Utilization of oil palm kernel shell as lightweight aggregate in concrete – A review

Construction and Building Materials 38 (2013) 161–172

Contents lists available at SciVerse ScienceDirect

Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

Review

Utilization of oil palm kernel shell as lightweight aggregate in concrete – A review U. Johnson Alengaram ⇑, Baig Abdullah Al Muhit, Mohd Zamin bin Jumaat Department of Civil Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia

h i g h l i g h t s " Seventy-four recent and past papers have been reviewed on oil palm kernel shell concrete (OPKSC). " Physical, mechanical, durability, functional and structural behaviors of OPKSC reviewed. " Data of past 28 years on OPKSC are tabulated for reference. " Properties of lightweight concrete (LWC) compared with OPKSC. " Discussion on very recent paper on foam concrete with OPKS included.

a r t i c l e

i n f o

Article history: Received 16 October 2011 Received in revised form 25 July 2012 Accepted 11 August 2012 Available online 21 September 2012 Keywords: Oil palm kernel shell Lightweight aggregate Mechanical properties Structural behavior Functional properties

a b s t r a c t This paper reviews previous research carried out on the use of oil palm kernel shell (OPKS) as lightweight aggregate (LWA). OPKS is a waste material obtained during the extraction of palm oil by crushing of the palm nut in the palm oil mills. It is one of the most abundantly produced waste materials in South East Asia and Africa; OPKS has been experimented in research as lightweight aggregates (LWAs) to produce lightweight concrete (LWC) since 1984 and today there are many researchers working in this area. In this paper the physical and mechanical properties of OPKS are summarized along with mechanical, durability and functional properties and structural behavior of OPKS concrete (OPKSC). Recent papers on foamed and fiber reinforced OPKSC are also included. It is seen from the results that OPKSC has comparable mechanical properties and structural behavior to normal weight concrete (NWC). Recent investigation on the use of crushed OPKS shows that OPKSC can be produced to medium and high strength concrete. Sustainability issues combined with higher ductility and aggregate interlock characteristics of OPKSC compared to NCW has resulted in many researchers conducting further investigation on the use of OPKS as LWA. Ó 2012 Elsevier Ltd. All rights reserved.

Contents 1. 2.

3. 4.

5.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Physical properties of OPKS as aggregate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Specific gravity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Shape, thickness and texture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3. Bulk density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4. Water absorption and moisture content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mechanical properties of OPKS and comparison with NWA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fresh concrete properties of concrete with OPKS as coarse aggregate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1. Materials used by researchers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2. Slump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3. Flow table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4. Air content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Physical properties of OPKSC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1. Plastic density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

⇑ Corresponding author. Tel.: +60 379677632. E-mail address: [email protected] (U.J. Alengaram). 0950-0618/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2012.08.026

162 163 163 164 164 164 164 164 164 164 164 164 165 165

162

6.

7.

8.

9.

10.

11. 12. 13.

14.

U.J. Alengaram et al. / Construction and Building Materials 38 (2013) 161–172

5.2. Density of hardened concrete. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mechanical properties of OPKSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1. Compressive strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2. Modulus of rupture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3. Splitting tensile strength. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4. Static and dynamic moduli of elasticity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Durability of OPKSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1. Water absorption and permeability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2. Initial surface absorption (ISA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Functional properties of OPKSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1. Thermal conductivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2. Sound absorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Time-dependent properties of OPKSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.1. Creep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.2. Shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Structural behavior of OPKSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.1. Flexural behavior. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.2. Shear behavior. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.3. Bond strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Comparison of OPKSC with other agricultural wastes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OPKS as partial replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Oil palm kernel shell aggregate in foam concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.1. Foam concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.2. Mechanical properties OPKS foamed concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.3. Shear behavior of OPKS foamed concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1. Introduction The high demand for concrete in construction using normal weight aggregates (NWAs), such as gravel and granite, has drastically reduced natural stone deposits and this has caused irreparable damage to our environment. As a result, the emphasis on sustainable materials has intensified recently. The growing need for sustainable development has motivated researchers to focus their investigation on the use of waste or recycled materials into potential construction material. Lightweight aggregates (LWAs) from industrial waste materials such as fly ash, expanded slag cinder, and bed ash has led for sustainable materials. However, the lack of production techniques in developing and underdeveloped countries has not brought much advantage to them. A substantial amount of cost can be reduced if the weight of the structure is decreased. LWA had been in use for a long period of time in developed countries and it proved cost effective. It served the purpose of both the structural stability and economic viability. The lower the weight, the more versatile are the structures. Since 2nd A.D. different types of LWA such as clinker, foamed slag, and expanded clay has been used as construction material [1]. Recently, because of growing environmental concerns, waste materials are being used as aggregates for construction [2]. During the last 27 years, oil palm shell (OPS) or palm kernel shell (PKS), has been used by researchers as LWA to replace conventional NWA in structural elements and road construction [3–6] in Africa and Southeast Asia. For simplicity, oil palm kernel shell, abbreviated as OPKS is used to represent OPS or PKS in this paper. OPKS is one kind of organic aggregate with better impact resistance compared to NWA. Numerous articles on the physical, mechanical, structural and functional properties using OPKS as LWA have been published. OPKS is a waste product at the time of extracting oil from oil palm tree [3,7]. Oil palm tree, being as in the same genera as Coconut palm tree, shares many features with it. Its scientific name is Elaeis guineensis and is found mainly in East Africa [8]. Previously, cultivation of oil palm tree was remained secluded in the East

165 166 166 166 167 167 167 167 168 168 168 168 168 168 168 169 169 169 169 169 169 170 170 170 170 170 171 171

Africa because trace of oil palm tree have been found in the era of Pharaohs some 5000 years ago but now-a-days, its cultivation is focused in South East Asia, in countries such as Malaysia and Indonesia. Olanipekun et al. [9] reported that oil palm trees can be found in large quantities in America, Asia and Africa, especially in Nigeria. Malaysia alone produces 52.8% of the total production of palm oil and Malaysia and Indonesia produce about 80% of the total palm oil of the world. Furthermore, these two countries export about 90% of the total palm oil produced altogether. There are two kinds of oil in palm nut; one is palm oil, which remain in outer core of the nut and the other is palm kernel oil which is extracted from the inner core, known as palm kernel. Palm kernel is covered by a hard endocarp which is called palm kernel shell and is alternatively known as oil palm shell [8,9]. However, the term oil palm kernel shell is also adopted by the researchers to avoid confusion and unnecessary debate. Malaysia produces 4 million tons of OPKS annually [3,4,10–14] and according to Ramli [11] nearly 5 million hectare (ha) of palm oil trees are expected by the year 2020. Being the second largest palm oil producing country in the world, Malaysia is also responsible for producing a large amount of palm oil wastes. To preserve the environment, researchers have taken initiative to utilize OPKS as LWA [2,13,15]. Proposals were made to substitute OPKS as road based materials instead of asphalt on various occasions [6,7,9,15,16]. Teo et al. [4,15] used OPKS as LWA to build a onestorey building and a foot bridge which are being monitored for their structural behavior. OPKS is also used as granular filter material for water treatment [9,17], floor roofing and road based material [15]. Okpala [3] reported the thermal conductivity of 0.19 W m1 K1 for OPKS which is much lower than the value of 1.4 W m1 K1 for conventional stone aggregate. Thus the lightweight concrete (LWC) made with OPKS having low thermal conductivity and high insulation capacity may result in low energy consumption and greener environment. Recently, attempts have been made to incorporate OPKS as a substitute for poor lateritic soil. But the result shows that the composite mix of OPKS

163

U.J. Alengaram et al. / Construction and Building Materials 38 (2013) 161–172 Table 1 Physical properties of OPKS aggregate. Name of the author (year)

Specific gravity

Loose bulk density (kg/m3)

