# Mechanical Behavior of Steel Fiber-Reinforced Lightweight Concrete Exposed to High Temperatures
## 5 Conclusions  
In this work, an experimental investigation of the residual mechanical behavior of steel fiber-reinforced LWC (SFLWC) under high temperatures has been presented. The UPVs, indirect tensile and axial compressive strengths, elastic modulus, and peak strain of these LWC specimens were evaluated. Significantly, the influences of different steel fiber types on the residual mechanical behaviors, including energy absorption capacity, elastic modulus,  
Figure 15: Comparison of the developed stress–strain relationships and experimental results: (**a**) NWC; (**b**) ALWC; (**c**) CFAL; (**d**) HFAL; (**e**) SLWC; (**f**) CFSL; (**g**) HFSL.  
and strength, have been comprehensively analyzed. The following conclusions can be drawn from the test results and analyses:  
1. The evolution of the residual compressive properties of concretes after thermal treatment is mainly related to the aggregate type. It should also be noted that, in the present study, the amount of fly ash and silica fume in the concrete mixes is very small. However, further research is required to clarify the effects of mineral additives and amount of aggregate on the post-fire behavior of concrete.
2. The presence of steel fibers improved the tensile strength of both pre- and post-fire exposure. SFLWC with hooked end steel fiber lost a lesser amount of strength, which is attributed to the stronger reinforcing action to bridge the cracks. The steel fiber-reinforced ALWC had higher residual compressive and tensile strengths after heating and increased ductile performance due to the homogenous characteristics of the concrete matrix.
3. Steel fibres improve the compression absorbed energy of LWC at room temperature as well as at high temperatures. The energy absorption capacity of most concrete mixes increases for temperatures below 400 \({}^{\circ}\)C, but decreases above 400 \({}^{\circ}\)C. However, the influence of fibers on the residual elasticity modulus is minimal.
4. Simple models have been proposed to characterize the material properties as a function of temperature. The regression coefficient were all above 0.96, which indicates that the models were in good agreement with the experimental results. A numerical model is also established to predict the compressive stress-strain relationships of the heated and unheated SFLWC. The theoretical fitting curve complies well with the test results.  
Conceptualization, H.W., J.H., and B.C.; methodology, H.W., M.W., H.C., and B.C.; formal analysis, H.W., M.W., Y.W., and B.C.; writing--original draft preparation, H.W., M.W., H.C., B.C., and Y.W.; writing--review and editing, H.W., M.W., J.H., Y.W., and B.C.; visualization, B.C.; supervision, H.W.; project administration, H.W.; funding acquisition, H.W. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Guangxi University under contract no. XGZ160701, National Natural Science Foundation of China (Grant no. 51768003; 51868005), and the Science and Technology Planning Project of GuangXi Province (Grant no.2017 GXNSFAA198360).  
The raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.  
All authors declare that they have no conflict of interest.  
All-lightweight concrete  
All-lightweight concrete with crimped shape steel fiber  
CPSL Semi-lightweight concrete with crimped shape steel fiber  
HFF Hooked end steel fiber  
HFAL All-lightweight concrete with Hooked end steel fiber  
HFSL Semi-lightweight concrete with Hooked end steel fiber  
HFSG High strength concrete  
LVDT Linear Variable Differential Transformer  
LWA Lightweight aggregate  
LWC Lightweight concrete  
MIMWC Multi-walled carbon nanotubes reinforced LWC  
NWVC Normal-weight concrete  
RPC Reactive powder concrete  
SCC S Steel fiber-reinforced self-consolidating concrete  
SFLWC Steel fiber-reinforced lightweight concrete  
SLWC Semi-lightweight concrete  
UPV Ultrasonic pulse velocity