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Engineering and environmental properties of foamed recycled glass as a lightweight engineering material
Journal of Cleaner Production 94 (2015) 369e375
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Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Engineering and environmental properties of foamed recycled glass as a lightweight engineering material Arul Arulrajah a, *, Mahdi M. Disfani b, Farshid Maghoolpilehrood a, Suksun Horpibulsuk c, **, Artit Udonchai c, Monzur Imteaz a, Yan-Jun Du d a
Swinburne University of Technology, Melbourne, Victoria 3122, Australia The University of Melbourne, Melbourne, Victoria 3010, Australia Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand d Southeast University, Nanjing 210096, China b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 March 2014 Received in revised form 21 January 2015 Accepted 26 January 2015 Available online 3 February 2015
Lightweight fill materials, including foamed aggregates are increasingly being used in civil engineering and infrastructure applications. This research assessed the engineering properties of foamed recycled glass through a laboratory evaluation to ascertain this novel recycled material as a lightweight fill material in civil engineering applications. The engineering assessment included particle size distribution, particle density, water absorption, minimum and maximum dry densities with a vibrating table, California Bearing Ratio (CBR) and Los Angeles (LA) abrasion tests. Shear strength properties of the recycled foamed glass were studied through large-scale direct shear tests. This recycled foamed glass is classified as a gap graded material. Due to high porosity, the coarse particles of this material have high water absorption of 60% and low particle density of 4.54 kN/m3, which is much lower than that of water. The minimum and maximum dry densities of this material are very low of 1.67 and 2.84 kN/m3, respectively. The LA abrasion of foamed recycled glass is lower than the requirement for pavement base/subbase material, being of 94%. The shear resistance at small shear displacement is thus low as shown by low CBR value of 9e12%. However, the shear resistance at large shear displacement is high as shown by high cohesion and friction angle of 23.36 kPa and 54.7, respectively. The environmental assessment included pH value, organic content, total and leachate concentration of the material for a range of contaminant constituents. All the hazardous concentrations in the leachate are far lower than 100 times of those of the drinking water standards, indicating the foamed recycled glass as a non-hazardous material. The energy savings assessment demonstrates that the use of foamed recycled glass as engineering material has much lower energy consumption relative to a conventional aggregate-cement material in construction projects. The lightweight properties of the foamed recycled glass coupled with its satisfactory engineering and environmental results, particularly its high friction angle, indicates that the material is ideal for usage as a lightweight construction material in engineering applications such as non-structural fills in embankments, retaining wall backfill and pipe bedding. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Lightweight material Embankment fill Foam glass Waste materials
1. Introduction
* Corresponding author. Faculty of Engineering (H38), Swinburne University of Technology, PO Box 218, Hawthorn, VIC 3122, Australia. Tel.: þ61 3 92145741; fax: þ61 3 92148264. ** Corresponding author. School of Engineering, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand. E-mail addresses: [email protected] (A. Arulrajah), [email protected] (S. Horpibulsuk). http://dx.doi.org/10.1016/j.jclepro.2015.01.080 0959-6526/© 2015 Elsevier Ltd. All rights reserved.
Lightweight fill materials are increasingly being used in civil engineering applications such as backfill, slope stability, embankment fills, pavements and pipe bedding (Horpibulsuk et al., 2014). The applications of lightweight fill materials are fairly broad but the main intent of this alternative construction material is to significantly reduce the weight of fills, thereby mitigating excessive settlements and bearing failures. This can subsequently result in more economic designs for structures such as retaining walls. Various lightweight fill materials have been developed in recent years for
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usage in various civil engineering applications and these particularly include expanded polystyrene (Athanasopoulos-Zekkos et al., 2012; Deng and Xiao, 2010; Ertugrul and Trandafir, 2011; Lin et al., 2010; Trandafir and Erickson, 2012; Zou et al., 2013), lightweight cellular cemented clays (Horpibulsuk et al., 2014), tires (Cecich et al., 1996; Hodgson et al., 2012; Moghaddas Tafreshi et al., 2012; Nakhaei et al., 2012) and lightweight concrete (Chindaprasirt and Rattanasak, 2011; Wang et al., 2012; Wang and Tang, 2012). With the aim of increase in usage of recycled foamed glass for a cleaner production of lightweight materials as well as a greener and more sustainable environment, this study investigates suitability of recycled foam glass for various engineering applications. In recent years, there has been an environmental push worldwide to continually seek new reuse applications for various waste materials inclusive of demolition wastes (Arulrajah et al., 2013b; Rahman et al., 2014a), municipal solid wastes (Reddy et al., 2009; Zekkos et al., 2006), calcium carbide residue (Phetchuay et al., 2014) and other commercial and industrial wastes (Disfani et al., 2014; Du et al., 2014; Grubb et al., 2006; Landris, 2007; Wartman et al., 2004). Industrial waste materials are increasingly being implemented in various projects for use as an aggregate in applications such as pavements (Akbulut and Gurer, 2007; Hoyos et al., 2011; Puppala et al., 2011; Taha et al., 2002) and road embankments (Puppala et al., 2011; Wartman et al., 2004). Municipal recycled glass is obtained mostly from curbside collection and comprises mainly packaging containers for food and drinks as well as sheet glass or glass from demolition activities. While the glass recycling industry aims to process waste glass back into bottle making industry by color sorting, this is not always possible because a large amount of waste glass delivered to the recycling industry is broken into small pieces during handling and collecting, which makes it difficult to color sort waste glass. Sorting facilities in Australia for example can only color sort recycled glass particles that are larger than 10 mm in particle size and smaller sized glass particles, enter the waste stream (Arulrajah et al., 2014a). Recycled waste glass has been researched in recent years and found to be a viable construction material for embankments and pavement subbases (Arulrajah et al., 2014b; Grubb et al., 2006; Wartman et al., 2004), footpath bases (Arulrajah et al., 2013a) as well as in the manufacture of fibers for problematic soil treatment (Ahmad et al., 2012; Mujah et al., 2013). In recent years, there has been interest in the development of foamed materials with the usage of waste materials in engineering applications (Jana et al., 2013; Wang et al., 2012, 2013a). Foamed glass has been developed particularly for usage in various structural and insulating applications (Bumanis et al., 2013; Guo et al., 2013; Kazantseva, 2013; Pawanawichian et al., 2013; Ponsot and Bernardo, 2013; Wang et al., 2013b; Wu et al., 2013). The usage of recycled glass to manufacture foamed glass is however still in its infancy, with limited works to date in this area apart from some work with the production of ceramics (Fernandes et al., 2009; Ponsot and Bernardo, 2013) and with no known work having been undertaken on its usage as a lightweight aggregate construction material. The usage of recycled products results in significantly less energy production as well as limits the opening of new quarries for virgin quarry products. To achieve sustainability various industries and end-users seek a cleaner production usage for waste materials and view recycled materials as a resource rather than a waste material destined for landfills. The focus of this research is to assess the engineering properties of foamed recycled glass through a laboratory evaluation and to ascertain this novel recycled material as a suitable lightweight fill material in civil engineering applications. An extensive suite of engineering and environmental tests, as well as energy savings assessments were undertaken on foamed recycled glass to assess its engineering properties.
