concrete Structures in Bangladesh
Several construction sites were visited to identify the causes associated with the early
deterioration of concrete structures at service. The followings are identified:
1. Un-sieved poorly graded aggregates,
2. Unwashed aggregates,
3. Mud in mixing water,
4. Used reinforcement,
5. Excess water in mix,

23
6. Higher W/C,
7. Excess sand,
8. Excess coarse aggregate,
9. Poor mixing/ mixture proportion,
10. Problems associated with volumetric mix proportions,
11. Lack of cover concrete,
12. Problems associated with formwork (leakage of mixing water),
13. Placing of concrete from a large height by labors,
14. Inappropriate compaction,
15. Inappropriate curing,
16. Brick efflorescence,
17. Poor workmanship,
18. Unskilled workers, and
19. Inappropriate storage of construction material.
Volumetric mix proportions are generally used for most of the construction works except ready
mix concrete industries. Generally mix proportions for concrete are set at 1:1.5:3 (compressive
strength 20.7 ~ 27.6 MPa) or 1:2:4 (compressive strength 17.2~20.7 MPa) for most of the
construction works. The amount of water for concrete works is recommended to be 25 liter per
bag of cement as per Bangladesh National Building Code (BNBC).
Unfortunately, at the construction sites, water is added till the mix become workable without any
measure. For this reason, in actual construction, the strength of concrete becomes lower than the
target strength. The use of a high W/C makes concrete relatively porous and consequently
creates easy paths for ingress of harmful constituents into concrete and thereby early
deterioration of structures.
3.4 Properties of Concrete Made with Various Aggregates Commonly Used in
Bangladesh
Brick chips are commonly used in Bangladesh for making concrete since long ago due to lack of
availability of stones. Stone chips are also used but the quality of stone chips is questionable.
Shingles (round shaped stone) are also used in construction for its better workability. Jhama

24
brick chips are also found in the market which is used rarely in construction. A detailed study
was carried out from the study of Mohammed Tarek Uddin to compare the properties of concrete
made with these aggregates. The properties of aggregates are summarized in Table 3.1. Brick
chips were also investigated with the variation of moisture content (SSD-Saturated Surface Dry
Condition, AD-Air Dry Condition, CAD-Controlled Air-Dry Condition, and OD-Oven Dry
Condition). Concrete cylinder specimens (15 cm diameter and 30 cm height) were made with
water-to-cement ratio of 0.55. Cement content of the mix was 340 kg/m3. Sand to aggregate
volume ratio of the concrete was set at 0.44. FM of coarse aggregates was 6.69. FM, specific
gravity, and absorption capacity of sand was 2.64, 2.61, and 3.9% respectively. For comparison
of brick and stone aggregates, the brick aggregates with similar abrasion of stone aggregate were
selected. The absorption of brick aggregates (11.5%) and jhama brick chips (12.2%) is higher
than the stone aggregates (0.8%) and shingles (2%). The abrasion value of brick chips was
26.3%, and for stone chips was 25%. The abrasion value of shingles and jhama brick chips were
20.78 and 37.16% respectively.
The workability of concrete made with different aggregates is shown in Figure 3.1. Concrete
made with brick chips shows the lowest workability due to the more internal friction between the
brick aggregates as well as higher absorption capacity. Due to its round shape, shingles shows
the highest workability. In construction sites, it was found that water is added to the mix as long
as the mix becomes workable, therefore it is likely that more water is added in brick aggregate
concrete for improving workability. The strength of concrete at 7, 14, and 28 days are shown in
Figure 3.2(a) for concrete made with different aggregates. Interestingly, brick aggregates give
higher strength compared to the stone aggregates. It is happened due to the development of
strong interfacial transition zone around brick aggregates compared to the same with stone
aggregate.
The compressive strengths of concrete with the variation of moisture condition of brick
aggregates (NB) are shown in Figure 3.2(b). In all cases, the amount of water in concrete is kept
same (amount of water to make SSD sample plus amount of water required from W/C) except
NBEW55 case. In the case of NBEW55 (Normal brick aggregate with excess water and
w/c=.55), the aggregates with surplus amount of water on the surface were used. The
compressive strength of concrete remains same with the variation of moisture condition. But, the
presence of excess water on the surface leads to the reduction of strength due to the increase of
the amount of water in the system. In addition to these factors, dust contaminated aggregates,
pre-heated aggregates, and cement paste-coated aggregates were also investigated. These results
will be incorporated in the future reports.

