## 5 Parametric Study
### Effect of Saw-Cut Depth on Early-Age Crack Induction  
CRCP is known for its random cracking at the early-age. The elimination of randomness in an early-age crack pattern of CRCP has been a point of research interest among the researchers for a long time. The previous field studies have revealed that the early-age behavior of CRCP significantly influences its long-term performance [5; 6; 9; 12; 13; 14; 22]. The primary factor affecting the development of early-age cracking in CRCP is the resistance to the change of length of the concrete slab [20]. In Belgium, the active crack control CRCP test sections exhibited the crack induction over the saw-cut tips which ultimately led to the development of a regular spaced crack pattern in comparison to the passive crack control sections. The crack induction over the saw-cut tips is explained with respect to the development of maximum concrete tensile stress along the length of the concrete slab. As shown in Figure 11, among different saw-cuts, the deeper saw-cut exhibits the largest maximum concrete tensile stress by taking an advantage of deeper cut-depth into the concrete slab. Regular crack survey of active crack control E313 test sections revealed that there was a much more regular crack pattern in CRCP sections with deeper partial surface notches [12; 22]. However, the potential risk of steel corrosion would be significantly increased when the saw-cut will be made deeper into the concrete slab as the steel is being placed at a depth of 80 mm from the pavement surface in accordance with the current design concept for CRCPs in Belgium. Preventive measures would be required to minimize the accumulation of dust particles and the water infiltration through the cracks into the steel of the pavement slab. The 3 rd longitudinal steel bar from the outer end of the concrete slab just ahead of saw-cut tips is selected for comparison purposes. The development of maximum stress along the length of the steel bar for each saw-cut depth is depicted in Figure 12. As expected, the deeper saw-cut induces the largest maximum steel stress exactly over the saw-cut tips where the concrete tensile stress is maximum in comparison to the rest of the bar length. It  
Figure 11: Comparison of maximum concrete tensile stress over the saw-cut tips along the length of concrete slab for different saw-cut depths. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**No.** & **Saw-Cut Type** & **Depth, D (mm)** & **Length, L (mm)** & **Width (mm)** \\ \hline
1 & Shallower & 20 & 400 & 4 \\
2 & Conventional & 40 & 400 & 4 \\
3 & Deeper & 60 & 400 & 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Type of saw-cut based on cut-depth. may translate that the deeper the cut-depth, the larger the concrete tensile stress, and the greater the incidence of cracking. These findings compare well with the field observation of crack developments on the CRCP sections of the Motorway E31 [12; 22]. Therefore, it can be expected that the application of deeper saw-cuts could effectively serve the original intention of the active crack control method for CRCP to induce cracks from the designated locations (saw-cut tips) of the concrete slab. This may lead to the elimination of randomness in an early-age crack pattern which is considered as one of the main contributing factors to the development of fatal distresses such as punch-outs and spalling in CRCP. The development of crack strain over the saw-cut tips with respect to time is depicted in Figure 13. It can clearly be observed that the deeper the saw-cut depth, the larger the crack strains. This could be the possible reason that the deeper saw-cut exhibits the larger crack strain by taking an advantage of the volumetric changes to the larger depth of the concrete slab. It was also reported that the deeper saw-cut depth on the E313 section remained quite effective in inducing new cracks even in the later age of CRCP in Belgium [12; 22]. Figure 12: Comparison of maximum steel stress over along the length of the longitudinal steel bar for different saw-cut depths.