# Shear Properties of the Interface Between Polyurethane Concrete and Normal Concrete
## 2 Materials and Methods
### Preparation of Specimens  
#### 2.2.1 Treatment of Concrete Roughness  
As shown in Figure 1, both the PUC and NC layers had a thickness of 50 mm. A total of 7 sets of shear test models were prepared, based on different interface treatment methods for NC. These included one smooth surface group, three roughened surface groups with depths of 2 mm, 3.5 mm, and 5 mm, and three grooved surface groups with groove depths of 2 mm, 3.5 mm, and 5 mm. Additionally, 3 groups of PUC were prepared with different mass fractions of steel fibers (2%, 4%, and 6% of the total solid mass). The PUC-NC interface was treated with adhesive in 6 different amounts (1 g, 1.5 g, 3 g, 5 g, 8 g, and 10 g). In total, 16 sets of models, consisting of 48 shear test specimens (3 specimens per group), were fabricated. The interface bonding agent was prepared by mixing Parts 1 and 2 in a 1:1 mass ratio.  
\begin{table}
\begin{tabular}{c c c} \hline
**Component** & **Main Chemical Compositions** & **Mixing Mass Ratio/(kg)** \\ \hline Part 1 & 90\% polyether polyols and 10\% chain & 1 \\  & & extender crosslinkers & \\ \hline Part 2 & MDI-based isocyanate group & 1 \\ \hline Part 3 & Stone and cement & 5:1 \\ \hline Part 4 & Molecular sieve activated powder & 0.3 \\ \hline \end{tabular}
\end{table}
Table 1: Chemical composition of PUC.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Density** & **Initial Setting** & **Final Setting Time** & **Compressive Strength at** & **Compressive Strength at** \\
**(g/m3)** & **Time (min)** & **(min)** & **3 Days (MPa)** & **28 Days (MPa)** \\ \hline
3.28 & 200 & 240 & 18.3 & 42.6 \\ \hline \end{tabular}
\end{table}
Table 4: Proportions of mixed NC.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Component** & **Main Chemical Compositions** & **Mixing Mass Ratio/(kg)** \\ \hline Part 1 & 90\% polyether polyols and 10\% chain & & \\  & & extender crosslinkers & 1 \\ \hline Part 2 & MDI-based isocyanate group & 1 \\ \hline Part 3 & Stone and cement & 5:1 \\ \hline Part 4 & Molecular sieve activated powder & 0.3 \\ \hline \end{tabular}
\end{table}
Table 2: Physical and chemical properties of molecular sieve activated powder.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Name** & **Particle Size** & **Bulk Density** & **Static Water Adsorption** & **PH Value** \\  & **(\(\mu\)m)** & **(g/mL)** & **(\%)** & **PH Value** \\ \hline Molecular sieve & & & & \\ activated powder & 2\(-\)4 & \(\geq\)0.45 & \(\geq\)25.0 & 9\(-\)11 \\ \hline \end{tabular}
\end{table}
Table 3: Physical properties of common Portland cement.  
The preparation procedure for the test models was as follows: First, the NC components were cast and cured at room temperature for 14 days. Then, the NC surface was subjected to the appropriate interface treatment or binder application. Finally, the PUC layer was cast over the NC surface, followed by curing at room temperature for a period before loading. In investigating the effect of different steel fiber contents, NC components were cast, and cured at room temperature for 14 days. Then, the steel fiber content in the PUC layer was adjusted before the specimens were cured and loaded. The parameters of the steel fiber are shown in Table 5.  
As shown in Figure 2, three methods were used to treat the NC surface, creating different interface roughness levels--smooth (GH), roughened (ZM), and grooved (KC). The specific interface morphology for GH is shown in Figure 2a, where the surface dust was removed and wiped with acetone solution, with no surface damage. The specific morphology for ZM is shown in Figure 2b, where a drill rod and chisel were used to increase the surface roughness. The specific morphology for KC is shown in Figure 2c, where a cutting machine was used to create a 20 mm wide, 2 mm deep grid groove on the NC surface to enhance the interface roughness.