POLITECNICO DI MILANO
Scuola di Ingegneria Civile, Ambientale e Territoriale
Master of Science in Civil Engineering
Transport Infrastructure
Analysis of the use of Reclaimed Asphalt
Pavement (RAP) in Europe
Relatore:
Dott. Emanuele Toraldo
Corelatore: Ing. Dario Topini
Xavier Planas Willis 815868
Anno accademico 2015/2016
A mis padres, por su esfuerzo, sacrificio y entrega desinteresados.
Acknowledgements
First of all, I would like to thank Prof. Ing. Emanuele Toraldo for giving me the opportunity of participating in this research, and for the supervision and advice given during the months of preparation and redaction of the current thesis.
I would strongly like to thank Ing. Dario Topini, because without his help and fully disponibility when needed this thesis couldn’t have been written. Thank you for always being helpful, patient and friendly.
I would also like to thank my friend Claudio Lombardi, because he has always worried about the situation of the thesis, helping me and giving advice when needed.
Finally, I would like to acknowledge my family because nothing would have been possible without their support, not only for the economical support during my stay in Milano, but also the moral and psychological one. They have made this opportunity possible for me, helping me to become a better student and better person.
To conclude, I would like to thank all of those that have not been mentioned directly,
but have also contributed supporting me or helping me on the realisation of this project.
Abstract
This thesis is carried out with the aim of studying and analysing the current situation in Europe of asphalt recycling. We will focus not only on the present situation, but also on how this recycling of the so-‐called Reclaimed Asphalt Pavement (RAP) has evolved in different European countries.
Specifically, what is wanted to study in this project is the total amount of Available RAP that each country has and how this amount evolves over the years. Not only will we study the total amount of available RAP in each country, but we will also be interested in knowing the effective percentage of all this recycled material that is being reused.
Once we know the amount of Reclaimed Asphalt that is effectively used, we will be interested in knowing how is this recycled material reused in different countries. We will see that all of this RAP can be reused through Hot and Warm Recycling, Half Warm Recycling, Cold Recycling, or even can be used in the Unbound Layers in the process of manufacturing a new pavement.
We will focus on detecting which countries have most internalized the concept of recycling asphalt pavement, being these ones the ones that recycle most, obviously.
We cannot compare the recycling of several countries in absolute terms, since the size of the different countries will vary, or even the amount of kilometres of paved road of each one. That is why an analysis that compares the different countries in Europe taking these factors into account will be also done.
The thesis is structured in the following Chapters:
Chapter 1, Introduction: This is the opening chapter; which provides an overview of
the context in which the work has been developed. A brief explanation of different technical terms is made, as well as a historical contextualization and the advantages for recycling asphalt pavement.
Chapter 2, EXAMPLE: Case Study of Asphalt Recycling in Italy: This chapter gives an
example of a real case study of Asphalt Pavement Recycling in Italy, the country where this thesis is being developed.
Chapter 3, Introduction to EAPA: In this Chapter we introduce EAPA (European Asphalt Pavement Association), which is the main organism from where we have obtained the data to carry on with our study.
Chapter 4, Total Production of Asphalt and Total Available RAP: On this chapter we
start to work on our final goals of the project. A study is carried out in order to find out the amount of Total Asphalt Production and the Total Available RAP in every country. These total values are seen and compared to the ones in the past years, observing their evolution during time, for several European countries being studied.
Chapter 5, Comparing Countries: In this chapter we can see a comparison of the
behaviour of different countries in Europe with regards to asphalt production and availability of RAP. To compare countries appropriately, a relativisation has been done, taking into account the paved road distance on every country being studied.
Chapter 6, Reuse of Reclaimed Asphalt: This chapter constitutes the main body of
the project. A study is carried out in order to find out how much of the amount of Total Available RAP is effectively being reused in every country, and once found out, how is it being reused. A final analysis of the data is also done in this section.
Chapter 7, Conclusions: This is the final chapter. Here we put altogether the
information found in previous chapters, commenting on the reasons for each of the behaviours of the different countries and suggesting future researches and investigations in order to increase the RAP recycling.
