Closing the clay brick cycle

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Closing the clay brick cycle

Proefschrift

ter verkrijging van de graad van doctor

aan de Technische Universiteit Delft,

op gezag van de Rector Magnificus prof. dr. ir. J.T. Fokkema,

voorzitter van het College voor Promoties,

in het openbaar te verdedigen op maandag 5 april 2004 om 10:30 uur

door

Koen VAN DIJK

civiel ingenieur

geboren te Noordwijk

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Dit proefschrift is goedgekeurd door de promotor:

Prof. dr. ir. Ch. F. Hendriks

Toegevoegd promotor:

Dr. ir. A.L.A. Fraaij

Samenstelling promotiecommissie:

Rector Magnificus

Prof. dr. ir. Ch. F. Hendriks

Dr. ir. A.L.A. Fraaij

Prof. dr. J. Schoonman

Prof. Dipl.-Ing. J. Vambersky

Prof. ir. W.L. Dalmijn

Prof. ir. N. Hendriks

Ir. E. Mulder

Prof. dr, ir. A.C.J.M. Eekhout

Voorzitter

Technische Universiteit Delft, promotor

Technische Universiteit Delft, toegevoegd promotor

Technische Universiteit Delft

Technische Universiteit Eindhoven

TNO, Milieu, Energie en Procesinnovatie

Technische Universiteit Delft

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ISBN 90-90 17911-9

Keywords: masonry, recycling, reuse

Copyright © 2004 by K. van Dijk

All rights reserved. No part of the material protected by this copyright notice may be

reproduced or utilized in any form or by any means, electronic or mechanical,

including photocopying, recording or by any information storage and retrieval system,

without written permission from the publisher: AVDS B.V.

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Acknowledgements

The research project 'Closing the clay brick cycle' started as a collaboration between the Civil Engineering Material Science department of the faculty of Civil Engineering and Geosciences at the Delft University of Technology and the department of Waste and Materials Technology at the TNO Institute of Environmental Sciences, Energy Research and Process Innovation in November 1998. Goal of the research is to close a material cycle in developing a sustainable solution for the recycling of masonry. The research was carried out at the TNO institutes in Apeldoorn and Eindhoven and at the faculty of Civil Engineering and Geosciences at the Delft University of Technology. I am most grateful to my supervisor, Charles Hendriks in giving me the opportunity to perform this Ph.D. research. He opened my eyes for sustainability in the building sector. I also want to thank Evert Mulder from the TNO-MEP institute in giving me the opportunity to work together with him in developing a method for the recycling of masonry. In a further stage of the research he was of great help in realizing the laboratory research and the practical pilot projects. Alex Fraaij is gratefully acknowledged, for all his support throughout the project. His large enthusiasm about material science and sustainability and as a result the fruitful discussions, strongly contributed to the development of this thesis. I strongly appreciate his patience in the first part of the research and the freedom in allowing me to do the research with an exploring character. There are so many people who conthbuted to this research. Some people, however did have a very big contribution. Job van der Zwan provided me the knowledge in performing research in the laboratory for ceramics at the TNO institute in Eindhoven. At the Panoven in Zevenaar experiments were done together with Jan van Weeghel, who helped me in molding clay bricks. And I like to thank Pons Wagener (technical director of Terca) for his support in performing the pilot projects in the factories of Terca. Finally, I would like to thank my colleagues at the material science department for being of great help and support duhng the last four years.

Koen van Dijk, Delft, October 2002

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1 General introduction

1.1 The responsibility of the building sector

In the Netherlands about ninety-five percent of all the building demolition debris is being reused. The stony fraction is almost totally reused as a granulated material for road bases and is called mixed granulated material. It concerns a total amount of about 13 million tons on yearly base. With this roadbuilding material a six lane highway can be built over 340 kilometers, which is from Rotterdam to Groningen, each year. The problems concerning traffic gym are not solved by building more roads according to the governmental policy. It can be expected that in the next few years this will lead to a saturation of the road building sector, It is remarkable that the developments in the building sector unfold so slowly.

Choices must be made concerning the use of urban space and the use of natural resources. Not only the policy makers have their responsibility, but also the actors in the building industry have. An holistic approach from the design stage to the demolition stage is essential to realize a sustainable urban environment. The policymaker, the developer, the builder, the user and the demolition contractor all have their responsibility. The demolition stage should be implemented in the early design stage. This makes selective deconstruction or

dismantling possible and makes it possible that demolition waste can be reused as a secondary raw material in order to close the building cycles. An holistic approach will lead to a reduction of waste, a smaller pressure on natural resources and finally to a reduction of building costs.

Subjects that are generally accepted in other sectors of the industry are still not applied in the building sector. An example is the car branch, in which the producer is responsible for the demolition stage. The car is assembled so that it can easily be dissembled after a total lifetime. In the building sector however, the builder or producer of building materials is responsible until the building project is finished, he should also be responsible in the demolition stage.

1.2 Construction and Demolition Wastes (CDW), the actual situation

The amount of construction and demolition waste CDW has been increased since 1990. The biggest part comes from the building sector and ground, road and waterworks. This waste stream mainly consists of stony CDW. Besides that there is a big waste stream of asphalt from road renovation. The government has decided to introduce the landfill ban, in order not to use valuable space for landfills. The landfill ban serves two goals, namely the reduction of waste streams and stimulating reuse and recycling. The amount of building demolition waste, that was landfilled has not increased since 1995. The next step was to introduce a landfill ban for al flammable or reusable building demolition debris. This was introduced in 2000 and resulted in a big increase for reuse and recycling. It was also a result of a strongly increased landfill tax. The amount of building demolition debris that was delivered at crushing and sorting plants was increased enormously. In the year 2000 the total amount of building demolition debris was 19 million tons, 18 million tons has been reused or recycled, 0,2 million tons is incinerated and 0,8 million tons was landfilled (table 1.1). About seventy percent of the total amount of CDW is the stony fraction, mostly concrete and masonry debris that is being processed as granulated material for road building.

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table 1.1 The total amount CDW on yearly base, 1985-2000 Total Reuse Ignition Landfill 1985 Million tons 12 6.1 0.1 6.1 1990 13 9.3 0.15 3.2 1995 14 12.8 0.15 1.0 1997 16 14.9 0.23 1.0 1998 17 15.8 0.23 1.0 1999 18 16.6 0.2 1.2 2000 19 18 0.2 0.8 Source: RIVIVI; WAR.

RIVM/MC2001

The figures look impressive, but it is still not an optimal situation. Sustainable alternatives are necessary to handle the enormous amount of waste in the future.

1.3 The Delft Ladder an instrument for sustainable decision making

For making decisions concerning sustainable alternatives an instrument like the Delft ladder can be used, which has been introduced in 1998 by the material science group of the civil engineering faculty of Delft technical university. The Delft ladder was based on the ladder that was published by Lansink in the beginning of the eighties. The Delft ladder is a supporting instrument for making sustainable decisions between alternatives. The following alternatives are arranged on sustainability:

1 prevention

2 reuse of entire constructions 3 reuse of elements

4 recycling of materials 5 useful application

6 immobilization with useful application 7 immobilization without useful application 8 incineration with energy recovery 9 incineration

10 landfill

The subject of this thesis is the recycling of masonry debris as a raw material for clay brick production. The reuse of entire constructions and building elements has already been described in the research of Te Dorsthorst [31]. The recycling of concrete debris was described by Ishiguro [79].

