## 3 Results
### Effects of CWP on Concrete Mechanical Properties
#### 3.2.2 Effects of Curing Age on the Mechanical Properties of CWP Concrete  
In addition to the replacement percentage and particle size, curing age is a critical factor. The compressive strength of concrete, measured at different day intervals, provides insights into the hydration rate of the binder materials. Pozzolanic materials such as GGBS, fly ash, and silica fume tend to hydrate more slowly, leading to a gradual increase in compressive strength over time compared to PC [71; 72]. This explains why pozzolanic cement concretes  
Figure 11: Compressive strength of nano CWP concrete at 7 and 28 days [77]. exhibit lower early-age strength than those made with PC [80; 81]. Figures 12 and 13 show the percentage change in compressive strength of CWP concrete at 7 and 28 days. The figures indicate that the compressive strength of the CWP concrete improved significantly with curing age. At 7 days, variations in strength change were observed across different replacement levels, with some studies reporting increases and others reporting reductions in strength. The strength changes ranged broadly from around +40% to \(-\)50% at this early age. However, at 28 days, the range of compressive strength changes narrowed, and the data points trended towards neutral or slightly negative changes. This suggests that CWP concrete benefits from an extended curing time, which is likely due to pozzolanic reactions contributing to strength development over time. [PERSON] et al. [69] report that CWP concrete mixes achieve satisfactory 28 and 56-day compressive strengths even at higher replacement levels of 20%, though strength development may be slower. This suggests that while CWP can initially inhibit early strength gain due to slower pozzolanic activity, it continues to contribute to strength development as curing progresses, ultimately meeting or exceeding the strength of PC concrete. In contrast, [PERSON] and [PERSON] [75] observed that the compressive strength of concrete with 10% CWP peaked at all curing ages up to 28 days. However, at 28 days, the strength declined significantly for mixes with higher CWP replacements (50%), indicating that a very high CWP content may negatively affect the long-term strength. In studies where the compressive strength is measured at extended curing durations, such as 56 and 91 days [41], reported only minor strength losses for mixes with 10-20% CWP, with a 0.4 MPa decrease compared to the control at 91 days. This suggests that CWP concrete maintains satisfactory long-term durability and compressive performance, particularly at low replacement levels and with fine particle sizes. Figure 12: Percentage change in the strength of the CWP concrete at 7 days [3; 16; 28; 41; 69; 75; 76]. Although the direct testing of flexural strength is limited, studies indicate trends similar to those observed for compressive strength. For instance, [PERSON] et al. [57] highlighted that flexural strength tends to improve at an early curing age, with CWP replacements around 5%. [PERSON] and [PERSON] (2018) [65] also observe enhanced flexural strength up to 15% CWP replacement, beyond which performance declines. This pattern suggests a limit for effective flexural performance, beyond which the CWP negatively impacts the concrete matrix. Studies such as those by [PERSON] and [PERSON] (2017) [75] and [PERSON] et al. (2024) [44] also support this, noting that CWP inclusion is suitable for applications where flexural strength is critical, provided the replacement level is carefully controlled. This improvement is consistent with the findings on compressive strength, suggesting that pozzolanic activity in CWP concrete supports both compressive and tensile strengths over time. Overall, it can be deduced that curing age positively influences the mechanical properties of CWP concrete, especially when moderate levels (<20%) of CWP are used.