With this thesis, we have wanted to broaden horizons regarding the recycling of asphalt pavement, giving a global view of its use in Europe and proposing alternatives for future uses.
Contents
1. Introduction
1.1. General
1.2. History about Recycling
1.3. What is RAP?
1.4. How is RAP recycled?
1.5. Mechanical Performance of RAP
1.6. Advantages of using RAP
2. EXAMPLE: Case Study of Asphalt Recycling in Italy
2.1. Location of the Case Study
2.2. The situation before the intervention
2.3. Description of the intervention
2.4. Preliminary studies and final choices
2.5. Problems during the operations
2.6. Final Results
3. Introduction to EAPA
4. Total Production of Asphalt and Total Available RAP
4.1. Total Production of Hot & Warm Mix Asphalt
4.2. Total Available Reclaimed Asphalt Pavement
4.3. Percentage of Available Reclaimed Asphalt Pavement
5. Comparing Countries
6. Reuse of Reclaimed Asphalt Pavement
6.1. How much RAP is reused?
6.2. How is RAP reused?
6.2.1. Hot & Warm recycling
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6.2.1.1. Hot Recycling
6.2.1.2. Warm Recycling
6.2.2. Half Warm & Cold Recycling and Unbound Layers
6.2.2.1. Half Warm Recycling
6.2.2.2. Cold Recycling
6.2.2.3. Unbound Layers
6.2.3. Results Analysis and Reuse Classification
7. Conclusions
References
Appendix
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List of Figures
Figure 1.1: Milled Reclaimed Asphalt Pavement (RAP)
Figure 1.2: Different images of pavement recycling in various years during history Figure 1.3: Milling machine grinding up asphalt
Figure 1.4.1: Scheme that shows the different ways of Asphalt Recycling Figure 1.4.2: Train operations for HIPR, from Maurizio Crispino, Tecnica delle Pavimentazioni.
Figure 1.4.3: Image showing Cold In-‐Place Recycling
Figure 1.5.1: Grading curve of sub base with only natural aggregates and with 50% RAP Figure 1.5.2: LWD Results
Figure 1.6: Accumulation of unprocessed RAP millings in a stockpile Figure 2.1.1: location of Crema in Northern Italy, from Google Maps
Figure 2.1.2: Position of Crema in relation to the most important cities of Lombardy, from Google Maps
Figure 2.1.3: The road where asphalt recycling was carried out, from Google Maps Figure 2.3: Train operations using of foamed bitumen
Figure 2.4: A hole left after a probing operation and some cores Figure 2.6: The road in June 2012, from Google Maps
Figure 6.2.1.1.: Hot Recycling of an urban road Figure 6.2.2.1.: Bituminous Emulsion
Figure 6.2.2.2.: Cold in-‐place Asphalt Recycling
Figure 6.2.2.3.: Spreading an Unbound Aggregate Base Layer
13 14 16 19 19 20 22 23 26 27 28 28 29 30 32 59 67 69 70
List of Tables
Table 2.4: Final choices for the Works
Table 4.1: Total Production of Hot and Warm Mix Asphalt (in million tonnes) Table 4.2: Total Available Reclaimed Asphalt (in million tonnes)
Table 5.1: Relative Values of the Total Production of Hot & Warm Mix Asphalt (tonnes/km)
Table 5.2: Relative Values of the Total Available Reclaimed Asphalt (tonnes/km) Table 6.1: Percentage of Reuse of the Available Reclaimed Asphalt
Table 6.2.0.1.: Recycling table provided by EAPA about year 2013 Table 6.2.0.2.: Example of Blank table for one Country
Table 6.2.1.: Total percentage of RAP destined to Hot and Warm Recycling (%) Table 6.2.2.1.: Half Warm Recycling, Cold Recycling and Unbound Layers Table App.1: Percentage of RAP in Denmark and how it is Reused Table App.2: Percentage of RAP in France and how it is Reused Table App.3: Percentage of RAP in Germany and how it is Reused Table App.4: Percentage of RAP in Italy and how it is Reused
Table App.5: Percentage of RAP in Netherlands and how it is Reused Table App.6: Percentage of RAP in Norway and how it is Reused Table App.7: Percentage of RAP in Spain and how it is Reused Table App.8: Percentage of RAP in Sweden and how it is Reused Table App.9: Percentage of RAP in Switzerland and how it is Reused Table App. 10: New classification of the Reused RAP in Denmark Table App. 11: New classification of the Reused RAP in France Table App. 12: New classification of the Reused RAP in Germany Table App. 13: New classification of the Reused RAP in Italy
