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Experimental investigation of using cross-linked polyethylene waste as aggregate in roller compacted concrete pavement
Accepted Manuscript Experimental investigation of using cross-linked polyethylene waste as aggregate in roller compacted concrete pavement
Mohsen Shamsaei, Iman Aghayan, Kani Akhavan Kazemi PII:
S0959-6526(17)31552-4
DOI:
10.1016/j.jclepro.2017.07.109
Reference:
JCLP 10112
To appear in:
Journal of Cleaner Production
Received Date:
29 November 2016
Revised Date:
16 June 2017
Accepted Date:
15 July 2017
Please cite this article as: Mohsen Shamsaei, Iman Aghayan, Kani Akhavan Kazemi, Experimental investigation of using cross-linked polyethylene waste as aggregate in roller compacted concrete pavement, Journal of Cleaner Production (2017), doi: 10.1016/j.jclepro.2017.07.109
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Experimental investigation of using cross-linked polyethylene waste as aggregate in roller compacted concrete pavement
Mohsen Shamsaeia, Iman Aghayana,*, Kani Akhavan Kazemia aDepartment
of Civil Engineering, Shahrood University of Technology, Shahrood, Iran
*Corresponding
author: Iman Aghayan, E-mail: [email protected]
Abstract In recent years, cross-linked polyethylene (XLPE) is one such waste material that has been growing rapidly. In fact, XLPE used for the insulation of electric wires and cables is a nonbiodegradable component. This study was carried out to investigate the use of XLPE waste as an aggregate in roller compacted concrete pavement (RCCP) mixes. XLPE waste as an aggregate with several volume percentages was utilized to replace the natural coarse aggregate of concrete mix. This replacement was conducted with 5%, 15%, 30% and 50% contents. The unit weight, VeBe time, compressive strength, splitting tensile strength, and flexural strength were measured for all the specimens. The results indicated that the use of XLPE waste changed the properties of fresh and hardened concrete. XLPE waste caused the reduction of unit weight and VeBe time. The results showed that replacing 5% of coarse aggregate with XLPE waste increased the 28-d splitting tensile strength of RCCP by 10%. In addition, the 28-d compressive and flexural strengths of this concrete mix were greater than the minimum compressive and flexural strengths determined by the RCCP guide. According to the test results, the use of XLPE waste for more than 5% of the coarse aggregate of the mix are recommended for low traffic pavements, rural roads and sidewalks. Moreover, the use of XLPE waste increased ductility and resistance against RCCP cracking. Overall, using XLPE waste in RCCP can prevent entering wastes into the environment. And, it reduces landfill cost and saves energy. Keywords: Cross-linked polyethylene; Mechanical properties; Recycling; Roller compacted concrete pavement
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1. Introduction Environmental impacts are one of the most important issues that have been the focus of global discussions in recent years. All over the world, large amounts of electric wires and cables are produced annually, and these products generate a lot of wastes. If these wastes return to the environment, it leads to grave environmental impacts. Cross-linked polyethylene (XLPE) is widely used as an insulating material for electric wires and cables. XLPE wastes are nonbiodegradable components. The accumulation of polymer wastes including waste plastic, waste rubber and polyethylene materials such as XLPE has become a worldwide concern. The total amount of cable waste produced in Japan in 2003 was approximately 10,000 tons (Tokuda et al., 2003). Also, in Sweden, the amount of electrical cables waste was estimated to be 40,000 tons in 2007 (Christéen, 2007). These statistics indicate large quantities of XLPE waste. These XPLE waste depots are illustrated in Fig. 1. XLPE waste is burned as a fuel or buried. Since XLPE has low fluidity and poor moldability, it is rarely recycled, though its recycling is of crucial importance for researchers. However, burning and incineration of these wastes lead to energy consumption and air pollution as well. Furthermore, burying wastes requires convenient locations and also leads to soil pollution. For these reasons, finding a suitable solution for recycling XLPE is very significant as well as for reusing this valuable material (Lu et al., 2009; Shang et al., 2010). Roller compacted concrete (RCC) is a zero-slump concrete that is applied in road pavements. Thus, this major advantage of RCC pavement makes it superior to asphalt and conventional concrete pavements. Moreover, there are some other advantages associated with RCC pavements such as their simple construction method and increased placement speed, no need for the use of dowels and steel reinforcement, low administrative costs, less cement consumption, and high resistance in hot or cold weather conditions. RCC is a mix in which there exists the possibility of passing roller over it in the fresh state. In this way, a stiff and compacted concrete surface is made by the roller. The United States Army Corps of Engineers first used the RCC pavement in 1942. Although reports of using this type of pavement were recorded in Sweden in 1930, the first industrial area from RCCP was built in Canada in 1976. The advantages of this type of pavement will make its use widespread in the following years (ACI 325.10R, 2001).
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RCCP is more economical compared to other concrete pavements due to the lack of dowels and steel reinforcement. Moreover, it has lower maintenance costs. The flexural strength of RCCP is equal to or even more than the conventional concrete pavement. Recent researches have shown that this type of pavement has a desirable long-term performance. Although this pavement is usually not applicable for high-speed traffic, in some cases, it has been implemented for high speeds as well (Delatte, 2014). In RCCP, the recycled materials can be used as fine and coarse aggregates. For example, research experiments conducted by Modarres and Hosseini (2014) indicated that the use of recycled asphalt pavement (RAP) resulting from the repair of asphalt pavements as aggregates decreased the compressive strength of RCCP. However, with regard to the accessibility of RAP in asphalt roads, using recycled materials for environmental protection and using them in lowtraffic pavements have been recommended. Also, Settari et al. (2015) investigated the mechanical properties and durability of RCCP. They used different sizes of RAP as a replacement for aggregates in RCCP. The test results showed that 50% of these aggregates could be replaced, and the pavement remained relatively desirable. Courard et al. (2010) studied the possibility of using recycled concrete in RCCP. Characteristics such as Los Angeles (L.A.) abrasion, water absorption, and specific gravity of the recycled aggregates were assessed appropriately. By replacing the natural aggregates with concrete road recycled aggregates, the compressive strength of RCCP decreased. Overall, the recycled aggregates in RCC mixes showed a good performance. Due to the growth of land transport and the increasing number of vehicles, tyre production has increased consequently. The recycling of tyre and rubber has been the focus of attention of researchers as an important issue. One of the ways for recycling these wastes is by using them as an aggregate in RCCP mix (Fakhri and Saberi, 2016). Some researchers (Meddah et al., 2014; Lv et al., 2015; Feng et al., 2015) have investigated various sizes of rubber particles in RCCP. Tests conducted by these researchers have revealed that after the replacement with pieces of rubber, there were changes in the concrete’s properties such as unit weight, modulus of elasticity, and mechanical properties. The elasticity modulus, compressive, splitting tensile and flexural strengths were reduced by adding recycled rubber. However, the addition of rubber particles to RCCP may be beneficial due to the improvement of some properties such as high ductility and
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fatigue life, low porosity and also low unit weight. By considering the minimum compressive strength in the RCCP guide, after the replacement of rubber as an aggregate in the RCCP mix, the resultant pavements were assessed to be appropriate for low traffic, rural roads and pedestrians. One of the disadvantages of rigid pavements is low flexibility. This causes cracking due to tensile and flexural strengths. The flexibility of concrete pavement can be increased by using some industrial wastes such as shredded tyre rubber and grinded plastic bottles (polypropylene, PP) as aggregates. Concrete pavement mix aggregates in quantities of 10%, 20%, 30% and 40% were replaced with shredded tyre rubber and grinded plastic bottles. The test results showed that the splitting tensile strengths related to the replacement contents of 10%, 20% and 30% were acceptable. Krishnamoorthy et al. (2016) showed that the use of recycled materials could improve concrete pavement characteristics including splitting tensile strength and reduce costs as well. Silva et al. (2013) investigated the effect of curing conditions on durability of concrete mixes after replacing waste plastics (polyethylene terephthalate) as coarse and fine aggregates. Actually, waste plastics of 7.5% and 15% contents replaced natural aggregates. Tests such as shrinkage and water absorption were performed on the specimens. Finally, the results indicated that the durability of the specimens containing waste plastic had reduced in comparison to the control specimens. Ashwini Manjunath (2016) also conducted a study on using E-plastic waste as a replacement for aggregates in concrete to improve some of its properties. Today, E-plastic waste is rapidly growing as it is a valuable resource of IT industries. These plastics are nonbiodegradable components with low recycling rate. This substance in different percentages such as 10%, 20% and 30% were used to replace fine and coarse aggregates. Tests were carried out to comparatively study the compressive strength, tensile strength and flexural strength of the control specimens and the specimens replaced by waste plastic, and the results revealed that the use of E-plastic waste as an aggregate decreased the density, compressive strength and tensile strength of the concrete. The use of 10% plastic waste increased the 28-d flexural strength of concrete as well as its plasticity. According to recent studies on the use of recycled materials in concrete pavements, RCCP in particular is a partial solution to environmental and ecological problems, and reduces
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construction costs by reducing the amount of natural aggregate. XLPE waste is nonbiodegradable components with low fluidity, and it is impossible to melt it down again for molding. Nowadays, almost all XLPE wastes are either burnt as fuel or buried. So, it is necessary to investigate the use of XLPE wastes as aggregates in RCCP mix. The tensile strength, the ductility, and the energy adsorption capacity of RCCP are lower than other concrete pavements that use dowels and steel reinforcement. Though finding a proper solution to recycle XLPE wastes at low costs still needs further studies, it seems that using these wastes as aggregate replacements can help alleviate environmental problems and save energy too. Moreover, since the costs of providing these wastes are low or often free, it leads to a reduction in construction costs. The most significant objectives of the present study include:
Using XLPE waste as aggregate in RCCP mix as partial substitution in different volume percentages of coarse aggregate of 5%, 15%, 30% and 50%.
