Autogenous Healing in 10-Years Aged Cementitious Composites Using Microfibers and Superabsorbent Polymers

Round 1

Reviewer 1 Report

The manuscrip describes an experimental campaign performed on 10-year old mortar samples, to evaluate their self-healing capability. Four mixes are compared, a reference one, a mix with a SAP type A, and two mixes with a SAP type B (in two dosages). Self-healing is evaluated by means of the strength regain.
The content and topic of the manuscript is of interest, since most of the experiments performed on self-healing cover younger age elements, and there is certainly a gap to cover concerning older elements. The experimental campaign performed and the conclusions are sound, but there are several points that should be improved.

Introduction
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- from line 45-64 clarify if the ages indicated in the text refer to cracking ages or start of the healing process
- sentences in lines 46 and 48 may benefit from an order change, please consider explaining first that there is a decrease in the healing capability with the age, before explaining the possible causes.
- line 79, consider moving the reference 36 to the following sentence

Materials and methods
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- The mix design would benefit from further clarification of the ratios indicated next to each component. As it is now, it is very hard for the reader to understand what 1:1 or 0.7:1 (etc.) are referring to.  
- Was wet-dry cycles' procedure performed daily during 10 years? Including weekends? Was it an automated system? Please clarify

Results and discussion
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- Lines 122 to 126. This paragraph would be clearer if the symbols from Table 1 were included here, instead of including them in the caption.
- Lines 122 to 126. The parameter to evaluate the ductility should be a strain. Strain-hardening is a specific type of behaviour, not a strain parameter. The author should be also careful, since when testing by bending test, if any hardening response is detected, it should be described as deflection-hardening (strain would be if tested under tension).
- Table 1, explain in the text previous to the table or in the caption what is the meaning of the number after the +- symbol. It is probably the standard deviation, but it should be explicitly mentioned. Also include the number of specimens tested per combination.
- Given the std. dev values of the first-cracking strength, it seems that the four mixes are similar in average, and it is worth mentioning the high dispersion of the SAP mixes.
- Line 146: is the presence of calcium carbonate an assumption or has it been tested? please clarify
- Fig 1-4. Please avoid the use of smooth curves, since they add artificial inflexion points that may not reflect the behavior of the results
- The parameters represented in Fig 2 and Fig 4 need further clarification of their meaning, with explanatory figures and/or expressions.
- Fig 4 needs further explanation. What is each curve representing? A group of specimens? Please clarify.

- The manuscript only provides results regarding the mechanical regain. Were the cracks visually fully closed or partially?


Conclusions
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The conclusions are too general, they should include more specific conclusions that can be deduced from this work.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

The submitted manuscript entitled as "Autogenous healing in 10-years aged cementitious composites using microfibers and superabsorbent polymers" written by Didier Snoeck presents a systematic study on the healing ability of a decade old cement-based composite which are reinforced by addition of PVA microfibers. The samples with superabsorbent polymers additionally contain two polyacrylate-type SAPs.  The assessment of the autogeneous healing efficiency was performed using the four-point-bending testing. Three different storage (temperature/humidity) conditions were used. The results showed that small crack widths can still be healed after 10 years. It was shown that the samples containing SAPs show greater healing capable of swelling what makes them a promising sustainable option for the future. A topic is very actual and interesting for many research groups around the globe, especially due to the lack of studies on the long period matured cementitious materials. The article is well written and nicely organized using the most relevant publications in the field and its introduction can serve as a sort of a review.

Based on all upon written I firmly believe that the manuscript can be published in its current state.

Author Response

Thank you for your very kind review of the paper. 

Reviewer 3 Report

In this work, Snoeck shows the healing capability of ten-year-old cementitious composites with microfibers and superabsorbent polymers curing under different conditions. The obtained experimental results were compared to the previous work without superabsorbent polymers. The work will interest researchers in the field of self-healing cement and those in the areas of cementitious composite using microfibers and superabsorbent polymers.

 

I have two comments, hopefully further strengthening this paper. After addressing these comments, I would be happy to recommend the publication of this work.

 

(1)   In the Materials and Methods or Results and Discussion section, the author should describe the Samples names shown in Table 1 before using them.

(2)   In the Conclusions section, the author should conclude more results, such as the difference between the three composites.

Author Response

Thank you for your kind review. Please find the answers below.

1) The samples are now specified in the Materials and Methods section. Following sentences have been added:

"The reference samples were called REF."

"The sample series names were respectively called: 0.5A, 0.5B, and 1.0B."

2) The three SAP mixtures are now added to the conclusions section. Please see the red additions to the text below: 

In general, the samples containing SAPs show greater healing compared to the reference samples and are still capable of swelling after decade of storage in an alkaline cementitious environment. This makes them a sustainable option for the future, as less maintenance and repair will be required. It is worth mentioning that the SAP particles were not exposed to UV light because they were stored inside in the cementitious material. These dark conditions are very beneficial in preventing SAP degradation.

Comparison of the different sample series showed that the healing conditions for 0.5A and 0.5B were similar in terms of self-healing ability and regain in mechanical properties, for all ages studied. However, more SAP B (0.5B towards 1.0B) could be added to the mixture as less initial mixing water is required as compared to the same amount of SAP A, without compromising the initial mechanical properties. This leads to a better overall healing performance as the healing is further promoted due a larger quantity of SAPs being present in the cementitious matrix, both at early age as well as after a decade of maturing.