# Meta-Analysis of the Performance of Previous Concrete with Cement and Aggregate Replacements
## 5 Results and Discussion
### Cement Replacement in Pervious Concrete
#### 5.2.1 Alternative Materials
While utilizing SCBA provided inferior mechanical performance--producing PC with a compressive strength of 5.2 MPa [40]--the replacement of cement with FA, SF, and RHA in PC led to superior properties, where PC reached respective strengths of 18.5, 23.8, and 43.5 MPa [4; 18; 36]. However, reduced hydraulic performance was observed in PC with FA and SG, with obtained permeability values of 0.58 and 0.51 mm/s, possibly due to the high fineness of these SCMs [9]. The limited replacement of cement by PR and BC was recommended, as the performance deteriorated with high replacement percentages (>20%) [20; 39]. Studies have explored the replacement of cement with a single replacement material in order to produce PC with superior strength coupled with adequate hydraulic performance as compared to OPC-based PC. A single replacement of FA, SF, and BC improved strength and durability, with no significant influence on the hydraulic performance [17; 29; 39; 40]. While a 5.5% cement replacement by SF improved workability, strength, and durability at a fixed void ratio of 20%, a further increase resulted in inferior workability, strength, and durability [18]. Conversely, reduced strengths coupled with improved hydraulic performance were observed in PR and POFA replacements [8; 20]. Furthermore, binary replacements were explored based on material combination and replacement percentage. SF and BL produced PC with improved strength and durability, while CR and polypropylene fibers had a negative effect on the strength [17]. The binary replacement of SF with MK, PU with NC, SF with NC, RHA with CCW, and FA with MK yielded PC with improved strength  
Figure 3: Distribution of materials used as a replacement for cement in the literature. and durability and with adequate permeability, owing to the micro-filling ability and pozzolanic reactivity of such materials [10; 21; 25; 27; 35]. Contrarily, the binary replacement of FA with SG and CA with RHA produced PC with inferior strength and durability due to the excessive presence of fillers and limited pozzolanic activity [4; 9]. Fibers, including STF, WPF, and MF, slightly influenced the performance of PC [10; 35]. Sintering temperature, NH concentration, aggregate gradation, and cement-aggregate ratio greatly influenced the PC performance with cement replacement [4; 29; 36; 41; 42]. Geopolymer PC produced with SG and MK improved the strength with adequate hydraulic performance [43]. Higher strengths were achieved in PC made with AASC and EAFS, achieving a compressive strength of about 35 MPa [44]. The feasibility of slag-based geopolymer concrete with RM was also explored based on strength and heavy metal absorption. It was deduced that RM has the ability to adsorb heavy metals without compromising the strength [45]. Out of the SCM used in PC, FA and SF were mostly used due to their abundance and pozzolanic behavior. Based on the obtained results, it can be noted that the majority of the SCMs can be utilized in PC production, as the values exceeded the minimum acceptable requirements stated by various transportation authorities [38]. While this is sufficient for its adoption by the industry, it is worth noting that PC mixes incorporating SF, FA, and RHA were superior to counterparts made with OPC only. Similarly, higher strengths coupled with adequate hydraulic performance were reported in geopolymer PC, with AASC exhibiting superior performance, followed by SG and FA. Nevertheless, the combined replacement of cement with fibers and SCMs are seen to produce PC with improved performance. It is clear that partial (single and binary) and complete (geopolymer) replacement have the potential to produce PC with improved mechanical, hydraulic, and durability performance.