When quarrying stone there may be areas in the Quarry where there is a large amount of clay contamination. These occur particularly in Limestone Quarries where the clay sediments collect in fissures in the stone. This clay slows down the Crushing and Screen process, so it is scalped off at a size (generally 80mm - 100mm). This allows the clean stone to be crushed without fear of blocking. So Scalpings are essentially the off-cuts of a quarry; quarry waste for want of better words.
The resulting Scalpings contain a large percentage of saleable stone in them and when washed and scrubbed produce premium aggregate. Granite Scalpings have clay to a lesser extent, if at all, but are produced to speed up the crushing process as the smaller material in the Scalpings is slower and more difficult to crush and uses more power.
DUO have been washing Scalpings of varying degrees for over 20 years and are currently processing at CEMEX Shap, CEMEX Roan Edge and CEMEX Gilfach. Scalpings have traditionally been used as a cheap alternative to processed Sub Base materials for a reduced price. Washing creates a Value Added Product.