## 4 Discussion  
Replacing PC with CWP in concrete has numerous effects on the fresh, mechanical, and microstructural properties of concrete, including its durability. However, gaps remain in understanding the performance of CWP in concrete, particularly regarding its pozzolanic reactivity. This discussion covers the observed effects of CWP on concrete properties and highlights some contradictions found in existing studies. The effect of CWP on the workability of concrete is inconsistent among studies. However, an increase in CWP content generally led to a reduction in slump. For instance, a decrease in slump was observed from 110 mm (0% CWP) to 95 mm (30% CWP) by [PERSON] et al. [65], and a more significant reduction was noted from 135 mm to 65 mm at 20% CWP replacement by [PERSON] et al. [67]. This is usually attributed to the fine particles in CWP, which increase the surface area and water demand, thus reducing the flowability of concrete. However, other studies have reported increased workability with CWP, especially when relatively coarser particles of CWP are used [57]. This indicates that the workability of CWP concrete depends on the particle size and the type of CWP used. CWP generally improves compressive and flexural strengths at low to moderate replacement levels, typically up to 5-20%. For instance, [PERSON] et al. [66] reported that the compressive strength increased by 8.75% within 28 days at 10% CWP replacement, and flexural strength also increased with up to 10% CWP according to [PERSON] et al. [57]. These improvements are attributed to pozzolanic reactions between CWP and cement hydrates, which enhance the formation of C-S-H gel, thereby strengthening the concrete matrix. However, higher CWP content beyond 20-30% generally leads to a decrease in strength. For example, at 30% CWP replacement, the compressive strength decreases by up to 11% [66], and the flexural strength declines progressively beyond 10% CWP contents, according to [PERSON] et al. [67]. These findings highlight the importance of optimising the replacement level to achieve the best balance between workability and strength. The observed reduction in strength at higher replacement levels is often attributed to the coarser particle size and reduced pozzolanic activity at elevated CWP levels. However, some studies contradict these findings. For example, some researchers have reported that CWP can enhance compressive strength by up to 30% replacement of PC [44]. This discrepancy indicates the need for further research to better understand the factors influencing CWP's contribution to compressive and flexural strengths. The incorporation of CWP into cement also has promising effects on concrete durability. The incorporation of CWP into concrete has been shown to enhance various durability properties, such as water absorption, permeability, chemical resistance, thermal insulation, and fire resistance [24; 25; 26; 27; 70; 85]. The ability of CWP to refine the concrete matrix through its pozzolanic activity is essential for its durability. By reacting with CH in a pozzolanic reaction, CWP forms additional C-S-H gel, which densifies the concrete structure and reduces the number of capillary pores. The improved durability was also attributed to the filler effects of the finer CWP particles. This process directly improves water absorption and permeability, as highlighted by [PERSON] et al. [68] and [PERSON] et al. [83]. Lower water absorption reduces the ingress of harmful chemicals and moisture, thereby enhancing chemical resistance [44]. Chemical resistance, particularly in acidic and chloride-laden environments, further highlights CWP's role in improving durability. [PERSON] et al. [67]demonstrated that CWP concrete performs well in aggressive environments due to its dense matrix, which limits ion penetration and structural degradation. SEM, XRD, and TGA provided valuable insights into the effects of CWP on the concrete matrix. [PERSON] et al.