Enhanced Flexible Pavement Performance Using Treated Compared to Untreated Aggregate Bases: A Comparative Case Study in the Southern United States

Round 1

Reviewer 1 Report

This is an interesting paper. Some comments:

1. Abstract: there are many description of the theory background, please shorten it. Please improve practical background since this is a case study paper.
2. Line 25: the authors mentioned the fatigue cracking, how about the cracking caused by instability base?
3. Line 55: I think all the asphalt pavement has this problem, it is independently with the materials(HMA, WMA, HWMA, CMA). Please consider this.
4. Literature Review: the aim of this paper is to compare treated base and untreated base. however, only the benefits of treated base and the possibility of using waste materials are shown, no previous studies on the comparison. Please revise.
5. line 146: why these three indicators are chosen? Please cite a reference or give an explanation.
6. Table 2: maybe it is better to divide the AADT data into two clusters, Alabama and Arkansas is quite lower than the others.
7. figure 3: the log axis make untreated section and treated section similar. Please try to use a normal axis.
8. Table 4: can the authors make a statistic analysis to see if the untreated and treated section are significantly different?
9. the conclusion is well organized.

Author Response

Please see attached file.

Author Response File: Author Response.docx

Reviewer 2 Report

The paper refers to the comparison of flexible pavement’s performance with treated and untreated aggregate base layer.

The paper is well structured and the English language is appropriately used. Correct terminology is used throughout the paper. The paper has 14 references.

Some minor corrections are indicated below:

• Page 3, line 146, Please replace “3 various performance indicatros…” with ‘Three (3) various performance indicators…’
• Page 4, line 177, Please replace “In the table 2, …” with “In table 2, …”
• Figures 2 to 7 need x and y axis legends
• Page 9, line 32, at the beginning of the sentence, please correct “of traffice” with ‘of traffic’
• Page 9, Line 244, Please replace “It is generally happened…” with ‘Rutting generally occurs by the accumulation of permanent deformation of all layers…’
• Page 9, Line 246, Please replace “Figure 4 tells the the mean rutting…” with ‘Figure 4 shows the mean rutting…’

However, the reviewer would like to stress the authors’ attention to the following major subjects:

• Line 176-177 the phrase “Increase in the base thickness for treated section is accompanied by the decrease in asphalt layer thickness” is not valid according to the data of Table 1. See sections 04-1065, 04-0115, 04-0117, 04-0123, 04-0126, 05-0116, 05-0123, 48-1047 and 48-1096.
• In order to compare fatigue cracking between flexible pavements with treated and untreated base layers (and having in mind that traffic and temperature are similar and alike layer materials are used), shouldn’t the authors have pavements with similar subgrade or capping layer bearing capacity? If different subgrade/capping layer capacities exist (even locally, which should be known) there is no way to know if the treated (for the treatments used in the paper) or untreated base had an effect on the fatigue cracking. Please make a paragraph referring to the above. Even further, and taking into account the sections mentioned in (1) above, how can the authors be certain that fatigue cracking has been affected by treatment or no treatment of base layer? (Since the rule of thumb -increase in treated base thickness is accompanied by asphalt layer thickness, is not applied)
• Are there any data for the overall thickness of the pavement? (Assuming that there is a subbase below the base and above the subgrade or capping layer). If so, please include it to Table 1 and comment on them with regards to fatigue cracking.
• Also, stiffness of the asphalt layers and elastic/resilient modulus (E) of the treated or untreated base layers if exist, would give a better picture on the effect of the treatment of the base layer to fatigue.
• Rutting is also another issue. How do the authors know that rutting is affected by the presence of treated or untreated base layer? You could have rutting coming from settlement of the subgrade, or you could also have rutting coming only due to failure of the asphalt layers. So how the authors are sure that the treatment or no-treatment of the base affects the overall rutting and relevant conclusions are drawn?
• Also, in both the above (fatigue cracking and rutting) what are the acceptable range of values of the pavement? Authors should provide a range of limits for acceptance or serviceability levels of pavements in relation to %fatigue cracking and surface rutting (inches or mm). Then see the ranking of the pavements in relation to the limits. The reason for this is simple. If the untreated base pavements are within the acceptable limits, why a contractor give money for treatment of the base layer?
• The authors should re-consider the IRI presentation results. IRI measurements are not related to the treatment or no-treatment of the base layer and are definitely affected by the presence of rutting and fatigue cracks and of the original construction of the pavement surface. So, it can not be concluded that the treated sections perform better in terms of IRI. If rutting and fatigue cracking are related to treatment or no treatment of the base layer, the IRI results are indirectly related and this should be shown by detailed analysis.
• It should also be mentioned that all the treated bases included in the research were either with HMAC or lime and not with concrete. All conclusions are valid, for those two cases. If concrete was used there maybe issues of reflective cracking and that would complex things even more.

