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Carrasco, E. V. M., Passos, L. B., Amorim, S. T. A., Ramos, F. M. G., Rodrigues, F. C., and Mantilla, J. N. R. (2019). "Glulam wood sleepers manufacturing from recycling discharge sleepers: An engineering recycling project," BioRes., 14(3), 5059-5070.


Feasibility was studied for the manufacture of glulam sleepers using wood sleepers that had been discharged or sold at low prices by railway companies. In principle, an engineering recycling project of this nature could contribute to the reduction of non-renewable natural resource extraction. The manufacturing stages of glulam recycled wood sleepers are shown. Ultrasonic tests were used for the classification of the wood sleepers’ parts and wood strength optimization. The results showed that it was possible to obtain one wood sleeper from the recycling of four or five used sleepers.

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Glulam Wood Sleepers Manufacturing from Recycling Discharge Sleepers: An Engineering Recycling Project

Edgar V. M. Carrasco,a,* Leonardo B. Passos,b Silvia T. A. Amorim,b Fernando M. G. Ramos,a Francisco C. Rodrigues,b and Judy N. R. Mantilla c

Feasibility was studied for the manufacture of glulam sleepers using wood sleepers that had been discharged or sold at low prices by railway companies. In principle, an engineering recycling project of this nature could contribute to the reduction of non-renewable natural resource extraction. The manufacturing stages of glulam recycled wood sleepers are shown. Ultrasonic tests were used for the classification of the wood sleepers’ parts and wood strength optimization. The results showed that it was possible to obtain one wood sleeper from the recycling of four or five used sleepers.

Keywords: Wood recycling; Glulam wood sleepers; Sustainability

Contact information: a: School of Architecture, Federal University of Minas Gerais, Brazil; b: Engineering school, Federal University of Minas Gerais, Brazil; c: Faculty of Engineering and Architecture, University FUMEC, Brazil; *Corresponding author:


The sleeper is a superstructure element installed across train rails that receives and transmits vehicle load stress to the lower structural elements (Brina 1979). The sleepers partially dampen vibrations and provide support and fixation of the rails, keeping the distance between them stable, that is to maintain the gauge width. Also, these structural elements are subjected to simultaneous shear and bending stresses, and thus they are also extremely important.

The demand for wood sleepers in the Brazilian railways is about 1,500,000 a year, according to the largest Brazilian railway company (Latin America Logistics, LAL). This information is for the three railroads that ALL company manages (Passos 2006).

Wood was the first material to be used to construct sleepers, and 2.5 billion wooden sleepers have been installed worldwide (Ets Rothlisberger 2007). The four countries with the largest rail networks are the U.S., Russia, China, and India (CIA 2013). Brazil occupies the tenth position in this ranking and 17th place when comparing railway densities (Icimoto 2013). The Brazilian rail network stretches over 30,402 kilometers (ANTF 2015).

The wood used in Brazil for manufacturing sleepers are noble timber species such as maçaranduba (Manilkara huberi), aroeira (Astronium lecointei Ducke), and ipe (Tabebuia serratifolia) from native forests (Passos 2006; Icimoto 2013). Because of their scarcity and the environmental impacts of harvesting these species, reforestation woods have been studied, tested, and used in the manufacture of wood sleepers (Da Rocha 2003; Icimoto 2013). Da Rocha (2003) evaluated the resistance of native and reforestation timber through non-destructive testing to explore their use alternatives to hardwoods in railroad sleepers.

Other materials such as concrete, steel, polymers, and composite materials are being used as an alternative to wood sleepers (Werner and Schrägle 2008). Washid et al. (2015) presented a brief review on sleepers, including the different types of materials and composite materials used to manufacture them.

Heebink et al. (1977), Geimer (1982) and Carrasco et al. (2012) studied the reuse and recycling of wood sleepers for the manufacturing of new ones. They studied laminated particle sleepers made from discharged sleepers that were ground into small flakes of 0.508 mm thickness and 50.8 mm length. These surveys were motivated by the high demand for timber sleepers for American railroads and contributing to environmental preservation by avoiding the burning and discharging of wood sleepers. Howe and Koch (1976) presented research on sleepers manufactured by joining two pieces of wood. In the 1970’s, sleepers were made by the pressing process of thin sheets, in which red oak logs were folded, dried, and glued into bars in a continuous process (Howe and Koch 1976). Icimoto (2013) manufactured glued laminated wood sleepers using Pinus oocarpa and polyurethane adhesive.

