Utilization of recycled mineral wool as filler in wood–polypropylene composites

Utilization of recycled mineral wool as filler in wood–polypropylene composites

Construction and Building Materials 55 (2014) 220–226 Contents lists available at ScienceDirect Construction and Building Materials journal homepage...

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Construction and Building Materials 55 (2014) 220–226

Contents lists available at ScienceDirect

Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

Utilization of recycled mineral wool as filler in wood–polypropylene composites Olli Väntsi ⇑, Timo Kärki 1 Lappeenranta University of Technology, Department of Mechanical Engineering, Fiber Composite Laboratory, P.O. Box 20, 53851 Lappeenranta, Finland

h i g h l i g h t s  A new recycling method for underutilized waste fraction is presented.  Properties of the composites utilizing recycled mineral wool as filler are presented.  Recycled mineral wool improved the moisture resistance properties of the composites.

a r t i c l e

i n f o

Article history: Received 5 April 2013 Received in revised form 9 January 2014 Accepted 11 January 2014 Available online 8 February 2014 Keywords: Construction and demolition waste Recycling Mineral wool Wood plastic composites Mechanical properties Moisture resistance properties

a b s t r a c t The construction and demolition (C&D) industry is a major source of waste. Environmental regulations and laws have been implemented in many countries to improve and encourage the recycling of C&D waste. To meet tightened regulations, new C&D waste recycling methods must be developed. Mineral wool is a waste fraction that is currently considered un-recyclable. In this study, the mechanical and moisture resistance properties of wood plastic composites utilizing recycled mineral wool as filler are presented. According to the findings, the addition of recycled mineral wool improved the moisture resistance properties of the composites noticeably, but a decrease in some mechanical properties was observed. Ó 2014 Elsevier Ltd. All rights reserved.

1. Introduction The construction and demolition (C&D) industry has been identified as a major source of waste, varying between 13% and 40% of the total solid waste generated, depending on the country [1,2]. Only fragmented information is available about the recycling rates of C&D waste. It has been estimated that about 46% of C&D waste generated in the EU27 countries is recycled [3]. In the US, the recycling rate is estimated to be 20–30% [2]. Environmental regulations and laws concerning the recycling of C&D waste have been implemented in many countries [4], and the European Union has set an binding legislation, according to which 70% of non-hazardous C&D waste has to be prepared for re-use, recycled or recovered by 2020 [5]. Increasing the rate of recycling C&D waste has multiple benefits. A direct effect of increased re-use would be a reduced amount of waste being disposed to legal and illegal landfill sites. ⇑ Corresponding author. Tel.: +358 400 367 322. 1

E-mail addresses: olli.vantsi@lut.fi (O. Väntsi), timo.karki@lut.fi (T. Kärki). Tel.: +358 40 770 8791.

http://dx.doi.org/10.1016/j.conbuildmat.2014.01.050 0950-0618/Ó 2014 Elsevier Ltd. All rights reserved.

The shortage of land for waste disposal and the rising landfilling costs increase the attractiveness of re-using materials instead of disposing them to landfills. There are environment benefits when leachates from landfilled C&D waste decrease. Natural resources are conserved when C&D waste materials are used to replace virgin raw materials [6,7]. The utilization of mineral wool waste could play an important role in improving the recycling percentage of C&D waste. Mineral wool is a general term covering a variety of inorganic insulation materials. Rock wool, glass wool and slag wool, all manufactured from different raw materials, fall under the general term mineral wool [8,9]. Mineral wool is typically used in construction industry for heat insulation, cold and fire protection, and noise insulation [8]. It accounts for about 60% of the total insulation product market [10]. Current solutions for the recycling of mineral wool waste include for example the utilization of mineral wool waste in cement-based composites [11], composite ceramics [12] or wood fiber composites [13]. A new solution for the recycling of mineral wool waste could be utilization of the waste as filler in wood polymer composites. The