Compacted bulk density (kg/m3)

Moisture content (%)

Water absorption, 24 h (1 h) (%)

Porosity (%)

Abdullah (1984) Okafor (1988) Okpala (1990) Basri et al. (1999) Mannan and Ganapathy (2002) Teo et al. (2006) Ndoke (2006) Jumaat et al. (2008) Mahmud et al. (2009) Alengaram et al. (2010)a Gunasekaran et al. (2011)

– 1.37 1.14 1.17 1.17 1.17 1.62 1.37 1.27 1.27 1.17

– 512 545 – – 500–600 – 566 – – –

620 589 595 592 592 – 740 620 620 620 590

– – – – – – 9 8–15 – – –

– 27.3 21.3 23.32 23.32 33 14 23.8 24.5 (10–12) 25 23.32

– 37 – – – 28 – – – –

with asphalt is inadequate for sub-grade, sub-base and base course in road construction [18]. The mechanical and structural properties of OPKS concrete (OPKSC) have been compared with normal weight concrete (NWC) by many researchers to show the effectiveness of OPKSC [2,4,10,19–22]. Physical and mechanical properties, and structural behavior with respect to bond, flexure and shear, have been investigated and reported [10,23]. Time-dependent behaviors of OPKSC such as creep [23] and shrinkage [13,23] were also compared with NWC. These properties are discussed in this paper in concise but in informative form. 2. Physical properties of OPKS as aggregate The mechanical properties of OPKSC change depending on the physical properties of OPKS. The established physical properties compared with NWA are specific gravity, thickness and shape, surface texture, loose and compacted bulk densities, air and moisture content, water absorption and porosity.

Fig. 2. Oil palm kernel shell dumped at the factory yards [4].

2.1. Specific gravity Specific gravity of a material expressed as the ratio of the density of that particular material and that of water [24,25]. Specific gravity of OPKS varies from but has never crossed the value of 2.0 as reported by various researchers (Table 1). The range of specific gravity for OPKS is around 1.17–1.62. The highest value of specific gravity of OPKS from Table 1 is reported to be 1.62 by Ndoke [6] who tried to use the OPKS for soil stabilization. Okpala [3] re-

Mining sand

Palm kernel shell

Percentage finer

100 80 Fig. 3. Oil palm kernel shell of different sizes [22].

60 40 20 0 0.1

1

10

Sieve Size (mm) Fig. 1. Particle size distribution of sand and OPKS [27].

100

ported the lowest value of specific gravity of 1.14, while Teo et al. [4], Mannan and Ganapathy [14], and Basri et al. [15] reported the same value of 1.17. This can be compared to the specific gravity NWA of 2.6 [13]. Specific gravity of other artificial LWA such as LECA and Lytag and natural LWA such as pumice and expanded shale is found in the range of 0.8–0.9 and 1.30–1.7, respectively [26]. Particle size distribution of typical OPKS is shown in Fig. 1 [27] and it is seen from the figure that OPKS has wide range of particles from 3 to 14 mm.

164

U.J. Alengaram et al. / Construction and Building Materials 38 (2013) 161–172

2.2. Shape, thickness and texture Fig. 2 shows the dumped OPKS that is left at the factory yard. The shape of OPKS aggregate varies irregular flaky shaped, angular, circular or polygonal as shown in Fig. 3; it depends on the extraction method or breaking of the nut [3,7,15]. The thickness of OPKS varies between 0.15 and 8 mm depending on the species [3,15]. Generally, the surface texture remains fairly smooth in both the concave and convex part of the shell. The broken edges show rough and spiky attire [7,15]. 2.3. Bulk density Loose and compacted bulk densities of OPKS aggregate varies in the range of 500–600 kg/m3 and 600–740 kg/m3, respectively [3,4,6,7,13,15,20–23,27,28]. Generally bulk densities are also affected by sizes of OPKS [22]. Due to lower density of OPKS, the density of concrete made of OPKS usually falls in the range of 1600– 1900 kg/m3 [29]. 2.4. Water absorption and moisture content As OPKS is an organic aggregate, it contains many pores and hence the water absorption is high. Depending on the species of the trees and matured age of OPKS, the 24-h water absorption varies in the range of 14–33%, as seen from Table 1. Although OPKS has high water absorption, even higher water absorption of 37% was recorded for pumice aggregate [30]. Alengaram et al. [22] showed that with varying OPKS sizes, water absorption also varies in the range of 8–15% and 21–25% for 1 h and 24 h, respectively. Table 1 shows that free moisture content of OPKS varies between 8% and 15%. Water absorption of NWA is typically found to be in the range of 0.5–1% [31]. Due to higher water absorption of OPKS compared to NWA, the mix design does not follow the conventional mix design of NWC or LWC [31,32]. The water absorption of OPKS aggregate is also similar to coconut shell aggregate which is 24% as found by Gunasekaran et al. [28].

Table 2 Mechanical properties of oil palm kernel shell. Name of author (year)

Abrasion value (Los Angeles) (%)

Aggregate impact value (AIV) (%)

Aggregate crushing value (ACV) (%)

Okafor (1988) Okpala (1990) Basri et al. (1999) Mannan and Ganapathy (2001, 2002) Olanipekun (2005) Mannan et al. (2006) Ndoke (2006) Teo et al. (2006 and 2007) Jumaat et al. (2008) Mahmud et al. (2009)

– 3.05 4.80 4.80

6.00 – – 7.86

10.00 4.67 – –

3.60 – – 4.90 8.02 –

– 1.04–7.86 4.50 7.51 3.91 3.91

– – – 8.00 – –

Table 3 Typical physical properties of oil palm kernel shell and crushed granite normal weight aggregate (NWA) [13]. Physical properties

OPKS

NWA

Specific gravity Water absorption for 24 h (%) Bulk density (kg/m3) Fineness modulus (FM) Flakiness index (%) Elongation index (%)

1.17 23.30 590 6.24 65.17 12.36

2.61 0.76 1470 6.33 24.94 33.38

tious material and found its influence effect on the mechanical properties of OPKSC. Moreover, it has pozzolanic property produces more C–S–H which adds to the strength. 4.2. Slump

4. Fresh concrete properties of concrete with OPKS as coarse aggregate

Slump test is the standard test for the workability of concrete. It measures the consistency according to ACI 116R [34]. It is very useful in calculating the variations in the uniformity of mix of given proportions [31]. It is seen from Table 4 that the slump value is increased when the water cement ratio is increased as with the normal concrete. Mannan and Ganapathy [14], Okpala [3] and Okafor [7] found the slump to be very low (0–4 mm) indicating S1 workability (ENV 206: 1992) or a very low workability [31]. Abdullah [23] achieved slump in the range of 0–260 mm with a compressive strength of 15 MPa. However, it does not necessarily mean that low slump ensures high compressive strength [13,14,35]; Alengaram et al. [20,36] showed that by incorporating a small percentage of superplasticizer a slump value of 105 mm (high workability) could be achieved [31]. High range water reducing admixtures (Superplasticizer or SP) are capable of dispersing cement grains which are directed towards high slump value resulting in high workability.

4.1. Materials used by researchers

4.3. Flow table

The fresh and hardened concrete properties of OPKSC are shown in the Table 4. Okafor [7] used superplasticizer in OPKSC and reported improvement in the workability of the concrete. As OPKS have different shapes-from angular to spike with rough edges, it adheres with the bulk cement paste more firmly along the edges. Okpala [3], Teo et al. [4], Mannan et al. [5]. and Okafor [7] used river sand as fine aggregate. For comparison with NWC, crushed granite stone is the most popular choice for the researchers. Class F fly ash has been used by Basri et al. [15] and Alengaram et al. [22,33] for its pozzolanic reaction. As silica fume is 100 times smaller than the particles of cement, Alengaram et al. [33] used it as cementi-

Flow table test on OPKSC samples showed a flow value of 400 mm [20]. Generally, flow is measured as the average diameter in both directions of the concrete and the mean is taken as the flow value. The addition of silica fume enhanced cohesiveness of the OPKSC. However, with the addition of 1% SP the flow of OPKSC tends to increase [20].

