Applications of Polyaniline–Alkaline Copper Carbonate Composites for Anti-Bio-Attachment of Concrete in Marine Environments
Round 1
Reviewer 1 Report
GENERAL COMMENTS
1. The manuscript deals with research work related to the use of polyaniline-alkaline copper carbonate composites for avoiding the bio-attachment on concrete exposed to the sea water. The subject is interesting. However, there are some issues which must be addressed by the authors.
2. The anti-bio-attachment is a property which is needed only at the surface of the concrete structures exposed to the sea water. In this sense using the composites as an additive to the whole bulk concrete might be considered as a waste of material and also as a possibly unnecessary increase of the economic cost of the concrete (not yet quantified). For this reason, I think that the research should give priority to the use of the composites as coatings, instead of using them as additives to the bulk concrete. The authors should at least discuss this point in Section 3 (Results and Discussion)
3. The composites contain copper ions, which eventually could be leached out of the concrete matrix (if used as an additive to concrete) or leached out of the coating (if used as a coating). The authors should at least discuss if there is a possibility of significative toxic contamination of the medium (sea water) in the case of leaching of the copper ions, and if some research on this subject is needed to ascertain the question. This could be included in Section 3 (Results and Discussion).
SPECIFIC COMMENTS
4. Abstract and Conclusions.
The authors state that “the yield of the composite was above 96.46% with a good output”.
It is unclear the meaning of the sentence. Is it the yield of the chemical reactions leading to the preparation of the composite?
This is especially relevant in the case of the Abstract, which should be able to be understood independently of the rest of the article.
5. Page 2, lines 48-49.
The authors write: “… the biological metabolic acids react with the concrete body to produce calcium alumina”.
Calcium alumina is not an acceptable name for a chemical compound. Most probably the authors refer to hydrated calcium aluminates (like ettringite) which have expansive character giving rise to concrete damage. Please, check and correct.
6. Page 2, lines 72-73.
The authors write: “polyaniline is a good choice for concrete coating materials [37]”.
Reference [37] is not a good reference for this sentence, since the research presented in [37] is related to coatings on steel surfaces, not on concrete. Please, check and correct.
7. Section 2.2.2, lines 201-202.
The authors write: “After the specimens were maintained”.
Most probably the authors mean: “After the specimens were cured”.
8. Section 2.5, lines 250-251.
The authors write: “The artificially enhanced marine wastewater was prepared using seawater salt (3.6 g/L)”.
The average sea water salinity is 35 g/L, see for instance ASTM D1141-98. Hence the artificial sea water used by the authors is far less concentrated (about ten times less concentrated) than the actual sea water. This means that the electrolyte used could be not representative of sea water. Please, check.
9. Section 3.3.2, lines 363-365.
The authors write: “the concrete test plates were removed, and more colonies and attachments of biological organisms appeared on the concrete test plates compared to that observed with the group with no additives”.
This sentence seems contradictory to the rest of the manuscript and to the results. Table 6 indicates that the plates with no additives had a higher number of organisms attached than those with additives. Please, check and correct.
10. Section 3.3.2, lines 376-379.
The authors write: “After 14 days of immersion, the concrete test plates were removed, and the mass of each test plate was measured. The mass before and after immersion was compared to obtain the difference, which represented the mass of the biological organisms attached to the test plate”.
Is there a possibility of errors in the mass differences due to water absorption by the porous concrete? It is not clear in the experimental procedure if the plates were water saturated or partially dry before immersing them into the liquid. Please, check and give information allowing to rule out the possibility of such type of experimental errors.
11. Section 3.3.3, lines 394-395.
The authors write: “concrete specimens with no addition of the composite were susceptible to the corrosive effects of seawater and organisms”.
Later, on lines 398-399: “concrete specimens were susceptible to biofouling and corrosion”.
In this work the authors have conducted experiments on biofouling, but not on corrosion of concrete. In my opinion these statements should be changed eliminating any mention to corrosive effects of sea water or to corrosion of concrete.