25
Table 3.1: Properties of Aggregates Investigated(Tareq,2013)
Figure 3.1: Workability of concrete made with different aggregates
(W/C=0.55) (Tareq,2013)
Figure 3.2: Compressive strength of concrete made with (a) different aggregates (Left)
(b) different moisture condition (Right) (Tareq,2013)

26
3.5 Recycling of Demolished Concrete as Coarse Aggregate
The global consumption of concrete is estimated at 17.5 billion tons (@ 2.5 tons/capita/year for 7
billion of world’s population). To make this huge volume of concrete, 2.62 billion tons of
cement, 13.12 billion tons of aggregate, and 1.75 billion tons of water are necessary. At present,
the global production of demolished concrete is estimated at 2~3 billion tons per year. In the next
ten years, the global production of demolished concrete will be raised to 7.5~12.5 billion tons. If
it is possible to recycle the total amount of demolished concrete, there will be no need for
production of new aggregates by destroying mountains or burning clay. The volume of
demolished concrete in Bangladesh is also increasing day by day due to the aging of
infrastructure as well as replacement of low rise buildings by relatively high rise buildings due to
the booming of real estate business. Therefore, an attempt was made to find out the possible
ways for recycling of demolished concrete for new construction as coarse aggregates. The
properties of recycled aggregates collected from 33 different sites are summarized in Table 3.2 .
1-Year old recycled brick and stone samples were collected by crushing cylinder specimens
tested at the concrete laboratory. The age of the recycled aggregate is varied from 1 to 60 years.
In most of the cases, the absorption capacity of the recycled aggregates is lower than the normal
brick aggregates. Also, in most of the cases, no significant difference is found between the
abrasion values of normal brick aggregate and recycled brick aggregate. The results indicate that
the quality of recycled brick aggregate (old brick aggregate with old adhered mortar) is very
similar to the quality of the normal brick aggregate commonly used in Bangladesh. Cylinder
concrete specimens (150 mm diameter) are made for 58 separate cases as summarized in Table
3.3.
The compressive strength of concrete with the variation of aggregate and W/C is shown in
Figure 3.3 (a). For W/C= 0.55, a reduction in strength of concrete is found for recycled brick
aggregate concrete compared to the normal brick aggregate concrete. But for W/C=0.45, the
compressive strength of recycled aggregate concrete is higher than the normal brick aggregate
concrete.
The results indicate that by reducing W/C, compressive strength of recycled aggregate concrete
can be improved to the level of the normal aggregate concrete. The variation of tensile strength
of recycled aggregate concrete with the compressive strength of recycled aggregate concrete is
shown in Figure3.3 (b). The relationship shown in Figure 3.3(b) can be used to calculate the
tensile strength of recycled aggregate concrete from the compressive strength of recycled
aggregate concrete.
The variation of compressive strength of recycled aggregate concrete with the wear value of
recycled coarse aggregate is shown in Figure 3.4 (a). It is observed that with an increase of wear
value, the compressive strength of recycled aggregate concrete is reduced. Using these
relationships (as shown in Figure 3.4 (a), the expected strength of recycled aggregate concrete
with a known wear value of recycled aggregate and W/C of concrete (0.45 or 0.55) can be
judged.

27
Table 3.2: Properties of Aggregates (Tareq, 2013)
Table 3.3: Cases Investigated ( 58 cases ) (Tareq, 2013)

28
Figure 3.3 : (a) Compressive strength of concrete with the variation of W/C (Left) (b)
Tensile strength versus Compressive strength of concrete (Right) (Tareq, 2013)
Figure 3.4: (a)Compressive strength of concrete versus wear (left), (b) cumulative probability
distribution of compressive strength of recycled aggregate concrete for w/c=0.55 and
0.45(right) (Tareq, 2013)
The cumulative probability distribution function (CDF) of 28-day compressive strength of recycled
aggregate concrete is shown in Figure 3.4 (b) using normal distribution. The average compressive
strength (with cumulative probability = 0.5) for W/C=0.55 is found at 20.7 MPa and the same for
W/C=0.45 is found at 25.5 MPa. The standard deviation was 2.6 MPa for W/C=0.55 and 3.5 MPa for
W/C=0.45. The ten percentile values (with cumulative probability = 0.1) of 28-day compressive strength
of recycled aggregate concrete is found at 17.2 MPa and 20.7 MPa for W/C=0.55 and W/C=0.45
respectively. It is important to note that similar strength of concrete is generally found for concrete made
with normal brick aggregates. The results indicate that the recycled brick aggregate can be utilized for
new construction works with design compressive strength of 20.7 MPa to 25.5 MPa.