I would suggest that the authors consider the above and revise the article accordingly.

Author Response

Please see attached file. 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Thanks to the authors' response. Some comments:

1. Line 25: the authors mentioned the fatigue cracking, how about the cracking caused by the instability base? The paper concentrated on fatigue cracking only. Future work will be done to include cracking caused by the instability of base courses. (This paper focused on the base treatment, however, the instability base caused cracking is not considered. Please add it by the end of conclusion as the future perspective)
2. Line 146: why these three indicators are chosen? Please cite a reference or give an explanation. It is a very well-known fact for any pavement engineer that the main three distresses that affect pavement structures the most are fatigue, rutting and surface rutting. Therefore, the authors felt that there is no need to reference that. (The four States the authors' selected are in the warm region, I agree fatigue, rutting, and surface roughness are the main distresses. However the main distresses can be very different in different climate regions, for example in Alaska in the US, the main distress will be thermal crackings, rutting is not a serious distresses. Just cite a reference or write several sentences related to the climate).
3. Line 55: I think all the asphalt pavement has this problem, it is independently with the materials(HMA, WMA, HWMA, CMA). Please consider this. Authors may agree but this paper only show HMA performance so the authors does not feel comfortable generalizing this sentence to all pavement structures. (The top of the asphalt and subgrade layer undergo compressive strains while the tensile strains occur in the bottom of the asphalt layer. This is the reason of bottom-up cracking occurs in asphalt pavement. It is independent of the materials of the asphalt layer. I do not see any conflict with all pavement structures).
4. Table 4: can the authors make a statistic analysis to see if the untreated and treated section are significantly different? The goal of table 4 was to show the average performance of different treatment methods. This table was not intended to compare treated versus untreated sections since that comparison was done earlier in the paper (Figures 3, 5, and 7) and there was enough difference to conclude that there is a measurable benefit of adding treatments to base courses. (The authors mentioned Figures 3, 5, and 7. I agree with Figure 3, we can see remarkable differences between these two methods. However, in both Figures 5 and 7, if the authors delete the three high values in the untreated section, the average values and distributions between these two methods may be similar. Please consider it, I still think a statistical analysis is needed).

 

Author Response

1-Noted! The authors added the following sentence at the last bullet of the conclusion section: "This paper focused on the base treatment, however, the instability base caused cracking is not considered and will be considered in future studies."

2-Noted! The Authors mentioned the following "Three various performance indicators (rutting, fatigue cracking, and surface roughness) were used as an overall field performance assessment tool for chosen flexible pavements in the states of Texas, Arizona, Arkansas and Alabama" This indicates that these three factors are for such states, not clod ones.

3- Noted! The authors mentioned the following "The compressive strains at the top of the subgrade layer and the tensile strains in the asphalt layers of flexible pavements are influenced by the stiffness of the base layer." "Asphalt layers" can include HMA, WMA, CMA, etc...

4- The goal of table 4 was to show the average performance of different treatment methods. This table was not intended to compare treated versus untreated sections.  More importantly, The authors are troubled by the suggestion made by the reviewer to arbitrarily (and including intentional bias) to remove the three top-performing treated sections!!! First, that action is not scientifically backed and second, someone else may suggest also to remove the three top-performing untreated sections which will lead to the same conclusion!! The authors respectfully disagree with arbitrarily removing data points to prove certain point of view.   

 

Reviewer 2 Report

Although the authors have addressed all the minor corrections, the reviewer is not satisfied by some of the answers given in the major remarks. According to the authors' answers, proximity of treated and untreated sections is the main reason that justifies their results (no data of layer thickness, or of subgarde capacity or of stiffness of asphalt layers or of elastic modulus of treated or untreated base). In any case, the reviewer will let the scientific community to decide whether the above is crucial or not. Hence the revised paper is accepted for publication.

Author Response

Thanks for your comments. Information on the subgrade thickness was not available. However, the authors intentionally picked treated and untreated sections to be on the same highway and within very close proximity to each other which led to the very safe assumption that both treated and adjacent untreated sections have similar subgrade thickness and/or properties. I think pavement engineering practitioners would totally agree with this safe assumption.