A Systematic Review of the Effects of Soil Stabilization on Soil Mechanical Properties: A Comparative Study of Fly Ash, Cement and Lime ()
1. Introduction
Soil is the most abundant construction or engineering material of nature. Nevertheless, the limited availability of appropriate subgrade soil for constructing infrastructure facilities has necessitated the enhancement of the characteristics of the existing soil through soil stabilization. Sinha and Iyer (2020) [1] state that soil stabilization has emerged as a highly advantageous method for the development of infrastructure and other significant geotechnical and civil engineering projects. Also, Vinai et al. (2022) [2] found that constructing any kind of structure on unsuitable soil can pose difficulties because of the soil’s high potential for swelling and/or low strength properties. Therefore, soil stabilization has become increasingly popular due to the limited availability of suitable soil for infrastructure projects and the substantial enhancement of soil properties attained through soil stabilization (Arias-Jaramillo et al., 2023 [3] ; Okonkwo and Kennedy, 2023 [4] ). Soil stabilization refers to the modification of soil properties, either through chemical or mechanical methods, in order to produce a more enhanced soil material with certain engineering characteristics (Dias-Miguel et al., 2021 [5] ; Hamzah et al., 2015 [6] ). According to Babu and Paulose (2018) [7] , soil stabilization is crucial for maintaining the stability of soil, particularly in cases when the soil is extremely active, to properly bear the weight of superstructures.
The primary objectives of soil stabilization are to enhance the soil’s load-bearing capacity, resistance to weathering, and permeability (Babu and Paulose, 2018 [7] ; Jawad et al., 2014 [8] ). Accordingly, the durability of any construction or engineering work is contingent upon the stability of the underlying soil, as unstable soil can give rise to substantial issues (Babu and Paulose, 2018 [7] ; Zuber et al., 2013 [9] ). According to Shah and Ahmad (2020) [10] and Singh et al. (2018) [11] , soil stabilization is typically required when the soil strength is inadequate. Soil stabilization methods are essential to ensure the stability of soil, particularly in cases when the soil is extremely active (Arias-Jaramillo et al., 2023 [3] ; Saleem, Kumar and Singh, 2020 [12] ; Utami, 2014 [13] ). Also, soil stabilization is a time and cost-effective alternative to the traditional process of removing and replacing unstable soil (Mahedi, Cetin and White, 2020 [14] ; Shekhar and Saxena, 2018 [15] ; Zuber et al., 2013 [9] ).
Various stabilizers are employed for soil stabilization, with Lime, Cement, and Fly ash being the commonly utilized agents or binders (Makusa, 2013 [16] ; Shah and Ahmad, 2020 [10] ). Researchers have conducted comprehensive laboratory, field, and experimental studies, which have demonstrated diverse effects of soil stabilizing additives, such as cement, lime, and fly ash on various soil parameters. Although several soil stabilization methods have been proposed to improve soil properties, there is a lack of comparative studies to find out the most effective soil stabilizing agent (Salimah et al., 2021 [17] ; Singh et al., 2018 [11] ; Vinai et al., 2022 [2] ). Previous studies have found inconclusive results where some found fly ash significantly improves soil mechanical properties (Dayalan and Dayalan, 2016 [18] ; Turan et al., 2022a; 2022b [19] ; Vinai et al., 2019) [2] whilst other studies found that lime significantly improves soil mechanical properties (Jin and Li, 2019 [20] ; Salimah et al., 2021 [17] ; Utami, 2014 [13] ) and others found cement to have significant effects on soil mechanical properties (Nazari, Tabarsa and Latifi, 2021 [21] ; Shooshpasha and Shirvani, 2015 [22] ). From this, it remains unclear on the most effective soli stabilizing agent among fly ash, cement, and lime. Engineers have therefore been concerned about the selection of the most efficient binders for soil stabilization, which is a well-known issue in civil and geotechnical engineering where the goal is to identify the appropriate type and proportion of stabilizing agents to enhance soil properties (Arias-Jaramillo et al., 2023 [3] ; Lindh and Lemenkova, 2023 [23] ).
