Application of life cycle assessment (LCA) for construction and demolition waste management: a Colombian case study

1 Application of life cycle assessment (LCA) methodology and economic 1 evaluation for construction and demolition waste: a Colombian case study 2 3 4 Sindy Sofía Suárez Silgadoa; Lucrecia Calderón Valdiviezob; Leandro Mahecha 5 Vanegasa 6 7 a Universidad Antonio Nariño, Faculty of Arts, Architecture Program, Group of city, environment and 8 popular habitat, Cra. 10 # 17 - 35 Barrio Ancón, Ibagué, Colombia. 9 b Universitat Politècnica de Catalunya, Technology Department of Architecture, Av. Diagonal 649, 10 08028, Barcelona, Spain. 11 12 Abstract 13 The construction industry not only consumes more raw materials and energy than 14 any other economic activity, but also generates the largest fraction of waste, known 15 as construction and demolition waste (CDW). This waste has major environmental 16 implications, most notably in South American countries such as Colombia, where it 17 is handled inappropriately. In this study, the management processes that are 18 currently used for fractions of construction and demolition waste (CDW) generated 19 in Ibagué (Colombia) were evaluated and the environmental impacts of the 20 management of 1 kg of CDW were calculated. Other CDW management alternatives 21 were evaluated, in which the percentage of the fraction of the waste and/or the 22 treatment or management process that is used was modified to determine its 23 environmental and economic viability. 24 The information was obtained through telephone interviews and visits to recycling 25 plants, construction companies, quarries, government entities, and inert landfills in 26 the country. It was completed with secondary sources and the Ecoinvent v.2.2 27 database. Life cycle assessment (LCA) methodology and SimaPro 8 software were 28 used to calculate the environmental impacts. An economic study of each 29 management process and each alternative was also carried out. 30 A comparison of the alternatives revealed the current alternative contributes most to 31 the environmental impacts in all categories. 32 The results of this study indicate that the most beneficial alternative in environmental 33 and economic terms in Ibagué (Colombia) is that in which 100% of the metals are 34 recovered, 100% of excavated earth is reused, and 100% of the stone waste is 35 recycled (alternative 3). 36 When a sensitivity analysis was carried out with different distances (30 km and 50 37 km), alternative 3 continued to be the most favorable. 38 Keywords: waste, management, construction and demolition waste, Life Cycle Assessment, impact 39 category. 40 * Corresponding author. Tel: + (057-82732323). E-mail address: sindysofi[email protected]. 41 42 1. Introduction 43 Construction is one of the essential industrial activities for the development and 44 progress of cities. However, it is also one of the sectors that contributes most to 45 2 environmental impacts, due to the extraction of raw materials, energy use, and waste 46 generation. 47 It is considered that the construction sector consumes more raw material and energy 48 than any other economic activity, and generates the largest fraction of waste. In 49 Europe alone, around 900 million t of construction and demolition waste are 50 produced every year (Bravo et al., 2015). 51 According to Ramesh et al. (2010), the term construction and demolition waste 52 (CDW) refers to solid waste produced in the construction sector. More specifically, 53 the term is defined as the waste that arises from construction, renovation and 54 demolition activities. 55 CDW includes a range of materials such as ceramic products, concrete waste and 56 asphalt material, and to a lesser extent other components such as wood, glass and 57 plastics (Yuan and Shen, 2011). The main components of this waste depend on the 58 materials used, the construction practices, and the technological development of the 59 sector. 60 There are various management options for this waste, whose hierarchy depends on 61 the environmental impacts they generate. The five levels of low to high 62 environmental impact are: reduction, reuse, recycling, incineration and final disposal. 63 Some authors (Yuan and Shen, 2011) have grouped these six levels into four: waste 64 reduction, reuse, recycling and disposal. However, the impacts of management 65 systems vary. For example, inadequate disposal of construction and demolition 66 waste (CDW) can generate negative environmental impacts such as soil degradation 67 and erosion, destruction of vegetation, and loss of environmental services (Mejía et 68 al., 2015). 69 The impacts of waste disposal in landfill are associated with the extraction or 70 obtaining of raw material, and land occupation. If waste is sent to landfill, then new 71 materials or products must be manufactured from original raw material (Suárez 72 Silgado, 2017). 73 Faced with this situation, European countries have tried to find innovative 74 alternatives for the recovery of waste from construction and demolition. Yilmaz et al, 75 (2018) have used construction and demolition waste as cemented paste backfill 76 material for underground mine openings. Also, numerous EU regulations have been 77 drawn up on this topic. One is the European Waste Directive, which foresees that by 78 2020, 70% of CDW should be properly valued. The objective is to achieve much 79 higher levels of recycling by minimizing the extraction of additional natural resources. 80 Thus, prevention and recycling are key elements of the new waste policy in Europe 81 (Suárez-Silgado, 2016). 