Recovered plastic and demolition waste blends as railway capping materials

Transportation Geotechnics 22 (2020) 100320

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Recovered plastic and demolition waste blends as railway capping materials a,⁎

a

a

Arul Arulrajah , Mahdi Naeini , Alireza Mohammadinia , Suksun Horpibulsuk Melvyn Leongc

b,⁎

T

,

a

Department of Civil and Construction Engineering, Swinburne University of Technology, Melbourne, Australia School of Civil Engineering and Center of Excellence in Innovation for Sustainable Infrastructure Development, Suranaree University of Technology, Nakhon Ratchasima, Thailand c Geofrontiers Group Pty Ltd., Melbourne, Australia b

A R T I C LE I N FO

A B S T R A C T

Keywords: Recovered plastic Demolition waste Recycling Railway

The sustainable utilization of plastic and demolition waste as an alternative civil construction material has garnered increasing interest in recent years. Usage of these sustainable recycled products in the civil construction industry will reduce the demand for quarry materials, costs associated with landfilling as well as reducing the carbon footprint of future infrastructure projects. This study is focused on the usage of recovered plastic (RP) blends with demolition aggregates, namely recycled concrete aggregates (RCA) and crushed brick (CB) as railway capping materials. RP used in this research is the mixture of various types of waste plastics, which neither can be separated nor recycled into new products. The influence of RP inclusion in RCA and CB was evaluated based on tests that incorporated the evaluation of particle breakage, compressibility behavior, stiffness and strength parameters of the blends. Resilient modulus, (Mr) of the recycled products was determined based on a proposed Repeated Load Triaxial (RLT) testing protocol, based on the range of relevant applied stresses to capping materials. Two types of conventional capping materials (CCMs) currently used as railway capping materials were also evaluated under similar testing conditions. The responses of the blends were evaluated against the range of results of CCMs to determine the optimum percentage of RP. It was determined that the inclusion of waste plastic in demolition aggregates could enhance the degradation resistance and energy absorption characteristics of blends. Inclusion of RP with 5% in RCA and 3% in CB was found to be the optimum blend, which furthermore was found to enhance the energy-absorbing capacity of this alternative recycled railway capping layer product.

Introduction

globally, being around 12% of total municipal solid waste [2]. In Australia, around 2.5 million tonnes of plastic waste was produced, only 12% of which was recycled, while almost all the rest was landfilled [3]. This is the lowest recovery rate among the key materials category of Australia [3]. Factors like population growth, ease of production, durability and wide range of applications have exacerbated the increase in plastic waste generation [4]. Limitations in the reuse potential for waste plastics in the reproduction of new materials and increased production of plastic signify the importance of finding sustainable alternative solutions for redirecting these waste materials from landfills. In recent years, limited studies have been conducted on the application of plastic waste in civil engineering projects, particularly in road construction. For example, Arulrajah, et al. [5] evaluated the stiffness and strength of blends of construction and demolition (C&D) aggregates

The sustainable construction of civil engineering infrastructures using recycled materials has been identified as a successful waste mitigation strategies worldwide. The reuse of recycled waste materials in civil infrastructure projects has garnered significant interest in recent years, as a sustainable alternative material to natural resources. Other advantages of this sustainability approach include reducing the high costs of landfilling, reduced demand for quarry materials as well as a significant reduction of the carbon footprint of infrastructure projects [1]. Solutions for the waste mitigation of non-biodegradable materials such as plastic waste has generated significant interest worldwide in recent years. In 2016 more than 240 million tonnes of plastic waste was produced

⁎

Corresponding authors at: Swinburne University of Technology, PO Box 218, Hawthorn, Victoria 3122, Australia (A. Arulrajah). School of Civil Engineering, and Center of Innovation in Sustainable Infrastructure Development, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand (S. Horpibulsuk). E-mail addresses: [email protected] (A. Arulrajah), [email protected] (M. Naeini), [email protected] (A. Mohammadinia), [email protected] (S. Horpibulsuk). https://doi.org/10.1016/j.trgeo.2020.100320 Received 26 November 2019; Received in revised form 7 January 2020; Accepted 10 January 2020 Available online 16 January 2020 2214-3912/ © 2020 Elsevier Ltd. All rights reserved.

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blended with polyethylene granules as the road base/subbase layer. Choudhary, et al. [6] examined the possibility of reinforcing subgrade soil with waste plastic strips. Implementation of waste plastic in concrete, asphalt and bitumen in pavement construction has also been reported [7]. Many studies have been looking at utilization of recycled materials including C&D materials as a sustainable replacement for quarry aggregates to reduce the stress on depletion of natural resources in different applications such as retaining walls, geosynthetic reinforced structures, and shallow and deep soil improvement [1,8–14]. C&D materials are increasingly being used as alternative materials to virgin quarry materials in road construction [1,15]. Extensive research on the geotechnical characteristics of recycled concrete aggregates (RCA) and crushed brick (CB) have been conducted to evaluate their performance for pavement construction projects [5,16,17]. C&D materials, when used appropriately are able to comply with the specified requirements for road base/subbase materials. However, limited studies have been undertaken to evaluate the behavior of these C&D materials in railway track substructures. Typical ballasted railway track substructure, in many countries including Australia, consists of a ballast, capping layer (also known as subballast) and subgrade. The main function of the capping layer is to reduce the induced cyclic stress of train to the maximum allowable stress at the top of subgrade [18]. The capping layer material should provide sufficient stability to the substructure and minimize undesirable deformations of the subgrade. The resilient modulus (Mr) and thickness of this layer have been identified as an influential factor affecting overall substructure stability and are important parameters for accurate determination of induced stresses in subgrade [19–22]. Recently, alternative materials have been evaluated as railway capping layer materials, to enhance the track performance. Signes, et al. [23] studied the possibility of using shredded waste tire rubber in coarse aggregates. Indraratna, et al. [24] and Qi, et al. [25] examined the effect of rubber crumb on the behavior of steel furnace slag and coal wash blends. In another study, the effect of rubber crumb on compaction characteristics of coal wash as the capping layer was evaluated [26]. Blends of waste plastic with C&D aggregates can provide an alternative energy-absorbing matrix with lower particle breakage to that of parent aggregates. Additionally, although many studies have focused only on one or two types of plastic in civil engineering construction [7], this study is particularly focused on recovered plastic (RP). RP is a mixture of different types of waste plastic, which neither can be separated nor further processed into other products. Inclusion of RP in civil engineering projects can minimize the recycling operations for separating or reshaping them which significantly reduces the cost and energy consumption of producing the final blend. In this study, the effect of RP on the behavior of C&D aggregates, namely RCA and CB as an alternative sustainable capping layer was evaluated. Performance of RCA/RP and CB/RP blends were compared with the range of results of two different control conventional capping materials (CCMs) under the same testing conditions. The CCMs were sourced from natural quarries of railway construction projects in Australia. After determining basic geotechnical engineering properties, the effect of RP inclusion on the particle breakage of C&D blends was evaluated. The compressibility behavior of both RCA/RP and CB/RP blends was determined at the k0-loading condition. A repeated load triaxial (RLT) testing protocol was proposed based on the combination of applied cyclic stresses in capping layer to determine the resilient response of materials. The quick shear test was also conducted to characterize the maximum shear strength of materials and influence of RP on the energy absorption capacity of the matrix under monotonic loading.