2. Materials and methods The municipal waste glass, obtained from a glass recycling operator site, was first ground and then fired with mineral additives in a furnace at temperatures up to 950 C. The recycled glass foams and is then removed from the furnace at which point it cools down quickly forming low weight foamed recycled glass aggregates of up to 40 mm in size. The foamed material comprises 98% ground recycled glass and 2% mineral additives. Foamed recycled glass for this research was obtained from a supplier in Melbourne, Australia. Fig. 1 shows foamed recycled glass aggregates after production. It is evident from Fig. 1 that the glass aggregates comprise vesiculars, due to the presence of air that forms small voids during the production process. Particle size analysis was undertaken by the Australian standards (AS, 1996). Particle density and water absorption tests of coarse aggregate (retained on a 4.75 mm sieve) and fine aggregate (passing through a 4.75 mm sieve) were both undertaken (ASTM, 2007a). Maximum and minimum dry densities were undertaken using the vibratory table method, which was suitable for this material as it was cohesionless and free-draining (ASTM, 2006b). The pH value of the foamed glass was determined following the Australian standards (AS, 1997a). Organic content tests were performed by the loss of ignition method to determine the organic content of the samples (ASTM, 2007b). CBR tests under standard compaction effort were carried out on specimens in dry and soaked conditions to simulate the worst-case scenario (AS, 2003). LA abrasion test was conducted to determine the abrasion loss of the material and to ascertain if the material could be considered for higher loading applications such as pavement base/subbase applications (ASTM, 2006a). A large-scale Direct Shear Test (DST) apparatus measuring 305 mm in length, 305 mm in width and 204 mm in depth was used to determine the shear strength of the foamed recycled glass, due to the large sizes of the aggregates. The tests were conducted as per ASTM D3080/D3080M standards (ASTM, 2011). The testing apparatus has two boxes: a fixed upper box and a moveable lower box. Initially, the lower and upper boxes were clamped when preparing samples for the tests. The samples were compacted in the shear box in three layers by using hand tamping with a plastic hammer to attain maximum dry density obtained from the vibratory table method. The samples were then submerged for 12 h before consolidation with three normal stress levels of 10 kPa, 20 kPa and 40 kPa. When the consolidation stage for the tests was completed, the connections between the lower and upper boxes was released, which provided an approximate 2 mm gap between the upper and
Fig. 1. Foamed recycled glass after production (courtesy of the Geotechnical laboratory at Swinburne University of Technology, Australia).
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lower boxes for friction minimization. The shearing stage of the test was next conducted under normal stress levels of 10 kPa, 20 kPa and 40 kPa. A shear displacement rate of 0.025 mm/min was maintained throughout the shearing stage. The horizontal displacements, vertical displacements and shear stresses were recorded. The tests were terminated once the horizontal shear displacement reached approximately 75 mm. The room temperature was maintained at 20 ± 1 C. The shear strength of the foamed recycled glass from the DST tests was obtained from the shear stress and horizontal displacement output graphs. The hazard category of foamed recycled glass was determined based on the Environmental Protection Authority (EPA) Victoria and Australian Standard Leaching Procedure (ASLP). If the Total Concentration (TC) is less than the specified limit, or if it can be demonstrated to be of natural origin, the foamed recycled glass is categorized as suitable for fill materials (EPA, 2010). The environmental properties of the foamed recycled glass were tested for different types of heavy metals by following the Australian standards protocol (AS, 1997b) for the preparation of leachate, using slightly acidic leaching fluid (pH ¼ 5) and alkaline leaching fluid (pH ¼ 9.2) leaching buffers. 3. Results and discussions The engineering properties of the laboratory evaluation of the foamed recycled glass are summarized in Table 1. Fig. 2 presents the
Table 1 Engineering properties of foamed recycled glass. Engineering parameters
Foamed recycled glass
Typical lightweight materiala
Typical heavyweight materialb
D10 (mm) D30 (mm) D50 (mm) D60 (mm) Cu Cc Gravel sized particles: 4.75 mme40 mm (%) Sand sized particles: 0.075 mme4.75 mm (%) Clay and Silt sized particles: <0.075 mm (%) Particle density e coarse fraction (kg/m3) Particle density e fine fraction (kg/m3) Minimum dry density (kg/m3) Maximum dry density (kg/m3) Water absorption e coarse fraction (%) Water absorption e fine fraction (%) pH Organic content (%) CBR (%) LA abrasion loss (%) DST: Peak apparent cohesion, c' (kPa) DST: Peak friction angle, f' (degrees) DST: Critical state apparent cohesion, c' (kPa) DST: Critical state friction angle, f' (degrees)
0.13 1.2 18.7 20.6 158 0.53 66
e e e e e e <70
0.09 1.30 4.40 6.70 78.83 2.97 47.9
32
<40
42.2
2
<3
9.90
462.8
408e1529
2600e2700
1508
408e1529
2400e2600
170
112e204
290
204e306
2080
60
50e60
6.50e6.70
0.3
<1.0
6.50e7.50
10.48 0 9e12 94 23.4
9e12 0 2e10 80e100 20e100
10.20e11.40 1.7e2.1 172 29.9e31.7 95
55.7
35e60
65
22.1
20e100
80
54.7
35e60
39
a b
Harmon (2014) and Misapor (2014). Rahman et al. (2014a, 2014b).
