## 3 Numerical Simulation of Early-Age Behaviour of Small Specimens to Actual Rc Deck Slabs
### Experimental Outline and Model Validation via Small-Scale Specimens (Decimetres)
#### 3.2.3 Influence of Curing Conditions on Concrete  
The use of a high-performance mix design as such requires a study on the curing period to determine the optimum choice for execution without being vulnerable to cracking risk. Thus, referring to Figure 10, five 100 \(\times\) 100 \(\times\) 400 mm\({}^{3}\) prismatic plain concrete specimens were prepared with five different curing periods (7, 14, 28, 56 and 91 days) before exposure to the environment of the control chamber (a constant 20 \({}^{\circ}\)C and 60% relative humidity). The mix design of these specimens was BFS44 (Table 2). Figure 11 shows the finite element of the prismatic specimens whereby the boundary conditions are applied in the same manner as that of previous cases. Unlike OPC concrete, the use of a low water-to-cement ratio as such in BFS concrete allows autogenous shrinkage to play a predominant role, on par with that of drying shrinkage, in determining the properties of the concrete. Thus, to properly capture the autogenous and drying shrinkage of BFS concrete, the driving force of shrinkage in the model is divided into two entities: capillary tension force and disjoining pressure. The former, which dominates the nanoscale pores, is of paramount significance under low relative humidity, but the latter, which governs the microscale pores, contributes significantly with a high relative humidity [6]. The applicability of the BFS model in actual specimens exposed to various curing durations would also be confirmed through this model validation.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Series**} & \multirow{2}{*}{**w/b (\%)**} & \multirow{2}{*}{**Air (\%)**} & \multicolumn{6}{c}{**Unit Proportion (kg/m\({}^{3}\))**} \\ \cline{3-8}  & & & **W** & **C** & **Ex** & **S** & **G** & **Ad** \\ \hline OPC53 & 52.9 & 4.5 & 166 & 314 & - & 802 & 1044 & 3.14 \\ OPC44 & 44 & 6 & 164 & 353 & 20 & 653 & 1112 & 2.24 \\ BFS44 & 44 & 6 & 160 & 344 & 20 & 662 & 1112 & 2.18 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Trial mixture designs of potential concrete to be used for Shinkesen Bridge deck.  
Figure 8: Environmental condition after 28 days of seal-curing.  
Figure 9: Compressive strength of concrete (M-Measured and A-Analytical).  
The trend of the analytical results shown in Figure 11 could be acceptable in terms of strain prediction despite some discrepancies, especially during the sealing period. Our current expansive additive model would only apply instantaneous expansive strain to concrete without consideration of its long-term effect, whereby complete expansion could continue to at least a week [14]. Although, to provide better accuracy in predicting strain at an early stage for cases in which expansive additives are applied, the authors aim to investigate the issue and develop a more sophisticated model. Because the most prevalent forms of cracks, that is, thermal and shrinkage-induced cracks, are more likely to occur after the curing period, the minimal variation during the sealing condition could be reasonably disregarded. Therefore, it could be concluded that the overall trend and strain value of concrete under seal-curing conditions could be acceptably traced.