# Experimental Study on Flexural Properties of Polyurethane-Cement Composites under Temperature Load
## 6 Results and Discussion  
Indicators of flexural properties include tensile strength at break, tensile strain at break, and modulus of stiffness. The flexural tensile strength, failure strain, and stiffness modulus are not only affected by the test temperature but also by the loading speed. This paper mainly studies the effect of temperature on the bending properties of polyurethane cement. Therefore, in the test groups of different temperatures, the loading speed is the same, and the vertical loading rate is 1 mm/min to carry out the bending test of polyurethane cement trabeculae. According to the test results, the flexural tensile strength \(\mathrm{R_{b}}\), the flexural tensile strain \(\mathrm{\varepsilon_{b}}\), and the stiffness modulus \(\mathrm{S_{b}}\) are calculated. The calculation equations are as follows:  
\[\mathrm{R_{b}}=\frac{3\mathrm{LP_{b}}}{2\mathrm{bh}^{2}}, \tag{1}\]  
\[\mathrm{\varepsilon_{b}}=\frac{6\mathrm{hd}^{2}}{\mathrm{L}^{2}}, \tag{2}\]  
\[\mathrm{S_{b}}=\frac{\mathrm{R_{b}}}{\mathrm{\varepsilon_{b}}}, \tag{3}\]  
In the formula, \(\mathrm{R_{b}}\) is the flexural tensile strength of the specimen at failure (MPa); \(\mathrm{\varepsilon_{b}}\) is the maximum bending and tensile strain when the specimen fails (\(\mathrm{\mu\varepsilon}\)); \(\mathrm{S_{b}}\) is the modulus of bending stiffness when the specimen fails (MPa); \(\mathrm{b}\) is the width of the cross-interruption interview (mm); \(\mathrm{h}\) is the height of the cross-interruption interview piece (mm); \(\mathrm{L}\) is the calculated span of the specimen (mm); \(\mathrm{P_{b}}\) is the maximum load when the specimen fails (N); and \(\mathrm{d}\) is the mid-span deflection when the specimen fails (mm). The width \(\mathrm{b}\) of the polyurethane cement small beam specimen is 30 mm, the height is 35 mm, the calculated span L is 200 mm, and the bending test results under different temperature levels are listed in Table 8. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Group** & \(\mathbf{T}^{\prime}\mathbf{C}\) & **Length \(\times\) Width \(\times\) Height (mm)** \\ \hline PUC 0 & \(-50\)\({}^{\circ}\)C & \\ PUC 1 & \(-40\)\({}^{\circ}\)C & \\ PUC 2 & \(-30\)\({}^{\circ}\)C & \\ PUC 3 & \(-20\)\({}^{\circ}\)C & \\ PUC 4 & \(-10\)\({}^{\circ}\)C & \\ PUC 5 & \(0\)\({}^{\circ}\)C & 250 \(\times\) 30 \(\times\) 35 \\ PUC 6 & \(10\)\({}^{\circ}\)C & \\ PUC 7 & \(20\)\({}^{\circ}\)C & \\ PUC 8 & \(30\)\({}^{\circ}\)C & \\ PUC 9 & \(40\)\({}^{\circ}\)C & \\ PUC 10 & \(50\)\({}^{\circ}\)C & \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Bending test protocol for polyurethane cement specimens at different temperatures. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Group** & \(\mathbf{T}\) (\({}^{\circ}\)C) & **d (mm)** & \(\mathbf{P_{b}}\) (\(\mathbf{k}\)N) & \(\mathbf{R_{b}}\) (MPa) & \(\mathrm{\varepsilon_{b}}\) (\(\mathrm{\mu\varepsilon}\)) & \(\mathrm{S_{b}}\) (MPa)** \\ \hline PUC0 & \(-50\) & 1.365 & 5.0308 & 41.068 & 9782 & 4198.3 \\ PUC1 & \(-40\) & 1.445 & 4.5314 & 36.991 & 10,962 & 3374.4 \\ PUC2 & \(-30\) & 1.522 & 4.1000 & 33.469 & 12,162 & 2752.1 \\ PUC3 & \(-20\) & 2.342 & 5.4260 & 44.294 & 28,796 & 1538.2 \\ PUC4 & \(-10\) & 2.991 & 6.0050 & 49.020 & 46,967 & 1043.7 \\ PUC5 & 0 & 3.670 & 6.3925 & 52.184 & 70,712 & 738.0 \\ PUC6 & 10 & 3.781 & 5.7346 & 46.813 & 75.054 & 623.7 \\ PUC7 & 20 & 3.989 & 5.3149 & 43.387 & 83,539 & 519.4 \\ PUC8 & 30 & 4.661 & 1.8184 & 14.844 & 114,048 & 130.2 \\ PUC9 & 40 & 22.925 & 1.1121 & 9.078 & 2,759,124 & 3.3 \\ PUC10 & 50 & 24.476 & 0.5093 & 4.158 & 3,145,039 & 1.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Polyurethane cement bending test results. As can be seen from Table 8, with the increase in the test temperature, the maximum deflection in the span of the polyurethane cement composite at the time of damage is increasing, and the change process can be divided into three stages.