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demand for wood polymer composites (WPC) is growing continuously. Typically, wood polymer composites consist of polymer, wood fiber and additives [14]. Coupling agents, lubricants, colorants, flame retardants and different inorganic filler materials are the most typical additives in wood polymer composites [15–18]. Wood polymer composites have a wide range of applications, including decking products, automotive parts and construction products [19–21]. Previously researched inorganic fillers for wood polymer composites include for example calcium carbonate, wollastonite, soapstone, talc, nanoclay, silica, and glass fiber [18,22–24]. These inorganic fillers have shown potential in improving the mechanical, fire retardant and thermal properties of WPC. Inorganic fillers are also cheaper than polymers, and therefore the raw material costs of WPC can decrease when polymers are replaced with inorganic fillers [25]. The chemical composition of mineral wool can vary depending on whether it is glass wool or rock wool. The main component in both rock and glass wool is SiO2 [8]. Glass wool has a slightly higher SiO2 content, while rock wool contains more Fe2O3, giving it a darker color and higher heat resistance [26]. As can be seen in Table 1, the chemical compositions of mineral wool are rather close to that of glass fibers which are used as filler in composites. Pure SiO2, the main component in mineral wool, is also used as filler in composites [24]. The diameter of mineral wool fibers can vary, usually between 0.2 lm and 20 lm [27]. Glass fibers used as filler in composites have diameters around 16 lm [23,26]. It has also been noted that rock fibers with a small diameter (<9 lm) have better diameterstrength relationship than fibers with a larger diameter [26]. The fiber diameter, thermal conductivity or density of mineral wool does not change notably during its service life (30–50 years) [28]. In this study, the effects of mineral wool waste on the mechanical and moisture resistant properties of WPC are investigated. Three different volumes: 20%, 30% and 40% of mineral wool waste have been added to wood/polypropylene composites. The above mentioned properties are investigated and compared to a wood/ polypropylene composite containing no mineral wool waste, and the results are discussed below. 2. Materials and methods 2.1. Materials The thermoplastic matrix in the composites was commercially available recyclable polypropylene supplied by Ineos Polyolefins (Eltex P HY001P). The melt flow index of the polypropylene was 45 g/10 min (230 °C), the melting point was 161 °C and the density 910 kg m 3. Maleated polypropylene (MAPP; OREVACÒ CA 100; Arkema) was used as the coupling agent (MFI 10 g/10 min/190 °C, melting point 167 °C). The Orevac CA 100 polymer has low functionality (1%) and a high molar mass (25 kg mol 1). Struktol TPW 113 was used as the lubricating agent.

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The wood fiber used in the study was conifer with specific gravity of 158 g dm 3 in the recipes containing 20% and 30% of mineral wool waste, and conifer with specific gravity of 180 g dm 3 in the recipe containing 40% of mineral wool. The wood chips with specific gravity of 158 g dm 3 were prepared from sawn timber with a combined chipper/hammer mill apparatus, and the wood chips with 180 g dm 3 were prepared with separated crusher and hammer mill apparatuses. The length distribution of the wood chips was analysed using a microscope camera, and ImageJ software was used to measure the lengths of the fibers in the microscope camera photos. The length distribution for both types of chips is shown in Fig. 1. The mineral wool waste was rock wool waste from a rock wool manufacturing process, and it was obtained from the landfill of a rock wool plant. It was processed with crusher and hammer mill apparatuses before the composite manufacturing stage. The fiber diameter distribution of recycled mineral wool fibers was measured from scanning electron microscope (SEM) pictures taken with Jeol JSM-5800 LV scanning microscope operating at 20 kV. IrfanView version 4.35 graphics software was used to measure the fiber diameters from the pictures. The measured fiber diameter distribution is presented in Fig. 2. 2.2. Manufacturing of wood–polymer composites The amount of polypropylene, coupling agent and lubricant agent were kept constant in all the recipes, at 30%, 3% and 3% by weight, respectively. The amount of wood fiber and recycled mineral wool were as presented in Table 2. All the materials were agglomerated together prior to extruding with agglomeration apparatus consisting of a PLASMEC TRL100/FV/W turbomixer and PLASMEC RFV-200 cooler. Hollow-shape decking boards were then produced with a counterrotating twin-screw extruder, Weber CE7.2. The die temperature was maintained at approximately 185 °C. The screw speed was maintained at 13 rpm and the screw had the L/D ratio of 17. The pressure at the die varied between 3 MPa and 4 MPa, depending on the material blend. The material output varied between 20 kg/h and 28 kg/h, also depending on the material blend. 2.3. Scanning electron microscopy Scanning electron microscopy (SEM) was performed with a Jeol JSM-5800 LV scanning microscope operating at 20 kV. Prior to the analysis, the fracture surfaces were covered with a layer of gold using a sputter coater. 2.4. Mechanical analysis The bending test, flexural impact/Charpy and tensile properties were determined according to standards SFS-EN 310 [29], SFS-EN ISO 179-1 [30] and SFS-EN ISO 527-1 [31], respectively. Brinell-hardness was measured from 75  75 mm samples according to standard SFS-EN 1534 [32]. Moisture resistance under cyclic test conditions was determined according to standard SFS-EN 321 [33], and three-point tests were carried out according to SFS-EN 310 [29] standard after 3 weeks of soak/freeze/dry cycles. The size of the specimens for the bending tests and for moisture resistance under the cyclic test conditions was 450  50 mm. For the flexural impact tests, the size of the specimens was 80  10  5 mm. For measuring the tensile properties, the thickness of the dumbbell-shaped samples were 5 mm, and the width of the narrow part in the samples was 10 mm. For the mechanical measurements, the average of 20 measurements was calculated, except for the tensile property (9–20 accepted measurements) and cyclic three-point tests (10 measurements). The mechanical properties were tested with a Zwick Roell (Z020) apparatus.

