Recycled Construction and Demolition Wastes as filling material for geosynthetic reinforced structures. Interface properties

Journal of Cleaner Production xxx (2016) 1e13

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Recycled Construction and Demolition Wastes as filling material for geosynthetic reinforced structures. Interface properties Castorina Silva Vieira*, Paulo M. Pereira, Maria de Lurdes Lopes CONSTRUCT-GEO, Department of Civil Engineering, University of Porto, R. Dr. Roberto Frias, 4200-465 Porto, Portugal

a r t i c l e i n f o

a b s t r a c t

Article history: Received 22 December 2015 Received in revised form 19 February 2016 Accepted 24 February 2016 Available online xxx

Construction and Demolition Wastes (C&DW) are increasingly being reused in civil engineering applications, mainly in concrete production and base layers of roadway infrastructures. However, frequently the fine grain portion of these recycled aggregates is not considered suitable for those applications being landfilled instead of recycled. Moreover, the value-added utilisation of recycled C&DW in the construction of geosynthetic reinforced structures (steep slopes and retaining walls) is almost an unexplored field. This research assesses the feasibility of using fine-grain recycled C&DW as filling material of geosynthetic reinforced structures (GRS), appraising the physical, mechanical and environmental characterization of the construction and demolition material (C&DM), as well as, the direct shear and pullout behaviour of the interfaces between this material and three distinct geosynthetics (two geogrids and one geocomposite reinforcement or high strength geotextile). Direct shear tests results have shown that finegrain recycled C&DW, properly compacted, exhibit similar shear strength to natural soils used commonly in the construction of GRS. The potential contamination of groundwater by these recycled C&DW was evaluated through laboratory leaching tests and, excepting the values of sulphate and total dissolved solids (TDS), this recycled C&DW complies with the provisions of European Council Decision 2003/33/EC for inert materials. High values of coefficients of interaction for C&DW/geosynthetic interfaces, a parameter of utmost importance in the design and performance of GRS, were achieved. The results herein presented support the viability of using these recycled C&DW as filling material for GRS construction. © 2016 Elsevier Ltd. All rights reserved.

Keywords: Environmental sustainability Construction and Demolition Wastes Geosynthetic reinforced structures Filling material Interface properties

1. Introduction The population growth and the rapid industrialization have been generating large amount of wastes all over the world, with a large portion of these wastes produced by the construction industry. The volume of Construction and Demolition Wastes (C&DW) is generated in large quantities, mainly in urban areas, causing damage to the environment by the lack of suitable sites for the disposal and also by the society's inattention (Poon, 2007). According to the environment department of the European Commission, C&DW is one of the heaviest and most voluminous waste streams generated in the European Union (EU). It accounts for approximately 25%e30% of all waste generated in the EU and consists of numerous materials, including concrete, bricks, gypsum,

* Corresponding author. E-mail address: [email protected] (C.S. Vieira).

wood, glass, metals, plastic, solvents, asbestos and excavated soil, many of which can be recycled (European Commission, 2015). There is a high potential for recycling and re-use of C&DW, as demonstrated by the numerous studies, with positive results, that have been carried out on the use of recycled aggregates from Construction and Demolition (C&D) materials in base and subbase layers of roadways (Arulrajah et al., 2013a; Barbudo et al., 2012a; Leite et al., 2011; Poon and Chan, 2006; Vegas et al., 2008; Vieira and Pereira, 2015c; Xuan et al., 2015; Rahman et al., 2015) and in concrete production (Behera et al., 2014; Bravo et al., 2015; Medina et al., 2014; Mefteh et al., 2013; Rao et al., 2007; Silva et al., 2014, 2016). Recycling and reuse C&DW has become a topic of global concern and there is an urgent need to develop research into alternative applications for these recycled C&D materials. The fine grain portion of recycled C&DW is commonly not considered appropriate for use in concrete or roadway base layers due to the high content of fines and scattering of its constituents (soil, glass, concrete,

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mortars, clay masonry units, …). Recent studies have been presented on the use of fine aggregates coming from C&DW as alternative pipe backfilling material (Rahman et al., 2014) and as filling material for geosynthetic reinforced structures (Santos et al., 2013; Vieira and Pereira, 2015a,b). This paper presents results of the physical, mechanical and environmental characterization of a fine grain recycled C&DW, as well as, the direct shear and pullout behaviour of the interfaces between C&DW and three different geosynthetics. The interaction mechanism between the geosynthetic and the filling material has an utmost importance in the design of geosynthetic reinforced structures (steep slopes and retaining walls). This mechanism depends on the fill properties, reinforcement characteristics and interaction between both elements (fill and reinforcement). The accurate identification of the interaction mechanism (shear or pullout) and the choice of the most suitable test for its characterization are key factors in GRS design. Fig. 1 presents a potential failure mechanism of a reinforced steep slope. In upper area of the retained or supported backfill mass, the reinforcement is pulled out, so the soil-reinforcement interaction can be best characterised by pullout tests. Near the base of the slope, sliding in the interface is expected and the interaction between the two materials is better characterised through direct shear tests (Vieira et al., 2013). Over the last decades many researchers have been investigated the behaviour of soil-geosynthetic interfaces through pullout tests (Esmaili et al., 2014; Ferreira et al., 2015b; Lopes and Ladeira, 1996b; Moraci and Cardile, 2009; Nayeri and Fakharian, 2009; Palmeira, 2004; Pinho Lopes et al., 2015) and direct shear tests (Ferreira et al., 2015a; Lee and Manjunath, 2000; Liu et al., 2009; Vieira et al., 2015; Vieira et al., 2013). Some studies relating to the direct shear behaviour of recycled C&DW/geosynthetic interfaces have also been arising in recent years (Arulrajah et al., 2013b, 2014; Vieira and Pereira, 2015b; Vieira et al., 2014). There are no known studies on the pullout behaviour of geosynthetics embedded in recycled C&DW. The effect of soil moisture content on soil/geosynthetic interfaces shear strength has been studied by several authors (AbuFarsakh et al., 2007; Esmaili et al., 2014; Ferreira et al., 2015a,b; Hatami and Esmaili, 2015). In general, these studies have indicated that the interface shear strength can reduce at higher moisture contents, especially in soils containing considerable amount of fines. However, considering that during construction the optimum or slightly lower moisture content is adopted, this study was carried out for recycled C&DW compacted at its optimum moisture content. This paper deals with the physical, mechanical and environmental characterization of an alternative filling material, as well as, the study of the interfaces between that material and three different geosynthetics through direct shear and pullout tests.