12. Section 3.4, lines 454-455.
The authors write: “the compressive suspension of the specimens”.
I think it should be: “the compressive strength of the specimens”.
13. Section 4 (Conclusions), lines 490-493.
The authors write: “In the accelerated laboratory experiments for the avoidance of biological organisms on suspension in actual sea environments, the concrete test slabs showed that the biological organisms that were attached were mainly barnacles and sea anemones in Zhoushan sea waters”.
It seems that in this Conclusion the authors are mixing the information obtained in accelerated laboratory experiments with that obtained in the real exposure tests (blocks exposed to Zhoushan sea waters). I recommend writing separate Conclusions for the results of experiments in laboratory and for the results obtained in the real exposure tests (blocks immersed in the sea).
14. Section 4 (Conclusions), lines 506-507.
The authors write: “Whether it was added directly to concrete as an additive or coated on concrete, it can effectively prevent concrete from being corroded by seawater…”.
This sentence should be eliminated since the authors have not performed any experiment of concrete corrosion by seawater. See my previous comment number 11.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
In the study, a chemical composite was developed in order to prevent biofouling in seawater. Sulfate attack, chlorine, CO2, and biological effects, as well as wetting-drying cycles, can be counted as factors that cause the deterioration of concrete exposed to seawater. It is understood that the additive used in the presented study reduces the biological effect. However, it should be explained with which mechanisms the other effects (sulfate, chlorine, sulfite, etc.) are reduced.
On the other hand, it is explained that the composite used is a toxic substance. For this reason, it should be investigated whether there is any leaching into the sea due to applying it as a coating or by adding it to the mixture.
Page 3 line 118: It is better to give the name of the reagents used before giving their formulas.
Page 4, line 165: More information should have been given about how the composite was added to the concrete. Furthermore, more information can be provided about the composition of the prepared concrete.
Page 5, line 187: Is it fly ash?
What was the mineral powder?
Page 5, line 206: How was the composite applied over the concrete specimens? What was the thickness of the coating?
Page 5, line 211: It should be explained in which part of the intertidal zone the specimens were stored. Were they exposed to both air and water subsequently?
Page 14, Fig. 11: Is there any reason for the slight increase in compressive strength for the coated specimens before sea trial hoisting?
age 15, Fig. 12: Is there any reason for the improvement of splitting tensile strength for the specimens before sea trial hoisting with the addition rates of 0.05% and 0.10%?
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
The authors ,compares polyaniline-alkaline copper carbonate composites as an additive and coating material, however to improve the reading experience and appreciate the work the following are suggested
The paper doesn’t present the technical details on how the polyaniline-alkaline copper carbonate composites is reacting with concrete as it is changing the setting time and influencing the strength characteristics.
The author should present the state of review using alkaline copper carbonate and polyaniline as bio-fouling and anti-corrosion in marine structures its merits and limitations which the present study is focusing or addressing.
Line 185-189, provide the mix design details in a table so that they are clear
Its not clear how many specimens were submerged in the sea for 30 d and how many for 90d and also how many were tested for accelerated test for bio organisms
Line 325, its mentioned that the setting time increases… pl. give the reasons for the same…. What is the reaction between the compound and other concrete constituents
Table 5 what does the total volume of concrete refers to and how it is significant in the present context
Table 6, How these biological organisms counted what is the methodology used
The authors claim that the durability of the structure is enhanced …. But how any tests or results related to durability are not presented
Line 497-500, what is happening to the concrete when the additive is more than or equal to 0.20%, explain the mechanism
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
All my previous comments to authors have been correctly addressed.
Reviewer 2 Report
While I did not get an answer to my question about why the chemical composite used prevented other effects of seawater (sulfates, chlorides, sulfides attacks) although it was an antifouling agent, other points I suggested were taken into account.
Reviewer 3 Report
The authors have addressed all the questions posed... The manuscript can be now accepted