29
3.6 Recycling of Recycled Fine Aggregate
Demolished concrete blocks from eight different demolished building sites were collected and
then manually crushed into aggregate (recycled aggregate). The concrete of the demolished
buildings was made with brick aggregate. Therefore, the scope of investigation will cover only
the recycling of fine aggregate obtained from brick made demolished concrete for making mortar
blocks. The ages of the demolished buildings were 30, 35, 37, 44, 45, 45 (denoted as 45a), 50,
and 60 years. During the production of coarse aggregate, smaller sizes aggregate less than 5 mm
(passing through #4 sieve) is produced as a by-product. The portion of the by-product aggregate
passing through #4 sieve and retained on #16 sieve are collected during breaking of demolished
concrete block. Similar portions of aggregate are also collected during crushing of brick and
stone for making coarse aggregate. It was done as aggregate portion passing through #4 sieve
and retained on #16 sieve is found in small proportion in fine aggregate commonly used in
Bangladesh. The coarse portion of the collected fine aggregate was mixed with natural coarse
sand (FM 2.6) and natural fine sand (FM 1.8) in different portion of the fine aggregate collected
during production of recycled coarse aggregate plus natural coarse sand plus natural fine sand in
different proportions as explained later. In the similar way, stone fine aggregate (SFA) and brick
fine aggregate (BFA) can be defined.
Mortar block specimens were made with different fine aggregates as explained before with
different grading as listed in Table 3.4. RFA45-40-30-30 indicates recycled fine aggregate (RFA)
of age 45 with 40% of recycled aggregate plus 30% of coarse sand and 30% of fine sand. W/C
ratios were 0.55 and 0.45. The mixture proportions were made based on the absolute volume
method explained before with constant FA/C = 5. Also, some cases were made with lower
values, such as 4.5, 4, 2.5, and 2 to increase the strength of the mortar blocks. CEM II/B-M was
used throughout this study.
Mortar blocks of size 100 mm in length, 100 mm in width, and 70 mm in height were made for
investigations which are half of a standard brick used in Bangladesh to measure compressive
strength. Compressive strength of the mortar blocks was determined at 28 days after making of
the specimens. The compressive strength of mortar block is shown in Figure 3.5(a) for all cases
of recycled fine aggregate made with W/C=0.55 with fine aggregate (FA) to cement ratio is 5. It
can be seen that with the increase of amount of finer portion of sand, the strength of mortar block
is reduced irrespective of the ages of recycled fine aggregate (say 45 and 50 years). The
compressive strength of mortar block is shown in Figure 3.5(b) for the cases W/C=0.45, and fine
aggregate to cement weight ratio is 5.0. As in W/C=0.55, it is found that with the increase of
finer portion of aggregate, the compressive strength of mortar block is reduced. Therefore, it can
be concluded that the finer portion in fine aggregate plays a vital role in compressive strength of
mortar blocks. The proportion of 50:25:25 gives the maximum compressive strength. Similar
observations are also found for W/C=0.45. By reducing the FA/C ratio, compressive strength of
RFA mortar block can be increased up to 31 MPa. Recycled fine aggregate gives higher strength
compared to the brick fine aggregate. The data are not included in this thesis.

30
Table 3.4 : Grading of Different Fine Aggregate (Tareq, 2013)
Figure 3.5: Compressive strength of recycled mortar block (a) w/c=0.55 (left) (b) w/c=0.45
(right) (Tareq, 2013)

31
3.7 Development of Permeable Concrete for Special Applications
Due to the construction of buildings and other infrastructures in the major cities in Bangladesh, it
is found that the uncovered ground area for infiltration of rain water to ground water reservoir is
reduced significantly. On the other hand, continuous sucking of ground water from underground
reservoir results in depletion of ground water level year by year. This environmental problem can
be reduced by application of porous concrete on parking areas, walkways, and roads for light
vehicles, etc. With this background, this study on pervious concrete has been planned. Cylinder
concrete specimens of diameter 100 mm and height 200 mm were made with locally available
coarse aggregates (1st class brick aggregate, crushed stone aggregate, and recycled brick
aggregate). Variables include type of aggregate and gradation of aggregate. Cement content was
300 kg/m3 and water-to-cement ratio was 0.33. Test items include void in aggregate, unit weight
of aggregate, specific gravity of aggregate, compressive and tensile strength of pervious concrete
at 28 days and permeability of water through the pervious concrete.
Three types of locally available aggregate ((1st class brick (FB), crushed stone (CS), and
recycled brick aggregate (RB)) were used in this study. The properties of these aggregate are
summarized in Table 3.5. Pervious concrete used in this study was prepared using 10 different
aggregate gradations. The cement used in this study was CEM II/A-M as per BDS EN 197-1.
Tap water was used for all mixture. All mixture had water-to-cement ratio 0.33 and cement
content 300 kg/m3. The mixture proportions are summarized in Table 3.6. Thirty different cases
were investigated by varying type of aggregate (CS, FB, and RB) and gradation of coarse
aggregate. Mixture ID 100#3/8 indicates 100% of coarse aggregate (CA) is retained on 3/8″
sieve. Similarly mixture ID 50#4 50#8 indicates 50% of CA is retained on #4 sieve and 50% on
#8 sieve.
Unit weight of concrete for different mix proportions are shown in Figure 3.6.The results
revealed that the unit weight of pervious concrete varied with respect to the gradation of CA and
the type of aggregate. It is observed that pervious concrete made with CS shows higher unit
weight with an average of 1885 kg/m3 compared to FB and RB pervious concrete. Unit weight
of pervious concrete made with FB varied from 1380 kg/m3 to 1730 kg/m3 with an average
value of 1520 kg/m3. Pervious concrete made with RB varied from 1450 kg/m3 to 1600 kg/m3
with an average value of 1510 kg/m3.
Table 3.5: Summary of Aggregate Properties (Tareq, 2013)

