ASPHALT ROAD PAVEMENTS LIFE CYCLE COST ANALYSIS

Transcription

1 ASPHALT ROAD PAVEMENTS LIFE CYCLE COST ANALYSIS Extended Abstract Hugo Bernardo Campos Branquinho Matos da Costa Dissertation to obtain the Degree of Master in Civil Engineering November 2008

2 ASPHALT ROAD PAVEMENTS LIFE CYCLE COST ANALYSIS Hugo Bernardo Campos Branquinho Matos da Costa Abstract The dissertation, developed in collaboration with the Laboratório Nacional de Engenharia Civil, reports to an economic study of costs associated with construction and maintenance of asphalt road pavements. In this study, the administration costs were evaluated, corresponding not only to the construction but also to the maintenance and rehabilitation during the life cycle of the road pavements. Besides these costs, users and environmental costs were also taken into account. The total period of this analysis was 35 years, in order to consider all the possible maintenance strategies in terms of long-term costs. Different structures of pavements, regarding different settings of traffic and subgrade classification, were taken into consideration. The results achieved in this work could be useful to responsible entities in future decisions concerning the selection of best strategies of construction and maintenance of pavements. 1. Introduction The high costs of the building, maintenance and rehabilitation of road infrastructure, associated with concerns over the viability of the adopted and the reduction of the environment impacts caused by the traffic, justify the need of doing the best use of the sums spent on these infrastructures and rationalize the use of natural resources. In order to achieve this goal it s essential to use the proper methodologies regarding the selection of solutions to adopt in each case to minimize the costs during the life cycle of the infrastructure, without compromising the quality of the service. Portugal is one the one of the countries with the highest rate in terms of highway kilometers per inhabitant in Europe. And this trend seems to keep on going, because there is a growing number of new highways which take the place of less important roads. In this context it s important to know, considering the existence of new materials for paving and new maintenance and rehabilitation techniques, which is best solution for paving in different circumstances. The choice of the paving solution is unique for each case because each situation has its own peculiarities. This way the systematic use of some solutions can be unsustainable. In order to optimize each solution for paving it s necessary to adequate them to the traffic conditions, subgrade, and methodologies of the project adopted. The traffic, where the heavy vehicles are predominant, can quicken the degradation of a pavement, it s important to consider its influence at first. The condition of the subgrade determines the absorption capacity of the weight of the vehicles influencing this way the characteristic of the pavement. On the other end the project methologies can affect the solution which was adopted. 1

3 In this study 15 types of pavement structures were defined and analysed, and which correspond to different classes of traffic and subgrade conditions. The costs born by the administrations were assessed and, as far as possible, the cost to the users and the environment. Afterwards, it was made an evaluation of the evolution cost during the life cycle of the pavements for each of the settings considered, in order to choose the best solution. 2. Presentation of the typical cases 2.1 Initial solution The selection of the new pavement structures, which will be examined, was done considering the different settings related to the class of traffic they are built for and the subgrade conditions. There settings were established and based on the series of classes of traffic and classes of subgrade presented in Manual de Concepção de Pavimento para a Rede Rodoviária Nacional - MACOPAV (JAE, 1995). Regarding the traffic, it was considered the existence of two types of heavy traffic corresponding to distinct situations of the Yearly and Daily Medium Traffic Tráfego Médio Diário Anual defined for the year of opening to the traffic, taking the direction into account and in the lane which is more frequently used (TMDAp): Type T 5 corresponding to reduced heavy traffic, with values of TMDAp between 150 and 300. Type T 1 corresponding to intense heavy traffic, with values of TMDAp between 1200 and Regarding the subgrade, the two kinds of more frequent conditions, defined by the mechanical behaviour through the resulting elastic modulus (Ef), mainly, from the characteristics of the soil upper level: Type F 2 defined by values of Ef, between 50 and 80 MPa. Type F 3 defined by values of Ef, between 80 and 150 MPa. When the standard structures were chosen, it was considered that it would be admissible a subgrade type F 3 for a type of traffic T 1. For the type of traffic T 5, both types of subgrade are acceptable. Through the different possible combinations of types of traffic and subgrade selected, the structures of the new pavement were fixed, based on the instructions given by the MACOPAV. The definition of the thickness of the layers was based on the recommendations for practice, reflected also in the good building performances presented in that Manual and in the Contract Provisions of EP (EP, 1998). It was considered that all the paving materials respect the technical requisites established, and that each structure of pavement will be built with a proper drainage system which will guarantee a normal mechanical behaviour for the layers of the subgrade and the pavement on soils and granular materials. Table 1 shows the adopted symbology in order to define the layer and its composing material, joining each symbol to the thickness of the corresponding layers, expressed in centimeters. 2

