Proceedings of the Institution of

Civil Engineers
Waste and Resource Management
163
August 2010 Issue WR3
Pages 123–127 Saud Al-Otaibi Moetaz El-Hawary Ali Abdul-Jaleel
doi: 10.1680/warm.2010.163.3.123 Associate Research Scientist, Building Research Scientist, Building and Research Associate, Building and
Paper 900015 and Energy Technologies Energy Technologies Department, Energy Technologies
Received 05/04/2009 Department, Kuwait Institute for Kuwait Institute for Scientific Department, Kuwait Institute for
Accepted 17/11/2009 Scientific Research, Kuwait City, Research, Kuwait City, Kuwait Scientific Research, Kuwait City,
Kuwait Kuwait
Keywords:
concrete structures/demolition/
recycling & reuse of materials

Recycling crushed concrete fines to produce lime–silica bricks

S. Al-Otaibi PhD, M. El-Hawary PhD and A. Abdul-Jaleel BSc

Concrete and building rubble waste from demolished 1.2. Recycled concrete in Kuwait
buildings presents an environmental problem in terms of In early 2004, the Environment Preservation Industrial
disposal and use. The amount of structural waste Company (EPIC) started to produce recycled concrete and
generated in Kuwait in 1996 was around 2 Mt, 30% of asphalt products. The plant comprises designated areas for
which was concrete. Recyclable concrete amounted to
(a) receiving building waste and debris
764 kt in 2002, and this is expected to exceed 1.21 Mt in
(b) sorting and classification
2020 as many old buildings will be demolished. This
(c) crushing and screening (Figure 1)
paper presents research carried out to assess the
(d ) storage and shipping.
suitability of crushed concrete for use in the
manufacture of lime–silica bricks. The results show that The main products resulting from the crushing process are
fine powder obtained from crushed concrete contains recycled aggregates of different sizes (Figure 2).
adequate amounts of lime (Ca(OH)2) as a result of the
hydration process, which may react with silica under high 1.3. Utilising crushed concrete fines
temperature and pressure to produce lime–silica bricks. The chemical reaction of calcium hydroxide with silica at high
The paper describes the production process, including temperature and pressure forms the basis for the production of
autoclaving time and temperature, along with the sand–lime bricks. The principal requirements of the lime and
specific gravity, compressive strength and absorption of sand are that both should be sufficiently reactive to yield a
the resulting bricks. The properties of the bricks were binder (calcium silicate hydrate) of sufficient quality (Al-Wakeel
compared with specification requirements, and were and Kishar, 1996). Autoclave hardening (i.e. steam curing at
found to satisfy and even exceed specifications. The high pressure and temperatures above 1708C) of lime–silica
effects of adding different ratios of lime, slag, fly ash and mixtures provides very strong, water-resistant and durable
silica fume on brick properties were assessed and the items. Under natural conditions, quartz sand in a sand–lime
results are reported. mixture is an inert material incapable of interacting with lime.
However, in a steam-saturated atmosphere (100% humidity) at a
1. INTRODUCTION temperature of 1708C and above, quartz becomes chemically
1.1. Environmental concerns active and quickly combines with lime according to the reaction
With resources increasingly scarce, recycling is essential to
conserve resources for future generations and to reduce levels of
CaðOHÞ2 þ SiO2 þ ðn
1ÞH2 O ¼ CaO:SiO2 :nH2 O
solid waste. Reutilisation and recycling of structural wastes and
crushed concrete from demolitions have been investigated in
many research works. The utilisation of waste arising from Crushed recycled concrete fines contain calcium hydroxide
concrete production has been addressed by many, including (hydrated lime) from hydrated cement and siliceous particles
Fumoto and Yamada (2002), Dhir et al. (2004), Weber et al. from aggregates, and there is thus potential for using them in
(2004) and El-Hawary et al. (2008). Many methods for recycling sand–lime bricks.
structural wastes have also been investigated; Kamon et al.
(1988), for example, investigated the possibility of using Hansen (1990) and Hansen and Narud (1983a) discussed the
concrete powder as a soil stabiliser or grout material. possibility of producing concrete from recycled concrete and fly
ash. The resulting concrete was found to gain strength very
The amount of structural waste generated in Kuwait in 1996 slowly due to the pozzolanic reaction of the fly ash and calcium
was around 2 Mt, of which 30% was concrete. In 2002, the hydroxide in the old concrete. Hansen and Narud (1983b)
amount of recyclable concrete was 764 kt, but this is expected addressed the production of lime–silica bricks using recycled
to exceed 1.21 Mt in 2020 as many old buildings will be concrete and silica fume. The utilisation of demolished concrete
demolished (Kuwait Municipality, 1999). In the past, dumping in the production of sand–lime bricks was also addressed by
was the only waste disposal measure taken, but this is no longer Al-Otaibi and El-Hawary (2005) and El-Hawary et al. (2008).
a valid option as it takes up land that is now in great demand This paper describes the properties of the resulting bricks and
for urban development. methods to improve those properties.