32
Table 3.6: Mixture properties of Pervious Concrete (Tareq, 2013)
Percentage void of pervious concrete with different type of aggregate is shown in Figure 3.7(a).
The percentage void of pervious concrete varied widely. It is observed that, pervious concrete
with large size aggregate shows more interconnected void than other mixes. It is also observed
that, pervious concrete made with RB shows higher interconnected pores, it is due to blunt edge
of the RB. Further research is necessary to give a conclusion with this respect. Percentage void
of pervious concrete made with CS is varied from 10% to 27%, from 12% to 28%for FB, 12% to
31%for RB. According to ACI 522-06 the typical void content of pervious concrete can range
from 15% to 35% . Most of the mix proportions (Table 3.6) satisfy the ACI specification.
Permeability of pervious concrete made with different type of aggregate is shown in Figure
3.7(b). Similar to percentage void, permeability of pervious concrete made with RB is higher in
most of the cases. Permeability of pervious concrete is varied from 15 mm/sec to 59 mm/sec for
CS, 16 mm/sec to 51 mm/sec for FB, from 17 mm/sec to 49 mm/sec for RB.
Compressive strength of pervious concrete made with different type of aggregate is shown in
Figure 3.8(a). For the investigated cases, compressive strength of pervious concrete made with
CS varied from 5.2 MPa to 12.0 MPa, from 4.3 MPa to 6.9 MPa for FB, from 5.5 MPa to 6.9
MPa for RB. Pervious concrete made with CS shows higher compressive strength compared to
FB and RB. RB shows higher average compressive strength compared to FB. It is due to the
rough and porous texture of recycled aggregate which gives good bonding with cementecious
matrix.
Same as compressive strength, pervious concrete made with CS shows higher tensile strength
compared to other two aggregates (FB and RB) as shown in Figure 3.8(b). Tensile strength of
pervious concrete made with CS varied from 1.03 MPa to 1.69 MPa, from 0.90 MPa to 1.45 MPa
for FB, from 0.86 MPa to 1.38 MPa for RB.

33
Figure 3.6: Unit Weight of pervious concrete made with different aggregates (Tareq, 2013)
Figure 3.7: Pervious concrete made with different aggregates (a)percentage void (left), (b)
permeability (right) (Tareq, 2013)
3.8 Determination of Carbonation Coefficient of Concrete
To determine carbonation coefficient of concrete, carbonation depth of concrete in real structures
was determined for different structural elements, such as beams, columns, stairs, and slabs.
Exposure environments were separated as indoor and outdoor. Carbonation depths were
measured by spraying phenolphthalein solution on freshly broken surface of concrete or on
powder sample collected from different depths of concrete by using a concrete drill. The results
are shown in Figure 3.9. The average carbonation coefficient was found to be 3.36 and 4.16 in
indoor and outdoor exposures, respectively. The results indicate that, for 100 years of service
life, minimum cover of concrete in indoor and outdoor exposure condition is to be 34 mm and 42
mm respectively. In general, for slabs cover concrete is specified to be 20 mm. Also, relative low

34
strength concrete is used for slabs. Therefore, within a short period of time, spelling of cover
concrete for slab is found due to carbonation induced corrosion. Cover thickness of slab is to be
increased from the currently specified value in the design code.
Figure 3.8: Pervious concrete made with different Aggregates (a) Compressive strength
(Left) (b) Tensile strength (Right) (Tareq, 2013)
Figure 3.9: Relationship between depth of carbonation and age of structure for indoor
exposure (left) and outdoor exposure (right) (Tareq, 2013)

35
3.9 Applications of Recycled Aggregate and Permeable Concrete
The roof-top community hall (columns, beams, and slab) of a six-storied building at Mirpur,
Dhaka was constructed with recycled aggregate. Concrete was made with 1:1.5:3 volumetric mix
ratio. Aggregate types include brick recycled aggregate, stone recycled aggregate, picked
recycled aggregate, and re-recycled brick aggregate. Also, 100 mm diameter and 200 mm height
cylinder specimens were made and exposed on the roof of the community hall for investigation
at 28 days, 5 years, 10 years, 20 years, and 50 years of exposure. In addition to the compressive
strength, carbonation depth of the specimens will also be recorded with time. A walkway of a
spinning mill in Chittagong, Bangladesh was constructed with permeable concrete. More
applications are necessary for wider acceptance of these environmentally friendly materials.
.