4 Table 1. Symbology and thickness adopted Layers Materials Symbol Thickness (cm) Bituminous concrete BD 5 Wearing course Ultrathin friction asphalt BDRug 3 Binder course Bituminous macadam MB 6, 7, 9, 11 7, 8, 10, 12, 14 (7+7), 16 (8+8), Bituminous macadam MB Base 18 (9+9) Crushed material BG 20 Crushed material SbG 20 Sub-base Cement-stabilized soil SC 20 On Table 2 are presented the structures of new pavements selected for testing, showing the types of subgrade and traffic associated with them, too. In the particular case of the base layer with bituminous macadam, it was adopted a two phase building process (Layers 1 and 2). Table 2. Structures of flexible pavement Designation FL1 FL1a FL2 FL3 Traffic Type T5 T5 T5 T5 Wearing course BD-5 BD-5 BD-5 BD-5 Bituminous layers Binder course MB-7 MB-7 MB-6 MB-11 Base - layer 2 MB-10 MB-8 MB-7 Base - layer 1 Base layer BG-20 Sub-base layer SbG-20 SbG-20 SbG-20 SC-20 Type of subgrade F2 Designation FL4.1 FL4.2 FL5 FL6.1 FL6.2 FL7 FL7a FL8.1 FL8.2 FL9 Traffic Type T1 T1 T5 T1 T1 T1 T5 T5 T1 T1 T5 Wearing course BDRug-3 BD-5 BD-5 BDRug-3 BDRug-3 BD-5 BD-5 BD-5 BDRug-3 BD-5 BD-5 Bituminous layers Binder course MB-7 MB-7 MB-6 MB-7 MB-6 MB-7 MB-11 MB-9 MB-7 MB-7 MB-7 Base - layer 2 MB-9 MB-8 MB-7 MB-8 MB-7 MB-7 MB-7 MB-12 Base - layer 1 MB-9 MB-8 MB-8 MB-7 MB-7 MB-7 Base layer BG-20 BG-20 BG-20 BG-20 BG-20 Sub-base layer SbG-20 SbG-20 SbG-20 SbG-20 SbG-20 SbG-20 SbG-20 SbG-20 SC-20 SC-20 SC-20 Type of subgrade F3 The pavements with the letter a in the designation section show that the previous pavement was an optimized that corresponds to the reduction of the thickness, respecting, all the same, the period of 20 years in terms of dimension for flexible pavements. In order to obtain additional elements related to the weight capacity of the pavement structures for testing, it was done an evaluation of its useful life, using measurement methologies for pavements based on the structural analysis complemented by the results of the observation of the pavement behavior. The methologies used for this purpose reflect the present practice during the phase of the 3

5 execution project of road infrastructures, selecting proper dimension criteria suitable for this type of pavement, considering the characteristics of the materials usually used in paving in our country. The results show that the selected structures meet the criteria regarding dimension. It also sees that the results refer only to the degradation mechanisms considered in the structural dimension of the pavements, expressed by the dimension criteria. However, other types of degradation occur during the life cycle of the pavements that demand the need the execution of maintenance and rehabilitation work that will be taken into account though the models of the degradation evolution which are presented in the following subchapter Standard Strategies In this subchapter are shown the types of maintenance and rehabilitation measures considered when the evaluation of the costs is done during the life cycle of the different types of pavement studied (Table 3). These measures include preventive maintenance actions taken periodically and structural rehabilitation, and they result of the pavements condition based on the PSI evolution and the surface cracking models of flexible pavements mentioned by the Laboratório Nacional de Engenharia Civil LNEC (Civil Engineering National Laboratory). (LNEC, 2008) Table 3. Maintenance and rehabilitation measures Identification Milling and reposition 5 cm, new Milling and reposition 5cm, new Recycling with cement 20cm deep, wearing layer of layer of MB Measures course in BD wearing with 6 cm (Combined (5 cm) course in actions) BBRug (4 cm) Milling and reposition 5cm, reinforcement in MBD(5cm), new layer of wearing course in BD (5 cm) Milling and reposition 5cm, reinforcement in MB (7cm), new layer of wearing course in BD (5 cm) Milling and reposition 5cm, reinforcement in MB (8cm), new layer of wearing course in BBRug (4 cm) Recycling with cement with 20 cm deep, layer of MB with 6 cm, layer of wearing course in BBRug (4 cm) In Table 4 it is shown the plan for of the maintenance and rehabilitation activities of the pavements during the period of analysis that is 35 years. Table 4. Plan for the maintenance and rehabilitation activities Pavement Dimension Period (years) Schedule for the maintenance and rehabilitation activities FL1 > 35 FL1a 25 FL2 30 FL3 25 FL Activity 1 1 Year Activity Activity (optional)

