## 2 Materials and Methods
### Mix Proportions and Test Specim Preparation  
This study adopted the specifications of the American Association of State Highway and Transportation Officials, the Road Traffic Bureau of each state in the United States, and the Korea Expressway Corporation for repairing pavement using rapid-set cement [19; 20]. The standards specify a traffic opening time of 4 h, at which point the material must reach a compressive strength of at least 21 MPa and a flexural strength of at least 3.5 MPa. Furthermore, these specifications require a minimum compressive strength of 35 MPa, a flexural strength of 4.5 MPa, and a splitting tensile strength of 4.2 MPa after 28 days of curing. Permeability, which strongly affects pavement service lifetime in terms of durability, was evaluated according to the ASTM C1202 chloride ion penetration test [21]. The acceptance criterion for permeability was a maximum of 2000 coulombs after 28 days of curing, as recommended by the Korea Expressway Corporation. Moreover, the durability acceptance criterion was a relative dynamic modulus of 80% or higher after 300 freeze-thaw cycles. The mix proportions of latex-modified rapid-set cement preplaced concretes containing single fiber types or hybrid fiber mixtures are provided in Table 5. Rapid-set cement was used at 400 kg/m\({}^{3}\) per mixture. The deployment of hybrid fiber-reinforced latex-modified rapid-set cement preplaced concrete (HFLMC) involves the use of a pressurized vibrating compactor. However, filling the voids in a coarse aggregate is only possible if the HFLMC has sufficient fluidity. Therefore, pressurized vibration compaction was used together with a rapid-set cement mortar with sufficient fluidity to allow self-leveling. Latex was added at a 15% weight ratio to rapid-set cement to ensure fluidity upon compaction. A water-cement ratio of 0.28 was applied. Fibers (single or hybrid mixtures) were added at a rate of 1.2 kg/m\({}^{3}\).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Properties** & **Jute Fiber** & **PVA Fiber** & **Nylon Fiber** \\ \hline Elastic modulus (GPa) & 61 & 45 & 35 \\ \hline Tensile strength (MPa) & 510 & 1600 & 800 \\ \hline Density (g/mm\({}^{3}\)) & 1.26 & 1.26 & 1.16 \\ \hline Fiber length (mm) & 6 & 3 & 3 \\ \hline Fiber diameter (mm) & 0.015 & 0.015 & 0.023 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Fiber properties.  
Figure 1: Type of fibers. (**a**) Jute fiber. (**b**) PVA fiber. (**c**) Nylon fiber.  
The specimen dimensions for testing mechanical properties and durability were as follows: cylindrical specimens measuring \(\mathcal{O}100\)\(\times\)\(200\) mm were used for compressive strength, splitting tensile strength, and chloride ion penetration tests; prism-shaped specimens with dimensions of 100 \(\times\) 100 \(\times\) 400 mm were used for flexural strength and freeze-thawing testing, and cylindrical specimens measuring \(\mathcal{O}150\)\(\times\) 150 mm were used in abrasion tests. Figure 2 shows the manufacturing process for HFLMC specimens. First, molds were filled with coarse aggregate (Figure 2a). Second, water, rapid-set cement, sand, latex, and fiber were mixed in a mixer for 1.5 min and then poured into a mold containing the coarse aggregate (Figure 2b). Finally, the surface of the specimen was compacted using a special vibratory press compactor (Figure 2c). Figure 2d shows manufactured compression and flexural strength specimens. Vibratory press compaction ensured that the latex-modified rapid-set cement material filled the voids in the coarse aggregate. No signs of insufficient compaction, such as persistent voids, were observed. In addition, no material separation of fibers from the latex-modified rapid-set cement was observed.