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Article

Swelling Behaviour of Sulfate Soil Treated with Lime–Metakaolin at Different Curing Ages

by
Mansour Ebailila
1,*,
Khaled Ehwailat
1 and
Jonathan Oti
2,*
1
Department of Civil Engineering, Faculty of Engineering, Bani Waleed University, Bani Waleed 238, Libya
2
Faculty of Computing, Engineering and Science, University of South Wales, Pontypridd CF37 1DL, UK
*
Authors to whom correspondence should be addressed.
Ceramics 2025, 8(4), 133; https://doi.org/10.3390/ceramics8040133
Submission received: 19 September 2025 / Revised: 26 October 2025 / Accepted: 4 November 2025 / Published: 6 November 2025
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Abstract

Sulfate soil stabilisation, while offering technical benefits for infrastructure, is a challenging process, complicated by the nucleation of ettringite, an expansive mineral that can cause soil deterioration. This study was undertaken to elucidate the synergistic effect of lime and metakaolin on the physico-mechanical performance of high-sulfate-bearing soil. The binder content in the stabilised specimens was fixed at 20 wt%, and metakaolin was used to partially substitute lime at different substitution levels. The physico-mechanical investigation revealed that supplementation of lime with metakaolin had a promotional effect on the unconfined compressive strength and swelling potential. The threshold of this effect was obtained by a binary blend of 7.5L–12.5MK, where the UCS was increased fourfold, while the swelling potential was reduced to a near-zero magnitude of 0.33%. This superior performance is due to the fineness and high reactivity of metakaolin, as both limit the nucleation of ettringite and promote the neoformation of further hydrated compounds, thus yielding a denser interlocked system and increasing its resistance to water soaking.

1. Introduction

Soil rich in sulfate, especially in the form of gypsum, is characterised as the most common and challenging type of soil encountered worldwide. This is due to its lower strength and its excessive swelling upon wetting, as a result of gypsum dissolution [1]. For this reason, the implementation of engineering structures on such problematic sulfate soil is highly hazardous [2], as they can suffer from several problems, including cracks, differential settlement, and structural deterioration [3]. Therefore, cementation of such soil with calcium-based binders, such as lime or cement, is traditionally applied to improve its geotechnical characteristics [4,5], including strength, permeability, and swelling [6]. For example, the study of [7] compared the impact of two types of lime (calcitic and dolomitic) on the stabilisation of tropical soil for resilient pavement application and observed higher mechanical performance in the case of calcitic lime, relative to the dolomitic lime, due to the higher calcium oxide content. Negawo et al. [8] examined the effect of various dosages (5, 7, and 9%) of quicklime on the swelling behaviour of an expensive clay with high plasticity and inferred that 7% of quicklime is the effective binder dosage for road subgrade applications. In addition, Baldovino et al. [9] evaluated the empirical relationship between the unconfined compressive strength and tensile splitting strength of lime-cemented silty soil, and established two equations that can be used for mix design.
However, the application of a calcium-based binder in the presence of sulfate can lead to a counterproductive impact [10], as it causes extensive swelling due to the neoformation of ettringite [3], i.e., an expansive mineral formed by the interaction of sulfate with calcium and alumina in the presence of water.
The utilisation of a binder rich in calcium is also of great environmental concern due to the environmental consequences related to its manufacturing [11]. For instance, the production of one tonne of cement requires 1.5 tonnes of natural non-renewable resources (mainly clay and limestone), thereby depleting the raw materials and threatening sustainability [12]. In addition, manufacturing one tonne of cement is responsible for the consumption of 5000 MJ/t and the emission of one tonne of carbon dioxide, accounting annually for 9% of total greenhouse gas emissions [13]. In this context, the use of multiple aluminosilicate pozzolans in the conventional stabilisation method to develop an effective and low-carbon-based binder for sulfate soil stabilisation has become the focus of many researchers.
Metakaolin, a dehydroxylated form of kaolinite minerals calcinated at a temperature range of 500–750 °C [14], is an amorphous aluminosilicate substance that has recently gained great attention in the field of soil stabilisation [15,16,17,18,19,20,21,22,23]. This is due to its richness in silica and alumina [24], extreme fineness, and its high reactivity/pozzolanicity, along with its positive role in reducing greenhouse gas emissions [15,23,25]. The fine metakaolin particles act as active seeds for hydration, thus optimising the distribution of pore structures and accelerating the consumption of portlandite [26]. This consequently promotes rapid nucleation and the neoformation of hydrated gels, improving bonding between soil particles and inducing enhanced strength.
Upon the use of metakaolin in the field of soil stabilisation, the study of [23], for example, evaluated the sole effect of metakaolin on lateritic soil, and observed a gradual improvement in the compressive strength, California bearing ratio, and durability index, as the metakaolin content increased up to 6%, beyond which a reversal effect was observed. A study by [27] discovered that the utilisation of metakaolin significantly improves the compressive strength and expansion of cement-stabilised expansive soil, and such improvement was optimal at 4% of metakaolin. Similarly, Wu et al. [14] found that the addition of 2% of metakaolin in cement-stabilised soil improved the compressive and tensile strength by 100% and 60%, respectively. Deng et al. [28] reported that the incorporation of 30% metakaolin enhanced the deterioration of cement-treated Mariane soft clay under saline solution and freeze/thaw curing conditions. Similarly, a study by Xu et al. [23] revealed an increase in the shear strength, compressive strength, and the durability of lime-treated saline soil through the incorporation of metakaolin.
While the literature previously mentioned underscores the potential application of metakaolin in soil stabilisation, its utilisation in combination with lime for sulfate soil stabilisation has not been thoroughly studied. For example, the optimal binary blend of lime and metakaolin for suppressing swelling, and the role of the moist curing period on the swelling behaviour of such binder, remain undiscovered. This study, therefore, bridges the research gaps by systematically analysing the physico-mechanical and microstructure of sulfate soil stabilised with different blending proportions of lime and metakaolin. The analysis adopted in this study comprises unconfined compressive strength testing under two curing conditions (moist curing and water soaking), swelling potential investigation after three different moist curing ages (7, 28 and 90 days), X-ray diffraction analysis, and scanning electron microscopy analysis. Accordingly, the viability of incorporating metakaolin in the lime stabilisation technique, in general, has been proven to be efficacious for suppressing the swelling of artificial sulfate soil, which may have some bearing on the current practices. This is particularly the case for the binder combination of 7.5L–12.5MK, as such a binder exhibits a high resistance to swelling without a comprise on strength performance. This swelling percentage is even expected to be further reduced by the loading of overlying engineering structures. Therefore, this binder combination is recommended to be used in a situation where no chance or only a negligible magnitude of swelling is tolerated, and is particularly pertinent to all geotechnical engineers involved in the development of an effective sulfate soil stabiliser and the application of by-product pozzolans.