36
CHAPTER 4
RECYCLE AGGREGATE CAN BE USE FOR
MORE AREAS

37
4.1 Possibilities for using RCA concrete in non-structural construction
materials:
Because of the uncertainty of the performance of RCA concrete, it is not allowed to use this
material for structural purposes, in some countries. It is especially reports of high water
absorption and low specific gravity of RCA which leads to higher drying shrinkage and creep
than in ordinary concrete aggregates (Portland Cement Association. [Online] 2013). In Spain,
which I consider to be an important country for this paper, the regulation of EHE-08 do not allow
RCA concrete fully formulated in recycled aggregates to be used for structural purposes. The use
of recycled aggregates is limited to the 20 % of the concrete formulation. This is why this study
has found some non-structural concrete products and considered the possibilities of using RCA
concrete in these products. Non-structural concrete can be considered all for structural purposes
that are critical for the safety of the structure. It should be noted that these suggestions are not
tested or proved to work. This is just a presentation of possibilities which can be research further.
4.1.1 Concrete sandwich panels
The sandwich panels for building constructions are made of two solid layers and a rigid
insulating layer in the middle. The solid layers can be made of aluminum, steel or concrete. The
concrete sandwich panels often have a load bearing interior layer and a non-load bearing
exterior. It is for this non load bearing exterior that it can be possible to use RCA concrete. Load
bearing layers can be made from natural concrete, while the non-structural layer can be made of
RCA concrete.
First of all, the sandwich panels are prefabricated. This means that the proportioning, mixing and
the curing can be completed in a controlled environment. And because of the high water
absorption it will be wise to suggest that the curing of RCA concrete happens in a moist
environment. This will make the concrete perform better (Thomas et al. 2012). Perfecting the
recycling process and the quality control for the crushed concrete are necessary. And research
shows that the concrete mix could be proportioned by the EMV method. There are so many
advantages when sandwich elements are used. Here is a list form the national precast concrete
association Australia (National precast concrete association Australia, 2013):
- High R-values
- Good thermal and acoustic behavior
- Simpler construction process
o Faster construction time
o Less weather dependent because it is prefabricate
o Less waste at the building site.
- There are a wide range of design possibilities
- Fire resistant and durable

38
Figure 4.1: Detail of a Sandwich panel (Mats , 2013)
Figure 4.1 shows the cross-section of the concrete sandwich element. It can be seen that the
interior layer is the structural layer. Their thickness can e.g. vary from 125 to 200 mm. This is of-
course dependent of how much load the walls are exposed to. It does not only have structural
purpose, but also a thermal. When the internal layer is heated, the heat is stored in the concrete
mass. So when the heat, which warmed the wall, is gone, the wall itself will keep warming the
inside of the building.
Although the construction with sandwich panels offers many advantages, there are some aspects
to be considered. Those are the concrete cover of the reinforcement, joints between elements,
perimeter around windows and the adherence between different building materials. And knowing
that concrete and steel have a high conductivity, it is important to connect the sandwich layers
without too many thermal bridges (Sintef, 1994).

39
Figure 4.2: Cross section of a sandwich panel (Mats , 2013)
The insulation layer is often made out of polystyrene, which is a type of plastic. In picture 2 we
can see the blue rigid insolating layer. It is this layer which contributes the most to the R value of
this material. The R-value is a measure of the thermal resistance, and in concrete sandwich
panels R-values up to 3 m2 *K/W can be achieved (National precast concrete association
Australia. 2013).
Connectors are placed between the two concrete layers. Their main function is to distribute loads
between the concrete layers and making sure that the layers stay together. A company called
Owens Corning has a product called Pinkcore Insulated Concrete Sandwich Panel Wall systems.
They distributes polystyrene insulation and low conductivity wall ties. The wall ties are made
from thermoplastic resin (Owens Corning, 2010).

40
Figure 4.3: Pinkcore Insulated Concrete Sandwich Panel System (Mats , 2013)
The Pink core ties have a low conductivity, which reduces the thermal bridges of the wall.
Picture 3 shows a cross section of how the sandwich panel layers are connected with Pink core
Tie. In figure 4.3 is the double-prong low conductivity wall tie. This can be applied in pre-
stressed non composite insulated concrete panels. It can be used for 38 mm thick insulation, and
it has an excellent alkaline and impact resistance. The dobble-prong res over 300 lb (136 kg) for
over 120 minutes of fire.
4.1.2 Concrete Sound Walls
Concrete fences are often made by erecting precast concrete elements. This can be nonstructural
elements, which only need to withstand their self-weight, wind pressure and the climatic
deterioration. Concrete fences are used to block out disturbing sound form e.g. traffic or serve as
a protecting layer against intruders. They can also serve as a complementary tool for residential
privacy, obstructing the view into the property.

41
Figure 4.4: Sound wall (Mats , 2013)
Tricon Precast Sound walls are non-structural concrete fences, which can both disrupt and reflect
sound energy (Tricon Precast Limited. [Online] 2013). These types of walls are installed over
proper foundation. One by one wall element erected and connected to the foundation and to a
column by welding or bolts. For some walls, the concrete column is connected to the wall
element during prefabrication. For aesthetic satisfaction, form liners can be used. Figure 4.5
shows some examples of form liners for concrete walls.
Figure 4.5: Form liners (Mats , 2013)
There are two types of Sound walls, absorptive and reflective. While a reflective wall bounces
the sound waves back, absorptive walls lets the sound waves enter the wall. In both cases the
sound walls makes the sound travel a longer distance before it hits the receiver. The longer
distance the sound travels, the more energy it loses, and the less sound arrives at the receiver.