CB

RCA

RP

Fig. 1. Recycled materials used in this study.

were collected from a recycling plant in the state of Victoria, Australia. Geotechnical characteristics of C&D materials and blends were compared with the range of results obtained from the two CCMs as control materials. The two CCMs were sourced from the available natural quarries of railway construction projects in Victoria and New South Wales. All the aggregates had a maximum particle size of 20 mm. RP as supplementary material was also obtained from a recycling facility in Victoria, having the maximum particle size of 9.5 mm. The physical appearance of the recycled materials is shown in Fig. 1. RP was blended with C&D aggregates in percentages of 3, 5, and 7% in RCA and 3 and 5% in CB by weight. These percentages were initially selected based on previous studies on stiffness and strength of recycled plastic blends with C&D aggregates [5]. The materials and blends studied in this research are presented in Table 1. A series of comprehensive laboratory experiments were undertaken on the C&D aggregates and their blends with RP. Their performance was compared with the CCMs under the same testing condition, to determine the performance of the C&D/RP blends in railway capping layer construction. Basic geotechnical tests include particle size distribution (PSD) [27], flakiness index [28], particle density and water absorption for aggregates [29,30], specific gravity for RP [31] using distilled air-free water following [32], standard Proctor compaction for determining the maximum dry density (MDD) and optimum moisture content (OMC) [33], Los Angeles abrasion [34] and California bearing ratio (CBR) [35]. In order to assess the influence of RP on the breakage potential of C &D aggregates, PSD tests were performed before and after compaction. Relative breakage (Br) was calculated using the procedure proposed in [36]. As presented in Fig. 2, Br is defined as a ratio of total breakage (Bt)

Table 1 Materials and blends used in this study.

Materials and methods In this study, two types of C&D aggregates, namely RCA and CB 2

Material/Blend name

Composition (by weight)

RCA RCA97/RP3 RCA95/RP5 RCA93/RP7 CB CB97/RP3 CB95/RP5 CCMs

100% RCA 97% RCA + 3% RP 95% RCA + 5% RP 93% RCA + 7% RP 100% CB 97% CB + 3% RP 95% CB + 5% RP Two types of natural capping materials (Control materials)

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100 100 90

80

Passing percentage (%)

70 60

Passing percentage (%)

90

Br=

80 70

Bt Bp

Bt =

60 50 40 30

Bp =

+

20

Initial PSD

10

After compaction

0 0.01

0.1

50

1 Particle size (mm)

10

100

40 30

RCA RCA97/RP3 RCA95/RP5 RCA93/RP7 CB CB97/RP3 CB95/RP5 RP ARTC ETM-08-03 (2017)

20 10 0 0.001

0.01

0.1

1

10

100

Particle size (mm)

Fig. 2. PSD curves of materials and definition of relative breakage, Br [36].

the applied stresses in pavement base/subbase layer. Additionally, the main advantage of the harmonized testing protocol of NCHRP 1-28A [43] over CEN EN 13286-7 [42] and AASHTO T307 [44] is that the sample is initially subjected to stress states farthest from the line of failure [45]. Thereafter, stress paths become more demanding and move toward the Mohr-Columb failure envelope. Consequently, more Mr points can be measured in a wider range of stress state using harmonized loading protocol [45]. Following the harmonized loading approach, a new harmonized testing protocol has been proposed for railway capping materials as presented in Table 2. The range of stress states where chosen based on the previous field and laboratory studies on capping materials. The confining pressure (σ3) is approximately in the range of 20–150 kPa in pavement base/subbase testing protocols. Nonetheless, capping materials usually experience a lower σ3 of 5 kPa at the edge of rail track to 75–80 kPa at the track centerline [25,26,46,47]. Cyclic deviator stresses (σcyc) were also designated to cover the ranges of induced vertical stresses from around 30 kPa to 300 kPa presented in [18,21,25,41,46–51]. Each loading sequence has been repeated for 100 cycles, while conditioning was applied for 500 cycles to eliminate the top and bottom irregularities of the sample [44]. The quick shear test was also performed after RLT tests to assess the shear strength response of C&D materials and blends with a strain rate of 1% per minute following AASHTO T307 [44]. Particle breakage, one-dimensional compression, RLT, and quick shear tests were performed on the samples prepared at target OMC and MDD which are presented in Fig. 3 and Table 3.