3. Results and discussion 3.1. Scanning electron microscopy analysis

Table 1 The chemical compositions of rock wool, glass wool and glass fiber.

SiO2 Al2O3 TiO2 Fe2O3 FeO MnO CaO MgO BaO Na2O K2O B2O3

Rock wool [8]

Rock wool [9]

Glass wool [8]

Glass fiber [26]

46.43 11.42 1.47 4.41 4.72 0.23 17.89 9.24 0.11 3.07 1.01 0

40–52 8–13 1.5–2.7 5.5–6.5 NR 0.1–0.3 10–12 8–15 NR 0.8–3.3 0.8–2.0 NR

56.89 3.47 0.12 0.57 0.18 0.56 12.61 3.61 1.49 12.86 1.36 6

58.25 11.86 0.41 0.30 NR NR 21.09 0.54 NR 0.30 0.43 NR

NR = not reported.

Fig. 3 shows scanning electron microscope pictures taken from the bending fracture surfaces of selected composites, as well as a picture of recycled mineral wool fibers. A good compatibility between the polymer matrix and the recycled mineral wool fibers can be observed in Fig. 3b–e. Both polypropylene and mineral wool fibers are hydrophobic materials, and thus good mechanical adhesion between the materials is expected. Fig. 3a shows micropores in the polymer matrix on the facture surface of composite MW0. It seems that there are less such pores visible in the composites containing recycled mineral wool fibers, although it can be sometimes hard to distinguish a pore from a hole caused by a recycled mineral wool fiber pulled out of the matrix during breakage of the composite. It can also be seen that some fibers pulled out of the polymer matrix. In Fig. 3d and e, holes where recycled mineral

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Fig. 1. Length distribution of the wood chips used in the study.

Fig. 2. Fiber diameter distribution of recycled mineral wool.

Table 2 Amounts of mineral wool waste, wood fiber, polypropylene, coupling agent, and lubricant agent by weight % in the manufactured composites. Recipe name

Recycled mineral wool

Wood fiber

Polypropylene

Coupling agent

Lubricating agent

MW0 MW20 MW30 MW40

0 20 30 40

64 44 34 24

30 30 30 30

3 3 3 3

3 3 3 3

wool fibers have been pulled out of the matrix can be observed. There is no polypropylene matrix attached on the visible surfaces of the recycled mineral wool fibers. This would suggest that the interfacial strength between the recycled mineral wool fibers and polypropylene matrix is lower than the tensile strength of the recycled mineral wool fibers or polypropylene matrix. Therefore, the reinforcing potential of recycled mineral wool fibers cannot be fully utilized unless the interfacial strength can be improved. Fig. 3f exhibits the structure of the mineral wool fibers. The fibers have smooth surfaces compared to wollastonite, for example, which can have similar fiber dimensions but rougher surfaces [18]. Smooth surfaces can ease the pull-out of the fibers, as the mechanical adhesion to the polymer matrix may be weaker than with particles with a rougher surface. It can, however, be observed that the recycled mineral wool fibers are well dispersed in the matrix.