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particle size distribution curves of the foamed recycled glass. The particle size distribution curves indicate that the material comprises essentially gravel and sand sized particles with no fines. Based on gradation curve (Fig. 2), coefficient of uniformity (Cu) and coefficient of curvature (Cc), this material is classified as poorly and gap grained, with two major grain size ranges: 0.08e0.3 mm and 10e35 mm. As no fines are present, Atterberg limit tests are not applicable for this material. The minimum and maximum dry density of the materials was low and with values typical of a lightweight construction material. The particle density of the coarse foamed recycled glass was found to be very low (4.54e14.79 kN/m3), lower than the density of water. The fine particle density of foamed glass was almost three times higher than the coarse particle density. The water absorption of fine particles was almost low while the coarse particle water absorption was high at 60%. pH value for the foamed glass was found to be in the alkali range, similar to that for typical construction and demolition aggregates (Arulrajah et al., 2013b). Organic materials are not present, likely due to the high temperatures used in the foamed glass process. Fig. 3 presents the CBR results for the foamed recycled glass. The CBR test results for the foamed recycled glass were within the local road authority specification requirements for a structural fill material in road embankments, which is typically specified within the range of 2%e5% (VicRoads, 2011). It is of interest to note that the load and penetration relationship of this material is not typical of coarse-grained geomaterials. This material exhibits peak and ultimate loads when subjected to penetration. The load increases with increasing penetration until the peak value. After a small decrease in load, the load again increases with increasing penetration to the ultimate value. The result implies that particle crushing occurs at peak state and then rearrangement of crushed particles contributes the ultimate strength. The material crushing is due to a low particle strength as indicated by the high LA abrasion value of 94%. A maximum LA abrasion value not exceeding 40% is typically specified for pavement base/subbase applications. The LA abrasion and CBR results indicate that the material is unsuitable for heavier duty applications such as in pavement base/subbases. LA Abrasion results also indicate the susceptibility of the material to crushing under repeated loading, which makes it unsuitable for application involving dynamic loads. Fig. 4 presents the DST results for the foamed recycled glass. The material shows completely dilatant behavior in vertical displacement and horizontal displacement relationship at 10 kPa, 20 kPa and 40 kPa normal stresses. It is of interest to note that this dilatant behavior is associated with hardening shear stresshorizontal displacement behavior. This shear response is in contradiction with the typical shear response for typical coarsegrained geomaterial, where dilatant behavior is associated with strain-softening behavior and the peak shear strengths are attained at the maximum dilatancy ratio (slope of the relationship between vertical displacement and horizontal displacement). The shear response of foamed recycled glass is found to be similar to that of recycled glass cullets that has been used as aggregates in pavements and designated as having dilatancy associated strainhardening response (Arulrajah et al., 2014). The peak shear stresses are observed at very large horizontal displacements while the maximum dilatancy ratios for all the normal stresses are found at approximately the same horizontal displacement of 23 mm. The maximum dilatancy ratio and maximum displacement decrease as normal stress increases, which are similar to typical coarsegrained geomaterials. The increase in shear stress even after the maximum dilatancy ratio (strain hardening) is caused by the rearrangement of crushed particles (fine crushed particles are driven into the voids or pores) as also happened in CBR tests. The
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Fig. 2. Gradation curves for foamed recycled glass.
Fig. 3. CBR results for foamed recycled glass.
cohesion and fraction angle based on the MohreCoulumb failure criterion are 23.36 kPa and 54.7, respectively (refer to Fig. 5), which meet the shear strength property requirement for lightweight fill materials and consistent to that of a dense gravel material (Bowles, 1988; Sivakugan and Das, 2010). The high shear strength parameters with strain-hardening response indicate that this material is strong and ductile, which can resist large deformation. As such, this material has an advantage over the typical coarse-grained materials such as sand and gravel, where the strain softening (shear strength reduction) occurs after the maximum dilatancy, when used as a backfill on soft clay deposits in coastal regions; i.e, no strength reduction even with a large settlement of soft clay foundation. Table 1 compares the properties of foamed recycled glass with that of similar lightweight foamed materials. It is evident from Table 1, that the foamed recycled glass meets the requirements of similar lightweight foamed materials. The tests undertaken also indicate that foamed recycled glass would meet the long term requirements for a foamed recycled material. In consideration of the usage of foamed recycled glass in lightweight engineering applications (such as backfill, embankment fills, pavements and pipe bedding) environmental effects have to be ascertained to ensure that environmental contamination will not arise. Environmental
Fig. 4. DST results for foamed recycled glass.
testing will ascertain if the material is within established local requirements for usage as fill materials (EPA, 1999, 2010). Table 2 presents total concentration (TC) results for trace elements in foamed recycled glass and compares the values with allowable TC values for soil, waste materials and backfill materials reported from EPA Victoria requirements for backfill material (EPA Victoria, 2007). The TC trace element results imply that for all cases, the contaminant constituents for the recycled foamed glass are far below the threshold limits specified for these applications.
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Fig. 5. DST total stress failure envelopes for foamed recycled glass.
Table 2 Total concentration results for trace elements in foamed recycled glass compared to established requirements. Soil (Rahman Waste material Backfill material Contaminant Foamed (EPA, 2007) recycled glass et al., 2014b) (EPA, 2009) (mg/kg) (mg/kg) (mg/kg) (mg/kg) Arsenic Barium Chromium Copper Mercury Nickel Lead Selenium Vanadium Zinc
7 6 10 9 <0.05 8 28 <3 <5 <5
0.1e40 100e3000 5e1500 2e60 10e150 0.01e0.5 2e100 0.1e5 3e500 25e200
500 6250 500 5000 75 3000 1500 50 e 35000
20 e 1 100 1 60 e 10 e 200
Table 3 presents the leachate analysis data of the foamed recycled glass and compares it to the requirements for fill material, drinking water and hazardous waste. Based on the U.S. Environmental Protection Agency, a material is designated as hazardous if any metal is present in concentrations greater than 100 times that of the drinking water standards (Wartman et al., 2004). A comparison of the leaching results indicates that all metal contaminants are well within allowable limits for the usage of foamed recycled glass as a fill material. Only for lead and arsenic, the leachate concentration gets close to threshold defined by EPA Victoria for solid inert waste. But considering that the leachate values, reported in Table 3 for recycled foam glass, are extracted using more aggressive acidic and borate solutions compared to neutral pH water, it can be expected that in case of using this material in the field and event of rainfall or storm water, the concentration of heavy metals will be less than what reported in Table 3. This means
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that the material will not pose any risk to the ground water tables or water streams beyond what is commonly accepted for fill material and solid inert waste. From an engineering material perspective, the lightweight properties of the foamed recycled glass coupled with its satisfactory engineering and environmental results indicate the material is ideal for usage as a lightweight fill material. The foamed recycled glass is suitable for lightweight engineering applications such as non-structural fills in embankments, retaining wall backfill and pipe bedding. Fig. 6 presents a schematic and a water flow balance diagram for the usage of foamed recycled glass as a lightweight non-structural fill material in a typical application in a road embankment. Precipitation due to rainfall will hit the pavement surface layer, with some of it subsequently evaporating and the balance becoming run-off that will discharge down the slopes and into the drains provided at the bottom of the road embankment. Some infiltration will occur into the foamed recycled glass non-structural fill material and moisture movement will occur into the sides of the structural fill layer. Leachate will seep into the ground water table below, hence the necessity for the environmental testing analysis undertaken in this research. The TC trace element results indicated that for all cases the contaminant constituents for the foamed recycled glass were below the threshold limits specified for these applications. Based on the TC element and the engineering analysis, the recycled foamed glass is found to be suitable as a non-structural fill material for road embankments. The lightweight nature of foamed recycled glass may however render the material unsuitable for heavier applications such as pavement base/subbases for which much higher CBR values will be desired. As a structural fill in road embankments, the particle size distribution of the aggregates needs to be verified with local road authority specifications, as often the presence of fines and cohesion is highly desired for compaction, properties which the foamed recycled glass lacks. The energy savings for the use of foamed recycled glass as an engineering material is assessed from two aspects: (1) previous studies have shown the use of recycled glass as engineering material is able to save energy at 1 to 2 orders of magnitude, as compared to aggregate-cement (EPA, 2012; Nassar and Soroushian, 2013; Tsai, 2005); (2) embodied energy concept. Embodied energy is the total energy in joules that is attributed to bringing an item to its existing state (Soga et al., 2011). Embodied energy is closely related to the resource depletion and greenhouse gas emission. Hence, this parameter reflects the energy-efficiency and environmental effect of a material. Foamed recycled glass is a recycled waste material from industrial by-products and is not intentionally produced for construction. Hence, the embodied energy of foamed recycled glass is regarded as zero. In contrast, the embodied energy of conventional Portland cement additive is as high as 4.6 MJ/kg (Hammond and Jones, 2008). The total energy consumption related to the use of foamed recycled glass as construction material in
Table 3 Leachate analysis data for foamed recycled glass. Contaminant
ASLP: acet. (mg/L)
ASLP: Borate (mg/L)
Threshold for solid inert waste (EPA, 2009) (mg/L)
Drinking water standards (EPA, 1999) (mg/L)
Hazardous waste designation (Wartman et al., 2004) (mg/L)
Arsenic Barium Cadmium Chromium Lead Mercury Selenium Silver
0.22 0.09 0.05 0.09 0.42 <0.001 <0.01 <0.01
0.1 <0.1 <0.02 <0.1 <0.1 <0.01 <0.1 <0.1
0.35 35.0 0.1 2.5 0.5 0.05 0.5 5.0
0.05 2.0 0.005 0.1 0.015 0.002 0.05 0.05
5.0 100.0 1.0 5.0 5.0 0.2 1.0 5.0
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Fig. 6. Water flow balance chart for foamed glass as a non-structural fill in road embankments.