More so, there is a lack of a systematic review of the studies to provide a summary of the outcomes of the previous studies on soil stabilization. This systematic review therefore aimed to analyse and compare the effects of soil stabilization on soil mechanical properties using cement, lime and fly ash as case studies. Over the past years, several studies on the effects of soil stabilization have been done such that there are varying results regarding the subject in the existing body of literature. As acknowledged by Makusa (2013) [16] and Tripathi (2020) [24] , the knowledge of soil stabilization in geotechnical and civil engineering has been well documented in existing literature. However, the effects of soil stabilization have been found to vary by admixtures used such as cement, lime, bitumen emulsion and fly ash and the findings are scattered across the body of knowledge. In this regard, the experimental research has not yet been summarised to guide engineers towards effective soil stabilization. Additionally, while the results presented in existing research are consistent across scholars, it is still unclear regarding the most effective soil stabilizing agent.
These therefore represent significant gaps in knowledge which this research sought to address by carrying out a systematic review on the comparative study on the effects of soil stabilization on soil mechanical properties focusing on cement, lime, and fly ash. Although several experimental studies have investigated the effects of these different soil stabilization methods on soil mechanical properties, a comprehensive comparative analysis of lime, fly ash and cement as soil stabilizing agents is lacking in existing literature. This systematic review therefore aimed to fill this knowledge gap by examining and synthesizing results of relevant experimental studies in order to assess the effectiveness of these three common stabilization agents. By synthesizing findings from existing knowledge in the field of soil stabilization, this review contributes to a better understanding of the most suitable and effective soil stabilization technique for geotechnical and civil engineering applications.
For comparison purposes, the study reviewed the effects of soil stabilization on soil mechanical properties such as plasticity, swelling, and strength using unconfined compressive strength (UCS) and California Bearing Ratio (CBR), maximum dry density (MDD) and optimum moisture content (OMC). The outcomes of this systematic literature review would be of value to practice and theory. Most importantly, the outcomes would be of great value to geotechnical engineers and civil engineers in soil stabilization. This systematic review of the literature was carried out using articles published from 2013 to 2023 accessed from numerous electronic databases. The time scale (2013-2023) was selected to gather a wide range of recent and relevant articles as possible. The systematic review therefore aimed to achieve the following research objectives:
1) To analyse the effects of fly ash, lime, and cement as soil stabilizing agents on soil mechanical properties.
2) To compare and determine the most effective soil stabilizing agent among fly ash, lime and cement.
2. Materials and Methods
This research followed the systematic literature review methodology elaborated in the following sections.
2.1. Materials
Search Strategy
This systematic literature review was guided by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Based on the PRISMA checklist, the research was conducted making use of articles from several databases. The main databases utilised include Elsevier, Scopus, Science Direct, MDPI, Springer, the American Society of Civil Engineers (ASCE) library as well as Google Scholar. Additional articles included peer-reviewed journal articles available from various journal publishers such as the International Journal of Geotechnical Engineering, the International Journal of Engineering, and the International Journal of Geo-Engineering. The search strategy was delineated to the period from 2013 to 2023 however articles published in the last five (5) years were prioritized to get more current evidence. Additionally, no geographical limits guided the article search.
The search of articles was executed in accordance with the PRISMA checklist where a preliminary search was carried out to find out the proper keywords as well as checking feasibility of the systematic literature review. The search keywords employed include “soil stabilization”, “soil mechanical properties”, “soil mechanical characteristics”, “soil mechanical behaviours”, “cement”, “fly ash”, “lime”, “comparative study”, “geotechnical properties”, “engineering properties” and “effects of” For a comprehensive search, Boolean operators namely as “OR” and “AND” were utilised to join the keywords. In addition, the author conducted manual searches of reference lists for the identified articles.
2.2. Methods
2.2.1. Inclusion Criteria
The following inclusion criteria were employed for this systematic literature review:
1) Articles written and published between 2013 and 2023 inclusive.
2) Articles written and published using the English language.
3) Articles based on experimental, field studies or laboratory tests.
4) Articles on soil stabilization using either lime, cement or fly ash or a combination.
5) Articles published as both abstract and full text.
2.2.2. Exclusion Criteria
The exclusion criteria for the research were as follows:
1) Articles published in other languages other than English language.
2) Articles published prior 2013 and after 2023.
3) Scoping, systematic and/or narrative review research articles.
4) Non-experimental research articles.
5) Articles only published as abstracts.
6) Newspapers, institutional reports, and other “grey” literature.
