This paper deals with the production of mortars prepared using a commercial CEMIIB-S 42.5N cement, a natural aggregate, steelmaking slag, a superplasticizer and water. The as-received unprocessed steel slag was milled by a hammer mill and then sieved to obtain batches with different maximum particle size. Each batch was used, together with the other components, in the production of mortars which were tested, by compression and water absorption, after different aging times in order to evaluate their long term stability. Several slag-free samples were also prepared as reference materials. All mortars were prepared with fixed aggregate/cement ratio (6/1), superplasticizer/cement ratio (s/c) and water/cement ratio (w/c). It has been demonstrated that an adequate protocol for the preparation and the use of slag containing particles with 2500 m maximum size lead to the production of materials with mechanical properties suitable for civil engineering applications after aging for 28, 90 and 180 days. However, samples containing slag particles with size equal or greater than 1000 m display a decay of mechanical properties after longer aging in water or after accelerated aging.