practice (e.g., non-structural fill in embankment, retaining wall backfill or pipe bedding) is therefore zero, whereas that of a conventional aggregate-cement material depends on the cement dosage and weight employed in any construction project.
needs to be verified with local road authority specifications, as often the presence of clay and silt fines is desired for compaction.
4. Conclusions
This research was supported under Australian Research Council's Linkage Projects funding scheme (project number LP120100107). This research was also supported by Australian Research Council's Linkage Infrastructure, Equipment and Facilities funding scheme (project number LE110100052). The fourth and fifth authors are grateful to the financial support from the Thailand Research Fund under the TRF Senior Research Scholar program Grant No. RTA5680002. The final author is grateful to the financial support from National Natural Science Foundation of China (Grant Nos. 51278100 and 41472258). The authors would like to thank Hamed Haghighi, PhD student at Swinburne University of Technology, for his assistance on this publication.
The particle size distribution curves indicate that the material comprises essentially gravel and sand sized particles and with no fines. The majority of the foamed recycled glass comprises 0.08e0.3 mm and 10e35 mm sized particles with no clay and silt fines present. The minimum and maximum dry density of the materials was low and with values typical of a lightweight construction material. From an engineering material perspective, the lightweight properties of the foamed recycled glass coupled with its satisfactory engineering and environmental results indicate the material is ideal for its usage as a lightweight fill material. The foamed recycled glass, given its desired high friction angle, is ideal for lightweight engineering applications such as non-structural fills in embankments, retaining wall backfill and pipe bedding. The material shows strain-hardening shear response, indicating ductile behavior. The environmental testing results imply that for all cases the contaminant constituents for the recycled foamed glass are below the threshold limits specified for these applications. However, as acid based leaching tests show Arsenic and Lead concentrations close to the EPA defined threshold (EPA, 2009) concentrations, it is recommended that prior to any practical applications of such recycled foamed glass, the samples should be tested for potential leaching of Arsenic and Lead. The energy saving assessment demonstrates that the use of foamed recycled glass as an engineering material in construction projects results in very low energy consumption as compared to the conventional aggregate-cement material. The lightweight nature of the material implies it is unsuitable for heavier loading applications such as pavement bases/subbases for which much higher CBR values and much lower LA abrasion values are desired. Foamed recycled glass may however be blended with higher quality aggregates to enable its usage as a supplementary additive in pavement subbases. As a structural fill in road embankments, the particle size distribution of the aggregates
Acknowledgements
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A. Arulrajah et al. / Journal of Cleaner Production 94 (2015) 369e375 AS, 2003. Soil Compaction and Density Tests e Determination of the Dry Density/ moisture Content Relation of a Soil Using Modified Compactive Effort. Australian Standard 1289.5.2.1. Australian Standard, Sydney, Australia. ASTM, 2006a. Standard Test Method for Resistance to Degradation of Small-size Coarse Aggregate by Abrasion and Impact in the Los Angeles Machine. ASTM Standard C131. ASTM International, West Conshohocken, PA. ASTM, 2006b. Standard Test Methods for Maximum Index Density and Unit Weight of Soils Using a Vibratory Table, D4253. ASTM International, West Conshohocken, USA. ASTM, 2007a. Standard Test Method for Density, Relative Density (Specific Gravity), and Absorption of Coarse Aggregate, ASTM C127. ASTM, West Conshohocken, PA, U.S.A. ASTM, 2007b. Standard Test Methods for Moisture, Ash, and Organic Matter of Peat and Other Organic Soils. ASTM Standard D2974. ASTM International, West Conshohocken, PA. ASTM, 2011. Standard Test Method for Direct Shear Test of Soils under Consolidated Drained Conditions. ASTM D3080/D3080M. ASTM International, West Conshohocken, PA, USA. Athanasopoulos-Zekkos, A., Lamote, K., Athanasopoulos, G.A., 2012. Use of EPS geofoam compressible inclusions for reducing the earthquake effects on yielding earth retaining structures. Soil Dyn. Earthq. Eng. 41, 59e71. Bowles, E.J., 1988. Foundation Analysis and Design, fourth ed. McGraw-Hill, Singapore. Bumanis, G., Bajare, D., Locs, J., Korjakins, A., 2013. Alkali-silica reactivity of foam glass granules in structure of lightweight concrete. Constr. Build. Mater. 47, 274e281. Cecich, V., Gonzales, L., Hoisaeter, A., Williams, J., Reddy, K., 1996. Use of shredded tires as lightweight backfill material for retaining structures. Waste Manag. Res. 14, 433e451. Chindaprasirt, P., Rattanasak, U., 2011. Shrinkage behavior of structural foam lightweight concrete containing glycol compounds and fly ash. Mater. Des. 32, 723e727. Deng, A., Xiao, Y., 2010. Measuring and modeling proportion-dependent stressstrain behavior of EPS-sand mixture. Int. J. Geomech. 10, 214e222. Disfani, M.M., Arulrajah, A., Haghighi, H., Mohammadinia, A., Horpibulsuk, S., 2014. Flexural beam fatigue strength evaluation of crushed brick as a supplementary material in cement stabilized recycled concrete aggregates. Constr. Build. Mater. 