Project

Nowadays, sustainable development and natural resource conserving criteria must direct the implementation of civil engineering works toward the preservation of non-renewable resources. The reduction of available land resources and increased costs from the use of high-quality materials lead to the need to re-employ any soil, irrespective of its geotechnical characteristics. In this context, soil stabilization by chemical binders (e.g. cement or lime) is widely recognized among the most effective techniques to improve the hydro-mechanical properties of poor quality soils. The geotechnical research and technological improvements in construction equipment have considerably increased the use of lime- and cement-based procedures because of technical, economic and environmental advantages irrespective of the dimensions or type of project. However, classical binders production causes significant CO2 emission (e.g. 1006.49 kg of CO2 /ton of lime) and thus the production of greenhouse gases could undermine the sustainability of the stabilization processes.

The first target of the project is to reduce the amount of soil to be landfilled as waste by means of a recycling action. In this respect, two types of materials are used in the research project: natural excavated soils unsuitable for earthworks and dredged sediments. The amount of excavated soils in construction sites (such as road construction sites, tunneling activities, re-profiling of unstable slopes) is huge therefore its handling and hauling have high environmental and economic costs. In Italy, beside this matter, the lack of available space in landfills and the difficulties in siting new landfills represent a current additional environmental problem to be addressed. In addition, dredged sediments represent a serious problem: the usability of ports and waterways for touristic and commercial shipping is contingent upon dredging to maintain adequate depths for navigation. The need to adapt, expand and deepen existing harbors involves dredging of more than 5 million tons of sediments per year in Italy (Source: CEDA – Central Dredging Association – In accordance with SEDNet, 2004). In addition, the tendency to increase the ship tonnage requires to extend the existing port facilities and to deepen access channels and maneuvering areas. In Europe there is an increasing pressure for combining dredging needs with land reclamation, encouraging the design and construction of confined disposal facilities to be filled with sediments.

A design strategy to reuse of excavated soils and dredged sediments for civil engineering purposes is a way to overcome the management and landfilling problems discussed above. In this respect, soil stabilization with binders is one of the most effective techniques that guarantees the achievement of adequate standards to make these materials suitable for engineering applications.

The selection of sustainable binders that allow to obtain high-quality materials in terms of chemo-hydro-mechanical behavior, represents the second target of this project. Although traditional binders (cement and lime) guarantee a soil stabilization with high standard quality, their production causes significant CO2 emission. There are several by-products of industrial and/or natural processes that could be adopted as binders. The search for a real possibility of reusing by-products as binders for soil stabilization is a fundamental part of the proposed project.

The third target of the project is oriented to offer an insight in the stabilization techniques from both a civil and environmental point of view, useful for the mixture design and set-up of efficient timetable of construction quality controls.

The project is fully developed through a detailed experimental program defined with the precise aim of achieving the following atteined results:

•  identification of promising innovative and sustainable binders and the definition of effective mix proportions;

•  assessment of outcomes in stabilizing: (1) poor quality excavated natural soils from a geotechnical point of view; (2) dredged sediments and (3) mono-mineral clay (e.g. bentonite) both from a geotechnical and an environmental (i.e. against pollution) point of view;

• optimization of the mix design procedure by identifying factors affecting the performance of the mixture (e.g. saturation conditions, curing temperatures) and by selecting reliable and easy-to-determine parameters to monitor the reaction progress over time;

• assessment of the capability of innovative binders for the application in impervious barriers for containment of both aqueous and non-aqueous pollutants (e.g. soil-binder mixtures for hydraulic cutoff walls);

• evaluation of the long-term behavior and durability of the stabilized materials after severe and prolonged environmental conditions (e.g. cyclic wetting/drying; freezing/thawing paths and presence of chemicals).

The project methodology is based on a set of experimental tests to characterize of the chemical, mineralogical, microstructural, geotechnical, geophysical and mechanical properties of soils and mixtures to select sustainable and potentially effective binders. The combination of different experimental techniques will allow an extensive characterization of the raw material and the soil-binders mixtures considering different scale levels of analysis (micro and macro) severe and prolonged environmental conditions. All conventional geotechnical tests will be conducted following the standard provided by the American Society for Testing and Materials (ASTM) International. Specific experimental procedures will be implemented for unconventional laboratory tests, taking into account the peculiarities of the tested materials and experimental equipment.