Abstract: The invention concerns a compound cement containing cement and a blast-furnace slag, more particularly for bore holes.This compound cement is characterized in that it comprises the following components:a Portland cement presenting, by weight, a magnesium oxide content of max. 6%, a sulphur trioxide content of max. 3%, an insoluble residue of max. 0.75%, a tricalcium silicate content between 48 and 65%, a tricalcium aluminate content of max. 3%, a total amount formed by the amount of tetracalcium aluminoferrite, plus the amount of dicalcium ferrite, plus two times the amount of tricalcium aluminate which is at most equal to 24%, and a total amount of alkalies, calculated as sodium oxide equivalents, of max. 0.75%.and a ground blast-furnace slag with a vitrification rate of 90 to 100%;these two components presenting a similar mesh size, comprised between 2,800 and 3,000 cm.sup.2 /g, and being mixed together in the following wt-% proportion: 50 to 10% of Portland cement and 50 to 90% of ground slag.