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2.2Knowledge found in European papers on alternative material re-use and assessment

2.2.1Useful information and recommendations on European level

The SAMARIS WP3 group has reviewed several recent papers from known EU-projects and other research papers (chapter 6 References). This also includes relevant standards from the European Standardisation Organisation, CEN. In addition, the partners have broad knowledge in relation to road construction and alternative materials. The aim is to find existing knowledge of elements and methodology in order to assess the suitability of use and reuse of materials (including road construction and industrial by-products) in road pavements.

Important general information has been found in the reviewed texts from Europe. Some of the findings from papers may be usable in further work with the purpose of defining a general methodology for assessment of materials suitable for road construction. This chapter summarize the important findings.

General information

The European Commission Framework Programme IV TRANSPORT Programme sponsored a project: Alternative Materials in Road Construction ALT-MAT. This study is a key document in the further work for WP3. The final report states the following:

Overall, the results of the ALT-MAT project are very positive and provide support for the use of alternative materials in road construction. The following alternative materials were studied in the project: MSWI bottom ash, crushed concrete from demolition, demolition rubble (mixture of brick and concrete), electric arc furnace steel slag, ferrochrome slag, blast furnace slag (both air cooled and granulated), recycling glass (crushed glass bottles) and two slags from a new thermal waste incinerator process. The case studies show that these materials perform as well as natural aggregates, and often better than suggested by standard laboratory tests. Methods for testing the mechanical and hydrodynamic properties of alternative materials and their leaching behaviour are listed, and a model for assessing the environmental impact on groundwater quality on a site-specific basis is presented. ALT-MAT (2001).

In the report Recycling Strategy for Road Works, a scientific expert group from the OECD, states ,among others, the two following conclusions of strategies that promote recycling:

• 
  In most countries, government takes the responsibility for increasing recycling and reuse of by-products. It also works to develop a system of laws and regulations that will restrict the construction industry in how they deal with wastes and encourages the use of by-product.
  
• 
  It is possible for government to influence the free market by tax enforcement or subsidy strategies that are designed to promote recycling and the use of recycled by-products. All market parties are encouraged to act in a market-conforming manner by actions such as: providing sufficient information on long-term performance of by-products, stimulating test or research projects, implementing a waste tax, providing recommendations and requirements for the use of by-products or subsidising recycling and reproduction facilities.
  

Furthermore the OECD-report gives ideas to develop a successful use of alternative materials: In order to get accepted specifications and requirements on which new regulations and policies for by-products can be based, the combined effect of government and industry is required. A combination of government incentives (subsidies, research) and disincentives (taxes, dumping fees) done co-operatively with industry seems to offer a good formula for success. OECD (1997).

The Federal Highway Administration sponsored a scanning tour to Europe in September 1999. Following is a summary of observation on the economical framework:

Engineering and environmental life-cycle cost and benefits are a basis for many of the recycling initiatives in Europe. The free market generally plays a central role in all aspects of the processing and utilization of recycled materials in the highway construction industry. In some cases, the governments have acted to implement policies and other mechanisms, including subsidies, to establish markets. Tax policies and structures play a significant role in promoting recycling in the highway environment.

This is especially true in Denmark and the Netherlands, and to a lesser extent in Sweden and France. High landfilling taxes and policies that ban or restrict waste in landfills are promoting recycling in Denmark and the Netherlands. Although landfill costs in Germany are low compared with other countries, Germany’s restrictions on landfilling promote recycling. Similar instruments also are expected to increase recycling in France and Sweden. Like Sweden, Denmark and the Netherlands also place taxes or other restrictions on the mining of natural materials. Germany is considering such a tax. FHWA-PL-00-025 (2001).

As an example, few factors are important for the promotion of a general use of alternative materials in Denmark. The most important motivating factors are:

(1) Taxes on incineration and disposal

(2) Standard specification for materials

(3) Business options and industrial development

(4) Technology transfer

(5) Financial incentives to research and development.

