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Properties of quiet pervious concrete containing oil palm kernel shell and cockleshell
Applied Acoustics 122 (2017) 113–120
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Properties of quiet pervious concrete containing oil palm kernel shell and cockleshell Elnaz Khankhaje a,⇑, Mohd Razman Salim b, Jahangir Mirza c, Salmiati b,⇑, Mohd Warid Hussin c, Rawid Khan d, Mahdi Rafieizonooz a a
Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor Bahru, Malaysia Centre for Environmental Sustainability and Water Security, Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor Bahru, Malaysia UTM Construction Research Centre (UTM CRC), Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor Bahru, Malaysia d Department of Civil Engineering, University of Engineering and Technology, Peshawar, Pakistan b c
a r t i c l e
i n f o
Article history: Received 29 November 2016 Received in revised form 21 February 2017 Accepted 22 February 2017
Keywords: Pervious concrete Noise reduction Cockle shell Palm oil kernel shell
a b s t r a c t Nowadays, the significant increase in noise has become a major problem in urban areas. Using pervious concrete pavement is recommended to reduce the noise. Unfortunately, standard materials used to produce pervious concrete are not completely environmental friendly. As a result, many researchers have devoted their attention towards identifying eco-friendlier substitutions to be used in the manufacturing of pervious concrete. In this respect, this current paper discussed the efficiency of two different sizes of oil palm kernel shell (KS) and cockle shell (CS) as partial replacement of natural coarse aggregate for sound absorption of pervious concrete. Thirteen mixtures were made, which replaced 6.30 mm limestone with 0, 25, 50 and 75% of 6.30 mm and 4.75 mm of both shells. The specimens were cured in a fog room and void content and compressive strength were tested. The replacement of both KS and CS as the natural aggregate decreased the compressive strength, although the range was still acceptable for pervious concrete at 28 days. However, the angular shape of both shells caused high void content. The maximum increase in void content compared to that of the control pervious concrete (CPC) was achieved with the use of 75% of 6.30 mm KS at 28 days. Moreover, by increasing sound absorption with the application of both shells, particularly KS, the concrete could be used as silent road pavement. It was therefore concluded that the use of both KS and CS to produce cleaner and quitter pervious concrete pavement is practical, both mechanically and environmentally. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction Of late, the significant increase in noise has become a major problem in urban areas. The said noise is typically generated from a variety of sources, including various types of vehicles on the road, airplanes, factories and construction sites. Noise exposure does not only impair human hearing capacity, but may also cause certain mental disorders [1]. Therefore, using of pervious concrete pavements have been recommended by Environmental Protection Agency (EPA) of the United State (US) to reduce traffic noise in urban area. Pervious concrete is one of the best materials used in top layer of permeable pavement system. In the past 30 years, pervious concrete has been gradually used in the United States (US),
⇑ Corresponding authors. E-mail addresses: [email protected] (E. Khankhaje), [email protected] (Salmiati). http://dx.doi.org/10.1016/j.apacoust.2017.02.014 0003-682X/Ó 2017 Elsevier Ltd. All rights reserved.
and is among the Best Management Practices (BMPs) recommended by EPA and American Concrete Institute (ACI) [2,3]. Due to the lower durability and strength of pervious concrete compared to normal concrete, the application of pervious concrete is limited to the roads that have light volume traffic [2,3]. However, due to the advantages of pervious concrete, the utilisation and construction properties of pervious concrete have been studied by many researchers [4–6]. The benefits of using pervious concrete are: reduction of downstream flows; reduction of large volumes of surface pollution flowing into rivers; decreasing of urban heat island effect; reducing traffic noise; enhancing safety of driving during raining; and removing heavy metal from stormwater runoff [3,7]. The use of pervious concrete in building site design can also aid in the process of qualifying the building for Leadership in Energy and Environmental Design (LEED) [8]. In pervious concrete, water passes through an interconnected network of voids structure, resulting from the constrained use of fine aggregates, uniform gradation and low water-to-cement ratio
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[3]. Void content of pervious concrete ranging from 20 to 30% is a consequence in a concrete with high drainage rate from 0.25 to 6.1 mm/s [6]. Moreover, typical range for the compressive strength of the pervious concrete are between 2 and 28 MPa [3,6,2]. Previous researches have reported that pervious concrete has the potential to reduce significantly the noise produced by vehicles due to high void content [9–12]. Normal concrete, for example, typically has an absorption coefficient (a) of 0.03–0.05 [13]. Pervious concrete typically has an absorption range from 0.1 (for poorly performing mixtures) to nearly 1 (for mixture with optimal pore volume and size) [3]. This is due to the voids inside the material, which absorbed the sound energy through internal friction. For pervious concrete to effectively absorb sound, 15–25% of connected void content is essential. Meiarashi et al. [14] compared the noise reduction levels of pervious asphalt and normal asphalt pavement. They found that 2–5 dB noise reduction was obtained by pervious asphalt, and concluded that it was crucial to keep the pavement porosity at 20% or higher for noise reduction purpose. In another study, Kim and Lee [15] investigated the effects of three levels of cement flow and five types of aggregates on the mechanical properties and sound absorption level of porous concrete. They observed that the sound absorption of specimens with smaller size was better than that of the control sample. This was because the total void ratios of the specimens were higher when smaller sized aggregates were used. Berengier [16] measured acoustical performance of porous pavement over real road surfaces and compared to theoretical predictions. They found that the microstructural model provided a good physical description of the acoustical properties of porous pavement. This was due to the flow resistivity and the porosity of the material and, to a lesser extent, on the tortuosity. Further, the properties of the pavement are relatively insensitive to pore shape factor. The effective management of by-product waste materials plays an important role in increasing environmental sustainability. One of the strategies in waste management is the utilisation of byproduct waste materials in the construction industry to reduce the landfill of waste materials. Moreover, with the application of waste materials, more sustainable, clean and green construction could be achieved due to the decrease of cost [17]. In addition, most materials used in concrete production are natural aggregates, and a majority of the materials are excavated from mines and river beds or dredged from sea shelves [18]. These activities have resulted in severe damage to the environment, including disruption of the ecosystem and contamination of soil, air and water [19]. Therefore, the construction industry encourages the incorporation of sustainability in production issues with the application of solid waste materials as aggregate in concrete [20–23]. Neithalath et al. [11] reviewed the benefits of using farming waste materials in concrete. They reported that both the reliance on standard materials used to produce concrete and adverse effects on the environment could be reduced with the reuse of farming waste materials in concrete. In addition, it was indicated that the method could also ensure waste conservation, and subsequently, decrease waste disposal in the involved sectors. Moreover, they concluded that by selecting proper farming waste materials, concrete with better performance could be produced. Asdrubali et al. [25] evaluated the acoustic performance of sustainable products made from natural and recycled materials. They concluded that the substitution of conventional sound insulating materials with sustainable ones has significant effects on the impact of all the various phases of the life of the building (construction, operation, end of life). Ibrahim and Razak [26] studied the use of palm oil clinker (POC) as coarse aggregate in the production of pervious concrete. They indicated that with using POC the compressive strength and density of the concrete reduced. However, the coefficient of permeability and porosity increased.
