**2. Content of Special Issue**

Qin et al. [1] performed a scientometric review on the utilization of waste glass (WG) in cement-based materials (CBM) along with an extensive discussion. The article uses scientometric analysis and a comprehensive manual review. Among other things, the scientometric analysis was conducted to establish the current research trends, to identify the publication fields, the sources with the most publications, the most quoted articles and authors, and the countries with a significant contribution to the field of WG utilization in CBMs for sustainable construction. In addition, the sustainable aspects of WG utilization in construction materials were reviewed, as well as the effect of WG on the workability, compressive strength, splitting tensile strength, flexural strength, microstructure and durability of CBMs was evaluated. The scientometric analysis exposed a remarkable increase in the number of publications on this topic in the last 5 years. It was observed that the largest number of documents have been published in Journal of Cleaner Production, Construction and Building Materials, and Resources, Conservation, and Recycling. Moreover, India, China and the United Kingdom contributed the most documents in the current research field. It was reported that WG can be used in CBMs as aggregate replacement and cement replacement, thus protecting natural resources, solving waste management problems, reducing CO2 emissions by reducing cement demand, protecting the environment from toxic chemicals, and producing cost-effective CBMs. It was found that generally finer glass particles increased, while coarser WG particles decreased the mechanical properties of

**Citation:** Smarzewski, P.; Stolarski, A. Properties and Performance of Concrete Materials and Structures. *Crystals* **2022**, *12*, 1193. https:// doi.org/10.3390/cryst12091193

Received: 19 August 2022 Accepted: 21 August 2022 Published: 25 August 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

CBMs. Increasing these properties is possible by replacing WG up to 25% of the cement or up to 20% of natural aggregate. The addition of WG can help improve the microstructure and reduce the permeability of CBMs, thus enhancing their durability. On the other hand, WG can reduce the resistance to carbonation. It was suggested that the amount, size, and type of WGs used in CBMs are adequate to achieve the appropriate mechanical properties and durability dependent on the anticipated applications. As a result of the discussion, it was identified, inter alia, that it is a necessity to explore the influence of WG on the rheological properties of CBM in terms of amount, type, particle size, and morphology of WG particles, or to determine the effect of the content and particle size of WG on the durability of CBMs at different w/b ratios.

Shahbazpanahi et al. [2] investigated the mechanical properties and microstructure of sustainable concrete produced by replacing the natural coarse aggregate (NCA) with recycled coarse aggregate containing used nano-silica (RCA-UNS). In the first group, specimens from the control normal concrete were studied. In the second group, specimens with 30%, 40% and 50% of NCA replacement by coarse aggregate obtained from crushed normal concrete from the first group and 0.5% addition of nano-silica were performed. In the third group, specimens with 30%, 40% and 50% of NCA replacement by RCA-UNS obtained from 90-day crushed specimens from the second group were made. Water absorption, fresh concrete slump, and compressive strength were determined and compared through Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) tests. The results showed that the water absorption of the RCA-UNS specimens decreased compared to the control specimens. Moreover, the results of the 28-day compressive strength test showed that the compressive strength in the third group increased by 12.8%, 10.9% and 10% after replacing 30%, 40% and 50% of NAC by RCA-NS in compared to the control specimens. The SEM results displayed that the 30% RCA-UNS specimens produced additional C–S–H, and the XRD and FT-IR graphs illustrated that in the RCA-UNS specimens more C–H crystals were consumed and converted to C–S–H. 30% replacement of NAC by RCA-UNS was found to be the best replacement for the production of sustainable concrete.

Soleimani et al. [3] performed a study the mechanical properties of green concrete containing recycled tire by-products for pavements. All tire by-products were tested individually and hybrid to investigate the concrete assets and determine their effect on the reference mixture. Eleven concrete mixtures were produced with different doses of shredded rubber (SR) or crumbed rubber (CR) or steel fibers (StF) from tire recycling, as well as twelve hybrid concrete mixtures containing different doses of various tire by-products were developed. Then, the impact of waste on the slump, compressive strength, splitting tensile strength, and modulus of rupture of the concrete were evaluated. The incorporation of SR to the reference concrete mixture had a significant impact on the 7 and 28-day compressive and splitting tensile strength. The results showed that the inclusion of CR had a detrimental effect on all the concrete properties tested, but the splitting tensile strength and modulus of rupture were the most evident. On the other hand, the introduction of 0.1% and 0.2% StF resulted in an increase in the 7-day compressive strength and the modulus of rupture. It was found that the incorporation of 5% rubber products and 0.1% steel fibers caused at least the maintenance of the reference mixture properties. The conclusions of this study showed that it is possible to hybridize all recycled tire materials to produce feasible pavement-grade concrete suited for hot weather conditions.