Evaluating the compressive strength, the splitting tensile strength, and the flexural strength of RCCP by replacing XLPE waste as coarse aggregate.
Examining the unit weight and the vibrating compaction time (VeBe time) variations in concrete mixes with regard to different volume contents of XLPE waste.
2. Materials The materials used in this study include Portland cement type II, crushed calcareous gravel, and dune sand. Calcareous gravel was provided from a mine 20 km from Shahrood city in Semnan province. These aggregates were used in three sizes, passed from sieve 3/8 in, sieve 1/2 in, and sieve 3/4 in (with maximum sizes of 10, 14, 19 mm). Dune sand was provided from a mine 5 km from Miami city in Semnan province. Water without any additives was used for the production of cement paste. The XLPE wastes were provided from Moghan Wire and Cable Co. in Iran. XLPE wastes were converted to the appropriate size by a special machine for recycling plastics. The size of the recycled XLPE waste materials was retained by sieve No. 4 (4/75 mm), and the size of the passing materials through sieve 3/8 in (10 mm). Fig. 2 illustrates the size of XLPE waste used in the study.
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The amount of cement used was about 12% to 14% of the mass of the aggregates. The maximum size of coarse aggregate for the gradation of concrete mix was considered to be 19 mm (ACI 325.10R, 2001; PCA, 2010). The recommended limits for the gradation used were extracted from ACI 211.3R. (1997), and the used limits and percentages are shown in Fig. 3. This guide is concerned with zero-slump concrete, and the recommended amounts of coarse and fine aggregates are almost equal. The recommended limits and designs are almost similar to ACI 325.10R. (2001) pertaining to RCCP. The gradation curve of the natural aggregates used in the research was selected in accordance with the mentioned guide illustrated in Fig. 3. The physical and the chemical properties of Portland cement are given in Table 1. The mechanical properties and the tests related to natural aggregates and the XLPE waste used are shown in Table 2.
3. Experimental study The appropriate mix design was obtained by using ACI 211.3R. (1997) and ACI 325.10R. (2001). In addition to the control mix design, we used XLPE as a replacement for different volume percentages of coarse aggregate in four concrete mixes at the varying rates of 5%, 15%, 30% and 50%. Then, these concrete mixes were compared with the control mix design without XLPE. The water to cement ratio (w/c) of the appropriate mix design was calculated by using the ACI 211.3R. (1997) guide (see in Appendix 3) as the basis to determine optimum workability. For all the tests, five mix designs were designed with XLPE wastes with 0%, 5%, 15%, 30% and 50% of coarse aggregates. These mix designs and the XLPE waste replacement content of each of the specimens are given in Table 3. The water content of all the mixes was equal to 163 Kg/m³. The VeBe time and the fresh concrete density were measured for each XLPE content and the control specimen according to ASTM C1170. (2008). The slump test was also conducted with standard ASTM C143. (2003). Concrete slump was equal to zero in accordance with the RCC properties (ACI 325.10R, 2001; PCA, 2010).
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3.1 Compressive strength test This test is used to determine the compressive strength of cylindrical concrete specimens. This test method consists of applying axial loading to molded cylinders at a rate which is within a prescribed range until the occurrence of failure. The compressive strength is calculated by dividing the maximum load carried by the specimen during the test by the specimen’s crosssectional area. The test loading rate was 0.3 MPa/s (ASTM C39, 2011). In this test, cylindrical specimens with 100 mm diameter and 200mm height were used. The specimens were compacted in three equal layers. Each layer was compacted with top surcharge of 50 g/cm². Compaction was continued until a paste ring was observed between the periphery of the surcharge and the cylinder. The vibration time for the control mix design was also calculated between 30 and 45 seconds in accordance with ACI 325.10R. (2001). In this study, regardless of the test specimens for determining the mix design, 45 main cylindrical specimens were prepared for the compressive strength test. After that, the molds were covered with plastic bags until demolding. Then, the specimens were demolded after 24 hours and immersed in normal water for curing until they reached the test age. The hardened properties of the concretes discussed in this paper were for 7, 14 and 28 days of water curing. Finally, the compressive strength test was accomplished based on the ASTM C39. (2011).
3.2 Splitting tensile strength test This test determines the splitting tensile strength of cylindrical concrete specimens, such as molded cylinders and drilled cores. Actually, the test method consists of applying a diametrical compressive force along the length of a cylindrical concrete specimen at a rate that is within a prescribed range until the occurrence of failure. When compressive failure is conducted, there is occurrence of tensile failure as well. Moreover, thin plywood bearing strips are used to distribute the load applied along the length of the cylinder. For the splitting tensile strength test, the size, the molding, the surcharge value, and the specimen preparation are also like those of the compressive strength test specimens. For this test, 45 main cylindrical specimens were prepared. The preparing process and the curing conditions were similar to the compressive strength test specimens. After curing time, the splitting tensile strength test was performed on the specimens in accordance with ASTM C496. (1996).
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3.3 Flexural strength test In this study, the four-point bending test was conducted to determine the flexural strength of concrete with the use of a simple beam. The results are calculated and reported as the modulus of rupture. The determined strength can vary with differences in specimen size, preparation, moisture condition, curing, or where the beam is molded or sawed to size. The span length of the specimen with 2% tolerance should be three times its depth. For the specimens cured in water, it should be conducted immediately after bringing them out from water curing. For this test, rectangular molds with a length of 35cm, width of 10cm and height of 10cm were used. Fortyfive rectangular specimens (beam shaped) were prepared for this test as well. The preparation of the specimens was performed on a vibrating table with a surcharge. The specimens were compacted with top surcharge of 25g/cm². The molds were covered with plastic bags until demolding. The specimens were demolded after 24 hours and immersed in normal water for curing. The hardened properties of the beams were for 7, 14 and 28 days of water curing. Finally, the flexural strength was achieved based on the ASTM C78. (2007).
