France produces about 37.6 million tons of non-hazardous household waste per year. 30% of this waste is treated by incineration. The main by-product of incineration is the Municipal Solid Waste Incineration – Bottom Ash (MSWI-BA). In France, the valorisation of BA is currently limited to road materials. The French decree from 18/11/2011 fixed the thresholds to recover BA in road materials. However, BA shows physical and mechanical properties that could make it suitable as secondary raw material in construction, preventing, moreover, the use of natural aggregates and reducing the landfill materials.
The aim of this study is to investigate the feasibility and potential use of bottom ash in ready-mix concrete (RMC) formulations. The bottom ash used in this study was recovered from an energy enhancement unit located in the Auvergne-Rhône-Alpes region in France. Three samples of BA with different granulometric fraction were used: a global fraction (0-31.5 mm), an intermediate fraction (3-6 mm) and a coarse fraction (6-31.5 mm). Next, three different substitution rates of natural aggregates were tested (10, 20 and 30 %). All the RMC formulations were defined with a constant water to cement ratio of 0.55. The environmental behaviour and mechanical performance of RMC samples were compared to the results obtained for the control sample.
The environmental assessment was performed on monolithic concrete samples, according to the dynamic surface leaching test CEN/TC351/TS-2. The results show that the potential leaching of different heavy metals remained below the thresholds of the Dutch Building Decree (Soil Quality Decree from 22/11/2007), whatever the granulometric fraction and whatever the substitution rate.
In order to ensure the technical performances, the compressive strength was measured for RMC samples after 7, 28 and 90 curing days. The results show that the compressive strength increased with time, whatever the substitution rate for the global granulometric fraction (0-31.5 mm). Smaller evolutions were observed for intermediate and coarse granulometric fractions. Moreover, the compressive strength of samples incorporating BA was twice as low as the compressive strength of control sample (e.g. 16 MPa towards 37 MPa, after 90 days curing, for 10 % substitution rate).
In conclusion, whatever the particle size fraction of MSWI-BA, or the rate of substitution, the incorporating of BA reduces the compressive strength of RMC samples. Further investigations need to be performed, such as the influence of pre-treatment methods (e.g. washing) on the technical performances of RMC, or the influence of the humidity rate of BA incorporated in RMC formulations.
Monitoring and long term performance, both technical and environmental
