## 2 Experimental Process/Program  
### Development of UHPC  
#### 2.1.1 Materials  
In the current research, ordinary Portland cement (PC) that satisfied the ASTM C 150 requirements was used to develop the UHPC, while silica fume (SF) and fly ash (FA, class F) were used as binders. The physicochemical properties of these types of cement are presented in Table 1. Moreover, two kinds of locally available natural desert sands identified as red sand (RS) and white sand (WS) were employed as the UHPC fine aggregates. Table 2 lists the physical characteristics of the RS and WS, and Figure 1 provides the particle size distribution of PC, SF, FA, RS, and WS.  
Additionally, microstreed smooth fibers with three different lengths (F1, F2, and F3) were employed to reinforce the UHPC. Figure 2 and Table 3 present the geometrical and physicochemical properties of these fibers, respectively. It is worth noting that the  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Oxides (\%)** & **PC** & **FA** & **SF** \\ \hline SiO\({}_{2}\) & 20.41 & 55.23 & 86.20 \\ Al\({}_{2}\)O\({}_{3}\) & 5.32 & 25.95 & 0.49 \\ Fe\({}_{2}\)O\({}_{3}\) & 4.10 & 10.17 & 3.79 \\ CaO & 64.14 & 1.32 & 2.19 \\ MgO & 0.71 & 0.31 & 1.31 \\ SO\({}_{3}\) & 2.44 & 0.18 & 0.74 \\ TiO\({}_{2}\) & 0.30 & - & - \\ Na\({}_{2}\)Oeq & 0.10 & 0.86 & 2.80 \\ L.O.I. & 2.18 & 5.00 & 2.48 \\ Relative density & 3.15 & 2.70 & 2.20 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Physicochemical properties of PC and SCMs.  
Figure 1: Grain size distribution of (**a**) types of cement and (**b**) aggregates.  
cementitious matrix is bonded strongly to the nonsmooth fibers. Their presence will, however, be limited as an increased amount normally hinders workability due to the snatching effect with the fresh matrix, which adversely affects rheology. As a consequence, the sharpness of the protrusion on the surface has a significant effect on the rheological properties of UHPC. A feasible alternative here would be to use smooth microsteel fibers.  
In this investigation, UHPC was designed by applying an optimization process to the concrete's packing constituents. This process was performed by applying the modified Andreassen model [Equation (1)] [40; 41; 42; 43] along with experimental observations of the fresh and hardened properties of UHPC--namely, flowability, compressive, and flexural strength tests. In Equation (2), CPFT is the cumulative (volume) percentage finer than, \(d\) is the particle size, \(d_{o}\) is the smaller particle size, \(D\) is the maximum particle size, and \(q\) is the modulus of distribution (an exponent that generally ranges from 0.21 to 0.37, depending upon the workability conditions [44]). Notably, the introduction of fibers could cause workability issues. Therefore, self-compacting UHPC was developed. For this purpose, a polycarbonate ether-based superplasticizer (commercially known as Master Glenium 51, SP) was utilized. The unit weight and water content of the SP were 1080 kg/m\({}^{3}\) and 65.19%, respectively. Table 4 presents the optimized constituent components of the UHPC. Moreover, the SP's water content and aggregate absorption of water were taken into consideration when calculating the UHPC's mixing water.  
\[\text{CPFT}=100\bigg{(}\frac{d-d_{o}}{D-d_{o}}\bigg{)}^{q} \tag{1}\]