4. Results and discussion 4.1 The effect of recycled XLPE waste on fresh concrete properties The density and the vibrating compaction time were calculated for each percentage of XLPE. The concrete density decreased regularly with the increasing percentage of XLPE in the concrete mix. When 50% of XLPE was replaced as coarse aggregate, the unit weight decreased from 2510 kg/m³ to 2152 kg/m³. The maximum loss of unit weight was related to the replacement of 50% XLPE, which was approximately 14% as shown in Fig. 4. This reduction might be due to the low unit weight of XLPE as compared to using natural aggregate as well as more voids in the concrete at the time of replacing XLPE. Since RCC has zero slump, its performance is measured with the VeBe test. The relationship between the XLPE content and the vibrating compaction time is depicted in Fig. 5. As can be seen, by increasing the XLPE percentage, the RCC workability increased and the VeBe time decreased. The vibrating compaction time decreased from 36 seconds for the control specimen to 21 seconds for the specimen containing 50% of XLPE. This reduction might be due
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to lower water absorption of XLPE (0%) as compared to natural aggregate. Thus, the amount of free water in the mixture increased, causing more workability and making the compaction process easier.
4.2 Compressive strength The minimum requirement for compressive strength pertains to the layer in which the RCC is used. The minimum 28-d compressive strength needed for RCCP, as the main structural layer, is 27.6 MPa (ACI 325.10R, 2001). The results indicated that along with the 28-d control specimens, just the strength of 28-d specimens with 5% of XLPE was more than the minimum allowable strength. However, these specimens containing 5% of XLPE also showed a slight loss in compressive strength as compared that of the control specimen. The compressive strength reduced with increased XLPE percentage. The average 28-d compressive strength decreased from 29.5 MPa for the control specimen to 8.75 MPa for the specimen containing 50% of XLPE. This strength loss might be caused by less adhesion of XLPE to the cement mortar in RCC mix in comparison to that of the natural aggregate, and also because of increased porosity of the specimens containing XLPE as compared to the natural aggregate specimens. The average compressive strength at 7, 14 and 28 days for different percentages of XLPE are shown in Table 4. The comparative compressive strengths of the specimens with different percentages of XLPE are shown in Fig. 6. The specimen with 5% XLPE had the minimum allowable compressive strength determined for RCCP. The compressive strength test was conducted by the universal testing machine. Fig. 7 illustrates the relationship between the average 28-d compressive strength of the specimens and the concrete density. With regard to the R² value, it can be concluded that the concrete density had a good correlation with the compressive strength.
4.3 Splitting tensile strength The tests revealed that replacement by 5% XLPE caused an increase in the observed splitting tensile strength. In the following, an increase in XLPE content negatively affected the tensile strength, so that the tensile strength decreased regularly. The tensile strength increased from 2.90
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MPa for the 28-d control specimen to 3.23 MPa for the specimen containing 5% XLPE. This 11% increase might be due to XLPE’s higher flexibility as compared to the natural aggregate as well as its irregular polygonal shape that caused the increase of aggregate interlocking in concrete. Moreover, with the increase in XLPE content, easier concrete failure due to XLPE’s lower adhesion as compared to natural aggregate and increasing air voids in RCCP mix were observed. Thus, the optimum replacement percentage, which even increased the tensile strength, was 5%. Finally, the maximum loss of tensile strength was observed for the mix containing 50% of XLPE. It decreased to 1.72 MPa. Table 5 demonstrates the average tensile strength at 7, 14 and 28 days. The comparative average tensile strength of the specimens for different contents of XLPE is depicted in Fig. 8. The relationship between the average 28-d compressive strength and the average 28-d indirect tensile strength is illustrated in Fig. 9. The ratio of the average 28-d indirect tensile strength to the average 28-d compressive strength for the control specimens increased from 10% to 20% for the specimens containing 50% of waste XLPE. Fig. 10 illustrates the split specimens under this test. Some particles of XLPE are represented inside red circles in the specimens with different percentages. According to Fig. 10, it can be concluded that XLPE distribution was almost uniform in the concrete pavement mix. As can be seen in Fig. 10, almost all the coarse aggregates were crushed and cracks passed through the aggregates. This reflects the appropriate amount of water to cement and the appropriate continuity between the aggregate and the cement paste in the used mix design.
4.4 Flexural strength The results showed greater flexural strength of the 7-d specimens containing 5% of XLPE than the 7-d control specimens. In the other specimens, with the increase of XLPE content, the flexural strength decreased regularly. This issue might be due to the lower adhesion of XLPE compared to the natural aggregate in RCCP. Moreover, the replacement of coarse aggregate by XLPE waste might also have increased the air voids of the mixtures. The average flexural strength of the specimens at 7, 14 and 28 days for the different percentages of XLPE are presented in Table 6.
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Fig. 11 shows the comparison of the flexural strength of the specimens with different contents of XLPE. Fig. 12 is related to the flexural strength test by the universal testing machine. It can be seen that the control specimens were broken into two pieces at the time of testing, but the other specimens containing 5%, 15%, 30% and 50% of XLPE were not separated into two parts. So, the crack in the specimens with XLPE was inversely proportional to the percentage of added XLPE. This test demonstrates that RCCP with XLPE waste has higher energy absorption capacity than RCCP without XLPE waste. As the XLPE content increased, the failure became more ductile. The relationship between the average 28-d splitting tensile strength and the average 28-d flexural strength are shown in Fig. 13. The ratio of the average 28-d flexural strength to the average 28-d compressive strength for the control specimens increased from 10% to 20% for the specimens containing 50% of XLPE waste.
5. Conclusion This study investigated the use of XLPE waste as a replacement for natural aggregate with varying volume percentages in RCCP mix. The results revealed that the use of XLPE waste as coarse aggregate improved some of the RCCP properties. Recycled XLPE waste decreased 42% of the vibrating compaction time by the partial substitution of gravel by 50% in the RCCP mix. The reduction in unit weight was directly proportional to the increase in XLPE content. When waste XLPE replaced coarse aggregate by 5%, the 7-d, 14-d and 28-d splitting tensile strengths compared to the control specimens increased by 18%, 9% and 10%, respectively. For the other tested percentages, with increasing XLPE contents, the splitting tensile strengths decreased regularly. When XLPE replaced 5% of the coarse aggregate, the 7-d flexural strength increased by 6%; however, the 14-d and the 28-d flexural strengths decreased slightly. For the other percentages, the flexural strength also decreased regularly, but ductility and cracking resistance increased. In addition, the 28-d compressive strength of specimens containing 5% of XLPE waste was more than the minimum compressive strength prescribed by the RCCP guide. Therefore, recycling 5% of XLPE waste as coarse aggregate in RCCP mix was not only allowable as the main structural layer according to ACI 325.10R, but it also increased the splitting tensile strength. Overall, using 5% of XLPE waste for all technical requirements was
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allowable. For the content percentages of 15, 30 and 50, a regular loss in strengths was observed; but some properties such as ductility and energy absorption increased, and unit weight decreased as well. These percentages can be used in some cases such as low traffic pavements, rural roads, large industrial areas and sidewalks. The use of appropriate percentage of XLPE waste depends on the technical requirements and aim of a particular project. Using recycled XLPE waste in RCCP removes some of these wastes from nature. It is a suitable way to recycle them with low cost. In addition, it simultaneously reduces the need for natural aggregates. Finally, the use of XLPE waste as an aggregate in RCCP mix is recommended.
Acknowledgments The authors would like to thank Mr. Gholamreza Ebrahimian, managing director of Moghan Wire & Cable Company, and Mr. Alireza Nazemi for their help and support.
References American Concrete Institute, 2001. Roller compacted concrete pavements, ACI 325.10R. American Concrete Institute, 1997. Guide for selecting proportions for no-slump concrete. ACI 211.3R. American Society for Testing and Materials (ASTM) C39/C39M-11a, 2011. Standard test method for compressive strength of cylindrical concrete specimens, Annual book of ASTM standards, West Conshohocken, Pennsylvania, USA. American Society for Testing and Materials (ASTM) C496-96, 1996. Standard test method for splitting tensile strength of cylindrical concrete specimens. Annual book of ASTM standards, Pennsylvania, USA. American Society for Testing and Materials (ASTM) C78-07, 2007. Standard test method for Flexural strength of concrete (using simple beam with third-point loading). West Conshohocken, Pennsylvania, USA. American Society for Testing and Materials (ASTM) C1170/C1170M-08, 2008. Standard test method for determining consistency and density of roller-compacted concrete using a vibrating table. West Conshohocken, Pennsylvania, USA. American Society for Testing and Materials (ASTM) C 143/C 143M – 03, 2003. Standard test method for slump of hydraulic-cement concrete. West Conshohocken, Pennsylvania, USA.
