A comparative study of red brick powder and lime as soft soil stabilizer

Background: The role of soil in building construction is to support the loads above it. Different types of soil with poor mechanical properties require more attention. Therefore, more effort is needed to stabilize the soil by improving its properties. These improvements are intended to modify soil properties to improve engineering performance, such as strength, decrease in compressibility and permeability. This study aimed to compare the potential of lime and brick powder as stabilizers based on the California Bearing Ratio (CBR) values. Soil stabilization can be defined as modifying the soil properties by chemical or physical means to improve its engineering efficiency. The main objectives of stabilizing soil are increasing its bearing capacity, resistance to weathering processes, and permeability. Methods: This work did laboratory tests with disturbed and undisturbed soil samples. The proportions of lime or red brick powder additives are 0%, 5%, 10%, and 15% of the soil sample. From the results of the laboratory tests, the soil type obtained is MH (low plasticity silt) as per the Unified Soil Classification System (USCS). Results: This study showed that soft soil could be improved by adding lime and red brick powder as a soil stabilizer. In both soaked and unsoaked CBR tests, there was an increase in the CBR value for each proportion of the mixed additives. However, the red brick powder addition (15%) has significantly increased the CBR value. Conclusions: The soil sample mixed with 15% red brick powder had the highest Maximum Dry Density (MDD), about 5.5% over untreated soil. The increment of lime to 15% has increased the CBR soaked by 61% in relation to untreated soil. The increment of red brick powder to 15% has increased the CBR unsoaked by 73% in relation to untreated soil.


Introduction
Soil is considered to be a three-phase system consisting of soil particles, pores (air) between its particles, and liquid (water) which varying degrees, fills and flows through the pores. 1 Based on the particle size of soil, there are several types of soil, namely gravel, sand, silt, clay. 2 The large content of silt and clay in soil affects its geotechnical characteristics that can vary: shrink when dry, and expand when wet; in the presence of water, they swell and become plastic. 3 Constructions such as buildings, highways, bridges, tunnels, dams, and towers are established on the ground that functions to support the loads above it. 4 Engineers often have problems using soft soil, which has; weak mechanical properties. Soft soil is a cohesive soil consisting of very small grains, characterized by low shear strength and high compressibility, which does not possess sufficient strength to support loads. It is necessary to treat these soils to provide a stable subgrade and avoid excessive land subsidence. A soil is categorized as soft soil if its shear strength value is 12 -25 kPa. 5 For these reasons, soft soils need treatment before they can be used as a material subgrade by enhancing their engineering properties. Soil stabilization aims at improving soil properties and increases its resistance to softening by water. In principle, it means rearranging soil grains for them to be very tight and interlocked together. 6,7 The stabilization process, which is mixing soil with additives, can change the texture or plasticity of soil, its gradation, or act as a binder for soil cementation. 8 In recent years, a considerable number of field and laboratory experiments have been carried out using various additives, such as lime, 9-11 silica fume, 12 and fly ash. 13,14 However, not much research has been done on soil stabilization using red brick powder as a soil stabilizer. 15,16 Moreover, every red brick manufacturer knows its history, which does not always have the same characteristics. This could indicate differences in the test results at every location. 17 Therefore, it is necessary to do more research on the effect of red brick powder on soil stability. Also, the stabilizing effect of lime and red brick powder are compared in this work. The influence of lime on the geotechnical qualities of soft soil was examined by conducting the CBR test. The CBR values for the soil mixture progressively increased. 18,19 Similar outcomes were observed by Refs. 20-22 when employing waste brick powder as a soil stabilizer.
The study aims to compare the potential of lime and brick powder in stabilizing soft soil. Soil stabilization parameters were measured based on their effect on the CBR values of soaked and unsoaked soil samples. This test is a penetration test which entails inserting an object into the test object. Through this way, the strength of the base or other materials used to make the pavement can be assessed. As soil is not always in a dry condition, it would not be enough to do the CBR test with unsoaked soil samples; it must be done also with soaked soil. Soaking simulates adverse moisture conditions such as those caused by possible rain or flooding, and it is used in most CBR test. The difference between the soaked and unsoaked CBR testing procedure is that in the soaked CBR, the soil sample that has been molded is first soaked for 4 days (96 hours) by placing a standard load of 10 lb above the mold and then penetration test is carried out afterward. The mixed proportions of lime or red brick powder are 0%, 5%, 10%, and 15% by dry weight of the soft soil. In this study, the index and engineering properties of the soft soil and treated soil were tested. Index properties test includes testing moisture content, specific gravity, Atterberg limit, and grain size analysis. While testing the soil with a variation of the mixture of lime or red brick powder, the standard compaction test and CBR analysis are carried out.
Lime is commonly used as additional material for soil stabilization, especially for the construction of highways. Lime reacts with soil and changes its mineral properties. This is due to its reaction with calcium ions, which leads to the formation of cementitious holding capacity of soil (decreases moisture content), reduced swelling, and improved soil stability. 23 Previous studies 24,25 revealed that the stabilization of subgrades by lime could significantly improve their engineering properties. Using lime for soil stabilization gives long-term strength gain, developed through a long-term pozzolanic reaction. 26 REVISED Amendments from Version 1 1. The authors have been citing current literature dealing with similar investigations and highlighting the contribution of this work that differs from similar studies. 2. The authors state the sources and content of the additives used for soil stabilization. 3. Statements that are not directly related have been deleted. 4. All figures have been adjusted. 5. The conclusion has been rewritten based on the author's work. 6. The grammatical errors have been corrected.
Any further responses from the reviewers can be found at the end of the article Alumina and silica are the main elements in brick obtained from the combination of clay and sand, which are the main ingredients for making bricks. After the mixture of clay, sand, and water becomes plastic and easy to form, the brick is burned at a high temperature until a reddish colour is obtained. It cannot be broken down when immersed in water. Red brick has refractory properties and can withstand compressive loads. 27 There are scanty research works that have used red brick powder as a stabilizer because it is not commonly used. Each area has different red brick characteristics. Previous research has found that CBR results substantially improved the primary strength parameters of soil by using brick powder. 28