82 In this same line, several studies have used life cycle assessment for effective 83 municipal waste management, because it helps in environmental evaluations of 84 alternative waste management systems (Koci and Trecakova, 2011). According to 85 ISO 14040 (2006), LCA is composed of an inventory of the relevant inputs and 86 outputs of the system, the definition of the goal and the scope, an assessment of the 87 potential environmental impacts associated with these inputs and outputs and, 88 finally, an interpretation of the results of the inventory and impact phases in terms of 89 the study objectives. This methodology has been used by several prominent authors 90 in the field, including Zabalza et al., 2011; Monahan and Powell, 2011 and Tošić et 91 al., 2015. 92 3 Mercante et al. (2012), Coelho and de Brito (2012), Yeheyis et al. (2013), Carpenter 93 et al. (2013), Dahlbo et al. (2015), Guignot et al. (2015) and Wang et al. (2018) have 94 used the LCA for the environmental assessment of CDW management systems in 95 Europe, North America and Asia. 96 The situation has led to the development and implementation of technologies in the 97 international area. The CDW in China are usually randomly dumped or disposed in 98 landfills and the average recycling rate of CDW is only about 5% (Huang et al., 2018). 99 In countries such as Denmark, the Netherlands, and Belgium, the recycling of CDW 100 for uses other than landfill is promoted, and recycling percentages of over 75% are 101 achieved. This high level of recycling is mainly due to the shortage of natural 102 aggregates and space for landfill sites (Zabalza Bribián et al., 2011). One factor that 103 has increased recycling rates has been the increase in the cost of landfilling, or its 104 prohibition in some cases, such as in Denmark or the Netherlands. However, in most 105 South American countries this is not the situation. The management of CDW waste 106 is carried out inadequately, and there is clearly a large gap between South American 107 and other countries in terms of management and technology. 108 In Colombia, CDW is sometimes managed using a controlled discharge system, but 109 usually its disposal is uncontrolled. The authorized sites for waste disposal are 110 disseminated widely, and there are few alternatives for recovery, recycling or reuse. 111 For this reason, only 5% of CDW is recycled in Colombia (Castaño et al., 2013). 112 The generation of CDW has great environmental implications in this country, as it is 113 sometimes disposed of in illegal landfills or thrown on public roads contributing to 114 changes in the landscape and urban areas (Aguilar et al, 2010 ; Pinzón, 2014). 115 The situation is particularly palpable in some municipalities in the country, such as 116 Ibagué, where around 488.000 t of CDW are generated per year (IBAGUÉ LIMPIA, 117 2017), without counting the waste that is generated and disposed of clandestinely. 118 The problem has increased in recent years, due to population growth, increased 119 construction activity, and remodeling of buildings. However, an attempt has been 120 made to advance in this area, and for this reason regulations and programs have 121 been promulgated at district level that encourage the adequate disposal of CDW. 122 Examples are Resolution Nº1115/2012, which technically regulates the treatment 123 and/or use of CDW in the capital district; and the Municipal Development Plan 124 "Bogotá Humana" (2012-2016) with the “Zero Waste-Rubble Zero” program. 125 In Ibagué, there have been new initiatives for CDW management, expressed in 126 Agreement No. 19 of 2013. The Agreement implements Environmental Compare as 127 a tool for citizens related to the proper management of solid waste in Ibagué, and 128 the Integral Solid Waste Management Plan of Ibagué (PGIRS, 2015), which aims to 129 promote the integral management of CDW, broaden the characterization of this 130 waste, and design programs to take advantage of CDW through feasibility studies. 131 In the same field, studies have been carried out at national level on the perspectives 132 and limitations of CDW management (Castaño et al., 2013; Pinzón, 2014), and on 133 the current waste situation in some municipalities (Jiménez, 2013). Technical 134 diagnoses have been made of the use of CDW in the capital district (Escandón, 135 2011; Chávez et al., 2014), along with studies of quantification and characterization 136 of CDW (SDA, 2012; Pinzón, 2014). Finally, in some cases, pilot proposals for 137 recycling plants have been made (Chávez et al., 2014). 138 4 However, despite these advances at national level, no studies have been undertaken 139 to date on the environmental assessment of managing fractions of this waste. 140 Therefore, to help solve the problem of CDW generation in Colombia, the objective 141 of this study was to evaluate the current treatment or management of each fraction 142 of CDW. Subsequently, other alternatives were evaluated in which either the 143 treatment that is used for fractions of waste or the percentage of waste in the 144 treatments was modified. Hence, the objective was to determine which is the most 145 beneficial management alternative at environmental and economic level. 146 The area chosen for the study was the department of Tolima, specifically, its capital 147 Ibagué. This area was selected for two main reasons: the current problems 148 associated with the generation of CDW because of population growth and an 149 increasing number of buildings, and the new waste management initiatives 150 described in Agreement No. 19 of 2013 and the PGIRS (2015), mentioned above. 151 The research is novel because the environmental impacts of waste management 152 systems in Colombia were evaluated using life cycle assessment (LCA), to obtain a 153 more realistic view of the impacts in this country, specifically in Ibagué. 