3.2. Flexural properties The flexural strength of the composites decreased when recycled mineral wool was used as filler. Composite MW20 had 20.0% lower flexural strength than composite MW0. Increasing the amount of recycled mineral wool in the composites had less significant effects, as the flexural strength of composites MW30 and MW40 had flexural strengths 24.9% and 26.7% lower than composite MW0, respectively. The flexural strengths of the manufactured composites are presented in Fig. 4. According to Duncan’s multiple range test, the difference in the flexural strengths of the composites MW20, MW30 and MW40 is not statistically significant at the 95% confidence level. The numerical values of the flexural strength and other mechanical properties of the studied composites, as well as the results of statistical analysis are presented in Table 3.

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Fig. 3. Scanning electron microscope pictures of bending fracture surfaces: (a) composite MW0, (b) composite MW20, (c) recycled mineral wool fibers in composite MW20, (d) composite MW30, (e) composite MW40, and (f) recycled mineral wool fibers.

Fig. 4. Flexural strength initially and after cyclic testing for the studied composites.

Ashrafi et al. [34] report that the addition of E-glass fibers to WPCs reduced their flexural strength, and this seemed to be the case with recycled mineral wool as well. Valente et al. [35] report a very slight increase in the flexural strength of WPCs when wood flour was replaced with recycled glass fiber. Ashrafi et al. [34] consider fiber orientation and interfacial bonding of glass fibers and polymer matrix to be the main factors affecting the flexural strength of the composites. They noticed that glass fiber tended to orientate normal to the plunger motion. The same factors could

be considered to affect the flexural strength of the mineral wool-filled composites, as the composites studied here show fiber orientation not parallel with the direction of extrusion in Fig. 3d and e, and as shown in Fig. 3d and e, some fiber pull-out could be observed. As for flexural strength after the cyclic testing, all the tested composites demonstrated lower flexural strength than initially. After the cyclic testing, the flexural strength values of the composites were 76.7%, 87.3%, 75.8% and 78.1% of the initial values for composites MW0-MW40, respectively. Duncan’s multiple range test shows that the difference in flexural strength after the cyclic testing of composites MW30 and MW40 is not statistically significant at the 95% confidence level. The decrease in the flexural strength of the composites after cyclic testing can be explained by changes in the interface bonding between the polymer matrix and wood fibers. Increase in the pore size and amount of pores in the composite matrix could also have contributed to the weakening of the flexural strength [36]. The addition of recycled mineral wool did not seem to change the relative amount of weakening notably, except in the case of MW20, which had lower relative weakening than the other composites. The flexural modulus of the composites decreased with the addition of recycled mineral wool to the composites. MW0 had

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Table 3 Numerical values and statistically meaningful differences of studied mechanical properties. Composite

Flexural strength (MPa)

Flexural strength after cyclic testing (MPa)

Flexural modulus (Gpa)

Flexural modulus after cyclic testing (GPa)

Tensile strength (MPa)

Tensile modulus (Gpa)

Impact strength (kJ/m2)

Brinell hardness (HB)

MW0

23.35 (1.20)A

17.92 (1.00)A

4.44 (0.16)A

3.78 (0.12)A

17.18 (1.08)A

6.04 (0.36)A

16.04 (2.95)A

MW20

18.68 (3.51)B

16.30 (1.16)B

3.78 (0.29)B

3.27 (0.10)B

13.50 (0.75)B

5.51 (0.24)B

MW30

17.53 (2.08)B

13.28 (1.57)C

3.59 (0.20)C

2.76 (0.22)C

8.52 (0.74)C

4.07 (0.43)C

MW40

17.11 (2.26)B

13.37 (1.47)C

4.10 (0.31)D

3.10 (0.14)D

10.41 (1.42)D

5.42 (0.45)B

2.07 (0.27)A 2.30 (0.33)A,B 2.20 (0.48)A,B 2.46 (0.63)B

14.35 (1.66)B 13.39 (1.73)B,C 12.73 (1.84)C

Note: Values in parentheses are standard deviations, means with the same letter in the same column are not significantly different (p > 0.05).

the flexural modulus of 4.44 GPa. The flexular modulus of composites MW20 and MW30 decreased gradually compared to MW0. MW20 had 14.9% lower flexural modulus than MW0, and MW30 had 19.1% lower flexural modulus compared to MW0. The flexural modulus of MW40 was higher than the modulus of MW20 or MW30, but still 7.7% lower than that of MW0. The cyclic testing reduced the flexural modulus of all the studied composites; the reduction was 14.7% for MW0, 13.6% for MW20, 23.0% for MW30 and 24.4% for MW40. The values of the flexural moduli initially and after cyclic testing are presented in Fig. 5.