The Delft ladder is an useful tool for policy making but must be applied flexible. It is not obvious that an alternative is better when it is higher on the ladder, because the environmental impacts are important in a sustainable assessment. For example, an alternative can be higher on the ladder, but requires an enormous environmental emission and is therefore from sustainable point of view not preferable.

According to an amendment of the law in 1999 the definition reuse was changed into useful application. The definition useful application contains beside the common applications also incineration in cement kilns and power plants. According to the Delft ladder it is incineration with energy recovery. Reuse of the stony fraction of CDW in the road building sector is also an useful application. This does not affect the appropriateness of the Delft ladder, when a further description of the definition useful application is given.

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1.4 Problem statement

There are two arguments for introducing alternative applications for the stony fraction of building demolition debris. Namely the dependence of the demolition industry on the road constructing industry and the limited processing capacity of this industry. A second argument is the effort for a high-grade application from sustainable point of view. An extra argument is that the Dutch government declared that the supply of some surface minerals like marlstone and gravel is limited. This encourages the concrete industry to use concrete granulated material as a concrete aggregate. This even reduces the processing capacity of the road constructing industry. Road building granulated material should at least contain 60 percent of concrete aggregate according to the RDW standard.

Mixed road constructing granulated material consists of a mixture of broken concrete and masonry debris, with a particle size range of for example 0-40 mm. It fulfills to the quality recommendations for road constructing granulated material, to the Dutch Building material Decree and is certified. Stony CDW is transported in big pieces to the processing plant or crushed onsite in a mobile crusher. In the process the material is crushed, sieved and the metal and light parts are removed. During the process a sieve fraction (< 2mm) is produced. When the amount of concrete debris that is processed on yearly base will decrease it results in a smaller market for road constructing granulated material, because the quality of the sub-base particles will decrease. According to the standard for road constructing materials it should contain less than 40% of soft materials like masonry. Masonry debris will end up as a useless product when no alternatives are available.

An alternative way of processing masonry debris is not only required for the current and future situation, but also for the environmental fnendly image of the clay brick industry. This was a reason to start a research program on the reuse or recycling of masonry debris in the clay brick industry, named 'Closing the clay brick cycle'. The research is focussed on the development of alternative reuse or recycling options in a sustainable way, for example the recovery of clay bricks from masonry debris or the reuse as a raw material in clay brick production.

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1.5 Aim of the research

The alternative way of dealing with masonry debris should be sustainable, environmental friendly and economical feasible. Based on those criteria the recycling schedule was developed (figure 1.1). In the first step reuse on material level, namely the recovery of clay bncks from masonry debris is depicted, in the second step on raw material level, namely the recycling of both rest streams for the production of clay brick and mortar production.

Masonry debris

Clay brick recovery (Chapter 3) /

Wliole clay bricks Reuse \ Rest fraction Separation process (Chapter 4) Clay-brick fraction Clay brick production (Chapter 5)

Mortar fractiot Mortar prodt iion

Figurel.1 Recycling schedule (the different aspects are described in the chapters)

In the recycling schedule three important steps can be distinguished which are part of the research. Most important research topics in this thesis are:

1. recovery of clay bricks from masonry debris (in chapter 3)

2. physical or mechanical separation of the clay brick and mortar fraction (in chapter 4) 3. clay brick production with a high percentage of clay brick or masonry granulated material

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1.6 Outline, research approach

Figure 1.2 shows the outline of this thesis.

Research question

Recycling schedule

rhermal process for "lay-brlck recovery

Separation of the clay-brick and mortar fractions

Clay-brick production with a high percentage of granulated material tion Evaluation: technical sustainability economical Conclusions/recommendations

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2 Theoretical approach for clay brick recycling

2.1 Introduction

Speaking of environmental friendly building a difference can be noticed In reusing and recycling of building materials. Reusing means that building components, without any necessary treatment can be used in new building projects. For example steel girders, roof-tiles and monumental clay bricks. Recycling means that an old building material is used as a raw material in the production of a new building product. Mechanical and thermal treatments are necessary to reach a final product. An example of recycling that has already been in use for decades is scrap that is re-melted in a converter to produce metal.

During the demolition of a building a big waste stream is created. A lot of building materials out of this stream can be or should be reused or recycled. One of the main parts of the building demolition waste stream is the stony demolition waste consisting concrete and masonry debris. The recycling of masonry is the topic of this research and in this chapter different recycling processes for masonry are developed.

2.2 Construction and demolition waste

2.2.1 Composition of CDW

During the demolition of a building, the separation of the big waste stream is done on site. Several materials like steel-girders are reused. The reason for this is their high value and their relatively simple way of reuse without special treatments. The wooden girder are collected and selected in three categories. The wooden girders can be reused for the production of wood chips or they are incinerated. They are not reused for construction, because a certification of the girders is required. Also the prefabricated concrete elements like floor plates can be reused. Many modern buildings for the industry are constructed of prefabricated elements. This gives a quick and practical way of construction and gives opportunities to make changes to the construction easily.

Also many utilitarian buildings are constructed with prefabricated elements nowadays. This reduces the labor intensity and gives high quality buildings, because the elements can be produced in an inside factory environment.

Most buildings that are demolished nowadays in the Netherlands, were built in a time-span around the 1920's and the 1960's and 1970's. The houses from the 1920's were constructed with masonry, because clay bricks were the common building material in that time. The bigger buildings were constructed with reinforced concrete, clay bricks and natural stone. The houses from the '60's and 70's were built in a short time span, because the demand for houses was very high in that time. Our way of living has changed and the demand for those houses decreased. A lot of houses have already been demolished or will be demolished. The main fraction in the demolition debris is concrete (figure 2.1).

The different kinds of building and demolition waste are: • building debris

• broken material from road maintenance (is treated separately) • mixed debhs from building sites and spoil from earth excavation

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Figure 2.1 gives an indication of the composition of CDW. The biggest part concerns concrete and bricks. A smaller part concerns asphalt (20 % m/m) and the remainder consists of natural stone and limestone and non-stony waste materials like steel, wood and plastics.

clay bricks 26% [m/m] concrete 4 2 % [m/m] asphalt 20% [m/m] remaining waste 6% [m/m] non stony waste 6% [m/m]

Figure 2.1 The composition of CDW [1]

In the modern architecture a lot of concrete elements are used. The result is that demolition waste of younger buildings contain a lot more concrete debhs, sand-lime brick, plasterboard and aerated concrete.

The recycling of demolition waste is hardly possible if it is only stimulated by the market situation. The government can influence the market by regulation, for example by means of the so called 'disposal bans' for recyclable wastes. An example of how regulation can influence the practical situation is given by the Dutch dumping decree. Only the

not-recyclable demolition debris can go to a dumping site. The dumping fee is high and therefore it becomes more attractive to recycle building waste. In the dumping decree is described that demolition debris can only be dumped if it contains less than 12 percent recyclable material.