Material and sampling
The type of soil used in this research is soft soil located in Hambalang, Bogor. The rock that makes up the area at the top is in the form of Quaternary volcanic breccia; it is less compacted, with its surface utterly weathered into sandy clay. Its colour is gray-brown, it is soft and 0.30-1.50 meters thick. In the breccia unit, the localities have lenses or inserts that are flaky, swollen, stiff, partially scraped, and soft when exposed to the surface. Their colour is gray to brownish-gray. Figure 1 shows a systematic geological map of Bogor, Indonesia. 29 The green area is the sampling location used in this study, where the surficial deposits show clay shale.

Experimental technique
The method used in this research is a descriptive method, with tests conducted in the laboratory. Soil samples were taken in October during rainy season near the project site of the homestead of Athlete Hambalang, Bogor, Indonesia. Its geographical coordinates are 6°33 0 14.5 00 S and 106°53 0 22.1 00 E. Soil sampling was taken from a depth of 1 m to approximately 200 kilograms. Soil materials used for the test were disturbed and undisturbed soil samples. The undisturbed soil sample was used for dry density and engineering properties testing. The test was applied to identify the existing soil. Also, several stages of the laboratory tests were carried out with the disturbed samples. The laboratory test included (i) index properties of soil test, (ii) standard Proctor compaction test, and (iii) soaked and unsoaked CBR test. Index properties of soil test included specific gravity, sieve analysis, hydrometer test, and Atterberg limit used to determine the classification of soil. Before the compaction and CBR test was started, the soil sample was dried and filtered with sieve number 4 (smaller than 4.75 mm). Also, lime and brick powder were filtered with sieve number 40 (smaller than 0.475 mm). Lime were obtained from Klapanunggal District, Bogor, West Java and brick powder were obtained from the waste generated by brick industries in the Bogor area. The additives were mixed as a percentage of 0%, 5%, 10%, and 15% of soft soil ratio by weight. In the Standard Proctor test, each mixture of the additives required 6 samples with the composition of each sample being 2 kg of soil mixed with either lime or brick powder, based on the percentage determined by each sample. Each percentage of the mixture has 6 samples where the total sample is 48 for lime and brick powder. Furthermore, the Standard Proctor test was carried out to obtain optimum moisture content (OMC) and maximum dry density (MDD) for each mixed sample of the various proportions of lime and brick powder. The CBR test compares the resistance to penetration of the test specimen to that of a standard sample of well-graded crushed stone material using a standard-sized piston in a simple empirical approach. CBR test is one of the ways used to measure the bearing capacity of subgrades. 30 Based on the OMC obtained from the standard Proctor test, we could use the OMC for the next stage, that is, to conduct the soaked and unsoaked CBR test with various mixtures of the additives. Each mixture of the additives required 2 samples, with the composition of each sample being 5 kg of soil mixed with lime or brick powder, based on the percentage determined by each sample. So for each soaked and unsoaked CBR test, 8 samples are needed. CBR tests were carried to study the behavior and bearing capacity of the soil when mixed with the additives (lime and brick powder). After molding the soil shape, each soil samples used for the soaked CBR test was soaked in water for 4 days (96 hours), before the penetration test. While in the unsoaked CBR test, no soaking was carried out, but a direct penetration test. The sample was left in the mold to be used for penetration test. The piston was placed on the sample with the perforated plate and the necessary surcharge weights were place on the soil. Loading began at a rate of 0.05 in (12.7 mm) per minute. Test loads were recorded at eleven predefined depths of up to 0.500in as the piston entered the soil (13 mm). All these tests are also referred to as ASTM standards. 31-36 Manufacturers of the dial gauge equipment used Mitutoyo analog type.