Table App. 14: New classification of the Reused RAP in Netherlands
30 35 38 44 46 52 56 57 61 71 92 92 93 93 93 93 94 94 94 95 95 96 96 96
Table App. 15: New classification of the Reused RAP in Norway Table App. 16: New classification of the Reused RAP in Spain Table App. 17: New classification of the Reused RAP in Sweden Table App. 18: New classification of the Reused RAP in Switzerland
97 97 97 98
List of Graphs
Graph 4.1: Total Production of Hot and Warm Mix Asphalt (in million tonnes)
Graph 4.2.1: Total Available Reclaimed Asphalt (in million tonnes)
Graph 4.2.2: Total Available Reclaimed Asphalt (in million tonnes) Graph 4.3: Evolution of the percentage of RAP
Graph 5.1: Absolute Values of the Total Production of Asphalt and Available RAP Graph 5.2: Relative Values of the Total Production of Asphalt and Available RAP Graph 6.1: Percentage of Reused RAP
Graph 6.2.1.1.: Percentage of Available RAP destined to Hot and Warm Recycling Graph 6.2.1.2.: Evolution of Hot and Warm Recycling for France and Spain
Graph 6.2.2.1.: Percentage of Available RAP destined to Half Warm Recycling, Cold Recycling or Unbound Layers
Graph 6.2.2.2.: Evolution of Half Warm Recycling, Cold Recycling or Unbound Layers for Denmark and Spain
Graph 6.2.3.1.: Distribution of the Available RAP in Denmark Graph 6.2.3.2.: Distribution of the Available RAP in France Graph 6.2.3.3.: Distribution of the Available RAP in Germany Graph 6.2.3.4.: Distribution of the Available RAP in Italy
Graph 6.2.3.5.: Distribution of the Available RAP in Netherlands Graph 6.2.3.6.: Distribution of the Available RAP in Norway Graph 6.2.3.7.: Distribution of the Available RAP in Spain Graph 6.2.3.8.: Distribution of the Available RAP in Sweden Graph 6.2.3.9.: Distribution of the Available RAP in Switzerland
36 39 40 42 47 48 52 62 63 72 73 76 77 78 78 79 80 81 82 82
1. Introduction
1.1. General
The pavement of a road is subject to the continuous action of traffic and meteorology. These two factors, together with the natural aging of the materials, make the pavement suffer a process of progressive deterioration. This aging and deterioration of the road entails a gradual decrease in the safety and comfort levels of traffic, which, when exceeding certain values, require a conservation operation.
The conservation of the road network is currently an aspect of great importance due to the resources that mobilizes. The necessary budget for the maintenance, as well as the environmental problems that derive from it, justify the search for new techniques that allows reducing costs and is respectful with the environment. In this context, the recycling of asphalt pavements, as a means of rationalizing resources, takes a renewed role and becomes a necessity.
In modern times, a high percentage of roads and highways around the world are constructed with hot-‐mix asphalt. As the infrastructure ages with time, these highways and roads must be maintained and rehabilitated. Preserving, maintaining and expanding the highway and road infrastructure require a continual supply of the natural resources that are used in pavements. In recent years, it has been found out that the same material used to build the original highway system can be reused as an additional source of asphalt and aggregate materials that can have economic and environmental advantages when used as a partial replacement for asphalt mixture material components.
Existing asphalt pavement materials are commonly removed during resurfacing, rehabilitation or reconstruction operations. Once these materials are removed and processed, the pavement material becomes Reclaimed Asphalt Pavement (RAP). This RAP contains valuable asphalt binder and aggregate, which can be useful for other road rehabilitation operations. In Figure 1.1 we can observe a picture of a close-‐up view of milled RAP that has been milled and stockpiled from an existing roadway.
