Experimental and Numerical Investigation of the Flexural Behavior of Mortar Beams Strengthened with Recycled Plastic Mesh

Round 1

Reviewer 1 Report

The article describes the methodology and results of an experiment to use waste material as reinforcement for concrete beams. I noticed serious errors at the level of experiment planning, materials and methods, and data analysis. These errors result in incorrect conclusions. The presented conclusions focus on the description of mechanical properties and have nothing to do with sustainability. The idea of using scraps of material from used PET bottles for critical structures can even lead to disasters.

Introduction

1. In the Introduction section, you should consider including papers related to 3D printed  reinforcements. That is close to Your approach.

Materials and Methods

2. The use of waste materials for critical structure reinforcement applications is highly unacceptable. Your approach is non-scalable. You cant make upscaling with Your material.

3. There is no information about the critical property in a specific application like elongation at break point and thermal resistance to degradation of mechanical properties.

4. You should include chemical identification of the material (polyethylene terephthalate). 

5. You should consider including a table comparing the mechanical properties of typical polymers (waste like ABS, PE, Nylon...) with your specific material.

6. Design of experiment should be proposed on the basis of plausible preliminary hypotheses and knowledge of the physical and chemical phenomena occurring in the experiment to be conducte. In Your proposition of the experimental plan, You do not present any preliminary hypotheses. You do not refer to the phenomena occurring in the beam bending experiment. In this particular case, this is not a correct scientific approach in accordance with the research methodology in civil engineering but just a "blind search". One can ask a whole series of "why ?" questions to which I find no answer. Why are the holes shaped like squares ? Why are they placed in 1 and 2 rows ? How does the shape of the reinforcement affect the transmission of tensile stresses ? Why squares and not circles or ellipses ? Why not to make wrapped strings out of Your particular material ?

7. In line 157 mortar cube molds is 5 mm size ?

8. The sample preparation methodology contains a serious error. (Lines 162-164) The reinforcing inserts, as a result of differences in material density and vibration, can undergo significant shifts in the mold. This can be clearly seen in Figure 9c. Displacement of the reinforcing material in the beam tensile stress zone can result in high process interference.

Results and Discussion

9. Graph 8 is highly unreadable. You should consider using Matlab to generate graphs. On this graph, you should clearly indicate the points described in 196-214 maybe at just one typical curve. At this point, You should consider showing the fracture models (classes, patterns) for individual samples in relation to the points described in lines 196-214.

10. No statistical analysis of the results from the same three samples. The average value does not show the quality of the results. Scatter/ranges of results should be added.

• 11. No reference of numerical results to Your reference samples. You have two reference samples at the limits of the experiment: one without amplification at all, the other with full amplification (no holes). Use normalization of the results between these two limits and You will have more valuable referenceed values.

12. The introduction of the EWR parameter should be in a separate subsection. The formula for EWR value with units should be clearly derived. However. The EWR parameter creates a DISCRETE space. It is assigned to a specific geometry of the mesch sample. To be strict, you can generate a sample with a completely different shape of holes and the same value of the EWR parameter and the results in teble 3 will be completely different. Therefore, you CANNOT do equation  of 1st, 2nd, or 3rd degree equation with discrete domain ! This is a serious data analysis error.  It also makes the conclusions wrong.

13. Flexuar Toughness. You should introduce an explicit formula that gives the value of this parameter. It is the integral of the loads in a specified domain. In Table 11. You also commit the error of analyzing the discrete space (just like EWR) , as if it were a continuous space. Therefore, you can not perform regression with a polynomial as in Figure 12. The conclusions are wrong and apply ONLY to specific shapes without generalizability.

14. The same applies to the Ductility Index.

Numerical Modeling

15. In Abstract lines: 18-20 and in lines 415-416 You wrote that numerical analisys was performer to validate the experimental analisys. NO. It is the other way around. It is the results of the real experiment that are used to validate the simulation model. 

16. As a result of the FEM analysis, you should consider a thorough analysis of the following phenomena: the effect of the friction coefficient between the polymer and cement phases, The effect of the number of reinforcement layers on energy absorption characteristics, a detailed analysis of the stresses in the reinforcing shape and the resulting conclusions for the mesh pattern shape. 

Conclusions.

17. As I mention before conclusion 3, 4 and 5 are wrong.

18. Your approach is non-scalable 

 

 

•  

Author Response

Please see attached pdf

Author Response File: Author Response.pdf

Reviewer 2 Report

1. L157: “According to ASTM C109 [58], mortar cube molds of 5 mm in size were used to determine the compressive strength (CS) of the mix.” Is the compressive strength of mortar determined by such a small cube?

2. L177: “two LDTVs symmetrically placed at both opposite side of the specimen were used to measure the mid-span deformation.” The reviewer do not see the LDTVs in the figure, please mark it in the figure.

3. L296: According to observation, after the mortar beam reaches the maximum load, the load will suddenly decrease to 50%-70% of the maximum load. However, the ductility is defined as the ability of a beam to sustain large permanent deformations under flexural loading without significant loss of strength. Then, according to the definition, the mortar beam in this paper does not have ductility due to the excessive loss of strength. It is suggested that the authors explain and revise this part of the analysis.

4. The author established a reasonable numerical model, but it was only used to verify the experimental results in this paper. It is suggested to supplement some parametric analyzes based on numerical models.

Author Response

please see attached pdf

Author Response File: Author Response.pdf

Reviewer 3 Report

Abstract is not clear and needs extensive work by the author.  focus on the main outcomes to be short listed in the abstract as well as samples number and concept.

Conclusions are not clear to the reader. this is the most important part in this research to be clearly presented.

Author Response

please see attached pdf

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Great improvement in methodology and results analysis. I still disagree with the course of DOE and general hypotesis but that will be judged by other scientists. I appreciate the effort to improve the article and hope that this will contribute to the competence of the authors. 

Reviewer 2 Report

The reviewer has no further questions about this manuscript.