In recent decades, adopting alternative resources in infrastructure applications has garnered global attention to address environmental concerns. Olive waste ash (OWA), a locally available byproduct obtained from the olive oil production process, is a promising green material that plays a vital role as a partial cement substitute. This paper evaluates the mechanical and durability properties of cement paste—a key component of paving blocks—incorporating OWA at replacement levels of 0, 5, 10, 15, and 20%, with a constant water-to-cementitious ratio of 0.45. Density, compressive strength, and flexural strength are assessed at 1, 7, 28, and 90 days, while total water absorption (TWA) and capillary water absorption (CWA) are measured at 28 days. The results reveal that OWA slightly reduces density, compressive strength, and flexural strength, with the optimal results observed at a substitution level of 10%. At 90 days, the compressive strength of the control cement paste is 50 MPa, whereas the 10% OWA mixture exhibits a value of 46 MPa, corresponding to only an 8% reduction. Additionally, two predictive models are proposed: the hyperbolic model for compressive strength variation with curing time and the capillary-diffusive model for capillary water absorption as a function of time. Both models demonstrate a strong fit with experimental data. Correlations between different properties indicate a strong correlation between compressive strength, density, and flexural strength, while a negative linear relationship exists between compressive strength and water absorption. This study underscores OWA’s potential to improve sustainable paving blocks by providing suitable mechanical and durability characteristics, offering both environmental and economic benefits.