# Meta-Analysis of the Performance of Previous Concrete with Cement and Aggregate Replacements
## 5 Results and Discussion
### Aggregate Replacement in Previous Concrete
#### 5.3.2 Performance Evaluation
The results show that incorporating IWA can positively impact the mechanical performance of PC. In contrast, a 23% average reduction in performance was observed when RA replaced NA in PC mixes. Meanwhile, respective interquartile for the compressive strength of NA-PC, IWA-PC, and RA-PC were 11-17, 16-22, and 5-14 MPa, while for tensile strength these were 1.25-2.25, 2.2-2.95, and 0.7-1.2 MPa, and for flexural strength these were 2.1-3.1, 2.7-3.9, and 1.8-2.0 MPa, respectively. Among the three PC mixes, IWA-based PC had a similar interquartile range as that of NA-based PC. This may be due to the limited variations in the types and chemical compositions found in these wastes [63]. Conversely, RA-based PC had the highest dispersion in results due to the inert variation of these aggregates, as they are produced from CDW acquired from concretes having different properties. Extreme whisker values were obtained for the types of mixes as 5-49, 6-39, and 3-17 MPa for compressive strength, 1.1-3.1, 1.6-3.0, and 0.6-1.6 MPa for tensile strength, and 1.8-4.1, 1.6-4.3, and 1.15-2.1 MPa for flexural strength. Based on these results, the mechanical performance of PC with aggregate replacement exhibits skewed distribution,  
Figure 8: Overall performance of PC with different aggregate replacements based on fixed effect. which indicates more dispersed performance, signifying a difference in performance based on the type of replacement used. Considering the hydraulic performance, the respective permeability medians of PC mixes made with NA, IWA, and RA were 7.0, 4.9, and 9.8 mm/s. Meanwhile, the respective medians for porosity were 20.4, 21.2, and 22.0%. Despite the changes due to aggregate replacement, these values remain within the minimum acceptable requirement for hydraulic performance [38]. Thus, it can be stated that replacing NA with IWA and RA generally increased the total pore volume of PC, as evidenced by the higher porosity values, but the connectivity of these pores, i.e., permeability, only increased upon RA replacement, possibly due to the porous nature of these aggregates. The variability in permeability was noted with respective interquartile ranges of 5.2-11.2, 3.5-8.1, and 6.5-19.9 mm/s for NA-, IWA-, and RA-based PC and 18.5-22.2, 19.7-23.0, and 20.0-25.1% for the porosity of the corresponding types of mixes. Apparently, the dispersion in the results of hydraulic properties decreased with IWA replacement and increased upon RA replacement, owing to the extent of variability in these aggregates. Similarly, the respective extreme whisker values, signifying the maximum and minimum, were 1-25, 1-13, and 6.5-25.5 mm/s for permeability and 10-27, 12.5-28, and 15-25% for porosity. Based on these whisker values, it is clear that the replacement of NA by other aggregates has limited or no negative impact on the hydraulic performance. In conclusion, IWA seems to be a better replacement for NA than RA with respect to the mechanical performance of PC, thus reducing the amount of landfill sites from industry practices. Although RA exhibits inferior performance compared to NA, it can still  
Figure 9: Variation in (**a**) Compressive strength, (**b**) Tensile strength, (**c**) Flexural strength, (**d**) Permeability, and (**e**) Porosity based on aggregate type (n = number of publications). be used in PC production as it can produce PC with adequate mechanical and hydraulic performance, which could be used in low-traffic pavement applications. Nevertheless, with conflicting results for RA-based PC, more research is needed in the future to confirm their effect on the mechanical and hydraulic performance of PC mixes. Moreover, further studies are required to evaluate the durability properties of PC made with different types of aggregates. Figure 10 shows the different aggregate replacement ratios in PC. While 0% served as a control mix with 100% OPC, partial replacement proportions were 1-10%, 11-20%, 21-30%, 31-40%, 41-50%, and 51-99%, and complete replacement was 100%.