2. MECHANical and engineering ASPECTS of PAVEMENTS and Material Re-USe 4
2.1 Structural layers in a pavement 4
2.2 Knowledge found in European papers on alternative material re-use and assessment 7
2.2.1 Useful information and recommendations on European level 7
2.2.2 Existing European frameworks found in reviewed documents 10
2.2.3 Information from CEN Standardisation work 14
2.2.4 Problems to be solved and research needed – European level 15
2.3 Knowledge found outside Europe 21
2.3.1 Information and recommendations from USA 21
2.3.2 USA frameworks found in reviewed documents 22
2.3.3 Problems to be solved and research needed from the USA point of view 27
3. IMPact evaluation 30
3.1 Introduction to environmental issues 30
3.1.1 General concepts related to environmental issues 30
3.1.2 General concepts related to eco-toxicity issues 31
3.2 Environmental studies in the field of road construction 34
3.2.1 General developments 34
3.2.2 Recent developments in the USA 35
3.2.3 Existing USA frameworks 36
3.2.4 Eco-toxicological characterisation of materials 36
3.3 Impact evaluation tools 37
3.3.1 LCA methods and methods to assess specific environmental impacts 37
3.3.2 European Methodology Guideline 39
3.3.3 Development of regulatory criteria for road construction (the European Landfill Directive approach) 41
3.3.4 Eco-toxicological assessment procedure 47
3.4 Environmental characterisation of alternative materials 49
3.4.1 Leaching 49
3.4.2 Previous leaching studies on road base and embankment 50
3.4.3 Suitable leaching test methods 53
3.4.4 Observations from leaching studies 56
3.5 Major developments within standardisation (CEN) and regulation in Europe 57
3.5.1 The European Construction Products Directive (CPD) – 89/106/EEC 57
3.5.2 The Dutch building materials decree (BMD) 58
3.6 The opinion of the WP3 group on environmental impact evaluation 61
4. Synthesis and COOPERATION 63
4.1 Recycling and cleaner technology today and in the future 63
4.2 Mechanical and engineering properties 63
4.3 Assessment of environmental impact 65
4.4 Complexity of the general assessment approach 69
4.5 Necessary cooperation between different cultures 70
5. Conclusion 72
6. references 74
6.1 References for mechanical and engineering elements 74
6.2 References for impact evaluation 75
APPENDIX 1. European standards for road materials 82
Appendix 2. Requirement pyramid - COST 337 86
Appendix 3. testing of unbound granulAr material 93
Appendix 5. Most common eco-toxicity tests 97
Appendix 6. Leaching testS description 103
APPENDIX 7. GLOSSARY 104
In recent years the pressure on primary materials for road construction has increased. As a consequence, more and more alternative materials are used in Europe in different parts of the road. Although alternative materials may technically prove suitable, the long-term environmental implications of several alternative materials are still uncertain. Alternative materials may perform well in the primary application. However, uncertainty exists for subsequent cycles of use (recycling, reuse in other applications and “end-of-life”). This has been partly caused by the lack of proper assessment tools.
The aim of Work Package 3 is to define a general methodology to assess the suitability of use and reuse of materials (including road construction and industrial by-products) in road pavements. The methodology has to guarantee the durability of the road structure and the eco-compatibility of the materials. This work will also serve to identify the functional and environmental tests, which are necessary in relation to the proposed context of the use of materials, from the construction phase to end of the service life of the road structure.
Work Package 3 (WP3) is divided into two tasks (and several subtasks): Task 1 deals with a review of present approaches in the field of alternative materials. Task 2 deals with the definition of a methodology applicable to road pavements. This document is a part of Task 1
Deliverable D9 is a literature review with special reference to assessment of alternative materials. The aim of D9 is to allow a better knowledge of the state of the art of alternative material assessment in the perspective of recycling thanks to an analysis of international research. This analysis lays on the knowledge gained and on the development of assessment procedures during the last decade, as well as on recent standardisation progress. These information will serve to design the methodology of assessment in the next step of WP3 (choice of assessment procedures and definition of use-scenarios). This methodology will aim at helping material users by providing recommendations for some of the most important alternative materials in Europe on the best way to characterize them (as stated in Deliverable 4 and aimed also in WP4). This approach may also induce recommendations on the quality to fulfil for some materials, and may therefore have some repercussion on the way to prepare them for use (which can be an output of interest for WP6). This document is divided into three main parts: one dedicated to the state of the art relative to the knowledge of mechanical properties of alternative materials, one dedicated to the state of the art relative to the environmental knowledge on these materials, and a third one dedicated to the issues of the merging of these two approaches today for the development of a general assessment methodology of alternative materials in road construction.