Fig. 1. Potential failure mechanism of a reinforced steep slope and the most suitable laboratory test for interface characterization.

2. Materials and methods A fine grain recycled C&DW coming from housing demolitions and cleaning of lands with illegal deposits of C&DW was used in this study. The recycled material was collected from a single batch in a Portuguese recycling plant located in the centre of the country. After transportation the recycled C&DW was stored in three big containers. The physical and environmental characterization of the material was carried out with samples resulting from the mixing of portions coming from each container. The constituents of this recycled C&DW have been evaluated following the European Standard EN 933-11 (2009), with a small change concerning the non-inclusion of soils in the constituent “other materials”. The sample, with weight of 20 kg approximately, was dried at 40
C, the floating particles were removed and the “clays and soils” were separated. Using a magnifying glass, a pair of tweezers and a magnet, the constituents were sorted out in the 6 classes defined by EN 933-11 (2009): Rc, concrete, concrete products, mortar, concrete masonry units; Ru unbounded aggregate, natural stone, hydraulically bound aggregate; Rb, clay mansonry units, calcium silicate masonry units; Ra, bituminous materials; Rg, glass; X, other materials. The constituents of the recycled C&DW are listed in Table 1. This recycled material comprises mainly concrete, unbounded aggregates, masonries and soils. It is worth remembering that the C&DW came from housing demolitions and cleaning of lands with illegal deposits. The particle size distribution determined by sieving and sedimentation of the material is represented in Fig. 2. The gradation of the material was first determined following the European Standard EN 933-1 (2009) for aggregates. However, as this recycled material has significant fines content, the particle size distribution was also determined according to ISO/TS 17892-4 (2004). The specified gradation limits for backfill materials of mechanically stabilized earth walls (MSEW), segmental retaining walls (SRW) and reinforced soil slopes (RSS) specified by the Federal Highway Administration (FHWA, 2010) and the National Concrete Masonry Association (NCMA, 2010) are also represented in Fig. 2. The particle size distribution of the C&DW is consistent with the requirements of FHWA for reinforced soil slopes (RSS) and the requirements of NCMA for segmental retaining walls (SRW). The gradation limits for backfill materials of MSEW are not fulfilled by this recycled material. The use of alternative filling materials imposes environmental concerns regarding the potential contamination of groundwater. Thus, the assessment of the release of dangerous substances by the recycled C&DW must be performed. To evaluate the short term release of contaminants of the recycled C&DW, laboratory leaching tests, in accordance with the European Standard EN 12457-4 (2002), were carried out. Following the standard EN 12457-4 (2002), the material was sieved through a 10 mm sieve. The oversized particles were crushed and added to the laboratory sample. Then an aliquot of the sample was dried at 105
C and the dry weight was evaluated. Approximately 90 g of the dried sample was moved to a 1 litre (l) leaching bottle and the leachant (water) was added at a liquid to solid ratio of 10 l/kg (L/S ¼ 10). After that, the leaching bottle was shaken for 24 h in a shaking device. The suspended matter was then filtered through a 0.45 mm membrane filter and aliquots of the filtrated leachate were transferred into separate containers, suitable for the individual analyses. The Federal Highway Administration (FHWA, 2010) recommends, for the construction of mechanically stabilized earth walls and reinforced soil slopes, using backfill materials with an organic content of less than 1%. The evaluation of the organic content

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C.S. Vieira et al. / Journal of Cleaner Production xxx (2016) 1e13 Table 1 Classification of recycled C&DWconstituents. Constituents Concrete, concrete products, mortar, concrete masonry units, Rc (%) Unbound aggregate, natural stone, hydraulically bound aggregate, Ru (%) Clay masonry units, calcium silicate masonry units, aerated non-floating concrete, Rb (%) Bituminous materials, Ra (%) Glass, Rg (%) Soils, Rs (%) Other materials, X (%) Floating particles, FL (cm3/kg)

40.0 36.5 10.8 0.5 1.2 10.8 0.1 10

(humus) of the recycled C&DW was carried out following the disposed in Section 15 of the European Standard EN 1744-1 (2009). The method is based on the principle that humus develops a dark colour when it reacts sodium hydroxide (NaOH). The intensity of the colour depends on the humus content. If the solution is clear or only slightly coloured, the aggregate does not contain an amount of humus that is considered to be significant (EN 1744-1, 2009). The sample was dried at 40
C and then passed on a 4 mm sieve. A 3% sodium hydroxide (NaOH) solution was poured into a glass bottle to a height of 80 mm. A portion of the dried material passed in the 4 mm sieve was then introduced in the glass bottle, until the height of aggregate and solution have reached about 120 mm. The bottle was shacked vigorously for 1 min and afterwards left to stand for 24 h. After this procedure, the colour of the solution is compared to a standard colour solution contained in a similar clear cylindrical glass bottle. Since the colour of the solution containing the recycled C&DW is lighter than the standard colour, it can be concluded that the amount of humus (organic material) is negligible. Three commercially available geosynthetics for soil reinforcement were used in this study: an extruded uniaxial high density polyethylene (HDPE) geogrid (Fig. 3a), a laid uniaxial geogrid manufactured of extruded polyester (PET) bars with welded rigid

