Reuse of sludge from the decorative quartz industry in hot bituminous mixes

The concept of sustainability has become crucial in today’s world. In fact, one of the major environmental priorities in scientific research is to discover innovative ways to recycle waste matter for its use in activities that benefit society. In the construction engineering sector, this trend has led to new techniques for recovering waste from industrial processes, and using it as a replacement for raw materials.The Construction Engineering Laboratory at the University of Granada carried out a research project to study the viability of using waste from the decorative quartz industry (sludge and chips from stone sheets) in the manufacture of bituminous mixes for road surfacing. This research study was performed in two phases. The first phase analyzed scraps and chips from stone sheets to see if they could be used to replace natural aggregate. The second phase focused on evaluating Silestone® sludge to see if it could be used as a substitute for the filler fraction in hot bituminous mixes. This paper presents the results obtained in this second phase in which different job-mix formulas were evaluated by varying their sludge content (0%, 60% and 100%). The properties of the various mixes were analyzed by subjecting them to a battery of mechanical tests that determined their susceptibility to moisture and resistance to rutting.The results obtained are eloquent proof of the viability of reusing Silestone® sludge as a replacement for conventional filler. This study showed that when performance of such mixes was tested, they amply fulfilled the standard technical requirements for roads in Spain. Furthermore, it was found that the job mixes with sludge had a significantly better performance than the standard F10 mix that did not contain it.

Research highlights
► Recycling Silestone® sludge as a filler in hot bituminous mixes is a viable solution.
► Silestone® sludge mixes require lower percentages of bitumen than conventional mixes.
► Silestone® sludge mixes have lower density than conventional mixes.
► Silestone® sludge improve the mechanical characteristics of hot bituminous mixes.
► Silestone® sludge is a useful material that can be used in road construction.