2. Materials and Methods

2.1. Materials

2.1.1. Kaolin

The kaolin (K) used for fabricating the laboratory specimens was a commercially industrial kaolin soil with oxides/elements and physical characteristics as specified in Table 1 and Table 2, respectively. K was supplied by KAOLIN (M) SDN BHD, Malaysia, under the brand name of MK40. The laboratory characterisation testing—conducted in accordance with the relevant British standard—suggested that the kaolin used has a liquid limit of 57.78%, a plastic limit of 38.13%, a shrinkage limit of 4.4%, and a plasticity index of 19.65%. Therefore, as per the plasticity index classification, the kaolin is classified as a silt of high plasticity. The particle size distribution curve (Figure 1) obtained from a hydrometer test in line with [29] suggested that the kaolin texture is made of 0% sand, 88% silt, and 12% clay.

2.1.2. Sulfate

Commercially available calcium sulfate dihydrate (gypsum) was used in the laboratory investigation to form the artificially sulfate-bearing soil. The oxide compositions, as supplied by Sungai Jawi, 14200, Penang, Malaysia, are given in Table 1. As for the selection of calcium-based sulfate, it stems from the fact that it is the most common type of sulfate found in sulfate-bearing soil [13], thus providing a basis for relevant comparison.

2.1.3. Binder

The artificial sulfate-bearing soil blended in the laboratory was stabilised using two different binders: (1) lime alone, used as a baseline, and (2) a blended binder comprising different proportions of lime and metakaolin. The lime used was a hydrated lime with a calcium hydroxide percentage of 92%, while metakaolin, a reactive form of calcined kaolinite minerals (a by-product of thermal activation of kaolin at 700–750 °C), mainly consists of SiO2 (52%) and Al2O3 (36%), as displayed in Table 1. Both ingredients (hydrated lime and metakaolin) were supplied by a local contractor from Sungai Jawi, Penang, Malaysia.