Two of the farming waste materials, which were successfully utilised as coarse aggregate in conventional concrete, were oil palm kernel shell (KS) and cockle shell (CS). KS is a waste product obtained from the production of oil from oil palm trees [27,28]. Malaysia produces over four million tonnes of KS annually [28,29], and the county is expected to grow five million hectares of oil palm trees by the year 2020 [30]. According to the Department of Fisheries Malaysia, 57,544 tonnes of cockles were harvested along the west coast of Peninsular Malaysia. In addition, it was reported that the retail value of cockles in Malaysia was estimated to be at over USD 32 million [32]. Boey et al. [32] also indicated that the active and lucrative industry has resulted in a significant amount of waste shells. Moreover, left untreated and dumped irresponsibly, CS may produce unpleasant odour [33]. In this paper, the effects of KS and CS as a partial replacement of natural coarse aggregate on the properties of especial type of concrete, pervious concrete, was investigated. To the author’s best knowledge, there are currently no studies investigating the effects of oil palm kernel shell (KS) and cockle shell (CS) on the noise absorption of pervious concrete. On a related note, the aim of this study was to replace KS and CS (0, 25, 50 and 75%) with two different sizes (6–9 mm and 4–6 mm) as natural coarse aggregate in pervious concrete. The effects of replacing coarse aggregate with KS and CS on void content and compressive strength of pervious concrete were investigated and compared against the control pervious concrete (CPC). In addition, sound absorption coefficient and sound transmission loss were also examined and analysed.
2. Specimen and preparation 2.1. Materials The cement used in this study was Ordinary Portland Cement (OPC) type I. To achieve a system with interconnection voids in the pervious concrete, the selection of single-sized aggregates is necessary [3,2]. The details of the aggregates are listed in Table 1. In this study, crushed limestone (LS) with a grain size of 6.30 mm (passed through a 9.5 mm sieve and retained on a 6.30 mm sieve) was used as the natural coarse aggregate. LS presented a specific gravity of 2.6 kg/m3 and water absorption of 1.8%. In addition, KS and CS was used as a replacement of natural coarse aggregate. In this study, KS was collected from a local palm oil producing mill located in Johor, a southern state of Malaysia. On the other hand, CS was obtained from a local market located in the south coast of Malaysia, and were crushed before they were used. Subsequently, both KS and CS were sieved and divided into two different size categories, namely (KS1, CS1) 6.30 mm (passed through a 9.5 mm sieve and retained on a 6 mm sieve) and (KS2, CS2) 4.75 mm (passed through a 6.30 mm sieve and retained on a 4.75 mm sieve), as illustrated in Fig. 1. Following that, they were washed and air dried in a laboratory. The purpose of washing both KS and CS was to remove oil and dirt. Fig. 2 presents the Scanning Electron Macroscopy (SEM) image of KS and CS particles. It can be seen that the high porous and heterogeneous structure of KS and CS respectively.
2.2. Mixture proportions Placement or compaction method plays an important role towards the properties of pervious concrete [34]. For this study, the technique of filling in three layers using 25 drops of a 15.9 mm diameter steel rod and 10 drops of a standard Proctor hammer (2.5 kg) for each layer was used from the results of Khankhaje et al. [35].
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Waste aggregates
Natural aggregate
CS
Gradation (mm) Bulk specific gravity (SSD) Water absorption (%) Dry rodded density (kg/m3)
KS
CS1
CS2
KS1
KS2
6.30 2.09 1.8 1408
4.75 2.64 2.5 1420
6.30 1.29 24.73 631
4.75 1.30 25.62 656
LS
Sand
6.30 2.6 1.8 1475
0–4 2.62 7.4 –
Fig. 1. Particle shapes of aggregates: (a) CS1, (b) CS2, (c) KS1 and (d) KS2.
Fig. 2. SEM image of (a) CS and (b) KS.
Table 2 Mixture proportion of pervious concrete. Mix
Cement (kg/m3)
Water (kg/m3)
CPC SPC1-25 SPC1-50 SPC1-75 SPC2-25 SPC2-50 SPC2-75 KPC1-25 KPC1-50 KPC1-75 KPC2-25 KPC2-50 KPC2-75
339.5 339.5 339.5 339.5 339.5 339.5 339.5 339.5 339.5 339.5 339.5 339.5 339.5
107.54 107.54 107.54 107.54 107.54 107.54 107.54 107.54 107.54 107.54 107.54 107.54 107.54
Table 2 shows the weight of each materials in one cubic metre of pervious concrete mixture. Each mixture proportion was designated with a specific code. The first labels represented the types of
Coarse aggregate (kg/m3)
Sand (kg/m3)
LS
CS
KS
1313.8 985.4 656.9 328.5 985.4 656.9 328.5 1094.9 729.9 365.0 1094.9 729.9 365.0
– 348.4 696.8 1045.2 348.4 696.8 1045.2 – – – – – –
– – – – – – – 157.6 315.3 472.9 157.6 315.3 472.9
139.0 139.0 139.0 139.0 139.0 139.0 139.0 139.0 139.0 139.0 139.0 139.0 139.0
coarse aggregates used. ‘CPC’, ‘SPC’ and ‘KPC’ representing control, cockle shell and oil palm kernel shell pervious concrete respectively. The second labels, ‘1’and ‘2’, referred to the size of the coarse
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aggregates used, big and small respectively. Finally, the third labels, ‘0’, ‘25’, ’50’ and ‘75’, indicated the percentage of waste aggregate added in terms of the weight percentage of the natural coarse aggregate proportion. All batches were designed with the purpose of investigating their void content as well as sound absorption. Both water cement ratio (w/c) and sand content were fixed at 32% and 10% (wt.% of the coarse aggregate) respectively. In addition, the mixtures with constant void content (23%), which were similar to that of the CPC mixture, were selected, given that void content is one of the factors that affects the sound absorption of pervious concrete [15]. Therefore, KPC1-25, KPC2-50, SPC1-25 and SPC2-50 were selected to investigate the influence of KS and CS on the sound absorption of pervious concrete. To prepare the needed pervious concrete, a small amount of cement (<5% by mass) was blended in a mixer with coarse aggregates for about one minute. Subsequently, sand and the remaining cement together with water were added into the mixture. Mixing was continued for another three minutes. The mixture was then rested for three minutes, and finally, was mixed again for another two minutes. After that, the void content and compressive strength of the pervious concretes were measured. In order to examine the void content as well as compressive strength, the pervious concrete specimens were casted in steel cylinder molds (100 mm diameter 200 mm high). Each test result of the properties examined was the average of at least three specimens. In addition, for both sound absorption and transmission loss evaluations, the cylindrical specimens with size of (99 mm diameter 100 mm thickness) and (28 mm diameter 100 mm thickness) were used in sound absorption test. The thickness of the samples was selected based on typical cross section of pervious concrete pavement. Immediately upon casting, all the specimens were cured for 24 h in a fog room, which was maintained at a temperature of 20 °C ± 2 °C and 95% ± 5% relative humidity. After 24 h, the specimens were removed from their molds and kept at the same conditions for 7 and 28 day curing periods. The structural arrangements of the pervious concrete mixtures containing limestone, KS and CS are shown in Fig. 3. It can be seen that angular shape of the KS and CS particles led to reduced compactness and increased void content. 2.3. Experimental details The void content of the hardened samples were tested based on ASTM C1754 [36] using the volumetric method.
