Cleaner Design and Production of Lightweight Aggregates (LWAs) to Use in Agronomic Application

Round 1

Reviewer 1 Report

The authors evaluated the LWA materials which have the possibility to use as fine aggregate with chemical analysis. Actually, this study was interesting. However, I found some significant problems.

 

So, I give to the authors some comments.

 

There are two things.

 

1. Lines 204-210: This is good information for readers to understand and studying the chemical aspect. But, How about using some algorithm form or figures?

 

    2. Table 3.

According to some studies, the Na2O and K2O are the critical components of ASR of aggregate. Usually, Natural sand almost has no Na2O and K2O, and Silica sand has 0.02~0.06% of Na2O and 0.01~0.03% of K2O. In addition, The normal coarse aggregate has 0.1~0.2% of Na2O and 0.04~0.15% of K2O.

These are the aggregate cases without the possibility of ASR.

According to the study of "Relation of ASR-induced expansion and compressive strength of concrete", It can be found that the ASR aggregate has upper than 2.5% of Na2O and K2O.

I think that the materials with RC, GS, K2CO3, and FG have the possibility of ASR risk when these materials are used as fine aggregate.

Therefore, this paper needs a revision of it.

Author Response

ANSWERS REVIEWER 1

 

Comments and suggestions for authors

1. Lines 204-210: This is good information for readers to understand and studying the chemical aspect. But, How about using some algorithm form or figures?

These lines describe the changes in mass and energy that the clays and wastewater sludge used in this research undergo with the increase in temperature and which are related to the different chemical transformations that take place during the heating process.  This description is linked to figure 1 where the TG-DSC curves of the indicated materials appear.

2. Table 3. According to some studies, the Na2O and K2O are the critical components of ASR of aggregate. Usually, Natural sand almost has no Na2O and K2O, and Silica sand has 0.02~0.06% of Na2O and 0.01~0.03% of K2O. In addition, The normal coarse aggregate has 0.1~0.2% of Na2O and 0.04~0.15% of K2O.

These are the aggregate cases without the possibility of ASR.

According to the study of "Relation of ASR-induced expansion and compressive strength of concrete", It can be found that the ASR aggregate has upper than 2.5% of Na2O and K2O.

I think that the materials with RC, GS, K2CO3, and FG have the possibility of ASR risk when these materials are used as fine aggregate.

 

We thank the reviewer for his indication that we consider very interesting and will take into account in the case that we design aggregates for use in lightweight concrete. However, we think that since the objective foreseen in the present investigation is the design of aggregates for use in agronomic applications it is not necessary to take into account the possibility of ASR risk since these materials are not going to be used as fine aggregate.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments in the attached document

Comments for author File: Comments.docx

Author Response

ANSWERS REVIEWER 2

 

1. The authors pay attention to the use of various types of waste to obtain lightweight aggregates. It is also worth describing the use of waste in the form of fly ash and used sorbents after sorption of petroleum substances and heavy metals.

The reviewer's indications regarding the recommended bibliography have been considered and a major revision of the different wastes used to obtain light aggregates has been carried out. New references have been included.

2. In Section 2.4. LWAS chemical-physical characterization when describing the MIP methodology, the authors of the manuscript present too many citations of using this technique to characterize the porosity of materials.,

 

The number of citations in this section has been reduced, leaving only the most relevant.

 

3. In Section 3.1. Materials characterization authors show mineral composition of selected clays in Table 4 (White (WC), black (BC) clays, red clay (RC)). According to the Reviewer, the diffractograms should be presented along with the interplanar distances characteristic for given crystalline phases (minerals) present in the clay.

 

The authors appreciate the reviewer's comment and will take it into account in future articles but have not included the diffractograms as only the mineralogical composition has been used in the discussion.

 

4. In Section 3.1. Materials characterization authors show Figure 1, which is not cited in the text of the manuscript.

 

Figure 1 is quoted in the text in line 205

 

5. In line 301, 303 it should be “lightweight aggregates instead of ”light aggregates”

 

It has been corrected

 

6. What is the correlation between the mineral composition of the raw materials (substrates) and the porosity of the obtained lightweight aggregates?