3. Mechanical properties of OPKS and comparison with NWA Researchers have reported the mechanical properties of OPKS such as Los Angeles Abrasion, aggregate impact and aggregate crushing values. Tables 2 and 3 show the results obtained by various researchers on the above said mechanical properties. Generally, the abrasion resistance of LWA is inferior to that of NWA due to lower stiffness of LWA. The range of abrasion values for OPKS aggregate is 3–8% whereas that of crushed stone is about 20–25%.

4.4. Air content In fresh concrete, air content is relatively higher in OPKSC than NWC. The irregular shapes of OPKS hinder the full compaction of

165

U.J. Alengaram et al. / Construction and Building Materials 38 (2013) 161–172 Table 4 Fresh and mechanical properties of concrete (All the mechanical properties reported at the age of 28-day.). Author (year)

Code used for mix proportions

W/C ratio

Mix proportions

Slump, (mm)

Compressive strength (MPa)

Flexural strength (MPa)

Splitting tensile strength (MPa)

Young’s modulus (GPa)

Abdullah (1984)

–

0.6

1:1.5:0.5–1.0 1:2.0:0.5–1.0 1:2.5:0.3–0.75 1:2:0.6

200–0 230–5 260–10 0–260

10.00–2.50 11.50–5.00 15.00–8.00 20.50–0

–

–

–

1:1.70:2.08 1:1.88:2.18 1:2.10:1.12 1:1:2

23 22 16 22.20 19.80 16.50 14.90 18.90 16.50 13.00 11.50 13.65

6.20 5.50 4.30 2.81 2.53 2.30 2.13 –

2.40 2.35 2.00 –

–

–

–

1:2.73:0.85

8 28 50 30 63 Collapse Collapse 3 28 55 80 0

–

–

–

4 0 Collapse Collapse –

6.30 13.15 11.80 14.35 14.40

–

–

–

Okafor (1988)

–

Okpala (1990)

–

–

Mannan and Ganapathy (2001)

ACI

0.40– 0.85 0.48 0.54 0.65 0.5 0.6 0.7 0.8 0.5 0.6 0.7 0.8 0.53

1:2:4

–

Mannan and Ganapathy (2002)

ACI

0.50

1:2.73:0.85 1:2.73:0.85 1:1.28:0.55 1:1.28:0.55 1:1.13:0.92

Olanipekun et al. (2005)

–

0.60 –

1:1.41:1.15 1:1:2

Collapse –

9.65 17.50

–

–

–

Teo and Liew (2006) Teo et al. (2007) Alengaram et al. (2008)

DOE method – Specific gravity method 0.35

0.41 0.38

1:2:4 1:1.12:0.80 1:1.66:0.60

13 60

14.70 22 28.00

2.30 –

2.24 –

– 5.31

–

105

37.41

0.35

1:1:0.8

160

3.83 36.70 26.98

2.10 3.50 2.79

11.15 1.95 1.98

10.05 7.08

1:1:0.8 (5%FA; 10%SF) 1:1:2.8 (5%FA; 10%SF) 1:1:6.8 (5%FA; 10%SF) 1:0.8:1 (5%FA; 10%SF) 1:1.0/1.2/1.6:0.8 (5%FA; 10%SF)

103

29.49

2.76

1.90

8.57

65

34.49

3.22

2.00

10.01

60

37.79

4.10

2.35

10.90

–

25.8–30.3

–

–

5.50–7.10

1:1.736:0.72 (steel fibers)

–

30.1–37.8 39.34–44.95

5.42–7.09

2.83–5.55

7.93–10.10 15.1–16.1

0.60

Mahmud et al. (2009)

Specific gravity method

Alengaram et al. (2011)

Specific gravity method

0.30– 0.35 0.35

Shafigh et al. (2011)

–

0.38

concrete, thus contribute to the higher air content. OPKS is also porous material which can be cause of higher air entrapment inside concrete. Mannan and Ganapathy [12] showed that the addition of FA in OPKSC can result in the lower air content than OPKSC without FA. The spherical particles of FA fill up the pores inside fresh concrete and lower the air content. They reported the air content to be 4.8–5.1% depending on the mix proportions and FA content. 5. Physical properties of OPKSC 5.1. Plastic density Fresh concrete densities of OPKSC are found to be in the range of 1753–1763 kg/m3 as shown by Okafor [7] depending on the mix proportions and w/c ratio. Usually the fresh concrete density is about 100–120 kg/m3 lower than the saturated density of LWC;

this might be attributed to water absorption of OPKS. Mannan and Ganapathy [12] also reported the fresh concrete density of OPKSC in the range of 1910–1958 kg/m3 depending on the mix proportions. 5.2. Density of hardened concrete Table 5 shows the mechanical properties of OPKSC. The compressive strength of concrete depends on density and it is one of the most important variables to consider in the design of concrete structures. ACI and ASTM specify a density less than 2000 kg/m3 for structural lightweight concrete (SLWC). According to Clarke [29], the density of SLWC is between 1200 and 2000 kg/m3 whereas Neville [31] observed the density of LWC to be between 350 and 1850 kg/m3. Attempts have been made by various researchers to decrease the density of OPSKC without affecting the strength. The density of OPKSC depends on various factors such

166

U.J. Alengaram et al. / Construction and Building Materials 38 (2013) 161–172

Table 5 Densities of oil palm kernel shell concrete reported by researchers.

a

Author (year)

SSD (kg/m3)

Oven-dry (kg/m3)

Air-dry (kg/m3)

Abdullah (1988) Okafor (1988) Okpala (1990) Okpala (1990) Okafor (1990) Basri et al. (1999) Mannan and Ganapathy (2001) Olanipekun et al. (2005) Mannan et al. (2006) Teo and Liew (2006) Teo et al. (2007) Alengaram et al. (2008) Alengaram et al. (2008) Jumaat et al. (2009) Alengaram et al. (2010) Shafigh et al. (2011)

– 1753–1763a 1630–1780 (1:1:2)a 1600–1700 (1:2:4)a 1863–1910a – 1655–1910 1700–1850 1865–1930 1792 – 1850–1960 1888 – 1880 –

– – – – – – – – – – – 1639–1715 – 1670 (foamed concrete) (varies) – 1868–1937

1725–2050 – – – – 1801–1856 – – – – 1960 – – – – –

Note: Values vary for different w/c ratios and superplasticizer or mineral admixture dosages.