154 As Life Cycle Analysis (LCA) is a decision tool, the results could help to encourage 155 or give greater impetus to the development of projects and programs that contribute 156 to CDW recycling or reuse. 157 The management scenarios were also evaluated from an economic perspective. In 158 addition to applying LCA methodology, a sensitivity analysis was carried out to 159 determine how the final results are affected. The results obtained may lead to the 160 creation of more demanding regulations in the field of waste management in 161 Colombia. 162 2. Data and methods 163 2.1 Study area 164 This study was carried out in Ibagué, a city located in the center-west of Colombia 165 on the Central Mountain Range of the Andes, at an altitude of 1.285 m.a.s.l. This 166 city has an extension area of 4.605 hectares, according to the Territorial Ordinance 167 Plan (POT, 2015), and a population of 553.524 inhabitants (DANE, 2015). The 168 average annual generation of construction and demolition waste is 488.000 t, 169 according to data provided by IBAGUÉ LIMPIA (2017). For this study, it is considered 170 that waste is generated in the expansion zone, where the largest amount of waste 171 is produced. 172 173 2.2 Description of the construction and demolition waste in the study area 174 In accordance with the regulations that apply in this country (Resolution 1115/2012), 175 construction and demolition waste are generated during the development of a 176 construction project, and include excavation products, leveling and leftovers from 177 site preparation; products used for foundations and pilings; stone waste (concrete, 178 sand, gravel, pieces of bricks and blocks, ceramics, leftovers of mortar and concrete 179 mix); and non-stone waste (glass, wood, plastics, metals, cardboard and gypsum). 180 Construction companies in the city were visited to gather information about the 181 current management of CDW in the city of Ibagué. Direct contact was also 182 established through telephone calls and email. According to the information obtained 183 from the companies, over 80% of them are engaged in constructing new dwellings. 184 Therefore, the largest amount of waste in this sector comes from construction 185 5 processes. Of all the construction activity, 92.8% corresponds to dwellings (ICER, 186 2016). 187 Figure 1 shows the composition of CDW in the study area. The highest percentage 188 corresponds to excavated earth. 189 190 Figure 1 Composition of CDW in Ibagué 191 192 193 194 The management system currently applied for CDW in the city of Ibagué (according 195 to the information provided directly by construction companies in the city in 2017) 196 consists basically of the generation of waste in construction, and its subsequent 197 transport to the landfill or final disposal site, without any treatment or recovery. In 198 some cases, around 50% of construction companies separate the metal and 199 excavated earth from the rest of the waste. The metals that are separated are 200 transported by managers to a metal classification or preparation plant for subsequent 201 recycling in a smelting plant in another city. Excavated earth is separated to be 202 reused in the same construction or on a nearby site. 203 In some construction projects, waste is not separated and is simply taken to landfill. 204 This management system is due partly to the fact that Ibagué does not have a 205 recycling plant for CDW, and therefore the waste is mostly taken to the final disposal 206 site. However, in the absence of sufficient control and monitoring in the management 207 of these sites, waste is also transported to non-formal disposal sites in some cases, 208 causing great damage to public roads, riverbeds, and vacant lots. Exact data on this 209 form of disposal are not known. 210 211 2.3 Life cycle assessment (LCA) methodology 212 213 2.3.1 Goal and scope definition 214 Considering the current management of CDW in Ibagué and the problems 215 associated with waste generation in this city, the objective was to identify the 216 potential environmental impacts associated with the management of construction 217 80 10 440.5 1.5 % Excavated earth Concrete and asphalt Brick and mortar Concrete and mortar blocks Steel Others 6 and demolition waste fractions and compare them with new alternatives. The 218 functional unit of the study was 1 kg of waste. 219 Based on the characterization of waste in Ibagué (Figure 1) and the information 220 obtained from construction and other companies that were consulted directly, the 221 three waste fraction considered were: stones (19.5%) (concrete, brick and other 222 inerts), excavated earth (80%) (essentially sands and clays; the organic material 223 content within the ground was considered negligible) and metals (0.5%) (steel). 224 225 2.3.2 Alternatives 226 Three alternatives were evaluated in the life cycle assessment (Figure ). They were 227 chosen according to the quantity and characterization of the waste and the current 228 waste management system in the study area; information that was provided by 229 IBAGUÉ LIMPIA (2017). 230 The first alternative (A1) corresponds to the current management of waste in the city 231 of Ibagué. In this alternative, all stone waste is taken to landfill, metals are taken to 232 the sorting and compaction plant and 50% of excavated earth is reused on a nearby 233 construction site (5 km), while the other 50% is taken to landfill. 234 In two alternatives (A2 and A3), the waste treatment and percentages were modified, 235 to determine viability. 