## 4 Results and Discussion  
### Compressive Strength  
Figure 7 illustrates a comparison between the compressive strength of all mixes at 7, 28, and 120 days. In there, compressive strength gradually increased for all mortar mixes, indicating continuous reactions over time [49], and the increased rate of compressive strength depends on the mortar's age and cement replacement ratio. Based on the compressive strength results at 7 days, in comparison to the control mix, cement replacement up to 20% led to an increase in compressive strength of mortar mixes to the extent of 7-14%. Moreover, cement replacement at 30, 40, and 50% led to a 4, 25, and 31% reduction in compressive strength, respectively. After 28 days of curing, 5, 10, 15, and 20% cement replacement resulted in an increase of 11, 9, 7, and 7% in compressive strength, respectively, while cement replacement at 30, 40, and 50% resulted in a decrease of 12, 22, and 31%, respectively. At 120 days of age, 20, 12, and 6% increment in compressive strength were achieved due to cement replacement by 5, 10, and 15%, respectively, while the compressive strength of specimens with 20% cement replacement and specimens with no waste (control specimens) was the same. Moreover, 30, 40, and 50% cement replacement led to a reduction in compressive strength to the extent of 18, 25, and 36%, respectively.  
The results show that cement substitution with RM, GGBFS, and EAFD (equal amounts) up to 20% leads to a slight increase in compressive strength, which can be attributed to the filler effect and the latent pozzolanic reactivity of aforementioned by-product powders. The filler effect and the latent pozzolanic reactivity of EAFD have been confirmed in the study done by [PERSON] et al. [27]. [PERSON] et al. [50] also reported that, for high replacement ratios, activation and the pozzolanic reactions of GGBFS could lead to higher strength in GGBFS_OPC systems. However, due to the low pozzolanic nature of  
\begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Test** & **Testing Age (Days)** & **Type of Specimens** & **Reference Test Method** & **Specific Information** \\ \hline Sodium sulphate attack & 28 (start of cycles) & Cube (50 mm) & ASTM C1012 [46] & 20\% sodium sulphate \\ \hline Sulphuric acid attack & 28 (start of cycles) & Cube (50 mm) & ASTM C267 [41] & 25\% sulphuric acid \\ \hline Water absorption & 28, 120 & Cube (50 mm) & ASTM C642 [47] & \\ \hline Electrical resistivity & 7, 28, 42 & Cylinder (50 \(\times\) 100 mm) & [PERSON] et al. [48] & Constant voltage of 30 V \\ \hline \hline \end{tabular}
\end{table}
Table 3: \(Cont.\)  
Figure 7: Compressive strengths at 7, 28, and 120 days.  
most SCMs, increasing the cement replacement ratio usually leads to a decrease in compressive strength. In fact, there is a limit for cement replacement with waste powders (20% in this study) after which the pozzolanic reactions slow down, and beyond that, additional waste content acts as an inert material. This is mostly because of the relationship between the cement content and the quantity of calcium hydroxide (Ca(OH)\({}_{2}\)), which is essential for pozzolanic reactions, as well as the pozzolanicity of SCMs. In concrete specimens with high amounts of SCMs, the excess SCMs are deactivated and operate like an inert material, as shown by [PERSON] and [PERSON] (2018). While studying the effect of waste glass powder (WGP) on concrete properties, they realized that, for more than 30% replacement of binder with WGP, any other pozzolanic reaction was not initiated, whereas 15% replacement resulted in maximum compressive strength.