42
Figure 4.6: Minimum length of sound wall (Mats , 2013)
Figure 4.7: The height of the wall reduces the sound (Mats , 2013)
Criteria which need to be fulfilled for sound walls are a minimum density of 37 Ib/yd2 (20
kg/m2), sufficient height and at least eight times the length of the distance from the receiver to
the barrier (Precast concrete absorptive sound walls. United States of America and Canada).
This can be seen in Figure 4.6.The distance from the sound wall to the receiver, also called the
line of sight, should be the length which reduces the sound by 5dB. The height of the wall than

43
reduces the sound with 1.5 dB for each meter of height, which can be seen in Figure 4.7. The
decibel scale is a logarithmic scale and therefore is reductions of 1.5 dB a significant difference.
E.g. a reduction of 9dB is equivalent of a reduction of 80 % sound elimination.
Porosity of the material is very important for sound walls. And this is may be a reason for using
RCA concrete in this application. There hasn’t any research found on the sound properties of
RCA concrete, but I know that in many of the research papers they have stated that one of the
most problematic features of RCA concrete is its porosity.
Figure 4.8 shows a micrograph of the RCA structure. There can be seen how much more porous
the RCA is, if it is compared to the new cement paste and the natural aggregates. Figure 4.9is a
detail image of the RCA microstructure mortar mix. And in figure 4.10 this can be seen how the
RCA content and the water / cement ratio contributes to a more porous concrete. Graph (a), (b)
and (c) is the open porosity in volume % after 28, 180 and 365 days respectively (Thomas,
2012).
Even if the porosity is a benefit for sound walls, it is a huge challenge for the durability of the
concrete. Concrete with an open porous micro structure is more exposed for contaminations like
chlorides from salting of the roads, carbonation, sulphates and nitrates intrusion. Therefore it can
be a good idea to have a protecting layer on the concrete surface.
One way of protecting the concrete is impregnation. There are different types of impregnation.
Some makes a water resistant surface, without covering the concrete surface. These types are
called hydrophobic impregnation and give the interior concrete voids a water resistant surface, as
seen in figure 4.11. According to the studied features of the material, this type of protection may
be used, because it protects the concrete, while the porous surface remains.
Another possibility of protecting the concrete is a dense impregnation or covering. Impregnation
protects the concrete by reducing surface voids. The voids become partial filled and thin, but not
continuously film, covers the concrete. This is illustrated in figure 4.11. The use of RCA
concrete in sound walls can be a good alternative for utilizing waste concrete. The huge amount
of concrete waste needs to be taken advantage of, and this will be even more important in the
future. Governments around the world have already intentions in reducing concrete waste, and to
reach these goals new ideas are necessary. Research about how RCA concrete performs in sound
walls is, important according to all papers reviewed. The research should follow investigations of
how RCA concrete performs as a sound reducing element. And how RCA concrete will survive
in the harsh outdoor climates where sound walls are constructed. Like along trafficked roads.
Also studies on how the impregnation and form liners coexist with RCA concrete would have
been interesting.

44
Figure 4.8: Micrograph of the RCA structure Figure 4.9: Detail image of the RCA
microstructure (Mats , 2013)
Figure 4.10: How the RCA content and the w/c ratio affects the porosity and concrete
(Mats , 2013)

45
Figure 4.11: Hydrophobic impregnation (Mats , 2013)
Table 4.1: Suggested possibilities for RCA concrete in concrete sandwich panels
(Mats , 2013)

46
4.1.3 Architectural precast concrete panels
Architectural precast panels also refer to as precast curtain walls. These panels are precast façade
panels. Precast concrete manufacturers produce either structural or architectural elements. The
panels are constructed in controlled environments by concrete manufactures .There are different
types of curtain façade panels. These panels can come as window wall panels, which typical
covers one floor, or as spandrels and infill panels. This is illustrated in figure 4.12.
Figure 4.12: Different types of curtain facades (Mats , 2013)
Important factors for precast curtain walls are an early high strength, a concrete quality of about
35 MPa and a certain wall thickness. The early high strength is important for the production.
When reaching a high strength early, the casting forms can be separated from the concrete faster.
This means a more rapid production of panels, and is therefore an economical factor. A certain
thickness of the panels is also needed, especially in conventional architectural panels. A
minimum thickness of about 125 mm in needed. However a thickness less than 150 mm rarely
occurs (Metha et al. 2011).
Architectural panels should span from column to column, avoiding torsion in the structure from
horizontal loading, caused by wind pressure. Architectural panels must carry their self-weight,
besides wind pressure and earthquake loadings. To withstand the vertical and horizontal
loadings, bearing supports and tiebacks are used. Bearing supports for the vertical gravity load
and tiebacks for the horizontal loading.