236 In alternative A2, the stone waste management was modified. In this case, 50% of 237 stone is recycled and the other 50% is taken to landfill. 238 In alternative A3, 100% of all waste is recovered. All the stone is recycled and all the 239 excavated earth is reused. 240 241 Figure 2 Alternatives evaluated. 242 243 244 Figure 3 shows the limits of the study systems. The generation and separation of 245 waste fractions were not considered, as waste is separated on site. Only the stages 246 A2 Stone Metal (St Excavated earth Landfill Recovery Reuse Landfill 9.75 % 0.5 % 40 % 40 % 9.75 % Recycling A3 Stone Metal (St Excavated earth Recovery Reuse 19.5 % 0.5 % 80 % Recycling Stone Metal (St Excavated earth A1 Landfill Recovery Reuse Landfill 19.5 % 0.5 % 40 % 40 % 7 of transportation and waste management were included. Once the waste has been 247 generated and separated, it is transported for treatment or final disposal. Thus, the 248 type of management (recycling/recovery, reuse and disposal) varied depending on 249 the waste fraction. Finally, the loads of processes that are avoided were subtracted. 250 Figure 3 Limits of study systems. 251 252 2.3.3 Life cycle inventory 253 254 The data for the inventory analysis were obtained from primary and secondary 255 sources. Information was obtained from primary sources through visits, telephone 256 calls and emails to construction companies, CDW and metal recycling plants, inert 257 landfill sites and quarries. Government organizations such as IBAGUÉ LIMPIA and 258 CORTOLIMA were contacted. Fifty-six construction companies registered in Ibagué, 259 the existing legal inert landfill, 4 metal recycling plants, and 6 quarries near the study 260 area were also contacted. 261 As the city of Ibagué does not have a CDW recycling plant, data had to be obtained 262 by visiting waste recycling plants that are currently in operation in Colombia. Data 263 were also collected from other facilities at national level and from 2 landfills to 264 complement and compare with data from landfills in the study area. 265 The data correspond to different years (2015-2017) with a similar production 266 capacity. The information was supplemented with secondary sources such as 267 articles, journals, projects on the same subject, and the Ecoinvent v3 database. 268 Transport Stone Energy Energy Excavated earth Energy Steel (Scrap ) Energy Stone/ earth Reuse at another construction site (extendedcompaction-leaching) Classification and compaction (scrap) Landfilling (Inert landfill) Avoided extraction of aggregates/ transport Avoided earth landfilling/ transport Avoided extraction of iron ore Emissions to air, water Steel waste (transport) Recycled aggregates Solid waste (transport) Steel scrap Wastes generation (separation) A1, A2, A3 A1, A2 A2, A3 A1, A2, A3 Emissions to air Stone, other raw Steel, other raw materials Wastes, other raw material Excavated earth Emissions to air, water and soil Emissions to air and water Solid waste (transport) Recycling (Crushing) 8 To evaluate the environmental impacts of each of the management processes 269 applied to the CDW fractions in Ibagué, new processes were created in Ecoinvent 270 v3, taking as a starting point the information collected from companies, recycling 271 plants and landfill, completed with the inventory of the Ecoinvent v3 database. The 272 electricity mix of Colombia was used for the calculations. 273 Each of the treatment or management processes was evaluated per kg of waste to 274 obtain the environmental impacts. To determine the environmental impacts of 275 managing 1 kg of CDW generated in Ibagué, a new process was created in which 276 each treatment was incorporated, considering the percentage that it occupies in the 277 total construction and demolition waste (Figure 2). In this way, each of the 278 alternatives was compared. 279 Next, each type of treatment or management was defined: earth reuse, metal 280 recovery (classification and compaction), stone recycling, stone and earth landfill. 281 282 • Excavated earth reuse 283 284 The process of reusing excavated earth was evaluated in another nearby 285 construction site. It was assumed that the excavated earth was not contaminated 286 and could therefore be reused without any other type of treatment. The external 287 transportation to the other site is considered. According to the information obtained 288 from the companies, 5 km was considered the maximum distance between the 289 extraction site and the reuse site. 290 The compaction of earth on the new construction site and the emissions (leached) 291 due to its use (100 years) were also considered. 292 Solid waste was considered as output, which is transported to a sanitary landfill 293 located 11 km from the site on which the waste is generated. 294 The reuse of excavated earth on a nearby construction site avoids disposal of this 295 material in landfill. Therefore, the costs of transporting excavated earth to the landfill 296 and its disposal were subtracted in this case. 297 Table 1 shows the input and output of the reuse of excavated earth and the process 298 that is avoided. 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 9 Table 1. Input and output of the reuse of excavation lands. 314 Excavated earth reuse Cant Unit Source Input Transport 5 km Ecoinvent v3; Companies consulted, 2017 Diesel (compaction) 0.001 MJ Companies consulted, 2017 Output Emissions to air Table 6 Ecoinvent v3 Emissions to water (Leached) Table 5 López and Lobo (2014) Waste solid (transport-11 km) 1.00E-02 kg Companies consulted, 2017 Avoided products Cant Unit Source Earth landfilling/transport 1 kg Ecoinvent v3; Companies consulted, 2017 315 • Metal (steel) recovery 316 For the recovery of metal, the stage considered was transport to the treatment plant, 317 where the waste is prepared (classified and compacted) before it is cast, since there 318 is currently no foundry for this material in Ibagué. 