NRC ¼
a250 þ a500 þ a1000 þ a2000
ð1Þ
4
where a indicates the sound absorption coefficient at different frequencies. As the pervious concrete can be used in wall [2], the transmission class (STC) also was evaluated. STC is an integer rating of how specimens stops or blocks airborne sound. In this study, STC calculation was performed according to ASTM E413 [41]. 3. Test results and discussion 3.1. Void content Typical range of void content for pervious concrete is between 15 and 25% [2]. Fig. 5 illustrates the void content of the pervious concrete mixtures containing natural and waste coarse aggregates. It can be seen that the void content increased with an increase in the percentage of waste. For instance, there was an increase of 2, 4 and 20% for the void content of SPC1-25, SPC1-50 and SPC1-75 respectively in comparison to that of CPC. This could be due to the angular shape of CS, which decreased the compactness of all SPC1 mixtures, and subsequently, disturbed the granular arrangement of the pervious concrete. Nguyen et al. [42] reported comparable findings, in which the void content increased along with an increase in the percentage of crushed crepidula seashells. The void content of mixtures containing the bigger sized KS, including KPC1-25, KPC1-50 and KPC1-75, increased about 1, 17 and 25% compared to that of CPC at the age of 28 days. From the results as shown in Fig. 5, it could be concluded that the void
Paste
Paste
CS
KS
LS
LS Void
(a)
The compressive strength test was measured according to ASTM C39 [37]. The cylindrical specimens for compressive strength tests were dried in room temperature for about two hours and then capped with sulphur capping compound at both ends in accordance to ASTM C617 [38]. This step was taken to fill up any voids and level both ends of the cylinder specimens. To evaluate the sound absorption and transmission loss characteristics of the pervious concrete, two impedance tube with 100 mm and 30 mm diameter were employed for low (50– 1500 Hz) and high frequency (1500–5000 Hz) test respectively, which was according to ASTM E 1050 [39] (Fig. 4). The ability of a material to absorb sound can be calculated using a single value known as the noise reduction coefficient (NRC), as given in Eq. (1) [40]:
(b)
Void
(c)
Fig. 3. Structural arrangement of the pervious concrete matrix (a) with natural aggregate (LS); (b) with KS and (c) with CS.
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Fig. 4. The impedance tube for acoustic test.
31
KPC1
KPC2
CPC
SPC1
SPC2
16
Compressive strength (MPa)
Void content (%)
29 27 25 23 21 19 17 15 0
25
50
75
Waste content (%)
KPC1
KPC2
CPC
SPC1
SPC2
14 12 10 8 6 4 2 0 0
25
50
75
Waste content (%)
Fig. 5. Void content of pervious concrete mixtures.
Fig. 6. Compressive strength of pervious concrete mixtures at 28 days.
content of the mixtures with KS was higher than that with CS. This could be due to the high water absorption of KS particles, which absorbed more water during the mixing process, and thus entrapping air on its surface causing the void content ratio of the KPC1 mixtures to increase. The highest void content ratio was obtained by KPC1-75. The mixtures containing the smaller sized waste materials (KS2 and CS2) showed lower void content than the mixtures with the bigger sized waste materials (KS1 and CS1). This might be because the smaller sized KS and CS were able to fit into the voids, and thus decreased the void content ratio.
tures was lower than the SPC mixtures. The entrapped air on the surface of the KS particles led to a reduction in the bonding area matrix. Furthermore, as discussed before the cement paste in the pervious concrete was very thin, and thus it was not able to fully bond with the KS particles. However, with natural coarse aggregate (LS), this was not a significant issue. As the load was applied to KPC during the strength test, micro cracks formed at the weak interface, between the cement paste and KS, due to stress focus. This resulted in the failure of continuous load application. Moreover, referring to Fig. 6, it could be concluded that the mixtures, which contained the smaller sized waste materials (KS2 and CS2), showed higher compressive strength than the mixtures containing the bigger sized waste materials (KS1 and CS1). This could be a result of the small parts of both KS and CS being able to fit into the voids, which then decreased the void content, and at the same time, increased the compressive strength of the mixtures. Furthermore, by decreasing the size of both KS and CS, the surfaces, which could be coated with cement paste, increased and resulted in better bonding between the cement paste and smaller coarse aggregate.
3.2. Compressive strength Typical range of compressive strength for pervious concrete is between 2 and 28 MPa [2]. As illustrated in Fig. 6, the compressive strength of the pervious concrete mixtures decreased as the percentage of waste materials replacement increased. For instance, there was a reduction of 20, 25 and 38% for the compressive strength of SPC1-25, SPC1-50 and SPC1-75 respectively in comparison to that of CPC. As previously discussed, this was caused by the angular shape and heterogeneous structure of the CS particles, which led to reduced compactness and increased void content (Figs. 2 and 3). Similar finding was reported by Nguyen et al. [42] in regards to the structure of crepidula seashells. On the other hand, the compressive strength of the mixtures contains KS1, including KPC1-25, KPC1-50 and KPC1-75, decreased about 27, 52 and 58% compared to that of CPC at the age of 28 days. The results showed that the compressive strength for the KPC mix-
3.3. Sound absorption and transmission loss The sound absorbing performance of a material is defined by its sound absorption coefficient (a), which is the incident sound energy that is absorbed by the materials and not reflected back. Generally, conventional concrete has a ‘a’ value of 0.05–0.10 [43]. According to the results in Fig. 7, it could be observed that ‘a’ values of pervious concrete mixture were almost higher than
E. Khankhaje et al. / Applied Acoustics 122 (2017) 113–120
CPC
KPC1-25
KPC2-50
SPC1-25
SPC2-50
0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0
500
1000
1500
2000
2500
3000
3500
4000
4500
Frecuency (Hz) Fig. 7. Sound absorption coefficient of pervious concrete mixtures.