68, 667e676. Du, Y.J., Jiang, N.J., Liu, S.Y., Jin, F., Singh, D.N., Puppala, A.J., 2014. Engineering properties and microstructural characteristics of cement-stabilized zinccontaminated kaolin. Can. Geotech. J. 51, 289e302. EPA, 1999. National Primary Drinking Water Standards. EPA-F-94-001. Environment Protection Agency, Washington, USA. EPA, 2007. Information Update for EPA 996. Environmental Protection Agency of Victoria, Australia, Victoria, Australia. EPA, 2009. Solid Solid Industrial Waste Hazard Categorization and Management, Industrial Waste Resource Guidelines. Publication No. IWRG 631. Environmental Protection Agency of Victoria, Australia, Victoria, Australia. EPA, 2010. Waste Categorisation Industrial Waste Resource Guidelines. Environmental Protection Agency of Victoria, Australia, Victoria, Australia. EPA, U., 2012. Methodology for Estimating MSW Recycling Benefits. Washington DC. Ertugrul, O.L., Trandafir, A.C., 2011. Reduction of lateral earth forces acting on rigid nonyielding retaining Walls by EPS geofoam inclusions. J. Mater. Civ. Eng. 23, 1711e1718. Fernandes, H.R., Tulyaganov, D.U., Ferreira, J.M.F., 2009. Production and characterisation of glass ceramic foams from recycled raw materials. Adv. Appl. Ceram. 108, 9e13. Grubb, D.G., Gallagher, P.M., Wartman, J., Liu III, Y., Carnivale, M., 2006. Laboratory evaluation of crushed glassedredged material blends. J. Geotech. Geoenviron. Eng. ASCE 132, 562e576. Guo, H.W., Mo, Z.X., Liu, P., Gao, D.N., 2013. Improved Mechanical Property of Foam Glass Composites Toughened by Mullite Fiber, pp. 1370e1373. Hammond, G.P., Jones, C.I., 2008. Inventory of (Embodied) Carbon and Energy. Department of Mechanical Engineering, 1.6a ed. University of Bath, Bath, United Kingdom. Harmon, K., 2014. Engineering Properties of Structural Lightweight Concrete. http:// www.stalite.com/uploads/EngineeringProperties.pdf (accessed 23.10.14.). Hodgson, I.F., Beales, S.P., Curd, M.J., 2012. Use of Tyre Bales as Lightweight Fill for the A421 Improvements Scheme Near Bedford, UK, pp. 101e108. Horpibulsuk, S., Wijitchot, A., Nerimitknornburee, A., Shen, S.L., Suksiripattanapong, C., 2014. Factors influencing unit weight and strength of lightweight cemented clay. Q. J. Eng. Geol. Hydrogeol. 47, 101e109. Hoyos, L.R., Puppala, A.J., Ordonez, C.A., 2011. Characterization of cement fibertreated reclaimed asphalt pavement aggregates: preliminary investigation. J. Mater. Civ. Eng. ASCE 23, 977e989.
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Contents lists available at ScienceDirect
Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Engineering and environmental properties of foamed recycled glass as a lightweight engineering material Arul Arulrajah a, *, Mahdi M. Disfani b, Farshid Maghoolpilehrood a, Suksun Horpibulsuk c, **, Artit Udonchai c, Monzur Imteaz a, Yan-Jun Du d a
Swinburne University of Technology, Melbourne, Victoria 3122, Australia The University of Melbourne, Melbourne, Victoria 3010, Australia Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand d Southeast University, Nanjing 210096, China b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 March 2014 Received in revised form 21 January 2015 Accepted 26 January 2015 Available online 3 February 2015
Lightweight fill materials, including foamed aggregates are increasingly being used in civil engineering and infrastructure applications. This research assessed the engineering properties of foamed recycled glass through a laboratory evaluation to ascertain this novel recycled material as a lightweight fill material in civil engineering applications. The engineering assessment included particle size distribution, particle density, water absorption, minimum and maximum dry densities with a vibrating table, California Bearing Ratio (CBR) and Los Angeles (LA) abrasion tests. Shear strength properties of the recycled foamed glass were studied through large-scale direct shear tests. This recycled foamed glass is classified as a gap graded material. Due to high porosity, the coarse particles of this material have high water absorption of 60% and low particle density of 4.54 kN/m3, which is much lower than that of water. The minimum and maximum dry densities of this material are very low of 1.67 and 2.84 kN/m3, respectively. The LA abrasion of foamed recycled glass is lower than the requirement for pavement base/subbase material, being of 94%. The shear resistance at small shear displacement is thus low as shown by low CBR value of 9e12%. However, the shear resistance at large shear displacement is high as shown by high cohesion and friction angle of 23.36 kPa and 54.7, respectively. The environmental assessment included pH value, organic content, total and leachate concentration of the material for a range of contaminant constituents. All the hazardous concentrations in the leachate are far lower than 100 times of those of the drinking water standards, indicating the foamed recycled glass as a non-hazardous material. The energy savings assessment demonstrates that the use of foamed recycled glass as engineering material has much lower energy consumption relative to a conventional aggregate-cement material in construction projects. The lightweight properties of the foamed recycled glass coupled with its satisfactory engineering and environmental results, particularly its high friction angle, indicates that the material is ideal for usage as a lightweight construction material in engineering applications such as non-structural fills in embankments, retaining wall backfill and pipe bedding. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Lightweight material Embankment fill Foam glass Waste materials
1. Introduction
* Corresponding author. Faculty of Engineering (H38), Swinburne University of Technology, PO Box 218, Hawthorn, VIC 3122, Australia. Tel.: þ61 3 92145741; fax: þ61 3 92148264. ** Corresponding author. School of Engineering, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand. E-mail addresses: [email protected] (A. Arulrajah), [email protected] (S. Horpibulsuk). http://dx.doi.org/10.1016/j.jclepro.2015.01.080 0959-6526/© 2015 Elsevier Ltd. All rights reserved.
