The use of existing materials in road embankments is an essential issue within the Sustainable Development policies, which have been promoted worldwide for many years. In the World Road Association (PIARC) this subject has been investigated by different Technical Committees over the last 20 years.

The optimization of earthwork projects is an obvious issue related to this concern, with important benefits (no spoil disposal or supply of natural noble materials can lead to a strong pollution reduction). But this may imply the use of materials whose geotechnical characteristics may not be as good as desired or required by usual standards.

The term “marginal material” is defined as “material which is not wholly in accordance with the standard specifications in use in a country or region for highway materials but which can be used successfully, either under special climatic conditions or following progress in construction techniques or treatment to enhance its properties”.

This work, carried out by PIARC Technical Committee D.4, focused on four points:

• The first one is related to the use of new natural marginal materials, little or not at all considered in previous works. Identification of these materials has been carried out by using data collected from a dedicated enquiry.
• The second one is focused on the identification of non-natural marginal materials, little or not considered previously, like industrial by-products, construction and demolition wastes, slags or recycled materials. Canada, Spain, France and Italy proposed most cases.
• The third one is focused on collecting new cases in which non-natural marginal materials, as identified in the second phase, have been used in road embankments: cases from Spain, France and Italy are comprehensively described.
• The fourth one is to get new data about the medium- and long-term behaviour of road embankments constructed with marginal materials, both natural and non-natural. Very likely, this task can only be outlined in the present cycle and its completion will be hopefully left to the following cycles, as medium- and long-term behaviour data are barely available at present.

This report first presents some generalities related to the design of earthworks for roads and reviews the most relevant aspects of previous PIARC reports, making a brief summary of the main issues addressed in them and summarizing the main conclusions reached on those previous works. The data collection performed at this new stage is then exposed.