to breakage potential (Bp). Bt is the area between initial and after compaction PSD curves, while Bp is the area between the initial PSD curve and vertical line of 0.075 mm. The main advantage of Br is its ability to capture the changes in gradation of the soil due to particle breakage as a single parameter [37]. One-dimensional compression tests were conducted following the proposed procedure of Yaghoubi, et al. [38] for aggregates with slight modifications to capture the materials’ behavior at k0-continuous loading-unloading. Samples were prepared using standard Proctor energy in two layers with the final height of approximately 42 mm and diameter of 105 mm to maintain a diameter to height ratio of 2.5 [38]. This diameter to height ratio of the sample was used to reduce the effects of friction between the boundary of the sample and the inside of the mold ring [39]. For coarse-grained materials and aggregates, the sample diameter to the maximum particle size of 4–6 is generally adopted [40]. The height of the sample is also determined based on the sample diameter to height ratio which is usually around two in the literature to minimize the side effects of the mold ring [39,40]. Ten cycles of displacement-controlled loading/unloading with the displacement rate of 0.1 mm/min were applied to the samples using a rigid plate with a thickness of 20 mm. Measurement of vertical strain was started after applying a constant axial pressure of 10 kPa to eliminate any irregularity at the top surface of the sample. Maximum applied stress of 200 kPa for loading and seating stress of 10 kPa for unloading were applied in the subsequent loading-unloading cycles. This range of vertical stresses was chosen to cover the range of induced vertical stresses on top of capping layers in Australia, which is mainly from 30 to 120 kPa for both freight and passenger trains [41]. Vertical stress of more than 200 kPa is unlikely to apply to capping layer during serviceability. Therefore, the maximum stress of 200 kPa was applied in onedimensional compression tests. Performance of C&D/RP blends at higher stress levels were examined with RLT tests with more representative loading conditions of moving wheel load. RLT testing protocols have been widely used in determining the Mr of pavement granular layers [42–44]. Mr is defined as a ratio of repeated axial stress to the corresponding recoverable strain [44]. The loading combinations of these protocols have been designated based on

Results and discussion The physical and geotechnical properties of RCA, CB and RP in comparison to the range of results of CCMs are presented in Table 3. The results will be examined in the following sections. Geotechnical properties Fig. 2 shows the PSD curves of the materials used in this research in 3

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Table 2 Loading sequences of the proposed RLT testing protocol for railway track capping materials. Sequence

Conditioning 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

b

Cyclic stressb, σcyc kPa

Max. axial stressc, σmax kPa

103.4 5 10 20 40 60 80 5 10 20 40 60 80 5 10 20 40 60 80 5 10 20 40 60 80 5 10 20 40 60 80 5 10 20 40 60 80

10.3 1.0 2.0 4.0 8.0 12.0 16.0 1.0 2.0 4.0 8.0 12.0 16.0 1.0 2.0 4.0 8.0 12.0 16.0 1.0 2.0 4.0 8.0 12.0 16.0 1.0 2.0 4.0 8.0 12.0 16.0 1.0 2.0 4.0 8.0 12.0 16.0

93.1 1.5 2.0 2.0 4.0 3.0 4.0 6.0 10.2 16.6 26.8 30.6 36.0 13.3 23.2 39.3 59.6 68.5 78.1 25.0 43.7 74.7 106.7 120.2 133.8 43.8 76.3 129.9 174.5 191.0 207.2 74.0 128.0 216.0 272.0 288.0 304.0

103.4 2.5 4.0 6.0 12.0 15.0 20.0 7.0 12.2 20.6 34.8 42.6 52.0 14.3 25.2 43.3 67.6 80.5 94.1 26.0 45.7 78.7 114.7 132.2 149.8 44.8 78.3 133.9 182.5 203.0 223.2 75.0 130.0 220.0 280.0 300.0 320.0

2.0

OMC of CB/RP

13.5

1.9

blends

13.0

1.8

OMC of RCA/RP blends

12.5

1.7

12.0

1.6

11.5

1.5

11.0

1.4

10.5

1.3

10.0

Geotechnical parameters

RCA

CB

RP

CCMs range

Gravel-sized particles (%) Sand-sized particles (%) Fines content (%) Flakiness index Particle density – coarse fraction (Mg/m3) Particle density – fine fraction (Mg/m3) Water absorption – coarse fraction (%) Water absorption – fine fraction (%) MDD (Mg/m3) – standard Proctor compaction OMC (%) – standard Proctor compaction Los Angeles abrasion loss (%) CBR

51.0 45.1 3.9 7.2 2.71 2.68 6.59 9.35 1.83

38.8 51.2 9.9 12.7 2.67 2.62 6.59 8.73 1.95

60.3 39.6 0.1 – – 0.97 – – –

33.1–51.2 33.3–53.1 13.8–15.5 – 2.73–2.74 2.69–2.76 1.43–1.64 2.35–2.59 2.09–2.21

13.14 31 74.2

11.10 33 71.7

– – –

7.61–8.42 14–17 53.5–67.9

not significantly change the PSD curve of the C&D aggregates by up to 7% in RCA and 5% in CB. Based on Table 3, gravel and sand content of RCA and CB were within the range of CCMs, while both C&D aggregates had lower fine content than CCMs. Additionally, both coarse and fine fractions of C&D aggregates substantially absorbed more water than CCMs. Although the particle density of both RCA and CB were similar to CCMs, the density of RP particles was measured to be less than one. The MDD and OMC of RCA and CB are also presented in Table 3. C& D materials had lower MDD than the CCMs, which could be related to the lower amount of fine content in their matrix. CCMs with around 14–15% fine content reached a more densified state than C&D aggregates in which fine particles fill the voids between the particles. Additionally, Fig. 3 illustrates the variation in MDD and OMC of C&D/ RP blends. Increasing the RP content resulted in a noticeable reduction in the MDD and an almost linear increase in OMC of C&D/RP blends. This was expected due to the lower density of RP particles compared to parent aggregates. Moreover, the variation in OMC of RCA/RP blends with increasing the RP content was around 0.2%, while that of CB/RP blends was approximately 1% which was within the range of error of the compaction test. Nonetheless, CB aggregates were generally finer in PSD (Fig. 2) with around 10% non-plastic fine content and a higher particle crushing value which led to lower initial OMC of CB compared to RCA. However, the presence of a large portion of platy aggregates in RP, altered the matrix of CB/RP blends and consequently lowered the aggregate crushing. Factors such as fine content and aggregate crushing made CB less dependent on water lubrication to reach to MDD, while introduction of RP has changed the nature of compaction for CB aggregates and increased the OMC accordingly. The generally coarser PSD of RCA along with the scarcity of fines made it less sensitive to water content when RP aggregates were added. Regarding the degradation of aggregates, both RCA and CB had higher Los Angeles abrasion loss than CCMs, however, the values for C& D aggregates were still below the maximum threshold of 50% suggested by Li, et al. [20] for capping materials. Moreover, a CBR value of more than 50% is recommended for capping materials by local Australian authorities [52]. Based on Table 3, RCA and CB both met this criterion with higher CBR values than the range of CCMs. The influence of RP inclusion on CBR strength of RCA/RP and CB/RP blends is also plotted in Fig. 4. The range of CBR values of two CCMs is also presented in this figure for comparing the results of C&D/RP blends with CCMs. CBR values of both C&D/RP blends decreased almost linearly with increasing the RP content. Both RCA and CB had a CBR value in the range of 70–75%. However, the rate of reduction in CBR values of CB/RP blends was noticeably higher than that of RCA/RP samples. The failure pattern of unbound CB and RCA was slightly different due to the existence of unreacted cement in RCA as discussed in [9]. CB aggregates were found to rely on particle contact forces for load-bearing under k0

