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Production of lightweight concrete using incinerator bottom ash
X.C. Qiao
a,*
, B.R. Ng
a
, M. Tyrer
b
, C.S. Poon
c
, C.R. Cheeseman
a
a
Department of Civil and Environmental Engineering, Imperial College, London SW7 2AZ, UK
b
Department of Materials, Imperial College, London SW7 2AZ, UK
c
Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
Received 25 September 2006; received in revised form 9 November 2006; accepted 21 November 2006
Abstract
The medium size fraction (14–40 mm) of aged incinerator bottom ash (IBA) obtained from a major UK energy from waste (EfW)
plant has been crushed to less than 5 mm (CIBA) and thermally treated at 600 C (TCIBA6), 700 C (TCIBA7), 800 C (TCIBA8)
and 900 C (TCIBA9). Thermal treatment reduced the organic carbon content and increased the amount of wollastonite (CaSiO
3
), may-
enite (Ca
12
Al
14
O
33
) and gehlenite (Ca
2
Al
2
SiO
7
). The crushed and thermally treated IBA has been mixed with Portland cement (PC) at
different water/solid (w/s) ratios and with different proportions of PC and Ca(OH)
2
. The volume expansion during setting and bulk den-
sities and compressive strengths were determined. Expansion occurred in all mixes contained IBA during curing. A lightweight material
(density less than 1.8 g/cm
3
) with 28 day compressive strength of higher than 10 MPa was prepared by mixing 20 wt% PC with 80 wt%
TCIBA8 at w/s ratio of 0.20. The expansion and associated lightweight properties result from gas evolution during curing due to residual
metallic Al in the IBA. The main crystalline hydration products in 28 day cured samples were portlandite (Ca(OH)
2
), calcite (CaCO
3
)
and calcium aluminate carbonate hydrates (Ca
4
Al
2
O
6
(CO
3
)
0.5
Æ12 H
2
O and Ca
8
Al
4
O
14
CO
2
Æ24H
2
O).
2006 Elsevier Ltd. All rights reserved.
Keywords: Incinerator bottom ash; Waste incineration; Thermal treatment; Light weight concrete; Pozzolanic
1. Introduction
Incineration of municipal solid waste (MSW) is expected
to increase in the UK, China and many other countries
where the availability of landfill is limited. In the UK
approximately 28 million ton of MSW are generated each
year, and this is increasing at about 3% per annum.
Although the incineration process reduces the volume of
MSW by up to 90%, 1 ton of MSW produces approxi-
mately 0.3 ton of incinerator bottom ash (IBA) [1]. In Eng-
land and Wales 642,088 ton IBA were generated annually
between 1996 and 2000 and the majority of this
(79 wt%) was sent direct to landfill [2].
As waste disposal by incineration increases, there is a
need to develop novel reuse applications for IBA that pro-
vide both environmental and economic benefits. IBA is a
heterogeneous mix of ceramic materials such as brick,
stone, glass, ferrous and non-ferrous metals and other
non-combustible inorganic materials, together with some
residual organic matter. A large number of studies have
reported reuse applications for IBA and the use of inciner-
ator ash in sustainable construction has been the exten-
sively discussed [3]. Part replacement of sand and cement
by IBA in cement mortar is reported to improve compres-
sive strength development of samples [4]. IBA with particle
sizes less than 50 mm has been reported to have similar
engineering properties to natural aggregates and has been
used in road construction [5]. IBA with particle sizes
between 2 and 32 mm has been found to be suitable for
reuse as aggregate in concrete [6,7]. However, the risk of
entrapment of hydrogen produced by corrosion of IBA
aluminium metal residue in fresh concrete has been high-
lighted [8,9].
IBA is normally naturally weathered and the easily
extractable ferrous and non-ferrous metals removed at
UK ash processing plants prior to any reuse. The remain-
ing non-metallic materials are graded into fine (<14 mm),
0950-0618/$ - see front matter 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.conbuildmat.2006.11.013
*
Corresponding author. Tel.: +44 207 594 5971; fax: +44 207 594 1511.
E-mail address: xcqiao505@hotmail.com (X.C. Qiao).
www.elsevier.com/locate/conbuildmat
Construction and Building Materials xxx (2006) xxx–xxx
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medium (14–40 mm) and coarse (>40 mm) fractions. The
medium fraction is used as secondary aggregates in bulk
civil engineering applications as road base and fill, but little
research has aimed at developing higher grade applications
for this material.