2.2. Mix Compositions

In this study, four soil–lime–metakaolin formulations (see Table 3) were prepared at a constant binder content of 20 wt%, by changing the proportion of lime and metakaolin. The nomenclature used for mix design was a three-part combination of acronyms (K10G, L, MK), of which G, L, and MK were preceded by a number referring to the contents of gypsum, lime, and metakaolin, respectively. For example, K10G–2.5L–17.5MK refers to the artificially blended gypseous kaolin soil containing 10% of gypsum and stabilised with a binary blend of 2.5% lime and 17.5% metakaolin in terms of the dry weight of soil. The choice to adopt 10% gypsum, which was in line with [30,31], was selected because gypsum is considered to be the most common source of sulfate encountered in natural sulfate soil. As for the percentage of 10%, it was adopted due to the fact that such a percentage is considered to cause a high to unacceptable risk according to AASHTO [32], as well as being classified as the worst-case scenario for ettringite formation [31]. Therefore, if the optimisation of the blended binder employed in this study was carried out using such a percentage, the formation of ettringite in any other natural sulfate soil stabilised by the optimal binder [13] would be suppressed to some reasonable degree. As for the 20% binder content, this was adopted based on the observation of previous studies [33], as such a binder dosage has shown strong performance in sulfate soil, relative to other relatively low binder contents.

2.3. Specimens’ Preparation

A set of 15-cylinder specimens, each measuring 50 mm in diameter and 100 mm in length, was produced for each mix, as per the mix proportions defined in Table 3, by using the optimum moisture content and maximum dry density shown in Table 4, as obtained from the proctor test, which was conducted in line with the BSEN 13286–2:2010 standard [34]. Each of these specimens followed a similar mixing protocol, in which the soil and lime or its substitute were mixed in a mixer for 3 min, before the water was gradually added and the mixing restarted for an additional 3 min.
The homogeneous mixture obtained was immediately compacted in a 2-piece cylindrical steel mould and extruded using a pre-lubricated plunger with the aid of a prefabricated steel frame, as shown in Figure 2. The extruded specimen was gently trimmed and wrapped in a polyethylene membrane and preserved in a closed container, allowing for moist curing at an ambient room temperature, until testing.

2.4. Testing Method

A series of laboratory experiments was performed to evaluate the binder blending proportions on the physico-mechanical and microstructure of sulfate soil. These experimentations included the following: swelling potential test, unconfined compressive strength, microstructure investigation and X-ray diffraction analysis. The swelling potential test was performed as described by [13,33], in which three specimens per mix after 7, 28, and 90 days of moist curing were embedded between two porous discs in a Perspex cell (see Figure 3). Such Perspex cells were kept in a temperature-controlled room at a temperature of 20 ± 2 °C. The Perspex cell was then covered with a lid equipped with a dial gauge to measure the vertical displacement. The water was then introduced through an inlet hole until about one-third of the specimens were submerged in water, and the water level was kept constant by adding some water daily when it was found to be necessary. Thereafter, the vertical change was recorded at an interval of a daily basis using dial gauges, and the average ratio of height increase to the original height was calculated and presented in this study as the representative swelling.
The unconfined compressive strength test, in which three specimens per mix at different ages of two curing conditions (7, 28, 90 days of moist curing, as well as after 90 days of water soaking curing), were subjected to a compressive force at a displacement ratio of 1 mm/min using a Hounsfield testing machine, in accordance with [35]. The microstructure investigation involved the analysis of the morphology of a pre-dried/powdered portion from the centre of broken UCS and swelling specimens using scanning electron microscopy at an accelerating voltage of 5 kV. XRD analysis involved the scanning of the mineralogy of a pre-dried portion from the middle of fractured UCS specimens at 1°/min speed for a 2θ range of 5° to 65°.

