# Study on Mechanical Properties of Modified Polyurethane Concrete at Different Temperatures
## 2 Experimental Program
### Experimental Setup and Loading Procedure  
To study the influence of temperature on the mechanical properties of modified polyurethane concrete, experiments were performed at temperatures of 0, 15, 40 and 60 \({}^{\circ}\)C, respectively. All the experiments were carried out in accordance with the GB/T 50081-2019 (China's Ministry of Housing and Urban-Rural Construction 2019) [26]. Under each temperature condition, a total of twelve specimens were tested. Two groups of cube  
Figure 4: Section of experiment specimen. (**a**) Concrete slice I. (**b**) Concrete slice II.  
Figure 3: Experiment specimens. (**a**) Cube specimens. (**b**) Prismatic specimens.  
specimens and two groups of prism specimens were designed, and each group consists of three identical specimens. One group of cube specimens for the compression experiment and the other for the splitting tensile experiment, while one group of prism specimens was used to measure the axial compressive strength and the other group was used to measure the compressive elastic modulus. To control the temperature, the specimens were heated or cooled in an environmental box with constant temperature and humidity. The constant temperature range of the environmental box was \(-40\) to \(150\)\({}^{\circ}\)C, as shown in Figure 5. The strain gauges were attached to the specimens before specimens were put into the environmental box. All specimens were placed in the environment box with the corresponding temperature for 6 h before loading. After taking out a single specimen, the test loading time shall be less than 3 min. If the loading time is too long, the temperature variations could affect the experiment results.  
Modified polyurethane concrete specimens that were subjected to a compressive test were loaded through a microcomputer-controlled electrohydraulic servo testing machine with a capacity of 2500 kN. The loading was controlled by force at a rate of 13,500 N/s following the code (GB/T 50081-2019) [26]. During the entire loading process, a data-acquisition system was used to synchronously monitor the load, strain and displacement  
Figure 5: Constant temperature box.  
data. Two quenched and tempered steel plates (with a size of 50 cm \(\times\) 50 cm \(\times\) 2 cm) were placed between the platens and specimen ends. For the static uniaxial compressive elastic modulus test, in order to measure the compressive strain of the specimen, three resistance strain gauges with a gauge distance of 100 mm were attached to the front face of the specimens along the loading direction. Figures 6 and 7 present the schematic diagram of the compression test setup. Prior to the test, preloading shall be carried out. The purpose of preloading was to check whether the testing setup and the instruments were operating normally or not. The channel of the measurement system was monitored, and it was ensured that specimens were properly balanced. The gap between the loading equipment and the samples was eliminated.  
An experimental tooling fixture was manufactured to conduct the splitting tensile test of modified polyurethane concrete specimens. The experimental tooling fixture was equipped with a steel arc pad with a radius of 75 mm and a length greater than the specimen size. The experimental tooling fixture was placed between the pressure plates and the cube specimens. The modified polyurethane concrete cube specimens that conducted the splitting tensile test were loaded in a universal testing machine with a capacity of 1000 kN (Figure 8). Specimens for splitting tensile tests should be continuously and evenly loaded  
Figure 6: Loading diagram of cube compressive experiment. (**a**) Test setup. (**b**) Schematic diagram.  
Figure 7: Loading diagram of prism compressive experiment. (**a**) Test setup. (**b**) Schematic diagram (unit: mm).  
without any impact, and the loading rate was controlled by applying vertical forces of 1350 N/s.