Light weight concretes are economical, environmentally
friendly, cellular, lightweight, structural materials that pro-
vide thermal and acoustic insulation as well as fire resis-
tance. It is an energy-efficient choice for moderate to cold
climates where outdoor temperature fluctuates frequently.
Aluminium powder has been always used as aerating agent
in the manufacturing process of light weight concretes. The
reaction between aluminium powder and alkaline content
in the concrete can generate hydrogen gas which introduces
macro-porosity in the matrix made of cement, lime, sand
and water [10–12]. Therefore, the IBA with aluminium
metal residue might have potential in manufacturing light
weight concretes under appropriate treatment.
The objective of this research was to investigate the
properties of mixes produced from crushed medium frac-
tion IBA and Portland cement (PC). The effects of ther-
mally treated crushed IBA, varying the water to solids
ratio and the PC to Ca(OH)
2
ratio used in the binder phase
have been investigated through volume expansion, bulk
density, compressive strength and X-ray diffraction tests.
2. Experimental
2.1. Preparation of materials
2.1.1. Incinerator bottom ash
The fraction of IBA with particle size between 14 and
40 mm was obtained from the ash processing plant associ-
ated with a major EfW facility operating in London, UK.
This facility processes approximately 420,000 ton of
MSW per year. The IBA had been naturally weathered
for between 6 and 8 weeks at the ash processing plant
and the readily extractable metals removed prior to
sampling.
2.1.2. Preparation of crushed IBA
The as-received medium sized IBA was oven dried over-
night at 105 C and crushed using a laboratory hammer
mill to pass through a 5 mm sieve. The elemental composi-
tion of the crushed materials was determined by lithium
metaborate and tetraborate flux fusion [13]. Digest analysis
used inductively coupled plasma atomic emission spectros-
copy (ICP-AES) and the results are given in Table 1. The
high SiO
2
content originates from the significant amount
of glass and other ceramic materials present in the medium
fraction of IBA. The loss on ignition (LOI) was determined
in accordance with BS EN 196-2: 1995 and involved mea-
suring the weight loss of samples heated to 950 C for 1 h
in air. Crystalline phases present in the milled IBA have
been characterized by X-ray diffraction (Philips PW 1820
System with a Cu target, run at 2hsteps of 0.04). Sieve
analysis was completed in accordance with BS 812-
103.1:1985 using 4.75 mm and 75 lm sieves as the maxi-
mum and minimum sieve sizes. Characterisation data for
the crushed medium fraction IBA (CIBA) is included in
Figs. 1 and 2.
2.1.3. Preparation of thermally treated crushed IBA
Samples of thermally treated crushed medium fraction
IBA (TCIBA) were produced by heating CIBA to 600 C
(TCIBA6), 700 C (TCIBA7), 800 C (TCIBA8) and
900 C (TCIBA9) in a rotary electric tube furnace (Carbo-
lite GTF R/95). The crushed IBA was allowed to gradually
tumble along the length of the furnace with the tube
inclined at an angle of approximately 3while rotating at
1.5 rpm. The rotating tube was open at both ends and
had an internal diameter of 7.7 cm and was 150 cm long
with a 90 cm heated zone. The average time for the IBA
to pass through the heated zone was approximately
15 min. The resulting thermally treated samples were ana-
lysed using the same procedures as for the crushed medium
fraction IBA (CIBA). Characterisation data for thermally
treated crushed IBA is included in Figs. 1 and 2.
2.2. Concrete samples
Sample constituents were mixed for 5 min and then
formed in steel cubic moulds (70 ·70 ·70 mm) using a
vibrating table. Control samples were prepared using natu-
ral aggregate and sand that was sieved and blended to give
a similar grading curve to the CIBA as shown in Fig. 2. All
the specimens were cured at 20 C and 98% relative humid-
ity and were removed from the moulds after 3 days. The
different samples prepared are summarised in Table 2.
