The Immobilisation of Heavy Metals from Sewage Sludge Ash in CO₂-Cured Mortars

Round 1

Reviewer 1 Report

Dear Editor and Authors.

It has been my pleasure to review this paper. The authors provide a propose about the use of sewage sludge ash in CO₂-cured mortars based on three different reactive compounds. The mixes were characterized and the compressive strength analysed. In addition, the content of heavy metals was measured.

The topic of this paper is appropriate to the scope of Sustainability. However, some corrections and comments should be taken into consideration before accepting it.

Starting by listing a few typos and misprint:

• Lines 83, 236, 241, 299, and 306: subindex for CO₂-mortar or CO₂-cured as authors wrote in lines 248, 292, 307, etc.
• Line 84: “… reactive magnesium…” instead of “…Reactive magnesium…” unnecessary capital letter.
• Line 228: “… remained uncarbonated brucite…” instead of “remained uncarbonated Brucite…” unnecessary capital letter.
• Line 112: Incorrect sub-section title (repeated from previous sub-section). Should be something as “3. Specimen preparation”.

On the other hand, I would like to give some questions to authors. In the first of these. In the subsection "Materials", the authors describe that they have ground and sieved reagents to certain particle sizes. Why was r-MgO material sieved to 125 µm and EAFS material to 45 µm?

In lines 108 to 110, the authors used different water-solid ratios and based this on previous experiments. Do you have a reference to these previous studies? If so, and they are published, they should include the bibliographic reference.

I insist on a pleasure review of the manuscript submitted by the authors. I look forward to hearing from you.

Regards,

Reviewer.

Author Response

Dear Reviewer,

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

According to the reviewer, the mortar rocks were not clearly described. It is proposed to introduce a description by weight that separates the aggregate fraction from the binder. How were mortars with such a low water-binder ratio made? What was the consistency of the mortars and thus the thickening procedure?

It is proposed to add an explanation of why such a low compressive strength characterizes the obtained mortars. Moreover,  there is a lack of data on the pH of water extracts, essential for the material's durability and the environment.

Author Response

Dear Reviewer,

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors presented a method of using accelerated carbonization curing technology to produce CO₂-cured mortars incorporating SSA, and carried out a series of evaluation to prove its feasibility. A big well done to the authors for choosing such a topic as only limited studies have been conducted in this area. The reviewer believes that this work is publishable after revision as follows:

1. In line 76，TG-DTG or FT-IR，it is the first time that mentioned in the article，the full name should be provided.
2. Section 2.2 has the same title as section 2.3.
3. Line 210 of the article” Besides that, the second peak of PC seems to be a little misplaced due to usually the peak of dehydration of calcium hydroxide is observed in temperatures slightly above 400 ˚C.” Please try to explain this phenomenon.
4. Figure 4，Legends need to be more clearly distinguished，colors or shapes.
5. Section 3.5 of the article: Please make a more in-depth analysis of the experimental data in Fig. 6.
6. Section 3.2 Compressive Strength, is it the uniaxial compressive strength or strength measured at different confining pressures?
7. Some recent relevant references should be included, such as “D Gu, H Liu, X Gao, D Huang, W Zhang. 2021 Influence of cyclic wetting-drying on the shear strength of limestone with a soft interlayer. Rock Mechanics and Rock Engineering. 54:4369–4378.” “Wang LQ, Yin YP, Huang BL, Dai ZW. 2019. Damage evolution and stability analysis of the Jianchuandong Dangerous Rock Mass in the Three Gorges Reservoir Area. Engineering Geology, 265: 105439.” “D Liu, H Liu, Y Wu, WG Zhang, Y Wang, M. Santosh. Characterization of geo-material parameters: Gene concept and big data approach in geotechnical engineering. Geosystems and Geoenvironment 1 (2022) 100003” Recent references are missing. 
8. The conclusion part should be further condensed and the innovation points should be stressed.

Author Response

Dear Reviewer,

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The authors have not responded to all my questions. Try to make point to point reply.