# Meta-Analysis of the Performance of Previous Concrete with Cement and Aggregate Replacements
## 5 Results and Discussion  
### Evaluated Properties of Previous Concrete  
The performance of PC is assessed by its engineering properties, including its mechanical, hydraulic, and durability properties. Generally, the parameters used for mechanical performance evaluation are compressive, tensile, and flexural strengths at ages of up to 28 days. The hydraulic performance of concrete is its capacity to allow the passage of water and air to a certain degree without undermining its mechanical and durability performance [17]. Permeability and porosity are the main parameters used in evaluating the hydraulic performance of concrete [15]. Furthermore, the durability of concrete is its ability to resist long-term weathering, chemical attacks, and abrasion while maintaining mechanical and hydraulic properties. The different durability properties relevant to PC include, but are not limited to, skid resistance, sound absorption capacity, clogging potential, freeze-thaw resistance, and abrasion resistance.  
Figure 2 shows the number of articles that considered the three categories for evaluating the performance of PC, i.e., mechanical, hydraulic, and durability. Of the various properties, 16 have been examined in PC manufactured with cement and aggregate replacements. In the first category, the mechanical properties comprise compressive strength, unit weight/density, flexural strength, tensile strength, and elastic modulus. At least 35 of the reviewed articles examined these properties, except for the elastic modulus. The most evaluated property was compressive strength, owing to its ease of testing and use as an indication of the general quality of the PC. This also emphasizes the abundance of research conducted to investigate the mechanical performance of PC while highlighting the need for more studies on the elastic modulus.  
Figure 2: Number of studies conducted on the examination of various PC properties.  
In the second category, the hydraulic properties encompass permeability and porosity. These were assessed by 37 and 41 of the reviewed articles, representing 67 and 75% of the total relevant studies, respectively. Indeed, the direct relationship between porosity and permeability justifies the comparable number of articles examining each property. The importance of such properties in PC also explains the high percentage of articles that have evaluated them.  
The third category on the durability properties includes abrasion resistance, thermal conductivity, freeze-thaw resistance, sound absorption, clogging potential, pull-off resistance, carbonation resistance, and alkali-silica reaction. Only 11% of the relevant studies assessed the durability properties of the produced PC, with the focus mainly being on evaluating the abrasion resistance. This focus on abrasion resistance was probably due to the interest in assessing the extent of raveling on the surface of the PC [10; 18; 25; 26]. Less interest was paid towards the remaining durability properties. In conclusion, most studies on PC made with cement and/or aggregate replacements focused on compressive strength for mechanical performance evaluation, coupled with permeability and porosity in order to evaluate hydraulic performance. Nevertheless, more work is needed to assess the durability performance of PC in order to ensure its reliability and long-term endurance for stakeholders and to promote its adoption by the pavement industry.