Especially the Danish taxes on waste and no tax on recycling are the most important factors. Having a standard specification for recycled products is also very important because this generates recognition and approval and general public acceptance. Pihl and Milvang-Jensen (2001).

For unbound material in general the variability in the material properties are discussed in the COST Action 333. Properties for materials, used as unbound layers or in a mix of materials, are not constant over the full service life. In the short time they will change during manufacture, transport and laying. In the long term, they will change under the combined effects of factors such as:

• 
  loading conditions which do not lead to a breaking point
  
• 
  ageing (and, in a similar way curing)
  
• 
  other factors (environmental, de-icing products, oil spilling, etc.). COST 333 (1999).
  

General recommendations

The scientific expert group from the organisation OECD makes the following statement: As much as possible, road by-products as well as non-road by-products should be recycled on as high a level as possible, preferably for the same purpose as previously used and not just as embankment fill or to be used in the lower layers of the pavement structure. A large volume of recycling is not an aim on its own. OECD (1997).

The European COST Action 337 concerning Unbound Granular Materials for Road Pavements gives the following recommendations to further work: The use of secondary (alternative) aggregates is increasing, but reliable use is hindered by the lack of experience in their application. To optimise the use of marginal and alternative materials in pavement layers requires a coupled structural layer design and material selection. Such a design / selection combination will require an overall project approach and, probably, an iterative solution method.

Specifications must be used that facilitate the use of alternative materials. To be fair to both novel and conventional materials will either require alternative strategies within the specification, or a move away from simple material characterisation tests. Trying to make alternative materials ‘fit’ into conventional aggregate roles will probably be either non-economic or unsuccessful. COST 337 (2002).

Arm (2003) concludes in her doctoral thesis that recycled aggregates and other residues, as well as conventional unbound road materials, should be analysed using cyclic triaxial load tests in the laboratory and falling weight deflectometer (FWD) measurements in the field, both of which take into account the hole composite material or layer. Consequently, a new methodology for materials assessment and comparison is proposed, based on deformation properties assessed by cyclic load triaxial tests. Arm (2003).

COST Action 333 concerning Development of New Bituminous Pavement Design Method, recommend that a pavement design method should take into accounts all the factors influencing pavement behaviour over its life cycle. Frost design criteria should include the elements essential to cover both the needs of the Nordic and Continental climate countries and those, with a milder oceanic climate. COST 333 (1999). This is true also for alternative materials.

Comments from SAMARIS WP3 group

There is a common agreement about some of the recommendations for the further work in WP3, but the group needs to discuss to which level the recommendation can be incorporated in the SAMARIS’ proposal for general methodology for assessment of alternative materials.

The OECD scientific expert group argued for high level uses of alternative materials. WP3 group will discuss this statement. Is it desirable that as much as possible of road by-products should be recycled preferably for the same purpose as previous uses, and that other alternative materials are used for highest level of quality and technical standards possible? Or is it desirable to use some of the largest amount of alternative aggregate in lower layers in the road structure or as embankment fill, landscaping and other fill? As regards the WP3 group, the latter should look at all possible uses .Finally in practice, the choice to actually go ahead with application of certain materials is a political choice.

The answer the WP3 can provide lies in the mechanical properties and the environmental constraints. MSWI bottom ash treatment with cement is presented as a way to make it “climb in the road structure” thanks to the improvement of its properties. It is also a way to improve the image of the material, which is good from the commercial point of view. On the other hand, for a given road project, this leads to less material used. The problem today for by-product producers is to find outlets. In the future, there is no reason not to apply to alternative materials the same rationality in the approach (i.e. based on a sound assessment procedure) than the one which has been used for natural materials. One day we will only speak of materials (natural or not).

SAMARIS WP3 group agrees with the necessity highlighted by the OECD report regarding recommendations and requirements for the use of by-products, based on collection of sufficient information on long-term performance of materials.

SAMARIS WP3 group agrees with COST 333 and 337 statements mentioned in this section and will follow the design/selection combination approach, if possible. The problem is that it is difficult to achieve a proper feed-back of experience.