Nowadays, in Europe we count on 50 million tonnes of available RAP, from which approximately 70 per cent of it is being recycled, making the asphalt the most frequently
RAP is most commonly used as an aggregate and virgin asphalt binder substitute in recycled asphalt paving, but it can also be used differently, such as a granular base or sub base, stabilized base aggregate and embankment or fill material, or even, in other construction applications.
Reclaimed Asphalt Pavement is, to sum up, a valuable, high-‐quality material that can replace more expensive virgin aggregates and binders.
Figure 1.1: Milled Reclaimed Asphalt Pavement (RAP)
1.2. History about Recycling
The recycling of asphalt in the pavement industry has become more popular as time has gone by. It is in 1915 where the recycling of asphalt pavements takes place for the first time (Kandhal & Mallick, 1997). Although old asphalt mixtures were removed and disposal of in landfills, the use of RAP (Reclaimed Asphalt Pavement) in new asphalt mixtures increased considerably during 1970s. In addition, this significant use of RAP in hot-‐mix asphalt started in the early 1970s due to extremely high prices of the crude oil as a result of the Arab Oil Embargo in 1973. This oil embargo made the binder prices skyrocket and obliged the asphalt paving industry to find a solution for not having to spend so much money on it with similar results when paving. The asphalt paving industry reacted to this situation by creating or developing recycling technologies that helped reducing the demand of asphalt binder, so consequently, reducing also the costs of the asphalt paving mixtures. Some of the practices that were developed during those times are still being used nowadays and have become
part of routine operations for pavement construction and rehabilitation.
Figure 1.2: Different images of pavement recycling in various years during history
Inclination towards recycling has been possible principally due to economic savings and environmental benefits. With regard to economic savings, it must be taken into account that recycling reduces the amount of new asphalt and aggregates being used, both non-‐ renewable resources. The material cost savings are the result from a replacement of a portion of virgin aggregates and binders, as the asphalt and aggregate components of an
asphalt mix constitutes the greatest portion of the cost of pavement construction (Copeland, 2011). These material savings are not only profitable for our economy, but make the recycling practice eco-‐friendly, as the energy and emissions associated with the extraction and transportation of the raw virgin materials mentioned before is also being reduced. Recycling have also reduced the amount of space used for landfilling of old pavement materials removed during rehabilitation, as part of this old material will be reused and will not occupy unnecessary space on the ground.
Since recycling started to gain popularity, two basic principles of asphalt recycling that have guided our actions have been:
• Mixtures containing RAP should meet the same requirements as mixes with all virgin materials.
• Mixes containing RAP should perform equal to or better than virgin mixtures.
1.3. What is RAP?
The acronym RAP stands for Reclaimed (or Recycled) Asphalt Pavement, and is the term given to removed and/or processed materials containing asphalt and aggregates. These materials are generated when asphalt pavements are demolished for construction, resurfacing, or to obtain access to buried utilities. When properly crushed and screened, RAP consists of high-‐quality, well-‐graded aggregates coated by asphalt cement. RAP is one of the most important elements to take into account during the process of recycling of road pavements, since it has great influence on the characteristics of the final product.
RAP is generated when asphalt pavements are removed as part of roadway reconstruction and maintenance (during excavations to access buried utilities, for instance) or during flexible pavement reconstruction or resurfacing (milling).
There are different sources from which RAP may be obtained, being pavement milling operations the most common method. There are other RAP sources that are also common, such as full-‐depth pavement demolition and waste asphalt plant mix. There are basically two steps for obtaining RAP, independently of the source from which is going to be obtained:
1) First of all we must identify which one of the processes we are going to use to acquire RAP. To obtain RAP through a milling process, a milling machine is needed, and can remove up to two inches in one pass. On the other hand, full-‐depth pavement demolition requires pneumatic pavement breakers or a bulldozer fitted with a rhino horn. By doing this, the pavement is crushed down.
