*3.2. Mechanical Properties of Cement Paste Samples*

#### 3.2.1. Compressive Strength

The results of 7- and 28-day compressive strength (CS) values obtained for the cement paste samples have been presented in Figure 3. Accordingly, the CS of each cement paste with the addition of the spent catalyst was found to be higher in comparison with the 0.30 ref sample, both at the 7th and 28th day of hydration. The highest 7- and 28-day CS values were measured for 0.30 15% and 0.30 10% sample, respectively, exceeding the CS of 0.30 ref for 36% and 17%, respectively. As expected, the CS enhances with the curing age.

**Figure 3.** Effects of cement substitution with a spent FCC catalyst on the 7- and 28-day compressive strength of cement paste samples.

### 3.2.2. Flexural Strength

The results of 7- and 28-day flexural strength (FS) values obtained for the respective cement paste samples have been presented in Figure 4. Accordingly, the FS tends to decrease with the increase in cement substitution level, mentioning that the FS of the respective samples is generally similar between the 7th and 28th day of hydration.

**Figure 4.** Effects of cement substitution with a spent FCC catalyst on the 7- and 28-day flexural strength of cement paste samples.