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Ashwini Manjunath, B. T., 2016. Partial replacement of e-plastic waste as coarse-aggregate in concrete. Procedia Environmental Sciences. 35, 731–739. doi:10.1016/j.proenv.2016.07.079. Christéen. J., 2007. Swedish cable waste for recovery in China or Sweden. Master thesis, Department of Management and Engineering, LiTH, Linköping Universitet. Courard, L., Michel, F., Delhez, P., 2010. Use of concrete road recycled aggregates for Roller Compacted Concrete. Construction and Building Materials. 24, 390–395. doi:10.1016/j.conbuildmat.2009.08.040 Delatte, N. J., 2014. Concrete pavement design, construction, and performance. United States. Second Edition. CRC Press. Taylor & Francis Group. Fakhri, M., Saberi, K. F., 2016. The effect of waste rubber particles and silica fume on the mechanical properties of Roller Compacted Concrete Pavement. Journal of Cleaner Production. 129, 521-530. doi:10.1016/j.jclepro.2016.04.017 Feng, L., Liang-yu, M., Guo-Fang, N., Li-Juan, L., 2015. Fatigue performance of rubbermodified recycled aggregate concrete (RRAC) for pavement. Construction and Building Materials. 95, 207–217. doi:10.1016/j.conbuildmat.2015.07.042 Krishnamoorthy, R. R., David, T. K., Mastor, N. A. B., Nadarasa, I. K., 2016. Repair of deteriorating pavement using recycle concrete materials. Procedia Engineering. 142, 371 – 382. doi:10.1016/j.proeng.2016.02.064 Lu, C., Zhang, X., Liang, M., 2009. Mechanochemical recycling and processing of waste crosslinked polymers: Waste tire rubber and waste XLPE from cables scraps. October 11-14. The 5th ISFR. Chengdu. China. Lv, J., Zhou, K., Du, Q., Wu, H., 2015. Effects of rubber particles on mechanical properties of lightweight aggregate concrete. Construction and Building Materials. 91, 145–149. doi:10.1016/j.conbuildmat.2015.05.038 Meddah, A., Beddar, M., Bali, A., 2014. Use of shredded rubber tire aggregates for roller compacted concrete pavement. Journal of Cleaner Production. 72, 187-192. doi:10.1016/j.jclepro.2014.02.052 Modarres, A., Hosseini, Z., 2014. Mechanical properties of roller compacted concrete containing rice husk ash with original and recycled asphalt pavement material. Materials and Design. 64, 227-236. doi.org/10.1016/j.matdes.2014.07.072 Portland Cement Association (PCA). 2010. Guide specification for the construction of roller compacted concrete pavements, Skokie, Illinois, USA.
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The list of table captions Table1: Chemical compositions, physical and mechanical properties of Portland Cement Type II Table 2: Physical properties of original aggregates and XLPE Table 3: Mix concrete proportions Table 4: The average compressive strength of specimens Table 5: The average tensile strength of specimens Table 6: The average flexural strength of specimens
The list of figure captions Fig. 1: Two XLPE waste storage sites Fig. 2: The used XLPE wastes Fig. 3: Recommended aggregate grading limits for RCCP Fig. 4: Effect of XLPE content on the density of fresh concrete Fig. 5: Effect of XLPE content on the concrete workability Fig. 6: The comparison of average compressive strength of specimens Fig. 7: The relationship between the average 28-d compressive strength of specimens and concrete density Fig. 8: The comparison of the average tensile strength of specimens Fig. 9: The relationship between the average 28-d indirect tensile strength and the average 28-d compressive strength Fig. 10: Distribution of different XLPE contents in specimens Fig. 11: The comparison of the flexural strength of specimens
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Fig. 12: Flexural strength test and specimens at failure Fig. 13: The relationship between average 28-day flexural strength and 28-day compressive strength
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Highlights
1. Cross-linked polyethylene (XLPE) wastes are used as a coarse aggregate in roller compacted concrete pavement (RCCP). 2. Increasing XLPE content in RCCP decreases its density and vibrating compaction time (VeBe time). 3. Increasing XLPE content in RCCP increases its ductility and cracking resistance. 4. 5 % max of XLPE content are recommended to be used in main structure layer of RCCP.
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Table 1 Chemical compositions, physical and mechanical properties of Portland Cement Type II Chemical compositions (%) Calcium oxide (CaO) 63.36 Silicon dioxide (SiO2) 21.20 Alumina (Al2O3) 4.48 Ferric oxide (Fe2O3) 3.96 Magnesium oxide (MgO) 1.52 Sulphur trioxide (SO3) 2.50 Sodium oxide (Na2O) 0.37 Loss on ignition (LOI) 1.18 Other 1.43 Physical characteristics Specific gravity Specific surface (cm²/g) Soundness (%) Initial setting time (min) Final setting time (min)
3.15 3309 0.05 140 210
Compressive strength (MPa) 3d 27.5 7d 37.2 28 d 46.9
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Table 2 Physical properties of original aggregates and XLPE Properties Specific gravity (kg/m³) Sand equivalent (%) Fineness modulus Water absorption (%) Los Angeles (%)
Standard ASTM C127 (CA) ASTM C128 (FA) ASTM D2419 ASTM C33 ASTM C127 (CA) ASTM C128 (FA) ASTM C131
Sand 2600
Calcareous gravel 3/8 1/2 3/4 2686 2660 2642
XLPE 800
77 2.9 2.2
0.7
0.33
0.55
0
-
23
21
21
-
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Table 3 Mix concrete proportions Mix
RCCP0 RCCP5 RCCP15 RCCP30 RCCP50
XLPE content %
Constituents (Kg/m³) Cement
Sand
0 5 15 30 50
298 298 298 298 298
772 772 772 772 772
Gravel 3/8 657.00 595.24 471.73 286.45 39.42
Gravel 1/2 234 234 234 234 234
Gravel 3/4 337 337 337 337 337
XLPE 0 18.40 55.18 110.36 183.94
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Table 4 The average compressive strength of specimens Mix RCCP0 RCCP5 RCCP15 RCCP30 RCCP50
Compressive strength (MPa) 7d 14 d 28 d 22.00 24.86 29.50 21.52 23.90 28.49 14.19 16.02 18.31 10.03 11.61 13.30 6.83 7.35 8.75
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Table 5 The average tensile strength of specimens Mix RCCP0 RCCP5 RCCP15 RCCP30 RCCP50
Splitting tensile strength (MPa) 7d 14 d 28 d 2.40 2.87 2.90 2.94 3.15 3.23 2.21 2.38 2.49 2.00 2.07 2.15 1.54 1.61 1.72
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Table 6 The average flexural strength of specimens Mix RCCP0 RCCP5 RCCP15 RCCP30 RCCP50
7d 5.06 5.39 4.72 4.03 3.10
Bending strength (MPa) 14 d 5.48 5.44 4.93 4.18 3.17
28 d 5.80 5.51 5.14 4.36 3.27
Mohsen Shamsaei, Iman Aghayan, Kani Akhavan Kazemi PII:
S0959-6526(17)31552-4
DOI:
10.1016/j.jclepro.2017.07.109
Reference:
JCLP 10112
To appear in:
Journal of Cleaner Production
Received Date:
29 November 2016
Revised Date:
16 June 2017
Accepted Date:
15 July 2017
Please cite this article as: Mohsen Shamsaei, Iman Aghayan, Kani Akhavan Kazemi, Experimental investigation of using cross-linked polyethylene waste as aggregate in roller compacted concrete pavement, Journal of Cleaner Production (2017), doi: 10.1016/j.jclepro.2017.07.109
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Experimental investigation of using cross-linked polyethylene waste as aggregate in roller compacted concrete pavement
Mohsen Shamsaeia, Iman Aghayana,*, Kani Akhavan Kazemia aDepartment
of Civil Engineering, Shahrood University of Technology, Shahrood, Iran
*Corresponding
author: Iman Aghayan, E-mail: [email protected]
Abstract In recent years, cross-linked polyethylene (XLPE) is one such waste material that has been growing rapidly. In fact, XLPE used for the insulation of electric wires and cables is a nonbiodegradable component. This study was carried out to investigate the use of XLPE waste as an aggregate in roller compacted concrete pavement (RCCP) mixes. XLPE waste as an aggregate with several volume percentages was utilized to replace the natural coarse aggregate of concrete mix. This replacement was conducted with 5%, 15%, 30% and 50% contents. The unit weight, VeBe time, compressive strength, splitting tensile strength, and flexural strength were measured for all the specimens. The results indicated that the use of XLPE waste changed the properties of fresh and hardened concrete. XLPE waste caused the reduction of unit weight and VeBe time. The results showed that replacing 5% of coarse aggregate with XLPE waste increased the 28-d splitting tensile strength of RCCP by 10%. In addition, the 28-d compressive and flexural strengths of this concrete mix were greater than the minimum compressive and flexural strengths determined by the RCCP guide. According to the test results, the use of XLPE waste for more than 5% of the coarse aggregate of the mix are recommended for low traffic pavements, rural roads and sidewalks. Moreover, the use of XLPE waste increased ductility and resistance against RCCP cracking. Overall, using XLPE waste in RCCP can prevent entering wastes into the environment. And, it reduces landfill cost and saves energy. Keywords: Cross-linked polyethylene; Mechanical properties; Recycling; Roller compacted concrete pavement