319 It was assumed that waste comprised of steel is separated on the construction site 320 and transported separately to the treatment site. The process in these plants 321 basically consists of classifying the material and compacting it, for subsequent export 322 and smelting. According to the companies consulted the steel waste is transported 323 from the expansion area of Ibagué to the classification and compaction plants 324 located at an average distance of 9 Km. 325 The production capacity of the metal treatment plant was taken to be approximately 326 3500 t/year of waste, with an infrastructure of 1500 m2. 327 As the recovery of this waste and its preparation for use as secondary raw material 328 (scrap) replaces the production of iron ore, this production is classified as an avoided 329 product, so the impacts due to this process can be subtracted. 330 Table 2 shows the inputs and outputs of the recovery of metal and the process that 331 is avoided. 332 333 334 335 336 337 338 339 340 341 342 343 344 16 483 484 485 486 Figure 4. Environmental impacts. a) Stone recycling; b) Excavated earth 487 reuse; c) Excavated earth and stone landfilling; d) Metal recovery. 488 489 490 -100 -50 0 50 100 CRI OLD RO LO A E GW NRE ME % Waste reinforcement steel Gravel extraction Tap water Diesel Electricity Synthetic rubber Transport Conveyor belt Infraestructure Crushing process -100 -50 0 50 100 CRI OLD RO LO A E GW NRE ME % Municipal solid Earth landfilling Diesel Transport Earth reuse 0 20 40 60 80 100 CRI OLD RO LO A E GW NRE ME % Transport Landfill infrastructure Landfill operation -100 -50 0 50 100 CRI OLD RO LO A E GW NRE ME % Municipal solid Extraction of iron ore Classification and compaction Electricity Diesel Transport a) b) c) d) 17 3.1.3 Excavated earth and stone landfilling 491 The process of earth and/or stone disposal does not avoid any processes, which is 492 why it contributed to positive environmental loads. The process that contributed most 493 to environmental impacts was the infrastructure of the landfill, especially in the 494 categories carcinogenic (81%), acidification (77%), non-renewable energy (77%), 495 depletion of the ozone layer (77%) and eutrophication (74%). Another process that 496 contributed to environmental impacts was transport, particularly in the global 497 warming category (44%). Transformation and use of earth for landfill had an impact 498 on the land occupation category (41%) (Figure 4 [c]). Leachate emissions are not 499 relevant in the process of earth and stone disposal, as they are inert materials. 500 501 3.1.4 Metal (steel) recovery 502 Metal recovery plays an important role as it avoids the process of extracting iron ore. 503 This had environmental benefits in all the impact categories. The greatest savings 504 were found in the inorganic respiratory (-100%), photochemical oxidation (-100%) 505 and mineral extraction (-100%) categories. Significant savings were also generated 506 in the following categories: acidification (-80%), reduction of the ozone layer (-37%), 507 non-renewable energy (-29%) and global warming (-27%). The infrastructure of the 508 classification plant contributes to greater impacts in the evaluated categories. The 509 greatest impacts were identified in the categories of eutrophication (98%), land 510 occupation (97%) and carcinogenic effects (91%) (Figure 4 [d]). 511 512 3.2 Comparison of the evaluated processes 513 514 515 516 Figure 5 Comparison of the processes evaluated for each type of waste per kg 517 -100 -80 -60 -40 -20 20 40 60 80 100 CRI OLD RO LO A E GW NRE ME % Stone recycling Excavated earth reuse Excavated earth and stone landfilling Metal recovery 18 In Figure 5, the processes that were evaluated are compared to determine the 518 environmental impacts of each one per kg of waste. 519 Figure 5 shows that the metal recovery process contributed to impacts on the 520 carcinogenic effects (100%), ozone depletion (67%), land occupation (100%), 521 acidification (64%), eutrophication (100%), global warming (100%) and non522 renewable energy categories (100%). However, there were also savings in the 523 inorganic respiratory (-100%), photochemical oxidation (-63%) and mineral 524 extraction (-100%) categories. These savings were due to avoidance of the 525 processes of extracting and producing raw material. The results agree with those 526 found by Mercante et al. (2012). 527 The stone recycling process led to savings in all categories. The biggest savings 528 were in photochemical oxidation and acidification (-100%). This is mainly due to the 529 avoidance of natural aggregate extraction loads. The lowest savings in the inorganic 530 respiratory category (-1%) were due to the emission of particulate material during 531 the stone crushing process. 532 As in Mercante et al. (2012), it was found that stone recycling led to savings in all 533 categories. 534 The results agree with those of Mercante et al. (2012), Coelho and de Brito (2012), 535 Kucukvar et al. (2014) ,Guignot et al. (2015) and Wang et al. (2018), who also found 536 that recycling CDW led to environmental savings. 537 The process of earth reuse resulted in environmental savings in all categories, as 538 the high loads in the earth landfilling process are avoided. The biggest savings were 539 in the categories of ozone depletion (-89%) and non-renewable energy (-86%). 540 Significant savings were also identified in photochemical oxidation (-46%), 541 acidification (-38%) and soil occupation (-38%) categories. 