The use of glulam techniques has increased in recent decades due to the advancement of adhesive technology and reforestation management. The term glulam refers to the act of gluing material that includes thin pieces of wood to form straight or curved shapes, with all of the sheets fibers parallel to the piece length (Carrasco 1989; Passos 2006; Icimoto 2013). For a better arrangement of the sheets in relation to the wood properties, the sheets must be selected and positioned considering their elastic modulus and the appearance of the parts, and the external tensioned sheets must be classified according to AITC (1992) (Carrasco 1989). This type of structure in most cases requires joints to bond the parts. One of the first studies on finger joints began around 1957 by Rico Laminated Products with a project whose aim was that the joints should reach 80% to 90% of the strength of the corresponding solid wood (Carrasco 1989).

The aim of the present work was to evaluate the manufacturing of new sleepers from the recycling of discharged ones by Brazilian railway companies. The work involved developing manufacturing procedures using the glulam technique and ultrasonic tests, and verifying the reuse rate capacity, all of which may contribute to reducing the environmental impact in the railway operation. So, an environmentally preferable product which minimizes the losses of wood waste and has a low manufacturing cost will be manufactured in this study.

The preservation of the environment has demanded a progressive increase in waste valorization in diverse areas. Ratajczak et al. (2015), in work related to resources of post-consumer wood waste, affirmed that the characteristic feature of wood as a raw material is the fact that it is the only major raw material fully reproduced by nature. Also, at the end of their life cycle, products made of wood may be reused or used for energy generation. In addition, such products biodegrade relatively quickly. Laleicke (2018) said that there is momentum towards increasing wood waste utilization, which will enable a truly sustainable resource management; all the benefits along the chain of production, such as the economic ones, to businesses, and to environment should be highlighted.

The present work, aiming to reuse discharged wood and minimize their losses, could be regarded as an example of ecological engineering. Odum (1963) and Bergen et al. (2001) defined ecological engineering as “environmental manipulation by man using small amounts of supplementary energy to control systems in which the main energy drives are still coming from natural sources.” Environmental manipulation means acting and controlling the environment. To Mitsh and Jorgensen (2003), ecological engineering is the design of sustainable systems, consistent with ecological principals, which integrate human society with its natural environment for the benefit of both.” Bergen et al. (2001) describe the applications of ecological engineering, which can include the management, use, and conservation of natural resources. The wood sleepers recycling project optimizes the use of this natural resource, contributing to forest conservation and the reduction of deforestation.

Bergen et al. (2001) identified five design principles for the ecological engineering project methodology. The present work would fit in the first of them “Designing consistent with ecological principles”. “When natural processes are included or reproduced, nature is treated as part of the design and not as an obstacle to be overcome and overwhelmed”. One important feature of nature ecosystems is that one process output subsequently become the inputs of other processes, so that there is a self-organization of the ecosystem. Thus, no waste is generated and the nutrients are used again from one level to another. The sleepers recycling project can be considered a facilitator in the self-organization of the ecosystem to which it is related. Wood waste generated by the maintenance of the railways would be processed to serve as raw material for the manufacture of new sleepers.


Procedures were developed for manufacturing glulam wood sleepers of metric gauge, an alternative sleeper type, which was called glulam recycled wood sleeper (GlulamRS).

Materials and Equipment

For manufacturing of GlulamRS, 46 discharged sleepers were donated by Vale Company (Belo Horizonte, Brasil). The discharged sleepers, according to the Brazilian standard NBR 7511 (2013) “are those which don’t perform well in the railway”. Taking into account their service life status, they are commonly classified as half-way (with standard dimensions and some flaws), scrap (with standard dimensions, but with lots of damage), or firewood (broken or badly damaged), as shown in Fig. 1.

Fig. 1. Discharged sleepers classification. (a) half-way; (b) Scrap; (c) Firewood

The railway metric gauge and 115-RE rail type (AREMA standard steel rails) were considered, and the minimum and maximum dimensions of the discharged sleepers are shown in Table 1, according to Brazilian standard NBR (Norma Brasileira) 7511 (2013).

Table 1. Sleeper Dimensions

To glue the timber sheets, emulsion polymer isocyarate (EPI) 1974 adhesive was used with the Hardener 1993 catalyst, both from Akzo Nobel-Casco Adhesives (Stockholm, Sweden). The adhesive was chosen due to its relatively low cost, low curing time, and resistance to bad weather. The 1974 EPI adhesive is water-based, with white color, a density of approximately 120 kg/m3, and pH 7. The Hardener 1993 catalyst is isocyanate-based, has a light brown color, and has the same density and pH of 1974 EPI. Instructions from the adhesive manufacturer were followed to determine the proportion and mixing time, adhesive application time, pressure and pressing time, and rest time of the workpiece.