3.3. Tensile properties

Fig. 6. Tensile strength of the studied composites.

The addition of recycled mineral wool into the composites decreased their tensile strength. Composite MW0 had the tensile strength of 17.2 MPa. MW20 had 21.4% lower tensile strength than MW0, and MW30 had a reduction of 50.4% compared to MW0. MW40 had 22.2% higher tensile strength than MW30, and the reduction in the tensile strength of MW40 compared to MW0 was 39.4%. The tensile strengths of the tested composites are shown in Fig. 6. Duncan’s multiple range test shows that there is a statistically significant difference between all the composites at 95% confidence level. Huuhilo et al. [18] have shown that the addition of inorganic fillers to WPCs improved their tensile strength slightly. Rizvi and Semeralul [23] also report an increase in the tensile strength of WPCs when glass fiber was used as filler. However, a decrease in the tensile strength of recycled mineral wool-filled composites was observed in this study. The fiber orientation and interfacial bonding may be factors explaining this phenomenon, as both factors are crucial for the mechanical properties of composites. The tensile modulus values of the studied composites follow the trend in tensile strength. The tensile modulus of the composites decreased for composites MW20 and MW30, but MW40 exhibited a higher tensile modulus than MW30. MW20 and MW30 had 8.8% and 32.6% lower tensile modulus than MW0, respectively. MW40

The impact strength of the composite increased slightly when recycled mineral wool was added to the manufacturing process. The differences were rather small, with relatively high standard deviation. MW0 had the impact strength of 2.07 kJ/m2. MW20 and MW30 had 11.1% and 6.3% higher impact strength than MW0, respectively. The impact strength of MW20 was 4.5% higher than that of MW30. MW40 had the highest impact strength of all the tested composites, 18.8% higher than MW0. Fig. 8 presents the impact strengths of the tested composites. Duncan’s multiple range test shows a statistically significant difference only between composites MW0 and MW40 at 95% confidence level. Cui and Tao [37] found out that the addition of glass fibers into WPCs can alter their impact strength. The impact strength was increased with the addition of L-glass fibers but reduced with S-glass fibers. The main factor affecting the impact strength of the filled composites was again the interfacial adhesion of the filler and

Fig. 5. Flexural modulus of the studied composites initially and after cyclic treatment.

Fig. 7. Tensile modulus of the studied composites.

had 10.3% lower tensile modulus than MW0. The tensile moduli of the studied composites are presented in Fig. 7. 3.4. Impact strength

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Fig. 8. Impact strength of the studied composites.

Fig. 10. Brinell hardness of the studied composites.

the polymer matrix, as poor interfacial adhesion of the filler prevents effective transfer of stress from the filler to the polymer matrix.

amount of wood fiber and the hydrophobic nature of the mineral wool fibers. It is likely that mineral wool fibers do not absorb water.

3.5. Thickness swelling and water absorption

3.6. Brinell hardness

The thickness swelling of the composites decreased with the addition of the recycled mineral wool filler. The thickness swelling of composites MW20, MW30 and MW40 were 27.1%, 39.6% and 73.2%, respectively, lower than the thickness swelling of composite MW0. The thickness swelling graphs of the composites are presented in Fig. 9a. It can be seen in Fig. 9a, that all the composites had similar rates of swelling during the first 7 days, except composite MW40, which had a lower rate of swelling. After 14 days of immersion, composite MW30 had higher swelling than composite MW20, but after 28 days of immersion composite MW20 had higher swelling than composite MW30. It can, however, be seen that the thickness swelling of all the composites increased with the duration of immersion. The water absorption, like the thickness swelling, of the composites decreased with the volume of recycled mineral wool filler added to them. The water absorption of composites MW20, MW30 and MW40 were 32.5%, 43.2% and 67.4%, respectively, lower than that of composite MW0. Graphs for the water absorption of the composites are shown in Fig. 9b. In wood/polypropylene composites, moisture is absorbed by the wood component, as polypropylene does not absorb water. Polypropylene also forms a protective barrier against moisture absorption for the wood particles encapsulated in the polypropylene matrix. Therefore, moisture absorption occurs mainly in the wood component exposed in the surface of the composites or as a result of breakage or cutting [38]. The improvement of the composites containing recycled mineral wool can be explained by the reduced