Waste and Resource Management 163 Issue WR3 Recycling crushed concrete fines to produce lime–silica bricks Al-Otaibi et al. 123

Downloaded by [ Kuwait University] on [17/02/19]. Copyright © ICE Publishing, all rights reserved.
 Control CF 100% crushed concrete fines
LCF-10 Crushed fines with 10% replaced by lime
LCF-20 Crushed fines with 20% replaced by lime
LCF-40 Crushed fines with 40% replaced by lime
SGCF-10 Crushed fines with 10% replaced by slag
SGCF-20 Crushed fines with 20% replaced by slag
SGCF-40 Crushed fines with 40% replaced by slag
FACF-10 Crushed fines with 10% replaced by fly ash
FACF-20 Crushed fines with 20% replaced by fly ash
FACF-40 Crushed fines with 40% replaced by fly ash
MSCF-5 Crushed fines with 5% replaced by silica fume
(Microsilica)
MSCF-10 Crushed fines with 10% replaced by silica fume
(Microsilica)
MSCF-20 Crushed fines with 20% replaced by silica fume
(Microsilica)

Figure 1. Crushing and screening of waste concrete Table 1. Sample mixes

2. MATERIALS AND TEST PROCEDURES mineral composition. The method used was fused bead analysis
2.1. Materials for the major oxides, which involves dissolving (usually) 1 g of
(a) Samples were prepared from crushed concrete obtained sample in 10 g of flux (lithium tetraborate).
from EPIC by sieving on an 850 micron sieve. The material
was then powdered using a disc crusher. X-ray diffraction (XRD) was used to confirm the presence of
(b) Commercial-grade hydrated lime was used. lime (Ca(OH)2) in the crushed concrete fines and cement paste.
(c) The ground granulated blastfurnace slag (ggbs) used
complies with BS 6699 (BSI, 1999) and ASTM C989 (ASTM,
2006).
(d ) Class F (according to ASTM standard C618-05 (ASTM,
2005a)) fly ash from a local supplier was used in the
mixtures.
(e) Elkem Microsilica was used.

2.2. Sample preparation

Mixtures of crushed concrete fines and supplementary
cementitious materials (Table 1) were prepared manually and
mixed with sufficient water to obtain a good consistency. Next,
700 g samples of the wet mixtures were moulded into 70 mm
cubes. The moulds were then placed in a compression machine at
a load of 60 kN. Figure 3 shows some of the resulting cubes. All
cubes were placed in an autoclave to be treated as sand–lime
bricks (Figure 4). The autoclaving conditions were a temperature
of 190–2008C and vapour pressure from 0 to 1 bar for 1 h, from 1 Figure 3. Prepared specimens
to 12 bar for 3 h, 12 h at 12 bar, followed by cooling.

2.3. Testing
The crushed fines were examined by X-ray fluorescence
spectrometry (XRF) to identify the main oxides and determine

Figure 2. Crushed concrete products Figure 4. Specimens in the autoclave

124 Waste and Resource Management 163 Issue WR3 Recycling crushed concrete fines to produce lime–silica bricks Al-Otaibi et al.