On Figure 1.3 we can see a milling machine that grinds up asphalt and removes it efficiently off of roadway surfaces.
2) Once the desired material is crushed, the second step basically involves the processing of this resultant material. The crushed material can either be taken to a central plant or used in place. For the first option, it can be collected and loaded into trucks for transportation to a central processing facility, where RAP is again crushed, screened, conveyed and stacked. Otherwise, by using an automatic pulverizing machine, the pavement can be crushed in place and added to stabilized or granular base aggregate.
According to the "Asphalt Recycling Guide" of Austroads, it can be said that, in general, 100% of the recovered materials of deteriorated pavements are susceptible to be recycled, either in the same place in which they are generated, in other pavements (more usual practice) or even for purposes not related to the creation of any other pavements. Generally, the use of recycled mixtures is focused on the rehabilitation of existing pavements; however, they can be part of new construction pavements, without this meaning a problem of quality, strength or durability.
1.4. How is RAP recycled?
Recycling of pavement material can be undertaken as an in-‐place or a central plant process. In addition, recycling can be grouped into hot, warm and cold processes depending on the virgin binder deployed in the recycling operation.
RAP can be used as an aggregate in the hot recycling of asphalt paving mixtures. This type of recycling involves the heating of aggregates and the mixing process is done at 150°C. This type of recycling can be done in one of two ways. The most common method (conventional recycled hot mix) involves a process in which RAP is combined with virgin aggregate and new asphalt cement in a central mixing plant to produce new hot mix paving mixtures. A second method (hot in-‐place recycling) involves a process in which asphalt pavement surface distress is corrected by softening the existing surface with heat, mechanically removing the pavement surface, mixing it with a recycling or rejuvenating agent, possibly adding virgin asphalt and/or aggregate, and replacing it on the pavement without removing the recycled material from the pavement site.
RAP can be used as an aggregate in the cold recycling of asphalt paving mixtures. This type of recycling does not involve the heating of aggregates and the recycling is done at environment temperature. This type of recycling can be done in one of two ways. The first method (cold mix plant recycling) involves a process in which RAP is combined with new emulsified or foamed asphalt and a recycling or rejuvenating agent, possibly also with virgin aggregate, and mixed at a central plant or a mobile plant to produce cold mix base mixtures. The second, more common, method involves a process in which the asphalt pavement is recycled in-‐place (cold in-‐place recycling (CIPR) process), where the RAP is combined without heat and with new emulsified or foamed asphalt and/or a recycling or rejuvenating agent, possibly also with virgin aggregate, and mixed at the pavement site, at either partial depth or full depth, to produce a new cold mix end product. A lot of countries have used cold in-‐ place recycling in conjunction with a hot mix overlay or chip seal.
Figure 1.4.1: Scheme that shows the different ways of Asphalt Recycling
After the scheme displayed in Figure 1.4.1, we can proceed to give a brief description of these techniques:
Recycled Hot Mix – Reclaimed asphalt pavement must be processed into a granular material
prior to use in hot mix applications. A typical RAP processing plant consists of a crusher, screening units, conveyors, and stacker. It is desirable to produce either a coarse or a fine fraction of processed RAP to permit better control over input to the hot mix plant and better control of the mix design. The processed RAP used in recycled hot mix asphalt should be as coarse as possible and the fines (minus 0.075 mm (No. 200 sieve)) minimized. Gentle RAP crushing (controlled crusher speed and clearance adjustment on exit gate) is recommended to minimize the fracture of coarse aggregate and excess fines generation.
Hot In-‐Place Recycling – In the HIPR process, the surface of the pavement must be softened
with heat prior to mechanical scarification. The HIPR process has evolved into a self-‐ contained, continuous train operation that includes heating, scarifying, rejuvenator addition, mixing, and replacement. This train operation is reflected on the following image (Figure
1.4.2):
Asphalt
recycling
Hot
recycling
in plant
in place
Cold
recycling
in plant
in place
Cold Plant Mix Recycling – Processing requirements for cold mix recycling are similar to
those for recycled hot mix. Recycled asphalt pavement must be processed into a granular material prior to use in cold mix applications. A typical RAP plant consists of a crusher, screening units, conveyors, and stackers.
