Abstract The reuse and reincorporation of waste generated in the production processes are becoming increasingly important in the world, due to the double effect that it has in terms of sustainability. The first one is the environmental factor, since the impact generated is reduced by reducing the amount of wastes. The second one is the financial factor, since new products are developed that companies did not initially have, generating financial profitability. Therefore, this research evaluates the possible reuse of waste from gravel and sand wash mud of an aggregate plant as a supplementary cementitious material (SCM) after being thermally activated, seeking to promote the circular economy in the construction materials sector. The physical, chemical, and mineralogical characterization of the waste is presented and its pozzolanic activity was evaluated by means of the SAI‐strength activity index. It was found that despite its low content of clay minerals, the thermally activated waste had very good performance as SCM with SAI between 81 and 106 with a tendency to increase with the age of cure. Showing that this can be a very promising potential use for this kind of waste.