## 1 Introduction
When mixed with water, these materials chemically react with hydration products (calcium hydroxide) to form additional calcium-silicate-hydroxide (C-S-H) gel, responsible for the strength development of ash-infused composites. In particular, the oxide composition of OWA indicates that this ash is predominantly composed of highly reactive SiO\({}_{2}\), rendering it an appealing precursor for pozzolan, as reported in the literature [23; 24]. This characteristic guarantees the potential OWA in light of its efficient properties and environmental friendliness, which are defined by its pozzolanic reaction, filler effect, and low-cost effectiveness [24]. It seeks to evaluate the features of cementitious systems employed in the construction of paving blocks. Given that concrete is one of the key components of these blocks, a wide range of green concrete that incorporates OWA is being explored, such as conventional concrete [2; 17], non-structural recycled concrete [25], concrete pavement [21; 26], and high-performance concrete [27]. Previous research pointed out that the utilization of 5% OWA in the concrete results in a compressive strength comparable to the reference mixture [28; 29]. Similarly, the beneficial impact of olive seed ash on the mechanical performance of concrete is also observed, demonstrating that OWA is a promising resource for producing concrete without compromising its structural integrity [30]. Furthermore, incorporating treated olive biomass bottom ash into concrete pavement improves its mechanical strength [31]. Moreover, olive waste biomass ash can act as a filler in self-compacting concrete with compressive strength similar to that of mixtures made with conventional fillers [32]. In brick manufacturing, olive pomace ash, which partly replaces clay, adversely affects both compressive strength and bulk density [33]. In addition, the inclusion of 30 to 40% olive biomass ash causes a drop in compressive strength, which is possibly attributed to an excess of waste content [19]. However, a previous investigation highlights the potential of using olive pomace ash as an effective method for boosting the strength of bricks [34]. In the construction of road embankments, OWA can be used as an economic agent for expansive soil stabilization. Hence, OWA is a pozzolanic material due to its high content of calcium, which improves the bearing capacity, unconfined compressive strength, and the dry density of the soil [35; 36]. Another study has been carried out on the implementation of OWA to produce rammed earth blocks [13]. The test results prove that OWA meets the pozzolanic properties due to its ability to enhance mechanical features [13]. In the case of rigid pavement, OWA enhances the durability and strength of concrete material at 7.5% of replacement for cement [37]. In addition, an investigation confirmed that olive pomace ash and olive stone biomass ash are two effective waste materials that serve as alkaline source activators to fabricate geopolymers with good bulk density [38; 39]. This study explores the impact of OWA as a partial cement substitute on the physical and mechanical properties of cement paste for paving block applications. Five partial substitution levels (0, 5, 10, 15, and 20%) are examined to determine their impact on density, compressive strength, flexural strength, and water absorption behavior, highlighting the correlations between diverse parameters. Furthermore, two predictive models--the hyperbolic model for compressive strength and the capillary-diffusive model for sorptivity and diffusion--are suggested to validate experimental data. The integration of these two models represents a significant contribution to this study by better understanding the interaction between mechanical and durability characteristics in the presence of OWA. In summary, this study underscores that OWA can be an ideal candidate to improve durability, promote sustainability, and reduce the carbon footprint of cementitious systems used in paving block applications, offering an eco-friendly solution.