Liu et al. [4] examined the resistance to chloride penetration, sulfate attack and frost of high-performance concrete (HPC). For this purpose, fifteen concretes with a different water-binder ratio with changes in the content of fly ash (FA), silica fume (SF), comminuted granulated blast furnace slag (GGBS), and admixture of sulfate corrosion resistance (AS) were designed. The compressive strength, the total electric flux of chloride permeability, the sulfate resistance coefficient and the freeze-thaw indexes of HPC were determined. The results showed that the compressive strength and the durability of HPC depends on the chemical composition, fineness and pozzolanic activity of the supplementary cementitious

admixtures. GGBS had a negative effect on the HPC properties. On the other hand, SF and FA presented beneficial effects on concrete, also when used in conjunction with GGBS. The AS also improved the compressive strength, the resistance to chloride penetration, and the sulfate corrosion resistance of HPC. The concretes were characterized by compressive strength ranging from 70 MPa to 113 MPa, except for the HPCs admixed with GGBS or GGBS + FA. All HPCs were the highest grade over F400 for the frost resistance, with a relative dynamic modulus of elasticity no less than 60% and a weight loss rate of no larger than 5%. The concretes with admixtures of 7% FA, 8% SF, and 8% GGBS or 7% FA, 8% SF, 8% GGBS, and 10–12% AS with a water to binder ratio of 0.29, a total binder of 500 kg/m3, and the compressive strength of about 100 MPa presented the highest grades of resistance to chloride penetration, sulfate corrosion, and frost.

Ding et al. [5] assessed the tensile strength of self-compacting steel fiber reinforced concrete (SFRC). Seven groups of self-compacting SFRC with steel fibers with the hooked ends with a length of 25.1 mm, 29.8 mm and 34.8 mm were prepared with a volume fraction ranging from 0.4% to 1.4%. The axial tensile tests and the splitting tensile tests were carried out. The results showed that the axial tensile strength was higher than the splitting tensile strength. Moreover, it was noted that the axial tensile work and toughness were not related to the length of the steel fiber. Additionally, the equations for the prediction of tensile strength of self-compacting SFRC were proposed taking into account the effects of fiber distribution, fiber ratio, and volume fraction.

Xia et al. [6] investigated the dynamic compressive strength, impact toughness, and fragmentation size distribution law of the plain concrete and the carbon nanofiber reinforced concrete with 0.1%, 0.2%, 0.3%, and 0.5% volume content. Tests were performed under impact load by using the Φ100 mm split-Hopkinson pressure bar. The influence of the strain rate and the dosage of carbon nanofibers (CNF) on the dynamic mechanical performance of concrete was analyzed. It was reported that the dynamic compressive strength and the impact toughness increased with the improvement of the strain rate level at the same fiber content. On the other hand, at the same strain rate, the impact toughness increased with the increase in the fiber dosage, but the dynamic compressive strength initially increased and then decreased. It was also observed that the higher the strain rate level was, the higher the number of crushed concrete fragments with the lower the size, and the larger the fractal particle dimension were obtained. It was found that the optimal dosage of CNF in order to improve the dynamic compressive strength of concrete is 0.3%.

Nduka et al. [7] carried out studies to determine the potential use of meta-illite calcined clay (MCC) as a supplementary cementitious material (SCM) in a binary Portland cement for the production of high-performance concrete (HPC). Quantitative analyses of the chemical composition, mineral phases, morphology, calcination efficiency, and physical properties were performed using X-ray fluorescence (XRF), scanning electron microscopy/energy dispersive X-rays (SEM/EDX), X-ray diffraction (XRD), Fourier transform infrared/attenuated total reflection (FTIR/ATR), thermogravimetric analysis (TGA), laser particle sizing and Brunauer-Emmett-Teller nitrogen absorption method (BET) to obtain the properties of the cementitious materials. Moreover, the influence of MCC on the workability, compressive strength, splitting tensile strength, and flexural strength as well as HPC microstructure were determined. The XRF results displayed that the MCC had a high useful oxides content. In turn, the XRD results showed that MCC was predominantly an illite-based clay mineral calcined, as revealed by TGA, at a maximum temperature of 650 ◦C. Furthermore, the addition of MCC at a 5–15% cement replacement increased the HPC slump flow. The inclusion of MCC with a 10% cement replacement best improved the porosity of the HPC resulting in increased mechanical properties. It was recommended that the addition of MCC within 10% cement replacement should be adopted for low w/b Class I HPC without detrimental effects on the mechanical and microstructural properties of concrete.