3

junctions (Fig. 3b) and a high-strength composite geotextile consisting of polypropylene (PP) continuous-filament needle-punched nonwoven and high-strength PET yarns (Fig. 3c). The main properties of these geosynthetics, provided by the manufacturers, are summarized in Table 2. The direct shear tests were performed on a large scale direct shear apparatus (Fig. 4). The equipment is composed by the shear box (split into two halves), a support structure, five hydraulic actuators and respective fluid power unit, an electrical cabinet, internal and external transducers and a computer to control the assemblage and run of the tests (Vieira et al., 2013). The upper shear box, with dimensions of 300 mm  600 mm  150 mm in width, length and height, respectively, is fixed in the horizontal dimensions. Its vertical position is controlled by two hydraulic actuators positioned in its short edges (Fig. 4). In the lower shear box, mobile in the horizontal direction, a rigid base or a rigid ring can be inserted. When the rigid base is placed inside the lower shear box, the apparatus is able to perform constant contact area direct shear tests. If the rigid ring is put in place, a reduced contact area shear box (with 300 mm  600 mm) is materialized. For the characterization of the shear strength of the recycled C&DW and of the interfaces with geogrids (with large apertures), reduced contact area direct shear tests (lower and upper shear boxes filled with fill material) were carried out. Following the recommendations of EN ISO 12957-1 (2005), direct shear tests with the rigid base placed inside the lower box (constant contact area shear test) were performed to characterize the C&DW/geocomposite interface. The dry density-moisture content relationship of the recycled C&DW was determined by Modified Compaction Proctor tests carried out following the European Standard EN 13286-2 (2004). Inside the shear boxes, C&DW samples were compacted in four layers (25 mm thick) at 90% of maximum Modified Proctor dry density (gdmax ¼ 19.2 kN/m3) and at the optimum water content (Wopt ¼ 12.5%). The geosynthetic specimens were held with screws at the front edge of the lower box outside the shear area (Fig. 4). All direct shear tests were performed with a constant displacement rate of 1 mm/min at normal stresses of 25, 50, 100 and 150 kPa. Prior to shearing, the normal stress was applied to the

100%

90%

80%

Limiting gradation requirements of reinforced backfill soil : According to NCMA for SRW structures According to FHWA for MSEW structures

Percent Passing

70%

According to FHWA for RSS structures

60%

50%

40%

30%

20%

10%

0% 0.001

0.01

0.1

Particle size (mm)

1

10

100

Fig. 2. Particle sizes recommended by FHWA (2010) and NCMA (2010) and particle size distribution of the recycled C&DW.

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Fig. 4. Direct shear tests apparatus (detail of geosynthetic fixing).

Fig. 3. Visual aspect of the geosynthetics (ruler in centimetres): (a) GGR1 e uniaxial HDPE geogrid; (b) GGR2 e uniaxial PET geogrid; (c) GCR e geocomposite.

Table 2 Main properties of the geosynthetics.

Raw material Unit weight (g/m2) Aperture dimensions (mm) Width of longitudinal members (mm) Width of transverse members (mm) Thickness of longitudinal members (mm) Thickness of transverse members (mm) Mean value of the tensile strength (kN/m) Strain at maximum load (%) a

Machine direction/Cross direction.

GGR1

GGR2

GCR

HDPE 450 16  219 6 16 1.1 2.5 to 2.7 68 11 ± 3

PET 380 30  73 10 7 1 1 80/20a 8

PP & PET 340 e e e e e 75/14a 10

specimens for 1 h. Vertical displacements of the loading plate before and during shear were recorded with a linear variable displacement transducer (LVDT) in the centre of the loading plate. The tests were stopped once the horizontal shear displacement reached approximately 60 mm. The interfaces C&DW/geosynthetic were also characterized through pullout tests. As recommended by the standard EN 13738 (2004), the test were carried out with a constant displacement rate of 2 mm/min. For the results herein presented, the pullout tests were performed under normal stress of approximately 31 kPa at interface level (25 kPa at the top of the box). The displacements at different points along the length of the geosynthetic were monitored using inextensible wires connected to the geosynthetics and to linear potentiometer placed outside the pullout box. To ensure repeatability of test results, three tests were carried out for each interface. The large-scale pullout test apparatus used in this research was developed within the scope of previous research (Lopes and Ladeira, 1996a, 1996b). The test apparatus is composed by a pullout box (1000 mm  1530 mm  800 mm), a vertical load application system, a horizontal force actuator device and all the required instrumentation (load cells, displacement transducers and linear potentiometers). Fig. 5a presents an overall view of the apparatus. To minimise the frictional effects of the frontal boundary, the apparatus is fitted with a 200 mm sleeve inside the box (Fig. 5b). Similarly to the procedure followed in direct shear tests, recycled C&DW was compacted inside the pullout box in four layers (150 mm thick) at 90% of maximum Modified Proctor dry density (gdmax ¼ 19.2 kN/m3) and at the optimum water content (Wopt ¼ 12.5%). When the fill level reached the sleeve, located at half height (300 mm), the geosynthetic was laid over the compacted C&DW (Fig. 5b) and fixed to the clamp outside the box. The inextensible wires were connected to the geosynthetic specimen at several

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5

Fig. 5. Pullout test apparatus: a) general overview; b) sleeve inside the box and inextensible wires fixed along the geosynthetic's length.