3. Results and Discussions

3.1. UCS Development

The UCS values obtained for the different lime–metakaolin mixes at 7, 28, and 90 days of moist curing are given in Figure 4. Therefore, the control mix, made with only lime, experienced the lowest strength at early curing age (534, 822, and 2114 kN/m2 at 7, 28, and 90 days, respectively). The strength growth, in general, lies in the fabric modification of soil particles and the neoformation of hydrated gels through pozzolanic interactions [1,4,5,13]. During lime hydration, ionised calcium and hydroxide are released, increasing the alkalinity value and promoting the solidification/flocculation of soil particles [36]. This therefore enables the release of aluminate and silicate units, thereby initiating the pozzolanic reactions [37]. These released aluminate and silicate units react with calcium ions, forming a mixture of hydrates such as CSH and CAH. Such hydrates promote proper interlocking forces between particles due to the high rigidity of the hydrated compounds [38]. The hydrated compounds also facilitate the densification/interlocking of the soil matrix, thus achieving a stronger performance [2,36].
Due to the time-dependent nature of pozzolanic interaction, the cementation of soil by lime is a long-term procedure, indicating that the longer the curing age, the greater the hydrated amount formed, thus the greater the enhanced strength. This provides an explanation as to why the stabilisation of soil with lime exhibited a gradual strength development over time [4]. During the pozzolanic reaction, calcium hydroxide may also remain in the system, particularly at high lime content, indicating a sign of surplus lime being utilised. This remaining calcium hydroxide (portlandite) is not favourable, as it negatively affects the cohesion of the system and further impedes the dissolution of dissolved silica and alumina from the soil [13]. Therefore, the negative effect associated with high lime content could be a possible rationale behind the lower strength magnitude brought about by the sole addition of 20% lime, as represented by K10G-20L.
Supplementation of lime hydration with metakaolin resulted in a noticeable strength gain, and such a strength gain is influenced by both curing age and lime substitution level. For example, relative to its counterpart of 20% lime the strength of 7.5L–12.5MK was increased by 350% at 7 days, 360% at 28 days, and 29% at 84% days. This highlights the critical role of the extreme fineness and high reactivity of metakaolin, along with its high content of soluble silica and alumina, in enhancing the mechanism of lime stabilisation. That is, the fine metakaolin particles act as well-distributed active seeds for hydration, thus optimising the distribution of pore structures and accelerating the consumption of portlandite [26]. This consequently promotes rapid nucleation and the neoformation of hydrated gels, improving bonding between soil particles and inducing enhanced strength. However, upon further metakaolin addition, the result indicated a reversed effect, whereby a 90-day strength decrease (relative to 7.5L–2.5MK) of 27% and 70% was detected for K10G–5L–15MK and K10G–2.5L–17.5MK, respectively. This decrease could arise from the augmentation in the quantity of fine particles (metakaolin) [39], which alters the distribution and grading of soil arrangement and acts as a filler rather than a reactive nucleation site. That is, the pore structure and the particle size distribution significantly influence the characteristics of the materials, with the particle gradation controlling the pore structure (connectivity and size distribution), which consequently determines the fluid transport characteristics and mechanical properties. Therefore, the excessive quantity of metakaolin in the system can lead to a less dense and more porous structure by reducing the formation of cementitious products responsible for enhancing their strength. This alteration subsequently induces a reduction in the cation exchange capacity and a decrease in the adhesive linkage between soil particles and ultimately compressive strength. A higher amount of metakaolin can also reduce the porosity due to its lower specific gravity, resulting in reduced strength. Ultimately, the use of lime and metakaolin has a beneficial effect on sulfate soil stabilisation, and such an effect was dominant at a ratio of 7.5L–12.5MK.

3.2. UCS of Soaked Specimens

The 90-day UCS of kaolin specimens stabilised with lime and metakaolin after 7 days of moist curing and 83 days of soaking curing is compared with the 90-day UCS of moist-cured specimens in Figure 5. Generally, all the stabilised specimens, except specimens stabilised with 7.5L–12.7MK, exhibited a compromise in strength under water-soaking conditions. In this context, the strength of K10–20L, K10–5L–15MK, and K10–2.5L–17.5MK was dropped by 57%, 23%, and 40% to 906 kN/m2, 2209 kN/m2, and 708 kN/m2, respectively. The reduction in soaked UCS values of K10–20L, in contrast to their unsoaked counterparts, stemmed mainly from (1) the poorer cohesion of the system due to the higher lime content and (2) the expansion of ettringite, which promotes the formation of cracks, thus reducing the capability against loading [37]. As for the decline in strength for K10–5L–15MK and K10–2.5L–17.5MK, this can be attributed to (1) the lower cation exchange (fabric modification), due to the extreme fineness and high reactivity of metakaolin, which facilitates the depletion of lime responsible for fabric modification, and (2) the infiltration of water, which compromise the integrity of the strength [39].
On the contrary, the blend of 7.5L–12.5MK yielded a strength increase of about 25% under water-soaking conditions, in which the strength was increased from 3981 kN/m2 to 4942 kN/m2. This observation, which was in line with [23], can be attributed to the extreme fineness and high reactivity of metakaolin, along with its richness in soluble silica and alumina, as it would act as well-distributed active seeds. These active seeds facilitate the rapid depletion of portlandite and the rapid neoformation of hydrated gels (CSH and CAH), thus densifying the system through pore-blockage effect, and enhancing strength against deformation and loading. By comparing the residual strength values with the minimum requirement (>80%) for retained strength after immersion in water, as stated in the standard code [40,41], only 7.5L–12.7MK fulfilled the durability assessment at 90 days.

