A large proportion of the stony fraction of C&DW can be recycled as aggregates within the construction sector, be it almost exclusively in low-grade unbound applications such as (sub)foundations. Within the HISER project, technological solutions are being developed for the purification and quality assessment of recycled aggregates and the development of new, more structural, products.
Through the integration and enhancement of automated sorting systems and selective electrofragmentation, an upgraded recovery of the stony fraction from complex C&DW can be achieved. The benefits of the electro-fragmentation technology for the treatment of concrete waste have already been discussed in a previous news item. But recent experiments performed by BRGM and Selfrag have also showed very good results for the liberation of adhered mortar (Figure 1) and adhered gypsum from bricks. The smart combination of selective fragmentation and automated sorting systems will result in the production of three high-purity fractions (unbound aggregates; mortar; bricks and tiles) that can be used in high-quality recycling processes (Figure 2). Quality of the resulting materials and overall cost of the combined processes will be taken into account to define the most convenient recycling routes.
Figure 1: Bricks with adhered mortar after electrofragmentation.
Figure 2: Output of sorting and selective fragmentation processes, linked to developed high-quality products.
In addition, an inline automated quality assessment system (based on Laser Induced Breakdown Spectroscopy, LIBS) provides potential users with higher levels of certainty about the quality of the secondary raw materials. The LIBS system (Figure 2) shows promising results on the quality assessment of both the “grey” (concrete) fraction as the “red” (ceramic) fraction.
Figure 3: The LIBS quality assessment system during the “Concrete to Concrete” demonstration day.
The higher quality of produced aggregates facilitates the development of new high-grade products through the partial replacement of virgin raw materials with higher amounts of upgraded C&DW.
Recycled materials in concrete production
Last month, an upscaled, mobile ADR (Advanced Dry Recovery) installation was demonstrated at the Strukton facilities. With this technology, 3 material fractions can be obtained: 1) a cement-rich fine fraction (<1 mm); 2) an intermediate sand fraction (1-4 mm) and 3) a coarse high-grade concrete aggregate fraction (Figure 3). Strukton is using these coarse aggregates in the production of high-grade structural concrete.
Figure 4: ADR installation. Left: input, right: output (coarse fraction).
Furthermore, Lafarge is currently producing a cement (CEM II 42.5 R) which will be used by Tecnalia and ACCIONA to design and to test a number of concrete recipes. For this cement, they intend to use 25% of recycled concrete waste. New concrete with selected recycled concrete coarse aggregates and partial incorporation of recycled concrete and ceramic fine aggregates will be manufactured at the Tecnalia and ACCIONA facilities.
Brick-to-brick
The project aims at the complete replacement of the opening agent fraction (10% of the total mixture) in the brick raw material mixture with the recycled ceramic fraction of C&DW (e.g. bricks, tiles). Preliminary results of lab experiments at VITO have shown that expected gypsum contents in the ceramic aggregate fraction (up to 1%) do not cause quality issues. Higher mortar contents (up to 50%) can have a negative effect on the strength of the produced samples, but this effect is lowered by crushing the recycled raw material (brick and mortar) to a lower particle size. The robustness to higher mortar contents will be tested in larger-scale production tests at the facilities of Dumoulin. Here, also tests with obtained masonry aggregates are planned.
Figure 5: Fired samples with masonry aggregates.