locations along its length (Fig. 5b) and to linear potentiometers at the back of the pullout box. Then, two additional layers of filling material were placed and compacted over the geosynthetic, using similar procedures to those for the two initial layers, resulting in a total height of 600 mm. In order to analyse the potential influence of the inextensible wires connected to the geosynthetics on their pullout behaviour, one of the three tests carried out for each interface was performed without these elements. The specimens of geogrid GGR1 were tested with initial dimensions (inside the pullout box) of 300 mm in width and 900 mm long, the specimens of geogrid GGR2 were tested with 250 mm in width and 750 mm in length and the geocomposite specimens were tested initial with dimensions of 330 mm in width and 1000 mm long. The ratio width/length of all the geosynthetic samples was kept equal to 1/3, being the differences in the initial dimensions due to the geometry of the geogrids (Fig. 3). 3. Results and discussion 3.1. Laboratory leaching tests Table 3 presents the results of laboratory leaching tests, as well as, the acceptance criteria for leached maximum concentration for inert landfill, define by the European Council Decision 2003/33/EC (Council Decision, 2003/33/EC). Only sulphate and Total Dissolved Solids (TDS) exceeded the maximum values stipulated by the European legislation for inert materials. In experiments (leaching columns tests) carried out by Townsend et al. (1999) on mixed C&DW, high concentrations of TDS and sulphate were also detected. As regard the sulphate value, the Directive 2003/33/EC states that “if the waste does not meet these values for sulphate, it may still be considered as complying with the acceptance criteria if the leaching does not exceed 6000 mg/kg at L/S ¼ 10 l/kg, determined either by a batch leaching test or by a percolation test under conditions approaching local equilibrium”. According to the same Council Decision, “the values for total dissolved solids (TDS) can be used alternatively to the values for sulphate and chloride”, which means its evaluation is not compulsory. According to Jang and Townsend (2001) the source of the sulphates in recycled aggregates is predominantly gypsum drywall

(CaSO4.2H2O), also known as wallboard or sheetrock, a very common component of mixed recycled aggregates. However, the contribution of other components to the leaching of sulphates have also been reported. Barbudo et al. (2012b) have observed, from leaching results, that the highest amounts of sulphates were detected in the recycled aggregates with the highest amounts of ceramic particles. On the other hand, the same researchers have also concluded that the correlation between the percentage of gypsum and the amount of sulphates leached was not relevant. Thus, the sulphates in leaching processes come not only from gypsum but also from other compounds of recycled aggregates such as concrete and mortar, natural aggregates and ceramic particles (Barbudo et al., 2012b). Based on column leaching test results carried out on mixed C&D wastes, Townsend et al. (1999) have concluded that sulphate and calcium ions are the largest contributors to the dissolved solids content. Townsend et al. (1999) have determined that gypsum drywall was the source of the high concentrations of TDS. It is important to point out that cement based materials contain usually gypsum as setting regulator. The addition of gypsum to the clinker is made in order to retard ‘‘fast setting’’. Gypsum undergoes rapid reactions with clinker minerals, forming a protective layer of calcium sulpho-aluminates (e.g., ettringite or monosulphate) on the reactive mineral phase (Conner, 1993). Therefore, the concentration of sulphates and TDS detected in the leaching of the recycled C&DW can have different sources: concrete, mortar, natural aggregates, ceramic materials and some gypsum amount that may not have been removed in the recycling process. It is worth mentioning that sulphate and TDS concentrations in the leachate are far away from the limit values for non-hazardous waste (20 000 mg/kg and 60 000 mg/kg, respectively). On the basis of the leaching tests results and provisions of Directive 2003/33/EC, one can considered that this recycled C&DW can be classified as inert material. The Federal Highway Administration (FHWA, 2010) recommends, for the construction of mechanically stabilized earth walls and reinforced soil slopes, using backfill materials with a pH value between 5 and 10. As shown in Table 3, this recycled C&DW has an alkaline pH value (pH ¼ 8.2) within the above mentioned range. The effects induced by recycled C&DW on geosynthetics mechanical behaviour have been studied through the construction of damage trial embankments (Vieira and Pereira, 2015a). The exposure of geosynthetics to recycled C&DW under real atmospheric

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Table 3 Results of laboratory leaching tests. Parameter

Value (mg/kg dry substance)

Acceptance criteria for leached concentrations e inert landfill

Arsenic, As Lead, Pb Cadmium, Cd Chromium, Cr Copper, Cu Nickel, Ni Mercury, Hg Zinc, Zn Barium, Ba Molybdenum, Mo Antimony, Sb Selenium, Se Chloride, Cl Fluoride, F Sulphate, SO4 Phenol index Dissolved Organic Carbon, DOC Total Dissolved Solids, TDS pH

0.021 <0.01 <0.003 0.012 0.10 0.011 <0.002 <0.1 0.11 0.018 <0.01 <0.02 300 6.1 3200 <0.05 220

0.5 0.5 0.04 0.5 2 0.4 0.01 4 20 0.5 0.06 0.1 800 10 1000 1 500

6580

4000

8.2

e

angles in the range 0e20 kPa and 40
e47
, respectively (Ferreira et al., 2015a). Direct shear test results provide evidence that this recycled C&DW meets the shear strength requirements for usage as construction material in geotechnical engineering applications, particularly in the construction of geosynthetic reinforced structures. 3.3. Characterization of recycled C&DW/geosynthetic interfaces through direct shear tests Fig. 8 presents results of direct shear tests carried out to study the shear strength of the interface between the recycled C&DW and the geogrid GGR1 (Fig. 3a). Fig. 8a illustrates the evolution of shear stresses as function of imposed shear displacements for different values of the normal stress (s). The maximum shear stress reached for each value of s and the corresponding best fit straight line (failure envelope) are shown in Fig. 8b. Shear stress-shear displacement curves have not revealed any peak of strength. After being reached a maximum value, the shear stress remained almost constant with increasing displacement. The results for the direct shear test carried out under s ¼ 100 kPa was 160

conditions for 12 months has induced a slight loss of geosynthetics' strength (with more significance for the high-strength composite geotextile, GCR). Notwithstanding, these losses of strength were only slightly higher than those induced by a granite residual soil under similar conditions.