2.2.2Existing European frameworks found in reviewed documents

General remarks

Assessment of a new material such as an alternative material is not a new discipline in road construction regarding mechanical and engineering aspects. Designers and constructers have always used their best knowledge from similar materials used as a layer in a road structure.

Often a new material is compared to, or assessed by, a natural material, and very often mechanical tests for the natural material are used uncritically for the alternative material. If the new material fulfils the requirements, the new material may be accepted. For some of the alternative materials (perhaps also for some natural materials) a chemical and environmental assessment is a necessity.

Very few European research documents describe general assessment systems or general methods to assess alternative materials for use in road construction. Instead many documents have descriptions of various aggregates from alternative sources and give detailed assessment of the specific materials.

The OECD scientific group - OECD (1997) - with members from Europe, United States and Japan stated that the use of by-products for road construction and rehabilitation is now common practice in many countries. The Group identified three areas that affect the success of recycling efforts. They are:

• 
  Engineering considerations
  
• 
  Environmental factors
  
• 
  Economic feasibility.
  

Comments from the SAMARIS WP3 group

The WP3 group has this in mind and will use the OECD report as a key document in the further work to define a general methodology for assessment of alternative materials.

Requirement pyramid

The European study COST Acton 337 delivered a report which gives broad and very detailed description of important mechanism, models and procedures in road construction on bases of the whole field of knowledge of unbound granular materials. COST 337 (2002).

The structure in requirements for roads is shown as pyramids, a political pyramid and a technical pyramid. Dienst Weg- en Waterbouwkunde, Rijkswaterstaat (CROW) in the Netherlands has published two reports in which all these relations have been described.

There is a political pyramid and a technical pyramid. Here only the technical pyramid is described in detail. The political pyramid can, for example, be used to stimulate the use and reuse of specific materials. In the technical pyramid, the functional requirements can be expressed as common, material-independent and quantitative technical requirements that can be measured.

In the following extracts from the European COST 337 Action each level is equally important, since the “lower” levels provide quality control tools to meet the end user requirements.

Looking at the requirements for a road, a base / sub-base layer and base / sub-base materials, one can distinguish five different levels of requirements (Figure 2.3).

These five levels in the technical pyramid are:

1. Requirements of interested parties / users; boundary conditions

2. Function / performance requirements during the road lifetime

3. Functional requirements on the structural behaviour properties of the base / sub-base itself

4. Material behaviour / properties

5. Material nature (particles).

Figure 2.3. Political pyramid and technical pyramid. Figure 4.7 COST 337 (2002).
These levels are used to look at the requirements and to determine the important properties in a structured way, starting with the requirements of the road user. As shown in Figure 2.3 there are relations between the levels in both directions. There are also a lot of relations between the items of one level with the items of the other level(s).

The requirements at level 5 can be regarded as requirements for the materials to be used for the construction of a base layer. All these requirements have to be checked for each grade and type of a material only once. For a given material, when its properties do not change significantly, this check can be regarded as an approval of a type of material. The requirements at level 3 can be regarded as requirements for the layer after construction.

Short descriptions of level 1 – 5 in the technical pyramid

The requirements reviewed in the following section are those for base and sub-base materials. The structural design of base and sub-base layers are mainly based on empirical knowledge and experience built up over many years.

Level 1: Requirement of interested parties/users; boundary conditions

The requirements at level 1 are important for the road as a whole. These requirements are not directly meant for base material, but are used to derive the requirements for base and sub-base layers. Interested parties and users of roads are very extensive groups. Not only the end-user is included, but also the financier, the contractor, the road-authority, persons and institutions in the direct surroundings of the road, and others directly affected by the road.

The requirements and boundary conditions at this level are often complex and subjective. The following elements are distinguished at this level: safety, comfort, environment, durability, economy, aesthetics, inconvenience for the surroundings, capacity / availability, construction materials policy, human (public) health. Detailed descriptions can be found in APPENDIX 2.