3.3. Swelling Behaviour

The effect of different moist curing ages (7, 28, and 90 days) on the swelling behaviour of kaolin specimens stabilised with a mixture of lime and metakaolin, over a longer soaking period of 90 days, is depicted in Figure 6.
In general, the swelling behaviour of all the stabilised specimens exhibited a reduction with curing age. This reduction in swelling with curing age can be attributed to particle rearrangement and the greater formation of hydrated products. These hydrates facilitate the densification and interlocking of the system, affecting the surface area adsorbing moisture, thus enhancing resistance to water infiltration and swelling [42].
The sole addition of lime induced a drastic increase in swelling, reaching the highest swelling magnitudes of 30%, 16%, and 4% for specimens cured for 7, 28, and 90 days, respectively. This behaviour is typically attributed to the formation of expansive mineral, i.e., ettringite, which was also detected in XRD and SEM analysis. However, by incorporating metakaolin as a lime substitute, the swelling magnitude was exponentially decreased from 30% to 0.33% for samples cured for 7 days, from 16% to 0.053% for samples cured for 28 days, and from 4% to 0.034% for samples cured for 90 days, as represented by 7.5L–12.5MK. A similar reaction in swelling was also observed for other binary blend-based specimens (5L–15MK and 2.5L–17.5MK). This suggests that supplementation of lime with metakaolin had a promotional effect on the swelling behaviour of sulfate soil. Like UCS, this decline in swelling is mainly due to (1) the restriction of ettringite neoformation as a result of the rapid consumption of calcium hydroxide, which is related to the extreme fineness and high reactivity of metakaolin, and (2) the availability of soluble silica and alumina, which strengthen the formation of further hydrated compounds, and consequently yield a denser interlocked system and increase its resistance capability to water soaking [39].

3.4. Analytical Analysis

Upon the completion of swelling, the new reflections of kaolinite (K), gypsum (G), ettringite (E), calcite (C1), portlandite (P), and calcium silicate hydrate (CSH) phases are detected in the diffractograms (see Figure 7) of kaolin specimens treated with lime and metakaolin.
The intensity of ettringite minerals at 2θ = 9°, 15.8°, 18.9°, and 41° appeared sharper in the sole-lime system and almost disappeared in specimens stabilised with 7.5L–12.5MK, suggesting the vital role of metakaolin in restricting the formation of ettringite. This variation in ettringite peaks was also validated by the photomicrographs depicted in Figure 8, i.e., where an excessive quantity of needle-like structures (ettringite minerals) was inspected in K10G–20L, relative to the small needles detected in K10G–7.5L–2.5MK. These observations, therefore, partially explain why specimens stabilised with the sole addition of lime experienced drastic swelling, relative to their counterparts of lime- and metakaolin-based specimens. In contrast, the intensity of gypsum reflection (2θ = 11.6°, 20.7°, and 29.1°) in Figure 5 appeared to increase with the substitution of lime with metakaolin, which also confirms the restriction of ettringite formation.
The portlandite peak at 2θ = 18.08° appeared sharper in specimens stabilised with 20% lime, the appearance of which indicates a sign of incomplete consumption of lime by the soil at 90 days of curing. This was also accompanied by the appearance of a calcium carbonate mineral in the form of calcite at a reflection angle of 2θ = 29.2°. However, in the case of a binary blend system, no traces of portlandite and calcite were detected in the diffractogram of 7.5L–12.7MK, the absence of which indicates the superiority of metakaolin in depleting the calcium hydroxide. The portlandite depletion was coupled with the increase in intensity of CSH reflection at 2θ = 30° and an increase in intensity of kaolinite minerals at 2θ = 12.3°, 19.8°, 21.2°, and 23°. This is because of the extreme fineness and high reactivity of metakaolin, along with its richness in soluble silica and alumina, which act as well-distributed active seeds. These active seeds facilitate the rapid portlandite consumption and the rapid neoformation of further hydrated gels, restricting the formation of ettringite and inducing lesser fabric modification, thus enabling higher reflection intensities of kaolinite minerals to occur.

