## 2 Methodology
### Curing Schemes and Field Test Procedure  
According to recent specifications [21; 22] published by China Railway Corp., the minimum time of wet-curing with compound geotextile for CRTS III base plate is 14 days. Hence, a standardized curing regime adopted by most railway construction enterprises includes a 14-day wet curing period and subsequent sealed curing for a few days. However, it is believed that the optimum curing scheme can reduce early-age transverse cracking, which is the motivation of the current research investigation. The test site is located in Tianjin, China. A total of eight full-size, cast-in-place concrete base plates were constructed in cold seasons and divided into four test series, as shown in Figure 3 and Table 1. During the tested days, the daily maximum temperature was 18.5 \({}^{\circ}\)C, and the daily minimum temperature was \(-\)15 \({}^{\circ}\)C. For the base plates in Series I, the curing stage consisted of a 14-day wet curing period and a subsequent 6-day sealed curing period. It is almost a standardized curing regime adopted in construction practice. Compound geotextile covers were used during wet and sealed curing. It has a double-layer structure formed by an outer geotextile layer and an inner polyethylene film; thus, it can stably retain high humidity by maintaining concrete. However, as noted above, early transverse cracks often occurred under this curing regime (Series I). In Series II and III, the duration of sealed curing was prolonged to 31 days and 106 days, respectively. In Series IV, after 3 days of casting, two layers of cotton quilts were covered on the top of the geotextile cover in order to enhance temperature preservation effects. Figure 2: The arrangement of VWSG: (**a**) on the plane and (**b**) in depth direction. The procedure of in-site CRTS III base plate construction is shown in Figure 4. This base plate was designed to be reinforced with a 250 mm \(\times\) 250 mm steel bar mesh at the top and bottom layers. The concrete cover to the top and bottom meshes of reinforcement was 50 mm thick. Prior to concrete casting, the two layers of steel mesh were placed on the bridge foundation, which facilitated the positioning of the strain gauges to the desired locations. The top, middle, and bottom VWSGs were instrumented at depths of 25, 100, and 175 mm from the top surface of the base plate (Figure 4a). All these plates were cast (Figure 4b) on 9 November 2020 by using the same concrete mixture proportion presented in Table 2. The slump of fresh concrete was maintained in the range of 120 to 160 mm for ease of casting and consolidation. Wet-curing was initiated after the final set of the concrete. After 10 h of casting, a sheet of compound geotextile was used to cover the top surfaces of these base plates (Figure 4c). Three days later, the steel side formwork was removed. The side surfaces of the plates were covered with the same geotextile in order to avoid, as much as possible, any water loss from its sides. All these concrete base plates were cured under water-saturated geotextile cover for 14 days (Figure 4d), followed by a period of sealed curing that corresponded to a curing condition in the absence of external water sources (Figure 4e). After the sealed curing period (note that the duration of this period varied among the different test series), the base plates were exposed to the natural environment directly (Figure 4f). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Test** & **Plate** & **Wet-Curing** & **Sealed-Curing** & **Total Curing** & **Covering Materials used in** \\
**Series** & **Quantity** & **Time (Days)** & **Time (Days)** & **Time (Days)** & **the Curing Period** \\ \hline I & 2 & 14 & 6 & 20 & composite geotextile \\ \hline II & 2 & 14 & 31 & 45 & composite geotextile \\ \hline III & 2 & 14 & 106 & 120 & composite geotextile \\ \hline IV & 2 & 14 & 106 & 120 & composite geotextile + quit \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Curing regimes adopted in the field test. Figure 3: Curing regimes adopted in the field test.