## 2 Research Design and Testing Plan
### Testing Plan  
Portland cement Type I served as the primary cementitious material, river sand with a unit weight of 2.62 \(\pm\) 0.1 kg/cm\({}^{3}\) was adopted as the fine aggregate, and crushed stone with a unit weight of 2.60 \(\pm\) 0.1 kg/cm\({}^{3}\) was used as the coarse aggregate. All aggregates were washed before being mixed. Test parameters included mixture proportion and pozzolanic material admixture; an appropriate amount of superplasticizer was also added to sustain workability. Cylindrical concrete specimens as shown in Figure 1 with dimensions of 10 cm (D) \(\times\) 20 cm (H) were used in this study. They were all placed in water at 23 \({}^{\circ}\)C for curing and taken out for measurement. Excess moisture on the surface was wiped away using a dry cloth to ensure that the specimens were dry outside but saturated inside (ASTM C128 [21]). ASTM C597 [22] and ASTM C39 [23] methods were then employed to obtain the UPV and compressive strength of the concrete specimens, respectively. Through a direct transmission mode, UPV was measured by a commercially available pulse meter with an associated transducer pair. The transducer pair had a nominal frequency of 54 kHz, which was relatively low compared to other ultrasonic applications and suitable for concrete. The principle of ultrasonic pulse velocity measurement involves sending a wave pulse into concrete and measuring the travel time for the pulse to propagate through the concrete. Knowing the path length, the measured travel time can be used to calculate the pulse velocity. In this study, concrete that had a volume fraction of cement paste of 36% (V\({}_{\text{paste}}\)) and had a sand-to-aggregate ratio (S/A) of 45% was used as the main research subject. The S/A refers to the percentage of fine aggregate in relation to the total aggregate weight. Variations were then introduced to this mixture proportion to investigate the effect of various factors on the relationship between UPV and the strength evolution index. Table 1 presents the mixture proportions of concrete specimens that comprised normal Portland cement (V\({}_{\text{paste}}\) = 36%, S/A = 45%) and had water-to-cementitious-material ratios (w/cem) ranging from 0.3-0.7. The specimens were numbered NC1 to NC5 to serve as a reference for establishing the relationship between UPV and the strength evolution index. Subsequently, to clarify the effect of various coarse-aggregate-to-fine-aggregate content proportions under a fixed paste volume ratio, the concrete mixture proportions listed in Table 2 were adopted. Specimens numbered NC6-NC20 had w/cem ranging from 0.3-0.7, a fixed V\({}_{\text{paste}}\) of 36%, and S/A of 30, 45 and 60%. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**No**} & \multirow{2}{*}{**w/cem**} & \multirow{2}{*}{\begin{tabular}{c} **S/A** \\ **(\%)** \\ \end{tabular} } & \multicolumn{6}{c}{**Mixture Proportion, kg/m\({}^{3}\)**} \\ \cline{4-9}  & & & \
\begin{tabular}{c} **V\({}_{\text{paste}}\)** \\ **(\%)** \\ \end{tabular} & **Water** & **Cement** & **Super-Plasticizer** & **Fine Aggregate** &
\begin{tabular}{c} **Coarse Aggregate** \\ **(Type 1)** \\ \end{tabular} \\ \hline NC1 & 0.3 & & & & 164 & 583 & 10.90 & & \\ NC2 & 0.4 & & & 193 & 502 & 7.25 & & \\ NC3 & 0.5 & & & 218 & 440 & 2.66 & 737 & 908 \\ NC4 & 0.6 & & & & 234 & 392 & 1.00 & & \\ NC5 & 0.7 & & & 248 & 354 & 0.00 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mixture proportions adopted to establish the reference relationship curve between UPV and the strength evolution index. Figure 1: Cylindrical concrete specimens. Tables 3 and 4 present the concrete mixture proportions containing pozzolanic materials. As indicated in Table 3, fly ash replaces cement at a ratio of 15% and two V\({}_{\text{paste}}\), 36 and 42%, were adopted; the specimens were labeled FC1-FC5. As seen in Table 4, slag replaces cement at a ratio of 30% and the two V\({}_{\text{paste}}\) of 36 and 42% were adopted; the specimens were labeled SC1-SC10.