Post-Fire Mechanical Properties of Concrete Reinforced with Spanish Broom Fibers
Round 1
Reviewer 1 Report
The reviewer considers that the manuscript "Post-fire mechanical properties of concrete reinforced with Spanish broom fibers" should be accepted for publication subject to minor revision. The manuscript presents preliminary results on the effect of high temperatures up to 400°C with the addition of Spanish broom fibers. The results are compared with those obtained with normal concrete and with concrete containing PP fibers. The manuscript is well written, with systematically organized sections, and attempts to address an interesting problem.
However, there are few minor shortcomings which the authors should addressed:
- abstract, line 13: Since the manuscript deals with the study of post-fire properties (i.e., residual properties), the mechanical properties were not determined at elevated temperatures as stated in the article. It is suggested that the above statement be corrected.
- I am a bit curious why the authors added 1% (9-10 kg/m3) of the studied fibers to the studied concrete mixes? It is well known that an amount higher than 3 kg/m3 significantly deteriorates the consistency of the fresh mix. Moreover, to avoid explosive spalling, an amount of 2 kg/m3 is recommended. Therefore, please explain the practical application of the studied concrete mixes.
- Please explain how the dynamic modulus was determined - how did the authors treat the Poisson's ratio required to calculate the dynamic modulus? It should change with changes in temperature.
- The explanation for the discrepancy between the results for compressive strength and modulus of elasticity on page 12, lines 341-444 is not clear: "This loss is probably due to the fact that the determination of compressive strength is only possible on different specimens....".
- Please also indicate how many specimens were tested for each temperature and mix, i.e. for the results given in Table 4 and Figures 6-11.
- Did any of the tested specimen undergo spalling during heating in the furnace? If so, please indicate the type of such specimen(s) and conditions of spalling.
Author Response
Dear reviewer, thank you for your comments - it helped us to improve the quality of our paper as follows:
The reviewer considers that the manuscript "Post-fire mechanical properties of concrete reinforced with Spanish broom fibers" should be accepted for publication subject to minor revision. The manuscript presents preliminary results on the effect of high temperatures up to 400°C with the addition of Spanish broom fibers. The results are compared with those obtained with normal concrete and with concrete containing PP fibers. The manuscript is well written, with systematically organized sections, and attempts to address an interesting problem.
However, there are few minor shortcomings which the authors should addressed:
Point 1: abstract, line 13: Since the manuscript deals with the study of post-fire properties (i.e., residual properties), the mechanical properties were not determined at elevated temperatures as stated in the article. It is suggested that the above statement be corrected.
Response 1: As per your suggestion, we have changed line 13: „The mechanical properties were determined at room temperature and post-fire mechanical properties on elevated temperature so its use for improving the fire resistance of concrete could be determined.“
Point 2: I am a bit curious why the authors added 1% (9-10 kg/m3) of the studied fibers to the studied concrete mixes? It is well known that an amount higher than 3 kg/m3 significantly deteriorates the consistency of the fresh mix. Moreover, to avoid explosive spalling, an amount of 2 kg/m3 is recommended. Therefore, please explain the practical application of the studied concrete mixes.
Response 2: Various percentages of fibers can be found in the papers, for example [25] used 27 kg of sisal fibers per m3 (3%). We have already tested Spanish broom and hemp in cement composite in the amount of 0.5 and 1% by volume [28] and according to [26], 1% PP and hemp fibers gave good results. So we decided to make mixtures with 1% fiber. In future research, we will reduce the amount of fiber.
[25] Nwankwo, P.O.; Achuenu, E.: Compressive Behaviour of Sisal Fibre Reinfoced Ternary Concrete at Elevated Temperatures. Int. J. Adv. Res. Technol. 2014, 3(8), 123-131.
[26] Netinger Grubeša, I.; Marković, B.; Gojević, A.; Brdarić, J. Effect of hemp fibers on fire resistance of concrete. Constr. Build. Mater. 2018, 184, 473–484.
[28] Juradin, S.; Boko, I.; Netinger Grubeša, I.; Jozić, D.; Mrakovčić, S. Influence of different treatment and amount of Spanish broom and hemp fibres on the mechanical properties of reinforced cement mortars. Constr. Build. Mater. 2021, 273, 121702.