Oluwaseun Azeez and Abd El Fattah [8] developed a new model to predict the effective diffusivity of concrete taking into account the effects of binding, age, temperature, carbonation, and free chloride. A new algorithm was developed to determine the corrosion

initiation time and to predict the concentration of free chloride at various depths in the concrete containing supplementary cementitious materials (SCM). The transport model uses the calibrated effective diffusion by considering the environmental impacts and experimental data of the binding capacity of concrete. Different mixtures of ordinary Portland cement and SCM were tested to determine the experimental binding capacity values used in the algorithm. Chloride profiles were measured on concrete blocks exposed to daily seawater, as well as exposed to harsh weather conditions for two years at the east coast of Saudi Arabia. Linear polarization and chloride profiling assessed the performance of the concrete mixtures in the corrosion environmental. The results generated by the model were compared with the performance of concrete blocks. Statistical analysis proved good accuracy of the model using experimental data from the binding capacity. The proposed transport model was evidenced to be effective in predicting free chloride profiles using the effective diffusion and binding capacity.

Sivtsev and Smarzewski [9] performed numerical modeling of the stress-strain state of steel fiber reinforced concrete using the method of numerical homogenization. In this paper, the description of the anisotropic nature of hardening of the composite material and the numerical homogenization for the J2 flow with isotropic hardening was proposed. The model problem was the deformation of the composite material with a periodic arrangement of inclusions in the form of steel fibers, assuming purely elastic properties for the fibers. Numerical homogenization of the elasticity and plasticity parameters were performed on the representative element. The calculated effective parameters were used to solve the problem on a coarse mesh. The accuracy of the application of the computational algorithm was checked on model problems in comparison with the hardening parameters of the base composite material. In accordance with the obtained results, the proposed model of homogenization of the hardening coefficient demonstrated satisfactory results when one of the components of the strain tensor was prevailed. However, when the components of the strain tensor had comparable values, the error values were already higher. This was due to the anisotropy of the plastic flow, which cannot be fully accounted for in the simple numerical change in the hardening coefficient. It was found that both approximations work quite accurately at small plastic deformations.

Alabduljabbar et al. [10] examined the bond behavior of a cleaned corroded reinforcing bar repaired with a partial depth concrete repair or a partial depth concrete repair using carbon fiber reinforced polymer (CFRP) sheets. Twelve lap splice beams were tested under static loading. The experiment variable was the repair method, i.e., a partial depth repair with pre-packaged self-consolidating concrete (SCC) in six lap splice beams, and additional confinement with CFRP sheets in other six beams. The test results of the repaired lap splice beams were compared with the results for a monolithic lap splice beam. The study showed that the average bond strength increased with increasing the reinforcing bar mass loss for all bonded lengths. The partial depth SCC repairing of the beams improved the average bond strength compared to the monolithic beams. For the lap splice beams repaired with a partial depth, higher concrete strength was obtained than for the monolithic beams. In addition, the beams confined with CFRP sheets displayed an increase in bond strength by 34–49%, an increase in the equivalent slip by 56–260%, a higher maximum load by 49% and a higher corresponding deflection by 191% compared to the unconfined beams.

Mateckova et al. [11] presented two variants of high-performance concrete (HPC), which were developed from the modification of ordinary concrete used for the production of pretensioned bridge beams. Both variants were produced in industrial conditions with commonly used raw materials. The basic mechanical properties of HPC and the resistance to chloride penetration were tested and compared. Moreover, the tests of model experimental pretensioned beams with a length of 7 m prepared of normal strength concrete and one variant of HPC were carried out, the load-deformation relationships were determined, and the calculation method of the load capacity were verified. The tests of pretensioned beams indicates the convenience of the calculation model of the ultimate bending moment capacity for structural beams prepared of concrete with compressive strength exceeding the

validity limit of the design code. The research also proved the increase in HPC resistance to chloride penetration compared to ordinary concrete.

Moghadasi et al. [12] studied the effect of height, plan geometry, and lateral load type on shear lag behavior of framed tube structures. The possible relation between the shear lag and the type of lateral load acting on structural systems was investigated. Twelve models with four different heights and three different plan geometry contrary to three different lateral load types were considered. Various plan geometry including rectangular, triangular and hexagon was modeled and subjected to the wind and earthquake load. It was observed that all types of structures subjected to the wind load had a higher value of shear lag factor in comparison with structures subjected to the static and dynamic earthquake loads. In addition, hexagon shaped plan structures had the most reasonable behavior versus lateral loads. In particular, the average of shear lag factors in the three types of analyses were about 25–29% less in the hexagon shaped plan structures compared to the control rectangular shaped plan structure.

The above-mentioned papers can significantly contribute to the development of advanced concrete materials and structures.

**Author Contributions:** Conceptualization, P.S. and A.S.; writing—original draft preparation, P.S. and A.S.; writing—review and editing, P.S. and A.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** We thank all the authors and peer reviewers for their valuable contributions to this Special Issue. We also thank the management and staff of MDPI for editorial support in the implementation of this project.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

