Properties of waste gneiss powder used to design eco-friendly cement mortar

The present work concerns the determination of the geological setting of a metamorphic rock quarry in operation for the production of aggregates and the valorization of the drilling waste as a cement additive. The aim is to identify the parameters that determine the composition of the geomaterial employed, highlight that composition, and investigate its pozzolanic activity. The structural study reveals that major discontinuities are oriented N180°. The minerals identified by microscopy and mineralogical investigations are quartz (Qt), plagioclase (Pl), mica (Mi), muscovite (Mu), orthopyroxene (Px), and biotite (Bt) which are characteristic of gneiss. After that, ten boreholes made for blasting provided the waste gneiss powder needed. The collected samples are homogenized and then used as a partial substitute for cement from 0 to 50% with 10% intervals, for the formulation of mortars. Depending on these percentages’ substitution, the setting time increases from 225 to 285 min, and the water absorption decreases from 6.05 to 2.36% at 28 days of curing. Moreover, the filler effect is underlined at 10% substitution by flexural strength enhancements of 2.22% and 1.89% between 2 and 7 days of curing. At 28 days, the compressive strengths fall from − 3.33 to − 20.00% for 10% and 50% substitution, respectively. The parameters that govern all of these behaviors are mainly the filler effect, the reduction in the amount of cement that increases the w/c ratio, and the size of the gneiss fines and sand used. In general, mechanical results decrease with the percentage of substitution, but the difference compared to the control specimen remains largely below the percentage substituted. The findings of this study set the groundwork for the recovery of dust from gneiss quarries as cementitious addition, as well as the limitations of this recovery.