542 The disposal of earth and/or stones had an impact on all categories. The greatest 543 impacts were found in the category of ozone depletion (100%) and non-renewable 544 energy (97%) as a result of energy consumption during the process. There were also 545 impacts on land occupation due to the transformation and use of the earth. The 546 impacts of leachate were not relevant in this process; therefore, eutrophication 547 effects were not very high (4%). The results coincide with Butera (2015), who found 548 impacts due to waste disposal and no savings from this process. 549 550 3.3 Analysis of the different alternatives 551 552 Finally, the environmental impacts of the current management system were 553 evaluated, considering the waste fraction and the management process applied to 554 each type of waste that make up 1 kg of the CDW generated in Ibagué (Colombia). 555 This management alternative (A1) was compared with two other alternatives in which 556 the percentage of the waste fraction and/or the management process was modified 557 (A2 and A3). 558 The results in Figure 6 show that the current management alternative (A1) for 1 kg 559 of CDW generated in Ibagué had an impact on all categories, except mineral 560 extraction, in which environmental savings were found (-21%) due to the metal 561 recovery process. The greatest impacts were in the eutrophication category (47%). 562 This may be due to the fact that in this alternative, 100% of the stone and 50% of 563 the excavated earth were dumped, which has a greater impact on this category due 564 19 to the infrastructure of the landfill and transport of waste to the landfill. Other impacts 565 associated with this alternative were in the categories of global warming (34%), non566 renewable energy (30%), land occupation (30%) and ozone depletion (29%). These 567 impacts are due to fuel consumption and the use and transformation of the earth in 568 the waste disposal process. 569 570 Figure 6 Comparison of the scenarios per kg of CDW 571 Alternative 2 had lower environmental impacts than A1 in all categories. In the 572 categories of photochemical oxidation and acidification, it led to environmental 573 savings, unlike A1, because it includes the process of recycling 50% of the stone 574 waste, thus reducing the disposal of this material. Alternative 3 led to environmental 575 savings in all the categories (-100%). This is due to the fact that disposal of waste is 576 eliminated and the percentage of stone waste recycling and reuse of earth 577 increased. In other words, in A3 all generated CDW is recovered. Since the impacts 578 that are avoided when waste materials are recovered and used instead of virgin 579 material are much greater than the impacts that are generated, the net result is that 580 recovery or recycling contributes to savings. 581 Table 8 shows the environmental impacts of the alternatives evaluated per kg of 582 CDW. 583 584 585 586 587 588 589 590 591 592 593 -100 -80 -60 -40 -20 0 20 40 60 80 100 CRI OLD RO LO A E GW NRE ME % A1 A2 A3 20 Table 8 Environmental impacts of the different alternatives evaluated per kg 594 of CDW. 595 Impact category Unit A1 A2 A3 C kgC2H3Cl eq 1.83 E-5 4.82E-6 -6.36E-5 RI Kg PM2.5 eq 8.57E-7 1.05E-7 -5.17E-6 OLD Kg CFC-11 eq 4.15 E-10 1.53E-10 -1.41E-9 PO Kg C2H4 eq 8.79E-7 -1.11E-7 -3.73E-6 LO m2org.arable 0.000209 0.00011 -0.000709 A Kg SO2 eq 6.67E-6 -1.97E-6 -3.08E-5 E Kg PO4 p-lim 3.47E-7 1.75E-7 -7.33E-7 GW Kg CO2 eq 0.00136 0.00037 -0.00402 NRE MJ primary 0.0381 0.0146 -0.128 ME MJ surplus -3.65E-5 -7.19E-5 -0.000177 596 3.4 Sensitivity analysis 597 It was considered necessary to carry out a sensitivity analysis to determine how the 598 final results varied. It was assessed how the results changed when the distance to 599 the recycling plant was altered. Previous studies were taken into account to select 600 the distances. Rodríguez et al. (2015) indicated that the maximum viable distance 601 between the sources of residues and recycling facilities is 30 km. Ulubeyli et al. 602 (2017) proposed that the maximum limit for viability is 50 km between facilities. 603 Therefore, a sensitivity analysis was required, for which scenario 3 was taken as a 604 basis and the environmental impacts were evaluated according to the distances of 605 30 km (A4) and 50 km (A5). 606 Figure 7 reveals that A3 continued to be the most favorable scenario, due to the 607 greater savings in the evaluated categories. When the transport distance to the 608 recycling plant was increased, savings were still made in the alternatives. The 609 savings decreased as the distance to the recycling plant increased. These results 610 agree with those found by Butera (2015), who considered that the process of 611 transporting CDW to the recycling plant contributes to environmental impacts. 612 21 613 Figure 7 Sensitivity analysis for different distances 614 3.5 Economic evaluation 615 616 The economic factor was also relevant when different alternatives were assessed. 617 In this study, the economic evaluation was undertaken on the basis of the cost of 618 each management process per ton, and considering the cost avoided by the 619 management process (Table 9). 620 The net cost of each alternative (Table 10) was obtained from: the values of the net 621 cost of Table 9 and the percentages of each process within the alternative (Figure 622 2). 623 Table 9 shows that A3 was the most beneficial scenario, from the economic 624 perspective, and that increasing the distance to which the recycling plant would be 625 located (50 km, A5) would continue to lead to economic savings, compared to the 626 current management alternative (A1). 