Level 2: Function / performance of the base during the road’s lifetime

The requirements of interested parties are often complex, subjective and indefinite. They have to be modified in terms of material-independent requirements, which are quantitative, if possible. Such functional requirements can be used in performance-related specifications. The authority can check the performance and the contractor has many possibilities to be innovative, for instance by using alternative materials or equipment. Detailed descriptions can be found in APPENDIX 2.

Level 3: The structural behaviour / properties of the base layer

The functional requirements are followed by the requirements for the behaviour of the construction under traffic loads. These requirements are related to the lifetime of the base layer, because normally there will be no maintenance carried out on the base layer during its lifetime. The expected lifetime of a base can be between 50 to 100 years, or even more, such as for instance the Via Apia Antica, or more recently within the emerging concept of Long Life Pavements or Perpetual Pavements.

As an answer to functional requirements, as an example, the structural behaviour is determined by measurable properties obtained from laboratory testing, Falling Weight Deflectometer and other non-destructive methods. Requirements for structural behaviour of the layer are listed in APPENDIX 2.

Level 4: Material behaviour / properties

Elementary material behaviour can be divided into three main items:

• 
  Mechanical properties such as: modulus, fatigue, - permanent deformation behaviour, compressive, bending- and tensile strength, creep, friction properties,…;
  
• 
  Other physical properties, such as: density, frost behaviour, moisture resistance, swelling, shrinkage,…;
  
• 
  Chemical properties such as: leaching behaviour, and those affecting hydraulic binding.
  

The elementary material behaviour is mainly determined by the nature of the material, for instance, by the shapes of the particles of the material, which in turn affect the compactability of a material and its mechanical properties. The following material properties influence the behaviour of base and sub-base layers. Requirements for the material behaviour of the layer are listed in APPENDIX 2.

Level 5: Material nature (particle)

The level 5 requirements, for the nature of the material, concern the requirements related to chemical-mineralogical, physical and morphological (shape) aspects. Required descriptions of the particulate and physical nature of the materials comprising the layer are listed in APPENDIX 2.

Comment from the SAMARIS WP3 group

In the technical pyramid from COST 337, the functional requirements can be expressed as common, material-independent and quantitative technical requirements that can be measured. This is exactly the idea of SAMARIS WP3, notably through the work done for Milestone 7.

The technical pyramid refers to base and sub-base, and the present technical requirement pyramid gives a general overview. Hopefully, the approach can be applied to all road layers. Level 2 (function / performance of the base during the road’s lifetime), level 3 (the structural behaviour / properties of the base layer) and level 4 (material behaviour / properties) seem to be of great interest as a starting point for the development of a general methodology for assessment of alternative materials which is the work for WP3. Level 5 (material nature) could also be included in our SAMARIS WP3 approach in order to include for example notions like “impurities”.

The WP3 group will use the final COST 337 report as a key document in further work.

Testing of unbound materials

COST 337 have done a review of tests, test procedures and methodology for unbound granular materials in common use in Europe. A questionnaire was sent to national experts from 17 European countries, and the result is a detailed description of the main tests. Tests have been divided into three main categories:

• 
  laboratory tests used to determine particle characteristics;
  
• 
  laboratory tests used to determine material characteristics;
  
• 
  in situ tests.
  

Important results from the questionnaire are shown in APPENDIX 3. COST 337 (2002).

The ALT-MAT final report present recommendations for test methods for alternative materials in general, including test methods for abrasion behaviour and test methods for frost resistance. The report also gives some proposed actions for further development of tests for alternative materials. ALT-MAT (2002).

2.2.3Information from CEN Standardisation work

In the last 10 - 15 years European standards have been developed. Concerning road materials CEN technical committees for aggregates and other materials used in road construction and engineering works have completed (or are close to complete) the first version of European product standards. These standards are based on the existing national standards in the countries.

Alternative materials can be used instead of natural materials according to the standards, but very often some problems arise using the standards strictly. Ongoing works in CEN committees are preparing a second version of product standards, and the aim should be to integrate requirements and tests which comply with the properties of the alternative materials.

The political precondition for creating an open European market – and thus for the common European standards –was to remove barriers to trade.

