Paper details

Title:

Wood Ash Utilisation as a Stabiliser in Road Construction - First Results of Large-scale Tests

Author(s):

Supancic, K., Obernberger, I.

Document(s):

Abstract:

In recent years the thermal utilisation of solid biomass for heat and electricity production has increased substantially in Austria and the European Union. This has also led to a strong increase in the amount of combustion residues, i.e. ashes. At present, a large fraction of the biomass ashes produced is disposed of in landfills. Ash from woody biomass fuels contains a significant amount of CaO. Therefore, the substitution of burnt lime as a binder for silt and clay soil stabilisation by wood ash seems to be a reasonable way of ash utilisation. The Austrian R&D project focuses on the substitution of burnt lime (CaO) as a binder for stabilisation of silt and clay soils with wood ash. The investigations followed a two­step approach with preliminary laboratory tests (wet chemical analysis and pressure resistance tests) to evaluate the principal suitability of different wood ash fractions from grate and fluidised bed combustion plants as a binder for soils and a large­scale field test, consisting of three road sections stabilised with burnt lime, ash from a bubbling fluidised bed furnace and ash from a grate furnace (with monitoring of the bearing capacity, the chemical composition of the stabilised soil and the leachate quality), in order to evaluate the technical, economical and ecological feasibility of this utilisation technology in comparison to burnt lime. The results show, that with the proper admixing rate applied, wood ash can substitute burnt lime as a binding material for soil stabilisation. Fly ashes from grate furnaces are not suitable under Austrian conditions since their high contents of volatile heavy metals would lead to concentrations in the stabilised soil which exceed the limiting values (especially for Cd and Zn). A mixture of bottom and coarse fly ash from grate furnaces can be utilised. Fly ashes from fluidised bed furnaces feature comparably lower heavy metal contents due to the dilution with bed material and are therefore suitable for soil stabilisation. The utilisation of wood ashes has the advantage of low raw material costs but due to the higher amount required, the processing time is longer compared to soil stabilisation with burnt lime. Based on the experience gathered from the field test, a detailed evaluation of the economic feasibility of the utilisation of wood ash as a binding material is currently underway. The ongoing ecological evaluation of soil stabilisation with wood ashes will focus on the analysis of the leachate samples collected regularly. The results of these investigations shall provide the basis for a successful implementation of wood ash utilisation as a binder for soil stabilisation in practice in the future.

Keywords:

ashes, biomass, recycling, sustainability, soil stabilisation

Topic:

Biomass Conversion Technologies for Heating, Electricity and Chemicals                  

Subtopic:

Recycling of conversion residues (session 1)

Event:

19th European Biomass Conference and Exhibition

Session:

OA3.2

Pages:

859 - 870

ISBN-13:

978-88-89407-55-4

ISBN-10:

88-89407-55-7

Paper DOI:

10.5071/19thEUBCE2011-OA3.2

Price:

FREE