We have changed on page 4: The amount of each sort of fiber was 1 % of the total volume, based on [26, 28].
and added the practical application of the studied concrete mixes, page 15: These results need further investigations to understand the behaviour of concrete reinforced with Spanish broom fibers at room temperature as well as exposed to elevated temperatures especially because these types of concrete can provide low-cost building material for residential and low-rise buildings.
Point 3: Please explain how the dynamic modulus was determined - how did the authors treat the Poisson's ratio required to calculate the dynamic modulus? It should change with changes in temperature.
Response 3: Thank You for Your comment, we added on page 8: The dynamic modulus of elasticity was calculated assuming a Poisson's ratio (µ) of 0.20 for all temperatures and cooling times. This value is selected based on [46] in which it is stated that a Poisson's ratio is ranged from 0.11 to 0.25 at 20 ºC to 400 ºC. Above 400 ºC, Poisson's ratio is increased, which is not related to this examination.
[46] Naus, D.J. The Effect of Elevated Temperature on Concrete Materials and Structures - A Literature Review, Oak Ridge National Laboratory, United States, 2006, pp. 204.
Point 4: The explanation for the discrepancy between the results for compressive strength and modulus of elasticity on page 12, lines 341-444 is not clear: "This loss is probably due to the fact that the determination of compressive strength is only possible on different specimens....".
Response 4: True, it is very vaguely written. It now says (page 14): This difference in results is probably due to the fact that the determination of compres-sive strength is possible only once on the specimens, while the UPV and dynamic mod-ulus of elasticity is determined on the same specimens after different test conditions (non-destructive method).
Point 5: Please also indicate how many specimens were tested for each temperature and mix, i.e. for the results given in Table 4 and Figures 6-11.
Response 5: page 7: “… a total of 60 cylinders. For each mixture with Spanish broom fibers, 10 specimens were made, due to the limited amount of processed fibers and 15 specimens were made for mixtures E and PP.”
Page 8: “At room temperature, the weight, UPV and dynamic modulus of elasticity were deter-mined on all specimens of each mixture. At 100 ºC (0h) the weight, UPV and dynamic modulus of elasticity were determined as well as for room temperature only reduced by the specimens on which the compressive strength was tested at room temperature. At other temperatures and cooling times, 3 and 2 specimens, respectively, were tested for all the above properties. Three specimens for EE and PP mixtures and 2 specimens for SB-concretes.”
Point 6: Did any of the tested specimen undergo spalling during heating in the furnace? If so, please indicate the type of such specimen(s) and conditions of spalling.
Response 6: page 15, “No test specimen underwent spalling during heating in the furnace”
The authors hope that the quality of the paper is better now, with your suggestions accepted.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The objective of the paper is to assess the fire behavior of concrete reinforced with Spanish broom fibers. The Authors compare the mechanical properties of fiber reinforced concrete characterized by a fixed amount of spanish broom fibers (10 kg/m3), obtained with different maceration techniques (mechanical, biological, chemical) after exposure to high temperature. The results are compared with those obtained on two reference concretes having the same compositions, without fiber reinforcement, and with polypropylene fiber reinforcement (9.1 kg/m3).
Although the assessment of fire behavior of concrete reinforced with natural fibers is an interesting topic, in the reviewer opinion the present version of the manuscript is unsatisfactory, since they are relevant issues that need to be addressed.
First of all, in the reviewer opinion the structure of the paper should be modified. In fact, it must be remarked that in the illustration and discussion of the results, the Authors mix observations derived from the study with findings derived from the literature, making very difficult the separation of the original contributions. Moreover, the discussion often appears too elementary, being an obvious summary of the tables and figures.
Anyhow, the main issue is concerning the setup of the experimental campaign. For each investigated case, compressive tests are performed on a single specimen: in this way the natural scattering of the experimental result is disregarded. This consideration could also explain some “strange” results in table 4. An appropriate comparison of different concrete mixes requires some statistical elaboration, so that several specimens should be tested for each case, to estimate the dispersion of the results. It must be observed that different mixes exhibit properties whose differences are comparable with the scattering of a single concrete. This aspect should be duly considered and discussed.
