# Shear Properties of the Interface Between Polyurethane Concrete and Normal Concrete
## 3 Results
### Shear Failure Modes  
As shown in Table 6, the ultimate shear strength at the interface indicates that the roughened group (ZM) exhibits a high interface shear performance due to its increased interface roughness. The bonding agent application group (NJJ) ranks second in terms of bond strength between interfaces, followed by the steel fiber addition group (GXW). The grooved group (KC) demonstrates the lowest shear resistance, with varying bond strengths within the groups due to different treatment extents. Figure 6 presents the shear failure modes at the interface for untreated (GH), roughened (ZM), and grooved (KC) specimens. The left-hand side of the shear failure surface corresponds to the PUC portion, while the right-hand side corresponds to the NC portion. For the untreated GH specimens, the failure mode is characterized by interface failure (Type A), where the bonding interface is relatively smooth, resulting in complete separation between PUC and NC as shown in Figure 6a. Figure 6b-d show the shear failure modes of the ZM group. The failure mode of ZM-2 is similar to the GH group, with only a small amount of NC adhering to the interface. In contrast, ZM-3.5 and ZM-5 specimens exhibit PUC interface failure and a combination of interface failure (A/B), where the residual PUC and NC portions remain bonded at the interface, with some PUC delaminating, while  
Figure 5: Failure modes at the bond interface of PUC–NC composite specimens. the NC portion remains undamaged and the shear surface is flat. As the roughening depth increases, the bonding depth becomes greater. This is primarily due to the influence of interface roughness, where rougher interfaces result in stronger bonding and deeper bonding penetration. Figure 6e,f depict the shear failure modes for the KC group. As the grooving depth increases, the failure mode transitions from interface failure (Type A) to a combination of PUC failure and interface failure (A/B), with slight remnants of PUC within the grooves, while the NC portion remains smooth. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample Number** & \(\mathbf{P_{u}}\) **(kN)** & \(\mathbf{S_{0.7 Pu}}\) **(mm)** & **Failure Mode** \\ \hline GH & 31.92 & 0.093 & A \\ ZM-2 & 84.03 & 0.191 & A \\ ZM-3.5 & 105.64 & 0.236 & A/B \\ ZM-5 & 96.68 & 0.276 & A/B \\ \hline KC-2 & 38.90 & 0.082 & A \\ KC-3.5 & 26.38 & 0.144 & A \\ KC-5 & 30.44 & 0.057 & B \\ \hline NJJ-1 & 66.85 & 0.161 & A/C \\ NJJ-1.5 & 87.08 & 0.190 & A/C \\ NJJ-3 & 76.92 & 0.145 & D \\ NJJ-5 & 74.34 & 0.200 & D \\ NJJ-8 & 63.22 & 0.222 & D \\ NJJ-10 & 70.98 & 0.208 & D \\ \hline GXW-2 & 55.11 & 0.207 & A/C \\ GXW-4 & 61.01 & 0.156 & A/C \\ GXW-6 & 34.61 & 0.463 & C \\ \hline \hline \end{tabular} Note: P\({}_{u}\) and S\({}_{0.7 Pu}\) represent the ultimate load and the corresponding strain.  
\end{table} 
Table 6: Summary of oblique shear test results. Figure 6: Shear failure interfaces under different surface treatments: (**a**) untreated (GH); (**b–d**) grooved group (ZM); (**e–g**) notched group (KC). Figure 7 illustrates the failure modes for specimens with a low steel fiber content (GXW-2 and GXW-4), where the failure mode is classified as (A/C), with a relatively flat shear failure surface and minimal NC adhesion. As the steel fiber content increases, the GXW-6 group exhibits a failure mode where polyurethane partially adheres to a substantial amount of NC matrix or aggregate. The NC portion shows exposed sand and gravel, with a roughened surface, transitioning to a NC failure mode (C), as shown in Figure 7c. Figure 8 shows the shear failure modes for the bonding agent application group (NJJ). When the application amount of the bonding agent is low (NJJ-1 and NJJ-1.5), the failure mode is characterized by interface failure and NC failure (A/C), with NC delamination. As the amount of bonding agent increases, the shear failure mode gradually transitions from interface failure to a mixed failure (D), with deeper bonding and an increasing bonding area.