In order to meet this political ambition, the Commission has issued a number of Directives which the individual Member States are under obligation to include in national legislation.

The Directives relevant for the road sector are mainly the Public Procurement Directive (Directives for public purchasing) and the Construction Products Directive. The Public Procurement Directive makes demands for wide European tendering of public assignments, while the Construction Products Directive requires CE-marking of products for the Building and Construction sector, according to technical specifications.

Technical specifications are common European product and testing standards, which are prepared by the European Standardisation Organisation, CEN, as ordered by the Commission (so-called harmonised standards). In addition there are a number of Standards, which have been prepared by mutual voluntary agreement between the Member Countries (so-called voluntary Standards), e.g. EN 13285 Specifications for unbound mixture for roads. Products which are exported on the basis of harmonised Standards must be CE-marked – in contrast to products exported on the basis of voluntary Standards.

Since the Public Procurement Directive does not differentiate between harmonised and voluntary Standards, the sum of European Standards to the extent to which they are available, are the basis for products in public roads.

The list of European Standards which are relevant for road materials is long (more than 100). As an example for the advance of standards it can be mentioned that standards for aggregates (sand, gravel and stones for road constructions, etc.) with accompanying test methods are in place from autumn 2003 and their use is compulsory since June 2004. In June 2004, conflicting national standards had to be withdrawn. The APPENDIX 1 shows some European standards with relevance to the road sector.

Standards for bituminous mixtures (asphalt and surface dressings) are still under preparation but will be ready by 2005.

The first generation of common European standards is often based on usual practice, meaning that test methods and product specifications are based on traditional, empirical approach.

One implication – as mentioned above – is that this often disfavours alternative materials. Due to tradition and lack of fundamental research results as to identifying and measuring functional requirements and related functional testing, the first generation of European standards created under the Construction Products Directive by CEN tends to be rather conservative. However, the Public Procurement Directive does not prevent the use of alternative and more modern functionally related tendering and techniques. The aim of the next generation of European standards should be to consider highlighting functional requirements and related testing.

Comments from the SAMARIS WP3 group

It is one of the main objective of SAMARIS project to suggest adapted requirements for alternative materials and especially functional requirements for the second generation of CEN product and aggregate standards which should be ready for use in 5 years from 2003. Functional requirements refer to section 2.2.2 and the COST 337 requirement pyramid.

2.2.4Problems to be solved and research needed – European level

Although recycling technology has now been used for many years, there are still technical issues - such as specifications, testing methods, characterisation of recycled materials, design procedures, suitable recycle agents and, most importantly, long-term performance of by-products - that need to be studied in further detail OECD (1997). In the reviewed nine European papers several issues that need to be studied are described.
Alternative materials behave differently

From the point of view of mechanical performance, uncertainties about alternative materials remain, especially with respect to the long-term performance. The nature and composition of alternative materials is often significantly different from that of natural aggregates, and existing tests for natural aggregates may not be appropriate. It is even more true for mixtures with binders because of uncontrolled reactions between the binder and the alternative material. However, most national technical specifications use the same test methods for alternative materials and natural aggregates stated in the ALT-MAT final report.

A programme of inter-laboratory tests showed that alternative materials behave in a different way to natural materials in tests such as the Los Angeles and Micro-Deval abrasion tests. Results of current classical tests for alternative materials should therefore be viewed with caution. Alternative materials often give better mechanical performance in the field than would be expected from laboratory test results. Inspection and monitoring of existing roads showed that alternative materials gave as good and sometimes better support to the road pavement layers as natural reference materials. Sites investigated ranged from the north of Sweden to south-west of France, and hence covered a wide range of climatic conditions. For some materials, notably crushed concrete and air-cooled blast furnace slag, an increase in stiffness with time was recorded, due to the self-binding properties of the material.

Design should rather be based on performance-related tests, such as cyclic-load triaxial or gyratory compaction tests. Work needs to be done to relate these tests to measurements of field performance made with the Falling Weight Deflectometer (FWD) and similar tests. ALT-MAT (2001).

