Hi GeordieboyNS,
Workers were employed on the Slagheap.Workers drilled into it, stemmed the holes with dynamite and blew it up like in a Quarry. Afterwards the 'rubble'was put through a massive Crushing machine on the Jarrow side where it was turned into various sizes of gravel for hardcore & roadbuilding.
My dad bought a wagon load for the base of our Garage & drive in Grasmere Rd, so a little bit of the heap is still 100yds from the heap.