47
Figure 4.12 (a): Detail section showing bearing support of panel
The bearing supports are usually made of steel. The steel has a tube form and is partially
embedded, and partially protruding from the concrete panel. These steel tubes lie over on a
supporting component on the building, usually over spandrel beams. If the supporting component
is made out of concrete, extra reinforcement is needed to comprehend the vertical load. The
bearing supports are usually connected with leveling bolts or leveling shims. It is also important
that the connection is made with the idea of allowing movement of the panel in the vertical
plane. If the connection is not free to move it can be broken because of inner stresses from
temperature, shrinkage and creep. In these figure we can see atypical bearing support for
concrete wall cladding.
Figure 4.12 (b): Steel tube bearing support viewing from the top.
The tieback is the connection which leads the horizontal loadings from wind in to the building
structure. Tieback connections are also designed to resist earthquake loadings. These loadings
occur as tension and compression perpendicular to the plane of the panel. Tiebacks are designed
to withstand these loadings and to allow movement in the panel plane. Figure 4.13 shows tieback
connections.

48
Figure 4.13: Tieback connections (Mats , 2013)
Metal Stud Crete, also called MSC, is a composite wall panel system (Metal Stud Crete, 2008).
This system has a50 mm thick concrete exterior layer and a light gauge steel frame inwards. This
paneling system carries roof and floor loads easily and it is quickly assembled due to the
prefabrication process. When the load bearing structure of a building is completed, Metal Stud
Crete wall paneling system can be used to enclose the building. This system can be used for both
pre-engineered concrete and steel structures. It has also less weight than conventional precast
concrete facades. MSC weighs about 35 pounds per square foot. This equals to 170 kg/m2.
Conventional panels weigh about 120 pounds per square foot which equals to 585 kg/m2. That
means that the MSC panel system only weighs about 30% of conventional panel systems.
Another benefit from using MSC panels is that there is no need for furring the inside of the wall.
Below is a picture of how the MSC panel system is built up.
Figure 4.14: Metal Stud Crete (Mats , 2013)

49
Slender Wall is another precast architectural panel system. It is made with galvanized wire,
stainless steel connectors and heavy gauge steel studs. This system, like Metal Stud Crete, is also
a lightweight panel system, which weighs a round two-thirds of a conventional system. The
Slender Wall system avoids the interaction of the structure of the building over the external wall.
Stresses like, frame movement, and expansion and contractions from e.g. the steel, will not affect
the exterior concrete panel.
Figure 4.15: Slender Wall (Mats , 2013)
The exterior concrete is about 50 mm and the interior steel studs are 150 mm. between the steel
studs and the exterior concrete is about 15 mm of air space. This space reduces the thermal
transfer. This air space is made from the DuraFlex 360 technology developed by Slender Wall.
This technology lets the concrete frame move 360 degrees in the panel plane and is the only
precast stud frame with this system. Because of DuraFlex 360, the concrete panel is isolated
from the steel frame and the two components can move independently. The Slender Wall has
also a wide range of designing finishes.

50
Figure 4.16: Slender Wall design finishes (Mats , 2013)
Another research possibility is based on how RCA concrete will behave if it is used in
architectural paneling systems like Metal Stud Crete or Slender Wall. The obvious reason for 46
This suggestion is the manufacturing of the panels. They are precast wall panels, and this means
that the process of producing this building system can be controlled. The proportioning, the
curing and how the system is build up. Maybe it is so easy, that RCA just can replace the
conventional concrete. However this can be researched and suggestions can be made on how to
construct these panels. So making a production line and a building system for the use of RCA
concrete in precast curtain wall systems can be a possibility.
There are several features with precast architectural panels, besides being prefabricated, which
make it a good element for utilizing RCA-concrete. These panels already use alternative
reinforcement like carbon fiber. And because of the high carbonation rate of RCA, it should be
used a non-corroding material for reinforcement. The connection of the concrete panel to the
underlying steel in both Metal Stud Crete and Slender Wall are possibilities that can be useful if
the panels were made out of RCA concrete. In the systems the concrete can move independently,
without being too much affected by the underlying structural movements. And the panel itself is
not vulnerable to external shrinkage and creep stresses, because of the connection systems.
Shrinkage and creep has been some of the most problematic features in RCA concrete. Therefore
investigations on how the connections will perform when the concrete is made from RCA would
have been interesting and necessary to complete.

