# Study on Mechanical Properties of Modified Polyurethane Concrete at Different Temperatures
## 3 Experimental Results and Discussion
### Cubic Compressive Strength and Splitting Tensile Strength  
In order to obtain the cube compressive strength and splitting tensile strength at different temperatures, the ultimate capacity of specimens is transformed into a strength value. The cubic compressive strength and the splitting tensile strength are calculated as follows:  
\[f_{\text{cu}}=\frac{F}{S} \tag{1}\]  
\[f_{\text{t}}=\frac{2F}{\pi S}=0.637\frac{F}{S} \tag{2}\]  
where \(f_{\text{cu}}\) and \(f_{\text{t}}\) are cubic compressive strength and splitting tensile strength (MPa), respectively. \(F\) is the failure load of the specimen. \(S\) is the bearing area or splitting tension area of the experiment specimen (mm\({}^{2}\)). The calculation result is accurate to 0.01 MPa.  
Figure 12: Compression failure modes of prism specimens. (**a**) 0 \({}^{\circ}\)C. (**b**) 15 \({}^{\circ}\)C. (**c**) 40 \({}^{\circ}\)C. (**d**) 60 \({}^{\circ}\)C.  
At different temperatures, the average value of the ultimate strength of specimens is taken as the strength value, and the dispersion degree of material strength is characterized by standard deviation and dispersion coefficient. Table 2 shows the average value of ultimate capacity, the average value of ultimate strength, standard deviation and dispersion coefficient of the specimens.  
Figure 13 shows the cubic compressive strength of the specimens at different temperatures. With the temperature increasing, the cubic compressive strength of the specimens decreased significantly. When the temperature is 15, 40 and 60 \({}^{\circ}\)C, the cubic compressive strength decreases by 7.4%, 46.0% and 67.1%, respectively. As shown in Figure 14, the splitting tensile strength at different temperatures is obtained. When the temperature is 15, 40 and 60 \({}^{\circ}\)C, the splitting tensile strength decreases by 10.3%, 39.8% and 66.3%, respectively. At different temperatures, the ratios of splitting tensile strength to cubic compressive strength (\(f_{\text{t}}/f_{\text{cu}}\)) are close. The ratio ranged from 9.8% to 11.0%. The average ratio of splitting tensile strength to cubic compressive strength is 10.1%.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Experimental** & **Temperature** & \multicolumn{2}{c}{**Average Value of**} & \multicolumn{2}{c}{**Average Value of**} & \multicolumn{1}{c}{**Standard**} & \multirow{2}{*}{**COV**} \\
**Project** & & **Ultimate Capacity (kN)** & & & \\ \hline  & 0 \({}^{\circ}\)C & 1791.47 & 79.62 & 2.58 & 0.03 \\ Cubic compressive & 15 \({}^{\circ}\)C & 1618.5 & 71.93 & 2.00 & 0.03 \\ strength & 40 \({}^{\circ}\)C & 966.87 & 42.97 & 3.09 & 0.07 \\  & 60 \({}^{\circ}\)C & 589.27 & 26.19 & 1.48 & 0.06 \\ \hline  & 0 \({}^{\circ}\)C & 280.07 & 7.93 & 1.10 & 0.14 \\ Split tensile & 15 \({}^{\circ}\)C & 251.1 & 7.11 & 0.41 & 0.06 \\ strength & 40 \({}^{\circ}\)C & 168.47 & 4.77 & 0.14 & 0.03 \\  & 60 \({}^{\circ}\)C & 94.2 & 2.67 & 0.14 & 0.05 \\ \hline  & 0 \({}^{\circ}\)C & 1713.03 & 78.52 & 4.81 & 0.06 \\ Axial compressive & 15 \({}^{\circ}\)C & 1324.6 & 58.87 & 0.63 & 0.01 \\ strength & 40 \({}^{\circ}\)C & 888.63 & 39.50 & 2.36 & 0.06 \\  & 60 \({}^{\circ}\)C & 470.47 & 20.91 & 0.60 & 0.03 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Strength values of the specimens.  
Figure 13: Relationship between compressive strength and temperature.