# Meta-Analysis of the Performance of Previous Concrete with Cement and Aggregate Replacements
## 5 Results and Discussion
### Cement Replacement in Pervious Concrete
#### 5.2.2 Performance Evaluation
In conclusion, it can be observed that the replacement of cement generally improved the mechanical properties of PC without any significant change in hydraulic properties as compared to OPC-based PC. The analysis of the durability results is inconclusive due to insufficient data in this area. The effect of cement replacement percentage was also evaluated. Studies were conducted with partial and complete replacements of cement. Figure 5 presents the replacement percentages of cement in the reviewed articles. Partial replacement proportions are categorized as 1-10%, 11-20%, 21-30%, 31-40%, 41-50%, and 51-99%. Complete replacement is designated as 100%, while the control mix has 100% OPC and 0% replacement. Considering each proportion separately, mean values were obtained by dividing all the values of a specific property by the total frequency from all the reviewed studies. The results show that the compressive strengths are not negatively affected by cement replacement, as most mean values were similar to or higher than that of the control. Indeed, the highest mean values were for PC mixes, with 21-30% of the cement replaced with an SCM. Nevertheless, it should be noted that 100% cement replacement was possible without compromising the compressive strength. Moreover, the tensile and flexural strength patterns were similar to that of compressive strength, except that the highest improvement in these properties was when 41-50% and 1-10% of cement was replaced, respectively. Figure 4: Overall performance of PC with different cement replacements based on fixed effect. Nevertheless, it should be noted that none of the investigated studies tested the tensile and flexural strengths of PC made with more than 50% cement replacement. Accordingly, future work is required to evaluate the mechanical properties of such PC mixes. Furthermore, the mean value of the permeability and porosity generally decreased with cement replacement, except for mixes replacing 41-50% and 100% of the cement, as seen in Figure 5. A higher mean value of 41-50% resulted from having fibers incorporated into the mixes, thereby producing more pore spaces at the fiber-binder interface [35]. To conclude, the viable partial cement replacement percentage that maintains the mechanical, hydraulic, and durability properties of PC is within the range of 1-40% while observing the acceptable replacement materials. Meanwhile, complete replacement (100%) of cement by FA or SG in geopolymer PC could also result in comparable performance. The studies were also grouped based on the number of SCMs used in cement replacement, showing the distribution of data. Figure 6a-e show the variation in compressive strength, tensile strength, flexural strength, permeability, and porosity as a function of the number of materials used to replace cement in PC, i.e., zero (cement only), one, and two or more. The respective compressive strength medians of these three types of mixes were 13.7, 16.9, and 14.4 MPa, while those for tensile strength were 2.1, 1.7, and 2.1 MPa. In addition, the flexural strength medians were 1.8, 3.1, and 1.4 MPa, respectively. It can be observed that all the median lines for the strengths lie approximately at the center of the box, except for flexural strength, signifying that the values are normally distributed. Similarly, median lines within the boxplots indicate little difference in performance between the PC mixes across different studies. The respective interquartile for compressive strength of the three types of mixes (0, 1, and 2 replacement materials) were 7-20, 9-24, and 10-21 MPa, and those for tensile strength were 1.4-2.3, 1.0-2.1, and 1.5-3.0 MPa, while the flexural strength medians were 1.1-2.5, 2.8-3.3, and 1.2-3.1 MPa, respectively. The ranges show that the values were less dispersed for the 50% middle interquartile, indicating that PC with and without cement replacement exhibit similar mechanical performance regardless of the type and number of replacement materials used.