(December 2008) Refuse from slate pits can be used as filler in asphalt road-work. This was the finding of a Brazilian project (Portuguese). In the state of Minas Gerais slate-producer Micapel and the Egesa road construction company merged to a joint-venture. They paved a 230 km stretch of heavily used road from Janeiro to Brasília with „slate-asphalt“ to test durability and wear. The project was monitored by state authorities.
It should be understood that today asphalt is no-longer bitumen, let alone tar (the latter having been banned for health reasons). The black road covering is comprised of 95 % stone granulate using bitumen only as an adhesive. Usually low-grade lime-stone or gneiss is used specifically produced for this purpose.
Around 300,000 t of slate refuse ground to the desired grade were used in the Minas Gerais project. Thus the costs of the project were reduced by 30 % according to the participants. The slate-producing company was able to recycle not only its slate wastage but also silt which is mixed in as sand and makes up 35 % of the asphalt mix. Nature profits as no additional quarries need be opened. Transportation was efficient as the Micapel production-site was situated in close proximity to the road.
The company’s CEO, Joaquim Campos Reis, sees near unlimited applications for slate gravel, from roadwork, to waterworks, and last but not least, structural engineering. was cautious. When asked if the slate producer was now going into the gravel business, he is relutant: „After all, the crusher requires an investment of a few 100,000 Brazilian Reais“.
Spanish railway rides on premium gravel
The gravel bed for the high-speed rail connection between Lisbon and Madrid is made of Rosa Portugal-gravel as reported in a Website. The Portuguese Marmetal S.A., most important producer of this exclusive natural stone, has been maintaining a crusher on site at its quarry for some time now to recycle the mountains of waste from its pits.
Other applications for the gravel in grades of between zero and 31.5 mm are industry, road-construction, and landscape architecture, as stated on the website. It is further to be used in cosmetics and fertilizer production.