Other minor remarks:
Please give explanation of acronyms as soon as they appear in the manuscript: for example, TG (Thermogravimetric), DTG (Derivative thermogravimetry) and DTA (Differential Thermal Analysis) are given only in the abbreviated form.
Quality of Figure 3 should be improved and other relevant points of the curves, recalled in the text, should be better identified, so making easier the exam of the figure itself.
Author Response
Response to Reviewer 2 Comments
Dear reviewer, thank you for your comments - it helped us to improve the quality of our paper as follows:
The objective of the paper is to assess the fire behavior of concrete reinforced with Spanish broom fibers. The Authors compare the mechanical properties of fiber reinforced concrete characterized by a fixed amount of spanish broom fibers (10 kg/m3), obtained with different maceration techniques (mechanical, biological, chemical) after exposure to high temperature. The results are compared with those obtained on two reference concretes having the same compositions, without fiber reinforcement, and with polypropylene fiber reinforcement (9.1 kg/m3).
Point 1: Although the assessment of fire behavior of concrete reinforced with natural fibers is an interesting topic, in the reviewer opinion the present version of the manuscript is unsatisfactory, since they are relevant issues that need to be addressed.
First of all, in the reviewer opinion the structure of the paper should be modified. In fact, it must be remarked that in the illustration and discussion of the results, the Authors mix observations derived from the study with findings derived from the literature, making very difficult the separation of the original contributions. Moreover, the discussion often appears too elementary, being an obvious summary of the tables and figures.
Response 1: Thanks for your observation. The structure of the paper is modified, Figure, reference and more discussion were added. We try to explain everything what is important for this subject of paper.
Point 2: Anyhow, the main issue is concerning the setup of the experimental campaign. For each investigated case, compressive tests are performed on a single specimen: in this way the natural scattering of the experimental result is disregarded. This consideration could also explain some “strange” results in table 4. An appropriate comparison of different concrete mixes requires some statistical elaboration, so that several specimens should be tested for each case, to estimate the dispersion of the results. It must be observed that different mixes exhibit properties whose differences are comparable with the scattering of a single concrete. This aspect should be duly considered and discussed.
Response 2: Answer: page 7: “… a total of 60 cylinders. For each mixture with Spanish broom fibers, 10 specimens were made, due to the limited amount of processed fibers and 15 specimens were made for mixtures E and PP.”
Page 8: “At room temperature, the weight, UPV and dynamic modulus of elasticity were deter-mined on all specimens of each mixture. At 100 ºC (0h) the weight, UPV and dynamic modulus of elasticity were determined as well as for room temperature only reduced by the specimens on which the compressive strength was tested at room temperature. At other temperatures and cooling times, 3 and 2 specimens, respectively, were tested for all the above properties. Three specimens for EE and PP mixtures and 2 specimens for SB-concretes.”
Standard deviation values have been added, Table 4.
Point 3: Please give explanation of acronyms as soon as they appear in the manuscript: for example, TG (Thermogravimetric), DTG (Derivative thermogravimetry) and DTA (Differential Thermal Analysis) are given only in the abbreviated form.
Response 3: Page 5: “The thermal properties of Spanish broom fibers prepared by maceration and fibers of PP were determined using an instrument for thermogravimetry–differential thermal analysis (TG/DTA) Pyris Diamond device (Perkin Elmer). Thermal properties were measured in the temperature range from 30 to 550 °C, at a heating rate of 20 °C /min. Measurements were performed in an inert atmosphere using nitrogen as a purge gas, with a constant flow rate of 100 mL/min. The thermogravimetry curves and their der-ivation curves (TG/DTG) of fibers prepared by maceration natural Spanish broom (SB-5, SB-15 and SB-S40) and TG/DTG-DTA curve of fibers of Polypropylene (PP) are shown in Figure 3.”
Point 4: Quality of Figure 3 should be improved and other relevant points of the curves, recalled in the text, should be better identified, so making easier the exam of the figure itself.
Response 4: Figure 3 is replaced by new one as You suggested.
The authors hope that the quality of the paper is better now, with your suggestions accepted.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
The Authors addressed the reviewer comments, The quality of the paper is now sufficient to make it acceptable for publication.