100 kPa Shear stress (kPa)

The shear strength of the recycled C&DW was evaluated through direct shear tests carried out under confining pressures of 25, 50, 100 and 150 kPa. The evolution of the shear stress as a function of the imposed shear displacement for these direct shear tests is shown in Fig. 6a. Fig. 6b presents the vertical displacements, recorded at the centre of the loading plate, during shear. Strain-hardening behaviour in shear stress versus shear displacement curves is evident particularly for high normal stress (100 kPa and 150 kPa). For lower normal stresses (25 kPa and 50 kPa), after being reached the maximum shear stress, it remains almost constant with increasing displacement until the end of test. As regards the vertical displacements of loading plate during shear (Fig. 6b), the behaviour was also different for low normal stresses (25 kPa and 50 kPa) and higher normal stresses (100 kPa and 150 kPa). For tests carried out under confining pressure of 25 and 50 kPa, the material showed a light compression at the early stages of the shearing, followed by a slight dilation with increasing the shear displacement. The vertical displacements recorded during the direct shear tests carried out under normal stress of 100 kPa and 150 kPa were quite similar, showing a compression on volume with the shear displacement increase. This response contradicts the typical behaviour of natural granular materials, for which a dilatant behaviour is associated with strain-softening behaviour. Fig. 7 presents the maximum shear stress for discrete values of normal stress (25, 50, 100 and 150 kPa), as well as, the corresponding the best fit straight line. Based on the MohreCoulomb failure criterion, this recycled C&DW revealed a friction angle of 40.4
and a cohesion of 13.8 kPa. Granular soils such as dense sands and gravels, typically specified in geotechnical applications, have generally peak friction angles of 40
e48
(Hough, 1957). Portuguese granite residual soils tested at its optimum moisture content have cohesion and friction

120

80

50 kPa 40

25 kPa

0 0

(a)

10

20

30

40

50

60

Shear displacement (mm)

2

1

Vertical displacement (mm)

3.2. Shear strength of the recycled C&DW

150 kPa

25 kPa 50 kPa 0

100 kPa

-1

150 kPa

-2 0

(b)

10

20

30

40

50

60

Shear displacement (mm)

Fig. 6. Results of direct shear tests of recycled C&DW under different confining pressures: a) shear stress vs shear displacement; b) vertical displacement of loading plate.

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C.S. Vieira et al. / Journal of Cleaner Production xxx (2016) 1e13

160

120

Shear stress (kPa)

150 kPa 80

100 kPa

50 kPa

40

25 kPa 0

(a)

0

10

20 30 40 Shear displacement (mm)

50

60

200

τ = 0.6188σ + 9.4 R2 = 0.999 150

Shear stress (kPa)

slightly different being visible some interface hardening. Following the MohreCoulomb failure criterion (Fig. 8b), this interface can be characterized through a friction angle of 31.7
and an adhesion of 9.4 kPa. The results of direct shear tests performed to characterize the shear strength of the interface C&DW/GGR2 are shown in Fig. 9. Although the physical and mechanical differences of these geogrids, shear stress versus shear displacement relationship of C&DW/GGR2 interface is similar to that observed for C&DW/GGR1 interface. As regard interface shear strength parameters C&DW/ GGR2 interface revealed a friction angle of 33.1
and an adhesion of 6.6 kPa (Fig. 9b). Fig. 10 presents results of direct shear tests carried out to study the shear strength of the interface between the recycled C&DW and the high strength geotextile GCR (Fig. 3c). Shear stress-shear displacement curves showed a slight decrease of shear stresses after a maximum value (Fig. 10a) not evidenced in geogrid interfaces (Figs. 8a and 9a). The maximum shear stress reached for each value of s and the failure envelope are shown in Fig. 10b. Based on the MohreCoulomb failure criterion, the C&DW/GCR interface presented a friction angle of 30.1
and a cohesive component of 12.2 kPa. The comparison of direct shear behaviour of the recycled C&DW and C&DW/geosynthetic interfaces is presented in Fig. 11 through shear stress-shear displacement curves. For simplicity, the curves presented in Fig. 11 refer only to direct shear tests carried out under s ¼ 25 kPa and s ¼ 150 kPa. Regardless of the normal stress, the shear strength of the interfaces is lower than that of the recycled C&D material, which suggests that C&DW/geosynthetic interfaces are potential sliding surfaces when the direct shear mechanism is of concern. Regarding the interfaces shear strength (maximum shear stress recorded during shear), the values achieved in the three interfaces are not very different. However, the shear displacement, for which the interface shear strength was obtained, was quite distinct. The maximum shear stresses for C&DW/GCR interface were achieved for lower shear displacements than those recorded for the C&DW/ geogrid interfaces (Fig. 11). This behaviour could be explained by the non-existence of apertures in the GCR, which means that there is no shear plan between recycled C&DW particles. On the contrary the geogrids have large openings allowing the shear through C&DW.

7

100

50

0 0

(b)

50

100

150

200

Normal stress (kPa)

Fig. 8. Results of direct shear tests carried out on C&DW/geogrid GGR1 interface: (a) shear stresseshear displacement curves; (b) failure envelope and direct shear strength properties.

The relationship between the shear strength of the C&DW and the shear strength of the interfaces will be quantitatively evaluated in Section 3.4 through the coefficient of interaction.

200

τ = 0.8512σ + 13.8

3.4. Characterization of recycled C&DW/geosynthetic interfaces through pullout tests

R2 = 0.998

Shear stress (kPa)

150

100

50

0 0

50

100 Normal stress (kPa)

150

200

Fig. 7. Failure envelope and direct shear strength properties of recycled C&DW.

As mentioned in Section 2, the influence of the use of potentiometers, glued to the geosynthetics through their length, was also studied in this work. One of the three pullout tests (for each interface) was carried without the inextensible wires. Sample 1 and sample 3 of the geogrid GGR1 and geotextile GCR were tested with the potentiometers while sample 2 was tested without the installation of potentiometers (i.e, without recording the displacements along the geosynthetic length). Geogrid GGR2 is manufactured of extruded flat bars with welded rigid junctions (Fig. 3b). Preliminary pullout tests carried out with potentiometers have revealed that the junctions (connection of longitudinal and transversal bars) at the end of tests were entirely broken. To avoid the potential reduction of the interface pullout strength due to the presence of the inextensible wires glued to the geogrid, geogrid GGR2 was tested without potentiometers.