2.2.2 Current treatment of demolition waste

Figure 2.2 gives an impression of the treatment of demolition debhs from the building-demolition site to the reuse in a road foundation. The building-demolition debris is separated on site, the steel and wooden girders are reused and the concrete and masonry debhs is collected. The concrete and masonry debris is transported to a plant, where it is crushed. Also mobile crushing is winning interest in The Netherlands. In the current situation the concrete and masonry debhs is transported to a road construction project, where it is used in the foundation of the road.

The proportion of concrete debhs in the road foundation material is required to be more than 60 percent. This means that the concrete debris is mixed up with masonry debns up to 60 percent. In the future situation, if the masonry debris can be recycled in the clay brick industry, the concrete debhs can be transported to a concrete production unit.

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Demolition of a building with separation on site

Transport

Demolition of a building without separation on site

i

Transport

1

Sorting/separation • Transport 1 Crush plant Transport HI Road foundation Concrete aggregate -at least 60% concrete aggregate -pure concrete fraction Figure 2.2 The treatment of demolition debris

Assuming that technically the recycling of masonry debris is possible, than there are still problems associated with recycling, namely:

• continuity in supply of materials • vahation in quality of waste over time • low added values of products

• market hesitation to buy recycled products instead of 'natural' ceramics • extraction of heavy metals

• color and esthetic value

Those problems can be solved when a suitable recycling method for masonry debris is developed. In this thesis the recycling opportunities are explored.

2.3 Options for the recycling of masonry

2.3.1 Introduction

Figure 2.3 shows that masonry debhs can be reused or recycled in several ways, namely: • The traditional way of using it as a component in road base mixtures. In the future this will

probably be limited, because the concrete industry wants to recycle their product. It is possible to make road-foundations of pure masonry debns for secondary roads or bicycle tracks.

• Reusing whole clay bricks: After a thorough demolition process in which the pieces of demolition debhs are as big as possible, the masonry debris is given a thermal or mechanical treatment to separate the mortar and the clay bricks. The clay bricks can be reused totally and also the mortar can be recycled. In figure 2.4 the process is visualized. • The masonry debris is crushed to a fraction smaller than 4 millimeter, and after a thorough

separation of the mortar the clay brick fraction is mixed with clay and fired in a kiln, to produce bricks.

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• The masonry is crushed to a fraction smaller than 0,5 millimeter and than mixed with clay

and fired in a kiln

Masonry debris

Crushing

i

Fraction < 0,5 mm

1

.

Mixing with clay

i

Firing in a kiln Type 2

i

Fraction < 4,0 mm

i

Mortar separation

1

Mixing with clay

i

Firing in a kiln Types

^

/

Temperature treatment

/

%

\

Selection clay bricks Broken clay brick parts

V

Mortar

\

•igure 2.3 Different ways to recycle masonry

%

^

Also see figure 2.4 Whole clay bricks Type 1

/

^

<^

3.2 Reusing the whole brick

I

' he masonry will be demolished in the usual way with heavy equipment. The parts are as big • 5 possible and are transported to the thermal treatment plant. The temperature that is

fieded in the thermal treatment plant depends on the mortar that is used. hardened cement will decompose at ± 650 °C

'•• hardened lime will decompose at ± 850 °C

" clay bricks are burned at a temperature between 1000-1100°C

After the thermal treatment the mortar can be removed easily and the whole bricks can be "ollected. The brickbats can be separated by sieving and can be used in the brick production. Mortar and sand can also be separated and be reused.

One of the problems in this process is that different kind of clay bricks are produced, with different colors and different dimensions. A data-bank is necessary to control the amounts of tjricks that are stored. In chapter three is shown that different kinds of mortar are present in masonry debris which must be treated at different temperatures in order to get a good separation. It will be necessary to sort the bncks into several types and colors; the hand molded and softmud press molded clay bhcks, the red and yellow colored clay bricks and the harder and softer quality clay bricks etc.

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1 r

Whole clay bricks

Demolition of a masonry structure

1

Big masonry parts

• Thermal treatment Y Separation

^

Mortar •

Broken brick parts

Figure 2.4 Reusing tlie whole clay brick (right part of figure 2.3)

2.3.3 Recycling of clay bricks with a thorough mortar separation

In this process masonry debris will be crushed and separated from the mortar. The masonry is crushed to a grain-size smaller than 4 millimeter. It is important that the separation of mortar and clay bricks is thorough. Remains of mortar can cause white spots on the brick surface, as a result of calcium transport to the surface during drying. The mortar can be separated in cement and sand by a thermal treatment.

The clay brick fraction is mixed with clay and fired in a kiln. The added clay gives the brick a higher 'green' strength. In chapter five is shown that a plastic clay results in a higher 'green' strength than a common clay.

Masonry debris

Crushing

Separation

Clay brick fraction < 4 mm

Mixing with clay

Mortar

' '

Sand 1 r Cement Firing in a kiln Clay bricks

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2.3.4 The recycling of clay bricks without mortar separation

In this recycling option masonry is crushed to a fine grain fraction, for example smaller than 0,5 millimeter. The clay brick fraction is mixed with clay and fired in a kiln. The cement fraction in the masonry will affect the strength of the clay bricks, therefore the added percentage of masonry granulated material will not be high. For example smaller than twenty-five percent in order to avoid problems with the lime content from the cement.

Masonry debris

Crushing

Masonry fraction < 0,5 mm

Mixing with clay

Firing in a kiln

Clay bricks

igure 2.6 The recycling of clay bricks witlnout mortar separation

'i Conclusions

ring the demolition of a building, a lot of building demolition waste is formed. In the current "• iüation the stony building demolition waste is mostly reused as an aggregate for road foundations. The concrete debris are crushed in a jaw crusher and than mixed up with masonry debris. According to the Dutch Road building standard RAW the percentage of masonry must be smaller than 40%.

For concrete debris there are other uses, for example: the use as a concrete aggregate. For masonry debris currently there are no other uses, than as a concrete aggregate for low grade applications. This research was for example performed by Fraaij et al. [41-52]. The reuse of masonry debris and concrete debris in road foundations is limited. Because the National Environmental Policy plan prescribes that 90 percent of the total amount building and demolition waste must be reused or recycled, other uses for masonry debris must be found.

Besides the National Environmental Policy plan there are other reasons to recycle bricks, for example the decrease of natural sources which causes an increase of costs of sand and gravel.

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• The reuse of whole bricks: After a demolition process in which the pieces of demolition debhs are as big as possible, the masonry debris is given a thermal or mechanical treatment to separate the mortar and the bricks. The bricks can be reused totally and also the mortar can be recycled. In figure 2.4 the process is visualized.

• The masonry debris can be crushed to a fraction smaller than 4 millimeter, and after a thorough separation of the mortar the masonry is mixed with clay and fired in a kiln. In figure 2.5 the process is visualized.

• The masonry is crushed to a fraction smaller than 0,5 millimeter and than mixed with clay and fired in a kiln. This process is visualized in figure 2.6.

