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Structural Lightweight Aggregate Concrete by Incorporating Solid Wastes as Coarse Lightweight Aggregate
Muhammad Aslam1,a, Payam Shafigh1,b and Mohd Zamin Jumaat1, c *
1Department of Civil Engineering, Faculty of Engineering, University of Malaya, 50603, Kuala Lumpur, Malaysia
a [email protected], b [email protected], [email protected]
Keywords: Lightweight aggregate, Lightweight aggregate concrete, Oil palm shell, Clinker, Compressive strength, Water absorption, Efficiency factor.
Abstract. Structural lightweight aggregate concrete offers several benefits as compared to the
normal weight concrete. Most common methods of producing structural lightweight concrete is by
using artificial lightweight aggregates. However, the cost of the production of artificial lightweight
aggregates is high due to energy and raw materials consumption. The use of waste and by-product
materials as lightweight aggregate in concrete can provide a better solution to reducing the negative
impact of the concrete industry. This paper reports an investigation to produce structural lightweight
aggregate concrete by utilizing the locally available solid waste materials, namely oil palm shell
(OPS) and oil-palm-boiler clinkers (OPBC) as coarse lightweight aggregates. Two different mix
proportions were studied. In the first concrete mix, just OPS was used as coarse aggregate.
However, 40% of OPS (by volume) of the first mix was replaced with OPBC in the second mix.
The test results showed that by replacing OPS with OPBC, it directly affects the characteristics of
the lightweight concrete. The 28-days compressive strength of the blended coarse lightweight
aggregate concrete was significantly increased compared to OPS concrete.
Introduction
Structural concrete is the most widely used construction material in all types of civil engineering
structures. It has an excellent resistance to water and can be formed into a variety of shapes and
sizes [1]. Nowadays, the concrete industry is annually consuming huge amounts of natural
resources and raw materials for the production of concrete around the world [2]. Because of the
huge amount of concrete produced daily, even a small reduction in the environmental impact per
ton of concrete will result in considerable benefits to the environment[3].
Lightweight concrete (LWC) has been widely used in buildings as masonry blocks, roof decks,
wall panels, and precast concrete units[4]. It can be produced with an oven dry density range of
approximately 300-2000 kg/m3, with corresponding cubical compressive strengths ranges
approximately from 1 to over 60 MPa. It was reported that the reduction in the dead weight of a
building by the use of LWC could result in a decrease in the cross section of steel reinforced beams,
columns, plates and foundations[5]. The most popular way of achieving LWC production is by
using lightweight aggregate (LWA) [6].
Since 2nd
A.D. different types of natural and manufactured LWAs such as foamed slag,
diatomite, pumice, volcanic cinders, scoria, tuff, expanded clay, shale, slate, perlite and vermiculite
and materials that occur as industrial byproducts such as sintered pulverized-fuel ash, sintered slate
and colliery waste, foamed or expanded blast-furnace slag has been used as construction material
[7-9]. Oil palm shell (OPS) and oil-palm-boiler clinker (OPBC) are solid waste LWA materials and
as an alternative LWA in tropical regimes and countries that have a palm oil industry. Malaysia
contributes about 58% of the total supply of palm oil in the world, and is one of the top listed
countries which has huge assets of solid wastes from palm oil industry [10]. OPS and OPBC are
produced in large quantities by the palm oil mills. For instance, in Malaysia and Nigeria it was
estimated that over 4 million tonnes of OPS solid waste is produced annually and only a fraction is
used for the production of the fuel and activated carbon [11]. The density of the OPS and OPBC
aggregates are within the range of most typical lightweight aggregates. It was found from the
Applied Mechanics and Materials Vol. 749 (2015) pp 337-342 Submitted: 07.01.2015© (2015) Trans Tech Publications, Switzerland Accepted: 08.01.2015doi:10.4028/www.scientific.net/AMM.749.337
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net. (ID: 103.244.188.231-04/02/15,15:58:29)
previous literature that OPS and OPBC can be used as coarse lightweight aggregate for producing
structural lightweight aggregate concrete with normal strength [12, 13]. However, recent studies
[14] revealed that OPS and OPBC can be used as lightweight aggregate for producing high strength
lightweight concrete.