Also COST Action 337 concluded that current standards for classification tests should be interpreted cautiously: A ‘good’ result from a certain test on a conventional aggregate may not be directly comparable to a ‘poor’ result in the same test on an alternative material. Eventually, CEN standards will need to be adapted to be more transparent in this respect, but the timescale for this to happen is likely to be rather large.

The mechanical properties of alternative granular materials can be very good, or can be very poor. Often, high quality derives from self-binding characteristics. Other materials are of poor mechanical performance and strategies now exist for improving performance at moderate effort and cost. There remain concerns about long term life and durability. COST 337 (2002).

Comments from the SAMARIS WP3 group

It is important for the further work in SAMARIS to know that alternative materials in many cases ( considering mechanical performance in the field or in laboratory tests) behave differently from the conventional materials. WP3 group agrees that design and requirements to some degree should be based on performance-related tests.

New and modified tests for alternative materials

In relation to research needs, one must say that in general, empirical laboratory tests are widely used in Europe at present. They are used for material assessment, but due to their simplistic nature they often fail to clearly differentiate between material qualities.

The ALT-MAT project has highlighted the gap between the actual behaviour of some alternative materials into road applications, and their predicted behaviour deduced from their results to usual laboratory tests. This gap, which is not acceptable for end users, is a brake to reliable and rational use of alternative materials in road construction. ALT-MAT (2001).

The material properties needed for solid mechanics models, like E-modulus and Poisson’s ratio, are quite different from the material properties used in specifications and for quality control, like size and shape of particles and degree of compaction. Standardized test procedures of a more fundamental nature need to be adopted more widely to assess the behaviour of these materials. Laboratory testing should be supplemented by in situ testing, including measurements of stresses, strains and plastic deformations in real pavements, under different types of loading. AMADEUS (2000).

The COURAGE study recommends that more effort should be given to determine the relevant mechanical properties of the compacted aggregate mixture, rather than to determining the properties of material indices (which are often performed only on some of the large particles taken loose from the mixture) which is currently the common European practice.

The project states that repeated load triaxial test (RLT) were found to give much more reliable indications than traditional laboratory tests. A draft CEN standard for the RLT has been shown to offer a significant advance.

The testing programme must assess unbound materials at the likely in-situ moisture contents which they will have during the life of the pavement. The moisture content variation may be expected to be large and further studies may be necessary to ensure that a reasonable estimate can be obtained. Some seasonal exhumation of current pavements in similar situations may be helpful. COURAGE (1999).

In the opinion of the COST 337 Action and other experts, the most important proposals for research on the use of unbound granular materials (UGM) in road pavements are:

• 
  - Determination of permanent deformation properties;
  
• 
  - Measurement and prediction of water movements in road pavement layers and sub grade soils;
  
• 
  - Assessment of mechanical properties of alternative unbound granular materials.
  

Accelerated Load Testing should be applied to pavements in which the UGM provides a significant structural contribution, in order that the long-term performance of largely granular pavements may be better understood. COST 337 (2001).

Cyclic load triaxial tests are suitable for assessing the deformation properties of alternative aggregate materials, e.g. when their equality to the replaced material is to be proved. It is anticipated that a wider use of cyclic load triaxial tests for characterising unbound materials, both conventional and alternative, will result in suitability for purpose use and thus more efficient use of materials and more sustainable resource management. Arm (2003).

In 2003 a new CEN standard for RLT was approved. It will be the new tool for evaluation of materials and will assist in the aim of maximising use of marginal materials (alternative materials) in pavement construction.

Comments from the SAMARIS WP3 group

There is a need for new and modified test methods for alternative materials. The WP3 group agrees with the conclusions from the ALT-MAT project that there is a gap between their behaviour in field and what could be deduced from the conventional tests in the laboratory for some alternative material. It is necessary to keep that in mind for the further work in the WP3 group.