The surface of the composites became softer as recycled mineral wool was added to the manufacturing process. Composites MW20, MW30 and MW40 had 10.5%, 16.5% and 20.6% lower Brinell hardness than composite MW0. Fig. 10 illustrates the Brinell hardnesses of the composites. According to Duncan’s multiple range test, there is no statistically significant difference at 95% confidence level between composites MW20 and MW30 or between composites MW30 and MW40. Huuhilo et al. [18] conclude that mineral filler addition improved the hardness of the wood plastic composites. Tasßdemır et al. [39] report an increase in hardness when wood fibers were added to the polymer matrix, but also noted that adhesion between the polymer matrix and wood fibers affects the hardness of the composites. Therefore, the decrease in the composite hardness when recycled mineral wool fibers were incorporated into the manufacturing process could be explained by weak interfacial adhesion of mineral wool fibers and the polypropylene matrix. 4. Conclusion In this work, recycled mineral wool was successfully used as filler in wood plastic composites, and the mechanical properties of the manufactured composites were studied. The flexural and tensile properties of the composites decreased with the addition of recycled mineral wool into them. This was likely caused by weak adhesion between the mineral wool fibers and the polypropylene matrix. The orientation of mineral wool fibers could also have

Fig. 9. Thickness swelling (a) and water absorption (b) of the studied composites.

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played a role in the formation of interfacial properties. Some of the mineral wool fibers were not oriented in the direction of extrusion, which combined with the weak interfacial adhesion could result in poor transfer of stress from the fibers to the polypropylene matrix. The mineral wool fibers were well dispersed in the polypropylene matrix. Some fiber pull-outs were examined from scanning electron microscope pictures, which further confirmed uneven adhesion of the mineral wool fibers to the polypropylene matrix. The addition of recycled mineral wool also led into lower surface hardness of the composites. The addition of recycled mineral wool to the composites did not have a severe effect on their impact strength. The impact strength improved very slightly with the addition of recycled mineral wool into the composites. The improvement of interfacial adhesion of the mineral wool fibers and polypropylene matrix could lead to greater improvements in impact strength. The addition of recycled mineral wool improved the moisture resistance properties of the composites noticeably. Water absorption was decreased by 32.5–67.4% when 20–40% of recycled mineral wool was added to the composites. Thickness swelling demonstrated similar improvements, the reduction was between 27.1% and 73.2%. If the interfacial adhesion between the mineral wool fibers and polypropylene matrix can be improved, many of the mechanical properties could be improved as well. This could be achieved via the addition of a different coupling agent or surface treatment of the mineral wool fibers. The result would be a wood plastic composite with good mechanical and moisture resistance properties. If satisfactory mechanical properties can be met, recycled mineral wool could prove to be an environmentally and economically viable alternative to commercial filler materials. References [1] Huang W-L, Dung-Hung L, Ni-Bin C, Kuen-Song L. Recycling of construction and demolition waste via a mechanical sorting process. Resour Conserv Recycl 2002;37:23–37. [2] Yuan H, Shen L. Trend of the research on construction and demolition waste management. Waste Manage 2011;31:670–9. [3] Monier V, Hestin M, Trarieux M, Mimid S, Domröse L, Van Acoleyen M, et al. Study on the management of construction and demolition waste in EU. Final report for the European Commission (DG Environment). 2011. Contract 07.0307/2009/540863/SER/G2. [4] Llatas C. A model for quantifying construction waste in projects according to the European waste list. Waste Manage 2011;31:1261–76. [5] European Commission. Commission Staff Working Document [Internet]. 2010 [cited 2012 Jan 30]. . [6] Weber WJ, Jang Y-C, Townsend TG, Laux S. Leachate from land disposed residential construction waste. J Environ Eng 2002;128:237–45. [7] Poon CS. Management of construction and demolition waste. Waste Manage 2007;27:159–60. [8] Müller A, Leydolph B, Stanelle K. Recycling mineral wool waste – technologies for the conversion of the fiber structure, Part 1. Interceram 2009;58:378–81. [9] Širok B, Blagojevic´ B, Bullen P. Mineral wool, production and properties. Cambridge (England): Woodhead Publishing Ltd.; 2008. [10] Papadopoulos AM. State of the art in thermal insulation materials and aims for future developments. Energy Build 2005;37:77–86.

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