Noise reduction coefficient (NRC) (%)
that of the conventional concrete in most of the frequencies. This could be due to the interconnected voids in the pervious concrete, which was able to reflect sound inside the said voids. Subsequently, this caused the sound to vibrate and convert into heat. Therefore, the incoming sound was easily absorbed through the voids on the pervious concrete. Fig. 8 shows the noise reduction coefficient (NRC). The pervious concrete mixtures, which contained waste materials, showed better sound absorption than CPC. For example, the NRCs for the SPC mixtures were almost 16% compared to 9% of the CPC mixture. This could be due to blending aggregates of different shape typically results in a higher void content as compared to the mixtures made using single sized aggregates. The blended aggregate system resulted in an increased sound absorption in most cases [44]. This could be due to the angular shape and heterogeneous structure of both KS and CS, which affected the macro and micro structure of the pervious concrete, and as a result, was capable of producing more voids on the structure of the pervious concrete. Moreover, void size, along with void content, is instrumental in determining the acoustic characteristic of pervious concrete mixture [13]. Neithalath [13] also found the linear relationship between the aggregate size (7.5 mm in this research) and characteristic void size Dvoid = 1.44 + 0.36 Daggregate. This characteristic void size value (4.14 mm) indicates that the CS 6.3 mm cannot enter into these voids. On the contrary, a part of CS 4–6 mm can fit into these voids and decreased the size of void for SPC2. This could be an explanation of the lower sound absorption of the pervious concrete made with CS 4–6 mm (SPC2-50) in comparison with that of SPC1-25. However, it could be noted that by using KS, the sound absorption strongly increased. The maximum sound absorption was achieved by KPC1-25 with NRC of 23%. This could be due to the entrapped air on the KS surface, which was inside the microstruc-
CPC
40
KPC1-25
KPC2-50
SPC1-25
SPC2-50
35 30 25 20 15 10 0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
Frequency (Hz) Fig. 9. Sound transmission loss coefficient of pervious concrete mixtures.
30
25
22.79 19.00
20 16.47
16.00
15
10
ture of KPC, and caused the sound to be easily absorbed. In addition, the high sound absorption of the KPC specimens could be due to the high porosity of KS in micro level, which increased the air void further (Fig. 8). Thus, sound was easily absorbed into the KPC specimens. However, this finding was in contrast to that of Kim and Lee’s [15]. They compared the sound absorption coefficient of porous concrete with normal and lightweight aggregate, and found that the size (in the range of 4–19 mm) and type of aggregate did not affect the sound absorption of porous concrete. Nonetheless, this could be due to the higher void content (30– 40%) of the specimens that was used in their study, which might have easily absorbed almost all incoming sound in comparison to the void content of 23% for this current study. Both transmission loss coefficients (TLC) and sound transmission class (STC) are shown in Figs. 9 and 10. The TLC of the pervious concrete specimens was much lower than that of the conventional concrete. This could be because the high connected void content in the pervious concrete had allowed sound to easily pass through the pervious concrete, and thus reduced both TLC and STC. With the use of waste materials, TLC decreased due to an increase in the air content in both SPC and KPC. It was observed that the STC of all mixtures, which ranged between 20 and 26, was much lower than the range of the conventional concrete (40–80). As the porosity of pervious concrete increases due to an increase in air content, the TLC decreased as the sound is easily passed through the air void present inside the pervious concrete by using KS and CS. In addition, the surface density of a material is a significant factor affecting the TLC [45]. In fact, with using KS and CS the surface density of the pervious concrete was decreased by 34 kg/cm2 and 37 kg/cm2 in comparison with that of CPC (38 kg/cm2), which caused the reduction of the STC and TLC. The
9.03
5
Sound transmission class (STC) (db)
Sound absorption coefficient ( )
0.9
Soumd tranmission loss coefficient (db)
118
26 25
23
24 20
20
KPC1-25
KPC2-50
20 15 10 5 0
0 CPC
SPC1-25
SPC2-50
KPC1-25
KPC2-50
Mixes Fig. 8. Noise reduction coefficients of pervious concrete mixtures.
CPC
SPC1-25
SPC2-50
Mixes Fig. 10. Sound transmission class of pervious concrete mixtures.
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reduction in TLC is marginal and can be partially restored by inclusion of boarder to the surface of pervious concrete such as gypsum boarder. Mohammed et al. [46] also reported almost similar findings. They investigated the effects of using crumb rubber (CR) as partial replacement to fine aggregate on sound absorption and transmission loss of concrete. They reported that with increasing CR the void content increased, which was due to the high porosity of CR, therefore, the sound easily absorbed into the concrete. However, TLC was decreased due to the present of air void inside the concrete [46]. 4. Conclusion In this paper, the effects of waste materials, specifically oil palm kernel shell (KS) and cockle shell (CS), on the fresh and hardened properties of pervious concrete mixtures were analysed. Generally, the utilisation of KS and CS in pervious concrete mixture was able to address the demand of preserving a cleaner environment and producing sustainable pervious concrete using waste materials. Based on the experimental results and observations made, the following conclusions could be drawn: 1. Void content significantly escalated with the increase of KS and CS. This is due to the angular shape of the waste materials. Smaller particles of KS and CS produced lower void content and permeability compared to that of the control pervious concrete (CPC). This was probably because the smaller parts were able to fit into the pores, and thus reduced the void content. 2. The compressive strength of pervious concrete decreased as the content of both KS and CS increased, owing to escalated void content. However, the values obtained were still within the typical range for compressive strength of pervious concrete (2– 28 MPa). 3. SPC and KPC showed better sound absorption with higher noise reduction coefficient in comparison to CPC. In addition, the sound transmission class (STC) for pervious concrete mixtures with KS and CS decreased compared with that of CPC. This could be due to the microstructure of KS and CS, which increased the entrapped air inside the pervious concrete. It could therefore be concluded that SPC, and especially KPC, could be used as quiet pavement to absorb the noise produced by tyres and traffic. However, the low STC indicated that the pervious concrete containing KS and CS should be partially restored by inclusion of boarder to the surface such as gypsum boarder. To summarise, the findings and observations of this study suggested that quieter pervious concrete incorporating KS and CS can be produced. However, it was recommended that future studies investigate the durability of pervious concrete containing KS and CS. References [1] Damian C, Fosßala˘u C. Sources of indoor noise and options to minimize adverse human health effects. Environ Eng Manag J 2011;10:393–400. [2] Tennis P, Leming M, Akers D. Pervious concrete pavements. Maryland:Silver Spring: Portland Cement Association Skokie Illinois and National Ready Mixed Concrete Association. Silver Spring; 2004. [3] ACI 552. Report on pervious concrete, American Concrete Institute. Farmington Hills, Mishigan: American Concrete Institute; 2010. [4] Yang J, Jiang G. Experimental study on properties of pervious concrete pavement materials. Cem Concr Res 2003;33:381–6. [5] Offenberg M. Is pervious concrete ready for structural applications? Struct Mag 2008;48. [6] Schaefer V, Wang K, Suleiman M, Kevern J. Mix design development for pervious concrete in cold weather climates. Cent Transp Res Educ Iowa State Univ 2006;67. [7] Na Jin BE. Fly ash applicability in pervious concrete. The Ohio State University; 2010.