Lightweight fill materials are increasingly being used in civil engineering applications such as backfill, slope stability, embankment fills, pavements and pipe bedding (Horpibulsuk et al., 2014). The applications of lightweight fill materials are fairly broad but the main intent of this alternative construction material is to significantly reduce the weight of fills, thereby mitigating excessive settlements and bearing failures. This can subsequently result in more economic designs for structures such as retaining walls. Various lightweight fill materials have been developed in recent years for
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usage in various civil engineering applications and these particularly include expanded polystyrene (Athanasopoulos-Zekkos et al., 2012; Deng and Xiao, 2010; Ertugrul and Trandafir, 2011; Lin et al., 2010; Trandafir and Erickson, 2012; Zou et al., 2013), lightweight cellular cemented clays (Horpibulsuk et al., 2014), tires (Cecich et al., 1996; Hodgson et al., 2012; Moghaddas Tafreshi et al., 2012; Nakhaei et al., 2012) and lightweight concrete (Chindaprasirt and Rattanasak, 2011; Wang et al., 2012; Wang and Tang, 2012). With the aim of increase in usage of recycled foamed glass for a cleaner production of lightweight materials as well as a greener and more sustainable environment, this study investigates suitability of recycled foam glass for various engineering applications. In recent years, there has been an environmental push worldwide to continually seek new reuse applications for various waste materials inclusive of demolition wastes (Arulrajah et al., 2013b; Rahman et al., 2014a), municipal solid wastes (Reddy et al., 2009; Zekkos et al., 2006), calcium carbide residue (Phetchuay et al., 2014) and other commercial and industrial wastes (Disfani et al., 2014; Du et al., 2014; Grubb et al., 2006; Landris, 2007; Wartman et al., 2004). Industrial waste materials are increasingly being implemented in various projects for use as an aggregate in applications such as pavements (Akbulut and Gurer, 2007; Hoyos et al., 2011; Puppala et al., 2011; Taha et al., 2002) and road embankments (Puppala et al., 2011; Wartman et al., 2004). Municipal recycled glass is obtained mostly from curbside collection and comprises mainly packaging containers for food and drinks as well as sheet glass or glass from demolition activities. While the glass recycling industry aims to process waste glass back into bottle making industry by color sorting, this is not always possible because a large amount of waste glass delivered to the recycling industry is broken into small pieces during handling and collecting, which makes it difficult to color sort waste glass. Sorting facilities in Australia for example can only color sort recycled glass particles that are larger than 10 mm in particle size and smaller sized glass particles, enter the waste stream (Arulrajah et al., 2014a). Recycled waste glass has been researched in recent years and found to be a viable construction material for embankments and pavement subbases (Arulrajah et al., 2014b; Grubb et al., 2006; Wartman et al., 2004), footpath bases (Arulrajah et al., 2013a) as well as in the manufacture of fibers for problematic soil treatment (Ahmad et al., 2012; Mujah et al., 2013). In recent years, there has been interest in the development of foamed materials with the usage of waste materials in engineering applications (Jana et al., 2013; Wang et al., 2012, 2013a). Foamed glass has been developed particularly for usage in various structural and insulating applications (Bumanis et al., 2013; Guo et al., 2013; Kazantseva, 2013; Pawanawichian et al., 2013; Ponsot and Bernardo, 2013; Wang et al., 2013b; Wu et al., 2013). The usage of recycled glass to manufacture foamed glass is however still in its infancy, with limited works to date in this area apart from some work with the production of ceramics (Fernandes et al., 2009; Ponsot and Bernardo, 2013) and with no known work having been undertaken on its usage as a lightweight aggregate construction material. The usage of recycled products results in significantly less energy production as well as limits the opening of new quarries for virgin quarry products. To achieve sustainability various industries and end-users seek a cleaner production usage for waste materials and view recycled materials as a resource rather than a waste material destined for landfills. The focus of this research is to assess the engineering properties of foamed recycled glass through a laboratory evaluation and to ascertain this novel recycled material as a suitable lightweight fill material in civil engineering applications. An extensive suite of engineering and environmental tests, as well as energy savings assessments were undertaken on foamed recycled glass to assess its engineering properties.
2. Materials and methods The municipal waste glass, obtained from a glass recycling operator site, was first ground and then fired with mineral additives in a furnace at temperatures up to 950 C. The recycled glass foams and is then removed from the furnace at which point it cools down quickly forming low weight foamed recycled glass aggregates of up to 40 mm in size. The foamed material comprises 98% ground recycled glass and 2% mineral additives. Foamed recycled glass for this research was obtained from a supplier in Melbourne, Australia. Fig. 1 shows foamed recycled glass aggregates after production. It is evident from Fig. 1 that the glass aggregates comprise vesiculars, due to the presence of air that forms small voids during the production process. Particle size analysis was undertaken by the Australian standards (AS, 1996). Particle density and water absorption tests of coarse aggregate (retained on a 4.75 mm sieve) and fine aggregate (passing through a 4.75 mm sieve) were both undertaken (ASTM, 2007a). Maximum and minimum dry densities were undertaken using the vibratory table method, which was suitable for this material as it was cohesionless and free-draining (ASTM, 2006b). The pH value of the foamed glass was determined following the Australian standards (AS, 1997a). Organic content tests were performed by the loss of ignition method to determine the organic content of the samples (ASTM, 2007b). CBR tests under standard compaction effort were carried out on specimens in dry and soaked conditions to simulate the worst-case scenario (AS, 2003). LA abrasion test was conducted to determine the abrasion loss of the material and to ascertain if the material could be considered for higher loading applications such as pavement base/subbase applications (ASTM, 2006a). A large-scale Direct Shear Test (DST) apparatus measuring 305 mm in length, 305 mm in width and 204 mm in depth was used to determine the shear strength of the foamed recycled glass, due to the large sizes of the aggregates. The tests were conducted as per ASTM D3080/D3080M standards (ASTM, 2011). The testing apparatus has two boxes: a fixed upper box and a moveable lower box. Initially, the lower and upper boxes were clamped when preparing samples for the tests. The samples were compacted in the shear box in three layers by using hand tamping with a plastic hammer to attain maximum dry density obtained from the vibratory table method. The samples were then submerged for 12 h before consolidation with three normal stress levels of 10 kPa, 20 kPa and 40 kPa. When the consolidation stage for the tests was completed, the connections between the lower and upper boxes was released, which provided an approximate 2 mm gap between the upper and
Fig. 1. Foamed recycled glass after production (courtesy of the Geotechnical laboratory at Swinburne University of Technology, Australia).
