## 1 Introduction
According to the United States Bureau of Reclamation (USBR), a paste-to-mortar ratio of not less than 42% can yield a design compressive strength and direct tensile strength of 11 to 40 MPa and 0.7 to 2.9 MPa, respectively [16; 17]. USACE also studied the relationship between the \(\alpha\) and \(\beta\) values for 12 mixes of (Super-High-Cementitious Roller Compacted Concrete (SHCRCC) to achieve optimized workability. The \(\alpha\) values ranged from 1.5 to 1.9, while the \(\beta\) values ranged from 1.8 to 2.2. When cementitious materials were partially replaced with Stone Powder (SP), the \(\alpha\) value decreased while the \(\beta\) value increased. It was concluded that this condition typically occurs because the proportion of fine aggregates rises and the proportion of coarse aggregates falls as the SP volume increases. As the fine aggregate content increases, the paste volume decreases, leading to a gradual reduction in workability and strength [17]. Beyond basic strength, a modern Roller Compacted Concrete (RCC) mix is defined by its paste-to-mortar (p/m) and sand-to-aggregate (s/a) ratios, Maximum Size of Aggregate (MSA), and modified Vee-Bee time. These factors influence the density, compaction ratio, and material segregation tendency. During construction, these properties determine workability and whether the RCC is permeable with weak planes or cohesive, seamless, watertight, and dense [18]. Interestingly, researchers tend to adopt mineral admixtures in low-cement mixtures to increase paste volume for filling aggregate voids and coating particles to achieve optimizedpaste and mortar margins. However, in mixtures with unprocessed aggregates containing clay and friable particles, these admixtures may not improve long-term strength, especially when high water-to-cement (w/c) ratios are used; therefore, sand containing deleterious fine content (natural particles < 80 \(\upmu\)m) of more than 20% needs to be avoided [19; 20]. To achieve a density of 98.5% in the overall approach of RCC (where the dam body is designed to withstand seepage), as opposed to the separate approach [7] (where a separate layer is designed upstream to manage seepage), a paste-to-mortar ratio of 0.37 needs to be considered. To minimize segregation from the usage of larger aggregates, it is suitable to consider a Maximum Size of Aggregate (MSA) of 37.5 to 40 mm. Additionally, the percentage of aggregate passing the 40 mm sieve should be 80% to 90% [18]. In a cementitious mix with a single-sized aggregate (as shown in Figure 1a), more cementitious paste is needed to fill gaps between fine aggregates and mortar to fill gaps in coarse aggregates to eliminate excess air voids. Using multi-sized aggregate (as shown in Figure 1b,c) reduces the gap volume, lowering the paste and mortar requirement. If the paste and mortar volumes remain constant with multi-sized aggregate, the excess paste and mortar increase, improving workability by coating the particles [21]. Therefore, aggregate grading significantly affects paste and mortar demand and cementitious mix workability, as indicated in Figure 1.  
[PERSON] et al. (2012) indicated during the study of the optimization of conventional concrete by minimizing void volume in the aggregate mixture system that the results emphasized the need for sufficient filler material and cement paste for larger particles to ensure effective binding. Slightly overfilling aggregate voids improves concrete workability and fluidity during casting. Replacing crushed material with sand enhances workability and reduces voids due to the easy slip of smooth, rounded grains. Additionally, slump tests indicated that concretes with optimal aggregate distribution and minimal voids require only a small amount of cementitious paste to achieve the high strength of the material [22]. Compared to Conventional Vibrated Concrete (CVC), a lower sand-to-aggregate ratio of less than 0.35 was optimal for achieving consistency in the RCC mix.