The objective of this paper is to investigate the possibility of producing structural lightweight
aggregate concrete by incorporating these two types of solid waste material as coarse aggregate. For
this purpose, two lightweight concrete mixtures were prepared. OPS concrete was considered as
control mix and in the second mix, 40% of OPS (by volume) was substituted by OPBC.
Experimental Details
Materials used
Ordinary Portland cement (OPC) with specific gravity of 3.14 and specific surface area of 3.52 m2/g
was used as binder.
OPS and OPBC were used as coarse aggregates. Before the OPS and OPBC were used, they
were washed and then air dried in the laboratory until surface dry. The physical properties and
grading of OPS and OPBCare shown in Table 1 and Table 2, respectively. The OPS and OPBC
aggregates are shown in Fig. 1. Local mining sand was used as fine aggregate. It has a fineness
modulus of 2.65, specific gravity of 2.68 and maximum grain size of 4.75 mm.
The super-plasticizer (SP) used in this study meets the requirements for superplasticizers
according to ASTM C494-86 Type G. It has a density of 1.09±0.02 kg/m3. The recommended
dosage is between 0.8-1.0 percent by mass of cement.
Table 1, Physical and mechanical properties of LWAs.
Physical and mechanical properties OPS OPBC
Specific gravity (saturated surface dry) 1.19 1.69
Bulk density (compacted) [kg/m3] 610 860
24 h water absorption 20.5 7.0
Crushing value (%) 0.2 21.2
Impact value (%) 5.5 36.3
Abrasion value (%) 5.7 23.9
Table 2, Grading of OPS and OPBC aggregates.
Sieve size [mm] 19 12.5 9.5 8 4.75
Cumulative % by
weight passing
OPS 100 96.80 84.24 61.20 2.98
OPBC 100 98.35 90.32 70.75 3.27
338 Materials and Manufacturing Engineering
Fig. 1 Oil palm shell (left) and oil-palm-boiler clinker (right).
Mix Proportions and Procedure
Two mixes of lightweight concrete were prepared by using oil palm waste materials. The OPS
concrete was considered as the control concrete, and in the second mixture, OPS of the first mixture
was replaced by 40%OPBC (by volume). Both of these concretes have water to cement ratio of 0.36
and the cement content 480 kg/m3. Details are given in Table 3.
Table 3, Mix proportions for concretes.
Mix code Content [kg/m
3]
w/c SP
(% cement) OPC Water Sand OPS OPBC
OPSC 480 173 890 360 0 0.36 1
OPBCC 480 173 890 216 205 0.36 0.90
For mixing, all materials, except water and SP, were mixed for one minute. Subsequently, the SP
was mixed with 70% of the mixing water for 3 minutes, and then the remaining water was added to
the mix. Fresh concrete was then cast into steel moulds and compacted in two layers using a
vibrating table in the laboratory at a temperature of 29 ± 2 oC and a relative humidity of about
70%.The specimens were demoulded after 24 hours of casting and specimens were immersed in
water at the temperature of 22 ± 2oC.
Results and Discussion
Workability and Density
The slump value and the density of the two mixes are given in Table 4. Mix OPBCC had good
workability without any segregation. However, OPSC mixture also had satisfactory workability.
Since OPBC aggregates were round in shape and have very low water absorption as compared to
OPS, therefore it gives better workability. Mehta and Monteiro [15] reported that for structural
lightweight concrete, slump value of 50 to 75 mm may be sufficient to obtain workability that is
similar to a 100 to 125 mm slump for normal weight concrete. As can be seen in Table 3, the SP
used in OPBCC is 10% less than OPSC. This isanother advantage of incorporating OPBC in OPS
concrete.
The demoulded and oven dried densities of OPSC is less than OPBCC. This is because the
density of OPS aggregate isless than OPBC aggregate (about 29%). Test results showed that, on
average, OPBCC is about 4.3% more than OPSC.
Applied Mechanics and Materials Vol. 749 339
Table 4, Slump and density.