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Properties of quiet pervious concrete containing oil palm kernel shell and cockleshell Elnaz Khankhaje a,⇑, Mohd Razman Salim b, Jahangir Mirza c, Salmiati b,⇑, Mohd Warid Hussin c, Rawid Khan d, Mahdi Rafieizonooz a a
Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor Bahru, Malaysia Centre for Environmental Sustainability and Water Security, Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor Bahru, Malaysia UTM Construction Research Centre (UTM CRC), Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor Bahru, Malaysia d Department of Civil Engineering, University of Engineering and Technology, Peshawar, Pakistan b c
a r t i c l e
i n f o
Article history: Received 29 November 2016 Received in revised form 21 February 2017 Accepted 22 February 2017
Keywords: Pervious concrete Noise reduction Cockle shell Palm oil kernel shell
a b s t r a c t Nowadays, the significant increase in noise has become a major problem in urban areas. Using pervious concrete pavement is recommended to reduce the noise. Unfortunately, standard materials used to produce pervious concrete are not completely environmental friendly. As a result, many researchers have devoted their attention towards identifying eco-friendlier substitutions to be used in the manufacturing of pervious concrete. In this respect, this current paper discussed the efficiency of two different sizes of oil palm kernel shell (KS) and cockle shell (CS) as partial replacement of natural coarse aggregate for sound absorption of pervious concrete. Thirteen mixtures were made, which replaced 6.30 mm limestone with 0, 25, 50 and 75% of 6.30 mm and 4.75 mm of both shells. The specimens were cured in a fog room and void content and compressive strength were tested. The replacement of both KS and CS as the natural aggregate decreased the compressive strength, although the range was still acceptable for pervious concrete at 28 days. However, the angular shape of both shells caused high void content. The maximum increase in void content compared to that of the control pervious concrete (CPC) was achieved with the use of 75% of 6.30 mm KS at 28 days. Moreover, by increasing sound absorption with the application of both shells, particularly KS, the concrete could be used as silent road pavement. It was therefore concluded that the use of both KS and CS to produce cleaner and quitter pervious concrete pavement is practical, both mechanically and environmentally. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction Of late, the significant increase in noise has become a major problem in urban areas. The said noise is typically generated from a variety of sources, including various types of vehicles on the road, airplanes, factories and construction sites. Noise exposure does not only impair human hearing capacity, but may also cause certain mental disorders [1]. Therefore, using of pervious concrete pavements have been recommended by Environmental Protection Agency (EPA) of the United State (US) to reduce traffic noise in urban area. Pervious concrete is one of the best materials used in top layer of permeable pavement system. In the past 30 years, pervious concrete has been gradually used in the United States (US),
⇑ Corresponding authors. E-mail addresses: [email protected] (E. Khankhaje), [email protected] (Salmiati). http://dx.doi.org/10.1016/j.apacoust.2017.02.014 0003-682X/Ó 2017 Elsevier Ltd. All rights reserved.
and is among the Best Management Practices (BMPs) recommended by EPA and American Concrete Institute (ACI) [2,3]. Due to the lower durability and strength of pervious concrete compared to normal concrete, the application of pervious concrete is limited to the roads that have light volume traffic [2,3]. However, due to the advantages of pervious concrete, the utilisation and construction properties of pervious concrete have been studied by many researchers [4–6]. The benefits of using pervious concrete are: reduction of downstream flows; reduction of large volumes of surface pollution flowing into rivers; decreasing of urban heat island effect; reducing traffic noise; enhancing safety of driving during raining; and removing heavy metal from stormwater runoff [3,7]. The use of pervious concrete in building site design can also aid in the process of qualifying the building for Leadership in Energy and Environmental Design (LEED) [8]. In pervious concrete, water passes through an interconnected network of voids structure, resulting from the constrained use of fine aggregates, uniform gradation and low water-to-cement ratio
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[3]. Void content of pervious concrete ranging from 20 to 30% is a consequence in a concrete with high drainage rate from 0.25 to 6.1 mm/s [6]. Moreover, typical range for the compressive strength of the pervious concrete are between 2 and 28 MPa [3,6,2]. Previous researches have reported that pervious concrete has the potential to reduce significantly the noise produced by vehicles due to high void content [9–12]. Normal concrete, for example, typically has an absorption coefficient (a) of 0.03–0.05 [13]. Pervious concrete typically has an absorption range from 0.1 (for poorly performing mixtures) to nearly 1 (for mixture with optimal pore volume and size) [3]. This is due to the voids inside the material, which absorbed the sound energy through internal friction. For pervious concrete to effectively absorb sound, 15–25% of connected void content is essential. Meiarashi et al. [14] compared the noise reduction levels of pervious asphalt and normal asphalt pavement. They found that 2–5 dB noise reduction was obtained by pervious asphalt, and concluded that it was crucial to keep the pavement porosity at 20% or higher for noise reduction purpose. In another study, Kim and Lee [15] investigated the effects of three levels of cement flow and five types of aggregates on the mechanical properties and sound absorption level of porous concrete. They observed that the sound absorption of specimens with smaller size was better than that of the control sample. This was because the total void ratios of the specimens were higher when smaller sized aggregates were used. Berengier [16] measured acoustical performance of porous pavement over real road surfaces and compared to theoretical predictions. They found that the microstructural model provided a good physical description of the acoustical properties of porous pavement. This was due to the flow resistivity and the porosity of the material and, to a lesser extent, on the tortuosity. Further, the properties of the pavement are relatively insensitive to pore shape factor. The effective management of by-product waste materials plays an important role in increasing environmental sustainability. One of the strategies in waste management is the utilisation of byproduct waste materials in the construction industry to reduce the landfill of waste materials. Moreover, with the application of waste materials, more sustainable, clean and green construction could be achieved due to the decrease of cost [17]. In addition, most materials used in concrete production are natural aggregates, and a majority of the materials are excavated from mines and river beds or dredged from sea shelves [18]. These activities have resulted in severe damage to the environment, including disruption of the ecosystem and contamination of soil, air and water [19]. Therefore, the construction industry encourages the incorporation of sustainability in production issues with the application of solid waste materials as aggregate in concrete [20–23]. Neithalath et al. [11] reviewed the benefits of using farming waste materials in concrete. They reported that both the reliance on standard materials used to produce concrete and adverse effects on the environment could be reduced with the reuse of farming waste materials in concrete. In addition, it was indicated that the method could also ensure waste conservation, and subsequently, decrease waste disposal in the involved sectors. Moreover, they concluded that by selecting proper farming waste materials, concrete with better performance could be produced. Asdrubali et al. [25] evaluated the acoustic performance of sustainable products made from natural and recycled materials. They concluded that the substitution of conventional sound insulating materials with sustainable ones has significant effects on the impact of all the various phases of the life of the building (construction, operation, end of life). Ibrahim and Razak [26] studied the use of palm oil clinker (POC) as coarse aggregate in the production of pervious concrete. They indicated that with using POC the compressive strength and density of the concrete reduced. However, the coefficient of permeability and porosity increased.
