# Mechanical Behavior of Steel Fiber-Reinforced Lightweight Concrete Exposed to High Temperatures
## 3 Test Results and Discussions
### Splitting Tensile and Axial Compressive Strength  
The relative and absolute values of residual axial compressive strength for all the concrete compositions under elevated temperature were plotted in Figure 6. The coefficient of variation of the compression tests were between 0.3% and 12.3%. As shown in Figure 6a, the axial compressive strengths of steel fiber-reinforced LWCs were relatively higher than those of LWC without steel fibers at room temperature. As expected, the decrease in the residual axial compressive strength of all the concrete mixtures was relatively small at 200 and 400 \({}^{\circ}\)C, while the strength reduction at temperatures of 600-800 \({}^{\circ}\)C was much stronger, as shown in Figure 6b. The strength reduction in the SLWC specimen is similar to that of the NWC test samples under 600 or 800 \({}^{\circ}\)C, while the relative residual compressive strength of ALWC was obviously greater than that of SLWC and NWC at about 600-800 \({}^{\circ}\)C. This may be because the thermal expansion coefficient of limestone aggregate was greater than LWAs, and limestone dissociates in the temperature range of 600-800 \({}^{\circ}\)C due to CaCO3 de-carbonation [36]. Much greater strength loss were observed for SLWC than ALWC. This may be because the bond between the sintered fly ash lightweight aggregates (spherical particle) used in SLWC and the mortar was weakened mainly at high temperatures. The average percentage loss in compressive strength of steel fiber-reinforced ALWC and SLWC were lower than those of LWC without steel fibers after heating at different temperatures. The above research findings agreed with [PERSON] et al. [37], which suggested that steel fiber enhances the compressive and residual strengths at room temperature and elevated temperature, respectively. However, the influence of steel fibers on the relative residual compressive strength of LWC was not as significant as the aggregate types.  
The absolute and relative values of the residual splitting tensile strength of all concrete compositions at elevated temperatures are plotted in Figure 7. The coefficient of variation of the splitting tension tests was between 0.7% and 9.1%. Figure 7a shows that the tensile strengths of steel fiber-reinforced LWC are significantly higher than those of LWC without steel fibers at room temperature, which proves the effectiveness of steel fiber in bridging cracks under splitting tensile loading. The enhancement of tensile strengths was more effective for HF types. From Figure 7b, the variation of the residual splitting tensile strength of no fiber concrete specimens was similar to that of the compressive strength. Moreover, it should be mentioned that the tensile strength decay pattern of three concrete batches without steel fiber was almost linear during the temperature range from 200 to 800 \({}^{\circ}\)C. It is exciting to find that the splitting tensile strength of LWC with HF suffers less loss than that of LWC with CF in the range of 600-800 \({}^{\circ}\)C. It is believed that the bonding strength between LWC matrix and CF reduces sharply at 600 \({}^{\circ}\)C, while the reinforcing action of HF drops sharply until 800 \({}^{\circ}\)C.  
Figure 6: Temperature effect on compressive strength: (**a**) absolute compressive strength; (**b**) relative compressive strength.