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3 Clay brick recovery by means of a thermal process

(experiments)

3.1 Introduction

Clay bricks from masonry constructions are reused on a very small scale in the Netherlands. The mortar is chipped from the bricks, which is a very labor intensive job. To encourage clay orick recovery on larger scale new technologies should be introduced.

*, thermal process might be a suitable technology to recycle clay bricks. Clay brick mortar separation can be achieved by heating to a temperature of 850 °C at which cement mortar •jöcomposes. Lime mortar decomposes at a temperature of 400 °C. In this laboratory it-search the recovery of clay bricks from masonry debris by thermal treatment was investigated. The effect of a temperature treatment on the properties of the clay brick was ';rso determined.

Oi-'.e of the risks of a thermal process is that internal cracking of the clay bricks occurs.

•• -rnal cracking will influence the mechanical properties of the clay brick. The quality of the )vered clay bricks can be checked by measuhng the tensile and compressive strength of

e bricks. In standard ISO 2859 a method is described for testing a batch. A distinction be made between defects and defective. A clay brick with some defects, for example 3 small cracks, does not necessarily be useless or defective. In this test ten clay bricks )atch were checked and the amount of defects per clay brick and the amount of ctive clay bricks per batch were registered.

C V' brick and mortar can be separated in a thermal process, because shear stresses are ir .'duced on the clay bhck mortar interface. Those shear stresses are a result of the d jrence in linear expansion coefficient between mortar and clay bhck. The mortar, that is nvv; vet delaminated, is compressed and in the clay bhck there are tensile stresses. On the c!i • bhck mortar interface there are shear stresses if there is still a bond between the two ci.i.ponents. The mortar clay brick interface is the weakest part of masonry and therefore miy.i-t break by thermal loading. The temperature for collapsing of the interface depends on thij properties of the clay brick related tot the properties of the mortar and the resistance of tile interface for shear stresses.

In the beginning of the temperature treatment, when the temperature in the oven is

increasing, water in the open pores starts to evaporate. It is possible that cracking occurs by thermal strains in the clay brick. This will decrease the mechanical quality of the clay bhck. It IS also possible that the cracking already occurred duhng technical life span of the masonry. The strains in the product can reach a maximum caused by frost/thaw loads or mechanical loads duhng the technical life span. This can cause damage to the clay brick and make it unsuitable for reuse.

3.2 Theoretic model

The situation of strains caused by thermal loads is modeled with a composite matenal, consisting of a layer of mortar and a layer of clay brick. The difference in expansion

coefficient between clay bhck and mortar introduces tensile and compressive stresses when thermally loaded. At the clay brick mortar interface a shear stress is introduced (figure 3.1).

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Now the boundary conditions for this loading situation were made up. The total expansion (formula 3.1) of a material is the sum of thermal expansion and expansion caused by stresses. The tensile or compressive load can be written as a function of expansion. The strain (formula 3.2) is the first derivative of the change in length in a certain direction.

compression tensile

<r--^

>\4 1

1 ->

<--^

<-Shear "~ mortar clay brick

Figure 3.1 Stresses in the clay brick mortar interface caused by a temperature load

E = a T - N

"ÊA (3.1)

dx (3.2)

This results in an equilibrium with a main force N, which is a function of the strain (c) and the thermal expansion coefficient (a). The shear stress (q) is the first derivative of the main force in the X direction. ON q = per mm 1 paper (3.3) dx E A , E A i 25 mm

Figure 3.2 Material model of the clay brick and mortar interface

In figure 3.2 the material model of clay brick mortar interfacial zone is shown. Both layers have a Youngs modulus, surface area and thermal expansion coefficient. The effective thickness of the mortar layer is 4 mm and for the clay bhck it is 25 mm.

Until the clay brick mortar interface is broken, there is an internal equilibrium. The compression force in the mortar layer equals the tensile force in the clay brick. The expansion for both materials is equal. For this loading situation a parallel system is valid, which means that the stiffness of both materials must be summed. Using formula 3.1 together with the second boundary condition results in formula 3.4.

N , + N , | = 0 e, = 8 . = £ EA = EA, + EA, N, N , + a,T = — ^ + a , T EA, ' EA, - _(3.4)

The solution is found by using boundary condition 3.1 and 3.3 with formula 3.4.

E A . - E A , / X E A , a , + E A , a , N , = - N - , = '——-(a,-a,)-T and s = —hr. ^ ^ - T

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EAitt, + E A j t t j Resulting in a total thermal expansion coefficient: a = —

The shear stress (q) is the first derivative of the main force in the x direction (figure 3.3).

N+AN

•*

"*" q

Figure 3.3 The shear stress

• he force N is independent on x, because formula 3.1 is valid on the clay brick mortar nterface. Therefore shear stress on the clay brick mortar interface must be constant. From •iterature values can be found for the thermal expansion coefficient and Youngs modulus 'joth for clay bricks and mortar.

•;:iay brick: a, = 3 - 9 - 1 0 ' K ' and E, = 10-20-lO'Pa Mortar: a , = 10-12-10"''K~' and E, = 20-40-10"Pa

T'te huge variation in values for different clay bricks and mortars results in a big range in

& leahng stress at certain temperatures. For example, when the temperature is 540°C then t'6 shearing stress ranges between 0,35 and 5,60 N/mm^ for the extreme values of the liiermal expansion coefficient and the Youngs modulus.

3.3 Laboratory experiments on thermal recovery of clay bricks

With the theoretic model it is shown that the temperature that is required for effective recovery depends on the extension coefficient and Youngs modulus of the clay brick and mortar and of the strength of the clay brick mortar interface. Thermal experiments were done with different types of masonry and different temperature treatments, which is described in the sections 3.3.1, 3.3.2 and 3.3.3. The strength of the mortar clay brick interface was measured and is described in section 3.3.4.

3.3.1 A description of the samples for the thermal experiments

The masonry pieces came from a recycling plant. The demolition companies deliver their building demolition debhs to the plant and the stony fraction is crushed in order to produce granulated material for building road foundations. Different types of masonry pieces were collected, which came from different buildings, that were demolished by different demolition companies. The masonry pieces, consisting 3 or 4 whole clay bricks were transported to the laboratory. In the laboratory both a gas heated chamber kiln and a electric heated kiln were used for clay brick recovery tests.

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The results of the gas heated kiln, were better than for the electric heated kiln. This might be a result of the heating process. In an electric kiln the masonry is heated by radiation. In the gas heated kiln, the masonry is heated by convection of heated air (flue gasses). Electric heating might result in a higher temperature coefficient in the masonry, as a result of which the clay bricks cracked.

3.3.4 Measuring the strength of the mortar clay brick interface

Different mortars were made consisting of Portland cement type CEM I 32.5. The mortars were prepared with the same consistence by using the vibration table (according to the standard NEN 3534). The composition of the mortars is shown in table 3.2.