Two of the farming waste materials, which were successfully utilised as coarse aggregate in conventional concrete, were oil palm kernel shell (KS) and cockle shell (CS). KS is a waste product obtained from the production of oil from oil palm trees [27,28]. Malaysia produces over four million tonnes of KS annually [28,29], and the county is expected to grow five million hectares of oil palm trees by the year 2020 [30]. According to the Department of Fisheries Malaysia, 57,544 tonnes of cockles were harvested along the west coast of Peninsular Malaysia. In addition, it was reported that the retail value of cockles in Malaysia was estimated to be at over USD 32 million [32]. Boey et al. [32] also indicated that the active and lucrative industry has resulted in a significant amount of waste shells. Moreover, left untreated and dumped irresponsibly, CS may produce unpleasant odour [33]. In this paper, the effects of KS and CS as a partial replacement of natural coarse aggregate on the properties of especial type of concrete, pervious concrete, was investigated. To the author’s best knowledge, there are currently no studies investigating the effects of oil palm kernel shell (KS) and cockle shell (CS) on the noise absorption of pervious concrete. On a related note, the aim of this study was to replace KS and CS (0, 25, 50 and 75%) with two different sizes (6–9 mm and 4–6 mm) as natural coarse aggregate in pervious concrete. The effects of replacing coarse aggregate with KS and CS on void content and compressive strength of pervious concrete were investigated and compared against the control pervious concrete (CPC). In addition, sound absorption coefficient and sound transmission loss were also examined and analysed.
2. Specimen and preparation 2.1. Materials The cement used in this study was Ordinary Portland Cement (OPC) type I. To achieve a system with interconnection voids in the pervious concrete, the selection of single-sized aggregates is necessary [3,2]. The details of the aggregates are listed in Table 1. In this study, crushed limestone (LS) with a grain size of 6.30 mm (passed through a 9.5 mm sieve and retained on a 6.30 mm sieve) was used as the natural coarse aggregate. LS presented a specific gravity of 2.6 kg/m3 and water absorption of 1.8%. In addition, KS and CS was used as a replacement of natural coarse aggregate. In this study, KS was collected from a local palm oil producing mill located in Johor, a southern state of Malaysia. On the other hand, CS was obtained from a local market located in the south coast of Malaysia, and were crushed before they were used. Subsequently, both KS and CS were sieved and divided into two different size categories, namely (KS1, CS1) 6.30 mm (passed through a 9.5 mm sieve and retained on a 6 mm sieve) and (KS2, CS2) 4.75 mm (passed through a 6.30 mm sieve and retained on a 4.75 mm sieve), as illustrated in Fig. 1. Following that, they were washed and air dried in a laboratory. The purpose of washing both KS and CS was to remove oil and dirt. Fig. 2 presents the Scanning Electron Macroscopy (SEM) image of KS and CS particles. It can be seen that the high porous and heterogeneous structure of KS and CS respectively.
2.2. Mixture proportions Placement or compaction method plays an important role towards the properties of pervious concrete [34]. For this study, the technique of filling in three layers using 25 drops of a 15.9 mm diameter steel rod and 10 drops of a standard Proctor hammer (2.5 kg) for each layer was used from the results of Khankhaje et al. [35].
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Waste aggregates
Natural aggregate
CS
Gradation (mm) Bulk specific gravity (SSD) Water absorption (%) Dry rodded density (kg/m3)
KS
CS1
CS2
KS1
KS2
6.30 2.09 1.8 1408
4.75 2.64 2.5 1420
6.30 1.29 24.73 631
4.75 1.30 25.62 656
LS
Sand
6.30 2.6 1.8 1475
0–4 2.62 7.4 –
Fig. 1. Particle shapes of aggregates: (a) CS1, (b) CS2, (c) KS1 and (d) KS2.
Fig. 2. SEM image of (a) CS and (b) KS.
Table 2 Mixture proportion of pervious concrete. Mix
Cement (kg/m3)
Water (kg/m3)
CPC SPC1-25 SPC1-50 SPC1-75 SPC2-25 SPC2-50 SPC2-75 KPC1-25 KPC1-50 KPC1-75 KPC2-25 KPC2-50 KPC2-75
339.5 339.5 339.5 339.5 339.5 339.5 339.5 339.5 339.5 339.5 339.5 339.5 339.5
107.54 107.54 107.54 107.54 107.54 107.54 107.54 107.54 107.54 107.54 107.54 107.54 107.54
Table 2 shows the weight of each materials in one cubic metre of pervious concrete mixture. Each mixture proportion was designated with a specific code. The first labels represented the types of
Coarse aggregate (kg/m3)
Sand (kg/m3)
LS
CS
KS
1313.8 985.4 656.9 328.5 985.4 656.9 328.5 1094.9 729.9 365.0 1094.9 729.9 365.0
– 348.4 696.8 1045.2 348.4 696.8 1045.2 – – – – – –
– – – – – – – 157.6 315.3 472.9 157.6 315.3 472.9
139.0 139.0 139.0 139.0 139.0 139.0 139.0 139.0 139.0 139.0 139.0 139.0 139.0
coarse aggregates used. ‘CPC’, ‘SPC’ and ‘KPC’ representing control, cockle shell and oil palm kernel shell pervious concrete respectively. The second labels, ‘1’and ‘2’, referred to the size of the coarse
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aggregates used, big and small respectively. Finally, the third labels, ‘0’, ‘25’, ’50’ and ‘75’, indicated the percentage of waste aggregate added in terms of the weight percentage of the natural coarse aggregate proportion. All batches were designed with the purpose of investigating their void content as well as sound absorption. Both water cement ratio (w/c) and sand content were fixed at 32% and 10% (wt.% of the coarse aggregate) respectively. In addition, the mixtures with constant void content (23%), which were similar to that of the CPC mixture, were selected, given that void content is one of the factors that affects the sound absorption of pervious concrete [15]. Therefore, KPC1-25, KPC2-50, SPC1-25 and SPC2-50 were selected to investigate the influence of KS and CS on the sound absorption of pervious concrete. To prepare the needed pervious concrete, a small amount of cement (<5% by mass) was blended in a mixer with coarse aggregates for about one minute. Subsequently, sand and the remaining cement together with water were added into the mixture. Mixing was continued for another three minutes. The mixture was then rested for three minutes, and finally, was mixed again for another two minutes. After that, the void content and compressive strength of the pervious concretes were measured. In order to examine the void content as well as compressive strength, the pervious concrete specimens were casted in steel cylinder molds (100 mm diameter 200 mm high). Each test result of the properties examined was the average of at least three specimens. In addition, for both sound absorption and transmission loss evaluations, the cylindrical specimens with size of (99 mm diameter 100 mm thickness) and (28 mm diameter 100 mm thickness) were used in sound absorption test. The thickness of the samples was selected based on typical cross section of pervious concrete pavement. Immediately upon casting, all the specimens were cured for 24 h in a fog room, which was maintained at a temperature of 20 °C ± 2 °C and 95% ± 5% relative humidity. After 24 h, the specimens were removed from their molds and kept at the same conditions for 7 and 28 day curing periods. The structural arrangements of the pervious concrete mixtures containing limestone, KS and CS are shown in Fig. 3. It can be seen that angular shape of the KS and CS particles led to reduced compactness and increased void content. 2.3. Experimental details The void content of the hardened samples were tested based on ASTM C1754 [36] using the volumetric method.