Maybe repeated triaxial load tests (RLT) in the laboratory and measurement of field performance with FWD are ways to go. However RLT is a tool for general research of materials and not a tool for end-users operational control. One consideration is how to pass from this sophisticated test to a simpler one for control purpose? Otherwise, should the full RLT be required as indispensable for control purpose, the question would be how to organise (and by who) the carrying out of this heavy test in the material preparation process.

It is important to specify that the RLT is carried out on a compacted material (rather than a granular material) representative of all the particle size distribution of the material which will be implemented in the actual road application. It is an important point for some materials that are rather heterogeneous or that can develop beneficial or harmful reactions.

Climatic conditions

On the assumption that a pavement design method should take into account all the factors influencing pavement behaviour over its life cycle, climatic effects related to temperature variations are also considered of importance (of. course, the situation differs from one country to the another).

For freeze/thaw, Mediterranean countries do not consider frost in their pavement design method, since frost is not a problem in these countries. In other European countries, freeze/thaw events are taken into account in pavement design methods through checks or preventive measures. In oceanic climate countries such as Ireland, the United Kingdom and Iceland, a minimum thickness of non-frost susceptible material is mandatory to avoid frost damage to the lower layers.

In general, it is observed that on one hand, some comparatively well known effects, such as moduli variation with temperatures still form the subject of many research actions, on another hand, effects, such as material changes that occur over a prolonged period in the road, have received little attention. COST 333 (1999).

The COST 333 and the EU project AMADEUS pointed out that climatic factors that are relevant to pavement design and they were classified into three main categories:

• 
  Freezing and thawing effects.
  
• 
  Temperature variations.
  
• 
  Variation of hydrological conditions.
  

Regarding the climatic conditions and the way to handle them at the European scale, AMADEUS team suggests presenting a system to characterise climatic conditions in such a way that they could be used in a flexible way in connection with pavement design models.

It is likely that the most efficient method consists in presenting the data in connection with a map or a set of maps covering Europe, and settling boundaries of climatic zones irrespective of the particular political boundaries between member countries. In each of these zones, of a size that varies with the geographical features, quantitative climatic indicators would be associated and made available from a data-base.

The temperature indicators to be supplied for each climatic zone and period should include at least:

• 
  Yearly average temperature.
  
• 
  Maximum air temperature over the period considered.
  
• 
  Minimum air temperature over the period considered. AMADEUS (2000).
  

Climate effects (moisture, temperature) need to be taken into account at all stages. For in situ assessments, it is important that the results obtained can be reliably extrapolated across those climate-induced conditions likely to be experienced in the life of the pavement. COST 337 (2002).

Comments from the SAMARIS WP3 group

The effect of climate needs to be taken into account in an assessment methodology framework. The assessment of climatic conditions in the case where alternative materials are used as unbound aggregate is more or less the same as the assessment for the use of natural materials in road construction. For some areas freeze/thaw tests are interesting, not in others .

Regarding alternative materials with a potential leachable pollutant load, the use of de-icing products can have an effect on the solubility of chemicals which has to be considered in the life cycle.
Variation in moisture content

Water movements in pavements are an important factor for the assessment of natural materials as well as for alternative materials used in road construction. Therefore measurements and prediction of water movements in unbound granular materials in road pavement layers and subgrade soils are important proposals for further research.

A new COST action (started December 2003) Water Movements in Road Pavements and Embankments has the objective to study conditions related to water flow and moisture in pavements. It will deal with :

• 
  - Water movement and moisture conditions associated with the soil properties, the terrain, the precipitation (seasonal variations) and the groundwater regime;
  
• 
  - Water movement and moisture conditions in roads, taking into account the vertical infiltration (permeability) through unpaved roads or damages on paved roads e.g. cracks or joints;
  
• 
  - Capillary rise from the groundwater level;
  
• 
  - Infiltration of surface water through the road shoulders;
  
• 
  - Transfer in the vapour phase associated with infiltration
  
• 
  - Various kinds of drainage systems and their efficiency in pavements
  

The main objective of the COST Action 351 « WATMOVE » is to increase the knowledge required for improving the highway performance and minimising the leaching of contaminants from roads and traffic. Improvement of pavement performance will lead to less road closures, better use of the road network, longer service life and more effective transportation of goods and people. The aim of the Action can further be divided into the following four secondary objectives:

- to identify water movement and moisture conditions in unbound pavement layers and subgrade for different types of road constructions in various climatic conditions;

- to investigate the relationship between the mechanical behaviour of materials/soils and their hydraulic conductivity and moisture condition;

- to implement finite element modelling based on laboratory analysis and field studies in order to simulate water movement and moisture conditions in road construction;

- to identify, investigate and control contaminants leaching from soils, natural aggregates and by-products. COST 351 (2002).

