# 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  
Figure 3 shows the materials that have been investigated to replace cement in PC production. These include fly ash (FA), silica fume (SF), palm oil fuel ash (POFA), slag cement (SG), sugarcane bagasse ash (SCBA), palm jaggery (PR), pumice (PU), biochar (BC), coal ash (CA), latex (LX), crumb rubber (CR), butadiene latex (BL), rubber fiber (RF), nano clay (NC), rice husk ash (RHA), metakaoin (MK), nanoparticles (NP), and fibers (FB). Among these materials, both FA and SF appeared in 15% of the reviewed articles as a replacement for cement. This finding is primarily due to their global abundance, availability, and pozzolanic behavior when incorporated into the concrete mixture [21; 27]. While FA is an amorphous industrial by-product of coal power plants with a surface area of 0.6-0.7 m\({}^{2}\)/g, SF is a non-crystalline by-product of silicon, comprising amorphous silicon dioxide with a surface area of 15-25 m\({}^{2}\)/g [18]. PC mixes incorporating FA as a partial replacement for cement, in binary or ternary form, exhibited comparable and superior properties to counterparts made with OPC as the sole binder [28]. An increase of about 59% in compressive strength was observed in the PC with 15% FA and 2% MK as compared to the PC with OPC. Meanwhile, comparable hydraulic performance was reported [27]. A 29% improvement in strength was reported in PC mixes with FA at C/A of (0.20-0.24), signifying the potential utilization of FA in PC without compromising performance [29]. Alternatively, reduced mechanical strengths coupled with enhanced hydraulic properties were noted for PC with FA, which were due to the porous nature of the aggregates used [30]. Moreover, most of the PC produced with an FA (single or binary) geopolymeric binder achieved satisfactory mechanical properties. This is evident in FA geopolymer concrete, where improved strength was observed at later ages compared to OPC-based PC [5; 31]. Additionally, PC with SF showed higher compressive and flexural strengths than OPC-based PC as well as an improved removal efficiency of heavy metals without undermining permeability and abrasion resistance. A 29% increase in strength coupled with a 9% increase in hydraulic performance was observed in the PC with SF. Furthermore, heavy metal concentrations in the PC with SF were reduced, including Cu, Pb, and Zn, with respective reductions of 56%, 67%, and 93% compared to the PC with OPC [18; 19; 21]. The inclusion of SF in PC also improved the strength without any significant change in the hydraulic properties [32]. Fibers (FB), including RF, STF, WPF, and LX, have also been incorporated into the PC mix design to improve its mechanical properties. Nearly 8% of the reviewed papers investigated the use of fibers in PC as a replacement for cement. Experimental findings reported superior compressive, tensile, and flexural strengths but inferior workability than the plain, non-reinforced counterparts [10; 33; 34; 35]. Similarly, NP was used in PC to improve its mechanical properties through the filling effect of the particles and good abrasion resistance, as noted in several studies [36; 37]. The remaining materials had been employed in limited studies to replace cement in PC. Their main aim was to improve/maintain the mechanical and hydraulic properties of PC regardless of the replacement [9; 18]. More details are given on this subject in later sections. The viable cement replacements with other materials were selected to satisfy the minimum strength and permeability requirements of PC as per international standards and regulations [38]. In summary, the practicable replacements for the investigated SCMs were found to be 20% for FA, 10% for SF, 10% for RHA, 10% for MK, 6.5% for BC, 10% for CCW, 0.05% for PR, 25% for PU, and 20% for POFA [8; 20; 21; 25; 29; 34; 39].