## 3 Results
### Effects of CWP on Concrete Mechanical Properties  
Table 4 provides a detailed overview of studies on the effects of CWP on the mechanical properties of concrete. Compressive strength-- the critical parameter in concrete load-bearing applications-varies notably depending on the percentage replacement of CWP and particle size. Most studies have identified optimal replacement levels between 10% and 30% to achieve enhanced or comparable performance to PC concrete. The enhanced performance of CWP concrete is usually attributed to the pozzolanic reactivity of CWP. Pozzolanic reactivity is the ability of a material to chemically interact with CH, a byproduct of cement hydration, in the presence of moisture [33]. Cement hydration is an exothermic chemical process that produces compounds such as C\(-\)S\(-\)H (the primary contributor to concrete strength), ettringite, monosulphate, and CH (also known as portlandite) [35; 71; 72]. Silica in CWP supposedly reacts with CH in a secondary pozzolanic reaction to form additional C\(-\)S\(-\)H, which acts as a glue that binds aggregates  
Figure 6: Slump test values of concrete specimens at different CWP replacement ratios of cement [44]. Figure 7: Slump flow of SCC containing different ratios of CWP replacing GGBS [69]. and other cementitious materials together [73]. This cohesion increases the overall load-bearing capacity of concrete. However, this pozzolanic reaction occurs slowly, which is why pozzolanic concrete typically exhibit lower early-age strength but higher long-term strength than conventional PC concrete [33; 73]. Although pozzolanic reactivity is most accurately analysed using microstructural techniques like Scanning Electron Microscopy (SEM) to observe hydration products, the Strength Activity Index (SAI) is also a practical method [69]. The SAI measures the compressive strength of cement-CWP blends relative to PC concrete. Studies have shown that CWP concrete achieves comparable performance at optimal replacement levels due to a combination of pozzolanic activity and enhanced particle packing. The fine particles of CWP improve the particle distribution of concrete and strengthen the interfacial transition zone (ITZ) between aggregates and cement paste [31; 74]. This refined microstructure also enhances the mechanical properties of concrete [31]. However, determining whether the improved strength or durability of CWP-based concrete is due to the pozzolanic reaction or merely the result of CWP filling voids in the concrete microstructure is challenging. Therefore, the mechanical behaviour of CWP-based concrete is often clarified by analysing the composition of its microstructure. [PERSON] et al. [65] and [PERSON] et al. [67] found that moderate (30% or below) CWP replacement levels produced enhanced mechanical properties. [PERSON] et al. observed that 15% replacement yielded the highest compressive, tensile, and flexural strengths in M30 grade concrete, with compressive strength rising from 34.1 MPa for conventional concrete to 38.56 MPa at 28 days as shown in Figure 8. Beyond 15%, the properties declined rapidly, possibly due to the dilution effect. Similarly, [PERSON] et al. identified 30% CWP combined with 2% sodium silicate as optimal for M25 grade concrete, significantly improving compressive strength while maintaining tensile strength and slightly reducing flexural strength. This study suggests that sodium silicate enhances pozzolanic activity at higher CWP levels. Both studies highlighted that moderate CWP levels optimise particle packing and pozzolanic activity, resulting in improved strength. [PERSON] et al. [57], [PERSON] et al. [44], and [PERSON] et al. [69] reported that lower CWP replacement levels (5-10%) offered peak mechanical properties. [PERSON] et al. observed a 15% increase in compressive strength with 5% replacement in bacterial concrete. The researchers attributed this performance to the improved early strength development due to the CWP.