NRC ¼
a250 þ a500 þ a1000 þ a2000
ð1Þ
4
where a indicates the sound absorption coefficient at different frequencies. As the pervious concrete can be used in wall [2], the transmission class (STC) also was evaluated. STC is an integer rating of how specimens stops or blocks airborne sound. In this study, STC calculation was performed according to ASTM E413 [41]. 3. Test results and discussion 3.1. Void content Typical range of void content for pervious concrete is between 15 and 25% [2]. Fig. 5 illustrates the void content of the pervious concrete mixtures containing natural and waste coarse aggregates. It can be seen that the void content increased with an increase in the percentage of waste. For instance, there was an increase of 2, 4 and 20% for the void content of SPC1-25, SPC1-50 and SPC1-75 respectively in comparison to that of CPC. This could be due to the angular shape of CS, which decreased the compactness of all SPC1 mixtures, and subsequently, disturbed the granular arrangement of the pervious concrete. Nguyen et al. [42] reported comparable findings, in which the void content increased along with an increase in the percentage of crushed crepidula seashells. The void content of mixtures containing the bigger sized KS, including KPC1-25, KPC1-50 and KPC1-75, increased about 1, 17 and 25% compared to that of CPC at the age of 28 days. From the results as shown in Fig. 5, it could be concluded that the void
Paste
Paste
CS
KS
LS
LS Void
(a)
The compressive strength test was measured according to ASTM C39 [37]. The cylindrical specimens for compressive strength tests were dried in room temperature for about two hours and then capped with sulphur capping compound at both ends in accordance to ASTM C617 [38]. This step was taken to fill up any voids and level both ends of the cylinder specimens. To evaluate the sound absorption and transmission loss characteristics of the pervious concrete, two impedance tube with 100 mm and 30 mm diameter were employed for low (50– 1500 Hz) and high frequency (1500–5000 Hz) test respectively, which was according to ASTM E 1050 [39] (Fig. 4). The ability of a material to absorb sound can be calculated using a single value known as the noise reduction coefficient (NRC), as given in Eq. (1) [40]:
(b)
Void
(c)
Fig. 3. Structural arrangement of the pervious concrete matrix (a) with natural aggregate (LS); (b) with KS and (c) with CS.
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Fig. 4. The impedance tube for acoustic test.
31
KPC1
KPC2
CPC
SPC1
SPC2
16
Compressive strength (MPa)
Void content (%)
29 27 25 23 21 19 17 15 0
25
50
75
Waste content (%)
KPC1
KPC2
CPC
SPC1
SPC2
14 12 10 8 6 4 2 0 0
25
50
75
Waste content (%)
Fig. 5. Void content of pervious concrete mixtures.
Fig. 6. Compressive strength of pervious concrete mixtures at 28 days.
content of the mixtures with KS was higher than that with CS. This could be due to the high water absorption of KS particles, which absorbed more water during the mixing process, and thus entrapping air on its surface causing the void content ratio of the KPC1 mixtures to increase. The highest void content ratio was obtained by KPC1-75. The mixtures containing the smaller sized waste materials (KS2 and CS2) showed lower void content than the mixtures with the bigger sized waste materials (KS1 and CS1). This might be because the smaller sized KS and CS were able to fit into the voids, and thus decreased the void content ratio.
tures was lower than the SPC mixtures. The entrapped air on the surface of the KS particles led to a reduction in the bonding area matrix. Furthermore, as discussed before the cement paste in the pervious concrete was very thin, and thus it was not able to fully bond with the KS particles. However, with natural coarse aggregate (LS), this was not a significant issue. As the load was applied to KPC during the strength test, micro cracks formed at the weak interface, between the cement paste and KS, due to stress focus. This resulted in the failure of continuous load application. Moreover, referring to Fig. 6, it could be concluded that the mixtures, which contained the smaller sized waste materials (KS2 and CS2), showed higher compressive strength than the mixtures containing the bigger sized waste materials (KS1 and CS1). This could be a result of the small parts of both KS and CS being able to fit into the voids, which then decreased the void content, and at the same time, increased the compressive strength of the mixtures. Furthermore, by decreasing the size of both KS and CS, the surfaces, which could be coated with cement paste, increased and resulted in better bonding between the cement paste and smaller coarse aggregate.
3.2. Compressive strength Typical range of compressive strength for pervious concrete is between 2 and 28 MPa [2]. As illustrated in Fig. 6, the compressive strength of the pervious concrete mixtures decreased as the percentage of waste materials replacement increased. For instance, there was a reduction of 20, 25 and 38% for the compressive strength of SPC1-25, SPC1-50 and SPC1-75 respectively in comparison to that of CPC. As previously discussed, this was caused by the angular shape and heterogeneous structure of the CS particles, which led to reduced compactness and increased void content (Figs. 2 and 3). Similar finding was reported by Nguyen et al. [42] in regards to the structure of crepidula seashells. On the other hand, the compressive strength of the mixtures contains KS1, including KPC1-25, KPC1-50 and KPC1-75, decreased about 27, 52 and 58% compared to that of CPC at the age of 28 days. The results showed that the compressive strength for the KPC mix-
3.3. Sound absorption and transmission loss The sound absorbing performance of a material is defined by its sound absorption coefficient (a), which is the incident sound energy that is absorbed by the materials and not reflected back. Generally, conventional concrete has a ‘a’ value of 0.05–0.10 [43]. According to the results in Fig. 7, it could be observed that ‘a’ values of pervious concrete mixture were almost higher than
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CPC
KPC1-25
KPC2-50
SPC1-25
SPC2-50
0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0
500
1000
1500
2000
2500
3000
3500
4000
4500
Frecuency (Hz) Fig. 7. Sound absorption coefficient of pervious concrete mixtures.
