# Experimental Study on Flexural Properties of Polyurethane-Cement Composites under Temperature Load
## 6 Results and Discussion
### Analysis of Failure Stiffness Modulus Test Results  
Figure 19 shows the modulus of damage stiffness of the polyurethane cement composites at different temperature levels. From Figure 22 and Table 8, it can be seen that the flexural modulus of damage modulus of polyurethane cement composites decreases continuously with the increase in temperature. When the temperature is lower than 20 \({}^{\circ}\)C (including 20 \({}^{\circ}\)C), the changing relationship of the bending modulus of the polyurethane cement composites is divided into two stages. The first stage is characterized by a nearly linear decrease (\(-\)50 \({}^{\circ}\)C\(\ldots\)\(-\)20 \({}^{\circ}\)C), and the second stage is characterized by a concave curve decrease (\(-\)20 \({}^{\circ}\)C\(\ldots\)20 \({}^{\circ}\)C). The average rate of change in the first half of the second stage is larger than the average rate of change in the second half. When the temperature is higher than 20 \({}^{\circ}\)C, the modulus of damage strength of polyurethane cement composites decreases sharply with the temperature increase. A temperature of 20 \({}^{\circ}\)C is the folding point of the change of modulus of damage strength of polyurethane cement composites, mainly because the mechanical properties of polyurethane cement composites change considerably at 20 \({}^{\circ}\)C; when the temperature is lower than 20 \({}^{\circ}\)C, polyurethane cement mainly shows the elastic characteristics, and as the temperature decreases, the elastic characteristics; when the temperature is lower than 20 \({}^{\circ}\)C, the polyurethane cement mainly exhibits elastic characteristics, and as the temperature decreases, the elastic characteristics become more apparent, the deformation capacity becomes smaller, and the modulus of damage strength becomes larger; when the temperature is higher than 20 \({}^{\circ}\)C, the polyurethane cement composites mainly exhibit viscous characteristics, and as the temperature increases, the viscous characteristics become more apparent, the deformation capacity becomes more extensive, and the modulus of damage strength becomes smaller.  
The temperature dramatically influences the failure stiffness modulus of polyurethane cement composites. During the process of increasing from \(-\)50 \({}^{\circ}\)C to 50 \({}^{\circ}\)C, the failure stiffness modulus of polyurethane cement decreases from 4198.3 MPa to 1.3 MPa, and the reduction range is extensive, decreasing by about 3228 times; the temperature change curve of the failure stiffness modulus maintains a continuous downward trend, and is generally a concave curve, the slope of each point is negative, the failure stiffness modulus and temperature performance is a negative relationship. The modulus of breaking strength is very small at 40 \({}^{\circ}\)C and 50 \({}^{\circ}\)C. It can be understood from the above analysis of breaking strain that the breaking strain of polyurethane cement composites is tremendous under these two temperature conditions, mainly because the adhesion of polyurethane is excellent at higher  
Figure 22: Failure stiffness modulus of polyurethane cement at different temperature levels.  
temperatures, which leads to the polyurethane cement composites mainly presenting as sticky. From a macroscopic point of view, polyurethane cement is softer and better able to withstand changes and has better ductility.