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4.4Complexity of the general assessment approach

The development of tools for assessing environmental impact from road materials can be adopted to a large extent from existing protocols, as the mechanism of release is the most essential parameter to consider in order to predict the future behaviour of the material in its use-scenario. Characterisation of leaching behaviour has been developed for more than a decade now and the approach has matured. In appendix 4 the complexity of the aspects that are or can be relevant is illustrated in one graph. In the Construction Product Directive (CPD) the development of horizontal methods for evaluation is strongly promoted. The aspects to be covered relate to different cross-section of the problem: characterisation compliance, laboratory field relations, understanding versus regulatory compliance, etc.

People have not always been afraid of using alternative materials (one can find traces of old use), but today, the introduction of predictive rational methods into the use of alternative materials in road constructions requires an important effort. for the comprehension of the behaviour of materials from the short to the long term, and also new practices.

Traditional road construction has well-known national customs and methods with which roads are constructed. Differences in road construction are primarily based on the climatic conditions and in the geology in the local area, since roads are usually constructed of local natural materials. Environmental considerations have close connections to the materials used and the climate. Environment and mechanical consideration have therefore usually to answer to the same imperative: the use of materials which are produced locally and which have to be used, as much as possible, also locally, due to the problem of the material transport cost.

With alternative material, the material deposit is no more the local geology but the local “by-production”. One can not neglect that alternative materials can also be sensitive to the same climate factors and they have to answer to the same performance requirements. The question is to be able to know – and be able to assess - these performances in an un-ambiguous way.

The construction complexity is markedly increased if “foreign” materials enter the picture. Several of the alternative materials must be considered different in relation to what is common: different appearance, colour, mechanical and environmental properties. The question also arises whether the expected properties for road construction will survive in time. In this, connection with life cycle analyses for natural as well as alternative materials becomes important.

Planning and constructing with alternative materials can be done either by general approval or as an approval for certain layers in a road construction or determined by environmental conditions at the site, where the use takes place (definition of use-scenarios). A similar approach as the latter has been proposed for mechanical purposes for natural unbound graded aggregate applications (COST 337) based on a climatic zoning, but up to now, nothing has been initiated for alternative materials, and notably their environmental behaviour.

For compliance with environmental aspects of road construction, a basis must be found that is on the one hand sufficiently detailed to be able to relate observations made as good as possible to actual practice as opposed to an arbitrary choice. On the other hand the need for relatively simple tests for compliance or quality control remains. For the judgement of acceptability of a given material in a given application, the proper comparison must be made taking into account a number of factors that are relevant to the site or locations under consideration.

4.5Necessary cooperation between different cultures

All important market actors involved in the construction sector, agencies and researchers must cooperate in order to make recycling more and more successful. Culture and ways of thinking must be exchanged so that complex situations can be solved by cooperation.

Even if consistent and common rules in the form of guidelines and requirements on the mechanical and environmental levels are achieved – to which the SAMARIS project contributes – success will depend on the positive will and know-how of the following chain : producers and suppliers, centres for recycling, contractors, road owners, authorities, government agencies, researcher and experts.

People from “Road” and “Environment” are forced to cooperate to choose the optimal solutions when recycling and use of alternative materials are on the agenda. The road has to be environmentally friendly, and it mustn’t be less environmentally friendly than a traditional road on the pretext of making beneficial use of a by-product and saving natural materials. The traditional cut between “environment” and “road” is outdated. The wall has to be broken and a rapprochement is necessary thanks to common efforts of explanation and comprehension, to create a new common agreement, a new technical culture, and a rational way to recycle and use alternative materials for the benefit of the society.

5.Conclusion

As expressed by the Standing Committee Construction and endorsed by the European Commission, a unified approach of assessment of environmental impact for a wide range of materials is aimed for. This implies the development of a methodology which includes also the road construction field.

The basis for such a methodology is established more and more by recent studies illustrating similarities in mechanisms of release and common behaviour of contaminants in different matrices. This leads to the question if the primary focus should be on a material or on the mechanisms of release. Many aspects play a role in judging the environmental compatibility of a material in its different life cycle stages. The framework approach for environmental evaluation of a wide range of materials provides several dimensions of the problem to be tackled: sufficient detail for regulatory setting of criteria, avoiding unnecessary duplication of work, ensuring optimum use of existing information, quick and simple methods for quality control purposes with frequency of testing and parameter selection related to a realistic need.

For the prediction of long term behaviour of materials in the environment, modelling is essential. Therefore, sufficient attention must be given to this aspect of the problem. Major improvements in modelling over the last couple of years ease this task considerably compared to a year ago.

Since proper characterisation of materials is costly, the development of a database/expert system for easy data retrieval and processing will be very beneficial for industry as a basis of reference. Also it will be a means to reduce the need for testing, once sufficient knowledge has been gained.

In view of the extended information available for inorganic constituents, it is considered better to develop the methodology first for these constituents, keeping criteria and test method developments for organic contaminants, and radioactivity, for a further step.

The approach of the WP3 group is in line with the European Commission view. The initiative for an assessment methodology for the use of alternative materials in road construction also follows this careful step by step approach : improving the points that can be improved with the available knowledge and leaving for latter the solving of secondary problems and the generalisation of the method. Respecting that rule, WP3 can contribute to its two different goals.

One is to provide an answer to the end-users regarding recommendations on the best way to characterise some of the most important alternative materials in Europe today (as stated in Deliverable 4 and aimed in WP4). This can induce recommendations on the quality to fulfil for certain materials, and consequently have repercussion on the way to prepare them for use (which is of interest for WP6).

The second is to provide a contribution to the general European trend of characterisation of environmental aspects of construction materials. In that perspective the description of the road characteristics and functionalities as it is started in WP3 may be a contribution at the European level, as the attempt to make close connections between engineering properties’ specialists and environmental properties’ specialist is particularly strong in that work package.

Both objectives are interdependent. One can expect that the clarification of a rational assessment methodology will make end-users more confident for some uses (in order to provide an easy-to-use method, routine test procedures will be proposed as far as possible). The development of a general methodology for assessment can benefit from a better knowledge of the actual in-situ behaviour of materials.

The purpose of the methodology is assessment of materials. Possible criteria that could be envisaged in such a methodology would be purely technical ones, based on a possible breakdown in the material properties. Regulatory considerations will be the responsibility of administrations, in the general context of material construction environmental assessment. The development of the methodology through the assessment of use-scenarios will benefit from modelling progress, event after the completion of WP3. The development of the assessment methodology will benefit from the work of database development which has been achieved recently thanks to various initiatives.