Abstract A “new” industrial by-product obtained from the fluid catalytic cracking (FCC) process in petrol refinery is studied for construction uses. This by-product, named as fluid catalytic cracking catalyst residue (FC3R), is composed of original spherically shape particles and fragments produced in the catalytic process (30–0.1 μm) that present highly irregular morphologies. FC3R presented a very high specific surface area that produced a decrease in workability of cement-based mortars containing FC3R. Workability of FC3R-cement mortars can be increased using a superplasticizer. Replacement of cement by ground FC3R in mortars produced a very important increase in compressive strength that exceeds plain cement mortar, probably due to pozzolanic reaction. Ground FC3R can be used for preparing cements with excellent mechanical properties.