**5. Evaluation of Current Findings with Previous Studies**

Since it has the potential to be preferred as aggregate in concrete mixture, the effect of CWG on engineering properties was examined by many investigators. CWG were used as either FA or CA replacement in concrete. To develop empirical equations, strength values (CS, STS, and FS) for plain concrete and concrete formed from CWG were collected from previous experimental studies [28,29,33,35,39,40,44,46,47,57–80]. The obtained strength values of concrete formed with CWG (*f*) were primary regularized by the strength value of concrete without glass (*f* ). These normalized strength values (*f***/***f* ) were then shown as a function of different replacement proportions. The changes in the normalized strength values were depicted in Figures 8–13.

**Figure 8.** Discrepancy of the normalized CS of the concrete formed with CWG as a partial replacement for CA [39,40,47,58–62,78,79].

**Figure 9.** Discrepancy of the regulated STS of the concrete formed with CWG as a partial replacement for CA [40,46,47,60,79].

**Figure 10.** Discrepancy of the normalized FS of the concrete produced with CWG as a partial replacement for CA [40,47,57,79].

**Figure 11.** Discrepancy of the normalized CS of the concrete formed with CWG as a partial replacement for FA [28,33,44,46,58,63–67,69–74,77].

**Figure 12.** Discrepancy of the regulated Splitting tensile strength of the concrete produced with CWG as a partial replacement for FA [29,35,63,64,69,70,73,80].

**Figure 13.** Discrepancy of the normalized FS of the concrete produced with CWG as a partial replacement for FA [29,33,35,44,46,63,64,66,68,75,76,80].

Considering both our findings and previous studies, an empirical equation was developed as follows to predict the CS, STS, and FS, respectively:

$$f = \left[1 + c\_1 \times (WGR) + c\_2 \times (WGR)^2\right] \times f' \tag{1}$$

where *f* = strength values to be calculated (*fc* = CS; *fs* = STS; *ff* = FS); *c*<sup>1</sup> and *c*<sup>2</sup> = the coefficients given in Table 2; *WGR*: CWG proportion (0 < *WGR* < 50); and *f* = strength values of the plain concrete.

**Table 2.** The parameters used in Equation (1).


As presented in Equation (1), engineering properties of concrete formed with CWG were identified as a function of the quantity of the CWG. The developed expressions for compressive, flexural, and splitting tensile strength of concrete produced with CWG can be employed in project phases.

#### **6. Conclusions and Summary**

In this study, the effects of different productions based features of concrete with different amounts of CWG as replacements of aggregates were investigated. For this purpose, fine and CAs were altered for 10%, 20%, 40%, and 50% (FA10%, FA20%, FA40%, FA50%, and CA10%, CA20%, CA40%, and CA50%). Penetrability and slump properties of produced concrete samples were also examined. Then, CS, STS, and FS of the produced test examples were investigated. Furthermore, SEM analyses were also performed to compare the strength consequences obtained from the experimental study. These specifications were then compared with those of reference concrete. Lastly, practical equations were derived to easily estimate the CS, STS, and FS of produced concrete samples. Considering our findings, the following consequences can be obtained from this study:

According to the slump test consequences, while the slump value reduces, the quantity of CWG rises. In other words, the workability of concrete reduces when the rate of glass powder as replacement for aggregates increases.

In this study, fine and CA for 10%, 20%, 40%, and 50% (FA10%, FA20%, FA40%, FA50%, and CA10%, CA20%, CA40%, and CA50%) were exchanged with CWG, and this tendency was inverted while fractional replacement of CA with CWG decrease the CS of concrete. In other words, while CA was swapped with CWG, a remarkable downgrade in strength was detected when compared with the reference concrete.

As mentioned above, the consequences of STS generally follow a similar trend as the CS. The significant progress in STS of the concrete is up to 13% with CWG used as fractional replacement for FA. Upon changing the quantity of CWG, consequences of STS are affected correspondingly to the CA.

While aggregates were swapped with CWG, there was an increase in the FS values up to a certain value of the quantity of the CWG. It was observed that with the addition of CWG at 10%, 20%, 40%, and 50% of FA swapped, the increase in FS was 3.2%, 6.3%, and 11.1% and 4.8%, respectively, compared to reference concrete sample.

From the SEM analyses, it can be observed that the use of both CWG together for concrete is a good match. Furthermore, similar to the studies in the literature, it is also

shown in this study that glass powder with finer particles has a high pozzolanic effect and provides better strength in concrete.

The developed empirical equations for the CS, STS, and FS are quite general and they have the potential to be implemented into design guidelines of the concretes with CWG.

The use of 20% replacement for fine and CA with CWG is recommended, considering both workability and strength.

**Author Contributions:** Conceptualization, Y.O.Ö. and D.D.B.-N.; methodology, Y.O.Ö. and D.D.B.-N.; data curation, Ö.Z., M.K., D.D.B.-N. and Y.O.Ö.; investigation, A.˙ I.Ç., Y.O.Ö., Ö.Z. and M.K.; writing—original draft preparation, A.˙ I.Ç., Y.O.Ö., Ö.Z., S.Q. and J.A.; writing—review and editing, S.Q., J.A., D.D.B.-N. and C.B.; funding acquisition, D.D.B.-N. and C.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by Gheorghe Asachi Technical University of Ia¸si—TUIASI-Romania, Scientific Research Funds, FCSU-2022.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** This paper was financially supported by the Project "Network of excellence in applied research and innovation for doctoral and postdoctoral programs"/InoHubDoc, project co-funded by the European Social Fund financing agreement no. POCU/993/6/13/153437. This paper was also supported by "Gheorghe Asachi" Technical University from Ia¸si (TUIASI), through the Project "Performance and excellence in postdoctoral research 2022".

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