6 FL FL5 25 FL Year Activity Year Activity Activity (optional) Year FL 6.1a 20 Activity Activity (optional) FL FL7 35 FL7a 20 FL FL FL 9 25 Year Activity Year Year Activity 3 1 Activity (optional) 6 1 Year Activity Activity (optional) Year Activity Costs involved 3.1. Unitary costs For all the selected pavement structures, we identified the unitary costs of the building, maintenance and rehabilitation thoroughly, taking the materials, the applications and the thickness into account. The unit costs that were able to get, refers to the minimum, maximum and average national cost of the works of several contractors. The unitary costs that it was able to obtain were evaluated according to the corresponding costs of applications in layers with a different thickness. It was the case of the bituminous macadam, applied in base or binder course layers, and cement-stabilized soil made in factory, the unitary costs of which were calculated for the different Kinds of thickness selected and based on the cost of the manufacturing in situ for a 25 cm thickness. The costs that are shown below refer to the area unity of paving Building costs The evaluation of the building costs of each pavement structure chosen for testing, came from the direct application of the unitary costs referring not only to the materials that are part of the layers, but also are associated with other materials, such as impregnation and tack coat. 5

7 Table 5 shows an estimate of the total cost of the building of pavement structures analysed for traffic type T 5. Table 5. Total costs of the building of the structures analysed for traffic type T 5 Designation FL1 FL1a FL2 FL3 FL5 FL7 FL7a FL9 Minimum Cost 14,11 13,47 14,97 12,76 12,02 13,74 13,17 10,92 Average Cost 24,28 22,73 25,30 19,49 21,05 23,14 21,84 16,45 Maximum Cost 33,28 30,91 34,47 25,53 29,49 30,89 29,54 22,21 Table 6 shows an estimate of the total cost of the building of pavement structures analysed for traffic type T 1. Table 6. Total costs of the building of the structures analysed for traffic type T 1 Designation FL4.1 FL4.2 FL6.1 FL6.2 FL8.1 FL8.2 Minimum Cost 18,44 18,00 20,82 18,38 19,00 17,89 17,58 Average Cost 29,65 29,59 32,13 29,61 32,14 26,77 26,50 Maximum Cost 38,32 39,23 40,02 38,27 43,55 34,00 34, Maintenance and rehabilitation costs According to the plan for the maintenance and rehabilitation activities previously described, the total cost of the maintenance and rehabilitation is calculated for each pavement that is analysed. Table 7 shows a calculation of the total cost of the maintenance and rehabilitation of the pavement structures analysed for traffic type T 5. Table 7. Total costs of the maintenance and rehabilitation of the structures analysed for traffic type T 5 Designation FL1 FL1a FL2 FL3 FL5 FL7 FL7a FL7a FL9 Minimum Cost 7,83 10,81 10,81 10,81 10,81 10,81 10,81 9,98 10,81 Average Cost 14,77 19,83 19,83 19,83 19,83 19,93 19,93 16,68 19,93 Maximum Cost 23,21 30,05 30,05 30,05 30,05 30,05 30,05 23,70 30,05 Table 8 shows a calculation of the total cost of the maintenance and rehabilitation of the pavement structures analysed for traffic type T 1. Table 8. Total costs of the maintenance and rehabilitation of the structures analysed for traffic type T 1 Designation FL4.1 FL4.1 FL6.1 FL8.1 FL4.2 FL6.1 FL6.2 FL8.1 FL8.2 Minimum Cost 19,04 19,41 15,68 19,04 19,41 19,04 19,41 15,68 19,04 19,41 15,68 Average Cost 28,64 29,01 28,86 28,64 29,01 28,64 29,01 28,86 28,64 29,01 28,86 Maximum Cost 36,58 37,27 43,83 36,58 37,27 36,58 37,27 43,83 36,58 37,27 43, Residual value The residual value of a pavement concerns the functional and structural quality. However, in this study it was only considered the structural component, since the functional component is less significative and common to all pavements in general terms. In Table 9 it is shown a calculation of the residual value of the pavements analysed, referring to a traffic type T 5. Table 9. Residual value of the pavements for traffic type T 5 in analysis FL7a Designation FL1 FL1a FL2 FL3 FL5 FL7 FL7a FL9 Minimum RV 0 5,17 5,17 5,17 5,17 5,86 0,69 0,61 5,17 6