For seasonal variations of hydrological conditions, the countries with high rainfall (Ireland, the United Kingdom, the Netherlands and Belgium) consider hydrological conditions in their pavement design methods. However, some other countries have also taken an interest in this and its ensuing effects. COST 333 (1999).

The final report from the EU project COURAGE dealing with Construction with Unbound Road Aggregates in Europe has following descriptions: In all European countries in which pavements were monitored for seasonal moisture changes, it was observed that the variation in all structural layers followed clearly defined seasonal variations, with the moisture content being the highest in autumn and spring.

Pavements founded on embankments are likely to perform better than pavements through cuttings. In pavement structures through cuttings the moisture content was found to be slightly higher, but the variation was lower than for pavements founded on embankment. For structures through cuttings, water may flow into the pavement layers particularly if deep side drains are not installed.

The sealing of the shoulders of the pavement was found to be an important issue for consideration in trying to keep water out of the pavement for improved performance. COURAGE (1999).

Comments from the SAMARIS WP3 group

Moisture content variation and water movement are important factors for alternative materials as well as for natural materials. A new COST action (COST 351, started December 2003) has a plan to study the impact of water and moisture on pavements. The SAMARIS group WP3 will have contact with COST 351 during the project period.

Other barriers for the use of alternative materials

Despite political and economic incentive, the extent to which alternative materials are used in road construction is generally small. This is partly to do with the perception of such materials as being “waste” and hence of inferior quality compared with natural materials, particularly for non-road by-products; partly for economic reasons; and partly because of concerns about the mechanical and environmental performance of the materials. In parts of Europe where natural aggregates are readily available, the use of alternative materials is not economical competitive. Elsewhere, transport costs are the dominant factor. Alternative materials such as blast furnace slag are used close to the source of production, and in urban areas building demolition material and crushed concrete are used. ALT-MAT (2001).

The barriers to a successful market introduction of alternative materials vary in different countries. In countries where raw material is still readily available or where space for landfill is plentiful, the need for recycling and reuse is not felt as strongly as in other countries.

In countries where market introduction of new by-products is done by the private sector, financial and economic barriers are the main reasons that some by-products cannot compete with conventional materials. Then price lowering may be necessary to encourage recycling. and penetrate the market.

The conservatism of road agency and awarding authorities in general, and a perception that the recycled product is not of comparable quality to conventional materials or more risky, are additional significant factors against the use of by-products.

The most common barriers, however, are the lack of: adequate information on long-term performance of by-products, standard requirements concerning recycling and knowledge of all potential applications. Also, the lack of standard testing procedures often impedes an easy acceptance of new materials. This is the case in almost all countries. OECD (1997).

Comments from the SAMARIS WP3 group

WP3 agrees that uses of the “right” terminology, e.g. materials (or aggregates) instead of waste plays a role for further use of alternative materials. Also lack of knowledge and of methodology methods for assessment of alternative materials are barriers for a more extensive use in road construction, for end-users as well as for researchers.

Initiatives as monographs on a given material (like for example the “Municipal solid waste incinerator residues” by Chandler et al (1997) or data bases (like for example the French watchdog of recycling in road construction called OFRIR, an Internet site developed by public organisations), are useful tools for the circulation of information and decision making. The OFRIR site (http://ofrir.lcpc.fr) aims at providing to all national parties involved in road construction in France, guidelines of good practice and elements of information for decision making, by providing an exchange platform between experts. It is also a tool for research.