# Special Issue Advances in High-Performance of Eco-Efficient Concrete
## 10 Mechanical Behavior of Steel Fiber-Reinforced Lightweight Concrete Exposed to High Temperatures  
[PERSON] et al. [9] show in their paper that the mechanical characteristics of steel fiber-reinforced lightweight concrete (SFLWC) under high temperatures are studied in this paper. Different concrete matrices, including all-lightweight concrete (ALWC) and semi-lightweight concrete (SLWC), and different steel fibers with hooked ends and crimped shapes, are considered as objects. In addition, normal-weight limestone aggregate concrete (NWC), no-fiber ALWC, and SLWC were tested after high-temperature treatment as a control group. The temperature effects on the splitting tensile strength, ultrasonic pulse velocity, compressive stress-strain curve, elastic module, peak strain and axial compressive strength of the SFLWC were investigated. The results showed that, with increasing exposure temperature, both the axial compressive strength and the elastic modulus decreased, whereas the axial peak strain has a certain increase, and hence, the stress-strain curves were gradually flattened. The toughness of all the concretes increased first and then reduced with increasing temperature, whereas the specific toughness of all the concretes increased with the increase in temperature. Compared with NWC and SLWC, ALWC had a better capacity to resist high temperatures, especially temperatures > 400 \({}^{\circ}\)C. Adding steel fibers can improve the capacity of energy absorption, specific toughness and residual splitting tensile strength of lightweight concrete (LWC) before and after it is exposed to high temperatures. Based on a regression analysis, a segmented constitutive equation for LWC and SFLWC under uniaxial compression was derived from fitting the experimental findings, and the fitting curve agrees well with the test results. Selection of the Optimum Carrier for Manufacturing Water-Repellent Concrete and Durability Evaluation of Cement Mortar Using It  
[PERSON] and [PERSON] [10] show in their paper that the purpose of this experiment was to complement the shortcomings of existing surface treatment methods and to implement water repellency inside concrete to prevent water penetration and improve the durability of concrete. Carriers to provide water repellency were fabricated using fly ash (FA), silica fume (SF) and natural zeolite, which are used as admixtures for concrete. They were mixed with cement mortar, tested and evaluated. The compressive strength of the water-repellent impregnated natural zeolite (ZWR) specimen was 83% of that of ordinary Portland cement (OPC), and its contact angle was found to be 124\({}^{\circ}\). The water penetration test and chloride ion penetration test confirmed that the water absorption and total passing charge were reduced, whereas the porosity and pore size were improved. For the other specimens, except ZWR, water repellency was judged to be insufficient due to the low fixing ability of the water-repellent's active ingredient. The results of evaluating the physical performance and durability of cement mortar for the selection of the optimum carrier revealed that powders other than ZWR are not suitable as a material for providing water repellency to concrete. Crack Width and Propagation in Recycled Coarse Aggregate Concrete Beams Reinforced with Steel Fibres  
[PERSON] et al. [11] show in their paper that reducing the crack width is a vital feature for protecting rebars from corrosion. In this investigation, the impact of steel fibers (SFs) on the cracking of recycled coarse aggregate reinforced concrete (RCARC) beams was investigated. Twenty-seven reinforced concrete (RC) experimental samples (150 mm \(\times\) 200 mm \(\times\) 1500 mm) were manufactured. Shear rebars were considered with different spacings. Specimens were tested under a four-point flexural setup. Recycled coarse aggregate (RCA) from a destroyed building was employed at 0%, 50% and 100% by weight. SFs were added at three contents (0%, 1% and 2%) in order to reduce the crack width.