2.2.1. Effect of thermal treatment temperature
A series of samples, all containing 20 wt% addition of
Portland cement were prepared using crushed IBA (CIBA)
and crushed IBA that had been thermally treated at 600 C
(TCIBA6), 700 C (TCIBA7), 800 C (TCIBA8) and
900 C (TCIBA9).
Table 1
Chemical compositions of crushed medium fraction (14–40 mm) IBA
(CIBA)
Major elements (oxide wt%) Trace elements (mg/kg)
SiO
2
51.8 Cu 2353.0
CaO 14.2 Pb 2869.7
Al
2
O
3
11.9 Ba 2557.5
Fe
2
O
3
6.0 Cr 1222.2
MgO 3.3 Sr 982.1
Na
2
O 1.9 Mn 980.1
K
2
O 1.3 V 916.7
P
2
O
5
1.1 La 307.4
TiO
2
0.4 Ni 295.0
ZnO 0.2 As 273.4
LOI 5.7 Mo 79.1
Ag 13.1
Be 3.2
Cd 2.6
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2.2.2. Effect of water to solids (w/s) ratio
Samples were prepared using crushed IBA thermally
treated at 800 C using w/s ratios between 0.15 and 0.35.
2.2.3. Effect of cement replacement by Ca(OH)
2
Mixes were prepared using TCIBA8 in which the
20 wt% PC addition was replaced using different amounts
of a commercially available hydrated lime (Limbux
Hydrated Lime, Buxton Lime Industries Limited, UK) that
contained 96.9 wt% Ca(OH)
2
content.
2.3. Physical tests
2.3.1. Volume expansion and bulk density
The Archimedes water displacement method (BS EN
12390-7:2000) was used to calculate the volume of samples
10 20 30 40
0
500
1000
1500
2000
2500
3000
3500
4000
S
S
SG WGW
C
G
MS
S
M
Intensity
2 Theta (K-Cu)
CIBA
TCIBA6
TCIBA7
TCIBA8
TCIBA9
Fig. 1. X-ray diffraction of crushed medium fraction (14–40 mm) incinerator bottom ash (CIBA) and the corresponding thermally treated materials
(TCIBA). C: calcite (CaCO
3
); G: gehlenite (Ca
2
Al
2
SiO
7
); M: mayenite (Ca
12
Al
14
O
33
); S: quartz (SiO
2
); W: wollastonite (CaSiO
3
).
100 1000
0
20
40
60
80
100
Accumulate Passing (%)
Sieve size (micrometer)
CIBA
TCIBA8
NAgg
TCIBA6
TCIBA7
TCIBA9
Fig. 2. Sieve analysis of different aggregates.
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cured for 28 days. The specimen were first covered using
plastic film before soaking in water and the volume expan-
sion calculated from the difference between the measured
volume and the original volume of the sample in the cubic
mould. The bulk density of cured samples was determined
from the specimen weight and measured volume. The data
presented on expansion and density is the average obtained
from testing three samples.
2.3.2. Compressive strength test
The strengths of samples after curing for 7 and 28 days
were measured using a compression testing machine (Auto-
max Series 5). Reported results are the average of three
specimens that varied by not more than 10%.
2.4. Microstructural characterisation
2.4.1. X-ray diffraction
Hydration reactions were inhibited after 28 day curing
by immersing samples in acetone for 14 days, with the ace-
tone being replaced with fresh solution after 7 days [14].
Samples were then dried at 50 C for one week. The
hydrated binder phase was separated from the larger
crushed IBA particles and passed through a 150 lm sieve
prior to analysis by X-ray diffraction (XRD) to determine
the crystalline phases present.
3. Results
3.1. Characterization of crushed and thermally treated IBA
samples
The XRD data in Fig. 1 shows that the major crystalline
phases present in the crushed medium fraction of IBA
(CIBA) were silica (SiO
2
) and calcium carbonate (CaCO
3
).
New crystalline phases including wollastonite (CaSiO
3
),
gehlenite (Ca
2
Al
2
SiO
7
) and mayenite (Ca
12
Al
14
O
33
) were
formed during subsequent thermal treatment, with the
amount of these phases increasing as the treatment temper-
ature increased. The CaCO
3
content present in the IBA
decreased after treatment at 600 C and was not detected
after treating at or above 700 C. The peak intensity of
quartz (SiO
2
) also decreased with increasing IBA treatment
temperature as other silicate containing phases formed.
The data given in Fig. 2 indicates that all the IBA sam-
ples have similar particle size distribution, although there is
a slight reduction in the accumulate passing of fine particles
in samples after thermal treatment due to agglomeration
effects.
3.2. Physical properties of cured samples
3.2.1. Effect of thermal treatment temperature
The effect of treatment temperature on the expansion,
density and compressive strength of samples containing
20% PC and thermally treated crushed medium fraction
IBA (TCIBA) is shown in Fig. 3. Control samples contain-
ing natural aggregate showed no expansion at 28 days.