2.2.3. Quality Assessment of Articles
For quality assessment and rigor of articles, the “Quality Assessment Tool for Diverse Design Studies” (QATSDD) tool. On the other hand, the articles that satisfied the inclusion criteria underwent a thorough evaluation of their quality by two independent reviewers. Based on the outcomes from the independent reviewers, articles were therefore considered of good quality if both independent reviewers agreed.
2.2.4. Data Extraction and Analysis
Before conducting the data analysis, the author collected information about the article, such as the author(s) names, publication year, region, or country, focus or aim, methodology and/or research design, key findings, as well as conclusions. This information was organized in a table format, as shown in Table 1. Thereafter data from the systematic literature review were analysed using the content analysis approach. Utilizing the content analysis technique, the primary themes from each article were integrated into data summary Excel sheets. To clarify, the process of extracting data was carried out utilizing Microsoft Excel spreadsheets. Thereafter, the PRISMA flowchart diagram was developed to summarize the article selection and screening process.
2.2.5. Ethical Considerations
For this systematic literature review, ethical approval for the research was sought. Thereafter, efforts were made rigorous efforts to circumvent search biases in conducting the systematic literature review. Additionally, citation and outcome reporting biases were prevented by not only selecting articles with results that suit the author’s personal perspectives and expectations. Moreover, database bias was prevented by not limiting the search to a single database.
3. Theory
The challenge of soil stabilization remains a significant issue for engineers due to
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Table 1. Summary of included articles.
the growing need for construction of infrastructure and engineering structures in places with inadequate or low-quality soils (Kalyane and Patil, 2020) [25] . Although soil stabilization can be traced back to more than 500 years ago, its application mostly in developing countries is still at its infancy stages (Archibong et al., 2020 [26] ; Makusa, 2013 [16] ; Rai et al., 2021 [27] ). As per Sharma et al. (2018) [28] , in recent decades, engineers have introduced a new technique for soil stabilization designated as chemical stabilization where chemicals such as cement and lime are used. In accordance with Singh et al. (2018) [11] , soil stabilization is a method used to enhance the properties of natural soil or granular material for the purpose of constructing pavement layers. From Jawad et al. (2014) [8] , soil stabilization refers to the modification of geotechnical parameters to meet engineering specifications.
Soil stabilization is necessary when the road alignment passes through a sub-grade of poor soil quality that does not meet the engineering qualities specified in any standard specifications such as the ASTM international standards (Taki and Bhattacharya, 2020) [29] . According to Jawad et al. (2014) [8] , soil stabilization can enhance shear strength, enhance bearing capacity, stabilize slopes, minimize structural settling, and increase soil density. On the other side, soil stabilization is used to alter the characteristics of soil to enhance its engineering performance, including its durability and strength (Babu and Poulose, 2018 [7] ; Jin and Li, 2019 [20] ). Firoozi et al. (2017) [30] argued that soil stabilization not only improves strength but also improves permeability and compressibility. From Salimah et al. (2021) [17] , soil stabilization refers to the process of altering the characteristics of soil by either physical or chemical methods to enhance its engineering performance. Babu and Poulose (2018) [7] contend that soil stabilization offers significant time and cost savings compared to the approach of removing and replacing unstable soil.
As summarized by Singh et al. (2018) [11] , there are several effects that may take place in a soil-stabilized mixture. The widely documented effects include 1) increased strength in terms of any standard test values such as CBR value, R-value and k-value, 2) decrease of plastic and liquid limit values, 3) important physical properties due to reactions with cementation agents mixed with soil, 4) decrease in water film thickness around each soil particle due to flocculation/agglomeration following addition of lime/cement, 5) decreased swelling and shrinkage rates and 6) improvement in overall pavement structural integrity (Archibong et al., 2020 [26] ; Singh et al., 2018 [11] ; Sinha and Iyer, 2020 [1] ). The effects differ depending on the admixture used, which includes various soil stabilization methods such as soil-cement, soil-lime, soil-fly ash and soil-bitumen stabilization (Afrin, 2017 [31] ; Archibong et al., 2020 [26] ; Huang et al., 2021 [32] ; Tripathi, 2020) [24] . Currently, all construction of roads or engineering projects include either one or both of these soil-stabilizing approaches (Tripathi, 2020) [24] . In addition, as stated by Archibong et al. (2020) [26] , Vinai et al. (2022) [2] , and Tripathi (2020) [24] , the different approaches to soil stabilization can be categorized into the proportioning techniques, cementing, moisture/waterproofing, modifying, water-repelling, moisture-retaining, heat treatment, as well as chemical stabilization agents.