as, the specific gravity of OPKS, water cement (w/c) ratio, sand and OPKS contents and water absorption of OPKS. Oven-dry densities are 200–250 kg/m3 lower than the saturated surface dry (SSD) densities [29]. Air-dry densities of OPKSC are in the range of 1725– 2050 kg/m3 as shown in the Table 5. 6. Mechanical properties of OPKSC 6.1. Compressive strength Compressive strength of concrete is the most desirable property for any new material used in concrete technology. All other mechanical parameters such as flexural strength, splitting tensile strength and modulus of elasticity directly depend on the compressive strength of the concrete. Attempts have been made to enhance the compressive strength of concrete using OPKS as coarse aggregate. Depending on the mix design and curing conditions different researchers have found different grades of strength. Abdullah [16,23] was the pioneer in using OPKS as LWA and a achieved a compressive strength of up to 20 MPa with w/c ratio of 0.4 as shown in Table 4. This value is almost equal to the specified cylindrical compressive (fc) strength of 17 MPa by ACI. Teo et al. [4] achieved a compressive strength of 22 MPa. Mannan and Ganapthay [14,15] used the ACI method of mixed design for NWC and reported the compressive strength of 13.65 MPa which greatly differed from the target strength of 28 MPa. Though Mannan and Ganapathy [14,15] used the method suggested by Short and Kinniburgh [32] they found the compressive strength to be around 14.40 MPa for a target strength of 25 MPa. So, it is evident from the results that neither of the previous methods is suitable for OPKSC. It can be seen from Table 4, that most of the researchers achieved the cylindrical strength of 17 MPa (equivalent of 20 MPa cube strength) benchmark for structural concrete set by ACI [37] and ASTM C330 [38]. Recent researches show that up to 30 MPa is achievable with [12,20,36]. Alengaram et al. [39] reported a strength of 37 MPa which is 85% higher than the minimum strength of 20 MPa. They used silica fume and class F fly ash to enhance the early and later day strength and sulfonated naphthalene formaldehyde condensate as superplasticizer to disperse the cement grains effectively [40]. It can be seen from other researches on LWC using sewage sludge, pumice, palm fiber, expanded polystyrene, ignimbrite, bottom ash, Lytag, Japanese, Chinese and Pinatubo, cenospheres, etc., as LWA, the compressive strength of 10–30 MPa was reported with a density range of

1500–1900 kg/m3 [30,41–50]. Generally, it is seen from the experimental results that the mechanical properties of OPKSC increased with decreasing w/c ratio. Shafigh et al. [51] investigated the probability of making high strength lightweight concrete (HSLWC) with crushed OPKS and steel fiber. They achieved 28-day compressive strength in the range of 41–45 MPa with steel fibers; however, they [52] achieved 28-day compressive strength of up to 48 MPa with crushed OPKS and lime stone powder as a filler. Okpala [3] reported that the compressive strength of OPKSC depends on the bond between paste aggregate interface. Okafor [7] concluded that the compressive strength depended on the strength of OPKS itself. Olanipekun et al. [9] showed that the compressive strength of the concrete decreased as the percentage of OPKS substitution increased. Mannan and Ganapathy [12] reported that the strength, thickness and density of OPKS aggregate are lower than those of crushed stone aggregate which are the governing factors for the compressive strength in concrete. On their account, the irregular shape of OPKS is one of the factors for strength. They also reported that compressive strength is controlled by both the strength of the aggregate and the strength of paste, and depends on one of these two that fails first. Mannan and Ganapathy [13] showed that at the earlier ages, the failure of OPKSC was governed by the failure of OPKS, but in the later ages the failure of OPKSC was governed by the strength of OPKS-paste bond. Alengaram et al. [39] reported that the suction of silica fume into the pores of OPKS enhanced the bond between OPKS and cement matrix. They reported a compressive strength of about 37 MPa. OPKS can also contribute to the mechanical properties by its aggregate interlock characteristic [21]. 6.2. Modulus of rupture Table 4 reports the modulus of rupture (MOR) by various researchers. Okafor [7] found that with different mix designs, the MOR varied in the range of 4.3–6.2 MPa and it was about 27% of the compressive strength. Okpala [3] also reported the MOR in the range of 2.13–2.8 MPa which is about 14% of the compressive strength. MOR reported by Teo et al. [4] also shows that it varied in the range of about 8–13% of the compressive strength. It can be observed from the Table 4 that the MOR is affected by the mixture proportion. Okafor [7] and Okpala [3] used almost similar w/c ratio, but with the use of higher fine aggregate content, Okafor [7] reported an increment of 1.20 times higher MOR than the latter. Similar trend was reported by Mahmud et al. [27], albeit with the use of cementitious materials. Mannan and Ganapathy [13] concluded that as with compressive strength, MOR is also

167

U.J. Alengaram et al. / Construction and Building Materials 38 (2013) 161–172

2=3 fcfc ¼ 0:3ðfcuc Þ ðR2 ¼ 0:92Þ;

ð1Þ

Here, fcfc and fcuc are the 28-day flexural and compressive strengths in MPa, respectively.

13 1.25

Es = 0.30Ed

Static modulus of elasticity, 2 Es (kN/mm )

depended on physical strength of OPKS itself. Alengaram et al. [22] reasoned that the failure of the flexural specimen is governed by both the strength of PKS and bond between OPKS and cement matrix. The relationship between the MOR and the compressive strength as reported by Mahmud et al. [27] is given below:

2

R = 0.88

11

9

7

6.3. Splitting tensile strength Okafor [7] showed that the splitting tensile strength varied in the range of 2.0–2.4 with varying w/c of 0.65–0.48. Teo et al. [4] reported the values of splitting tensile strength of 2.24 MPa. Mahmud et al. [27] also reported similar values for the splitting tensile strengths. These values are about 6–10% of their respective compressive strengths. Mannan and Ganapathy [13] reported that the splitting tensile strength also depends on the curing condition and physical strength of OPKS. Alengaram et al. [20,22] reported that the bond failure along the convex surface of OPKS of particle size more than 10 mm in splitting failure specimens. 6.4. Static and dynamic moduli of elasticity Young’s modulus or E-value of concrete is it is one of the most important parameters in the design of structural members. However, this is one of the least researched areas in OPSKC. There are only three references available on this important property [4,27,39]. Teo et al. [4] showed the E-value of 5.31 GPa; However, Alengaram et al. [39] used cementitious materials such as 5% fly ash and 10% silica fume and showed that E-value of OPKSC can be enhanced. Furthermore, Table 4 shows that the OPKS content of Alengaram et al. [39] was higher than Teo et al. [4]. Mahmud et al. showed E-values of up to 10.90 GPa [19] and this is about twice the value reported by Teo et al. [4]. They attributed the increase in E-value to the increase in sand content and subsequent reduction in OPKS content. They also concluded that the addition of silica fume in concrete mix enhanced the bond and between the OPKS and the cement matrix, which enhanced the overall mechanical properties. Silica fume is almost 100 times finer than the cement particles [40]. Silicon di-oxide (SiO2) of silica fume react with the liberated calcium hydroxide (Ca(OH)2) of hydrated cement, they produce more calcium silicate hydrate (C–S–H) gel than usual. Microscopic analysis of OPKS surface confirmed the suction of silica fume into the micro-pores of OPKS improved the bond [36]. Thus, Mahmud et al. [27] and Alengaram et al. [39] concluded that the addition of silica fume enhances the mechanical properties of OPKSC. The static modulus of elasticity of other LWAC using pumice, ignimbrite, or expanded polystyrene [30,43,44] as LWA varies in the range of 7.69–11.4 GPa depending on mix design and age of curing; these results show the E-values of are quite similar to other LWAC. Shafigh et al. [51] showed that the use of steel fibers in OPKSC enhances the elastic modulus up to 16.1 GPa. Dynamic modulus test is a simple non-destructive test and could be performed to establish the relationship between static and dynamic moduli of elasticity. The relationship between static and dynamic moduli of elasticity is shown in Fig. 4. Alengaram et al. [39] suggested an equation to predict the static modulus of elasticity from the dynamic modulus of elasticity,

Es ¼ 0:3ðEd Þ1:25

ðR2 ¼ 0:88Þ;

5 11

13

15

17

21 2

Fig. 4. Relationship between static and dynamic moduli of elasticity [39].

