A process for making hydraulic cements from spent oil shale is described. Inexpensive cement is needed to grout abandoned in situ retorts of spent shale for subsidence control, mitigation of leaching, and strengthening the retorted mass in order to recover oil from adjacent pillars of raw shale. A hydraulic cement was produced by heating a 1:1 mixture of Lurgi spent shale and CaCO/sub 3/ at 1000 C for one hour. This cement would be less expensive than ordinary Portland cement and is expected to fulfill the above requirements.