## 5 Conclusions  
In the present study, the compressive strength, splitting tensile strength, electrical resistance, water absorption, resistance to freeze-thaw cycles, durability against magnesium sulphate and sulphuric acid attack, and microstructure of mortar mixes containing RM, GGBFS, and EAFD as partial replacement of OPC were investigated. OPC was partially replaced by RM, GGBFS, and EAFD at different weight percentages (0, 5, 10, 15, 20, 30, 40, and 50%). Based on the experimental results, the following conclusions can be drawn:  
1. The slump of all the tested mixes ranged from 105 to 150 mm. In the specimens with 5% replacement ratio, slump was the same as that of the control specimen. However, increasing the replacement ratio over 5% resulted in the reduction in the slump;
2. Replacing cement by RM, GGBFS, and EAFD up to 20% led to an increase in compressive strength resulting from the filler effect and latent pozzolanic reactivity of the waste powders. However, specimens with waste content higher than 20% experienced lower compressive strength compared to the control specimen;
3. At 120 days of curing, the 30 min and 24 h water absorption test of specimens with 5 and 10% replacement showed the same results as that of control specimens. However, after passing the 10% replacement ratio, as the waste content increased, the water absorption followed the same trend, and the number of interconnected pores and water-saturated cavities rapidly multiplied, resulting in a higher water absorption capacity;
4. The electrical resistivity of the mix with 5% waste content is the same as that of the control mix, and by increasing the replacement ratio, it decreases. This can be attributed to the presence of high contents of heavy metals in the waste, which can considerably boost the conductivity;
5. By increasing the waste replacement ratio, the reduction in compressive strength as a result of sulphate attack escalated, while mixes with 10% replacement ratio had a higher compressive strength compared to that of the control mix. The higher reduction in compressive strength of specimens containing waste powders relative to the control specimen can be attributed to the slow pozzolanic reactivity of the waste powders;
6. As the replacement ratio increased, the reduction in compressive strength and weight of specimens as a result of sulphuric acid attack increased and reduced, respectively. Specimens made with 15% replacement ratio had the same compressive strength as the control specimens. The specimens were exposed to a sulphuric acid solution at an early age, meaning that waste powders did not have enough time to develop pozzolanic reactions. This can be the main reason for the higher compressive strength loss of all mixes made with waste powders;
7. Due to the filler effect of waste grains, improvement in the density of mortar mixes with low amounts of waste powders was observed in SEM images. In addition, 5% cement replaced with waste powders could improve the ITZ between aggregates and paste. However, increasing the replacement ratio degraded concrete properties as  
Figure 22: SEM images of mortars after 7 days of acid exposure: Ctrl (**a**), RGE5 (**b**), and RGE50 (**c**). the size of pores increased, and the volume of needle-like products (most probably ettrinigite, which is mainly responsible for concrete strength) decreased. Conceptualization, J.S. and E.A.S. ; methodology, J.S., E.A.S., and A.K. ; formal analysis, M.G., S.A.H., and J.A.B. ; investigation, J.S. and E.A.S. ; data curation, J.S., E.A.S., and A.K. ; writing--original draft preparation, J.S., E.A.S., and A.K. ; writing--review and editing, M.G., S.A.H., and J.A.B. ; visualization, J.S., E.A.S., and A.K. All authors have read and agreed to the published version of the manuscript. This research received no external funding. The support from the Ferdowsi University of Mashhad is gratefully acknowledged.