Downloaded by [ Kuwait University] on [17/02/19]. Copyright © ICE Publishing, all rights reserved.
 Prior to testing, specimens were crushed to a fine powder
(<75 mm) and examined using CuK
monochromatic radiation Composition: %
in a Philips PW1050 diffractometer. The range 5–758 2 was
scanned at a scanning speed of 2 per minute. SiO2 31.16
CaO 29.52
Al2O3 5.12
The water absorption of the specimens was tested in accordance Fe2O3 2.24
with BS EN 772-11 (BSI, 2000). Compressive strength was MgO 1.84
determined after 24 h of curing. K2O 1.08
Na2O 0.15
3. RESULTS AND DISCUSSION Loss on ignition 28.16
3.1. Composition of crushed fines
The chemical composition of the crushed fines is presented in Table 2. Chemical composition of crushed concrete fines
Table 2, the major oxides being CaO and SiO2 at around 30%
each. The results of the XRD for the crushed concrete fines are
shown in Figure 5, which shows dominant silica peaks 3.2. Absorption
overshadowing the other peaks. In order to qualitatively show The results for water absorption for the different mixes are
the presence of lime, XRD analysis was performed on a cement shown in Table 3. Although the specification for calcium silicate
paste sample; Figure 6 shows the presence of lime (Ca(OH)2) in bricks in BS EN 771-2 (BSI, 2003) does not specify any limits
very clear peaks. Although the XRD test is not used as a for water absorption, ASTM C73 (ASTM, 2005b) gives a limit of
quantitative measure, it gives a good indication of content. 208 kg/m3 for sand–lime bricks. The results indicate that water

1200
Powder concrete

1000 SiO2

800
Ca(OH)2
Counts

600

400
SiO2
SiO2
SiO2 Ca(OH)2
Ca(OH)2 SiO2
200 SiO2
Ca(OH)2

0
0 10 20 30 40 50 60 70
2θ

Figure 5. XRD patterns for crushed concrete powder

1200

1000 Ca(OH)2

Ca(OH)2
800
Counts

Ca(OH)2
600

400
Ca(OH)2 Ca(OH)2

200

0
0 10 20 30 40 50 60 70
2θ

Figure 6. XRD patterns for cement paste

Waste and Resource Management 163 Issue WR3 Recycling crushed concrete fines to produce lime–silica bricks Al-Otaibi et al. 125

Downloaded by [ Kuwait University] on [17/02/19]. Copyright © ICE Publishing, all rights reserved.
 4. CONCLUSIONS
Mix Absorption by Absorption by The potential for the utilisation of recycled waste concrete in
weight: % volume: kg/m3
the production of lime–silica bricks was illustrated. The main
conclusions from this work are as follows.
Control CF 19.28 303.18
LCF-10 21.52 328.91 (a) Crushed concrete fines can be used in the production of
LCF-20 23.60 352.90 lime–silica bricks, thus reducing waste and saving valuable
LCF-40 25.00 369.42
resources.
SGCF-10 14.10 245.97 (b) The resulting bricks could be produced along the lines of
SGCF-20 9.92 195.29
normal industrial lime–silica brick production when all
SGCF-40 7.60 126.58
measures to ensure quality and proper mix proportioning
FACF-10 16.14 256.92 are taken.
FACF-20 11.77 194.13
FACF-40 8.00 135.16 (c) The properties of the bricks can be improved by
incorporating additional lime or ggbs.
MSCF-5 19.26 309.03
(d ) Further detailed research is required into the quality of
MSCF-10 20.51 312.26
MSCF-20 22.13 329.05 crushed concrete when used in such applications in order to
have more control over the variability of lime content and the
fineness of the crushed materials. Proper classification of the
Table 3. Water absorption after 24 h
different grades of crushed concrete is also very important.

absorption for the control mix (comprising only crushed REFERENCES

concrete fines) was 303 kg/m3, which is higher than the ASTM Al-Otaibi S and El-Hawary M (2005) Potential for recycling
limit. The results of the slag and fly ash mixes at 20% and demolished concrete and building rubble in Kuwait.
above satisfy the ASTM limit. On the other hand, the addition of Proceedings of an International Conference on Achieving
lime increased absorption; this is to be expected as more lime in Sustainability in Construction, Dundee (Dhir RK, Dyer TD
the matrix forms lime mortar, which has a higher water and Newlands MD (eds)). Thomas Telford, London, 229–236.
absorption. The addition of silica fume did not affect the Al-Wakeel EI and Kishar E (1996) Hydrothermal characteristics
absorption when added at 5%, but increasing the absorption at of sand–lime brick production. ZKG International (Zement
higher dosages is influenced by the ineffectiveness of increasing Kalk Gips, Cement Lime Gypsum) 45(9): 260–264.
the quantity of silica fume beyond 5% and the reaction ASTM (American Society for Testing and Materials) (2005a)
stopping due to the high water demand of the silica fume. ASTM C618: Standard specification for coal fly ash and
raw or calcined natural pozzolan for use in concrete.
3.3. Compressive strength ASTM, West Conshohocken, PA, USA.
The results in Figure 7 show that the control mix gave a ASTM (2005b) ASTM C73-05: Standard specification for
compressive strength of 16.5 MPa; this is higher than the 13.8 MPa calcium silicate brick (sand–lime brick). ASTM, West
limit stated in ASTM C73 (ASTM, 2005b) but lower than the limit Conshohocken, PA, USA.
of 20.5 MPa required by BS EN 771-2 (BSI, 2003). Incorporating ASTM (2006) ASTM C989: Standard specification for ground
silica fume and fly ash increased the strength to around 19 MPa. granulated blast-furnace slag for use in concrete and
The effectiveness of silica fume and fly ash additions relies heavily mortars. ASTM, West Conshohocken, PA, USA.
on water content, level of workability and mixing procedure. On BSI (British Standards Institution) (1999) BS 6699: Specification
the other hand, as expected, 10% lime improved the strength to for ground granulated blastfurnace slag for use with
29 MPa, 20% to 31.5 MPa and 40% to 38.6 MPa. The Portland cement. BSI, Milton Keynes.
incorporation of 10, 20 and 40% slag also increased compressive BSI (2000) BS EN 772: Methods of test for masonry units;
strength to 28, 42 and 48 MPa, respectively. determination of water absorption of aggregate concrete,
manufactured stone and natural stone masonry units due to
60 capillary action and the initial rate of water absorption of
Silica fume clay masonry units. BSI, Milton Keynes.
Lime
50 Slag BSI (2003) BS EN 771-2-11: 2000: Specification for masonry
Compressive strength: MPa