Minimum vertical stress. Single amplitude haversine stress for determination of Mr. Total vertical stress including the contact and cyclic stresses.

MDD (Mg/m3)

c

Contact stressa, 0.2σ3 kPa

OMC (%)

a

Confining pressure, σ3 kPa

Table 3 Physical and geotechnical characteristics of C&D materials and RP in comparison with CCMs.

Fig. 3. Variation of MDD and OMC of C&D blends with RP content.

comparison to the specified range of capping materials [52]. PSD curve of RCA was within the range between 0.15 mm and 20 mm, while it was finer than the lower limit from 0.15 to 0.075 mm. PSD curve of the CB was within the required range, whereas, most particles of RP were distributed within the range of 1–9.5 mm. As shown in Fig. 2, PSD curves of both RCA/RP and CB/RP blends were not noticeably altered from those of their parent aggregates. Therefore, the inclusion of RP did

4

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80

(a)

RCA/RP blends CB/RP blends

75

0.0

65 60

CCMs range

55 50 Min. requirement of capping materials ARTC, ETC-08-03 (2017)

45 40

50

Vertical stress (kPa) 100

150

200 RCA RCA97/RP3 RCA95/RP5 RCA93/RP7

0.5 Vertical strain (%)

CBR value (%)

70

0

1.0 1.5 2.0 2.5 3.0

0

1

2

3 4 RP content (%)

5

6

7

3.5 (b)

Fig. 4. Variation of CBR values of C&D blends with RP content.

0.0

Vertical strain (%)

condition, while RCA/RP CBR samples can utilize the unreacted cement powder which could lead to an increase in the shear strength during the curing period. Therefore, the RP content had a lower rate of influence on the reduction of CBR values of RCA/RP samples compared to the CB/RP blends. The CBR value of RCA/RP blends with up to 7% RP was still higher than the minimum range of CCMs, while that of CB95/RP5 was below the minimum limit of 50%. Since CBR value is the only controlling strength parameter recommended by Australian agencies for capping materials [52], up to 7% RP with RCA and 3% RP with CB can be blended to comply with the minimum limit.

0

50

Vertical stress (kPa) 100

150

200 CB

0.5

CB97/RP3

1.0

CB95/RP5

1.5 2.0 2.5 3.0 3.5

Fig. 6. Stress-strain response of materials from one-dimensional compression test: (a) RCA/RP blends and (b) CB/RP blends.

Particle breakage Degradation of granular materials under impact loading can have an important effect on the stiffness and resilient response of granular materials [53]. Inclusion of RP in both RCA and CB with higher Los Angeles abrasion loss than that of CCMs can potentially reduce the susceptibility to degradation. In order to assess the effect of RP on reduction of particle breakage of blends, Br values of the C&D/RP blends were examined. Variation of Br with RP content for both RCA/RP and CB/RP blends are presented in Fig. 5. Br of CB was about 1% higher than that of RCA indicating more degradation of particles under impact loading, which was similar to the Los Angeles abrasion loss of CB which was 2% higher than that of RCA (Table 3). More breakage of CB than RCA could be related to the higher percentage of flaky particles as presented in Table 3. Flaky aggregates are more susceptible to breakage compared to rounded particles due to lower geometric shape stability. As expected, increasing the RP content considerably reduced the Br of C &D blends. This suggests that RP particles surrounding C&D aggregates acted as a cushion due to their elastic behavior under impact loading. Therefore, higher energy of impact loading was absorbed by RP

particles and lower dynamic forces were applied to the parent aggregates. For both C&D/RP blends with 5% plastic, Br had been reduced by more than 50% in comparison to parent aggregates. The addition of RP content after 5% had an insignificant impact on the Br value of RCA/ RP blends. Moreover, considering the volumetric increase in RP content (from 5% to 7%) due to the lower specific density of the plastic compared to recycled aggregates, the soil matrix changes quickly leading to the reduction in particle interlocking and compromise the stiffness of the blends. 5% RP content could have the advantage of higher stiffness and fairly similar breakage compared to 7% RP content. Compressibility behavior Inclusion of RP particles with compressibility behavior to C&D aggregates can increase the potential of undesirable deformations of capping materials which affect the overall railway track performance. Fig. 6 presents the stress-strain response of blends obtained from the displacement-controlled one-dimensional compression test. As evident, the majority of the strain had occurred in the first cycle of loading in all the samples. While a portion of this strain recovered during the first unloading, most of it turned to permanent strain. Both permanent and maximum vertical strains in the first cycle were found to be mainly governed by the RP content and the values were found to increase with increasing RP percentage in both C&D/RP blends. CB/RP blends showed more total and permanent strains than RCA/RP samples, which could be related to lower stiffness and higher particle breakage of CB aggregates. Therefore, the accumulation of permanent strains for CB/ RP blends occurred at a faster rate compared to RCA/RP samples. For both C&D/RP blends, between around 85% and 95% of permanent strain occurred at the first cycle followed by 1.5–5.5% at second cycle moving toward a minimal permanent settlement in the following cycles. Therefore, RCA/RP blends reached a stable condition in which the stress-strain curves were fairly similar to each other, while CB/RP samples, particularly CB95/RP5, had still experienced a slight

Relative breakage, Br (%)

6 RCA/RP blends

5

CB/RP blends

4 3 2 1

0

1

2

3 4 RP content (%)

