This paper presents an experimental study on a new mixture scheme of mortar. Unlike most of existing work, the present study investigates nano-CuO (NC), and its combined effects with cement replacement i.e., rice husk ash (RHA) on durability performance, as well as strength and permeability properties of mortars. Comprehensive observations of both the performance and properties improvements on RHA-containing mortar specimens were determined with the addition of NC. To this end, a series of tests for examining the strength both directly (compressive strength) and indirectly (Ultrasonic Pulse Velocity), electrical resistivity, chloride permeability, water absorption and microstructure characteristics (i.e., SEM micrographs, Mercury intrusion porosimetry (MIP) & capillary analyses) of mortar specimens were performed. A relationship between the Rapid chloride permeability test (RCPT) and electrical resistivity was also studied in order to recommend an alternative method for quality control in the presence of RHA and NC. Finally, a mixture scheme which provides relatively satisfactory properties improvement with positive environment credential is suggested. •Both single and combine effects of NC and RHA on mortar properties are reported.•Binary combination of NC and RHS markedly improves performance and properties of mortar.•A relationship between the RCPT and electrical resistivity was studied for quality control.•The opposite effects caused by RHA and nano-CuO on porosity and sorptivity are quantitatively discussed.•RHA20NC3 provides satisfactory properties improvement with positive environment credential.