According to Mannan and Ganapathy [13] the E-value is influenced by the type of coarse aggregate (OPKS or granite aggregate), w/c ratio of the mix and curing age. The E-value depends on the stiffness of OPKS, the interfacial transition zone between the paste and aggregate and the elastic properties of the constituent materials [13]. Alengaram et al. [39] reasoned that both fine aggregate and OPKS contents play role in the E-value; an increase in fine aggregate content with subsequent reduction in OPKS resulted in higher E-values compared to concrete with high OPKS content. 7. Durability of OPKSC 7.1. Water absorption and permeability Water absorption is defined as the transport of liquids in porous solids caused by surface tension acting in the capillaries [53]. It is shown by Teo et al. [2] that the water absorption by OPKSC is 11.23% and 10.64%, respectively for air-dry curing (CL) and full water curing (CC). The water absorption of LWC such as expanded polystyrene concrete and pumice aggregate concrete is in the range of 3–6% [50] and 14–22% [54], respectively. And both show higher water absorption than that of NWC [40]. Water permeability can be used as an indicator of durability of concrete. From Fig. 5, it is evident that OPKSC is less permeable over the time. At the age of 28 days, OPKSC under CC curing condition has one-sixth of the permeability value compared to that of concrete cured under CL condition [13]. High water absorption of OPKSC can be explained through microscopic analysis. Alengaram et al. [39] examined OPKS through microscopic analysis using scanning electron microscope

ð2Þ

where Es (GPa) and Ed (GPa) are the static and dynamic moduli of elasticity, respectively.

19

Dynamic modulus of elasticity, Ed (kN/mm )

Fig. 5. Water permeability of OPKSC [13].

168

U.J. Alengaram et al. / Construction and Building Materials 38 (2013) 161–172

Outer convex surface

(a) Outer surface of palm kernel shell Pore distribution

b) Pores on

crete specimen. Thus, it does not depend on the condition of the curing process such as whether it is moist cured or autoclaved. The thermal conductivity also depends on the pores inside the concrete [72]. Okpala [3] reported the thermal conductivity of OPKS and OPKSC of 0.19 W m1 °C1 and 0.45 W m1 °C1, respectively. Thus the thermal conductivity of OPKSC lies between 0.05 and 0.69 W m1 °C1 of other LWA as reported by Neville [31], Demirboga and Gul [56] and Zach et al. [57]. Thermal conductivity of OPKSC as reported by Okpala [3] is similar to that of other artificial inorganic LWA such as pumice, versalite or bottom ash (0.43 W m1 °C1) [26]. 8.2. Sound absorption Okpala [3] showed that sound absorption coefficient increases with increasing w/c ratio for the same mix design of OPKSC. The noise reduction coefficients for OPKSC were found as 0.34 and 0.35 for w/c ratio of 0.5 and 0.6, respectively; however, the noise reduction coefficient for NWC was only 0.02 which shows that OPKSC has better sound insulation. He concluded that the higher reduction coefficient for OPKSC was mainly due to more pores inside the concrete and also the OPKS in which the entrapped air acts as an insulator.

9. Time-dependent properties of OPKSC

(b) Micro-pores on outer surface

9.1. Creep

Fig. 6. Micro-pores on outer surface [39].

Abdullah [16] investigated creep tests on three 150 mm u cylindrical specimens based on ASTM standards [16] and reported that OPKSC showed inconsistent constant creep values even after 3 months. OPKSC showed a larger creep compared to that of NWC and kept on increasing after 3 months; in contrast NWC showed almost a constant value after 1 month. With 1:1:2 mix proportion and 0.55 w/c ratio, OPKSC showed a creep of about 350  105 mm/mm after 1 month and 400  105 mm/mm after 3 months. Conversely, NWC indicated a creep of about 45  105 mm/mm with 1:2:4 mix proportion and the same w/c ratio which is almost one-eighth creep value of OPKSC.

and the result is shown in Fig. 6. It shows tiny pores of size in the range of 16–24 lm on the convex surface of OPKS surface that are responsible for high water absorption [36]. It is observed by Chia and Zhang [55] that high quality and dense interfacial transition zone in cement paste generally leads to less permeable concrete. They also reported that 10% addition of silica fume generally decrease the water permeability of concrete, supposedly because of the aforementioned reason. Teo et al. [2] reported that the permeability of OPKSC is due to cracking of the paste aggregate interface which in turn is attributed to the internal stress. 7.2. Initial surface absorption (ISA) Mannan and Ganapathy [13] compared the initial surface absorption of NWC as control concrete with OPKSC cured under two different curing conditions, 6 days and 89 days in water. In both cases, the samples of OPKSC had shown greater absorptive capacity than that of control concrete. The primary reason attributed to higher surface absorption of OPKSC is high porosity of OPKS. But interestingly, for OPKS and control concrete, the ISA values remained the same at the age of 90-day for both curing conditions; however no apparent explanation was attributed to this behavior. On the other hand, early air drying of OPKSC also contributes to higher ISA, which in turn is attributed to micro-cracks developed in the concrete. 8. Functional properties of OPKSC 8.1. Thermal conductivity Thermal conductivity indicates the conduction of heat through materials. Thermal conductivity depends on the density of con-

9.2. Shrinkage Abdullah [16] used prisms of 50  50  250 mm3 as concrete specimens for the shrinkage test. The initial length of the specimen was measured and after drying for at least 44 h in a relative humidity of 17%, the final length of the specimen was measured. Drying shrinkage was reported as the ratio of the difference between the wet initial length and dry final length of the specimen to the dry final length of the specimen. It was shown by Abdullah that up to 1 month, the shrinkage of both OPKSC and NWC increased but after that the shrinkage was found constant. Nonetheless OPKSC showed about five times higher shrinkage strain than that of NWC. Mannan and Ganapathy [13] carried out drying shrinkage test on OPKSC and compared it with NWC on 7, 28, 56 and 90 days. They reported that the drying shrinkage of both the OPKSC and NWC increased with age but OPKSC showed higher increment. At the age of 28 and 90 days OPKSC showed 64 and 182 microstrain which was 6% and 14% higher increment of drying shrinkage compared to NWC, respectively. Drying shrinkage occurred due to loss of free water from concrete. It depends on variables such as w/c ratio, cement composition, type of aggregate, degree of hydration, curing condition, temperature of curing, relative humidity, moisture content and duration of drying [58,59]. Usually, the higher shrinkage showed by OPKSC was attributed to the loss of water

169

U.J. Alengaram et al. / Construction and Building Materials 38 (2013) 161–172

in the early age of plastic concrete and the irregular surface of OPKS [13]. 10. Structural behavior of OPKSC 10.1. Flexural behavior Flexural behavior of reinforced beams was reported by Teo et al. [10] and Alengaram et al. [19]. Six beams, three each of singly and doubly reinforced were tested with different reinforcement ratios [10]. Vertical flexural cracks were observed in the constant-moment region and final failure occurred due to crushing of the compression concrete with significant amount of ultimate deflection. Since all beams were under-reinforced, yielding of the tensile reinforcement occurred before crushing of the concrete cover in the pure bending zone. Eventually, crushing of the concrete cover occurred during failure, with a significant amount of deflection. A comparison between the experimental ultimate moments (Mult) and the theoretical design moments show a closer relationship for doubly reinforced beams than singly reinforced ones [10]. The theoretical design moment (Mdes) of the beams was predicted using the rectangular stress block analysis as recommended by BS 8110 [60]. For beams with reinforcement ratios of 3.14% or less, the ultimate moment obtained from the experiment was approximately 4–35% higher compared to the predicted values. They concluded that for OPKSC beams, BS 8110 [60] can be used to obtain both a conservative estimate of the ultimate moment capacity and adequate load factor against failure for reinforcement ratios up to 3.14%. The beam with the highest reinforcement ratio of 3.14% showed slightly higher mid-span deflection than the other two beams which indicates more ductile behavior. They also concluded that the ductility and moment curvature for OPKSC beams follows the same trend as those of the NWC beams [10]. 10.2. Shear behavior Shear strength of concrete is one of the most controversial topics in structural behavior [61]. Alengaram et al. [62] compared grade 30 OPKSC beams with NWC beams. They concluded that reinforced OPKSC beams showed higher ultimate shear strength to density ratio. They found that both OPKSC and NWC beams showed independent shear cracks and concluded that ACI, BS and Eurocode 2 (EC2) underestimate the shear capacity of OPKSC. The shorter, narrower cracks in their investigation, proved higher aggregate interlock capacity and thus OPKSC beams showed 24% higher shear capacity and that of NWC beams [62]. The OPKS vary in shapes from angular to flaky. It is seen by visual observation that mortar generally adheres to the concave portion of the aggregate which may contribute to the aggregate interlock and thus higher shear strength was reported [62]. 10.3. Bond strength The bond between the reinforcement and OPKSC was investigated by pull out tests using deformed bars of various diameters [2,10,20]. The 28-day bond strength for plain and deformed bars was found in the range of 3–5.59 MPa and 6.32–9.36 MPa, respectively depending on the curing condition and size of the bar used. The experimental bond strength was always much higher than the theoretical bond strength [2,10,20]. The bond strength of OPKS was 26–33% of the compressive strength and comparable to the bond strength of other LWA such as sintered pulverized fuel ash [63] and aerocrete [64]. It was also observed that the compression failure at the earlier ages of samples

