Round 1

Reviewer 1 Report

 

Dear authors,

Thanks for your contribution to Fire.

With minor revisions of the manuscript, it might be accepted.

The opinions are set out below:

 

1. Please revise structure of the manuscript according to the guide for authors, which could be accessed from the following web link. https://www.mdpi.com/journal/fire/instructions#preparation
2. The spelling and writing of this manuscript should be verified accurately.
3. Please prepare the manuscript concisely.

Sincerely yours,

Author Response

• Manuscript has been revised to meet the structure and formatting of the MDPI guide. Citations have been changed to ACS style and in text references have been numbered accordingly.  Figures have been converted to images.
• Spelling has been reviewed.
• Manuscript has been revised.

Reviewer 2 Report

The paper is well written and coherent. More details should be provided such as the criteria for selection of the test attributes (see also comment below). Also, a description of the common test methodology for measuring the compressive strength would be useful, because is not clear whether all reviewed tests follow the same procedure.

 

Specific

Line 12 - heat release rate (HRR) is more precise than heating rate, in the context of fire development.

Line 56 - that the natural curve could provide a reduction of the strength in relationship with the nominal fire is improbable, as the latter is very conservative

Line 71 – how is the choice of the set of parameters conducted? What are the criteria for this selection?

Line 68 - a short description of the test, the existence of standard procedures and of the results would be useful here.

Line 165 – the rate of heating is very low and corresponding to quasi-static condition, not very common in real-world fires.

Author Response

1. Rates of compartment heating and cooling are evaluated in this paper due to their common usage in existing experimental work and design standards. Looking specifically at HHR may be an avenue for future work.
2. This statement is the basis of the paper. Although the standard fire reaches conservatively higher temperatures than typical natural fires, the impact of variable heating rates, exposure durations, and cooling rates also influence concrete strength.  Understanding these influences helps designers in two ways.  One, they can be confident they are always producing a conservative and safe design.  Two, when justified, they can tailor their design to a natural fire resulting in a more efficient and economical solution.
3. The goal for criteria selection was to get concrete samples to their most basic state. By looking at just plain NSC concrete we can get a baseline, which further research work can expand on.  A revision has been added to Line 71 explaining this methodology.  Furthermore, the majority of existing experimental work is conducted on plain NSC samples.  Restricting the parameters defined in Line 71 allowed for the use of more existing work.
4. A revision has been added to Section 3 providing reference for the testing methodology and results.
5. It is agreed that the heating rate of 3°C/min is very low.  But establishing a low and high rate and comparing the two results is the goal of the evaluation.  Our findings showed that whether a fire heats at 3°C/min or 30°C/min, the influence on concrete strength is comparable.

Reviewer 3 Report

This report is well presented and organized.

The results are rather qualitative and they are a first good step for a more quantitative approach to this interesting problem between fire dynamics , heat transfer and material ( concrete) molecular and strength response.

The starting and ending conditions for cooling must be quantified precisely. This is an important revision to the paper.

A short list of abbreviations may be useful.

 

Author Response

1. The cooling section has been revised to provide greater clarity to the definition of cooling rates and Figure-2 has been revised to include annotations for the start and end of the cooling period.
2. It is our preference that the abbreviations be defined in text as the majority of them have accompanying graphics to provide greater clarity to their definition.  A list at the beginning of the paper would likely create greater confusion than not.

Reviewer 4 Report

The paper is a collection of several experiments on concrete materials at high temperatures in different conditions and under different fire curves, underlining the influence of several parameters on the concrete behaviour. Even if no relevant news is reported, the paper can represent a good review for the scientific community.  Please consider the following suggestion for improving the paper.

• Page 1, in the introduction, in order to underline the advantages of the concrete in fire, briefly describe the fire behaviour of the other structural materials (e.g. steel) in which you have to use also protection materials; about this topic please consider the following research “Approach for modelling thermal properties of intumescent coating applied on steel members, by de Silva, D., Bilotta, A., Nigro, E.”
• Page 2 line 45; please replace “broken” with “ divided”
• Page 2 line 54; the nominal fire curve, such as the ISO834 is not a constant curve; indeed it has an exponential growth over time; please pay attention to this aspect and clarify it;
• Page 2 line 59-61 the heating rate does not depend only on the fire load, but also on compartment ventilation; please pay attention to this aspect and clarify it;
• Page 2 line 66-67 please check the English;
• Page 3 line 84 please replay “displays” with “shows”;
• Page 9 line 220; one of the main problem of the concrete spalling is not also the reduction of the section, but the direct exposure of the steel reinforcement due to the concrete cover spalling…please clarify this aspect.

General in all the paper:

• Please take into account the following recent research “Considerations on computational modeling of concrete structures in fire” by Shuna Ni and Thomas Gernay;
• The English need to be improved.

Author Response

• The need for protective coatings with steel and timber has been added to the introduction.
• Wording has been changed from “broken” to “divided”.
• The wording of “constant” has been changed to “always the same” to better represent the intent of this sentence.
• The context of slow and rapid heating has been revised for clarity.
• English has been reviewed.
• Wording has been changed from “displays” to “shows”.
• A revision has been made indicating the importance of rebar exposure as well.  This subject is largely avoided however as this paper focuses on unreinforced specimens and concrete strength.  The impact on reinforcement is a subject for further work.
• English has been reviewed.