5

6

7

Fig. 5. Variation of Br values of C&D blends with RP content. 5

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Table 4 Compressibility and shear strength parameters of C&D aggregates and blends in comparison with CCMs. Test

One-dimensional compression

Parameters

ε10 (%) εp10 (%) εp10 − εp1 εp10

Quick shear test

(%)

qpeak (kPa) E50 (kPa) Energy absorption (kJ/m3)

Materials RCA

RCA97/RP3

RCA95/RP5

RCA93/RP7

CB

CB97/RP3

CB95/RP5

CCMs range

1.62 1.14 5.5

1.93 1.19 8.0

2.32 1.54 10.0

2.89 2.06 13.3

2.32 1.97 6.6

2.65 2.00 16.0

3.25 2.33 16.9

1.76–2.54 1.05–1.55 14.4–16.1

660.9 304.6 6.16

667.0 261.6 6.78

585.0 195.9 6.96

544.4 156.5 7.88

496.8 158.1 3.72

482.7 123.8 3.76

462.0 97.3 5.59

417.1–470.7 144.0–164.6 1.97–3.38

(a)

permanent strain accumulation at the last few cycles. Maximum vertical strain at 200 kPa axial stress at the last cycle (ε10) and permanent vertical strain at the final cycle (εp10) were calculated and their values for all the C&D blends are presented in Table 4. ε10 of RCA, CB and RCA/RP blends with up to 5% RP were within the range of CCMs. However, RCA93/RP7 and both blends of CB with 3% and 5% RP content experienced more axial strain at 200 kPa of the last cycle of loading-unloading. An almost similar trend was observed regarding the εp10, except that CB and its blends had higher total permanent strains than the range of CCMs. To better evaluate the effect of first loading cycle and RP content on the permanent deformation of materials, the difference between the permanent strain of the first (εp1) and last (εp10) cycle over the εp10 was calculated and reported in Table 4. For RCA/RP blends, the permanent strain of the samples from cycle two to ten was less than 14% of εp10 and the range of CCMs, while CB and CB97/RP3 had similar values to the range of conventional materials. CB95/RP5, however, experienced more percentage of permanent strain from cycle two to ten compared to CCMs, which was around 17%. This indicates that more than 80% of permanent strain occurred in the first cycle of loading and unloading for all the materials. The induced stresses during the construction of railway track can substantially reduce the permanent deformations of the C&D/RP blends, which in turn increases the stiffness of the materials prior to serviceability. The range of stresses applied to capping layer during the construction of railway track substructure and superstructure usually exceeds the cyclic stresses induced by train wheels on top of this layer during the operation of railway track. The stresses during construction are generated by the vehicles and equipment used for transferring the materials, spreading, placing, compaction and trimming of the capping and ballast layer and installation of the superstructure components. Thus, RCA/RP blends, CB and its blend with 3% RP as the capping layer can reach a stable condition due to these loadings during the construction period and can perform with similar compressibility to the natural aggregates during serviceability of the railway track.

500

RCA RCA97/RP3 RCA95/RP5 RCA93/RP7

M r (MPa)

420 340 260 180 100 20

CCMs range 1

(b) 500

11

16 21 Sequence No.

26

31

36

16 21 Sequence No.

26

31

36

CB CB97/RP3 CB95/RP5

420

M r (MPa)

6

340 CCMs range 260 180 100 20

1

6

11

Fig. 7. Mr values: (a) RCA/RP blends and (b) CB/RP blends.

demanding stress paths, however, this ratio reached a value of 2.8 on average, signifying the superior stiffness of RCA to conventional aggregates. Therefore, RCA as sustainable materials in capping layer construction can enhance track performance and reduce the induced vertical and horizontal stresses to the subgrade [49,54], particularly in heavy-duty railroads, which in turn decrease the overall deformation of track substructure. CB, however, had slightly lower Mr than CCMs in the first six sequences with the least stress ratio (ratio of σcyc to σ3) for each σ3 as presented in Fig. 7(b). In the following sequences, Mr of CB was slightly lower than the range of CCMs in the sequences with σ3 of 5 and 10 kPa and it was similar to the CCMs in other ranges of σ3. However, CB had higher Mr values to the range of 55–105 MPa [20], which is usually adopted for capping materials and can be considered as a suitable alternative material to CCMs. The influence of RP on the resilient response of RCA and CB can also be observed in Fig. 7(a) and (b) respectively. Mr of both RCA/RP and CB/RP decreased with increasing RP percentage. This could be related to the low particle roughness and stiffness of plastic particles compared to those of parent materials [5]. However, RCA97/RP3 and RCA95/RP5 still had higher Mr than both CCMs. RCA93/RP7 also had more stiffness than the range of CCMs until the loading sequence of 24. After this

Resilient modulus of materials The RLT test can simulate railway traffic to determine the Mr of materials under repeated loading. The proposed RLT testing protocol (Table 2) used in this research covers the range of σ3 and σcyc from low to high-stress levels. While σcyc of more than 200 kPa is unlikely to happen in capping layers, more demanding σcyc was also applied in the last few sequences to capture the stiffness of the materials at high-stress levels. Fig. 7 illustrates the Mr of C&D aggregates and blends obtained from the proposed testing protocol for capping materials in comparison to CCMs. The Mr envelope of CCMs was relatively thin ranging from around 65–232 MPa. This range falls within the range presented in the literature for conventional or alternative capping materials [18,20,25,49]. RCA in Fig. 7(a) showed the highest Mr values among all the aggregates used in this study. Mr of RCA was approximately 1.5 times higher than that of CMMs on average at low-stress levels. At more 6

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Deviator stress (kPa)

300

RCA

250

RCA97/RP3

RCA95/RP5

CB97/RP3

CB95/RP5

RCA93/RP7 CB

200 150 100

Dissipated energy

50 0

0

0.5

1

1.5

Axial strain (%) Fig. 8. Stress-strain hysteresis loop of the last cycle of RLT loading sequence 28 with σ3 = 40 kPa and σcyc = 174.5 kPa.

