Conventional building materials are widely used in a developing country like Malaysia. This type of material is costly. Oil palm shell (OPS) is a type of farming solid waste in the tropical region. This paper aims to investigate strength characteristics and cost analysis of concrete produced using the gradation of OPS 0–50% on conventional coarse aggregate with the mix proportions 1 : 1.65 : 2.45, 1 : 2.5 : 3.3, and 1 : 3.3 : 4.2 by the weight of ordinary Portland cement, river sand, crushed stone, and OPS as a substitution for coarse aggregate. The corresponding w/c ratios were used: 0.45, 0.6, and 0.75, respectively, for the defined mix proportions. Test results indicate that compressive strength of concrete decreased as the percentage of the OPS increased in each mix ratio. Other properties of OPS concrete, namely, modulus of rupture, modulus of elasticity, splitting tensile strength, and density, were also determined and compared to the corresponding properties of conventional concrete. Economic analysis also indicates possible cost reduction of up to 15% due to the use of OPS as coarse aggregate. Finally, it is concluded that the use of OPS has great potential in the production of structural lightweight concrete.
Malaysia is well known as one of the world’s largest producers and exporters of palm oil. Palm kernel shells are a product of oil palm tree which are available in Malaysia in large quantity. Presently, 4.49 million hectares of land in Malaysia is under oil palm cultivation, producing over 17.73 million tonnes of palm oil and 2.13 tonnes of palm kernel oil annually, accounting for the biggest share of the global export market to date and yielding nearly about 18.9 tonnes/hectare of fresh fruit bunch (FFB) [
OPS are not commonly used in the construction industry but are often damped as agricultural wastes [
Recently, some researches [
This paper represents the result of an investigation carried out on the comparative cost analysis and strength characteristics of concrete using the different proportions of palm shells as substitutes for conventional coarse aggregate. The properties of OPS are also compared with conventional concrete. The main objective is to encourage the use of these “seemingly” waste products as construction materials in low-cost housing and where crushed stones are costly for producing lightweight concrete.
OPS were collected from a local palm oil mill at RH Lundu Palm Oil Mill, Kuching. It was obtained after the oil extraction in the factory from the fresh fruit bunch. The shells were then washed and air-dried for some days under ambient temperature and later graded in accordance with the ASTM [
The coarse aggregate form crushed granite was collected from igneous origin. The particle size used ranges between 5 and 20 mm. River sand as fine aggregate was used to mix the concrete. All particles were passed through ASTM sieve number 4 aperture 4.75 mm but retained on sieve 5 number 230, aperture 63
Malaysian ordinary Portland cement type whose properties conform with the requirement of ASTM type I was used with the content of 480 kg/m3 and the water was collected from the laboratory stand post. The physical properties of OPS and crushed granite aggregate are illustrated in Table
Properties of OPS and crushed stone aggregate.
Properties | Palm shell aggregate | Crushed stone aggregate |
---|---|---|
Specific gravity | 1.21 | 2.72 |
Bulk density (Kg/m3) | 572 | 1445 |
Los Angles abrasion value, % | 5.1 | 24.5 |
Water absorption for 24 h (%) | 25.64 | 0.7 |
Aggregate crushing value | 6.78 | 17.92 |
Aggregate impact value | 6.65 | 12.32 |
Fineness modulus | 6.24 | 6.76 |
Shell thickness, mm | 0.5–4.0 | 5–20 |
Maximum aggregate size, mm | 12.5 | 20 |
To achieve a 28-day design strength of concrete cube, three mix proportions of 1 : 1.65 : 2.45, 1 : 2.5 : 3.3, and 1 : 3.3 : 4.2 by the weight of ordinary Portland cement, river sand, crushed stone, and OPS as a substitution for coarse aggregate were used to cast the specimens. The corresponding water/cement ratio was 0.45, 0.6, and 0.75, respectively. For each mix, the water/cement ratio was maintained constant at all percentage replacements of crushed stone with OPS aggregate.
Concrete cubes sizes of
Fresh concrete workability was investigated immediately after the final mixing of the concrete using slump test. The cubes and cylinders were cast by filling each mould in three layers; each layer had been compacted normally with 25 blows from a steel rod of 16 mm diameter before the next layer was poured. Each prism was applied a hundred and fifty strokes per layer distributed along the whole length of the prisms. Slump values achieved 62 mm at 0% replacement level (normal weight concrete) for mix proportion 1 : 1.65 : 2.45, 48 mm for mix proportion 1 : 2.5 : 3.3, and 42 mm for 1 : 3.3 : 4.2, representing high and medium workability. These values decreased gradually as the percentage of OPS substitution increased in the mix. All specimens were left in the moulds for 24 h to set under ambient temperature. They were removed from the mould and transferred into a curing tank that contained clean water. The curing temperature was
The cubes and cylinders were tested on 2000 kN capacity Electronic Compression Machine using a loading rate of 6 kN/sec and 4.42 kN/sec, respectively, in 7 and 28 days. The average value of the load at which the group rate of three tested cubes for each mix failed was calculated and finally used to determine the compressive strength. A third point bending test was conducted for a simply supported beam over an effective span of 300 mm using a loading rate of 4.42 kN/sec. The maximum mean value of the load at which the beams failed was used to determine the flexural strength for each percentage of oil palm shells in the mix. Compressometer-extensometer (mechanical strain gauge) with the accuracy of
The density of the concrete produced has decreased with the increase in the percentage of OPS substitution with conventional coarse aggregate (crushed granite) as illustrated in Figure
Density of OPS at three mix ratios.