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160

Shear stress (kPa)

120

150 kPa 80

100 kPa

50 kPa

40

25 kPa 0 0

(a)

10 20 30 40 Shear displacement (mm)

50

60

200

Shear stress (kPa)

τ = 0.5808σ + 12.2 R2 = 0.998

150

100

50

0 0

50

100

(b)

Fig. 12 presents the results of pullout test carried out with geogrid GGR1. The evolution of pullout force, per unit width, with the actuator displacement is shown in Fig. 12a. The displacements (resulting from sliding and elongation of the geogrid), recorded by the potenciometers along the geogrid's length, at maximum pullout force are plotted in Fig. 12b. Analysing Fig. 12a one can concluded that sample 2, tested without potentiometers, showed greater pullout resistance, while small differences between specimens tested with potentiometers are visible. Indeed, the pullout test carried out without the installation of potentiometers led to a slight increase in pullout resistance of the geogrid mobilized to larger displacement. The pullout force increased progressively with actuator displacement until a maximum value, then a sudden failure occurred showing that the geogrid failed by insufficient tensile strength under pullout test conditions (Fig. 13). The mean value and the coefficient of variation (COV) of maximum pullout resistance are 41.9 kN/m and 8.3%, respectively. The tensile strength of this geogrid in confinement conditions was significantly lower (38.5%) than that reported by the manufacturer in in-isolation conditions (Table 2). This reduction of tensile strength should be attributed mainly to the different test conditions, as well as, some damage induced by the recycled C&DW on

200

Normal stress (kPa)

Fig. 10. Results of direct shear tests carried out on C&DW/geotextile GCR interface: (a) shear stress-shear displacement curves; (b) failure envelope and direct shear strength properties.

160 140

C&DM C&DM/GCR

120

Shear stress (kPa)

Fig. 9. Results of direct shear tests carried out on C&DW/geogrid GGR2 interface: (a) shear stresseshear displacement curves; (b) failure envelope and direct shear strength properties.

150

150 kPa

100

C&DM/GGR2

80

C&DM/GGR1

60

C&DM/GCR

40

25 kPa

C&DM

20

C&DM/GGR2 0 0

10

20

30

40

50

60

Shear displacement (mm) Fig. 11. Comparison of shear stress versus shear displacement curves for C&DW and C&DW/geosynthetic interfaces (s ¼ 25 kPa and s ¼ 150 kPa).

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C.S. Vieira et al. / Journal of Cleaner Production xxx (2016) 1e13

the geogrid. This evidence has also been reported by other researchers (Ferreira et al., 2015b; Lopes and Ladeira, 1996a; Moraci and Recalcati, 2006) in pullout tests carried out with soils. Regarding the displacements recorded along the geogrid's length at maximum pullout force (Fig. 12b) it is possible to notice the progressive decrease with the distance from the actuator being the displacements at rear end of the geogrid very small. This displacements pattern agrees with the failure by insufficient tensile strength (also called tensile failure). Fig. 14 presents the evolution of pullout force, per unit width, with the actuator displacement for pullout test carried out with geogrid GGR2. All the samples of this geogrid failed due to a deficient adherence with the surrounding material, i.e pullout failure occurred. Sample 1 had a slightly different behaviour with some sudden decreases of the pullout force. These failures correspond to the rupture of the junctions between the longitudinal and transversal bars. Fig. 15 shows that, even without the installation of potentiometers, almost all the junction areas at the end of the pullout tests were broken. Although the rupture of the junctions during the pullout tests, the transversal bars have a significant contribution to the pullout resistance due to the passive resistance mobilised on these elements. The maximum pullout force reduces approximately 60% when the geogrid transversal bars are removed (Pereira et al., 2015).

50 Sample 1 Sample 2

Pullout force (kN/m)

40

Sample 3

30

20

10

0

(a)

0

50

100 150 Actuator displacement (mm)

200

9

Fig. 13. Geogrid GGR1 specimen at the end of a pullout test.

The mean value of maximum pullout force was 39.4 kN/m (COV ¼ 13%) for mean frontal displacement of 59.3 mm (COV ¼ 18%). Fig. 16 exhibits the results of pullout test carried out with the high strength geotextile, GCR. The evolution of pullout force, per unit width, with the frontal displacement is shown in Fig. 16a while the displacements recorded by the potentiometers along the length of the geotextile, at maximum pullout force, are plotted in Fig. 16b. As observed for geogrid GGR1, the sample tested without potentiometers (Sample 2) exhibited slightly higher pullout resistance, while small differences in the pullout strength of the other specimens are noticeable. The pullout force increased progressively with actuator displacement until a maximum value then several sudden decreases were observed. These variations result from the rupture of PET yarns (Fig. 3c) that provide the main portion of the geocomposite tensile strength (the contribution of the nonwoven PP

70

50

Sample 1

60

Sample 1 Sample 2

40

50

Pullout force (kN/m)

Displacement (mm)

Sample 3

40 30 20

Sample 3

30

20

10

10 0

(b)

0

0.2

0.4 0.6 Geogrid length (m)

0.8

1

Fig. 12. Results of pullout test for geogrid GGR1:(a) pullout force-frontal displacement; (b) displacements along the specimens at maximum pullout force.

0 0

50

100 150 Actuator displacement (mm)

200

Fig. 14. Results of pullout tests for the geogrid GGR2.