Crushed IBA treated at 600 C and 700 C (TCIBA6 and
TCIBA7) resulted in reduced expansion compared to
crushed IBA. However, more than 17% volume expansion
was observed in samples containing IBA thermally treated
at 800 C and 900 C (TCIBA8 and TCIBA9). Densities of
all the samples are lower in comparison with control mixes
and samples with high expansion show low density charac-
teristic of lightweight concretes. The compressive strengths
of all the IBA containing samples are comparable to the
control mixes and are typically greater than 10 MPa after
28 days curing. It is worthy to be mentioned that samples
contained thermally treated IBA showed rapid setting
characteristics in comparison with control sample.
3.2.2. Effect of w/s
The effect of w/s ratio on the expansion, density and
compressive strength of samples made with 20 wt% PC
and 80 wt% medium fraction IBA, crushed to less than
Table 2
Mix proportions of samples (wt%)
Sample code CIBA TCIBA Cement Natural aggregate Ca(OH)
2
w/s
Control S1 – – 20 80 – 0.2
CIBA S2 80 – 20 – – 0.2
TCIBA S3 80 (600 C) 20 – – 0.2
S4 – 80 (700 C) 20 – – 0.2
S5 – 80 (800 C) 20 – – 0.2
S6 – 80 (900 C) 20 – – 0.2
Water/solids ratio (w/s) S7 – 80 (800 C) 20 – – 0.15
S5 – 80 (800 C) 20 – – 0.20
S8 – 80 (800 C) 20 – – 0.25
S9 – 80 (800 C) 20 – – 0.30
Replacement of cement by Ca(OH)
2
S5 – 80 (800 C) 20 – 0 0.2
S10 – 80 (800 C) 15 – 5 0.2
S11 – 80 (800 C) 10 – 10 0.2
S12 – 80 (800 C) 0 – 20 0.2
CIBA = medium fraction of IBA (14–40 mm) crushed to <5 mm; TCIBA = thermally treated CIBA.
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5 mm and thermally treated at 800 C (TCIBA8) is shown
in Fig. 4. Expansion during curing is approximately at
between 12 and 18 volume percent for all mixes. However
the density decreases with increased water in the mix.
Water content also has a significant effect on compressive
strength with low water content mixes (w/s = 0.15) having
strengths exceeding 20 MPa.
3.2.3. Effect of replacing cement with Ca(OH)
2
The effect of cement to Ca(OH)
2
binder ratio on the vol-
ume expansion, density and compressive strength of sam-
ples made with 20 wt% binder and 80 wt% medium
CIBA 600 700 800 900
-5
0
5
10
15
20
control 28 days
Volume expansion (%)
Treatment Temperature(oC)
28days CIBA28days
MIBA 600 700 800 900
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
2.1
2.2 control 28 days
Bulk Density (g/cm3)
Treatment Temperature(oC)
7days 28days
CIBA7days CIBA28days
CIBA 600 700 800 900
0
5
10
15
20
25
control 28 days
Compressive strength (MPa)
Treatment temperature (oC)
7days 28days CIBA7days CIBA28days
Fig. 3. Effect of treatment temperature on the expansion, density and
compressive strength of samples containing 20% PC and thermally treated
crushed medium fraction IBA (TCIBA).
0.10 0.15 0.20 0.25 0.30 0.35 0.40
0
5
10
15
20
Volume expansion (%)
water/solids ratio
0.10 0.15 0.20 0.25 0.30 0.35 0.40
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
2.1
2.2 control 28 days
Bulk density (g/cm3)
water/solids ratio
0.10 0.15 0.20 0.25 0.30 0.35 0.40
0
5
10
15
20
25
Compressive strength (MPa)
water/solids ratio
control 28 days
Fig. 4. Effect of water/solids ratio on the expansion, density and
compressive strengths of 28 day samples made with 20 wt% PC and 80
wt% medium fraction IBA, crushed to less than 5 mm and thermally
treated at 800 C (TCIBA8).
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fraction IBA, crushed to less than 5 mm and thermally
treated at 800 C (TCIBA8) is shown in Fig. 5. The volume
expansion decreases with increasing Ca(OH)
2
in the binder
from approximately 18% for the cement binder to around
8% for samples made with a Ca(OH)
2
binder. The bulk
density of samples remains approximately constant at
1.8 g/cm
3
while the compressive strengths at 28 days
decrease with increasing Ca(OH)
2
content.