Fig. 7. Crack paths (a) at earlier ages (b) at later ages [4].

was caused by the failure of the bond between aggregate and the cement matrix, where the crack paths goes around the aggregates as shown in Fig. 7a. But at later ages (56–180 days), the mortaraggregate bond becomes stronger and as such, crack paths travel through the aggregate as illustrated in Fig. 7b.

11. Comparison of OPKSC with other agricultural wastes Comparison of density and strength of OPKSC and concrete with other agricultural wastes such as oil palm clinkers, rice husk and coconut shells as coarse aggregates was done by Abdullah [16]. From the experimental test results, he concluded that concrete made with rice husk had the lowest bulk density with 136 kg/m3 and the lowest compressive and tensile strengths. Concrete made with oil palm clinker showed the highest bulk density and 28day compressive and tensile strengths. The 28-day compressive strength of OPKSC with a density of 620 kg/m3 of 17.4 MPa was found lower than the concrete made with oil palm clinker that produced 29.8 MPa. Gunasekaran et al. [28] showed that water absorption, specific gravity, impact value and bulk density of coconut shell aggregate were comparable to those of OPKSC. The 28day compressive strength of coconut shell concrete was found to be in the range of 5–27 MPa; however with a slump of only 5 mm, the coconut shell concrete exhibited a very poor workability. Moreover, the compressive strength, modulus of rupture, splitting tensile strength, theoretical and experimental bond strength performed on coconut shell concrete were comparable to OPKSC [28].

12. OPKS as partial replacement Olanipekun et al. [9] studied the mechanical properties of OPKS using 1:1:2 and 1:2:4 mix ratios with 0%, 25%, 50%, 75% and 100% replacement with OPKS. He showed that with the increasing ratio of OPKS, the compressive strength of concrete decreased. He also reported a cost reduction of 42% with OPKSC.

Table 6 Strength characteristics of the asphalt oil palm shell concrete [6]. Oil palm kernel ratio (%)

Density (kg/m3)

Water absorption, (%)

Marshal stability (kN)

Flow (mm)

0 10 30 50 70 100

2.40 2.28 1.90 1.87 1.85 1.70

0.20 1.20 6.30 8.20 8.60 14.0

14.44 13.46 11.96 11.10 10.90 7.78

3.42 3.71 3.78 3.80 4.10 4.32

170

U.J. Alengaram et al. / Construction and Building Materials 38 (2013) 161–172

Fig. 8. Crack patterns and failure modes of OPKSFC beams without shear reinforcement [21].

OPKS was also used as partial replacement for coarse aggregate of up to 10% for heavily trafficked roads and up to 50% for lightly trafficked roads. But for rural areas, replacement of up to 100% was used [6]. It can be seen from the Table 6 that the marshal stability and flow values for 10% replacements of OPKS were found 13.46 kN and 3.71 mm, respectively. For 100% replacement i.e. with only OPKS, the marshal stability value was 7.78 kN which reinforces the reason for its use in rural areas. The flow of asphalt concrete increases from 3.42 mm to 4.32 mm for 0–100% OPKS replacement. Water absorption increases from 0.20% to 14% due to increase in OPKS ratio. 13. Oil palm kernel shell aggregate in foam concrete 13.1. Foam concrete Foam concrete as defined by Ramamurthy et al. [65] is either a cement paste or mortar, classified as LWC, in which air-voids are entrapped by suitable foaming or aerating agent. Aerated concrete falls under the category of broader cellular concrete whose other member is microporite [66]. It possesses high flowability, self-compacting ability, controlled low strength, excellent thermal insulation capacity and moderate sound absorption capacity. Ever since foam concrete was patented in 1923, it had been in use in the concrete industry. First comprehensive review on the composition, properties, and used of cellular concrete worldwide was done by Valor [67] in 1954. This was followed by Rudnai [68], Short and Kinniburgh in 1978 [32] and recently by Jones and McCarthy [69]. The density range for aerated concrete is 300–1800 kg/m3 depending on the production method which indicated greater flexibility for use. Though foam concrete has been traditionally used as insulating concrete without any coarse aggregates, it was Weigler and Karl [70] who combined both pre-formed foam and leca as LWA to produce structural grade lightweight aggregate foamed concrete (LWAFC). 13.2. Mechanical properties OPKS foamed concrete The use of OPKS for making foam concrete is relatively new and first attempted by Jumaat et al. [21]. They reported that the density of OPKS foam concrete (OPKSFC) remained in the range 1600–1700 kg/m3 which falls under the category of foam concrete of density range of 300–1800 kg/m3 [66,71]. The cube compressive strength of OPKSFC found to be in 16–24 MPa range which satisfies the requirement for structural lightweight concrete set by ASTM and ACI. But usually, the compressive strength of foam concrete falls in the range of 1–43 MPa depending on the density and use of fly ash and silica fume as cement replacement [65]. Actually, air-void characteristics primarily determine the

strength of foam concrete. The filler materials like fly ash and silica fume helps to make uniform distribution of air-voids by making uniform coating on each bubble, therefore, preventing the merging of the bubbles. For higher density of foam concrete, the compressive strength decreases with an increase in void diameter. If the pore diameter increases the air bubbles merge with each other resulting in lesser paste volume and as a result lower compressive strength [72,73]. Higher compressive strength can be obtained using fly ash up to 67% [74]. Small changes in w/ c ratio has not affected the strength of foam concrete [69]. The modulus of rupture and splitting tensile strength for OPKSFC were found 9–11% and 7%, respectively of the compressive strength as opposed to 12–16% for NWC. Modulus of elasticity (E-value) for OPKSFC was found one-fourth as that of NWC and generally the E-values of foam concrete falls in the range of 1–8 GPa [65]. Jones and McCarthy [57] reported that the use of polypropylene fiber in the foam concrete increased the E-value by two to four times [69]. 13.3. Shear behavior of OPKS foamed concrete Jumaat et al. [21] investigated the shear behavior of reinforced OPKSFC beams (see Fig. 8). They reported that OPKSFC beam showed a greater number of flexural and shear cracks than the corresponding NWC beams. Subsequently, the crack widths of OPKSFC were found lower. The shear strength predicted using ACI code’s equation was close to that of experimental values; however, the BS code underestimated the shear strength. They also concluded that the 10% increase of shear strength by OPKSFC beams compared to the NWC beams due to aggregate interlock property of OPKS. 14. Conclusions The utilization of OPKS as LWA to produce OPKSC was reviewed through 74 recent and past literatures. The physical, mechanical, durability, functional and structural behaviors of OPKSC were discussed. The behavior of OPKSC was compared with NWC and conventional LWC. Based on the review, several conclusions can be drawn and these are listed below: 1. Oil palm kernel shell (OPKS) is irregular shaped i.e. oval, circular, polygonal or flaky shaped with 0.15–8 mm thickness. The surfaces of both convex and concave portions of OPKS are quite smooth with rough surfaces along the cracked edges. OPKS can be termed as LWA as it has low specific gravity in the range of 1.17–1.6. 2. Loose and compacted bulk densities of OPKS falls in the range of 500–600 kg/m3 and 600–620 kg/m3, respectively. Thus, the saturated surface density (SSD) of OPKSC falls in the range of 1600–1960 kg/m3.