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1. Introduction Environmental impacts are one of the most important issues that have been the focus of global discussions in recent years. All over the world, large amounts of electric wires and cables are produced annually, and these products generate a lot of wastes. If these wastes return to the environment, it leads to grave environmental impacts. Cross-linked polyethylene (XLPE) is widely used as an insulating material for electric wires and cables. XLPE wastes are nonbiodegradable components. The accumulation of polymer wastes including waste plastic, waste rubber and polyethylene materials such as XLPE has become a worldwide concern. The total amount of cable waste produced in Japan in 2003 was approximately 10,000 tons (Tokuda et al., 2003). Also, in Sweden, the amount of electrical cables waste was estimated to be 40,000 tons in 2007 (Christéen, 2007). These statistics indicate large quantities of XLPE waste. These XPLE waste depots are illustrated in Fig. 1. XLPE waste is burned as a fuel or buried. Since XLPE has low fluidity and poor moldability, it is rarely recycled, though its recycling is of crucial importance for researchers. However, burning and incineration of these wastes lead to energy consumption and air pollution as well. Furthermore, burying wastes requires convenient locations and also leads to soil pollution. For these reasons, finding a suitable solution for recycling XLPE is very significant as well as for reusing this valuable material (Lu et al., 2009; Shang et al., 2010). Roller compacted concrete (RCC) is a zero-slump concrete that is applied in road pavements. Thus, this major advantage of RCC pavement makes it superior to asphalt and conventional concrete pavements. Moreover, there are some other advantages associated with RCC pavements such as their simple construction method and increased placement speed, no need for the use of dowels and steel reinforcement, low administrative costs, less cement consumption, and high resistance in hot or cold weather conditions. RCC is a mix in which there exists the possibility of passing roller over it in the fresh state. In this way, a stiff and compacted concrete surface is made by the roller. The United States Army Corps of Engineers first used the RCC pavement in 1942. Although reports of using this type of pavement were recorded in Sweden in 1930, the first industrial area from RCCP was built in Canada in 1976. The advantages of this type of pavement will make its use widespread in the following years (ACI 325.10R, 2001).
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RCCP is more economical compared to other concrete pavements due to the lack of dowels and steel reinforcement. Moreover, it has lower maintenance costs. The flexural strength of RCCP is equal to or even more than the conventional concrete pavement. Recent researches have shown that this type of pavement has a desirable long-term performance. Although this pavement is usually not applicable for high-speed traffic, in some cases, it has been implemented for high speeds as well (Delatte, 2014). In RCCP, the recycled materials can be used as fine and coarse aggregates. For example, research experiments conducted by Modarres and Hosseini (2014) indicated that the use of recycled asphalt pavement (RAP) resulting from the repair of asphalt pavements as aggregates decreased the compressive strength of RCCP. However, with regard to the accessibility of RAP in asphalt roads, using recycled materials for environmental protection and using them in lowtraffic pavements have been recommended. Also, Settari et al. (2015) investigated the mechanical properties and durability of RCCP. They used different sizes of RAP as a replacement for aggregates in RCCP. The test results showed that 50% of these aggregates could be replaced, and the pavement remained relatively desirable. Courard et al. (2010) studied the possibility of using recycled concrete in RCCP. Characteristics such as Los Angeles (L.A.) abrasion, water absorption, and specific gravity of the recycled aggregates were assessed appropriately. By replacing the natural aggregates with concrete road recycled aggregates, the compressive strength of RCCP decreased. Overall, the recycled aggregates in RCC mixes showed a good performance. Due to the growth of land transport and the increasing number of vehicles, tyre production has increased consequently. The recycling of tyre and rubber has been the focus of attention of researchers as an important issue. One of the ways for recycling these wastes is by using them as an aggregate in RCCP mix (Fakhri and Saberi, 2016). Some researchers (Meddah et al., 2014; Lv et al., 2015; Feng et al., 2015) have investigated various sizes of rubber particles in RCCP. Tests conducted by these researchers have revealed that after the replacement with pieces of rubber, there were changes in the concrete’s properties such as unit weight, modulus of elasticity, and mechanical properties. The elasticity modulus, compressive, splitting tensile and flexural strengths were reduced by adding recycled rubber. However, the addition of rubber particles to RCCP may be beneficial due to the improvement of some properties such as high ductility and
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fatigue life, low porosity and also low unit weight. By considering the minimum compressive strength in the RCCP guide, after the replacement of rubber as an aggregate in the RCCP mix, the resultant pavements were assessed to be appropriate for low traffic, rural roads and pedestrians. One of the disadvantages of rigid pavements is low flexibility. This causes cracking due to tensile and flexural strengths. The flexibility of concrete pavement can be increased by using some industrial wastes such as shredded tyre rubber and grinded plastic bottles (polypropylene, PP) as aggregates. Concrete pavement mix aggregates in quantities of 10%, 20%, 30% and 40% were replaced with shredded tyre rubber and grinded plastic bottles. The test results showed that the splitting tensile strengths related to the replacement contents of 10%, 20% and 30% were acceptable. Krishnamoorthy et al. (2016) showed that the use of recycled materials could improve concrete pavement characteristics including splitting tensile strength and reduce costs as well. Silva et al. (2013) investigated the effect of curing conditions on durability of concrete mixes after replacing waste plastics (polyethylene terephthalate) as coarse and fine aggregates. Actually, waste plastics of 7.5% and 15% contents replaced natural aggregates. Tests such as shrinkage and water absorption were performed on the specimens. Finally, the results indicated that the durability of the specimens containing waste plastic had reduced in comparison to the control specimens. Ashwini Manjunath (2016) also conducted a study on using E-plastic waste as a replacement for aggregates in concrete to improve some of its properties. Today, E-plastic waste is rapidly growing as it is a valuable resource of IT industries. These plastics are nonbiodegradable components with low recycling rate. This substance in different percentages such as 10%, 20% and 30% were used to replace fine and coarse aggregates. Tests were carried out to comparatively study the compressive strength, tensile strength and flexural strength of the control specimens and the specimens replaced by waste plastic, and the results revealed that the use of E-plastic waste as an aggregate decreased the density, compressive strength and tensile strength of the concrete. The use of 10% plastic waste increased the 28-d flexural strength of concrete as well as its plasticity. According to recent studies on the use of recycled materials in concrete pavements, RCCP in particular is a partial solution to environmental and ecological problems, and reduces
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construction costs by reducing the amount of natural aggregate. XLPE waste is nonbiodegradable components with low fluidity, and it is impossible to melt it down again for molding. Nowadays, almost all XLPE wastes are either burnt as fuel or buried. So, it is necessary to investigate the use of XLPE wastes as aggregates in RCCP mix. The tensile strength, the ductility, and the energy adsorption capacity of RCCP are lower than other concrete pavements that use dowels and steel reinforcement. Though finding a proper solution to recycle XLPE wastes at low costs still needs further studies, it seems that using these wastes as aggregate replacements can help alleviate environmental problems and save energy too. Moreover, since the costs of providing these wastes are low or often free, it leads to a reduction in construction costs. The most significant objectives of the present study include:
Using XLPE waste as aggregate in RCCP mix as partial substitution in different volume percentages of coarse aggregate of 5%, 15%, 30% and 50%.