According to the experimental results (refer to Table
Modulus of elasticity of 0%, 10%, 15%, and 25% OPS replacement concrete.
Modulus of elasticity (N/mm2) | ||||
---|---|---|---|---|
Mix proportions | 0% replacement | 10% replacement | 15% replacement | 20% replacement |
1 : 1.65 : 2.45 | 28350 | 20338 | 16350 | 12343 |
1 : 2.5 : 3.3 | 23850 | 18478 | 15800 | 11982 |
1 : 3.3 : 4.2 | 22100 | 17122 | 14620 | 11238 |
It was observed from the test results (refer to Figures
Compressive strength of OPS (1 : 1.65 : 2.45).
Compressive strength of OPS (1 : 2.5 : 3.3).
Compressive strength of OPS (1 : 3.3 : 4.2).
Comparison of compressive strength of OPS at 28 days of curing (1 : 2.5 : 3.3).
Comparison of compressive strength of OPS at 7 days of curing.
It is concluded that the concrete strength depends on the strength, stiffness, and density of coarse aggregates. Generally, lower density causes lower strength. Increased percentage of OPS lower the density of concrete, hence, giving less compressive strength.
The result has shown that the flexural strength of concrete decreased as the percentage of OPS increased in the mix proportions. Figures
Comparison of flexural strength of OPS at 7 days of curing.
Comparison of flexural strength of OPS at 28 days of curing.
Table
Splitting tensile strength of 0%, 10%, 15%, and 20% OPS replacement concrete.
Splitting tensile strength (N/mm2) | ||||
---|---|---|---|---|
Mix proportions | 0% replacement | 10% replacement | 15% replacement | 20% replacement |
1 : 1.65 : 2.45 | 2.96 | 2.50 | 2.30 | 2.07 |
1 : 2.5 : 3.3 | 2.82 | 2.36 | 2.18 | 1.94 |
1 : 3.3 : 4.2 | 2.58 | 2.14 | 1.96 | 1.73 |
Cost analysis result of OPS substitution per cubic meter concrete cost production is shown in Table
Crushed stone and OPS substitute per cubic meter concrete cost (Malaysian ringgit: RM)*.
Concrete category | Mix proportions | ||
---|---|---|---|
1 : 1.65 : 2.45 | 1 : 2.5 : 3.3 | 1 : 3.3 : 4.2 | |
Crushed stone concrete | 272 | 256 | 238 |
OPS concrete (15% replacement) | 236 | 228 | 216 |
The following observations and conclusions can be made on the basis of the current experimental results. In all cases, the compressive strength of the concrete decreased as the percentage of OPS substitution increased in the mix. Concrete compressive strengths with the 15% OPS substitution are between 17.01 and 17.7 N/mm2 at the age of 28 days for different mix proportions of concrete and it satisfies the structural requirement of lightweight concrete. Splitting tensile strength of 15% OPS substitute concrete is an average 2.15 N/mm2 at 28 days which is approximately 12% of its compressive strength. This strength is considered satisfactory for the lightweight concrete. The 28-day modulus of elasticity of 15% OPS substituting concrete varies from 14620 to 16350 N/mm2 for the mix proportions considered in this paper. These values are on average less than 50% of the corresponding value of conventional concrete. Flexural strength of 15% OPS substitute concrete is on average 2.4 N/mm2 at 28 days which is approximately 14% of its compressive strength. On the other hand, the flexural strength of conventional concrete is nearly about 13% of its compressive strength. The cost reduction was 15%, 12%, and 10% with the substitution of 15% OPS as coarse aggregates in concrete for the mix ratios 1 : 1.65 : 2.45, 1 : 2.5 : 3.3, and 1 : 3.3 : 4.2, respectively. OPS concrete appears to be cheaper compared to the conventional aggregate concrete. It is concluded that OPS has the potential to be used as substitute coarse aggregate in the production of low-cost lightweight concrete.
The authors declare that there is no conflict of interests regarding the publication of this paper.
This study was conducted at the Heavy Structures Laboratory, Department of Civil Engineering, Universiti Malaysia Sarawak, Malaysia, and the authors would like to thank the technicians in the laboratory for providing assistance in specimen fabrication and testing.