8 Average RV 0 9,33 9,33 9,33 9,33 10,58 1,24 0,93 9,33 Maximum RV 0 13,83 13,83 13,83 13,83 15,68 1,84 1,21 13,83 In Table 10 it is shown a calculation of the residual value of the pavements analysed, referring to a traffic type T 1. Table 10. Residual value of the pavements of traffic type T 1 in analysis Designation FL4.1 FL4.1 FL6.1 FL8.1 FL4.2 FL6.1 FL6.2 FL8.1 FL8.2 Minimum RV 2,41 2,50 1,96 8,18 8,50 2,41 2,50 6,68 2,41 2,50 1,96 Average RV 3,65 3,74 3,52 12,39 12,71 3,65 3,74 11,98 3,65 3,74 3,52 Maximum RV 4,61 4,78 5,16 15,66 16,25 4,61 4,78 17,53 4,61 4,78 5, Costs supported by the users Because of lack of information related to this kind of costs, it was decided to quantify this cost when the activity of maintenance and rehabilitation that a certain pavement is being subject to during the period of analysis. This association is possible because of a direct proportionality that exists between the cost to the users and the duration of the operations. So it becomes necessary to estimate the duration of each intervention, maintenance and rehabilitation measure, and then sum up all the hours of intervention during the analysis period, corresponding to every each pavement. In order to estimate the time spent in intervention measures, it has considered the profit income revenue which is associated with each intervention measure (COST, 2003) and an area with of square meters (length of the lane 10 km, lane wide 7m). In table 11 it s shown an estimate of the duration of the intervention for each pavement in analysis, belonging to traffic type T 5. Table 11. Duration of the intervention for each pavement of traffic type T 5 Designation FL1 FL1a FL2 FL3 FL5 FL7 FL7a FL7a FL9 Duration(days) In table 12 it s shown an estimate of the duration of the intervention for each pavement in analysis, belonging to traffic type T 1. Table 12. Duration of the intervention for each pavement of traffic type T 1 FL4.1 FL6.1 FL8.1 Designation FL4.1 FL4.2 FL6.1 FL6.2 FL8.1 FL8.2 Duration(days) Environmental costs The environmental costs considered in this study concern the amount of material used in a specific pavement when it was built, maintained and restored. The amount of material is estimated according to the volume of materials used in each square meter of the pavement area, so the bigger is the volume of construction, the higher will be the environmental cost. The analysis of the environmental cost mustn t compare pavements with different types of subgrade, since it has in mind the dimension of the pavements when we study the subgrade, changing the 7