Table 3.2 Composition of the mortars

Mortar sample 1 2 3 4 5 CEM 1 32.5 sand 4 4 4 4 4 lime 0.6 0 0 0 0 water 1.2 1.15 1 0.9 0.75 other substitutes none 0.6 fly ash (EFA) A.E.A. (30 cc/50kg cement) A.E.A. (90 cc/50kg cement) A.E.A. (300 cc/50kg cement)

For every type of mortar samples were made in order to measure the strength of the mortar. The samples have a standard size of 40.40.160 mm^. The samples were stored for 28 days and then the three point bending test and compression test was performed.

For two clay brick types, a clay paver and a clay brick, three 'shear stress' samples were made for all the mortar types. The clay bricks have a sanded site that was in the mold and an unsanded site. This layer of sand probably has influence on water suction of the clay brick and therefore differences were made in sample preparations.

Sand site up Sand site down Sand site variation up/down

Figure 3.4 Samples for shear stress measurements

After 28 days of hardening the samples were tested. The mortar clay brick interface was loaded on shear stress. The load was increased slowly, until one of the interfaces broke.

' '

P[N

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Then the load was increased until the other interface also collapsed. The shear stress in the

p

clay bhck mortar interface is: r = [NI mm']

1-h-l

Table 3.3 Strength of the mortars and of the clay brick mortar interface

mortar 1 2 3 4 5 Compressive strength [N/mm'l 12.5 0.6 14.6 1.9 4.8 0.5 5.3 1.2 4.3 0.7 3 p.b. strength [N/mm^] 3.4 0.4 4.3 0.3 2 0.2 2 0.1 1.9 0.2 Clay paver shear stress [N/mm'j 0.9 0.2 1.4 0.5 0.7 0.3 0.4 0.2 0.5 0.1 Clay brick shear stress [N/mm^] 1.2 0.3 1.4 0.2 0.8 0.4 0.3 0.1 0.2 0.1 Air [%] 7.8 3.0 17.5 24.5 20.3

; he density of the mortars is calculated by measuring the volume and the weight of the nortar bars. With the mixture composition the 'real' volume of cement, water and sand can t:-e calculated. Also the percentage of water can be calculated.

Compressive strength 16 14 12

I" 10

£ 8 ?, 6 4 2 0 -. •.. ... . . I * _ 0 5 10 15 20 25 30 Air [%]

Figure 3.6 Compressive strength of the mortar samples

5 n 4 | 3 1 0 • 3 pb s t r e n g t h

1 I 1

• • •

j

*

)

5 10 15 Air [%] 20 25 3 0

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shear stress |

« clay brick • clay pa\«r

0 5 10 15 20 25 30 Air [%]

Figure 3.8 Shear stress of the masonry samples

In the theoretic model (section 3.2) is shown that the compression force in the mortar is equal to the tensile force in the clay brick. The shear stress is the first derivative in x direction. It can be concluded that the clay brick mortar interface is the weakest part, no values were found higher than 1.4 N/mm^. The shear stress was varying between 0.35 and 5.60 N/mm^, according to the model. The measured shear stress in the test varied between 0.2 and 1.4 N/mm^, it can be concluded that for most of the masonry types the clay brick mortar interface will break at 540°C. The hardness of the clay brick does not influence the strength of the clay brick mortar interface. Some values for the shear strength were higher foi the harder type of clay brick and some values for the softer clay brick.

3.4 Conclusions/recommendations

One of the possibilities of closing the clay bnck cycle is to recover clay bricks from masonry debris. The difference in thermal expansion coefficient, between mortar and clay brick causes shear stresses on the clay brick mortar interface.

A theoretic model was made to calculate the forces in masonry caused by a temperature load. In the mortar a compression force and in the clay brick a tensile force was introduced. The shear stress on the clay brick mortar interface varied for different clay brick and mortar types, because of the difference in thermal expansion coefficient and Youngs modulus. According to the theoretical model the shear stress ranges between 0.35 and 5.60 N/mm^ at a temperature of 540°C, for the extreme values of the thermal expansion coefficient and the Youngs modulus.

With laboratory experiments the temperature at which the clay brick mortar interface breaks were checked. The experiments showed that the most effective temperature is 540°C. The quartz phase transformation takes place at 573°C and can cause cracking of the clay bricks. A gas heated kiln gave better results than the electric kiln.

In the next part of the laboratory study the strength of the clay bhck mortar interface was measured. The measured shear stress varied between 0.2 and 1.4 N/mm^. It can be concluded that for most of the masonry types the clay brick mortar interface will break at

E E z 1.4 1.2 1 0.8 0.6 0.4 0.2

1 töStfo^ "

•

''Z'Zi

y~i)' . ...:.!.. i . ,...„:.._ -^S '100 éM *0

>-m

h.

1 •

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540°C. For most masonry types the temperature can even be lower. The hardness of the clay brick in this particular test is not of Influence on the strength of the clay brick mortar interface.

Clay brick recovery by means of a thermal treatment can be successful. It is recommended to perform a pilot project in a clay bhck factory to check the practical adaptability.

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4 Physical/mechanical separation techniques for clay brick and

mortar

4.1 Introduction

According to the recycling schedule the clay brick and mortar part should be separated in order to recycle both materials. But also the two main materials in CDW, namely concrete and brick should be recycled or reused respectively as concrete aggregates and brick aggregates as a replacement of original raw materials. This research focuses on effective separation techniques. Both dry and wet separation techniques were tested, based on the differences in physical properties between concrete/mortar and brick, in particular, differences in density and Fe203 content.

The main goal of this research is to select suitable separation methods in use in the mining industry to separate concrete or mortar and clay brick fractions from each other. The

effectiveness of the separation techniques is determined by the physical differences between the materials. In this study, two kinds of samples were used. One was the actual CDW taken from a Dutch CDW processing plant. The second was a mixture of brick and mortar that was prepared in the laboratory, and of which the ratios of brick to mortar were known. All separations were executed in the Mining Department, Delft University of Technology.

4.2 Available separation processes

The suitable separation methods were chosen, based on the differences between concrete/ mortar and clay brick as shown in table 4.1. The differences in properties between mortar and clay-brick are:

The difference in color, mortar is gray and clay-brick red or yellow The density for mortar is 2.0-2.2 gr/cm^ and for clay brick 1.5-1.8 gr/cm^

magnetic behavior of both materials, Portland cement (PC) mortar contains 25% PC which contains 1-5% Fe203 this results in a Fe203 content of 0-1% Fe203 for PC mortar and a Dutch river clay contains 3-5% Fe203.

Table 4.1 Suitable separation techniques Properties Magnetic behavior Density Color Bricl< 3 to 5% Fe203 1.5 to 1.8g/cnT' Red or yellow Mortar 0 to 1 % Fe203 2.0 to 2.2 g/cnr' gray Techniques magnetic separation jigging orfluidized bed method

color separation

In the next paragraphs an explanation is given concerning the different separation techniques.