sequence, the value of Mr roughly dropped in the range of CCMs indicating that at more demanding stress levels, RCA93/RP7 showed similar behavior to conventional aggregates. In terms of CB/RP blends, Mr of both CB97/RP3 and CB95/RP5 were lower than CCMs, indicating approximately 80% and 65% stiffness of CCMs respectively. Additionally, minimum Mr values of CB97/RP3 and CB95/RP5 were approximately 46 and 34 MPa respectively, which was lower than the limit of 55 MPa for capping materials [20]. Therefore, CB/RP blends should be used for higher thicknesses of capping layer than CCMs in railway track substructure to prevent the progressive failure and deformation of subgrade based on the current railway track design methods that take into account the Mr of granular layers [22]. To better evaluate the effect of RP on the behavior of C&D/RP blends under cyclic loading, the stress-strain response of cycle 100 of sequence 28 is plotted in Fig. 8. This loading sequence with σ3 of 40 kPa and σcyc of 174.5 kPa is one of the cycles with a representative combination of loadings in the Australian railway tracks [25,41]. As evident, the stress-strain response of both RCA and CB formed a nonlinear hysteresis loop which is the typical behavior of granular materials under cyclic loading. However, the significant influence of RP on the stress-strain and shape response of the C&D/RP blends can be seen in Fig. 8. For both C&D/RP blends, permanent strain up to cycle 100 of sequence 28 increased with increasing the RP content. The axial strain of hysteresis loops of CCMs was also determined to be in the range of 0.48–0.98%. Therefore, RCA and its blends with up to 5% RP showed lower strains than CCMs, while RCA93/RP7, CB and CB97/RP3 were within the same range of stains as those of CCMs. CB95/R5, however, experienced higher strains compared to CCMs. Moreover, as the RP content increased, the nonlinearity of the stress-strain curve of the blends increased with respect to their parent materials. This nonlinearity was observed in inclination of the hysteresis loop which was related to the increase of recoverable strain as well as the increase in the convex curve upon unloading. Therefore, as the RP content increased, the area of hysteresis loop increased. This area is defined as the dissipated energy per unit volume of the sample [55], which is related to the movement of aggregates and compression of RP particles. As shown in Fig. 8, inclusion of RP could enhance the energy dissipation of the C&D blends under cyclic loading. Energy dissipation under repeated loading can be evaluated using the damping ratio parameter. As plotted in Fig. 9(a), damping ratio under cyclic loading is defined as the ratio of dissipated energy to the maximum elastic energy capacity of the sample [25]. Fig. 9(b) demonstrates the calculated damping ratio of the materials using the hysteresis loop response of materials in Fig. 8. For CB/RP blends, damping ratio increased linearly with increasing RP content, while for RCA/RP blends the general upward trend could be observed. For both C &D/RP blends with 5% RP content, the damping ratio was improved by more than 20% to that of the parent aggregates and it was higher than

Fig. 9. (a) Definition of damping ratio and (b) variation of damping ratio of C& D/RP blends with RP content.

(a) 800

RCA RCA97/RP3 RCA95/RP5 RCA93/RP7

Deviator stress (kPa)

700 600 500 400 300 200 100 0 (b)

0

1

2 3 Axial strain (%)

800

5

CB CB97/RP3 CB95/RP5

700 Deviator stress (kPa)

4

600 500 400 300 200 100 0

0

1

2 3 Axial strain (%)

4

5

Fig. 10. Stress-strain response to quick shear test: (a) RCA/RP blends and (b) CB/RP blends.

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particle breakage was found to be 5% in both C&D blends.

the range of results of CCMs.

• RP content governed the compressibility behavior of the C&D/RP

Stress-strain characteristics The stress-strain response of materials to the quick shear test is plotted in Fig. 10 and the results obtained are presented in Table 4. Strain softening behavior of all the blends observed in Fig. 10 is the typical behavior of capping materials [47]. Based on Fig. 10 and Table 4, the peak deviator stress (qpeak) decreased and axial strain corresponding to qpeak increased with increasing RP content. Lower particle strength, elastic and higher compressibility of RP to those of parent materials could contribute to this trend. Therefore, the ductility of blend in comparison with parent materials improved with increasing RP percentage. Based on Table 4, qpeak of RCA and RCA/RP blends was higher than that of CB and its blends due to about 33% more strength of RCA than CB. However, qpeak of all the C&D blends was higher than the range of CCMs except for CB95/RP5 falling in the upper range of conventional aggregates. Therefore, in terms of strength, all the C&D/RP blends evaluated in this study can be considered as suitable alternative materials to CCMs. Stiffness of the materials during shearing was also determined using Young modulus at 50% of qpeak (E50) and presented in Table 4. The reduction in E50 of blends with increasing RP content was associated with lower stiffness of RP particles as well as the increase in ductility behavior shown in Fig. 10. Interestingly, the trend of reduction in E50 of blends was similar to Mr obtained from RLT test (Fig. 7). Therefore, RCA/RP blends with up to 5% RP had higher E50 of CCMs, RCA93/RP7 and CB fell within the range of CCMs, while CB/RP blends were off the limit. Energy absorption capacity under monotonic shearing was also evaluated by measuring the area under the stress-strain response of materials to qpeak and presented in Table 4. This is equivalent to the work related to frictional resistance of particles up to qpeak [19]. Noticeable improvement in the energy absorption capacity of parent materials was observed when they were blended with RP, in spite of the slight decrease in qpeak. While RP particles had lower frictional resistance to the parent materials, the energy absorbed by blend increased due to the higher compressibility of RP particles. RCA and its blends tended to have higher energy absorption than CB mainly due to higher stiffness and strength of RCA which resulted in higher stress-strain area until the qpeak. The energy absorption capacity of both RCA95/RP5 and CB95/RP5 was more than 2.5 times of that of CCMs, indicating the significant advantage of adding RP to C&D aggregates.