Cold In-‐Place Recycling – CIPR (like hot in-‐place recycling (HIPR)), requires a self-‐contained,
continuous train operation that includes ripping or scarifying, processing (screening and sizing/crushing unit), mixing of the milled RAP, and the addition of liquid rejuvenators. Special asphalt-‐derived products such as cationic, anionic, and polymer modified emulsions, rejuvenators and recycling agents have been developed especially for CIPR processes. These hydrocarbon materials are sometimes, but not always, used to soften or lower the viscosity of the residual asphalt binder in the RAP material so that it is compatible with the newly added binder.
On the following image (Figure 1.4.3) we can observe how this Cold In-‐Place Recycling is been carried out. There is cold milling, sizing/crushing, mixing with emulsion, reprofiling/placing with paver and compaction.
Figure 1.4.3: Image showing Cold In-‐Place Recycling
1.5. Mechanical Performance of RAP
The mechanical performance of a road or pavement is one of the main worries when using RAP. Because of RAP’s precedence as material that consists of aggregate and bitumen that has been removed and/or reprocessed from an asphalt pavement, it may be thought that it will not be able to handle the properties requested for the desired road. It is certain that Reclaimed Asphalt Pavement is produced when old, damaged pavement materials are milled and crushed, but this is done for subsequent addition of it as a component in new asphalt mixtures. So that this old material can be reused as an asphalt pavement, it must satisfy different requirements regarding to mechanical properties and behaviour in response to stretches and strain. There is an important fact that must be satisfied that says: Mixes containing RAP should perform equal to or better than virgin mixtures.
As mentioned in the previous chapter, RAP can be used in different modes and placed on different places of the pavement (surface, binder, base, foundation, base and sub base). It is well known that as higher the layer that is using RAP is, the more requirements or mechanical restrictions that there will be. For example, the surface layer of a pavement will have to deal with much more mechanical exigency than the sub base layers, as the efforts suffered are much more direct to the higher layers. This is why the amount of RAP being reused depends also on the layer it is going to be used. In hot-‐mix recycling, EN Specification (EN 13108-‐1) suggests using no more than 10% for surface layers and 20% for binder and base layers (EN 13108 – 2006). Exceeding this percentage, additional tests are needed to evaluate the effect of aged binder on the stiffness and durability of the mix. On the other hand, cold recycling, sometimes allows us to recycle the 100% of RAP extracted from the bituminous layers, and use it to make base or binder layers. This is why, in the recent years, many researches have been carried out regarding the use of Reclaimed Asphalt Pavements for sub base layers.
D’Andrea et al. (2001) [1] suggest that the use of RAP for sub base layer and subgrade is a useful solution in order to dispose of the large amount of waste produced during maintenance and rehabilitation activities.
To avoid the problems related to the excessive deformations provided using only RAP is necessary to combine it with other type of aggregates, such as virgin or Construction and Demolitions aggregates, that are able to strengthen the mixture until reaching a suitable level of resistance to static and dynamic loads.
A field-‐testing study in order to demonstrate the potential of use RAP as a pavement base, carried out by Garg N. et al (1996) [2], demonstrated that the performance of the RAP base was comparable to the one of a crushed stone base. Some years later, Cosentino et al (2003) [3] studied the comparison between RAP and limerock’s behavior, and by using the Clegg impact hammer, Falling Weight Deflectometer (FWD) and Soil Stiffness Gauge (SSG), the study showed that RAP achieved 80 to 115% the stiffness of limerock during the eight week testing intervals. These specific tests proved that the stiffness in RAP is equivalent to limerock’s, but didn’t take into account other important properties such as permeability. So, after some experiments, it was found out that adding 20% of virgin aggregates provide the best strength properties and at the same time maintains a reasonable permeability coefficient. Furthermore, they demonstrated that the addition of RAP generally improves
the drainage characteristics of base and sub base layer mixtures.