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C.S. Vieira et al. / Journal of Cleaner Production xxx (2016) 1e13

3.5. Coefficients of interaction In the design of geosynthetic reinforced structures, the interfaces strength is typically based on interaction coefficients. The value of these parameters is particularly important to define the geosynthetics' length. When direct shear tests are carried out, the coefficient of interaction, fg, is defined as the ratio of the maximum shear stress in a C&DW/geosynthetic direct shear test, to the maximum shear stress in a direct shear test on C&D material, under the same normal stress, s:

fg ¼

tmax C&DW=geo ðsÞ tmax C&DW ðsÞ

(1)

When pullout failure is expected, the pullout interaction coefficient, fb, should be estimated. The pullout interaction coefficient, fb, could be defined as:

50 Sample 1 Sample 2

40

Pullout force (kN/m)

geotextile to the tensile strength is very small). Pullout failure of geotextile GCR results from sliding and rupture of PET yarns. At maximum pullout force the displacements at the free end of the specimens were almost null (Fig. 16b) proving that tensile failure of the PET yarns has occurred. Notwithstanding the tensile strength reached in pullout tests is quite lower than the tensile strength obtained from wide width tensile tests. The mean value of the maximum pullout force was 41.8 kN/m (COV ¼ 8.1%), very similar to the value achieved for the geogrid GGR1, and it was mobilised for a mean frontal displacement of 83.4 mm (COV ¼ 8.7%). Fig. 17 compares the evolution of pullout force with the actuator displacement for one sample of each geosynthetic under analysis. Although their tensile strength values are in the same range (Table 2), these three geosynthetics exhibited different pullout behaviour. The geogrid GGR2, being the more resistant and less extensible geosynthetic, fails by lack of adherence. The geogrid GGR1, having a lower tensile resistance than that of geogrid GGR2, fails by insufficient tensile strength under pullout test conditions. Although geotextile GCR has exhibited a pullout resistance similar to the geogrid GGR1, the failure was more ductile, resulting from the progressive failure or sliding of the PET yarns. Due to its structure (more flexible continuous sheet) the geocomposite GCR exhibited a smaller initial stiffness during pullout.

Sample 3

30

20

10

(a)

0 0

50

100 150 Actuator displacement (mm)

200

100 Sample 1 80

Displacement (mm)

10

Sample 3

60

40

20

0 0

(b)

0.2

0.4 0.6 Geogrid length (m)

0.8

1

Fig. 16. Results of pullout test for geotextile GCR: (a) pullout force-frontal displacement; (b) displacements along the specimens at maximum pullout force.

fb ¼

tmax ðsÞ pullout max tdirect shear ðsÞ

(2)

where tmax is the maximum shear stress mobilised at C&DW/ pullout geosynthetic interface during a pullout, test carried out under

Fig. 15. Rupture of the junctions between the longitudinal and transversal bars at the end of pullout test (GGR2).

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C.S. Vieira et al. / Journal of Cleaner Production xxx (2016) 1e13

50

11

1

Geogrid GGR1

Pullout force (kN/m)

Coefficient of interaction, fg

Geogrid GGR2

40

Geotextile GCR

30

20

10

0.75

0.5

C&DW/GGR1

0.25

C&DW/GGR2 C&DW/GCR

0 0

50

100 150 Actuator displacement (mm)

200

confining pressure of s, and tmax is the direct shear strength direct shear of the recycled C&D material under the same value of confining pressure, s. The maximum shear stress mobilised at C&DW/geosynthetic interface in pullout conditions could be estimated by:

PR ðsÞ 2  LR

0

25

50

75

100

125

150

175

Normal stress (kPa)

Fig. 17. Comparison of pullout behaviour of the geosynthetics used in this study.

tmax pullout ðsÞ ¼

0

(3)

where PR is the maximum pullout force, per unit width, under the confining pressure of s and LR is the confined length of the geosynthetic at the maximum pullout force. Fig. 18 presents the coefficients of interaction, fg, estimated by equation (1), for the three interfaces under analysis. The coefficients of interaction are in the range 0.70e0.73 for C&DW/GGR1 interface, ranged from 0.65 to 0.74 for the interface C&DW/GGR2 and ranged from 0.70 to 0.76 for the C&DW/GCR interface. Even if the materials tested are distinct (two different geogrids and a high strength geotextile), the shear strength of the interfaces are quite similar. It should be highlighted that the coefficients of interaction achieved for these interfaces are higher than the value usually assumed (in the absence of test results) in the design of geosynthetic reinforced structures. These values are generally consistent with those reported by other researchers for soilegeogrid interfaces. The coefficients of interaction achieved for the C&DW/geogrid interfaces (HDPE and PET geogrid) are similar to the values reported by Abu-Farsakh et al. (2007) for clay/geogrid interfaces at the optimum compaction conditions and by Ferreira et al. (2015a) for residual soil/HDPE geogrid at the optimum moisture content. The values of fg are slightly higher than those presented by Arulrajah et al. (2013b) for interfaces between a PP biaxial geogrid and recycled concrete aggregate or crushed bricks. For the interface C&DW/GCR the coefficients of interaction, fg, are within the same order of magnitude as those presented by AbuFarsakh et al. (2007) for soil/geotextile interfaces and higher than those presented by Ferreira et al. (2015a) for the interface between a similar geocomposite and a granite residual soil. Table 4 presents the mean values of the maximum shear stress mobilised at C&DW/geosynthetic interfaces in pullout conditions, tpullout, the direct shear strength of the recycled C&DW, tdirect shear, and the pullout interaction coefficient, fb.

Fig. 18. Coefficients of interaction for shear strength against normal stress.

