ABSTRACT Climate change and the depletion of natural resources are causing society to adopt more environmentally sustainable approaches. In areas such as construction and civil engineering, waste and by-product valorisation could help in the fight against climate change, reducing the consumption of raw materials. Thus, the use of residues or by-products in asphalt mixture manufacturing as road pavement layers has great potential due to their characteristics. This study aimed to characterise a flotation sterile (low-grade magnesium carbonate; LG-MC) generated in the beneficiation process of natural magnesite and to analyse its potential as a filler in asphalt mixture manufacturing. The physical, chemical, and microscopic properties of LG-MC were characterised and its potential use as a filler for asphalt mixtures was evaluated using the UCL (Universal de Caracterización de Ligantes) method. The optimum filler/bitumen ratio for LG-MC was 1.49, higher than the 1.33 of calcium carbonate. Results showed a protective effect of LG-MC against ageing both in the short and long- term, reducing losses from abrasion.