<b>ABSTRACT </b></br>

In the present paper, waste products from the steel-making industry are reused as fine raw material in rehabilitation mortars for construction works. Two cement mixes are evaluated: masonry mortars and structural mortars. The study is focused on two steel-making by-products: electric arc furnace slag and ladle furnace slag. The mortar design proposed here incorporates the former in partial substitution of fine aggregates (sand) and the ladle furnace slag in partial substitution of Portland cement and, in some cases, as aggregate (filler). Several partial substitutions of mortar binders/aggregates were prepared which yielded different mixes: 8 masonry mortars whose compressive strengths were below 20 MPa and 12 structural mortars whose compressive strengths were over 50 MPa. At the lab scale, various physical and chemical tests were performed on batches in both the fresh and the hardened state (densities, spreading, mechanical strength, porosity and weathering studies). Our results fully support the use of these siderurgical mortars for architectural (non-structural) rehabilitation purposes and in structural refurbishments for strengthening reinforced concrete elements. </br>

<b>ACKNOWLEDGEMENTS</b></br>

The authors thanks for funding to MCIN/AEI/10.13039/501100011033/FEDER, UE [PID2021-

124203OB-I00; PID2020-113837RB-I00; RTI2018-097079-BC31; FPU17/03374]. Our thanks also go to SAREN research group (IT1619-22, Basque Government), the Junta de Castilla y León (Regional Government) and ERDF [UIC-231, BU119P17] and BASKRETE initiative and the Transnational Common Laboratory “Aquitaine-Euskadi Network in Green Concrete and Cement-based Materials”.