## 3 Cracking Behavior of CRCP Sections in Belgium  
Since 1970, Belgium has been using the CRCP concept to construct motorways. To achieve a desirable crack spacing pattern, the standard design concept for CRCP in Belgium has been modified over the years, as demonstrated in Table 1[12; 13; 20; 21; 22; 23; 44]. However, the cluster crack formations and associated distresses could not be effectively eliminated. The field observations of cracking development on the CRCP sections without an active crack control method on the E17 Motorway in Belgium exhibited the randomly occurring transverse crack pattern with a higher percentage of closely spaced cracks, as shown in Figure 3. It was also observed that this passive nature of crack induction was one of the main contributing factors towards the development of punch-out and spalling in CRCP sections [12; 13; 20; 44]. \begin{table}
\begin{tabular}{c c c c} \hline
**Design Concept** & **Concept 1** & **Concept 2** & **Concept 3** \\ \hline Time period & 1970–1981 & 1981–1995 & 1995–onwards \\ Longitudinal reinforcement & 0.85\% (\(\mathcal{O}\)18@150 mm) & 0.67\% (\(\mathcal{O}\)16@150 mm) & 0.75\% (\(\mathcal{O}\)20@170 mm) \\ Cover depth & 60 mm & 90 mm & 80 mm \\ Slab thickness & 200 mm & 200 mm & 230/250 mm \\ Asphalt interlayer & Yes, 60 mm & No & Yes, 50 mm \\ \hline \end{tabular}
\end{table} 
Table 1: Overview of design concepts for continuously reinforced concrete pavement (CRCP) in Belgium. Figure 3: Passive crack development on the Motorway E17 section. Figure 2: Cracking development in advanced reinforced concrete pavement (ARCP) with (**a**) partial length steel bars and (**b**) continuous steel bar. To eliminate the potential risk of the punch-out development associated with the clusters of closely spaced cracks in CRCP, the transverse partial surface saw-cuts as a crack induction method was proposed for Belgian conditions [13]. This method was applied to the CRCP sections in the reconstruction project of Motorway E313 in Belgium. In this project, two saw-cut depths of 30 mm and 60 mm were used to evaluate the effect of notch-depth on the cracking characteristics of active crack control CRCP sections. Partial surface saw-cuts were made at the edge of the outer pavement lane within 24 h after the concrete placement [12; 13], as shown in Figure 4. More details related to the construction of both motorways are represented in the literature [12]. Regular surveys of crack developments on the active crack control CRCP sections were conducted right after the construction without considering the traffic load. It was observed that cracks initiated exactly from the tips of partial surface saw-cuts and propagated along the width of the concrete slab, as illustrated in Figure 5. A desirable crack pattern with uniform crack spacing was observed [12; 13]. To evaluate the effectiveness of partial surface saw-cuts to induce cracks over the designated locations of the concrete slab, the observed crack patterns of these test sections were compared with those of CRCP sections on Motorway E17 in Belgium. Field investigation indicated that the CRCP sections on Motorway E17 (passive crack control sections) experienced the punch-out development more than those on Motorway E313 (active crack control sections) [12; 20; 44]. The majority of punch-out formations and concrete spalling over the surface of the pavement slab were triggered by the cluster of closely spaced crack patterns, as illustrated in Figure 3.  
The survey results of crack developments on the CRCP sections of Motorway E313 are demonstrated in Table 2. For the CRCP sections with deeper saw-cut (60 mm), all the observed cracks were induced from notches during the initial days after construction, as shown in Figure 5. As can clearly be observed in Table 2, about 78.6% of cracks were initiated from notches after a period of two months. Meanwhile, the shallower saw-cut CRCP sections exhibited this value equal to 56.5% [12; 13].