Fly ash units; calcium silicate masonry units. BSI, Milton Keynes.
40 Dhir R, Paine K and Dyer T (2004) Recycling construction and
demolition wastes in concrete. Concrete 38(3): 25–28.
30 El-Hawary M, Al-Otaibi S, Abdul-Jaleel A, Al-Enezi S and
Al-Sanad S (2008) Recycling of Concrete and Masonry.
20 Kuwait Institute for Scientific Research, Kuwait, Report
No. 9046.
10 Fumoto T and Yamada M (2002) Applicability of crush stone
powder and recycled concrete powder to high fluidity
0 concrete. Zairyo Journal of the Society of Materials Science
0 5 10 15 20 25 30 35 40 45 51(10): 1105–1110.
Replacement level: %
Hansen T (1990) Recycled concrete aggregate and fly ash
Figure 7. Compressive strength results produce concrete without Portland cement. Cement and
Concrete Research 20(3): 355–356.

126 Waste and Resource Management 163 Issue WR3 Recycling crushed concrete fines to produce lime–silica bricks Al-Otaibi et al.

Downloaded by [ Kuwait University] on [17/02/19]. Copyright © ICE Publishing, all rights reserved.
 Hansen TC and Narud H (1983a) Recycled concrete and fly ash Kuwait Municipality (1999) Specifications of the Project:
make calcium silicate bricks. Cement and Concrete Research Utilization of Structural Waste. Kuwait Municipality,
13(4): 507–510. Kuwait (in Arabic).
Hansen TC and Narud H (1983b) Recycled concrete and silica Weber S, Pommerenke S and Schwambera C (2004) Green
fume make calcium silicate bricks. Cement and Concrete concrete or the alternative use of wastes. Proceedings of an
Research 13(5): 626–630. International Conference on Sustainable Waste Management
Kamon M, Tomohisa S, Tsubouchi K and Nontananand S (1988) and Recycling, London (Limbachiya M and Roberts J (eds)).
Reutilization of waste concrete powder by cement Thomas Telford, London, 317–324.
hardening. Zairyo Journal of the Society of Materials
Science 37(422): 1260–1265.

What do you think?

To discuss this paper, please email up to 500 words to the editor at journals@ice.org.uk. Your contribution will be forwarded to the
author(s) for a reply and, if considered appropriate by the editorial panel, will be published as a discussion in a future issue of the
journal.
Proceedings journals rely entirely on contributions sent in by civil engineering professionals, academics and students. Papers should be
2000–5000 words long (briefing papers should be 1000–2000 words long), with adequate illustrations and references. You can submit
your paper online via www.icevirtuallibrary.com/content/journals, where you will also find detailed author guidelines.

Waste and Resource Management 163 Issue WR3 Recycling crushed concrete fines to produce lime–silica bricks Al-Otaibi et al. 127

Downloaded by [ Kuwait University] on [17/02/19]. Copyright © ICE Publishing, all rights reserved.
Downloaded by [ Kuwait University] on [17/02/19]. Copyright © ICE Publishing, all rights reserved.