EMPLOYEE WAS ATTEMPTING TO BREAK UP AGGLOMERATEDSLAG BY DIGGING INTO THE BASE OF THE PILE WHILE ATTEMPTING TO LIFT THE LOADER BUCKET. DURING THE PERFORMANCE OF THIS TASK THE BACK END OF THE LO ADER LIFTED OFF THE PAVEMENT UNTIL SLAG FRACTURED CAUSING LOADER TO DROP BACK TO THE PAVEMENT. ALTHOUGH THE EMPLOYEE WAS BELTED IN THE RESULTING BOUNCE CAUSED HIS A WHIPLASH TYPE OF INJURY.