4.2.1 IVIagnetic separation

In a strong magnetic field the magnetic particles can be separated from the non- or weakly magnetic. A simple magnetic separator consists of a conveyor belt with the magnets placed on the pulley drum. In this study, a Frantz Isodynamic separator (Photo 4.1) was used to assess the magnetic properties of the materials. The Frantz isodynamic magnetic separator is widely used for accurate dry separation on the basis of magnetic susceptibility of

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a few hundred grams of matehal. The feed passes down a shallow vibrating chute between the poles. Both the forward and side slope of the chute are adjustable. A partition at the end of the chute separates in magnetic and nonmagnetic particles. The magnetic field is controlled by adjusting the d-c magnetic current and the machine angle. For a pure material, an average magnetic susceptibility can be found with the suitable current and angle to reach a balance point of magnetic force and gravity. However the magnetic field it is too weak to separate materials containing larger particles. The separation of particles by a magnetic moment is generated by unit of volume of the material.

4.2.2 Jigging

Separation by means of jigging is based on the difference in apparent densities in water. These are (2.4-1.0) = 1.4 for concrete, (2.1-1.0) =1.1 for mortar and (1.7-1.0) = 0.7 for clay brick. The ratio of the apparent densities of concrete (or mortar) and brick is bigger than those in air, i.e. 2.4 (or 2.1) and 1.7, respectively. Therefore, the separation will be more effective in water. In a jig, the separation of materials with different specific densities is accomplished in a bed which is rendered fluid by a pulsating current of water (Figure 4.1). When water is put under pressure by a plunger, the particles fall with different speeds to the bottom, depending on their densities. The heavy fraction will sink faster and is discharged at the bottom of the apparatus. Jigging is generally used to concentrate relatively coarse materials down to 3 mm. The advantages of jigging are the inexpensive technique, the simple control to obtain a good separation, and at the same time, the waste is washed. The disadvantage is that there is slurry left, and this slurry may be contaminated.

feed

**^°-*o2#!Lo**

_{f n i c j}

.8!b.o»2 o

o

^QS^S

^oo;

oo ® oo

o

o ^ ^ o

o

Heavy particle (^X5 O O O discharge ^ J X L Q D j a . _ C

Pulsing water flow

Light particle discharge

(1) Before (2) After

Figure 4.1 Sketch of the principle of jigging

4.2.3 Color separation

Color separation is based on the principle that a 3d camera, which can clearly recognize the difference between the particles, detects the color of a particle and blows the particle out when it does not have the color of the predefined particles. The particles are blown out by blowing air through a nozzle. In practice this means that together with the detected particle another or more particles are blown out. Color separation can only be successful when the input contains a main fraction of predefined particles. The benefit of separation on color is that it result in one pure fraction and one mixed fraction. For example when the feeding consists offer about ninety percent of predefined particles and about ten percent of contamination, then the recovery is about 80% and 20% tailings. The recovered fraction is

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pure, but the tailings contain both predefined particles and contamination, both about 50%. Therefore the process is not successful when the mixture contains about 50% of

contamination, because most particles are blown out.

The contamination rate in the clay brick mortar fraction might be about 25%, therefore it should be better to take it as a second or third treating step in a total separation process. In this study, color was also used as a visual check to judge the separation results of magnetic separation and jigging.

4.2.4 Fluidized bed

Fluidized bed separation is a sinking floatation separation with a dry fluid. The fluidized bed is filled with fine sand (with a grain size between 150 and 250 pm). An air flow goes through a screen and through the sand bed. The materials can float or sink in the fluidized bed when the airflow is controlled.

The advantage of a fluidized bed is that no slurry is left after separating. The disadvantage is that the fractions are contaminated with sand and that the particles have a round shape. When the particle size is smaller than 2 mm the use of a fluidized bed is less effective.

4.3 Experiments on separation

In this paragraph the experiments with the different separation techniques are described. 4.3.1 Preparation of the raw materials

The materials that were used in this study were taken from a recycling plant where mixed granulated material is processed. The amount of concrete in this material is about 70 to 80% and the amount of masonry 20 to 30%. The sample was sieved according to Dutch standard NEN 2560. The result is shown in figure 4.2. About 50 percent of the particles is bigger than 8 mm and about 10 percent of the particles is smaller than 4 mm (sand fraction). For the jigging experiments, the material was wet sieved into the fractions 2 to 5 mm, 5 to 10 mm, 10 to 19 mm, and larger than 19 mm. Prior to jigging, the different fractions were analyzed by hand sorting into two fractions, i.e. the brick and concrete fractions. The ratios (by mass) of brick, concrete, and other particles were measured by hand sorting. The results are shown in table 4.2. The finest fraction (2-5 mm) was not handsorted, because the particles could not be distinguished. ^o

ro

Ï S F <=^ 1-90 80 70 6 5 40 30 20 10 0 - O r i g i n a l ^ ^ j

y

/ / /

/ 1

/ / / .----' 0.063 0.71 0 063-0,125 1.08 0 125-0 2 5 mm 1.35 0 25-0 5 1.S2 0 5 - 1 2.16 1-2 mm 3.07 2-4 110.53 4-8 8-11 1 1 - 1 6 . 1 6 - 2 2 22-32 40.62 J69.34 176.92 |90.34 |l00 0o|

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2-5 mm 5-10 mm 10-19 mm >19 mm D brick D concrete 15.4% 84.6% 21,1% 78.9% 26.9% 73,1% Ratio [%]

Figure 4.3 Ratio of contents in the mixed granulated materials as a result of bandsorting

I he percentages in weight for the concrete and brick fraction are shown in figure 4.3. For the fraction > 19 mm, the concrete part is 73,1%. The smaller fractions contain a higher concrete f>ercentage.

4 3 2 Magnetic separation

N'.-gnetic separation might be a suitable separation technique for separating clay brick and ri"; -!tar from masonry. Portland cement mortar was made in the laboratory and was stored fo' 28 days. Figure 4.4 shows the material preparation in order to perform the magnetic e •leriments. Mortar, yellow clay bricks and red clay bhcks samples were made.

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Figure 4.4 Materials preparation for magnetic separation

An amount of 2 kilogram of the fraction 0,15 - 2,36 mm was produced for doing the

expehments. The apparent magnetic susceptibility of the materials were determined by using the Frantz Isodynamic separator (Photo 4.1). Both the field strength and angle can be changed. By changing the parameters a suitable magnetic field for separation was found.

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Photo 4.1 Frantz Isodynamic separator

Model: L-1, Volts: 125 max, Amperes: 1,84 max, PSI*10 °: 1,50 S. G. Frantz Co. INC TRENTON. New Jersey

Tr' •• Frantz isodynamic magnetic separator is widely used for accurate dry separation on the bo:.IS of magnetic susceptibility of paramagnetic and diamagnetic particles between 10 pm and 2,0 mm is size in quantities up to a few hundred grams. Separations can be made on the basis of specific magnetic susceptibilities as low as 1.10"^ m^/kg. The separator consists of an 'electromagnet with two 25 cm long pole pieces, separated by a contoured air gap ranging between 5 and 12 mm in length which is designed to produce a constant magnetic force on particles whose magnetic susceptibility does not depend on field strength. The feed passes down a shallow vibrating chute between the pole pieces. Both the forward and side slope of the chute are adjustable. A partition at the end of the chute separates the particles that are more strongly affected by the magnetic force. The magnetic field is controlled by adjusting the dc magnetic current. It should be noted that for many minerals the magnetic susceptibility varies with applied field strength and that the apparent susceptibility can be greatly affected by small ferromagnetic inclusions. Because of the demagnetizing effect the analyzing method can not be applied to highly magnetic particles with susceptibilities in excess of about3.10-=m^/kg.