Statistical analysis
Statistical analysis using 2nd order polynomial regression was done on the moisture content and dry density data. The software used was Microsoft Excel 2019. Polynomial relation regression results show quadratic regression function and coefficient of determination (R 2 ). The coefficient of determination is a statistical measurement that shows how much ability the independent variable has in explaining the dependent variable. A value close to 1.0 indicates a regression function that explains a lot of the function variable. This makes it a very reliable model for forecasting the future. While a value close to 0.0 indicates that the calculation fails to simulate the data accurately.

Results and discussion
The physical and mechanical properties of the soil can be seen in Table 1. 39 The soil samples contained more than 95% fine-grains, with size smaller than 0.075 mm. Based on the results, Hambalang soils can be classified as soft soils with high plasticity (symbol MH based on the Unified Soil Classification System) due to their undrained shear strength of >25 kPa. Also, in a previous report, the Department of Settlements and Regional Infrastructure classifies Hambalang soil as fat clay because it has a high swelling potential. Lime and brick powder have notable effect on the soil's MDD in all the mixed samples. The highest is observed in the samples with 15% additive, where the value increased from 1.58 for the soil not mixed to 1.7 for the soil mixed with 15% lime and 1.68 for the soil mixed with 15% brick powder. These were obtained at OMC of 21.12% for brick powder and 21.06% for lime. Optimum moisture in the compaction test was used as a mixture in the CBR test. The MDD of the soil samples increased because lime and brick powder have relatively higher specific gravities than soil. When the proportion of lime and brick powder increases, the MDD of the soil increases compared to the soil. The increase in water content at MDD conditions can be seen in Figures 2 and 3. This can occur because of the pozzolanic reaction, which causes the maximum density conditions to require a little more water.
As seen in Figure 4, the MDD of the mixture of lime and brick powder is at the 15% additive level. The increase in dry bulk density (γd) was due to additional material filling the cavities in the soil, decreasing the pore number. A decrease in the incidence of an increase in soil density leads to an increase in dry density.
The CBR soaked and unsoaked tests were carried out with the soil from lime and red brick powder at predetermined levels (5%, 10%, and 15%) by observing any changes in the CBR value at the top and bottom. The relationship between the addition of lime and red brick powder to the soil on the CBR values of soaked and unsoaked is shown in Figure 5.   The results of the test data on the discovery of CBR values that were soaked and unsoaked increased with the addition of lime or red brick powder. This is because the soil grains and additives react with one another in a process known as pozzolanization reaction. In treated soil, the strength generated is determined by the strength of the grain and the friction between the grains. So, the increased strength of the soil is not only a pozzolanization reaction but also friction between grains. This finding agrees with another result, which explained the strength of mixed soils in different cases. 37 The highest CBR value of lime and red brick powder is found in the 15% mixture. The CBR-soaked result for lime has a higher value (7.58%) than that of brick powder (4.55%). While the CBR unsoaked result of red brick powder has the highest CBR value (19.2%) compared to lime (16.91%).
The CBR soaked value is smaller than the CBR unsoaked value because, at the time of immersion, the water initially fills the pore cavities. Over time, the size of the soil grains expands to their maximum when the water is saturated. In these conditions, the bonds between the soil grains become weak so that the bearing capacity of the soil decreases. This result is similar to another finding which showed that the more saturated the soil is, the less its bearing capacity. 38 The increase in CBR value is due to the cementation process, which makes the soil clump, thus increasing the binding power between the grains. This makes the pore cavity to be surrounded by a more rigid cementation material, which results in the grains becoming strong and not easily destroyed. 24