Table 4 shown the mineralogical composition of the clays. WC and BC have as a majority phase calcite (CaCO₃) and dolomite (CaMg(CO₃)₂) as a minority phase. These calcium and magnesium carbonates undergo a process of thermal decomposition. The temperature at which this phenomenon occurs depends on the chemical composition. Thus, calcite decomposes around 950 ºC while dolomite decomposes around 850 ºC according to the following reactions:

The release of carbon dioxide during thermal decomposition reactions contributes to the appearance of porosity in these clays as the gases produced are trapped by the vitreous phase in formation. In addition, the formation of the vitreous phase is favoured by the presence of the calcium and magnesium released, which can act as refractory elements, preventing the melting temperature from being reached and favouring the stabilization of the porosity before total melting is achieved. This would explain the high values of open porosity observed in the aggregates obtained from the WBC clay mix without additives (47.60%).

In contrast, the mineralogical composition of RC clay presents as its majority phases illite and kaolinite, minerals which present a high degree of vitrification. This, together with the absence of calcite and dolomite (the latter only appears as a minority phase) means that low porosity is generated in the aggregates obtained from RC (22.16 %).

 

Linares González, J., Huertas García, F., Capel Martínez, J. La arcilla como material cerámico. Características y comportamiento. Cuadernos de Prehistoria y Arqueología de la Universidad de Granada. 1983, 8, 479-490.

Betancourt, D., Martirena, F., Day, R., Díaz, Y. The influence of the addition of calcium carbonate on the energy efficiency of fired clay bricks manufacture. Revista de Construcción. 2007, 22(3), 187-196.

 

7. In Section 3.2.2. SEM surface analysis the presented SEM scan pictures (Figure 3) have too low magnification to be able to determine the open porosity which was described.

New SEM images have been added with higher resolution.

 

8. In Section 3.2.3. Mercury intrusion porosimetry (MIP) the authors present the results of total intrusion volume (TIV) and total pore area (TPA) by MIP. The results are discussed too generally, there is no correlation between the water absorption and open porosity of the studied aggregates.

A further discussion of the results obtained has been incorporated considering the recommendations of the reviewer.

 

9. Is manufacturing the fertilizer glass for economically justified in terms of energy consumption during ich thermal cycle for glass fusion?

The authors have not performed a complete Life Cycle Costing (LCC) in order to verify the economic impact of the glass fusion on the LWAs manufacturing. The use of organic compounds (brewery sludge or spent coffee grounds) as ore forming agents reduces the costs and improve the energy saving of the firing step respect to the traditional LWAs containing only clayed materials. Instead, the authors calculated according to the Method IPCC 2013 GWP 20y. the carbon footprint (CFP) of the LWAs mixtures with and without residues, as well as the presence of vitrified material within the specimens. The results underlined that the replacement of 15wt% of clay by brewery sludge (BS), corresponding to 15wt% less extraction of virgin raw materials, acts as alternative fuels inside the furnace, and reduces the demand for non-removable resources (electric energy, diesel, pet-coke). This directly affects the gas emissions, associated with the greenhouse effect and global warming. The use of 15wt% of BS reduces about 20% the emissions of Greenhouse Gases (GHG) (4.78 KgCO2 eq. ) respect traditional only clay mixtures. On the contrary, mixtures containing fertilizer glass are penalized by the fact that the process to produce the fertilizer glass increases the energy input due to the thermal cycle (increasing of 11% of the GHG emissions ( 5.33 KgCO2 eq. )) which has a total duration of 6.50 hours, reaching maximum temperatures of 1450°C. These findings are reported in the following paper: “ENVIRONMENTAL IMPACT ESTIMATION OF CERAMIC LIGHTWEIGHT AGGREGATES PRODUCTION STARTING FROM RESIDUES” (2020), International Journal of Applied Ceramic Technology. DOI: 10.1111/ijac.13665.

The use of vitrified nutrients (fertilized glass) is justified from an agronomic point of view at longer times (21 days) LWAs containing FG release more amounts of P and K. In particular, WBFG and RCFG show better phosphorus-controlled release capability in 21-days period (during the growing plants)respect to those containing the nutrients not vitrified (ashes) . This fact confirms the positive effect of the presence of glass within the aggregates.

 

10. When discussing results, please refer to the current research results of other researchers describing the discussed issues.

The bibliography recommended by the reviewer has been considered in the discussion of the research results. The conclusions reached have also been improved.

 

 

 

 

 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

No comment for this paper.

Reviewer 2 Report

I recommend for publication.