Best results are obtained when screen size fractions are tested. The material is then separated on the Frantz separator by removing the magnetic fraction at successively higher field strengths. The feed rate can be controlled by adjusting the feeder. For the most accurate separation the feed rate is chosen to minimize interactions between particles. It may range from 1 g/min for 2 mm particles to 1 g/hour for 10 pm particles. Best results are generally obtained with side slopes of between 10 and 20°. However slopes down to 2° may be used for separating weakly magnetic minerals. The forward slope can be vahed between 10 and 30° with little effect on the separation, the larger slope being used to facilitate the movement of smaller particles.

The separation of particles by a magnetic moment is generated by unit of volume of the material. The magnetic force on a particle is given by Svoboda (1987).

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Fm

Figure 4.5 Forces on a magnetic particle

Fg = Fm-sina m.V.VB = p.V.g

VB. (k. B)lno = P- g; fJo = 4m10'^ k/p = X

Z(B).B. VB//JO = g

The magnetic force on a particle is given by Svoboda (1987);

F„,^(pxVBVB)/no

Ho - permeability in vacuum (47r*10'^) X = specific susceptibility [m^/kg] p = density [kg/m^]

V = volume [m^]

B = magnetic field Induction [T]

In which, Ho- 47iy.10'^\s the permeability in vacuum, p{kg/m^) is the particle density, V(m^) is the volume and x {m'^/kg) is the specific magnetic susceptibility. B (T) is the magnetic induction. For the Frantz isodynamic separator 6 is proportional to the current / [A) led to the magnet. If the chute is set at some angle a, the magnetic force and the gravity of the particle are at equilibrium \i pVgslna= F^ or, if j = slna/(kxl^).

k= 4.1x10^ is a constant reflecting the geometry of the separator.

For a rotary drum separator, the balance of forces is pVg = Fm Here, the magnetic field and its gradient are given by;

IBI =(2/7t)xiJoxmxe^'^'''

IVBI = (4n/m)xpo-^mxe^'^'''

Where, d (m) is the gap between the magnet surface and the center of the particle, m (A/m) is the magnetization of the magnet poles and aris their width.

The equilibrium for the Frantz isodynamic separator is given by;

g.sln(a)=(x^')/2po

The apparent magnetic susceptibility:

X = sin(a)/(k.|2) (4.1) a = angle

I = current [A] k = constant [4,1.10^]

The magnetic susceptibility can be measured using the Frantz. At different angles and currents the separated fractions are weighted. The equilibrium is reached when 50% goes to the magnetic site and 50% goes to the non-magnetic site. With this equilibrium the apparent magnetic susceptibility for the material with a specific granular size can be calculated using

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formula 4.1. The results of the measurements are shown in table 4.2 to table 4.4. The equilibrium and the apparent magnetic susceptibility is calculated in table 4.5.

Table 4.2 Magnetic separation results for the red clay brick sample

Current 1 (A) 1 0.5 0.5 0.5 0.5 0.3 0.3 0.3 Machine angle a 10 10 12.5 15 17.5 10 7.5 8.5 Magnetic part Weight (g) 53.71 34.76 31 23.12 15.9 22.79 31.18 27.7 Percentage (%) 96.4 61.7 58.2 41.3 28.4 40.9 56.0 49.9 Non-magnetic part | Weight (g) 2 21.56 22.23 32.83 39.99 32.94 24.48 27.81 Percentage (%) 3.6 38.3 41.8 58.7 71.6 59.1 44.0 50.1

T )le 4.3 Magnetic separation results for the yellow clay brick sample

irrent 1 (A) 0.5 0.5 0.3 0.3 0.3 0.3 0.2 0.2 Machine angle a 15 20 15 12.5 10 12.5 10 7.5 Magnetic part Weight (g) 50.06 35.29 15.22 21.47 36.57 27.45 12.08 26.89 Percentage (%) 84.3 60.9 26.3 37.3 63.5 47.8 21.1 46.9 Non-magnetic part J Weight (g) 9.31 22.64 42.66 36.11 21.04 29.96 45.24 30.4 Percentage (%) 15.7 39.1 73.7 62.7 36.5 52.2 78.9 53.1

Ts 2 4.4 Magnetic separation results for the PC mortar sample

C rrent 1 (A) 1.5 1.5 1.5 1.2 1.2 Machine angle a 10 7.5 8.5 5 7.5 Magnetic part Weight (g) 27.59 34.17 28.44 37.9 28.92 Percentage (%) 45.1 56.1 47.0 62.9 48.2 Non-magnetic part 1 Weight (g) 33.56 26.69 32.09 22.31 31.12 Percentage (%) 54.9 43.9 53.0 37.1 51.8

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Table 4.5 Calculation of the apparent magnetic susceptibility for the samples

Materials Red clay brick

Yellow clay brick

PC mortar

Red clay brick (hard)

Lime mortar Current 1 (A) 0.5 0.3 0.3 0.2 1.5 1.2 0.7 0.5 0.3 1.5 Machine angle a 13.5 8.5 12.5 7.5 8.5 6.0 15.0 7.5 6.0 3.0

/(io-^) 1

227.8 400.6 586.6 795.9 16.0 17.7 128.8 127.3 283.3 5.7

1

The results are visualized in figure 4.6. It can be concluded that the yellow clay brick particles have the highest magnetic susceptibility. For the red clay brick particles the magnetic susceptibility is for both clay brick types about the same. The mortars have a low magnetic susceptibility. 900 800 700 b 500 L 400 ^ 300 200 100 0

ÏÏ

^ ^

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 I [A] - clay-brick powder red x PC mortar - clay-brick red hard x lime mortar

- clay-brick yellow

Figure 4.6 Magnetic material properties for the samples

The pole size and field strength for a magnetic separator can be calculated using the figures from table 4.6. For the red clay brick sample; / e / = 0.3 and j = 400x70'^ IVBJ=

(2nJw)y.0.3, m= 18^10'^ = 18 mm fpole size = 9 mm), and when /B! = 0.5 and x = 228xia\ m= 28.5x10'^ = 28 mm (pole size = 14 mm). So, the pole size must be 9 mm for a field

strength of 0.3 Tesia or 14 mm for a field strength of 0.5 Tesla.

Clay brick is considered as the magnetic material and mortar as the non-magnetic material. Mixtures were made with the ratios of brick to mortar of 1:1, 3:7, and 7:3. The mixtures were separated by using the Frantz Isodynamic separator, the results are shown in table 4.6. When the current was weaker than 1 A, it was impossible to obtain a good separation result.

