Microstructure and Mechanical Behavior of Concrete Based on Crushed Sand Combined with Alluvial Sand
Federico Aguayo
Round 1
Reviewer 1 Report
In green the page and line numbers, in black the article sentences the reviewer refer to and in red the questions/changes suggested.
Manuscript ID: civileng-870717
Type of manuscript: Article
Title: Microstructure and mechanical behaviour of concrete based on crushed
sand combined with alluvial sand
Authors: EMMANUEL ELAT *, PROSPER PLIYA, ALEXANDRE PIERRE, Michel Mbessa,
ALBERT NOUMOWE
Abstract:
- Introduction:
Page 4, Table 3: How many tests have been carried out? I am surprised not to see standard deviation on results.
- Materials and Methods
2.2.2. Experimental Schedule
Page 7, line 191: “Next, the specimens were placed in an oven at a temperature of 100 to 110 °C for 24 h.” I am pretty sure that samples are not dried after 24h at 110°C. Why don’t you measure loss mass until stabilization? It is better to measure mass variation during 24h and define a criterion for mass stabilization, for example 0.05% of mass variation.
Page 8, line 228: “For the static modulus analysis, cylinder specimens 110 mm in diameter and 220 mm in height were used”. What are the storage conditions and the ages of concrete? Are they the same than for compressive strength? Do they put lime in water for avoiding lixiviation and concrete degradation?
Page 8, line 231: “The concrete specimens were instrumented by a set of four strain gauges placed on the lateral surface and at the mid-height of the specimen, two of which were placed longitudinally, two of which were placed horizontally, and two of which were diametrically opposite, as shown in Fig. 5.” Usually, three strain gauges are glued in an angle of 120°. It permits to avoid an important flexion phenomenon. How to be sure that there is no flexion?
- Results and discussion
3.1. Concrete workability
Page 9, line 261-274: They show that increasing the amount of crushed sand decrease the slump. The relation is clear, and hypothesis are good. Do the authors know the Eff/C? What is the real proportion of water which reacts with cement? Do they measure hydration products or rate? It could be interesting to know how the concretes can evolve on long term due to differential hydration.
3.2. Drying shrinkage of concrete
Page 10, line 280-293: I am surprised to see such a stabilization after only one week on drying shrinkage. How the author can explain that? Do they continue measurement on long term behavior to quantify differences?
Why don’t they measure on concrete with 70 and 50% of replacement? Does the drying shrinkage evolve linearly with the amount of replacement?
3.3. Water porosity and density of concretes
Page 11, Fig. 9: All the results are expected. Why don’t the author measure on 70% and 100% of replacement? The densities are quite high for concretes. Maybe some voids are still fulfilled with water even if the evolution are good.
3.4. Gas permeability
Page 11, Fig. 10: Why don’t the author measure on 70% and 100% of replacement?
3.5. Compressive strength at 7, 21, and 28 days
Page 12, line 323 and 324: “The values of the compressive strength of the concrete mixtures at 7, 21, and 28 days of curing in water are shown in Figure 11.”. Previously, line 225, authors said that compressive strength are carried out after 90 days of water curing. Where are the results?
The explanations of the difference are light. What is the origin of the differences? Aggregate mineralogy? What are the storage conditions for the other study? It seems in accordance with drying shrinkage and all other results. The capillary tension developed are less important due to the slight amount of fine in river sand. Do the authors make a mercury porosity to see the difference in porosity? If concretes with crushed sand have smaller porous network, it can explain a lot of differences on microstructural behavior.
3.6. Static modulus of elasticity and compressive strength at 90 days
Page 12, Table 9: It is pretty sure there is still free water after 90 days. I think the difference is more due to hydration difference between concretes. At the beginning (after casting concretes) water is not available for all cement hydration in case of crushed sand. Water is adsorbed by fines. If concretes are stored in water, crushed concrete can easily be better hydrated with water penetrating on concrete. Maybe for almost complete hydration the difference on compressive strength could be lower. This is possible only if concretes are stored on water what is not the reality. Do the authors have thought about making endogenous curing for concrete?
Moreover, maybe the effect of cement is non negligible. With CEM I the difference will be greater.
3.7. SEM and-EDS analysis
Explanations in this section are not relevant. How big was the studied surface?
- Conclusions
Conclusions do not reflect the overall explanations on the paper.
Author Response
The authors acknowledge the reviewer for these relevant comments. Responses to the comments are detailed point by point.
Please see the attachment
Author Response File: 
Author Response.docx
Reviewer 2 Report
The authors present an article on the properties of concrete blended with manufactured and natural sand.
The reviewer suggest doing more statistical significance evaluation of the data, especially the mechanical strength. Some conclusions were drawn based on small percentages that needed more justification. The manuscript would also be strengthen with more discussion on the impacts of the gravel aggregates on the results.
The reviewer also suggest strengthening the literature review with rewording of some of the sentences. There are some issues with English and wording structures.
The conclusions based on the SEM analysis is also weak and doesn’t really provide much significance.
Comments for author File: 
Comments.pdf
Author Response
The authors acknowledge the reviewer for these relevant comments. Responses to the comments are detailed point by point.
Please see the attachment
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
All the changes are ok.