However, existing experimental studies have shown varying effects for soil stabilizing agents such as cement, lime, and fly ash on soil mechanical properties. There is a lack of comparative studies to find out the most effective soil stabilizing agent among cement, lime, and fly ash. More so, there is lack of systematic review studies to provide a summary of the outcomes of the previous studies on soil stabilization effects on soil mechanical properties. This systematic review therefore aimed fill the existing gap in knowledge by examining and synthesizing results of relevant experimental studies to assess the effectiveness of these three common stabilization agents on soil mechanical properties.
4. Results and Discussion
4.1. Results
Following the comprehensive search of relevant articles and quality assessment, twenty-two (22) articles were included in the systematic review as demonstrated in Figure 1.
As demonstrated in Figure 1, the comprehensive search of articles from various databases yielded 539 research publications on soil stabilization. Out of these, 513 articles were directly obtained through database search whilst 26 were identified following manual scanning reference lists of the 513 articles. Among the 539 research articles, a total of 88 duplicates were discovered and subsequently discarded from screening such that only 451 went through the article screening process. Out of the remaining 451 articles, 378 articles were excluded due to issues of either the abstract or title or both. Resultantly, a total of 73 full-text articles were assessed for eligibility whilst 51 articles were excluded as they lacked relevance. Subsequently, only twenty-two (22) articles met the inclusion criteria and quality assessment such that they were included in this systematic literature review. A summary of the 22 included articles is presented in Table 1.
The findings summarised in Table 1 provide an analysis on the effects of soil
stabilization on different soil mechanical properties through the application of lime, fly ash and cement. From the findings presented in Table 1, lime, cement, and fly ash have significant effects on different mechanical properties such as plasticity, swelling, UCS, CBR, OMC and MDD. The effects of the three stabilizers (fly ash, cement, and lime) on soil mechanical properties as cited in the reviewed articles summarised in Table 1 are further shown in Table 2.
From the results in Table 2, a significant number of studies found that lime soil stabilization significantly improves the mechanical properties of soil such as plasticity, CBR, UCS, OMC and MDD and reduce swelling (Ali and Yousof, 2019 [36] ; Andavan and Pagadala, 2020 [41] ; Asgari et al., 2015 [34] ; Krithiga et al., 2017 [40] ; Navale et al., 2016 [43] ; Sharma and Hymavathi, 2016 [28] ; Shekhar and Saxena, 2018 [15] ; Talabi et al., 2019 [42] ; Zhou et al., 2019 [38] ). However, a few studies (Okonkwo and Kennedy, 2023 [4] ; Rai et al., 2021 [27] ) found that soil stabilization using lime reduces plasticity and OMC. In overall, soil stabilization using lime has proved to have a significant improvement on the mechanical properties of soil. The findings are consistent with those of previous studies (Jin and Li, 2019 [20] ; Salimah et al., 2021 [17] ; Taki and Bhattacharya, 2020 [29] ; Utami, 2014 [13] ) which found that lime significantly improve soil
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Table 2. Summarised effects of fly ash, cement and lime soil stabilization.
mechanical properties.
Similarly, from the reviewed experimental studies, it has been noted that just like lime, cement soil stabilization significantly improves most of the mechanical properties of soil. From the results in Table 1 and Table 2, stabilization of soil using cement improve mechanical properties of soil such as plasticity, CBR, UCS, OMC and MDD whilst reducing soil swelling (Bayat et al., 2015 [35] ; Mahedi et al., 2020 [14] ; Nguyen and Phan, 2021 [39] ; Sharma et al., 2018 [28] ; Shekhar and Saxena, 2018 [15] ; Talabi et al., 2019 [42] ). Contrastingly, a few studies by Okonkwo and Kennedy (2023) [4] and Rai et al. (2021) [27] found that cement soil stabilization reduce OMC. In overall, the results indicate that cement soil stabilization significantly improves the mechanical properties of soil. The findings are in line with the findings of previous studies such as Nazari et al. (2021) [21] and Shooshpasha and Shirvani (2015) [22] which found that cement soil stabilization has significant positive effects on soil mechanical properties such as permeability, strength, and stability of soil.