627 628 629 630 631 632 633 634 635 636 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 CRI OLD RO LO A E GW NRE ME % A3 A4 A5 22 Table 9 Economic cost of each process per kg 637 Waste Management process Process cost ($/kg) Avoided cost ($/kg) Net cost ($/kg) Source Stone Recycling Cra1+Tc2=16+27=43 Cna4+Tc2=23+136=159 -116 1 Recycling plants consulted 2017; 2 IBAGUÉ LIMPIA 2017; 3 Metal recovery plants 2017; 4 Quarries consulted, 2017; 5 Companies consulted, 2017 Landfilling Ct2+Clr2=44+5=49 ------ 49 Earth Reuse ex situ Tc2 + C= 17+20=37 Tc2+Cg2=36+49=85 -48 Landfilling Ct2+Clr2=44+5=49 ------ 49 Metals Recovery Tc2+Ccc3=30+22=52 CIron=167 -115 Cra= cost of recycled aggregate; Tc= transport cost; Clr= cost of landfill rate; Lc= labour cost (separation); Ccc= Classification and compaction cost; Cna= cost of natural aggregate; Cg=cost of earth; Sc= scrap cost 638 Table 10 Net economic cost of each alternative evaluated 639 Process A1 A2 A3 A4 A5 Stone recycling ----- -11.3 -22.6 -7.99 5.07 Metal recovery -0.58 -0.58 -0.58 -0.58 -0.58 Earth reuse -19.2 -19.2 -38.4 -38.4 -38.4 Stone landfilling 9.55 4.77 ----- ----- ----- Earth landfilling 19.6 19.6 ----- ----- ----- Net cost by scenarios ($) 9.38 -6.70 -61.6 -46.97 -33.91 640 641 642 643 4 Conclusion 644 In this study, management processes for construction and demolition waste fractions 645 in Ibagué (Colombia) were evaluated. The environmental impacts of the 646 management of 1 kg of generated CDW were calculated, considering the current 647 management of each fraction of waste and the percentage of the fraction within the 648 23 total CDW that is generated (A1). New management alternatives were evaluated (A2 649 and A3) in which the percentage of the waste fraction or the type of treatment applied 650 to each one was varied, to determine viability. The environmental evaluation was 651 performed using LCA methodology. An economic evaluation of alternatives was also 652 carried out to determine viability. 653 The comparison of processes evaluated per kg of waste fraction revealed that metal 654 recovery contributed to impacts in some categories and savings in others. Savings 655 were found in the categories inorganic respiratory (-100%), photochemical oxidation 656 (-63%) and mineral extraction (-100%). Impacts were identified in the rest of the 657 categories. In contrast, the stone recycling process led to savings in all evaluated 658 categories. The greatest savings were in photochemical oxidation and acidification 659 (-100%). Likewise, the process of earth reuse resulted in environmental savings in 660 all categories, due to the high loads of the process that was avoided (disposal of 661 earth in landfill). The last process to be evaluated corresponded to earth and stone 662 landfilling, which had an impact on all categories. The greatest impacts were in the 663 ozone depletion (100%) and non-renewable energy (97%) categories. 664 The comparison of management alternatives evaluated per kg of CDW revealed that 665 A1, which corresponds to the current management of CDW in Ibagué, contributed to 666 environmental impacts in all categories, except mineral extraction (-21%). A2 led to 667 savings in photochemical oxidation (-3%), acidification (-6%) and mineral extraction 668 (-41%). A3 brought about great savings in all categories (-100%). 669 Alterative 3 was the most environmentally beneficial, which is why it was taken as a 670 basis to carry out a sensitivity analysis. In this analysis, the impacts were evaluated 671 teniendo en cuenta diferentes distancias a las que se encuentra ubicada la planta 672 de reciclaje (30 km (A4) and 50 km (A5)). The results verified that A3 was the most 673 favorable, due to the greater savings in the categories. There were still savings in all 674 impact categories when the recycling plant is located at 50 km. 675 Thus, the results of this study allow us to verify that the most beneficial CDW 676 management scenario from the environmental and economic point of view in Ibagué 677 is that in which 100% of the metals are recovered, 100% of the earth is reused, and 678 100% of the stone waste is recycled. 679 The results could help to raise awareness among all the agents involved in the 680 construction sector, who can clearly see the vital role they play in the proper 681 management of CDW and, as a result, promote the implementation of mechanisms 682 and infrastructure for waste recovery and recycling. 683 Likewise, the results could contribute to enhancing environmental awareness in the 684 educational and professional field, leading to more sustainable production and 685 consumption habits in Colombia. Finally, it is hoped to help solve current problems 686 related to the inadequate management of CDW, and contribute to progress in this 687 area, as has occurred at international level. 688 689 5 Acknowledgments 690 The authors thank Antonio Nariño University for the financial support. We also 691 appreciate all the support provided by construction companies and organizations in 692 Ibagué, as well as recycling plants, governmental entities and inert landfills in 693 Colombia that provided information for the project. 694 695 24 References 696 697 Aguilar, Mónica; Ardila, Ferney. (2010). Study of waste management alternatives generated 698 by the construction and demolition of buildings in the city of Bogotá (Estudio de alternativas 699 de manejo de escombros generados por la construcción y demolición de edificaciones en 700 la ciudad de Bogotá). Industrial University of Santander. Specialization monograph. 701 Bucaramanga, Colombia. 702 703 Bovea, M.D. and Powell, J.C., (2016). Developments in life cycle assessment applied to 704 evaluate the environmental performance of construction and demolition wastes. Waste 705 Management, 50, pp.151–172. 