## 3 Fundamental Properties of RP  
### RP Preparation Methods and Equipment  
At present, the recycling of concrete waste into RP involves four distinct phases [38; 85; 86; 87]. During the initial phase, concrete waste is segregated and gathered from CDW. The remaining components of CDW are sorted and recycled through their respective designated pathways. Then, the concrete waste is pulverized into reclaimed materials measuring 0-31.5 mm. The coarse aggregates that have been recycled and have low absorption are used in the preparation of concrete. The fine aggregate and the large particle powder acquired from recycling are commonly employed in the preparation of RP. Nevertheless, the recycled fine aggregate (RFA) and the large particle powder have a significant particle size and a limited reactivity [44; 88; 89; 90], and they are unsuitable for use as an SCM. To employ these two materials as an SCM, it is possible to grind them into fine powders, which are referred to as RP, which allows for the  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Abbreviation** & **Designation** \\ \hline CFs & Concrete fines \\ CSFs & Concrete screening fines \\ CW & Concrete waste \\ CWFs & Concrete waste fines \\ CWP & Concrete waste powder \\ FRC & Fine recycled concrete \\ GCP & Ground concrete powder \\ GRC & Ground recycled concrete \\ GWCP & Ground waste concrete powder \\ HHCW & Humid hardened concrete waste \\ RP & Recycled powder \\ RCFs & Recycled concrete fines \\ RCCFs & Recycled crushed concrete fines \\ RCCFPs & Recycled concrete fines powder \\ RCP & Recycled concrete powder \\ RCWP & Recycled concrete waste powder \\ RFAP & Recycled fine aggregate powder \\ RFP & Recycled fine powder \\ RHCP & Recycled hardened concrete powder \\ RVC & Recycled powder concrete \\ RWC & Recycled waste concrete powder \\ WC & Waste concrete concrete \\ WCFs & Waste concrete fines \\ WCP & Waste concrete powder \\ WCRP & Waste concrete recycled powder \\ WP & Waste powder \\ WPC & Waste powder concrete \\ \hline \hline \end{tabular}
\end{table}
Table 1: Concrete waste-based powders (CDW origin).  
efficient exploitation of CDW [91]. For this purpose, the materials are dried until they reach a constant weight, and then they are ground into RP using grinding equipment. Additionally, the particle size distribution can be enhanced by modifying the type of grinding equipment and the time of grinding [86,87,91].  
The recycled material from crushed CDW can be classified into three distinct forms based on the particle sizes: RCA (5.00-31.5 mm) [38,70,92,93], RFA (0.15 mm-5.00 mm) [94,95,96,], and RP (<0.15 mm) [5,65,78,95,97,98].  
It is worth mentioning that some scholars define the fine particles obtained by a mechanical pre-treatment (crushing, grinding, and sieving) from CDW as RP if the particle size is below 75 \(\upmu\)m [10,32,73,99] and others define it as RP if the particle size is below 150 \(\upmu\)m [44,56,59,71,81,84,100,101,102,103,104,105,106,107,108,109,100,100,101,102,103]. In this study, the term \"RP\" is used to refer to particles with a size smaller than 150 \(\upmu\)m, to encompass a wide range of studies.  
Different grinding equipment can be utilized for the preparation of RP, and the specific type of grinding equipment employed significantly affects the qualities of RP [38]. The microstructure of RP generated by a jet mill exhibits greater regularity compared to that produced by a ball mill.  
The effectiveness of size reduction is affected by various factors, such as the velocity of the mill, the diameter of the balls, the rate at which the mill is filled, the distribution of feed sizes, the density of the pulp, the hardness of the material, the characteristics of dispersion, revolutions per minute, and the method of grinding (wet or dry) [104,105,106,107,108,109,110].