Evaluating the compressive strength, the splitting tensile strength, and the flexural strength of RCCP by replacing XLPE waste as coarse aggregate.
Examining the unit weight and the vibrating compaction time (VeBe time) variations in concrete mixes with regard to different volume contents of XLPE waste.
2. Materials The materials used in this study include Portland cement type II, crushed calcareous gravel, and dune sand. Calcareous gravel was provided from a mine 20 km from Shahrood city in Semnan province. These aggregates were used in three sizes, passed from sieve 3/8 in, sieve 1/2 in, and sieve 3/4 in (with maximum sizes of 10, 14, 19 mm). Dune sand was provided from a mine 5 km from Miami city in Semnan province. Water without any additives was used for the production of cement paste. The XLPE wastes were provided from Moghan Wire and Cable Co. in Iran. XLPE wastes were converted to the appropriate size by a special machine for recycling plastics. The size of the recycled XLPE waste materials was retained by sieve No. 4 (4/75 mm), and the size of the passing materials through sieve 3/8 in (10 mm). Fig. 2 illustrates the size of XLPE waste used in the study.
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The amount of cement used was about 12% to 14% of the mass of the aggregates. The maximum size of coarse aggregate for the gradation of concrete mix was considered to be 19 mm (ACI 325.10R, 2001; PCA, 2010). The recommended limits for the gradation used were extracted from ACI 211.3R. (1997), and the used limits and percentages are shown in Fig. 3. This guide is concerned with zero-slump concrete, and the recommended amounts of coarse and fine aggregates are almost equal. The recommended limits and designs are almost similar to ACI 325.10R. (2001) pertaining to RCCP. The gradation curve of the natural aggregates used in the research was selected in accordance with the mentioned guide illustrated in Fig. 3. The physical and the chemical properties of Portland cement are given in Table 1. The mechanical properties and the tests related to natural aggregates and the XLPE waste used are shown in Table 2.
3. Experimental study The appropriate mix design was obtained by using ACI 211.3R. (1997) and ACI 325.10R. (2001). In addition to the control mix design, we used XLPE as a replacement for different volume percentages of coarse aggregate in four concrete mixes at the varying rates of 5%, 15%, 30% and 50%. Then, these concrete mixes were compared with the control mix design without XLPE. The water to cement ratio (w/c) of the appropriate mix design was calculated by using the ACI 211.3R. (1997) guide (see in Appendix 3) as the basis to determine optimum workability. For all the tests, five mix designs were designed with XLPE wastes with 0%, 5%, 15%, 30% and 50% of coarse aggregates. These mix designs and the XLPE waste replacement content of each of the specimens are given in Table 3. The water content of all the mixes was equal to 163 Kg/m³. The VeBe time and the fresh concrete density were measured for each XLPE content and the control specimen according to ASTM C1170. (2008). The slump test was also conducted with standard ASTM C143. (2003). Concrete slump was equal to zero in accordance with the RCC properties (ACI 325.10R, 2001; PCA, 2010).
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3.1 Compressive strength test This test is used to determine the compressive strength of cylindrical concrete specimens. This test method consists of applying axial loading to molded cylinders at a rate which is within a prescribed range until the occurrence of failure. The compressive strength is calculated by dividing the maximum load carried by the specimen during the test by the specimen’s crosssectional area. The test loading rate was 0.3 MPa/s (ASTM C39, 2011). In this test, cylindrical specimens with 100 mm diameter and 200mm height were used. The specimens were compacted in three equal layers. Each layer was compacted with top surcharge of 50 g/cm². Compaction was continued until a paste ring was observed between the periphery of the surcharge and the cylinder. The vibration time for the control mix design was also calculated between 30 and 45 seconds in accordance with ACI 325.10R. (2001). In this study, regardless of the test specimens for determining the mix design, 45 main cylindrical specimens were prepared for the compressive strength test. After that, the molds were covered with plastic bags until demolding. Then, the specimens were demolded after 24 hours and immersed in normal water for curing until they reached the test age. The hardened properties of the concretes discussed in this paper were for 7, 14 and 28 days of water curing. Finally, the compressive strength test was accomplished based on the ASTM C39. (2011).
3.2 Splitting tensile strength test This test determines the splitting tensile strength of cylindrical concrete specimens, such as molded cylinders and drilled cores. Actually, the test method consists of applying a diametrical compressive force along the length of a cylindrical concrete specimen at a rate that is within a prescribed range until the occurrence of failure. When compressive failure is conducted, there is occurrence of tensile failure as well. Moreover, thin plywood bearing strips are used to distribute the load applied along the length of the cylinder. For the splitting tensile strength test, the size, the molding, the surcharge value, and the specimen preparation are also like those of the compressive strength test specimens. For this test, 45 main cylindrical specimens were prepared. The preparing process and the curing conditions were similar to the compressive strength test specimens. After curing time, the splitting tensile strength test was performed on the specimens in accordance with ASTM C496. (1996).
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3.3 Flexural strength test In this study, the four-point bending test was conducted to determine the flexural strength of concrete with the use of a simple beam. The results are calculated and reported as the modulus of rupture. The determined strength can vary with differences in specimen size, preparation, moisture condition, curing, or where the beam is molded or sawed to size. The span length of the specimen with 2% tolerance should be three times its depth. For the specimens cured in water, it should be conducted immediately after bringing them out from water curing. For this test, rectangular molds with a length of 35cm, width of 10cm and height of 10cm were used. Fortyfive rectangular specimens (beam shaped) were prepared for this test as well. The preparation of the specimens was performed on a vibrating table with a surcharge. The specimens were compacted with top surcharge of 25g/cm². The molds were covered with plastic bags until demolding. The specimens were demolded after 24 hours and immersed in normal water for curing. The hardened properties of the beams were for 7, 14 and 28 days of water curing. Finally, the flexural strength was achieved based on the ASTM C78. (2007).
4. Results and discussion 4.1 The effect of recycled XLPE waste on fresh concrete properties The density and the vibrating compaction time were calculated for each percentage of XLPE. The concrete density decreased regularly with the increasing percentage of XLPE in the concrete mix. When 50% of XLPE was replaced as coarse aggregate, the unit weight decreased from 2510 kg/m³ to 2152 kg/m³. The maximum loss of unit weight was related to the replacement of 50% XLPE, which was approximately 14% as shown in Fig. 4. This reduction might be due to the low unit weight of XLPE as compared to using natural aggregate as well as more voids in the concrete at the time of replacing XLPE. Since RCC has zero slump, its performance is measured with the VeBe test. The relationship between the XLPE content and the vibrating compaction time is depicted in Fig. 5. As can be seen, by increasing the XLPE percentage, the RCC workability increased and the VeBe time decreased. The vibrating compaction time decreased from 36 seconds for the control specimen to 21 seconds for the specimen containing 50% of XLPE. This reduction might be due
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to lower water absorption of XLPE (0%) as compared to natural aggregate. Thus, the amount of free water in the mixture increased, causing more workability and making the compaction process easier.
