Microstructure and Strength Properties of Sustainable Concrete Using Effective Microorganisms as a Self-Curing Agent

Round 1

Reviewer 1 Report

This manuscript reports the use of Effective Microorganism Solution as curing agent in self-curing concrete. The authors studied the physical and chemical properties of Effective microorganisms, workability performance, strength properties and microstructure characterization of self-healing concrete mixtures.

I am evaluating this paper for the third time. The manuscript is much improved, but the authors still have to perform some experiments in order to prove their results.

I can re-evaluate the appropriateness for publication when these comments cited below are properly addressed.

1- What is the effect of pH on the microorganism’s viability?

2- Samples of concrete with molasses and without EM must be prepared to conclude about the effect of molasses on concrete proprieties.

3- What is the type of OPC used in this study. A mechanical strength value of 33Mpa at 28 days is little according to the amount of cement used in concrete specimens (455 kg/m3 with E/C=0.52). The authors must justify this mechanical strength.

4- Which number of samples was tested?

Author Response

Reviewer' comments are greatly appreciated. 

Authors' response to reviewer' comments as attached. 

Author Response File: Author Response.pdf

Reviewer 2 Report

Manuscript ID：sustainability-1833624

Title：Microstructure and Strength Properties of Sustainable Concrete Using Effective Microorganism as Self-curing agent

Suggestion: Major revision

Review: This paper investigated the impact of effective microorganism (EM) as a new self-curing agent on the microstructures and strength properties of sustainable concrete. The following comments are noticed during the reviewing:

Detailed comments:

1. The application of bacterias in concrete has been investigated a lot. The authors are encouraged to present the new findings in their work compared with the previous studies.

2.  5, 10, 15, 20 and 25% of EM are the solution or the dry weight? If it is dry weight, is it only the bacterias or including the molasses. Please state clearly.

3. Error bars must be provided in Figs. 12, 20-22.

4. Influence of molass on the strength of concrete should also be discussed in details.

5. I think the strength increasement is mainly due to the reduction of effective w/c, and further decreasement is mainly due to the molass and organism parts, which could weaken the connections between hydration products. What is the main novelty of this paper?

6. More recent literature on additives used in concrete materials should be discussed and compared, such as the work on upcycling waste seashells by Prof. Engui Liu, and the work on sludge ceramsite concrete，the role of silica fume and steel fibre on recycled aggregate concrete from Prof. Jianhe Xie.

Author Response

Reviewer comments is highly appreciated.

Our response to reviewer' comments as attached. 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Sustainability-1833624R1

First, I want to thank the authors for their efforts in responding to my comments. The main problem of this paper is the lack of a reference concrete. To conclude correctly about the results, it is necessary to have samples with molasses and without EM for all the studied properties.

Throughout their manuscript, the authors discuss the effect of molasses on the fresh and hardened properties of concrete. For example L368-369, L435-453, L474-477, L512-515... and L485-494 when the authors have shown through their experiments that molasse slightly improve the compressive strength of concrete at 28 days. Then, we agree that molasses influences the fresh and hardened properties of concrete. Therefore, all conclusions in this paper must be supported by a lack of molasses effect. The same idea must also be applied to the conclusions about the physicochemical properties of microorganisms.

Moreover, the authors showed an increase in compressive strength from 35.8 to 42.8 MPa when effective microorganisms are used. Is this difference significant? What are the values of the obtained standard deviation.

In figure 17, the microstructure of concrete without EM seems to be denser than concrete with EM. This result contradicts the Figure description L691-699 and the main conclusion of this paper.

Author Response

Reviewer' comments are greatly appreciated. please see attached file. 

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper has been revised accordingly. The XRD of concrete sample is not recommended because of the aggregates. Fig. 16 and 17, the indicated Ca(OH)2 may not be correct, this must be modified. More recent literature on CaCO3 should be cited, such as upcycling waste seashells in RCR by Engui Liu. In Fig.1, I see the two different phases are similar. Fig. 19, below one, the abrupt drop at 900 degrees?

Author Response

Reviewer' comments are greatly appreciated. 

Author Response File: Author Response.docx

Round 3

Reviewer 1 Report

Please italicize the name of the bacteria

Bacillus subtilis