# Special Issue: New Trends in Recycled Aggregate Concrete
## 8 New Applications of Recycled Aggregate Concrete  
[PERSON] et al. [13] studied the mechanical characteristics and water absorption properties of blast-furnace slag concrete with fly ash or micro silica additions. The results show the following: (i) the use of fly ashes, and especially silica fume, together with slag in concrete enhances the compressive strength of concrete mixes and shows very high water/cement ratios; (ii) micro silica concrete shows a specific weight lower than slag and fly ash concrete; (iii) for both types of concrete, the splitting tensile strength is consistent with the compressive strength, whereas flexural tensile strength is rather low, especially for slag and silica fume concrete; and (iv) compared to an ordinary concrete, the types of concrete examined in this research have a lower water absorption value, especially silica fume concrete.  
[PERSON] et al. [14] presented a material characterization for sustainable concrete paving blocks. Five types of waste materials were used in this project, including recycled concrete coarse aggregate (RCCA), recycled concrete fine aggregate (RCFA), crushed glass (CG), crumb rubber (CB), and ground granulated blast-furnace slag (GGBS). Using either RCCA or RCFA can decrease the blocks' strength and increase their water absorption. The suggested incorporation levels of RCCA and RCFA are 60% and 20%, respectively. Adding CG to the concrete paving blocks as a type of coarse aggregate can improve their strength and decrease their water absorption. The addition of CR causes a significant deterioration of the blocks' properties, except for their slip resistance.  
[PERSON] and [PERSON] [15] analyzed the crushing performance of ultra-lightweight foam concrete with fine particle incorporation. The results indicate that the use of fine-graded sand particles in a small content simultaneously reduces the cement content and enhances the crushing performance. However, poor performance is observed for a high sand content. The cellular structure of the foam-sand composite, and thus its mechanical behavior, can be substantially weakened by larger sand particles, especially when the particle size is larger than the voids in the foam.  
The effect of the addition of nylon fibers (NFs) on the performance of recycled aggregate concrete (RAC) was studied by [PERSON] [16]. RAC showed a lower performance than crushed stone aggregate concrete (CAC) because of the adhered mortars in the recycled aggregates. However, it was obvious that the addition of NFs in RAC mixes was much more effective in enhancing the performance of concrete, due to the crack bridging effect from NFs. In particular, a high content of NFs (1.2 kg/m\({}^{3}\)) led to a beneficial effect on the concrete properties compared to a low content of NFs (0.6 kg/m\({}^{3}\)) with respect to mechanical properties and permeability, especially for RAC mixes.  
Thanks are due to all the authors and peer reviewers for their valuable contributions to this Special Issue. The MDPI management and staff are also to be congratulated for their untiring editorial support for the success of this project.  
The authors declare no conflict of interest.