• •

•

blends for both maximum axial strain and permanent strain. Most of the permanent deformation of C&D/RP blends occurred in the first cycle of loading-unloading, which is likely to happen during the construction of railway track substructure and superstructure. After several cycles, all the C&D blends experienced a stable condition in which stress-strain curves of loading and unloading has become almost similar to each other. Mr of RCA with 5% RP was still higher than the range of CCMs, while CB/RP blends had lower Mr than the conventional aggregates. However, the damping ratio, which is associated with energy dissipation, increased with increasing RP content for both blends and with 5% RP was higher than the range of CCMs. Regarding the shear strength parameters, all the C&D aggregates and their blends had higher shear strength than the CCMs, except for CB95/RP5 which was found just below the upper limit. E50 of all the materials were also similar or higher than CCMs except for CB/RP blends. The energy absorption capacity of all the blends under monotonic loading was also found to be higher than CCMs. RCA95/RP5 was found to be the optimum blend with higher energy absorption capacity and superior stiffness and strength to the CCMs. Additionally, CB97/RP3 was found to be a suitable alternative energy-absorbing capping layer with slightly lower stiffness than the conventional aggregates.

CRediT authorship contribution statement Arul Arulrajah: Conceptualization, Supervision, Funding acquisition, Methodology, Writing - review & editing. Mahdi Naeini: Conceptualization, Project administration, Methodology, Formal analysis, Investigation, Writing - original draft. Alireza Mohammadinia: Conceptualization, Supervision, Funding acquisition, Writing - review & editing. Suksun Horpibulsuk: Conceptualization, Writing - review & editing. Melvyn Leong: Funding acquisition, Methodology, Writing review & editing. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments

Conclusions This research was conducted by the Australian Research Council Industrial Transformation Training Centre for Advanced Technologies in Rail Track Infrastructure (IC170100006) and funded by the Australian Government.

In this study, the application of RP blends with C&D aggregates including RCA and CB was evaluated and results compared with the range for two control CCMs. After determining the basic geotechnical characteristics of the materials, effect of RP inclusion on particle breakage, compressibility, resilient behavior and shear strength of RCA/RP and CB/RP blends were evaluated. The key research findings can be summarized as follows:

Appendix A. Supplementary material Supplementary data to this article can be found online at https:// doi.org/10.1016/j.trgeo.2020.100320.

• In terms of gradation, RCA and CB had similar sand and gravel

• •

content to CCMs. However, RCA had slightly lower fine content that the required limit. Additionally, PSD curves of C&D/RP blends with 7% RP in RCA and 5% in CB were similar to the PSD curve of their parent aggregates. Additionally, while C&D aggregates had higher water absorption, OMC and Los Angeles abrasion loss, the MDD of RCA, CB and their blends were lower than the range of CCMs. RCA with up to 7% RP and CB with 3% RP were found to have higher CBR value of 50% suggested by local authorities for capping materials. Inclusion of RP had a significant effect on reduction of particle breakage of RCA and CB. The optimum RP content in terms of

References [1] Vieira CS, Pereira PM. Use of recycled construction and demolition materials in geotechnical applications: a review. Resour Conserv Recycl 2015;103:192–204. [2] Kaza S, Yao L, Bhada-Tata P, Van Woerden F. What a waste 2.0: a global snapshot of solid waste management to 2050. Washington, DC: World Bank Publications; 2018. [3] J. Pickin, P. Randell, J. Trinh, B. Grant, Australian national waste report 2018. Department of the Environment and Energy; Blue Environment Pty Ltd; 2018. p. 1–126. [4] Wong SL, Ngadi N, Abdullah TAT, Inuwa IM. Current state and future prospects of plastic waste as source of fuel: a review. Renew Sustain Energy Rev 2015;50:1167–80. [5] Arulrajah A, Yaghoubi E, Wong YC, Horpibulsuk S. Recycled plastic granules and

8

Transportation Geotechnics 22 (2020) 100320

A. Arulrajah, et al.

[6]

[7]

[8] [9]

[10]

[11]

[12]

[13] [14] [15] [16]

[17]

[18] [19] [20] [21] [22] [23]

[24]

[25]

[26]

[27]

[28] [29]

[30]

demolition wastes as construction materials: Resilient moduli and strength characteristics. Constr Build Mater 2017;147:639–47. Choudhary A, Jha J, Gill K. Utilization of plastic wastes for improving the subgrades in flexible pavements. Paving materials and pavement analysis; 2010. p. 320–6. Poulikakos LD, Papadaskalopoulou C, Hofko B, Gschösser F, Cannone Falchetto A, Bueno M, et al. Harvesting the unexplored potential of European waste materials for road construction. Resour Conserv Recycl 2017;116:32–44. Wu J, El Naggar MH, Li X, Wen H. DEM analysis of geobag wall system filled with recycled concrete aggregate. Constr Build Mater 2020;238:117684. Kianimehr M, Shourijeh PT, Binesh SM, Mohammadinia A, Arulrajah A. Utilization of recycled concrete aggregates for light-stabilization of clay soils. Constr Build Mater 2019;227:116792. Tarawneh B, Al Bodour W, Shatnawi A, Al K. Ajmi, Field evaluation and behavior of the soil improved using dynamic replacement. Case Stud Construct Mater 2019;10:e00214. Wang Z-F, Shen S-L, Modoni G. Enhancing discharge of spoil to mitigate disturbance induced by horizontal jet grouting in clayey soil: theoretical model and application. Comput Geotech 2019;111:222–8. Wang Z-F, Shen JS, Cheng W-C. Simple method to predict ground displacements caused by installing horizontal jet-grouting columns. Math Probl Eng 2018;2018:11. Shen S-L, Wang Z-F, Yang J, Ho C-E. Generalized approach for prediction of jet grout column diameter. J Geotech Geoenviron Eng 2013;139(12):2060–9. Wang Z-F, Shen S-L, Ho C-E, Xu Y-S. Jet grouting for mitigation of installation disturbance. Proc Inst Civil Eng – Geotech Eng 2014;167(6):526–36. Gautam PK, Kalla P, Jethoo AS, Agrawal R, Singh H. Sustainable use of waste in flexible pavement: a review. Constr Build Mater 2018;180:239–53. Saberian M, Li J, Setunge S. Evaluation of permanent deformation of a new pavement base and subbase containing unbound granular materials, crumb rubber and crushed glass. J Cleaner Prod 2019;230:38–45. Arulrajah A, Piratheepan J, Aatheesan T, Bo MW. Geotechnical properties of recycled crushed brick in pavement applications. J Mater Civ Eng 2011;23(10):1444–52. Selig ETA, Waters JM. Track geotechnology and substructure. Management 1994. Li D, Selig ET. Method for railroad track foundation design. I: Development. J Geotech Geoenviron Eng 1998;124(4):316–22. Li D, Hyslip J, Sussmann T, Chrismer S. Railway geotechnics. CRC Press; 2016. Sayeed MA, Shahin MA. Design of ballasted railway track foundations using numerical modelling. Part I: Development. Can Geotech J 2017;55(3):353–68. Indraratna B, Ngo T. Ballast railroad design: smart-uow approach. CRC Press; 2018. Signes CH, Fernández PM, Perallón EM, Franco RI. Characterisation of an unbound granular mixture with waste tyre rubber for subballast layers. Mater Struct 2015;48(12):3847–61. Indraratna B, Qi Y, Heitor A. Evaluating the properties of mixtures of steel furnace slag, coal wash, and rubber crumbs used as subballast. J Mater Civ Eng 2018;30(1):04017251. Qi Y, Indraratna B, Heitor A, Vinod JS. Effect of rubber crumbs on the cyclic behavior of steel furnace slag and coal wash mixtures. J Geotech Geoenviron Eng 2018;144(2):04017107. Indraratna B, Rujikiatkamjorn C, Tawk M, Heitor A. Compaction, degradation and deformation characteristics of an energy absorbing matrix. Transp Geotech 2019;19:74–83. ASTM D6913/D6913M. Standard test methods for particle-size distribution (Gradation) of soils using sieve analysis. West Conshohocken, PA, USA: ASTM International; 2017. British Standards Institution, BS 812-105.1: Method for Determination of Particle Shape; Flakiness Index, London, UK, 1989. ASTM C127. Standard test method for relative density (specific gravity) and absorption of coarse aggregate. West Conshohocken, PA, USA: ASTM International; 2015. ASTM C128. Standard test method for relative density (specific gravity) and