To determine the dynamic elastic modulus (Ed) with non-destructive ultrasonic tests, two types of equipment were used. The first one from Sylvatest (Lausanne, Switzerland), uses the exponential transducers of 39 kHz, and the second one, James K Metter II (James Instruments Inc., Chicago, IL, USA), uses transducers of 150 kHz.

Fig. 2. Ultrasonic equipment. (a) Sylvatest with 30 kHz transducer, (b) James MK II transducers of 150 kHz. From Carrasco (2004)

The discharged sleepers were numbered in sequence from 1 to 46, and each of them were marked with three dividing lines along their lengths, dividing them into four equal and numbered parts from Q1 to Q4 (Quadrant 1 to 4) from left to right and each quadrant has 50 cm. The sleepers were weighed, and the height, width, and length of all quadrants was measured. The density of the sleepers was obtained using this information. Any imperfections, cracks, fractures, and flaws caused by insects or fungi were measured and cataloged, as the flaws influence the ultrasonic readings.

The ultrasonic tests were performed on the discharged sleepers to determine Ed. The propagation time of the ultrasonic pulse along the sleeper length was measured using the Sylvatest equipment with the 30 kHz transducers positioned directly in four points of each sleeper, with a minimum distance of 30 cm between the transducers based on the recommendation of Duarte et al. (2004), as shown in Fig. 3.

Fig. 3. Positioning of the transducers directly along the length of the sleeper. (a) The proposed scheme, (b) sleepers tests, and (c) sheets tests

Considering the length of each piece and the time of the ultrasonic wave course, the speed of propagation of the longitudinal ultrasonic wave and Ed was determined by Eq. 1,


where v is the wave propagation speed (m/s), the wood density (kg/m3), and g is gravity. Wood density values were calculated for each wood sleeper, considering their weight divided per volume.

To determine the propagation time of the pulses in height, width, and length (L1) of each quadrant, James MK II equipment was used, with the 150 kHz transducer positioned directly in height and in width (Fig. 4) and indirect length (Fig. 5).

Fig. 4. Positioning of transducers directly with the transducers MK II over the height and width of each sleeper quadrant. (a) The proposed scheme, and (b) positioning of transducers and test

Fig. 5. Positioning of the transducers in an indirect way along the length of each sleeper quadrant. (a) The proposed scheme, and (b) positioning of transducers and test

GlulamRS Manufacturing

After the discharged sleepers were tested, they were cut and unfolded into smaller pieces. This procedure was performed in the carpentry shop of the Structural Department of Engineering School of the Federal University of Minas Gerais.

To cut the sheets, the discharged sleepers were first brought to the planer, to the left or right surface, and subsequently the upper or lower surface, where it was flattened, thereby obtaining the square between the two faces. Next, cuts of 36 mm thickness were made with a circular saw. Flaws and defects were removed from the sheet side and mainly from the sheet top, as the top bonds would be made by finger-joint and in this type of bond there cannot be any flaws in the wood.

The ultrasonic tests were performed again with Sylvatest equipment with the transducers positioned directly over the length of at least two parts of each sleeper. The dimensions and weight of the pieces were measured in order to obtain Ed. They were trimmed to obtain a standard thickness of 34 mm with a circular saw. For a better use of the sheets, the existing holes were filled with a compound obtained from the EPI-1974 (2003) adhesive mixed with sawdust from the sleepers.

Mapping was carried out for the newly manufactured sleepers using the Ed values of the wood sheets. Sheets with higher Ed’s were disposed on upper and lower surfaces of the GlulamRS. The sheets with intermediate values of Ed were positioned so as to achieve better utilization, as they had different values of width and length. To obtain a better utilization of the timber and make the process more productive, 4 m long pieces were manufactured using finger-joints, which enabled two GlulamRS to be produced. During the process, some sheets were either replaced, their positions were exchanged, or their dimensions were altered, as some of them would fit better elsewhere. Other sheets which still had flaws at this stage were recovered or replaced.

Figure 6 shows the joining of the top sheets with a 25 mm length finger joint. These joints were made with cutters in a modified router using three cutting mills and a finish mill. The cuts of the sheets were made gradually to avoid damaging the cutters because the wood had great hardness and some of them were too oily from the chemical preservative treatment.

This led to the formation of a film, which along with the rotation of the router caused the cutting blade loss, requiring the blade to be sharpened. For bonding each finger-joint, the EPI adhesive 1974 and the Hardener 1993 catalyst were used. The sheets were joined together, lined up, and pressed using a hand press and with a 1 MPa pressure. The entire process, except for the pressing, lasted about 6 min. After 24 h of pressing, the width of the pieces bonded with finger-joint was standardized in using a circular saw.