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lower boxes for friction minimization. The shearing stage of the test was next conducted under normal stress levels of 10 kPa, 20 kPa and 40 kPa. A shear displacement rate of 0.025 mm/min was maintained throughout the shearing stage. The horizontal displacements, vertical displacements and shear stresses were recorded. The tests were terminated once the horizontal shear displacement reached approximately 75 mm. The room temperature was maintained at 20 ± 1 C. The shear strength of the foamed recycled glass from the DST tests was obtained from the shear stress and horizontal displacement output graphs. The hazard category of foamed recycled glass was determined based on the Environmental Protection Authority (EPA) Victoria and Australian Standard Leaching Procedure (ASLP). If the Total Concentration (TC) is less than the specified limit, or if it can be demonstrated to be of natural origin, the foamed recycled glass is categorized as suitable for fill materials (EPA, 2010). The environmental properties of the foamed recycled glass were tested for different types of heavy metals by following the Australian standards protocol (AS, 1997b) for the preparation of leachate, using slightly acidic leaching fluid (pH ¼ 5) and alkaline leaching fluid (pH ¼ 9.2) leaching buffers. 3. Results and discussions The engineering properties of the laboratory evaluation of the foamed recycled glass are summarized in Table 1. Fig. 2 presents the
Table 1 Engineering properties of foamed recycled glass. Engineering parameters
Foamed recycled glass
Typical lightweight materiala
Typical heavyweight materialb
D10 (mm) D30 (mm) D50 (mm) D60 (mm) Cu Cc Gravel sized particles: 4.75 mme40 mm (%) Sand sized particles: 0.075 mme4.75 mm (%) Clay and Silt sized particles: <0.075 mm (%) Particle density e coarse fraction (kg/m3) Particle density e fine fraction (kg/m3) Minimum dry density (kg/m3) Maximum dry density (kg/m3) Water absorption e coarse fraction (%) Water absorption e fine fraction (%) pH Organic content (%) CBR (%) LA abrasion loss (%) DST: Peak apparent cohesion, c' (kPa) DST: Peak friction angle, f' (degrees) DST: Critical state apparent cohesion, c' (kPa) DST: Critical state friction angle, f' (degrees)
0.13 1.2 18.7 20.6 158 0.53 66
e e e e e e <70
0.09 1.30 4.40 6.70 78.83 2.97 47.9
32
<40
42.2
2
<3
9.90
462.8
408e1529
2600e2700
1508
408e1529
2400e2600
170
112e204
290
204e306
2080
60
50e60
6.50e6.70
0.3
<1.0
6.50e7.50
10.48 0 9e12 94 23.4
9e12 0 2e10 80e100 20e100
10.20e11.40 1.7e2.1 172 29.9e31.7 95
55.7
35e60
65
22.1
20e100
80
54.7
35e60
39
a b
Harmon (2014) and Misapor (2014). Rahman et al. (2014a, 2014b).
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particle size distribution curves of the foamed recycled glass. The particle size distribution curves indicate that the material comprises essentially gravel and sand sized particles with no fines. Based on gradation curve (Fig. 2), coefficient of uniformity (Cu) and coefficient of curvature (Cc), this material is classified as poorly and gap grained, with two major grain size ranges: 0.08e0.3 mm and 10e35 mm. As no fines are present, Atterberg limit tests are not applicable for this material. The minimum and maximum dry density of the materials was low and with values typical of a lightweight construction material. The particle density of the coarse foamed recycled glass was found to be very low (4.54e14.79 kN/m3), lower than the density of water. The fine particle density of foamed glass was almost three times higher than the coarse particle density. The water absorption of fine particles was almost low while the coarse particle water absorption was high at 60%. pH value for the foamed glass was found to be in the alkali range, similar to that for typical construction and demolition aggregates (Arulrajah et al., 2013b). Organic materials are not present, likely due to the high temperatures used in the foamed glass process. Fig. 3 presents the CBR results for the foamed recycled glass. The CBR test results for the foamed recycled glass were within the local road authority specification requirements for a structural fill material in road embankments, which is typically specified within the range of 2%e5% (VicRoads, 2011). It is of interest to note that the load and penetration relationship of this material is not typical of coarse-grained geomaterials. This material exhibits peak and ultimate loads when subjected to penetration. The load increases with increasing penetration until the peak value. After a small decrease in load, the load again increases with increasing penetration to the ultimate value. The result implies that particle crushing occurs at peak state and then rearrangement of crushed particles contributes the ultimate strength. The material crushing is due to a low particle strength as indicated by the high LA abrasion value of 94%. A maximum LA abrasion value not exceeding 40% is typically specified for pavement base/subbase applications. The LA abrasion and CBR results indicate that the material is unsuitable for heavier duty applications such as in pavement base/subbases. LA Abrasion results also indicate the susceptibility of the material to crushing under repeated loading, which makes it unsuitable for application involving dynamic loads. Fig. 4 presents the DST results for the foamed recycled glass. The material shows completely dilatant behavior in vertical displacement and horizontal displacement relationship at 10 kPa, 20 kPa and 40 kPa normal stresses. It is of interest to note that this dilatant behavior is associated with hardening shear stresshorizontal displacement behavior. This shear response is in contradiction with the typical shear response for typical coarsegrained geomaterial, where dilatant behavior is associated with strain-softening behavior and the peak shear strengths are attained at the maximum dilatancy ratio (slope of the relationship between vertical displacement and horizontal displacement). The shear response of foamed recycled glass is found to be similar to that of recycled glass cullets that has been used as aggregates in pavements and designated as having dilatancy associated strainhardening response (Arulrajah et al., 2014). The peak shear stresses are observed at very large horizontal displacements while the maximum dilatancy ratios for all the normal stresses are found at approximately the same horizontal displacement of 23 mm. The maximum dilatancy ratio and maximum displacement decrease as normal stress increases, which are similar to typical coarsegrained geomaterials. The increase in shear stress even after the maximum dilatancy ratio (strain hardening) is caused by the rearrangement of crushed particles (fine crushed particles are driven into the voids or pores) as also happened in CBR tests. The
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Fig. 2. Gradation curves for foamed recycled glass.
Fig. 3. CBR results for foamed recycled glass.
cohesion and fraction angle based on the MohreCoulumb failure criterion are 23.36 kPa and 54.7, respectively (refer to Fig. 5), which meet the shear strength property requirement for lightweight fill materials and consistent to that of a dense gravel material (Bowles, 1988; Sivakugan and Das, 2010). The high shear strength parameters with strain-hardening response indicate that this material is strong and ductile, which can resist large deformation. As such, this material has an advantage over the typical coarse-grained materials such as sand and gravel, where the strain softening (shear strength reduction) occurs after the maximum dilatancy, when used as a backfill on soft clay deposits in coastal regions; i.e, no strength reduction even with a large settlement of soft clay foundation. Table 1 compares the properties of foamed recycled glass with that of similar lightweight foamed materials. It is evident from Table 1, that the foamed recycled glass meets the requirements of similar lightweight foamed materials. The tests undertaken also indicate that foamed recycled glass would meet the long term requirements for a foamed recycled material. In consideration of the usage of foamed recycled glass in lightweight engineering applications (such as backfill, embankment fills, pavements and pipe bedding) environmental effects have to be ascertained to ensure that environmental contamination will not arise. Environmental
Fig. 4. DST results for foamed recycled glass.
testing will ascertain if the material is within established local requirements for usage as fill materials (EPA, 1999, 2010). Table 2 presents total concentration (TC) results for trace elements in foamed recycled glass and compares the values with allowable TC values for soil, waste materials and backfill materials reported from EPA Victoria requirements for backfill material (EPA Victoria, 2007). The TC trace element results imply that for all cases, the contaminant constituents for the recycled foamed glass are far below the threshold limits specified for these applications.
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Fig. 5. DST total stress failure envelopes for foamed recycled glass.