U.J. Alengaram et al. / Construction and Building Materials 38 (2013) 161–172

3. The existence of numerous pores in the OPKS is responsible for high water absorption in the range of 14–33%. The free surface moisture content is reported to be in the range of 8–15%. 4. OPKS has very low abrasion of about 3–8% compared to 20– 25% of natural crushed granite aggregate and thus shows higher resistance to abrasion. 5. OPKSC is reported to have very low workability as seen from low slump values due to angular and rough edges of OPKS. However, the problem associated with low workability can be solved using superplasticizer to disperse the cement grains. 6. The hardened density of OPKSC was found in the range of 1650–1950 kg/m3 and various factors such as w/c ratio, inclusion of fine aggregate, water absorption and grain size of OPKS etc. affect the density. The oven-dry density was found 200–250 kg/m3 lower than that of SSD density. 7. Generally, the compressive strength of 13–22 MPa was reported for OPKSC by many researchers. But with the inclusion of fly ash, silica fume and superplasticizer, compressive strength of 37 MPa has been achieved. Using crushed OPKS and lime stone powder, a compressive strength up to 48 MPa has been reported. MOR and splitting tensile strength is reported to be 8–14% and 6–10%, respectively of the compressive strength. However, use of steel fibers in the fiber reinforced OPKSC enhanced the elastic modulus up to 16 GPa. 8. Water absorption of OPKSC was reported to be more than 10% due to the micropores on the surface of OPKS. OPKSC shows higher initial surface absorption than that of NWC irrespective of curing conditions. 9. The reinforced concrete beams made of OPKSC showed higher ductile behavior compared to the beams made of NWC. The moment curvatures of the beams of OPKSC also followed the same trend as that of NWC. 10. The aggregate interlock property of OPKS contributed to higher shear strength in OPKSC compared to NWC. 11. The bond strength of OPKSC was reported to be 26–33% of its compressive strength. 12. The creep value of OPKSC was found to increase even after 3 months compared to NWC. Moreover, OPKSC showed eight times the creep value of NWC. The shrinkage value for OPKSC kept on increasing for 1 month and after 1 month became constant, nonetheless, showed five times the value obtained by NWC. 13. It was reported that OPKS can also be used in asphalt concrete in pavement construction. It was shown that, in urban areas where traffic load is heavy, a replacement up to 10% can be allowed whereas the replacement can be up to 100% in rural areas. 14. Thermal conductivities of OPKS and OPKSC were 0.19 W/m K and 0.43 W/m K, respectively and it was lower than 0.76– 3.68 W/m K for NWC. The higher noise reduction coefficient of OPKSC proved its superior sound insulating property compared to NWC. 15. OPKS foamed concrete with a saturated density and compressive strength in the range of 1600–1700 kg/m3, and 16–24 MPa, respectively can be considered as structural grade concrete. Acknowledgement This research work is funded by University of Malaya under Ministry of Higher Education (MOHE) research fund: High Impact Research Grant (HIRG) No. UM.C/HIR/MOHE/ENG/02 (D00000216001) (Synthesis of Blast Resistant Structures).

171

References [1] Chandra S, Berntsson L. Lightweight aggregate concrete – science, technology, and applications. Norwich, New York: William Andrew Publishing; 2003. [2] Teo DCL, Mannan MA, Kurian VJ, Ganapathy C. Lightweight concrete made from oil palm shell (OPS): structural bond and durability properties. Build Environ 2007;42(7):2614–21. [3] Okpala DC. Palm kernel shell as a lightweight aggregate in concrete. Build Environ 1990;25(4):291–6. [4] Teo DCL, Mannan MA, Kurian VJ. Structural concrete using oil palm shell (OPS) as lightweight aggregate, Turkish. J Eng Environ Sci 2006;30:1–7. [5] Mannan MA, Alexander J, Ganapathy C, Teo DCL. Quality improvement of oil palm shell (OPS) as coarse aggregate in lightweight concrete. Build. Environ. 2006;41(9):1239–42. [6] Ndoke PN. Performance of palm kernel shells as a partial replacement for coarse aggregate in asphalt concrete. Leonardo El J Pract Technol 2006;5(9):145–52. [7] Okafor FO. Palm kernel shell as a lightweight aggregate for concrete. Cem Concr Res 1988;18(6):901–10. [8] Pantzaris TP, Ahmad MJ. Properties and utilization of palm kernel oil. MPOB (Europe), editor. Hertford, SG13 8NL, UK: Brickendonbury; 2001. [9] Olanipekun EA, Olusola KO, Ata O. A comparative study of concrete properties using coconut shell and palm kernel shell as coarse aggregates. Build Environ 2006;41(3):297–301. [10] Teo DCL, Mannan MA, Kurian JV. Flexural behaviour of reinforced lightweight concrete beams made with oil palm shell (OPS). J Adv Concr Technol 2006;4(3):1–10. [11] Ramli A. Short-term and long-term projection of malaysian palm oil production (MPOB). editor; 2003. [12] Mannan MA, Ganapathy C. Concrete from an agricultural waste – oil palm shell (OPS). Build Environ 2004;39(4):441–8. [13] Mannan MA, Ganapathy C. Engineering properties of concrete with oil palm shell as coarse aggregate. Constr Build Mater 2002;16(1):29–34. [14] Mannan MA, Ganapathy C. Long-term strengths of concrete with oil palm shell as coarse aggregate. Cem Concr Res 2001;31(9):1319–21. [15] Basri HB, Mannan MA, Zain MFM. Concrete using waste oil palm shells as aggregate. Cem Concr Res 1999;29(4):619–22. [16] Abdullah AAA. Palm oil shell aggregate for lightweight concrete. In: Waste material used in concrete manufacturing. Noyes Publication; 1997. [17] Jusoh A, Noor MJMM, Ghazali AH. Potential of burnt palm shell (BOPS) granules in deep bed filtration. J Islam Acad Sci 1995;8(3):143–8. [18] Amu OO, Haastrup AO, Eboru AA. Effects of palm kernel shells in lateritic soil for asphalt stabilization. Res J Environ Sci 2008;2(2):132–8. [19] Alengaram UJ, Jumaat MZ, Mahmud H. Ductility behaviour of reinforced palm kernel shell concrete beams. Eur J Sci Res. 2008;23(3):406–20. [20] Alengaram UJ, Mahmud H, Jumaat MZ. Comparison of mechanical and bond properties of oil palm kernel shell concrete with normal weight concrete. Int J Phys Sci 2010;5(8):1231–9. [21] Jumaat MZ, Johnson Alengaram U, Mahmud H. Shear strength of oil palm shell foamed concrete beams. Mater Des 2009;30(6):2227–36. [22] Alengaram UJ, Mahmud H, Jumaat MZ, Shirazi SM. Effect of aggregate size and proportion on strength properties of palm kernel shell concrete. Int J Phys Sci 2010;5(12):1848–56. [23] Ali AAA. Basic strength properties of lightweight concrete using agricultural wastes as aggregates in low-cost housing for developing countries. India: Roorkee; 1984. [24] Schetz JA, Fuhs AE. Fundamentals of fluid mechanics. Wiley, John & Sons; 1999. [25] Dana ES. A text-book of mineralogy: with an extended treatise on crystallography. New York, London (Chapman Hall): John Wiley & Sons; 1922. [26] Hemmings RT, Cornelius BJ, Yuran P, Wu M. Comparative study of lightweight aggregates. In: 2009 world of coal ash (WOCA) conference 2009. Lexington, KY, USA. [27] Mahmud H, Jumaat MZ, Alengaram UJ. Influence of sand/cement ratio on mechanical property of palm kernel shell concrete. J Appl Sci 2009;9(9):1764–9. [28] Gunasekaran K, Kumar PS, Lakshmipathy M. Mechanical and bond properties of coconut shell concrete. Constr Build Mater 2011;25(1):92–8. [29] Clarke DJL. Structural lightweight aggregate concrete. London: Routledge, UK; 1993. [30] Hossain A, Khandaker M. Properties of volcanic pumice based cement and lightweight concrete. Cem Concr Res. 2004;34(2):283–91. [31] Neville AM. Properties of concrete. Harlow, Essex, England: Wiley; 1995. [32] Short A, Kinniburgh W. Lightweight concrete. London: Applied Science Publishers; 1978. [33] Alengaram UJ, Jumaat MZ, Mahmud H. Influence of cementitious materials and aggregates content on compressive strength of palm kernel shell concrete. Int J Phys Sci 2008;8(18):3207–13. [34] ACI116R. Cement and concrete terminology; 2000. [35] Mannan MA, Ganapathy C. Mix design for oil palm shell concrete. Cem Concr Res 2001;31(9):1323–5. [36] Alengaram UJ, Mahmud H, Jumaat MZ. Development of lightweight concrete using industrial waste material, palm kernel shell as lightweight aggregate and its properties. In: 2nd International conference on chemical, biological and environmental engineering (ICBEE 2010); 2010. p. 277–81.