The pullout interface coefficients summarized in Table 4 are in the usual range of this parameter for soil/geosynthetic interfaces under similar conditions. Goodhue et al. (2001) reported values ranging between 0.25 and 1.4 for different geosynthetics embedded in uniformly-graded quartz sand. Tang et al. (2008) reported values of the pullout interaction coefficient ranging from 0.62 to 1.00 for geogrids tested in well-graded crushed stone. Hsieh et al. (2011) obtained values comprised between 0.18 and 1.25 from pullout tests of geosynthetics. Ferreira et al. (2015b) presented values of fb in the range 0.25e0.52 for interfaces between different geosynthetics and a granite residual soil. 4. Conclusions Physical, mechanical and environmental characterization of a fine grain recycled C&DW, as well as, the direct shear and pullout behaviour of the interfaces between this recycled material and three different geosynthetics were presented in this paper. Laboratory leaching tests carried out on recycled C&DW revealed high concentrations of total dissolved solids (TDS) and sulphate. However, since the concentration of sulphate in the leachate did not exceed 6000 mg/kg and the evaluation of TDS is not compulsory, this recycled C&DW can be classified as inert material in accordance with the provisions of European Directive 2003/33/EC. An alkaline pH within the range recommended for the construction geosynthetic reinforced structures was found in the leachate. Notwithstanding additional studies on the potential degradation induced by recycled C&DW on geosynthetics mechanical behaviour should be carried out. The mechanical characterization of the recycled C&DW pointed out that these materials if properly compacted exhibit shear strength similar to the backfill materials commonly used in the construction of geosynthetic reinforced structures.

Table 4 Values of the parameters tpullout, tdirect

shear

and fb.

Interface

tpullout (kPa)

tdirect shear (kPa)

fb

C&DW/GGR1 C&DW/GGR2 C&DW/GCR

25.18 23.47 25.62

40.19

0.63 0.58 0.64

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C.S. Vieira et al. / Journal of Cleaner Production xxx (2016) 1e13

The interaction mechanism between the geosynthetic and the filling material has an utmost importance in the design of geosynthetic reinforced structures (GRS). This mechanism depends on the fill properties, reinforcement characteristics and interaction between the reinforcement and the surrounding material. The coefficients of interaction, based on direct shear test results, reached for C&DW/geosynthetic interfaces compare well with those reported in the literature for soil/geosynthetic interfaces under similar conditions. Pullout interaction coefficients, estimated through laboratory pullout tests, are also in the usual range of this parameter for soil/geosynthetics interfaces. This paper presents preliminary results of a broader research project currently under development. The potential degradation induced by recycled C&DW on geosynthetics mechanical behaviour has also been studied (Vieira and Pereira, 2015a). The results available to date have revealed that the loss of geosynthetics' strength after 12 months of exposure to recycled C&DW under real atmospheric conditions is not particularly significant. The long term behaviour of the recycled C&DW, its leaching behaviour, as well as, the effect of its moisture content should also be studied. Even so, it is possible to state that the use of recycled C&DW as filling material of geosynthetic reinforced structures seems to be an auspicious solution, able to balance the environmental and economic demands of current societies. Acknowledgements The authors would like to thank the financial support of Portuguese Science and Technology Foundation (FCT) and FEDER, through the Research Project: FCOMP-01-0124-FEDER-028842, RCD-VALOR e (PTDC/ECM-GEO/0622/2012). The authors also thank Tensar International, Naue and TenCate Geosynthetics Iberia for providing the geosynthetics used in the study. References Abu-Farsakh, M., Coronel, J., Tao, M., 2007. Effect of soil moisture content and dry density on cohesive soilegeosynthetic interactions using large direct shear tests. J. Mater. Civ. Eng. 19 (7), 540e549. Arulrajah, A., Piratheepan, J., Disfani, M., Bo, M., 2013a. Geotechnical and geoenvironmental properties of recycled construction and demolition materials in pavement subbase applications. J. Mater. Civ. Eng. 25 (8), 1077e1088. Arulrajah, A., Rahman, M., Piratheepan, J., Bo, M., Imteaz, M., 2013b. Interface shear strength testing of geogrid-reinforced construction and demolition materials. ASTM Adv. Civ. Eng. Mater. 2 (1), 189e200. Arulrajah, A., Rahman, M.A., Piratheepan, J., Bo, M.W., Imteaz, M.A., 2014. Evaluation of interface shear strength properties of geogrid-reinforced construction and demolition materials using a modified large scale direct shear testing apparatus. J. Mater. Civ. Eng. 26 (5), 974e982.
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Vieira, C.S., Lopes, M.L., Caldeira, L., 2015. Sand-Nonwoven geotextile interfaces shear strength by direct shear and simple shear tests. Geomech. Eng. 9 (5), 601e618. Vieira, C.S., Lopes, M.L., Caldeira, L.M., 2013. Sand-geotextile interface characterisation through monotonic and cyclic direct shear tests. Geosynth. Int. 20 (1), 26e38. Vieira, C.S., Pereira, P.M., 2015a. Damage induced by recycled construction and demolition wastes on the short-term tensile behaviour of two geosynthetics. Transp. Geotech. 4, 64e75. Vieira, C.S., Pereira, P.M., 2015b. Interface shear properties of geosynthetics and construction and demolition waste from large-scale direct shear tests. Geosynth. Int. 23 (1), 62e70. Vieira, C.S., Pereira, P.M., 2015c. Use of recycled construction and demolition materials in geotechnical applications: a review. Resour. Conserv. Recycl. 103, 192e204. Vieira, C.S., Pereira, P.P., Lopes, M.L., 2014. Behaviour of geogrid-recycled construction and demolition waste interfaces in direct shear mode. In: Proc. of the 10th International Conference on Geosynthetics, ICG 2014, ESTREL Convention Center Berlin, Germany, 21e25 September 2014. Xuan, D.X., Molenaar, A.A.A., Houben, L.J.M., 2015. Evaluation of cement treatment of reclaimed construction and demolition waste as road bases. J. Clean. Prod. 100, 77e83.

Please cite this article in press as: Vieira, C.S., et al., Recycled Construction and Demolition Wastes as filling material for geosynthetic reinforced structures. Interface properties, Journal of Cleaner Production (2016), http://dx.doi.org/10.1016/j.jclepro.2016.02.115