3.3. Microstructural characterisation of cured samples
XRD data of samples containing crushed IBA that
had been thermally treated at 800 C are given in Figs.
6and7. These show that the main crystalline hydration
products in 28 day cured samples are portlandite
(Ca(OH)
2
), calcite (CaCO
3
), C–S–H and calcium alumi-
nate carbonate hydrates (Ca
4
Al
2
O
6
(CO
3
)
0.5
Æ12H
2
O and
Ca
8
Al
4
O
14
CO
2
Æ24H
2
O). Carbonated hydration products
are very common in porous concretes [15–17]. Thermal
treatment increases the formation of calcium aluminate
carbonate hydrates and increased w/s ratios results in
increased formation of portlandite. Fig. 7 indicates that
replacing PC with Ca(OH)
2
increases the calcite (CaCO
3
)
content and also appears to result in increased levels of
quartz (SiO
2
) except for replacing cement with 5 wt%
of Ca(OH)
2
.
4. Discussion
The 14–40 mm medium fraction of IBA tends to be the
most consistent material extracted from bulk IBA and it
is known that most heavy metals of environmental con-
cern tend to be found in the finer particle size fractions
[6]. Crushing the 14–40 mm medium IBA and sieving to
less than 5 mm has the effect of producing a more homog-
enous sample. Thermal treatment introduces a number of
effects on the CIBA including decomposition of CaCO
3
,
formation of new mineral phases, reduction in the organic
carbon content present in the sample and increase in
reactivity.
Expansion effects result from IBA is usually thought to
be due to the presence of residual aluminium metal in the
IBA that reacts with hydroxide ions under high pH condi-
tions to produce hydrogen gas [9,18]:
Al þ2OHþ2H2O!H2þAlðOHÞ
4ðaqÞ
The decomposition of CaCO
3
presented in CIBA to give
CaO in the thermally treated CIBA (TCIBA) increases
the above reaction. However, humus presented in the
CIBA has potential to neutralize alkaline content and de-
lays the above reaction. The elimination of organic con-
tents from CIBA through thermal treatment decreases
the neutralization reaction and increases simultaneously
the relative aluminium content presents in the TCIBA.
Therefore, the reaction between aluminium and alkaline
content in the TCIBA became stronger than in the CIBA.
The AlðOHÞ
4formed by this reaction is believed to react
with calcium dissolved in the pore water to produce hy-
drated calcium aluminate phases, and these are normally
associated with rapid setting cement systems [9].
20:0 15:5 10:10 0:20
0
5
10
15
20
Volumeexpansion (%)
cement : Ca(OH)2
20:0 15:5 10:10 0:20
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
2.1
2.2
Bulk density (g/cm3)
cement : Ca(OH)2
control 28 days
20:0 15:5 10:10 0:20
0
5
10
15
20
25
Compressive strength (MPa)
cement : Ca(OH)2
control 28 days
Fig. 5. Effect of the cement: Ca(OH)
2
binder ratio on the volume
expansion, density and compressive strength of 28 day cured samples
made with 20 wt% binder and 80 wt% medium fraction IBA, crushed to
less than 5 mm and thermally treated at 800 C (TCIBA8).
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In order to meet the requirements for buildings light
weight concretes usually possess characteristics of high
porosity, low density and relative high strength [10,12].
This research has shown that it is possible to produce
a lightweight concrete material using crushed medium
fraction of IBA and Portland cement. The samples con-
taining either crushed medium fraction IBA or crushed
IBA thermally treated at 800 C show significant volume
expansions during curing and produced block samples
with densities significantly below the 1.8 g/cm
3
limit
which is the maximum value for concretes to be consid-
ered lightweight. However, higher w/s ration than 0.20
resulted in lower volume expansion and compressive
strength. Quit setting time occurred in samples TCIBA6
10
0
500
1000
1500
S9
Intensity
2 Theta (K-Cu)
S1
S2
S5
S7
S8
CAC
10 20 30 40
0
1000
2000
3000
4000
5000
6000
7000
S9
Intensity
2 Theta (K-Cu)
S1
S2
S5
S7
S8
CH
S
S
S
S
S
C
CAC CS
CSH
CH
CH
Fig. 6. XRD data for 28 day cured samples containing natural aggregate (S1), CIBA (S2) and TCIBA (S5) and 28 day cured samples with w/s ratio of 0.15
(S7), 0.20 (S5), 0.25 (S8) and 0.35 (S9). C: calcite (CaCO
3
); CAC: calcium aluminate carbonate hydrates (Ca
4
Al
2
O
6
(CO
3
)
0.5
Æ12H
2
Oor
Ca
8
Al
4
O
14
CO
2
Æ24H
2
O; CH: portlandite (Ca(OH)
2
); CS: Ca
2
SiO
4
; CSH: calcium silicate hydrates; S: quartz (SiO
2
).