Noise reduction coefficient (NRC) (%)
that of the conventional concrete in most of the frequencies. This could be due to the interconnected voids in the pervious concrete, which was able to reflect sound inside the said voids. Subsequently, this caused the sound to vibrate and convert into heat. Therefore, the incoming sound was easily absorbed through the voids on the pervious concrete. Fig. 8 shows the noise reduction coefficient (NRC). The pervious concrete mixtures, which contained waste materials, showed better sound absorption than CPC. For example, the NRCs for the SPC mixtures were almost 16% compared to 9% of the CPC mixture. This could be due to blending aggregates of different shape typically results in a higher void content as compared to the mixtures made using single sized aggregates. The blended aggregate system resulted in an increased sound absorption in most cases [44]. This could be due to the angular shape and heterogeneous structure of both KS and CS, which affected the macro and micro structure of the pervious concrete, and as a result, was capable of producing more voids on the structure of the pervious concrete. Moreover, void size, along with void content, is instrumental in determining the acoustic characteristic of pervious concrete mixture [13]. Neithalath [13] also found the linear relationship between the aggregate size (7.5 mm in this research) and characteristic void size Dvoid = 1.44 + 0.36 Daggregate. This characteristic void size value (4.14 mm) indicates that the CS 6.3 mm cannot enter into these voids. On the contrary, a part of CS 4–6 mm can fit into these voids and decreased the size of void for SPC2. This could be an explanation of the lower sound absorption of the pervious concrete made with CS 4–6 mm (SPC2-50) in comparison with that of SPC1-25. However, it could be noted that by using KS, the sound absorption strongly increased. The maximum sound absorption was achieved by KPC1-25 with NRC of 23%. This could be due to the entrapped air on the KS surface, which was inside the microstruc-
CPC
40
KPC1-25
KPC2-50
SPC1-25
SPC2-50
35 30 25 20 15 10 0
500
1000
1500
2000
2500
3000
3500
4000
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5000
Frequency (Hz) Fig. 9. Sound transmission loss coefficient of pervious concrete mixtures.
30
25
22.79 19.00
20 16.47
16.00
15
10
ture of KPC, and caused the sound to be easily absorbed. In addition, the high sound absorption of the KPC specimens could be due to the high porosity of KS in micro level, which increased the air void further (Fig. 8). Thus, sound was easily absorbed into the KPC specimens. However, this finding was in contrast to that of Kim and Lee’s [15]. They compared the sound absorption coefficient of porous concrete with normal and lightweight aggregate, and found that the size (in the range of 4–19 mm) and type of aggregate did not affect the sound absorption of porous concrete. Nonetheless, this could be due to the higher void content (30– 40%) of the specimens that was used in their study, which might have easily absorbed almost all incoming sound in comparison to the void content of 23% for this current study. Both transmission loss coefficients (TLC) and sound transmission class (STC) are shown in Figs. 9 and 10. The TLC of the pervious concrete specimens was much lower than that of the conventional concrete. This could be because the high connected void content in the pervious concrete had allowed sound to easily pass through the pervious concrete, and thus reduced both TLC and STC. With the use of waste materials, TLC decreased due to an increase in the air content in both SPC and KPC. It was observed that the STC of all mixtures, which ranged between 20 and 26, was much lower than the range of the conventional concrete (40–80). As the porosity of pervious concrete increases due to an increase in air content, the TLC decreased as the sound is easily passed through the air void present inside the pervious concrete by using KS and CS. In addition, the surface density of a material is a significant factor affecting the TLC [45]. In fact, with using KS and CS the surface density of the pervious concrete was decreased by 34 kg/cm2 and 37 kg/cm2 in comparison with that of CPC (38 kg/cm2), which caused the reduction of the STC and TLC. The
9.03
5
Sound transmission class (STC) (db)
Sound absorption coefficient ( )
0.9
Soumd tranmission loss coefficient (db)
118
26 25
23
24 20
20
KPC1-25
KPC2-50
20 15 10 5 0
0 CPC
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SPC2-50
KPC1-25
KPC2-50
Mixes Fig. 8. Noise reduction coefficients of pervious concrete mixtures.
CPC
SPC1-25
SPC2-50
Mixes Fig. 10. Sound transmission class of pervious concrete mixtures.
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reduction in TLC is marginal and can be partially restored by inclusion of boarder to the surface of pervious concrete such as gypsum boarder. Mohammed et al. [46] also reported almost similar findings. They investigated the effects of using crumb rubber (CR) as partial replacement to fine aggregate on sound absorption and transmission loss of concrete. They reported that with increasing CR the void content increased, which was due to the high porosity of CR, therefore, the sound easily absorbed into the concrete. However, TLC was decreased due to the present of air void inside the concrete [46]. 4. Conclusion In this paper, the effects of waste materials, specifically oil palm kernel shell (KS) and cockle shell (CS), on the fresh and hardened properties of pervious concrete mixtures were analysed. Generally, the utilisation of KS and CS in pervious concrete mixture was able to address the demand of preserving a cleaner environment and producing sustainable pervious concrete using waste materials. Based on the experimental results and observations made, the following conclusions could be drawn: 1. Void content significantly escalated with the increase of KS and CS. This is due to the angular shape of the waste materials. Smaller particles of KS and CS produced lower void content and permeability compared to that of the control pervious concrete (CPC). This was probably because the smaller parts were able to fit into the pores, and thus reduced the void content. 2. The compressive strength of pervious concrete decreased as the content of both KS and CS increased, owing to escalated void content. However, the values obtained were still within the typical range for compressive strength of pervious concrete (2– 28 MPa). 3. SPC and KPC showed better sound absorption with higher noise reduction coefficient in comparison to CPC. In addition, the sound transmission class (STC) for pervious concrete mixtures with KS and CS decreased compared with that of CPC. This could be due to the microstructure of KS and CS, which increased the entrapped air inside the pervious concrete. It could therefore be concluded that SPC, and especially KPC, could be used as quiet pavement to absorb the noise produced by tyres and traffic. However, the low STC indicated that the pervious concrete containing KS and CS should be partially restored by inclusion of boarder to the surface such as gypsum boarder. To summarise, the findings and observations of this study suggested that quieter pervious concrete incorporating KS and CS can be produced. However, it was recommended that future studies investigate the durability of pervious concrete containing KS and CS. References [1] Damian C, Fosßala˘u C. Sources of indoor noise and options to minimize adverse human health effects. Environ Eng Manag J 2011;10:393–400. [2] Tennis P, Leming M, Akers D. Pervious concrete pavements. Maryland:Silver Spring: Portland Cement Association Skokie Illinois and National Ready Mixed Concrete Association. Silver Spring; 2004. [3] ACI 552. Report on pervious concrete, American Concrete Institute. Farmington Hills, Mishigan: American Concrete Institute; 2010. [4] Yang J, Jiang G. Experimental study on properties of pervious concrete pavement materials. Cem Concr Res 2003;33:381–6. [5] Offenberg M. Is pervious concrete ready for structural applications? Struct Mag 2008;48. [6] Schaefer V, Wang K, Suleiman M, Kevern J. Mix design development for pervious concrete in cold weather climates. Cent Transp Res Educ Iowa State Univ 2006;67. [7] Na Jin BE. Fly ash applicability in pervious concrete. The Ohio State University; 2010.
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