Conclusions
This study examined lime and red brick powder in a few geotechnical engineering applications to improve the strength of soft soil. The soft soil samples have undertaken a thorough laboratory test, including Specific gravity, Sieve analysis, Hydrometer test, Atterberg limit, Proctor test, and CBR. The soft soil mixed with lime and red brick powder (0%, 5%, 10%, and 15% by dry weight of the soft soil). The MDD of the soil sample increases when mixed in various proportions of lime and red brick powder. The soil sample mixed with 15% of additives had the highest MDD. The increment of red brick  powder into the soil progressively caused an increase in MDD by 5.5% when the red brick powder ratio was increased to 15%. The soaked and unsoaked CBR values increased with lime and red brick powder variation. The highest CBR soaked value is obtained from a lime mixture of 15%. The increase is 61% over that of the untreated soil. The highest CBR unsoaked value is obtained from a 15% addition of red brick powder. The increase is 73% over that of the untreated soil. © 2023 Cherian C. This is an open access peer review report distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Chinchu Cherian
The University of British Columbia, Vancouver, British Columbia, Canada

General comments:
The article titled "A comparative study of red brick powder and lime as soft soil stabilizer", authored by Salimah et al., presents a laboratory study conducted to understand the effects of lime or red brick powder additives on a soft soil stabilization. In general, the topic is well within the scope of the journal, and the authors have provided a clear rationale or justification for conducting this study. However, there have been relevant prior studies performed on this topic of interest.

Literature review:
Although the study is relevant, there is ample amount of research work done in this topic before. The authors have missed many such studies while discussing the literature review. It is recommended to incorporate these articles and provide a more critical summary of the literature findings and thereby the important knowledge gap addressed in this study.

Objectives and scope of work:
This study has made significant contributions by considering both undisturbed and disturbed soil samples. They also used statistical analysis for the data interpretation. The authors have clearly defined the objectives and outlined the experimental methods.

Results and discussion:
The authors have performed an in-depth analysis of the obtained experimental data and discussed the major results/findings with ample reasons, particularly in a manner that is both comprehensive and accessible to readers. ○ It is however recommended to perform some additional analytical tests on the treated soil samples (like SEM and XRD) to comprehend the chemical changes that led to the mechanical improvement of the soil.

Conclusions:
Although the authors wrote a clear summary and conclusions of the study, the reviewer feels that the implications of this study for future research and practical applications is missing.

Are sufficient details of methods and analysis provided to allow replication by others? Yes
If applicable, is the statistical analysis and its interpretation appropriate? I cannot comment. A qualified statistician is required.
Are all the source data underlying the results available to ensure full reproducibility? Yes Are the conclusions drawn adequately supported by the results? Yes laboratory tests with disturbed and undisturbed soil samples where the proportions of lime or red brick powder additives are 0% up to 15% of the soil sample. In general, the topic is of great interest and is well within the scope of the journal. The authors have provided a significant contribution that is sufficiently performed and interesting for readers. They used an appropriate method to address the objectives, and the obtained results are both interesting and relevant. The findings were successfully explained in the manuscript, and most of the references used are related to the objective of the work. The scientific contribution of this paper highly meets the requirements of the journal F1000Research.

Abstract section:
The abstract effectively provides a brief overview of the study's background, methods, and results. The language used is clear and concise, with technical terms explained where necessary, making it easy to understand for readers without prior knowledge of the topic. The abstract follows a structured approach, starting with the study's background and objectives, followed by the methods and results, and ending with conclusions. This helps readers quickly understand the main purpose and outcomes of the study. Overall, the abstract is well-written and effectively conveys the main findings of the study.

Introduction section:
In the introduction section of this scientific paper, the author extensively discussed the characteristics of soft soil with weak geotechnical properties, as well as the importance of studying it before undertaking any civil engineering project. The author touched on the most important numerical models developed by researchers regarding geotechnical projects in general, and shallow tunnels modeling in particular, based on studies conducted and published in relevant scientific journals. The author relied on several important references related to the subject matter. The introduction is clear in terms of linguistic structure, where we find that the problem is completely clear.

