# Experimental Study on Flexural Properties of Polyurethane-Cement Composites under Temperature Load
## 6 Results and Discussion
### Analysis of Failure Strain Test Results  
Figure 18 shows the breaking strains of the polyurethane cement composites at different temperature levels. It can be seen from Figure 21 and Table 8 that the breaking strain of the polyurethane cement composites increases with the increase in temperature. The reason for this is that at temperatures below and including \(30\)\({}^{\circ}\)C, polyurethane mainly exhibits britteless and viscoelasticity [56], resulting in polyurethane cement exhibiting more pronounced elasticity, and the lower the temperature, the more significant the elastic characteristics of polyurethane cement composites are, and the smaller the strain in bending damage of polyurethane cement specimens. A local analysis of the disruption strain in the temperature range of \(-50\)\({}^{\circ}\)C change to \(30\)\({}^{\circ}\)C shows that the disruption strain is gradually increasing; in the process of increasing from \(-50\)\({}^{\circ}\)C to \(30\)\({}^{\circ}\)C, the temperature-destructive strain curve can be divided into three stages as the temperature continues to increase, the first stage is the increase from \(-50\)\({}^{\circ}\)C to \(-30\)\({}^{\circ}\)C, the deadly strain grows slowly, the increase rate is low and approximates a straight line, the second stage is \(-30\)\({}^{\circ}\)C to \(0\)\({}^{\circ}\)C, the damaging strain proliferates, the increase rate is more significant, and it is approximately a straight line. The third stage is \(0\)\({}^{\circ}\)C to \(30\)\({}^{\circ}\)C; the damaging strain proliferates, the increase rate is low at the beginning and then increases rapidly, and it is approximately a concave curve. The higher the temperature is, the more pronounced the viscoelastic characteristics of polyurethane cement composites are. The greater the strain when the polyurethane \begin{table}
\begin{tabular}{l c} \hline
**Type** & \(\mathrm{T_{g}}\)/\({}^{\circ}\)C \\ \hline MDI-BDO & \(-46\)\({}^{\circ}\)C \\ MDI-PPG & \(-32\)\({}^{\circ}\)C \\ TDI-BDO & \(-71\)\({}^{\circ}\)C \\ TDI-PPG & \(-48\)\({}^{\circ}\)C \\ \hline \end{tabular}
\end{table} 
Table 9: \(\mathrm{T_{g}}\) of common polyurethane colloids. cement specimen is bent and damaged, the greater the change of damage strain rate is with the change of temperature. In the process of increasing from \(-50\)\({}^{\circ}\)C to \(50\)\({}^{\circ}\)C, changing the damaging strain of polyurethane cement composites mainly shows a trend of two stages of change. The first stage is in the temperature range of \(-50\)\({}^{\circ}\)C to \(30\)\({}^{\circ}\)C, the damaging strain of polyurethane cement composites is minor and reaches a significant value at \(30\)\({}^{\circ}\)C, and the damaging strain reaches 114,048 \(\mu\varepsilon\); the second stage is in the temperature range of \(30\)\({}^{\circ}\)C to \(50\)\({}^{\circ}\)C, the damaging strain suddenly increases a lot at \(40\)\({}^{\circ}\)C, the damaging strain is 2,759,124 \(\mu\varepsilon\) at this time, which is \(30\)\({}^{\circ}\)C 24.2 times, indicating that in the range of \(30\)\({}^{\circ}\)C to \(40\)\({}^{\circ}\)C, the polyurethane cement composites transformed into plasticity and the elastic characteristics decreased, which showed an obvious turning point in the damage strain curve. The shape of the damage strain curve in the temperature range of \(-50\)\({}^{\circ}\)C to \(50\)\({}^{\circ}\)C is approximately L-shaped, and the damage curve in the temperature range of \(-50\)\({}^{\circ}\)C to \(30\)\({}^{\circ}\)C is similar to the flat side of the \"L\" shape. The damage curve in the temperature range of \(30\)\({}^{\circ}\)C to \(50\)\({}^{\circ}\)C is similar to the \"L\" shape. The damage curve is similar to the vertical side of the \"L\" shape. Polyurethane is a polymer with a large number of polar bonds in the system, which can be divided into hard chain segments, hydrogen bonds between soft chain segments, and intra-molecular hydrogen bonds.