This review of present approaches is based on already known proposals for assessment of alternative materials described in papers from other EU-projects, research papers and knowledge from the United States. The international references come from USA as the use of alternative materials for road construction in this country is, like Europe, a major issue, and technical and scientific efforts have been carried out for years on this topic for a broad range of materials.
The partners involved in WP3 have broad knowledge of mechanical and engineering conditions as well as chemical and environmental conditions in relation to road construction. Relevant literature is gathered by the group itself from the member’s daily work and from homepages of relevant research organisations and bodies, including relevant standards from the European Standardisation Organisation, CEN.
The extensive experience gained in European projects such as the Harmonisation of Leaching/Extraction tests (van der Sloot et al, 1997), leaching studies in national research programmes (Wascon series 1991, 1993, 1995 and 1997), European standardisation activities (CEN/TC 292; ISO/TC 190) as well as international standardisation work (ISO) and activities related to the development of acceptance criteria for landfill of Waste (Annex II) can be used beneficially in adopting leaching test methods for construction materials as well as developing a methodology to come to regulatory criteria (not the acceptance levels!). The extensive leaching studies on a wide range of materials has led to the conclusion that a limited number of characterisation methods suffice to address the environmental aspects of a wide range of materials. The variety of scenario conditions can be addressed based on a selection of the proper conditions and interpreting the test results according to those parameters settings. For compliance purposes, relatively simple procedures can be derived from the characterisation tests to demonstrate compliance with the more detailed testing needed for regulatory limit setting and understanding material behaviour, when quality improvement is needed. Many well defined production processes have the tendency to generate rather constant product quality, which requires less testing once the characteristics are sufficiently known.
One of the aims of the work is to provide guidance in the selection of design parameters when environmental properties of materials need to be factored in besides the mechanical properties of a material. A key element of such an environmental evaluation of construction materials implies considering the fate of a material from cradle to grave, even though this aspects is not addressed in the CPD (Construction Product Directive, 1989). From an end-user point of view it is highly undesirable to be faced with a disposal problem at the end of the service life of an alternative construction material.
Deleterious environmental effects of pollutant released by a waste-based road could be prevented and partially anticipated by a preliminary assessment of the (eco)-toxic potential of potentially re-used waste. In the past, this was mainly based on the total content in hazardous substances or components. Then, the leachable fraction was also taken into account. More recently, the number of studies dealing with the hazard assessment based on eco-toxicological tests has exponentially increased. There is a clear need for methods able to take into account information of "mixed" type (chemical, geo-technical, physical, environmental...). It may be a consequence of the general interest of both the scientific community and the civil society in the conservation of prime natural resources as well as in the protection of ecosystems.
It is now accepted that a more ecologically sustainable and responsible attitude has to be adopted. In this context, bioassays play a crucial role in assessing the actual or potential impacts on pollutants on environment.
Recent emphasis on the need for testing eco-toxicity of material expected to be used as secondary material has resulted in requirements for the definition of a reference evaluation method.
At present, several alternative materials are considered good aggregates or fill materials for road construction. As an example, in some product standards for aggregates from CEN, alternative materials are no longer “alternative”, but are manufactured aggregates, by-product aggregates, and recycled aggregates, similar to natural aggregates (e.g. sand, gravel, stone, crushed rock).
Alternative materials originate from materials that in the past were disposed of, or a waste, and to a large extent still are disposed of in some countries. This explains why they have been considered a waste since, despite the fact that some of them have been recognized as materials with beneficial characteristics for construction applications, especially in the field of road construction. Producers of alternative materials have made efforts and are still making efforts to improve the quality of their production to better meet users’ requirements and technical or environmental specifications. This had led to the sometimes long debates about “waste” or “product”.
The WP3 group has agreed that uses of the “right” terminology play an important role for further use of alternative materials. In this document, the term alternative material will be used in general. In some situations the words by-product, secondary (raw) material and waste are used, often in these connections: citation from literature, description of origin of the material, administrative documents etc.
The aim of the review is to choose elements for further work: Identification of scenarios for assessment of alternative materials for suitable uses in road construction and a definition of a general methodology and recommendations for the selection of test methods.
A list of all the reviewed papers can be found in chapter 6 “References”. If a paper is available from the internet the link is given in the list. A list of relevant CEN standards can be found in APPENDIX 1.