706 https://www.sciencedirect.com/science/article/pii/S0956053X16300368 707 708 Bravo, M. et al. (2015). Durability performance of concrete with recycled aggregates from 709 construction and demolition waste plants. Construction and Building Materials, 77, 357– 710 369. https://www.sciencedirect.com/science/article/abs/pii/S0950061814014056 711 712 Bueno, G., Latasa, I. and Lozano, P.J., (2015). Comparative {LCA} of two approaches with 713 different emphasis on energy or material recovery for a municipal solid waste management 714 system in Gipuzkoa. Renewable and Sustainable Energy Reviews, 51, pp.449–459. 715 https://www.sciencedirect.com/science/article/abs/pii/S1364032115005912 716 717 Butera, S. et al. (2015). Life cycle assessment of construction and demolition waste 718 management. Waste Management, 44, 196-205. 719 https://www.sciencedirect.com/science/article/pii/S0956053X15300283 720 721 Carpenter, A., Jambeck, J. R., Gardner, K. and Weitz, K. (2013), Life Cycle Assessment of 722 End-of-Life Management Options for Construction and Demolition Debris. Journal of 723 Industrial Ecology. doi: 10.1111/j.1530-9290.2012.00568. 17(3), 396-406. 724 https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1530-9290.2012.00568.x 725 726 Castaño J. et al. (2013). Management of construction and demolition waste in Bogotá: 727 perspectives and limitations. Tecnura, 17, n 38, 121-129. 728 http://www.scielo.org.co/pdf/tecn/v17n38/v17n38a10.pdf 729 730 Chávez et al. (2014). Logistic unit for the recovery of construction and demolition waste: 731 case study Bogotá C.D (Unidad logística de recuperación de residuos de construcción y 732 demolición: estudio de caso Bogotá D.C). Ciencia e Ingeniería Neogranadina. Vol. 23, 733 pp.95-118. http://www.scielo.org.co/pdf/cein/v23n2/v23n2a06.pdf 734 735 Coelho, André, and Jorge de Brito. (2012). Influence of Construction and Demolition Waste 736 Management on the Environmental Impact of Buildings. Waste Management 32 (3): 532– 737 541. doi:http://dx.doi.org/10.1016/j.wasman.2011.11.011. 738 https://www.sciencedirect.com/science/article/pii/S0956053X11005356 739 740 Colomer, F., Altabella, J.E. and Izquierdo, A.G., (2017). Application of inert wastes in the 741 construction, operation and closure of landfills: Calculation tool. Waste Management, 59, 742 pp.276–285. https://www.sciencedirect.com/science/article/pii/S0956053X16306122 743 744 745 25 Dahlbo, H. et al., (2015). Construction and demolition waste management – a holistic 746 evaluation of environmental performance. Journal of Cleaner Production, vol. 107. pp. 333747 341. https://www.sciencedirect.com/science/article/pii/S0959652615001985 748 749 DANE (2015). National Administrative Department of Statistics (Departamento 750 Administrativo Nacional de Estadística). Available at: 751 https://colaboracion.dnp.gov.co/CDT/Inversiones%20y%20finanzas%20pblicas/Tolima%2 752 015.pdf, accessed: 27/07/2017. 753 754 Escandón, Juan Camilo. (2011). Technical and economic diagnosis of the use of 755 construction and demolition waste in buildings in the city of Bogotá (Diagnóstico técnico y 756 económico del aprovechamiento de residuos de construcción y demolición en edificaciones 757 en la ciudad de Bogotá). Final Degree Project. Pontifical Javeriana University. Bogotá D.C. 758 https://repository.javeriana.edu.co/bitstream/handle/10554/7516/tesis603.pdf;jsessionid=F 759 1B8A7A9ADCB48759FB2EBF32E84FD33?sequence=1 760 761 Guignot, S., Touzé, S., Von der Weid, F., Ménard, Y., Villeneuve, J., (2015). Recycling 762 construction and demolition wastes as building materials: A life cycle assessment. J. Ind. 763 Ecol. 19 (6), 1030–1043. https://onlinelibrary.wiley.com/doi/abs/10.1111/jiec.12262 764 765 Heinonen, J. et al., (2016). Pre-use phase {LCA} of a multi-story residential building: Can 766 greenhouse gas emissions be used as a more general environmental performance 767 indicator? Building and Environment, 95, pp.116–125. 768 https://www.sciencedirect.com/science/article/abs/pii/S0360132315301141 769 770 Hossain, M.U. et al., (2016). Comparative environmental evaluation of aggregate production 771 from recycled waste materials and virgin sources by {LCA}. Resources, Conservation and 772 Recycling, 109, pp.67–77. 773 https://www.sciencedirect.com/science/article/pii/S0921344916300295 774 775 Hossain, M.U. et al., (2017). Comparative LCA on using waste materials in the cement 776 industry: A Hong Kong case study. Resources, Conservation and Recycling, 120, pp.199– 777 208. https://www.sciencedirect.com/science/article/pii/S0959652619335929 778 779 Hoxha, E. et al., (2017). Influence of construction material uncertainties on residential 780 building {LCA} reliability. Journal of Cleaner Production, 144, pp.33–47. 781 https://www.sciencedirect.com/science/article/pii/S095965261632131X 782 783 Huang, Beijia, Xiangyu Wang, Harnwei Kua, Yong Geng, Raimund Bleischwitz, and 784 Jingzheng Ren (2018). Construction and Demolition Waste Management in China through 785 the 3R Principle. Resources, Conservation and Recycling 129: 36–44. 786 https://www.sciencedirect.com/science/article/pii/S0921344917303142 787 788 ICER. Regional Economic Situation Report (2016). Tolima, Ibagué. DANEBanco de la 789 República. Colombia. ISSN 1794-3582. 790 791 Jimenez, Heidy (2013). Evaluation of the current situation of the management of 792 construction and demolition waste (CDW) in the municipality of Madrid (Evaluación de la 793 situación actual del manejo de residuos de construcción y demolición (RCD) en el municipio 794 de Madrid (Cundinamarca) (Colombia)). Final Career Project. Pontificia Universidad 795