Recycling biomass ashes on the road pavements: a multimethod approach

Recent international climate commitments promote the use of renewable energy sources to make waste recycling possible and reduce fossil fuels utilization. Following these goals, biomass-fuelled thermal power plants, considered a zero CO2-emission sources, are expected to increase. Nevertheless, the large amount of biomass combustion ash is a major problem that needs to be addressed by encouraging reuse. In this research, it is investigated the possible use of two biomass ashes deriving from the combustion of wood chips, as stabilizing agent of a clay soil from Central Italy, as an alternative to traditional lime treatment. Samples were mineralogically and physically characterized by using X-Ray powder diffraction and by determining their grain size distribution and plasticity characteristics. Clay ash mixtures were prepared since the results on the Initial Consumption in Lime test. The effects of the ashes addition was evaluated in the modification field and compared with those obtained by standard lime treatment. Such comparison was finally extended to both densification and mechanical properties of samples, which were investigated through Proctor and unconfined compressive strength tests. It is shown that the addition of ashes determines a reduction of soil plasticity and a shift toward coarser sizes of the grain distribution, similar to those obtained by adding lime. The compaction properties of treated mixtures behave similarly, regardless of the stabilising agent used. Finally, the comparative analysis demonstrates that the biomass ash stabilizing process provides a positive impact on the compressive behaviour (strength and stiffness) of mixtures after 7 curing days.