Furthermore, from the included articles, the majority of the experimental studies (Andavan and Pagadala, 2020 [41] ; Krithiga et al., 2017 [40] ; Mir, 2015; Navale et al., 2016 [43] ; Nguyen and Phan, 2021 [39] ; Shekhar and Saxena, 2018 [15] ; Teerawattanasuk and Voottipruex, 2019 [37] ; Zhou et al., 2019 [38] ) revealed soil stabilization using fly ash improved soil strength as measured by CBR and UCS. These results clearly indicate that fly ash-soil stabilization significantly improves the mechanical properties of soil such strength. The findings agree with the findings of previous studies (such as Dayalan and Dayalan, 2016 [18] ; Turan et al., 2022a; 2022b [19] ; Vinai et al., 2019 [2] ) which found fly ash significantly improves soil mechanical properties such as strength and stability.
Besides, the reviewed studies have shown that among the three stabilizers (fly ash, cement, and lime), there are some more effective compared to others. In terms of cement, the study by Mahedi et al. (2020) [14] found that cement is more effective in soil stabilization compared to lime and fly ash. Similarly, Sharma et al. (2018) [28] revealed that cement has relatively higher effects on mechanical properties of soil compared to lime. Supporting evidence was also obtained from the studies by Asgari et al. (2015) [34] , Bayat et al. (2014) [35] and Okonkwo and Kennedy (2023) [4] which revealed that improvements in soil mechanical properties were relatively higher in cement treatment compared to lime treatment.
However, studies such as Rank et al. (2019) [33] found that fly ash has significant effects on soil mechanical properties compared to cement. Similar to Rank et al. (2019) [33] , Teerawattanasuk and Voottipruex (2019) [37] found that fly ash stabilized soil had higher CBR values compared to cement-stabilized soil. Rai et al. (2021) [27] also established that fly ash is more effective compared to cement. Also, the study by Zhou et al. (2019) [38] reported that fly ash showed better soil strength compared to lime. Kalyane and Patil (2020) [25] also found that fly ash is more effective compared to lime. In the context of Vietnam, Nguyen, and Phan (2021) [39] also proved that fly ash had significant effects compared to cement. The experimental studies by Andavan and Pagadala (2020) [41] , Arias-Jaramilo et al. (2023) [3] , Krithiga et al. (2017) [40] and Mir (2015) also revealed that soil stabilization using fly ash is more effective in soil strengthening compared to lime.
On the other hand, several studies reported that lime is the most effective soil stabilizing agent. For instance, Sharma and Hymavathi (2016) [28] and Rank et al. (2019) [33] concluded that lime is the best soil stabilizing agent compared to fly ash. Consistent with Sharma and Hymavathi (2016) [28] , Ali and Yousuf (2019) [36] found that lime stabilization is more efficient compared to cement stabilization. Comparably, Saleem et al. (2020) [12] and Talabi et al. (2019) [42] revealed that lime is more effective in improving strength and stability of soil compared to cement. In their experimental research, Shekhar and Saxena (2018) [15] found that lime stabilized soil had higher CBR values compared to cement and fly ash stabilized soil. Navale et al. (2016) [43] found that lime was more effective compared to fly ash.
From the aforementioned analyses, out of the included articles, majority them proved that fly ash is the most effective soil stabilizing agent compared to alternatives such as cement and lime. However, Shekhar and Saxena (2018) [15] concluded that whilst fly ash alone works much better as a soil stabilizing agent, a combination of cement, lime and fly ash can be more effective and beneficial. In the same view, Lindh and Lemenkova (2023) [23] reported that best performance in soil stabilization can be attained by blending cement, lime, and fly ash. Similarly, Kalyane and Patil (2020) [25] concluded that a combination of lime and fly ash proves to very effective as it results in improved soil strength. Arias-Jaramillo et al. (2023) [3] also concluded that mixture of lime and fly ash demonstrated increased bearing capacity compared to cement and lime. The technique of blending admixtures was also supported by Okonkwo and Kennedy’s (2023) [4] study which concluded when used together, cement and lime provide significant outcomes in terms of soil strength and stability.