Methods section:
The authors conducted a rigorous experiment using a variety of tests to assess the effectiveness of the two different stabilizers. Their findings suggest that the method used in the study is not only appropriate but also highly effective in improving the strength and stability of soft soil, which has important implications for construction projects in areas with problematic soil conditions." This sentence highlights the fact that the authors used a rigorous approach in their study, which involved various tests to assess the effectiveness of the stabilizers. Additionally, the sentence emphasizes that the method used is not only appropriate but also highly effective, which is a strong endorsement of the validity of the research findings. Finally, the sentence suggests that the implications of the research are significant for construction projects in areas with problematic soil conditions, which adds further weight to the importance of the study.
The statistical analysis performed on the moisture content and dry density data was useful, which indicates that the use of 2nd order polynomial regression with Microsoft Excel 2019 software is a meticulous approach to the data analysis process. The inclusion of the coefficient of determination (R2) is noteworthy as it provides crucial insight into the explanatory power of the independent variable with respect to the dependent variable. The successful calculation of the quadratic regression function and R2 value highlights a significant correlation between the two variables, making the regression model a dependable tool for predicting future trends. In conclusion, this "statistical analysis" establishes a robust foundation for the statistical analysis of the data, and the results can be interpreted confidently to derive meaningful insights.

Results and discussion section:
That said, the article is a well-written and informative piece of research that successfully presents the findings of the study. The authors have clearly outlined their methodology and have presented the results in a manner that is both comprehensive and accessible to readers. Overall, the article is a valuable contribution to the field of soft soil stabilization and provides important insights into the effectiveness of different stabilizers in enhancing soil strength and stability." The authors provide a detailed discussion section that highlights the significance of their findings and their implications for future research and practical applications. The discussion section begins by summarizing the key results of the study, emphasizing the effectiveness of both red brick powder and lime as soft soil stabilizers. The authors then provide an in-depth analysis of their findings, discussing the various factors that may have contributed to the effectiveness of the stabilizers, including their chemical composition and particle size. In addition to discussing their own research, the authors also reference previous studies on soft soil stabilization, providing a broader context for their findings and highlighting areas where further research is needed. They also discuss the practical applications of their research, such as the potential use of red brick powder and lime in construction projects to improve the stability and safety of buildings and infrastructure in areas with problematic soil conditions. Overall, the discussion section of the article is wellwritten and thorough, providing a detailed analysis of the study's findings and their implications for the field of soft soil stabilization. The authors' ability to contextualize their research within existing literature and to provide practical applications for their findings is a testament to the strength of the study and the potential impact it could have on future research and real-world applications.

Conclusion section:
Based on this section, the authors have effectively summarized the key findings of the study in a concise and clear manner. The conclusion begins by stating the aim of the study, which is to investigate the effectiveness of lime and red brick powder as soft soil stabilizers. The authors then highlight the various laboratory tests that were conducted to evaluate the performance of the stabilizers, including Specific gravity, Sieve analysis, Hydrometer test, Atterberg limit, Proctor test, and CBR. The authors then proceed to summarize the key findings of the study, noting that the addition of lime and red brick powder to soft soil samples resulted in an increase in MDD (Maximum Dry Density) and CBR (California Bearing Ratio). They further note that the highest values of MDD and CBR were obtained with a 15% addition of the respective stabilizer. The authors provide specific percentages of increase in CBR values over the untreated soil for both soaked and unsoaked conditions, which suggests a significant improvement in soil strength with the addition of stabilizers. Overall, the conclusion section effectively highlights the key results of the study and their significance for the field of geotechnical engineering. The authors have effectively communicated their findings in a clear and concise manner, which adds to the strength and clarity of the article.
However, based on the above comments, the present paper "A comparative study of red brick powder and lime as soft soil stabilizer" can be Approved for indexing as it is

Is the work clearly and accurately presented and does it cite the current literature? Yes
Is the study design appropriate and is the work technically sound? Yes

If applicable, is the statistical analysis and its interpretation appropriate? Yes
Are all the source data underlying the results available to ensure full reproducibility? Yes

If applicable, is the statistical analysis and its interpretation appropriate? Yes
Are all the source data underlying the results available to ensure full reproducibility? Yes Are the conclusions drawn adequately supported by the results? Yes