51
Table 4.2: Suggested possibilities of using RCA concrete in precast curtain walls
(Mats , 2013)
4.1.4 Stonework
Stonework or brickwork consists of many units. The units can be bricks or blocks made from
different types of stone. The main feature of stonework depends on the properties of the
individual units and the mortar which binds the parts together. A stonework wall consisting of
high quality stones and a weak mortar can have a lower strength than a wall with weak stones
and high strength mortar. Because the walls made from stonework consists of many units the
wall acts like an anisotropic material. This means that the direction of the forces have a
significant impact on the walls resistance. Stonework walls have a low tensile, shear and
flexural strength. This must be considered during the planning process.
Figure 4.17 shows two load situations on a stonework wall. These situations introduces tensile
stresses into the wall, therefore the wall should resist them. The wall on the left in picture has
load around the x axis and the wall on the right has loads around the y axis. Another way of
differing between them is to say that the wall on the left needs vertical flexural tensile resistance
and the wall on the right need horizontal flexural tensile strength. Stonework walls have typically
two to three times higher flexural tensile strength when the load gives horizontal bending instead
of vertical bending (Sintef et al. 2011). There are a lot of different types of stones in stonework
walls. Fired clay bricks also called just bricks are one type. Light expanded clay aggregate
blocks also called LECA-blocks, air entrained concrete and bricks and blocks made out of
concrete are all different types of stonewall units. Figure 4.18 shows some typical stones which
is used in stonework walls

52
Figure 4.17: Flexural tensile load on a stonework wall (Mats , 2013)
.
Figure 4.18: Stones used in stonework (Mats , 2013)

53
The focus in this part of the paper is going to be concrete blocks. The reason is that these types
of stones seem to be the most suitable for utilizing RCA. The other types of stones are not made
with larger size aggregates. Bricks are made from extruded clay and LECA blocks are also made
from clay. Air entrained concrete is made from fine-ground quartzite, cement and lime. The
porous structure of these blocks is made by adding an aluminum powder. So the potential for
recycling of concrete is largest in concrete blocks where the aggregates size can be up to 16 mm
(Sintef et al. 2011).
Concrete blocks are made with the same materials as regular concrete. Cement, water and
aggregates. The aggregates are usually smaller in concrete blocks than in larger concrete
elements. The water / cement ratio is usually recommended to be 0.5. And common cement /
aggregates ratios are one part cement and six to eight parts aggregate. The cement amount that is
needed to produce one concrete block is usually 250 to 300 kg per m3 (Swiss Resource Centre).
Due to variation in size, types and shapes of concrete blocks the area of use is large. It can be
used in basement walls, structural walls, partition and fire walls, cavity walls, facades, sound
walls, elevator walls, retaining walls and as a windscreen. The most common area to use
concrete blocks in Norway is in garage walls, ring walls, foundation and partition walls.
Concrete blocks can be roughly divided into two types. Solid and hollow core blocks. The solid
blocks have a high compressive strength. Besides from being fire protective they also have a
good weather, impact and abrasion resistance. A large variety of size and shapes can be
produced. Hollow core concrete blocks are more common to use compared to solid concrete
blocks. This is because of the light weight compared with solid blocks. The lightweight makes
the construction time shorter. Up to 50% of the gross cross section can be void area. Voids can
be filled with equipments like pluming or electrical installations. This makes it very practical to
use. Concrete and re-bars can also be used in the hollow space of 49these blocks. If this is done
the wall will become very solid and have a good earthquake resistance. Hollow core walls have
also good thermal properties.
Figure 4.19: Solid concrete blocks (Mats , 2013)

54
One example of a concrete block product is the 2000 Solid Dense Ready Block. It is the building
material manufacturer CEMEX which produces the Ready blocks. This company started in
Mexico in 1906, and in 1989 CEMEX was one of the top then cement producers in the world and
in 1992 they started to grow international and today CEMEX is one of the global leaders with its
presence in over 50 countries. However, the Ready Block is a common building material to use
in construction and it can be used both inside and outside. It can be applied both above and
underground, in cavity walls or as a solid wall. It has good sound and air permeability properties
and the thermal mass function as heat storage. The Ready Block is produced both as a
lightweight and a dense block. And these have different properties .The compressive strength of
the blocks can be 7.3 MPa, 10.4 MPa and 17.5 MPa. The moisture movement is below 0.05 mm
per m and the bonding strength is 0.15 MPa. Because of the small settlements of concrete
construction after being built it is important to design expansion joints. This is applied also for
concrete block walls. Settlements occur because of temperature and moisture changes, and
carbonation. Generally it is usual to have movement joints for every 6 meters, when using Ready
Blocks in exterior works (CEMEX READYBLOCK, 2003). It is not normally required to use
movement joints in basic domestic dwellings. The places were movement joints should be
considered are at changes in wall height or thickness, at changes of loading conditions, at
abutments of different types of material, between one to three meters from a corner and at
locations of chases, recesses and openings. Around openings and in other areas with
concentrated stress it must be considered if reinforcement is necessary. The Ready blocks are not
ready to paint, plaster or render should be applied first. Ready Blocks are not currently produced
with any recycled material. But these types of concrete blocks can be an alternative to use RCA.
The CEMEX Company has a clear goal to create sustainable materials, and have already taken
some steps. Furnace bottom slag is used and all of the packaging of Ready Blocks is 100%
recycled. It is also mentioned that Ready Blocks contains dust which otherwise would go to the
landfill. CEMEX are working with the possibility of using recycled materials to replace the
virgin aggregates in the blocks. There are some attempts in applying this technology.
Figure 4.20: 2000 Solid Dense ReadyBlock (Standard finish) (Mats , 2013)

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