10 20 30 40
0
1000
2000
3000
4000
5000
S
Intensity
2 Theta (K-Cu)
S5
S10
S11
S12
CSH
CS
S
S
C
CH
SCH
CH
CAC
S
Fig. 7. XRD data showing the effect of cement/Ca(OH)
2
binder ratio on the crystalline phases present in 28 day cured samples (20 wt% binder:80 wt%
TCIBA8). PC:Ca(OH)
2
ratio, S5 = 20:0, S10 = 15:5, S11 = 10:10, S10 = 0:20. C: calcite (CaCO
3
); CAC: calcium aluminate carbonate hydrates
(Ca
4
Al
2
O
6
(CO
3
)
0.5
Æ12H
2
OorCa
8
Al
4
O
14
CO
2
Æ24H
2
O); CH: portlandite (Ca(OH)
2
); CS: Ca
2
SiO
4
; CSH: calcium silicate hydrates; S: quartz (SiO
2
).
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and TCIBA7 decreased the development of volume
expansion, which resulted in higher densities of samples
than 1.8 g/cm
3
.
Lime is always used to react with aluminium powders in
aerated concretes to help produce hydrogen gas which help
result in cellular products [12]. However, the addition of
lime into thermally treated CIBA (TCIBA) decreases the
volume expansion and strength of sample. This suggests
that the addition of lime into TCIBA take less effect in
the formation of light weight concretes.
Carbonation is a common phenomenon occurred in
concretes, especially in aerated concretes [15–17]. It can
be a reaction between atmospheric carbon dioxide and cal-
cium hydroxide or C–S–H in concretes. During the hydra-
tion of sample thermally treated CIBA leads to form more
calcium aluminate carbonate hydrates (Ca
4
Al
2
O
6
(-
CO
3
)
0.5
Æ12H
2
OandCa
8
Al
4
O
14
CO
2
Æ24H
2
O) but less cal-
cite (CaCO
3
) at w/s of 0.20. This may benefit to the
strength development of sample contained thermally trea-
ted CIBA.
It should be noted that recent research has investigated
thermal treatment of IBA as a potential treatment to
reduce metal leaching and was found to be the most effect
technique investigated. Therefore this type of crushing,
thermal treatment and beneficial reuse of IBA in light-
weight block type products may offer a way to increase
the beneficial reuse of this important waste.
5. Conclusions
1. Thermal treatment of crushed medium size IBA pro-
duces new crystalline phases including wollastonite
(CaSiO
3
), gehlenite ((Ca
2
Al
2
SiO
7
) and mayenite
(Ca
12
Al
14
O
33
).
2. 80:20 treated IBA: PC samples prepared at w/s of 0.20
show significant volume expansion during curing with
>12% occurring for crushed IBA and >17% for 800 C
treated crushed IBA.
3. Calcium aluminate carbonate hydrates (Ca
4
Al
2
O
6
(-
CO
3
)
0.5
Æ12H
2
O and Ca
8
Al
4
O
14
CO
2
Æ24H
2
O), portlan-
dite (Ca(OH)
2
) and calcite (CaCO
3
) are the main
hydration products present in the samples containing
IBA.
4. The resulting density and strength of samples containing
IBA are appropriate for use as lightweight concrete
blocks.
5. Further research is necessary to optimise IBA reuse to
develop a more resource efficient economy.
Acknowledgement
This research and funding for Dr. Qiao from Wuhan
University of Technology was made possible through an
International Incoming Fellowship award from The Royal
Society, UK. We also acknowledge the help provided by
Mr. Peter Lewis, Onyx SELCHP.
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8X.C. Qiao et al. / Construction and Building Materials xxx (2006) xxx–xxx
ARTICLE IN PRESS
Please cite this article in press as: Qiao XC et al., Production of lightweight concrete using incinerator bottom ash, Constr Build Mater
(2006), doi:10.1016/j.conbuildmat.2006.11.013