[31] [32]

[33]

[34]

[35] [36] [37] [38]

[39] [40] [41]

[42] [43]

[44]

[45] [46]

[47] [48] [49] [50]

[51] [52] [53]

[54] [55]

9

absorption of fine aggregate. West Conshohocken, PA, USA: ASTM International; 2015. ASTM D854. Standard test methods for specific gravity of soil solids by water pycnometer. West Conshohocken, PA, USA: ASTM International; 2014. ASTM D792, Standard test methods for density and specific gravity (relative density) of plastics by displacement. West Conshohocken, PA, USA: ASTM International; 2013. ASTM D698. Standard test methods for laboratory compaction characteristics of soil using standard effort (12 400 ft-lbf/ft3 (600 kN-m/m3)). West Conshohocken, PA, USA: ASTM International; 2012. ASTM C131/C131M. Standard test method for resistance to degradation of smallsize coarse aggregate by abrasion and impact in the Los Angeles machine. West Conshohocken, PA, USA: ASTM International, 2014. ASTM D1883. Standard test method for california bearing ratio (CBR) of laboratorycompacted soils. West Conshohocken, PA, USA: ASTM International, 2012. Hardin BO. Crushing of soil particles. J. Geotech. Eng. 1985;111(10):1177–92. Yu F. Particle breakage and the drained shear behavior of sands. Int J Geomech 2017;17(8):04017041. Yaghoubi E, Disfani MM, Arulrajah A, Kodikara J. Impact of compaction method on mechanical characteristics of unbound granular recycled materials. Road Mater Pavement Design 2018;19(4):912–34. Indraratna B, Ionescu D, Christie D, Chowdhury R. Compression and degradation of railway ballast under one-dimensional loading. Aust Geomech J 1997:48–61. Tapias M, Alonso EE, Gili J. A particle model for rockfill behaviour. Géotechnique 2015;65(12):975–94. Indraratna B, Nimbalkar S, Christie D, Rujikiatkamjorn C, Vinod J. Field assessment of the performance of a ballasted rail track with and without geosynthetics. J Geotech Geoenviron Eng 2010;136(7):907–17. CEN EN 13286-7. Unbound and hydraulically bound mixtures-part 7: cyclic load triaxial test for unbound mixtures. European Committee for Standardization; 2004. NCHRP 1-28A. Laboratory determination of resilient modulus for flexible pavement design. Washington, D.C., United States: National Cooperative Highway Research Program; 2004. AASHTO T307. Standard method of test for determining the resilient modulus of soils and aggregate materials. Washington: American Association of State Highway and Transportation Officials; 2012. Andrei D, Witczak MW, Schwartz CW, Uzan J. Harmonized resilient modulus test method for unbound pavement materials. Transp Res Rec 2004;1874(1):29–37. Indraratna B, Biabani MM, Nimbalkar S. Behavior of geocell-reinforced subballast subjected to cyclic loading in plane-strain condition. J Geotech Geoenviron Eng 2015;141(1):04014081. Suiker ASJ, Selig ET, Frenkel R. Static and cyclic triaxial testing of ballast and subballast. J Geotech Geoenviron Eng 2005;131(6):771–82. Adegoke CW, Chang CS, Selig ET. Study of analytical models for track support systems. Transp Res Rec 1979;733:12–20. Shahu JT, Kameswara Rao NSV. Yudhbir, Parametric study of resilient response of tracks with a sub-ballast layer. Can Geotech J 1999;36(6):1137–50. Rose J, Su B, Twehues F. Comparisons of railroad track and substructure computer model predictive stress values and in-situ stress measurements. In: Proceedings of the AREMA 2004 annual conference & exposition, Nashville, TN; September, 2004. Leshchinsky B, Ling HI. Numerical modeling of behavior of railway ballasted structure with geocell confinement. Geotext Geomembr 2013;36:33–43. ARTC ETC-08-03. Earthworks materials specification. Australian Rail Track Corporation Limited (ARTC); 2017. Caicedo B, Coronado O, Fleureau JM, Correia AG. Resilient behaviour of non standard unbound granular materials. Road Mater. Pavement Design 2009;10(2):287–312. Smith M, Bengtsson P, Holm G. Three-dimensional analyses of transition zones at railway bridges. Numer Methods Geotech Eng 2006:237–42. Navaratnarajah SK, Indraratna B. Use of rubber mats to improve the deformation and degradation behavior of rail ballast under cyclic loading. J Geotech Geoenviron Eng 2017;143(6):04017015.