4.2 Compressive strength The minimum requirement for compressive strength pertains to the layer in which the RCC is used. The minimum 28-d compressive strength needed for RCCP, as the main structural layer, is 27.6 MPa (ACI 325.10R, 2001). The results indicated that along with the 28-d control specimens, just the strength of 28-d specimens with 5% of XLPE was more than the minimum allowable strength. However, these specimens containing 5% of XLPE also showed a slight loss in compressive strength as compared that of the control specimen. The compressive strength reduced with increased XLPE percentage. The average 28-d compressive strength decreased from 29.5 MPa for the control specimen to 8.75 MPa for the specimen containing 50% of XLPE. This strength loss might be caused by less adhesion of XLPE to the cement mortar in RCC mix in comparison to that of the natural aggregate, and also because of increased porosity of the specimens containing XLPE as compared to the natural aggregate specimens. The average compressive strength at 7, 14 and 28 days for different percentages of XLPE are shown in Table 4. The comparative compressive strengths of the specimens with different percentages of XLPE are shown in Fig. 6. The specimen with 5% XLPE had the minimum allowable compressive strength determined for RCCP. The compressive strength test was conducted by the universal testing machine. Fig. 7 illustrates the relationship between the average 28-d compressive strength of the specimens and the concrete density. With regard to the R² value, it can be concluded that the concrete density had a good correlation with the compressive strength.
4.3 Splitting tensile strength The tests revealed that replacement by 5% XLPE caused an increase in the observed splitting tensile strength. In the following, an increase in XLPE content negatively affected the tensile strength, so that the tensile strength decreased regularly. The tensile strength increased from 2.90
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MPa for the 28-d control specimen to 3.23 MPa for the specimen containing 5% XLPE. This 11% increase might be due to XLPE’s higher flexibility as compared to the natural aggregate as well as its irregular polygonal shape that caused the increase of aggregate interlocking in concrete. Moreover, with the increase in XLPE content, easier concrete failure due to XLPE’s lower adhesion as compared to natural aggregate and increasing air voids in RCCP mix were observed. Thus, the optimum replacement percentage, which even increased the tensile strength, was 5%. Finally, the maximum loss of tensile strength was observed for the mix containing 50% of XLPE. It decreased to 1.72 MPa. Table 5 demonstrates the average tensile strength at 7, 14 and 28 days. The comparative average tensile strength of the specimens for different contents of XLPE is depicted in Fig. 8. The relationship between the average 28-d compressive strength and the average 28-d indirect tensile strength is illustrated in Fig. 9. The ratio of the average 28-d indirect tensile strength to the average 28-d compressive strength for the control specimens increased from 10% to 20% for the specimens containing 50% of waste XLPE. Fig. 10 illustrates the split specimens under this test. Some particles of XLPE are represented inside red circles in the specimens with different percentages. According to Fig. 10, it can be concluded that XLPE distribution was almost uniform in the concrete pavement mix. As can be seen in Fig. 10, almost all the coarse aggregates were crushed and cracks passed through the aggregates. This reflects the appropriate amount of water to cement and the appropriate continuity between the aggregate and the cement paste in the used mix design.
4.4 Flexural strength The results showed greater flexural strength of the 7-d specimens containing 5% of XLPE than the 7-d control specimens. In the other specimens, with the increase of XLPE content, the flexural strength decreased regularly. This issue might be due to the lower adhesion of XLPE compared to the natural aggregate in RCCP. Moreover, the replacement of coarse aggregate by XLPE waste might also have increased the air voids of the mixtures. The average flexural strength of the specimens at 7, 14 and 28 days for the different percentages of XLPE are presented in Table 6.
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Fig. 11 shows the comparison of the flexural strength of the specimens with different contents of XLPE. Fig. 12 is related to the flexural strength test by the universal testing machine. It can be seen that the control specimens were broken into two pieces at the time of testing, but the other specimens containing 5%, 15%, 30% and 50% of XLPE were not separated into two parts. So, the crack in the specimens with XLPE was inversely proportional to the percentage of added XLPE. This test demonstrates that RCCP with XLPE waste has higher energy absorption capacity than RCCP without XLPE waste. As the XLPE content increased, the failure became more ductile. The relationship between the average 28-d splitting tensile strength and the average 28-d flexural strength are shown in Fig. 13. The ratio of the average 28-d flexural strength to the average 28-d compressive strength for the control specimens increased from 10% to 20% for the specimens containing 50% of XLPE waste.
5. Conclusion This study investigated the use of XLPE waste as a replacement for natural aggregate with varying volume percentages in RCCP mix. The results revealed that the use of XLPE waste as coarse aggregate improved some of the RCCP properties. Recycled XLPE waste decreased 42% of the vibrating compaction time by the partial substitution of gravel by 50% in the RCCP mix. The reduction in unit weight was directly proportional to the increase in XLPE content. When waste XLPE replaced coarse aggregate by 5%, the 7-d, 14-d and 28-d splitting tensile strengths compared to the control specimens increased by 18%, 9% and 10%, respectively. For the other tested percentages, with increasing XLPE contents, the splitting tensile strengths decreased regularly. When XLPE replaced 5% of the coarse aggregate, the 7-d flexural strength increased by 6%; however, the 14-d and the 28-d flexural strengths decreased slightly. For the other percentages, the flexural strength also decreased regularly, but ductility and cracking resistance increased. In addition, the 28-d compressive strength of specimens containing 5% of XLPE waste was more than the minimum compressive strength prescribed by the RCCP guide. Therefore, recycling 5% of XLPE waste as coarse aggregate in RCCP mix was not only allowable as the main structural layer according to ACI 325.10R, but it also increased the splitting tensile strength. Overall, using 5% of XLPE waste for all technical requirements was
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allowable. For the content percentages of 15, 30 and 50, a regular loss in strengths was observed; but some properties such as ductility and energy absorption increased, and unit weight decreased as well. These percentages can be used in some cases such as low traffic pavements, rural roads, large industrial areas and sidewalks. The use of appropriate percentage of XLPE waste depends on the technical requirements and aim of a particular project. Using recycled XLPE waste in RCCP removes some of these wastes from nature. It is a suitable way to recycle them with low cost. In addition, it simultaneously reduces the need for natural aggregates. Finally, the use of XLPE waste as an aggregate in RCCP mix is recommended.
Acknowledgments The authors would like to thank Mr. Gholamreza Ebrahimian, managing director of Moghan Wire & Cable Company, and Mr. Alireza Nazemi for their help and support.
References American Concrete Institute, 2001. Roller compacted concrete pavements, ACI 325.10R. American Concrete Institute, 1997. Guide for selecting proportions for no-slump concrete. ACI 211.3R. American Society for Testing and Materials (ASTM) C39/C39M-11a, 2011. Standard test method for compressive strength of cylindrical concrete specimens, Annual book of ASTM standards, West Conshohocken, Pennsylvania, USA. American Society for Testing and Materials (ASTM) C496-96, 1996. Standard test method for splitting tensile strength of cylindrical concrete specimens. Annual book of ASTM standards, Pennsylvania, USA. American Society for Testing and Materials (ASTM) C78-07, 2007. Standard test method for Flexural strength of concrete (using simple beam with third-point loading). West Conshohocken, Pennsylvania, USA. American Society for Testing and Materials (ASTM) C1170/C1170M-08, 2008. Standard test method for determining consistency and density of roller-compacted concrete using a vibrating table. West Conshohocken, Pennsylvania, USA. American Society for Testing and Materials (ASTM) C 143/C 143M – 03, 2003. Standard test method for slump of hydraulic-cement concrete. West Conshohocken, Pennsylvania, USA.
