## 4 Application Example  
### Case for Blast Loading  
#### 4.1.1 Field Blast Test  
In this section, the AC material is used in the multi-layer pavement. Figure 7 shows the cross-sectional view of the multi-layer pavement slab including 100 mm-thick engineering cementitious composite (ECC) at the bottom, 100 mm-thick high strength concrete (HSC) in the middle and 75 mm-thick AC at the top. The geogrid (GST) was placed at the middle of the AC layer to reinforce the AC material. The numerical model for the multi-layer pavement system under blast load is developed based on the configuration of the full-scale field blast test [23]. Selected key features of the field blast test and numerical model are presented below. In the field blast test, a bomb with the equivalent of a 7.3 kg Trinitrotoluene (TNT) charge weight was selected for testing and placed at about 170 mm above the surface of the pavement. The charge weight was evaluated based on the typical terrorist weapon attack. This multi-layer pavement slab was cast at site with a dimension of 2800 mm \(\times\) 2800 mm \(\times\) 275 mm (width \(\times\) depth \(\times\) thickness). The pavement slab was anchored to the ground to simulate the practical boundary condition, and a vertical anchor was installed at each corner. Figure 8 presents the multi-layer pavement slab before the blast load. Figure 6: Tensile and compressive dynamic increase factor (DIF) curve used in the numerical model for asphalt concrete. Figure 7: Cross-section of the multi-layer pavement slab. HSC, high strength concrete; ECC, engineering cementitious composite. Various instruments were installed onto the slab to measure its responses during blast loading. Figure 9 shows the instrumentation installed on the pavement slab. Four accelerometers were installed at the middle of the side of the slab to measure both vertical (V1 and V2 in Figure 9) and horizontal accelerations (H1 and H2 in Figure 9). The accelerometers were mounted onto steel frames that were cast together with the slab. Three total pressure cells (TPC) (TPC1, TPC 2 and TPC3 in Figure 9) were buried in the soil just below the slab to measure the pressure transferred from the pavement slab. A numerical model is established using LSDYNA package [24]. In this model, the slab and foundation soil are discretised in space with one point Gauss integration eight-node hexahedron Lagrange element. Only a quarter of the slab is modelled with symmetric boundary conditions (as shown in Figure 10). The geogrid is spatially discretised with the shell element, and it is assumed that the geogrid is fully bonded within the AC layer. The anchors on the pavement slab are simulated as the fixed points (fixed in vertical direction) in the corresponding position in the numerical model. The non-reflection boundary is applied on the side and bottom of the foundation soil to model semi-infinite space. Based on the mesh study on the numerical model, the 10-mm element size is adopted for the pavement slab, geogrid and soil mass. The blast pressure is extracted from AUTODYN and used for numerical model analysis. The detailed process of applying pressure to the pavement surface can be referred to elsewhere [20; 25]. Figure 8: Plan view of the multi-layer pavement slab before the blast event. Figure 9: Layout of instrumentation for field blast test. TPC, total pressure cell. In the numerical model, AC, ECC and HSC are all grouped as concrete-like materials and modelled by the KCC model [20, 23]. The basic parameters for these three materials are listed in Table 3. The parameters for AC material in the KCC model can be found in Section 3. While the process of the determination of HSC and ECC parameters for KCC model is the same as that mentioned in Section 3, the detailed parameters can be referred to Wu [20]. The Drucker-Prager model and plastic-kinematic model [17] are employed to model the foundation soil and geogrid, respectively. The AUTOMATIC_SURFACE_TO_SURFACE contact algorithm is employed to model the interaction between pavement slab and soil.