Mix code Slump
[mm]
Density [kg/m3]
Demoulded Oven dried
OPSC 55 1920 1790
OPBCC 100 2010 1860
Compressive Strength
The development of compressive strength of both mixes up to 56 days is shown in Fig.2. Both
mixes have almost similar 1-day compressive strength, but for all later ages the compressive
strength of the OPBCC is more than OPSC. Compared to the mix OPSC, mix OPBCC has higher
compressive strengths of about 10.7%, 3.5%, 13.4% and 17% at 3, 7, 28 and 56 days,
respectively.From the Fig. 2, it can be seen that the difference between the strength of two concretes
is significant and it increases with time. The compressive strength of the OPS lightweight concrete
(OPSC) showed a 11.4%, 16.8% and 20.2% increase at 7, 28 and 56 days, respectively, when
compared to the strength obtained at the age of 3 days. While, forOPBCCthese ratios are 4.2%,
19.2% and 25.8%, respectively. Therefore, the OPBCC showed a higher rate of strength gain.
The 28-day compressive strength of OPSC and OPBCC are 36.90 and 42.60 MPa, respectively.
It was observed that the OPS concrete showed 13.4% lower compressive strength than the OPBCC,
because the main problem of OPSC is due to the smooth surface texture of the shell for both convex
and concave faces. Shafigh et al. [16] recommended that the strength of lightweight aggregate
concrete depends on the strength of the LWA used and the hardened cement paste, as well as the
bonding of the aggregate/cement paste in the interfacial zone. Mannan et al.[17] stated that the
failure of OPS concrete specimens in compression were initially due to the failure of the adhesion
between the OPS and cement paste. They improved the quality of OPS aggregates by using various
pre-treatment methods and found that the 28-days compressive strength of about 33 MPa could be
achieved. According to Okpala[18], the failure of the OPS concrete at 28 days was dependent upon
the breakdown of the bond between the aggregate and the paste. Mohammed et al. [19] reported that
the OPBCC aggregates have high water absorption and it will be beneficial to the resulting
hardened concrete. It was further that the LWCs with porous aggregate are less sensitive to poor
curing as compared to NWC especially in the early ages due to the internal water supply stored in
the porous lightweight aggregate.With limit data from current study it can be concluded that the
internal curing process in the case of OPBCC may be better than oil palm shell. However, this
needs more investigation in the future.
Fig. 2 Development of compressive strength.
Efficiency Factor
The low efficiency factor (strength/weight ratio) of concrete compared to steel is a disadvantage of
concrete. However, by increasing its compressive strength or by reducing specific gravity of
concrete the efficiency ratio can be improved[20]. The efficiency factor of OPBCC and OPSC are
22903 and 20615 N.m/kg. This shows that at the same mix proportions, the OPBCC has 10%
15
20
25
30
35
40
45
50
0 10 20 30 40 50 60
Co
mp
ress
ive
Str
eng
th [
MP
a]
Age (days)
OPSC
OPBCC
340 Materials and Manufacturing Engineering
greater efficiency factor than OPSC mix. It is worth to note that although the OPBClightweight
aggregate is heavier than OPS lightweight aggregate, however it has significantly greater efficiency
factor. This is an important point that OPS and OPBC are solid waste materials of the palm oil
industry.
Table 5, Compressive strength and efficiency factor.
Mix code 28-day compressive
strength [MPa]
Efficiency factor
[N.m/kg]
OPSC 36.90 20615
OPBCC 42.60 22903
Conclusions
After the experimental investigation, it can be concluded that it is possible to produce a structural
lightweight aggregate concrete by incorporating two types of waste materials. The OPS coarse
aggregate was replaced (by volume) up to 40% of the OPBC coarse aggregate. At the same mix
proportions, the substitution of the OPBC in OPS concrete significantly increased the compressive
strength of the concrete. Although, the density of the OPBC concrete is slightly higher than the OPS
concrete, but it is in the acceptable range of the structural lightweight concretes.However, the
efficiency factor of the OPBC lightweight concrete is significantly greater than OPS concrete. In
addition, it was also found that the internal curing process in the OPBC concrete might be better
than the OPS concrete, so by incorporating the OPBC aggregates in the OPS concrete it
significantly improves the quality of the structural lightweight concrete.By incorporating of OPBC
in OPS concrete, the lightweight concrete not only can be a low cost construction material but it can
be also called as a green high strength lightweight concrete.
Acknowledgement
This research was funded by the University of Malaya, High Impact Research Grant (HIRG) No.
UM.C/625/1/HIR/MOHE/ENG/36 (16001-00-D000036) -“Strengthening Structural Elements for
Load and Fatigue”.
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