9 thickness of the pavement layers. This being the case, it has only done an analysis of the environmental costs for the pavements of traffic type T 1, as they all belong to the same subgrade F 3. In table 13 it s shown the calculation of the environmental costs for each pavement in analysis and belonging to traffic type T 1. Table 13. Calculation of the environmental costs for pavements of traffic type T 1 Designation Volume of construction (m 3 /m 2 ) FL4.1 FL4.1 FL4.2 FL6.1 FL6.1 FL6.2 FL8.1 FL8.1 0,75 0,71 0,77 0,93 0,89 0,90 0,86 0,95 0,71 0,67 0,73 FL Economic analysis of standard cases It has carried out three types of analysis: determining, in terms of risk and multi-criteria, that will be referred afterwards. All of them bring into focus aspects as the best dimension of pavements, the use of recycling, the application of cement-stabilized soil as sub-base, the application of a granular base and the formation of the wearing course layer (that can be made with bituminous concrete with 5 cm or ultrathin friction asphalt with 3 cm). After obtaining the costs born by the road department, it was used the present worth method to evaluate economically the standard cases through a determining analysis. In order to study the total actual value of the costs for a specified and alternative pavement (NPV), during a period of 35 years of analysis, it was also carried out a risk analysis that allowed us to understand the costs variability. For each unit cost it was considered a triangular distribution, being the most likely value the average cost. It has carried out a multi-criteria analysis too, during which several reflections were given to different costs. This kind of analysis has also served to include the costs supported by the users and the environmental costs, which so far, haven t been considered by the previous analysis which were presented here. They were studied cases that represent the point of view of several decision makers. The first case tries to examine study the influence of the cost for the users over the selection of the pavement, where as the second examines study the influence of the environmental cost. The third case simulates more importance given to the initial cost by the decision-maker and more importance to the cost of maintenance and rehabilitation. The weight attributed to each criterion, case by case, is presented in Table 14. 8

10 Table 14. Weight attributed to each case Case Traffic Type T 5 Traffic Type T 1 Weight Weight %NPV 70%CSU 30%NPV 70%CSU %NPV 30%CSU 70%NPV 30%CSU %NPV 30%CA %NPV 70%CA %CI 30%CCR 10%VR 60%CI 30%CCR 10%VR %CI 60%CCR 10%VR 30%CI 60%CCR 10%VR 5. Conclusion 5.1. From the analysis of costs obtained on section 3 Building costs The optimized pavements are of great value. The lower cost corresponds to pavements in which is used cement-stabilized soil instead of granular base. Similar cost for both types of wearing course layer. Maintenance and rehabilitation costs The optimized pavements aren t of great value. Recycling is only worthwhile with a FL7a pavement. Similar cost between cement-stabilized soil or granular base. The cost associated with the wearing out layer of ultrathin friction asphalt is slightly lower. Costs supported by the users The optimized pavements aren t of great value. Recycling increases the total duration of the interventions in about 44%. Similar cost between cement-stabilized soil or granular base. Similar cost for the two types of wearing course layer. Environmental costs Recycled and optimized pavements are of great value. The lower cost corresponds to pavements in which is used cement-stabilized soil instead of granular base From the economic analysis in section 4 In general terms, the optimized pavements don t reach the best places, they only become advantageous when it gives more importance to the building cost (case 3). In the pavements with traffic type T 1, the use of recycling is inconvenient whenever it gives more importance to the costs of maintenance and rehabilitation, because this technique is too expensive. This situation changes when we deal with pavements of traffic type T 5, since recycling is a cheaper structural technique. 9

11 In terms of environment, recycling is worthwhile, and this don t happen when the criterion in analysis is the cost born by the users, due to the long period of structural intervention. Regardless of the traffic type, a pavement made of cement-stabilized soil in the sub-base layer generally wins the best qualification. In general, the pavement of bituminous base follow up for the traffic type T 5 and the pavements of granular base when it faces a traffic type T 1. Examining only the NPV criterion for the traffic type T 1, it infers that the pavements that have a wearing course layer of ultrathin friction asphalt are more advantageous. It must be noted that the type of standardization used in the multi-criteria analysis presents the disadvantage because they are sensible to the set of alternatives compared, that is, if it includes a complementary alternative, we will risk to have a global change of the standard results. This obstacle can be overtaken, using the absolute minimum and maximum instead of the relative that are obtained through each attribute of each set of alternatives. 6. Bibliography Costa, H. (2008); Análise de Custos de Ciclo de Vida Relativa a Pavimentos Rodoviários Flexíveis; Essay to receive a Master s Degree in Civil Engineering; Instituto Superior Técnico; Lisboa COST 343 (2003); Reduction in road closures by improved pavement maintenance procedures; Final Report of the Action; European Commission EP (1998); Caderno de Encargos Tipo; Pavimentação; Estradas de Portugal; Almada JAE (1995); Manual de Concepção de Pavimentos para a Rede Rodoviária Nacional; Junta Autónoma de Estradas; Almada LNEC (2008); Avaliação económica de diferentes soluções de pavimentação ao longo do ciclo de vida das infra-estruturas rodoviárias Relatório Intercalar; Relatório 140/2008 NIRA (RELATÓRIO CONFIDENCIAL) 10