172

U.J. Alengaram et al. / Construction and Building Materials 38 (2013) 161–172

[37] ACI318M-08. Building code requirements for structural concrete (ACI 318M08) and commentary; 2008. [38] ASTMC330. Standard specification for lightweight aggregates for structural concrete; 2009. [39] Alengaram UJ, Mahmud H, Jumaat MZ. Enhancement and prediction of modulus of elasticity of palm kernel shell concrete. Mater Des 2011;32(4):2143–8. [40] Newman J, Choo BS. Advanced concrete technology. Oxford: Jordan Hill; 2003. [41] Mun KJ. Development and tests of lightweight aggregate using sewage sludge for nonstructural concrete. Constr Build Mater 2007;21(7):1583–8. [42] Ramli M, Dawood ET. Effects of palm fiber on the mechanical properties of lightweight concrete crushed brick. Am J Eng Appl Sci 2010;3(2):489–93. [43] Sabaa B, Ravindrarajah RS. Engineering properties of lightweight concrete containing crushed expanded polystyrene waste. Adv Mater Cem Compos 1997. [44] Aydin AC, Karakoç MB, Düzgün OA, Bayraktutan MS. Effect of low quality aggregates on the mechanical properties of lightweight concrete. Sci Res Essays 2010;5(10):1133–40. [45] Haque MN, Al-Khaiat H, Kayali O. Long-term strength and durability parameters of lightweight concrete in hot regime: importance of initial curing. Build Environ 2007;42(8):3086–92. [46] Fajardo JJP, Ootaki A, Kono K, Niwa DJ. Shrinkage and mechanical properties of lightweight concrete. in: Symposium on infrastructure development and the environment. University of the Philippines, Diliman, Quezon City, Philippines; 2006. [47] Yasar E, Atis CD, Kilic A, Gulsen H. Strength properties of lightweight concrete made with basaltic pumice and fly ash. Mater Lett 2003;57(15):2267–70. [48] Shannag MJ. Characteristics of lightweight concrete containing mineral admixtures. Constr Build Mater 2011;25(2):658–62. [49] Blanco F, García P, Mateos P, Ayala J. Characteristics and properties of lightweight concrete manufactured with cenospheres. Cem Concr Res 2000;30(11):1715–22. [50] Babu KG, Babu DS. Behaviour of lightweight expanded polystyrene concrete containing silica fume. Cem Concr Res 2003;33(5):755–62. [51] Shafigh P, Mahmud H, Jumaat MZ. Effect of steel fiber on the mechanical properties of oil palm shell lightweight concrete. Mater Des 2011;32(7):3926–32. [52] Shafigh P, Jumaat MZ, Mahmud H. Oil palm shell as a lightweight aggregate for production high strength lightweight concrete. Constr Build Mater 2011:1848–53. [53] Basheer L, Kropp J, Cleland DJ. Assessment of the durability of concrete from its permeation properties: a review. Constr Build Mater 2001;15(2-3):93–103. [54] Guduz L, Ugur I. The effects of different fine and coarse pumice aggregate/ cement ratios on the structural concrete properties without using any admixtures. Cem Concr Res 2005;35(9):1859–64.

[55] Chia KS, Zhang M-H. Water permeability and chloride penetrability of highstrength lightweight aggregate concrete. Cem Concr Res 2002;32(4):639–45. [56] Demirboga R, Gül R. Thermal conductivity and compressive strength of expanded perlite aggregate concrete with mineral admixtures. Energy Build 2003;35(11):1155–9. [57] Zach J, Hubertova M, Hroudova J. Possibilities of determination of thermal conductivity of lightweight concrete with utilization of non stationary hotwire method. In: The 10th international conference of the slovenian society for non-destructive testing, Ljubljana, Slovenia; 2009. [58] Brandt AM. Cement-based composites: materials, mechanical properties and performance. London: E&FN SPON; 1995. [59] Mindess S, Young JF, Darwin D. Concrete. Englewood Cliffs, NJ: Prentice Hall; 1981. [60] BS8110-1. Structural use of concrete. Code of practice for design and construction; 1997. [61] Kong F, Evans R. Reinforced and prestressed concrete. third ed. Berlin: Springer; 1987. [62] Alengaram UJ, Jumaat MZ, Mahmud H, Fayyadh MM. Shear behaviour of reinforced palm kernel shell concrete beams. Constr Build Mater 2011;25:2918–27. [63] Orangun CO. The bond resistance between steel and lightweight-aggregate (Lytag) concrete. Build Sci 1967;2(1):21–8. [64] Chitharanjan N, Sundararajan R, Devadas Manoharan P. Development of aerocrete: a new lightweight high strength material. Int J Cem Compos Light Concr 1988;10(1):27–38. [65] Ramamurthy K, Kunhanandan Nambiar EK, Indu Siva Ranjani G. A classification of studies on properties of foam concrete. Cem Concr Res 2009;31(6):388–96. [66] Narayanan N, Ramamurthy K. Structure and properties of aerated concrete: a review. Cem Concr Res 2000;22(5):321–9. [67] Valor RC. Cellular concretes – physical properties. J Am Concr Inst 1954;25:817–36. [68] Rudnai G. Lightweight concretes. Akademiai Kiado; 1963. [69] Jones MR, McCarthy A. Preliminary views on the potential of foamed concrete as a structural material. Magn Concr Res 2005;57(1):21–31. [70] Weigler H, Karl S. Structural lightweight aggregate concrete with reduced density – lightweight aggregate foamed concrete. Int J Cem Compos Lightweight Concr 1980;2(2):101–4. [71] Narayanan N, Ramamurthy K. Microstructural investigations on aerated concrete. Cem Concr Res 2000;30(3):457–64. [72] Nambiar EKK, Ramamurthy K. Air-void characterisation of foam concrete. Cem Concr Res 2007;37(2):221–30. [73] Wee TH, Babu DS, Tamilselvan T, Lim H-S. Air-void system of foamed concrete and its effect on mechanical properties. Mater J 2006;103(1):45–52. [74] Kearsley EP, Wainwright PJ. The effect of high fly ash content on the compressive strength of foamed concrete. Cem Concr Res 2001;31(1):105–12.