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Table 4.6 Optimum parameters to separate the mixtures Ratio of brick to mortar

hard red brick red brick 50% : 50% 30% : 70% 70% : 30% 50% : 50% 30% : 70% 70% : 30% Current 1 (A) 1.2 1.2 1.2 1.2 1.2 1.2 Machine angle a 17 17 15 17 17 15 Purity of brick fraction at the eye + + ++ ++ + ++ Purity of mortar fraction at the eye

++ + ++ ++ ++ ++

Good separations were obtained, when the ratio of brick to mortar was 1:1 and the machine angle was 15° to 17° with a 1.2 A current. At 17°, not only the purity was high, but also the recovery. When the ratio of brick to mortar was 3:7, a good separation was obtained at a m^ichine angle of 17° with a 1.2 A current; when the ratio of brick to mortar was 7:3, a good secaration was obtained at a machine angle of 15° with the same current. When the ratio of bn.-K to mortar was 3:7, and the machine angle was smaller (15°), the separator did not tilt,

ar.'; some particles of non-magnetic material contaminated the part of magnetic fraction,

because the amount of non-magnetic matehal was bigger than the magnetic material.

Wi ;n the ratio of brick to mortar was 7:3, and the machine angle was larger (17°), the se, erator tilt, and some particles of brick went to the nonmagnetic side. For the mixture of bri -, and mortar with ratio of 3:7, a good separation can be obtained at 17°, while for the mi; ure of brick and mortar with ratio of 7:3, a good separation can be obtained at 15°.

Prepared sample (purity 93%) Separated clay brick fraction

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Prepared sample (purity 87%) Separated mortar fraction

Figure 4.8 Purity of mortar fraction

The purity of the separated brick or mortar fractions were compared with mixtures that were prepared in the laboratory. In figures 4.7 and 4.8 the separated brick fraction and mortar fraction are shown compared with a manually mixed sample. This comparison gives an indication about the purity of the separated fraction. Hence, the purity of the separated brick is around 93%. Similarly, the purity of the separated mortar is around 87% (Figure 4.8). Magnetic separation is a suitable separation method for clay brick and mortar. The purity can even be increased when several magnetic separation steps are being used.

4.3.3 Jigging

Jigging is a wet separation method and can be achieved at low costs. In this part of the research the clay brick and concrete fraction of CDW was separated. The materials were taken from a recycling company. First the materials were wet sieved into five fractions, i.e. <2 mm, 2 to 5 mm, 5 to 10 mm, 10 to 19 mm, and >19 mm. Each fraction, excluding the fraction with a particle size smaller than 2 mm, was jigged separately. This resulted in two

concentrates for each fraction, a brick fraction and a concrete fraction.

Concrete fractie,. Brick fraction Figure 4.9 Separated fractions by jigging (particle size > 19 mm)

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Brick fraction Concrete fraction

gure 4.10 Separated fractions by jigging (2 mm <particle size < 5 mm)

• or the fractions with larger particle sizes, it was easy to obtain a good separation result igure 4.10). The purity of the brick and concrete fraction were high. For the fraction with the nallest particle size (2 to 5 mm), a good separation was obtained by an asymmetric pulse t a low frequency. The pulse was not totally optimized. The slurry that is left in the jig must -e cleaned for organic contamination.

1 3.4 Fluidized bed

a fluidized bed a separation can be made between particles with a difference in density or ^v.ecific surface area. Both mortar and brick were tested in a fluidized bed, using Zircone • -ind and quartz as a medium. The properties of the sand types are shown in table 4.7.

"^ ïbJe 4.7 Results of the fluidized bed test for mortar and clay brick

•Jircone sand ZrSiO? jQuartz From literature P [g/cm'j 4.60 2.65 Hardness [Brinell] 7.5 7.0 Measured Result mortar Floating Sinking Result brick floating sinking

With the Zircone sand the particles were floating, while with quartz the particles were sinking. The density of the sand should be in between. The sand types that are suitable are

summarized in table 4.8.

Table 4.8 Sand types for separation mortar and clay brick in a fluidized bed [89]

Andalusite Corundum Oiamond Olivine Sillimanite Spinel lourmaline p [gr./cm^] 3.15 3.97 3.50 3.81 3.25 3.55 3.14 hardness 7.5 9.0 10 6.8 7.0 7.8 7.0

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4.3.5 Conclusions

Magnetic separation and jigging are separation methods that are suitable to treat construction and demolition waste. Mortar and brick can be separated according to their different apparent magnetic susceptibility, measured with the Frantz isodynamic magnetic separator. By jigging, the waste must be separated into different fractions, with particle sizes of 2 to 5 mm, 5 to 10 mm, 10 to 19 mm, and >19 mm. Then it can be successfully separated into a concrete concentrate and brick concentrate by controlling the frequency and speed of the water current. Magnetic separation and jigging are both easily controlled methods with low costs. It is possible to apply to treat a large amount of construction and demolition waste.

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5 Clay brick production on laboratory scale

In the recycling schedule (figure 1.1) from chapter one whole clay bricks are recovered from masonry debris. The remainder contains both bricks and mortar. After separation the clay brick debris should be crushed and reused as a raw material for the production of clay bricks. In this chapter the production of clay bricks from granulated masonry is described. During the first experiments in the laboratory, clay bricks were made by using pure granulated masonry. Some water was added and a mold was made in which the granulated masonry was compacted. The ideal amount of water for compaction was measured by performing the RAW compaction test (road building standard).The 'green' strength of the dried product was too low and therefore a binder is necessary to get enough 'green' strength of the dried clay body. The 'green' strength is required to enable internal transport in the factory. Clay might be the best binder for ceramic products and therefore the crushed materials were mixed with common Dutch river clay. The mixing and molding of the mass should take place in the traditional clay bricks production process. The granulated clay bricks should contain less cortamination for the production of high quality clay bricks. Another option is to use granulated masonry in the mixture for the production of clay bricks. In this chapter the laboratory research is described in which the mixing and molding properties of mixtures with a high percentage of granulated masonry or granulated clay bhcks are determined. The woi xability of the mixtures and the plasticity related to the water content in the mixture is dei.:> mined by using the Pfefferkorn test. Then the clay bricks were dried and fired in the lab atory kiln. The properties of the fired product were measured like the density, 3 pb strength and firing shrinkage.

5.: Raw materials 5.1 Introduction

In 1' .! laboratory research clay bricks were made using granulated clay bricks and granulated ma. onry in a mixture with three different types of common Dutch river clay and a plastic Mu ikenland clay. Table 5.1 shows an overview of the materials that were used in the labi atory research.

Tabe 5.1 Raw materials from the laboratory research Raw materials 1 2 3 4 5 6 7 8 9

Granulated red and yellow masonry Granulated yellow masonry Granulated red clay bricks Granulated yellow clay bricks

Granulated clay bricks both red and yellow Red firing clay

Yellow firing clay Bronze firing clay Munnikenland clay Code MM MY GR GY GM CR CY CB CM

Dutch river clay was added to give the product its 'green' strength. The granulated masonry Was produced on the production plant for road construction material. The jaw crusher was cleaned and masonry debris was added to the conveyor belt. The material was precrushed and collected in big bags. The big bags were transported to the laboratory, where the granulated masonry was crushed in the laboratory jaw crusher. The granulated clay bricks was produced by crushing some red and yellow clay bricks from the factory in the laboratory

Closing the clay brick cycle