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Ashwini Manjunath, B. T., 2016. Partial replacement of e-plastic waste as coarse-aggregate in concrete. Procedia Environmental Sciences. 35, 731–739. doi:10.1016/j.proenv.2016.07.079. Christéen. J., 2007. Swedish cable waste for recovery in China or Sweden. Master thesis, Department of Management and Engineering, LiTH, Linköping Universitet. Courard, L., Michel, F., Delhez, P., 2010. Use of concrete road recycled aggregates for Roller Compacted Concrete. Construction and Building Materials. 24, 390–395. doi:10.1016/j.conbuildmat.2009.08.040 Delatte, N. J., 2014. Concrete pavement design, construction, and performance. United States. Second Edition. CRC Press. Taylor & Francis Group. Fakhri, M., Saberi, K. F., 2016. The effect of waste rubber particles and silica fume on the mechanical properties of Roller Compacted Concrete Pavement. Journal of Cleaner Production. 129, 521-530. doi:10.1016/j.jclepro.2016.04.017 Feng, L., Liang-yu, M., Guo-Fang, N., Li-Juan, L., 2015. Fatigue performance of rubbermodified recycled aggregate concrete (RRAC) for pavement. Construction and Building Materials. 95, 207–217. doi:10.1016/j.conbuildmat.2015.07.042 Krishnamoorthy, R. R., David, T. K., Mastor, N. A. B., Nadarasa, I. K., 2016. Repair of deteriorating pavement using recycle concrete materials. Procedia Engineering. 142, 371 – 382. doi:10.1016/j.proeng.2016.02.064 Lu, C., Zhang, X., Liang, M., 2009. Mechanochemical recycling and processing of waste crosslinked polymers: Waste tire rubber and waste XLPE from cables scraps. October 11-14. The 5th ISFR. Chengdu. China. Lv, J., Zhou, K., Du, Q., Wu, H., 2015. Effects of rubber particles on mechanical properties of lightweight aggregate concrete. Construction and Building Materials. 91, 145–149. doi:10.1016/j.conbuildmat.2015.05.038 Meddah, A., Beddar, M., Bali, A., 2014. Use of shredded rubber tire aggregates for roller compacted concrete pavement. Journal of Cleaner Production. 72, 187-192. doi:10.1016/j.jclepro.2014.02.052 Modarres, A., Hosseini, Z., 2014. Mechanical properties of roller compacted concrete containing rice husk ash with original and recycled asphalt pavement material. Materials and Design. 64, 227-236. doi.org/10.1016/j.matdes.2014.07.072 Portland Cement Association (PCA). 2010. Guide specification for the construction of roller compacted concrete pavements, Skokie, Illinois, USA.
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Settari, Ch., Debieb, F., Hadj Kadri , El., Boukendakdji, O., 2015. Assessing the effects of recycled asphalt pavement materials on the performance of roller compacted concrete. Construction and Building Materials. 101, 617–621. doi:10.1016/j.conbuildmat.2015.10.039 Shang, L., Wang, Sh., Zhang, Y., Zhang, Y., 2010. Pyrolyzed wax from recycled cross-linked polyethylene as warm mix asphalt (WMA) additive for SBS modified asphalt. Construction and Building Materials. 25, 886–891. doi:10.1016/j.conbuildmat.2010.06.097 Silva, R, V., de Brito, J., Saikia, N., 2013. Influence of curing conditions on the durabilityrelated performance of concrete made with selected plastic waste aggregates. Cement & Concrete Composites. 35, 23–31. doi:10.1016/j.cemconcomp.2012.08.017 Tokuda, Sh., Horikawa, S., Negishi, k., Uesugi, K., Hirukawa, H., 2003. Thermoplasticizing technology for the recycling of crosslinked polyethylene, Furukawa Review, Japan.
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The list of table captions Table1: Chemical compositions, physical and mechanical properties of Portland Cement Type II Table 2: Physical properties of original aggregates and XLPE Table 3: Mix concrete proportions Table 4: The average compressive strength of specimens Table 5: The average tensile strength of specimens Table 6: The average flexural strength of specimens
The list of figure captions Fig. 1: Two XLPE waste storage sites Fig. 2: The used XLPE wastes Fig. 3: Recommended aggregate grading limits for RCCP Fig. 4: Effect of XLPE content on the density of fresh concrete Fig. 5: Effect of XLPE content on the concrete workability Fig. 6: The comparison of average compressive strength of specimens Fig. 7: The relationship between the average 28-d compressive strength of specimens and concrete density Fig. 8: The comparison of the average tensile strength of specimens Fig. 9: The relationship between the average 28-d indirect tensile strength and the average 28-d compressive strength Fig. 10: Distribution of different XLPE contents in specimens Fig. 11: The comparison of the flexural strength of specimens
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Fig. 12: Flexural strength test and specimens at failure Fig. 13: The relationship between average 28-day flexural strength and 28-day compressive strength
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Highlights
1. Cross-linked polyethylene (XLPE) wastes are used as a coarse aggregate in roller compacted concrete pavement (RCCP). 2. Increasing XLPE content in RCCP decreases its density and vibrating compaction time (VeBe time). 3. Increasing XLPE content in RCCP increases its ductility and cracking resistance. 4. 5 % max of XLPE content are recommended to be used in main structure layer of RCCP.
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Table 1 Chemical compositions, physical and mechanical properties of Portland Cement Type II Chemical compositions (%) Calcium oxide (CaO) 63.36 Silicon dioxide (SiO2) 21.20 Alumina (Al2O3) 4.48 Ferric oxide (Fe2O3) 3.96 Magnesium oxide (MgO) 1.52 Sulphur trioxide (SO3) 2.50 Sodium oxide (Na2O) 0.37 Loss on ignition (LOI) 1.18 Other 1.43 Physical characteristics Specific gravity Specific surface (cm²/g) Soundness (%) Initial setting time (min) Final setting time (min)
3.15 3309 0.05 140 210
Compressive strength (MPa) 3d 27.5 7d 37.2 28 d 46.9
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Table 2 Physical properties of original aggregates and XLPE Properties Specific gravity (kg/m³) Sand equivalent (%) Fineness modulus Water absorption (%) Los Angeles (%)
Standard ASTM C127 (CA) ASTM C128 (FA) ASTM D2419 ASTM C33 ASTM C127 (CA) ASTM C128 (FA) ASTM C131
Sand 2600
Calcareous gravel 3/8 1/2 3/4 2686 2660 2642
XLPE 800
77 2.9 2.2
0.7
0.33
0.55
0
-
23
21
21
-
ACCEPTED MANUSCRIPT
Table 3 Mix concrete proportions Mix
RCCP0 RCCP5 RCCP15 RCCP30 RCCP50
XLPE content %
Constituents (Kg/m³) Cement
Sand
0 5 15 30 50
298 298 298 298 298
772 772 772 772 772
Gravel 3/8 657.00 595.24 471.73 286.45 39.42
Gravel 1/2 234 234 234 234 234
Gravel 3/4 337 337 337 337 337
XLPE 0 18.40 55.18 110.36 183.94
ACCEPTED MANUSCRIPT
Table 4 The average compressive strength of specimens Mix RCCP0 RCCP5 RCCP15 RCCP30 RCCP50
Compressive strength (MPa) 7d 14 d 28 d 22.00 24.86 29.50 21.52 23.90 28.49 14.19 16.02 18.31 10.03 11.61 13.30 6.83 7.35 8.75
ACCEPTED MANUSCRIPT
Table 5 The average tensile strength of specimens Mix RCCP0 RCCP5 RCCP15 RCCP30 RCCP50
Splitting tensile strength (MPa) 7d 14 d 28 d 2.40 2.87 2.90 2.94 3.15 3.23 2.21 2.38 2.49 2.00 2.07 2.15 1.54 1.61 1.72
ACCEPTED MANUSCRIPT
Table 6 The average flexural strength of specimens Mix RCCP0 RCCP5 RCCP15 RCCP30 RCCP50
7d 5.06 5.39 4.72 4.03 3.10
Bending strength (MPa) 14 d 5.48 5.44 4.93 4.18 3.17
28 d 5.80 5.51 5.14 4.36 3.27