Table 2 Total concentration results for trace elements in foamed recycled glass compared to established requirements. Soil (Rahman Waste material Backfill material Contaminant Foamed (EPA, 2007) recycled glass et al., 2014b) (EPA, 2009) (mg/kg) (mg/kg) (mg/kg) (mg/kg) Arsenic Barium Chromium Copper Mercury Nickel Lead Selenium Vanadium Zinc
7 6 10 9 <0.05 8 28 <3 <5 <5
0.1e40 100e3000 5e1500 2e60 10e150 0.01e0.5 2e100 0.1e5 3e500 25e200
500 6250 500 5000 75 3000 1500 50 e 35000
20 e 1 100 1 60 e 10 e 200
Table 3 presents the leachate analysis data of the foamed recycled glass and compares it to the requirements for fill material, drinking water and hazardous waste. Based on the U.S. Environmental Protection Agency, a material is designated as hazardous if any metal is present in concentrations greater than 100 times that of the drinking water standards (Wartman et al., 2004). A comparison of the leaching results indicates that all metal contaminants are well within allowable limits for the usage of foamed recycled glass as a fill material. Only for lead and arsenic, the leachate concentration gets close to threshold defined by EPA Victoria for solid inert waste. But considering that the leachate values, reported in Table 3 for recycled foam glass, are extracted using more aggressive acidic and borate solutions compared to neutral pH water, it can be expected that in case of using this material in the field and event of rainfall or storm water, the concentration of heavy metals will be less than what reported in Table 3. This means
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that the material will not pose any risk to the ground water tables or water streams beyond what is commonly accepted for fill material and solid inert waste. From an engineering material perspective, the lightweight properties of the foamed recycled glass coupled with its satisfactory engineering and environmental results indicate the material is ideal for usage as a lightweight fill material. The foamed recycled glass is suitable for lightweight engineering applications such as non-structural fills in embankments, retaining wall backfill and pipe bedding. Fig. 6 presents a schematic and a water flow balance diagram for the usage of foamed recycled glass as a lightweight non-structural fill material in a typical application in a road embankment. Precipitation due to rainfall will hit the pavement surface layer, with some of it subsequently evaporating and the balance becoming run-off that will discharge down the slopes and into the drains provided at the bottom of the road embankment. Some infiltration will occur into the foamed recycled glass non-structural fill material and moisture movement will occur into the sides of the structural fill layer. Leachate will seep into the ground water table below, hence the necessity for the environmental testing analysis undertaken in this research. The TC trace element results indicated that for all cases the contaminant constituents for the foamed recycled glass were below the threshold limits specified for these applications. Based on the TC element and the engineering analysis, the recycled foamed glass is found to be suitable as a non-structural fill material for road embankments. The lightweight nature of foamed recycled glass may however render the material unsuitable for heavier applications such as pavement base/subbases for which much higher CBR values will be desired. As a structural fill in road embankments, the particle size distribution of the aggregates needs to be verified with local road authority specifications, as often the presence of fines and cohesion is highly desired for compaction, properties which the foamed recycled glass lacks. The energy savings for the use of foamed recycled glass as an engineering material is assessed from two aspects: (1) previous studies have shown the use of recycled glass as engineering material is able to save energy at 1 to 2 orders of magnitude, as compared to aggregate-cement (EPA, 2012; Nassar and Soroushian, 2013; Tsai, 2005); (2) embodied energy concept. Embodied energy is the total energy in joules that is attributed to bringing an item to its existing state (Soga et al., 2011). Embodied energy is closely related to the resource depletion and greenhouse gas emission. Hence, this parameter reflects the energy-efficiency and environmental effect of a material. Foamed recycled glass is a recycled waste material from industrial by-products and is not intentionally produced for construction. Hence, the embodied energy of foamed recycled glass is regarded as zero. In contrast, the embodied energy of conventional Portland cement additive is as high as 4.6 MJ/kg (Hammond and Jones, 2008). The total energy consumption related to the use of foamed recycled glass as construction material in
Table 3 Leachate analysis data for foamed recycled glass. Contaminant
ASLP: acet. (mg/L)
ASLP: Borate (mg/L)
Threshold for solid inert waste (EPA, 2009) (mg/L)
Drinking water standards (EPA, 1999) (mg/L)
Hazardous waste designation (Wartman et al., 2004) (mg/L)
Arsenic Barium Cadmium Chromium Lead Mercury Selenium Silver
0.22 0.09 0.05 0.09 0.42 <0.001 <0.01 <0.01
0.1 <0.1 <0.02 <0.1 <0.1 <0.01 <0.1 <0.1
0.35 35.0 0.1 2.5 0.5 0.05 0.5 5.0
0.05 2.0 0.005 0.1 0.015 0.002 0.05 0.05
5.0 100.0 1.0 5.0 5.0 0.2 1.0 5.0
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Fig. 6. Water flow balance chart for foamed glass as a non-structural fill in road embankments.
practice (e.g., non-structural fill in embankment, retaining wall backfill or pipe bedding) is therefore zero, whereas that of a conventional aggregate-cement material depends on the cement dosage and weight employed in any construction project.
needs to be verified with local road authority specifications, as often the presence of clay and silt fines is desired for compaction.
4. Conclusions
This research was supported under Australian Research Council's Linkage Projects funding scheme (project number LP120100107). This research was also supported by Australian Research Council's Linkage Infrastructure, Equipment and Facilities funding scheme (project number LE110100052). The fourth and fifth authors are grateful to the financial support from the Thailand Research Fund under the TRF Senior Research Scholar program Grant No. RTA5680002. The final author is grateful to the financial support from National Natural Science Foundation of China (Grant Nos. 51278100 and 41472258). The authors would like to thank Hamed Haghighi, PhD student at Swinburne University of Technology, for his assistance on this publication.
The particle size distribution curves indicate that the material comprises essentially gravel and sand sized particles and with no fines. The majority of the foamed recycled glass comprises 0.08e0.3 mm and 10e35 mm sized particles with no clay and silt fines present. The minimum and maximum dry density of the materials was low and with values typical of a lightweight construction material. From an engineering material perspective, the lightweight properties of the foamed recycled glass coupled with its satisfactory engineering and environmental results indicate the material is ideal for its usage as a lightweight fill material. The foamed recycled glass, given its desired high friction angle, is ideal for lightweight engineering applications such as non-structural fills in embankments, retaining wall backfill and pipe bedding. The material shows strain-hardening shear response, indicating ductile behavior. The environmental testing results imply that for all cases the contaminant constituents for the recycled foamed glass are below the threshold limits specified for these applications. However, as acid based leaching tests show Arsenic and Lead concentrations close to the EPA defined threshold (EPA, 2009) concentrations, it is recommended that prior to any practical applications of such recycled foamed glass, the samples should be tested for potential leaching of Arsenic and Lead. The energy saving assessment demonstrates that the use of foamed recycled glass as an engineering material in construction projects results in very low energy consumption as compared to the conventional aggregate-cement material. The lightweight nature of the material implies it is unsuitable for heavier loading applications such as pavement bases/subbases for which much higher CBR values and much lower LA abrasion values are desired. Foamed recycled glass may however be blended with higher quality aggregates to enable its usage as a supplementary additive in pavement subbases. As a structural fill in road embankments, the particle size distribution of the aggregates
Acknowledgements
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