A study realised in 2012 by Montepara, Tebaldi, Marradi and Betti [4] “Effect on Pavement Performance of a Subbase Layer Composed by Natural Aggregate and RAP” was carried out, with the objective of evaluating the possibility to use RAP as a virgin aggregate supplement into unbound mixture to be placed in sub base layers. To achieve this objective, different non-‐destructive tests were carried out in order to assess the short and long term performance of a mixture blended with 50% of RAP, comparing results with those obtained on a mixture composed by only natural aggregates.
Different tests (LWD and FWD+GPR) were carried out by using two consecutives sections (tracks) 30 m long and 5 m wide made by two different sub base mixture compositions: the first is made by 100% natural aggregates while the second is a blend of 50% natural aggregates and 50% RAP. Both samples should have the same grading curve, so that compaction was done equally on both cases. On Figure 1.5.1, we can observe both grading curves used to carry out this experiment:
The results of the tests showed us there were not significant differences between performance of a sub base with RAP and a sub base with only virgin materials.
We can see for example, in the results of the LWD test, represented in Figure 1.5.2, that even if the differences were not significant, the energy provided to the soil seems to be slightly higher for mixture with 50% RAP.
Figure 1.5.2: LWD Results
To sum up, the results of all three tests carried out reflects that, in this case, that the sub base made by blending high percentage of RAP with natural aggregates show the same short and long term performances, appearing to be slightly higher than the one with only natural aggregates in it.
1.6. Advantages of using RAP
The increase in addition of RAP to pavement mixtures is not surprising, given that the availability of high-‐quality virgin materials is declining and landfilling is becoming less practical and more expensive as time goes by. There are plenty of benefits for reusing RAP when paving new roads. These benefits can be attributed to the reduction in costs of new construction and rehabilitation projects, environmental conservation of energy and the preservation of road geometry.
Some of these benefits can be reflected on three key requirements that must be satisfied for a recycled asphalt pavement to be successful. These three requirements are the following:
1) It should be cost-‐effective
This means that the fact of using a recycled asphalt pavement should represent a lower monetary cost than using fully new materials.
2) It should be eco-‐friendly
By eco-‐friendly we understand that the use of the recycled asphalt pavement should represent a loss of contaminating emissions with respect of using the new materials. Not only this, but the fact of using recycled materials imply that there is not an unnecessary waste of raw or new natural materials.
3) The recycled asphalt should perform well
Its properties should be those that allow the pavement to work under the corresponding stresses of the road.
1) It should be cost-‐effective
As in almost all fields, the cost-‐benefit ratio is the basis of much of the initiatives for the recycling of pavements. For this reason, it is very important to make a careful analysis to ensure the economic feasibility of the use of recycling in the different construction and rehabilitation projects.
Generally, the free market is in charge of regulating and promoting the reuse of materials in the construction of roads, due to the savings that the different recycling techniques usually generate. However, in some cases, governments must promote recycling, through restriction of the use of landfills, or the application of high fees for the discharge or exploitation of quarries, or giving economic or technological support to companies that make efforts to recycle.
The recycling of asphaltic pavements implies first of all the reuse of the available resources in the current road or pavement. Aged materials can be reused using a suitable technique so that they are again valid for the construction of the firm. With this type of techniques, the demand for materials (aggregates, bitumen, etc.) can be greatly reduced in conservation operations. Not only costs are reduced by needing less new virgin materials, but the fact of not needing to find quarries and landfills near to where the works are being realised also reduce costs improving fabrication efficiency.
In addition, "in situ" recycling methods allows us to avoid transport operations, not only of aged materials from it’s original place to a dump, but also the new material’s being carried from their point of supply to where the new construction or rehabilitation is been carried out.
Avoiding these unnecessary transportation operations also reduces considerably the monetary cost of the corresponding work.