Effects of Combinations of Soil Stabilization on Mechanical Properties
Through out this paper we assesed individual soil stabilizers, however there are situations where they are combined in an attempt to give satisfactory results to engineering. The three stabilizers fly ash, lime and cement analyzed here provide us with 3 combinations: 1) fly ash and cement 2) lime and cement 3) fly ash and lime.
Table 3 below outlines the pros and cons of soil stabilizers combinations.
4.2. Discussion
Firstly, this paper has discussed the effects of soil stabilization on soil mechanical properties using three different materials―fly ash, cement and lime individually. It is explained how each material affects the strength, compressibility, and permeability of the soil. It also compared the effectiveness of each material, and found that fly ash and lime are the most effective when used together. These findings ultimately suggested that lime and fly ash are great in many engineering aspects and even better more when compared.
Looking at the effect of fly ash and lime on soil strength. Fly ash is known to increase the strength of the soil by filling in the voids between the soil particles. This reduces the amount of water that can be held by the soil, and also makes the soil more resistant to compression. Lime, on the other hand, works by increasing the pH of the soil and causing the soil particles to flocculate (stick together). This makes the soil more cohesive and resistant to shearing. When fly ash and lime are used together, they work synergistically to increase the strength of the soil even further.
Fly ash and lime combined together were more compatible. Here are several reasons why fly ash and lime are more compatible than the other combinations you mentioned. First, the chemical composition of fly ash and lime is similar, which means they react well together. Second, the pH levels of fly ash and lime are close to each other, so they don’t react negatively with each other. Third, the physical properties of fly ash and lime are also similar, which means they can be mixed easily without causing problems. Fourth, fly ash and lime are both abundant compatible combinations than the other options you mentioned. Fly ash and lime have a lower environmental impact than cement, and can also help to reduce
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Table 3. Summarised effects of cimbining soil stabilizers.
the amount of carbon dioxide emissions associated with construction projects. This is also seen and proven in studies done on the following researches, Deflection analysis of flexible pavements-Materials and Test Division Report Passuello A. Rodríguez E. D. Hirt E. Longhi M. Bernal S. A. Provis J. L. Kirchheim A. P. Construction and Building Materials (2015), Quantification and micro-mechanisms of CO2 sequestration in magnesia-lime-fly ash/slag solidified soils Wang D. Zhu J. He F. International Journal of Greenhouse Gas Control (2019), 10.1016/j.ijggc.2019.102827, Improved mechanism of expansive soils by lime and fly-ash Hui H. Q. Hu T. K. Wang X. D. Chang’an Daxue Xuebao (Ziran Kexue Ban)/Journal of Chang’an University (Natural Science Edition) (2006).
5. Conclusions
The main purpose of this systematic review was to compare the effects of soil stabilization on mechanical proprieties of soil using lime, cement, and fly ash. From the systematic review conducted focusing on articles published between 2013 and 2023 guided by the PRISMA guidelines, the effects of soil stabilization on mechanical properties were established. From the outcomes of the systematic review, it can be concluded that soil stabilization using either lime, cement or fly ash has significant effects on the mechanical properties of soil. The results of the systematic review indicated that all three stabilizers (cement, lime, and fly ash) can significantly improve soil mechanical properties such as strength and stability. Overall, fly ash was found to be the most effective soil stabilizer in terms of reducing soil plasticity and increasing strength according to the outcomes of the systematic review.
Fly ash showed great results in improving soil mechanical properties compared to lime and cement. Therefore, based on the outcomes, it can be concluded that fly ash represents the most effective soil stabilizing agent for geotechnical and civil engineers. However, whilst fly ash alone can be more effective in soil stabilization, a combination of cement, lime and fly ash can be more effective. We therefore also noted that combinations of lime and fly ash bring satisfactory results. Lastly, it is noteworthy to mention that the effects of soil stabilization by lime, fly ash and cement can also vary with type of soil. Overall, the findings highlighted the potential of soil stabilizing agents in enhancing the mechanical properties of soils and hence provide valuable insights for geotechnical and civil engineers and practitioners. Nevertheless, further experimental or field studies are required to comprehensively compare the short-term and long-term effects of fly ash, cement, and lime on soil mechanical properties.