2) It should be eco-‐friendly
On modern times, there is an increasing social awareness about the need to preserve the environment, which has made legislation today much more protectionist than in the past. This makes it difficult to obtain suitable raw materials, increasing not only their cost but also transport to the work, as they are almost never produced where they are needed. Not only that but also the difficulty in finding a landfill for materials removed from the firm at a reasonable price is increasing. These problems are especially important in urban settings. Recycling of old pavements presents environmental opportunities and challenges, which, when appropriately addressed, can maximize the benefits of re-‐use. The use of most recycled materials presume no threat or danger to the air, soil, or water. Moreover, careful design, engineering and application of recycled materials can reduce or eliminate the need to search for and extract new, virgin materials from the land, being less harmful for the environment.
On Figure 1.6, we can see a stockpile of unprocessed reclaimed asphalt pavement (RAP) millings of various sizes.
Figure 1.6: Accumulation of unprocessed RAP millings in a stockpile
3) The recycled asphalt should perform well
The disposal of aged materials of the firm, in addition to causing problems related to the acquisition of new materials and their discharge, is technically counterproductive because, despite being old, they retain a good part of their qualities.
The milling and reuse of the asphalt conglomerate benefits us by a great saving, since it requires a very little amount (1 – 3%) of additional bitumen, whereas a new asphalt concrete may need much more ( > 6%). This aspect, together with the low transport costs and the low energy required for the production of a solid recycling, make the energy saving important for conventional pavement construction.
As we have just seen on the previous section, it is very important that the Reclaimed Asphalt being reused in the new pavement can deal with the same stresses, as raw virgin material would do.
We can consider very positive the fact of having recycled material that can suffer the same efforts as new virgin material when building a new pavement. If we can guarantee that the use of this material will not be harmful to anything on the new pavement under construction, we will always be convenient to use it, as we save costs and protect the environment.
In addition, it must be taken into account the fact that the management system of any pavement must control its properties (or mechanical performance) throughout its useful life. This way you can decide at any time the best conservation option to maintain the level of service required by the needs of the user. These systems aim to be the ideal tool to find the optimum time and procedure to perform the conservation in order to obtain the best possible result at the lowest cost to society.
2. EXAMPLE: Case Study of Asphalt Recycling in Italy
The following example is a translation and adaptation from an article by Cristiano Rebecchi, published on “La rassegna del bitumen” [5].
2.1. Location of the Case Study
On this section, we will talk about one case of asphalt recycling carried out in Italy between 2003 and 2006.
This recycling operation was executed along a quite important road located in Crema, in Northern Italy.
Figure 2.1.1: location of Crema in Northern Italy, from Google Maps
The road connects Cremona with Milan and it is located in Lombardy, the region of the country where are located most economical activities and it is characterized by much traffic, including many heavy vehicles.
Figure 2.1.2: Position of Crema in relation to the most important cities of Lombardy, from
Google Maps
Figure 2.1.3: The road where asphalt recycling was carried out, from Google Maps
2.2. The situation before the intervention
The road was built in the 1980s and there were problems since it was opened, due mainly to the settlements of the base course. The base course was full of voids and this was the main cause of the settlements. In 2006 the wearing layer of the road was characterized by rutting and both longitudinal and transversal cracking (also deep crack, > 20 cm) and the conditions were no more suitable for allowing the safe circulation of the vehicles.
An operation of asphalt recycling was thought to be the best solution for the mentioned situation. It could be possible to solve the problems of the road: since the settlements could be considered finished because of the time passed after the road opening, it was only necessary to put a new regular wearing course and to solve the problem of deep cracking.
This intervention was considered to give the pavement 10 more years of life with the waste of a rather low amount of money and the production of a limited quantity of landfill waste.
2.3. Description of the intervention
The works included the following phases:
-‐ removal of the first 3 cm of the existing pavement by cold scarification. Some of this material was used to fill the shoulders.
-‐ cold recycling of the remaining asphalt pavement and of part of the granular base course (average depth of 30 cm), using asphalt emulsions. In order to optimize this operation, the whole road was divided in three parts and in every of them a study was carried out to discover the best solution in term of asphalt emulsions or foamed bitumen.
-‐ construction of a new 5 cm layer in asphalt mix, made with asphalt modified with elastomers.
-‐ construction of a new 3 cm wearing layer with antiskid properties, using asphalt modified with elastomers.
Figure 2.3: Train operations using of foamed bitumen