4. Conclusions

This study delved into the potential application of a sustainable binder, enriched in metakaolin and hydrated lime, to stabilise an artificial high-sulfate-bearing soil. A laboratory program, entailing swelling potential testing, unconfined compressive strength testing, X-ray diffraction analysis, and scanning electron microscopy analysis, was performed to assess the efficacy of this binder. The following conclusions were drawn accordingly:
  • Replacement of lime with metakaolin remarkably improved the unconfined compressive strength and significantly suppressed the swelling potential of sulfate soil. This is probably due to its fineness, its high reactivity, and its significant capability in the decalcification of calcium hydroxide, which consequently promotes the restriction of ettringite and the neoformation of further hydrated compounds.
  • The physico-mechanical assessment identified 7.5L–12.5MK as the optimal blend for sulfate soil stabilisation, specifically increasing the strength to about fourfold and suppressing the swelling to near-zero (0.33%).
  • A high substitution level of lime with metakaolin suppresses the swelling potential of sulfate soil, but also induces a compromise on strength, probably because the faster depletion of lime negatively affects the fabric modification; thus, it is not recommended for better strength performance.
  • The limitations of this research study, which may influence the authenticity of the findings, are the use of an artificial laboratory-blended sulfate soil and the use of a single calcination degree (700–750 °C) for the production of metakaolin from kaolin.
Overall, the viability of incorporating metakaolin into the lime stabilisation technique, in general, has been proven to be efficacious for suppressing the swelling of kaolin soil dosed with gypsum, which may have some bearing on the current practices. This is particularly the case for a binary blend of 7.5L–12.5MK, as such a binder exhibits a high resistance to swelling as low as 0.33%, 0.05%, and 0.03% after 7, 28, and 90 days of curing, without a comprise on strength performance. This swelling percentage is even expected to be further reduced by the loading of overlying engineering structures. Therefore, this binder combination is recommended to be used in a situation where no chance or only a negligible magnitude of swelling is tolerated. However, further study considering the use of different natural sulfate soils and the examination of the durability performance is recommended for validation.

Author Contributions

Conceptualization, M.E., K.E. and J.O.; methodology, M.E., K.E. and J.O.; software, M.E. and K.E.; validation, M.E., K.E. and J.O.; formal analysis, M.E. and K.E.; investigation, M.E. and K.E.; resources, M.E., K.E. and J.O.; data curation, M.E. and K.E.; writing—original draft preparation, M.E. and K.E.; writing—review and editing, J.O.; visualisation, M.E., K.E. and J.O.; supervision, J.O.; project administration, M.E., K.E. and J.O.; funding acquisition, J.O. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding authors.

Acknowledgments

All authors would like to acknowledge the Advanced Testing Centre, within the School of Civil Engineering at Universiti Sains Malaysia, for the administrative and technical support during the implementation of the laboratory experimentations.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
UCSUnconfined Compressive Strength
CSHCalcium Silicate Hydrate
CAHCalcium Aluminate Hydrate
KKaolin
GGypsum
LLime
MKMetakaolin

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Figure 1. Particle distribution of kaolin, lime, and metakaolin.
Figure 1. Particle distribution of kaolin, lime, and metakaolin.
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Figure 2. Process of sample preparation.
Figure 2. Process of sample preparation.
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Figure 3. Partial soaking of specimens for the swelling test.
Figure 3. Partial soaking of specimens for the swelling test.
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Figure 4. UCS of kaolin specimens treated with lime and metakaolin.
Figure 4. UCS of kaolin specimens treated with lime and metakaolin.
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Figure 5. The 90-day UCS of unsoaked/soaked kaolin specimens treated with lime and metakaolin.
Figure 5. The 90-day UCS of unsoaked/soaked kaolin specimens treated with lime and metakaolin.
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Figure 6. The swelling potential and ultimate swelling magnitude of kaolin specimens treated with lime and metakaolin and cured for (a,b) 7 days, (c,d) 28 days, and (e,f) 90 days.
Figure 6. The swelling potential and ultimate swelling magnitude of kaolin specimens treated with lime and metakaolin and cured for (a,b) 7 days, (c,d) 28 days, and (e,f) 90 days.
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Figure 7. X-ray diffraction diagrams of gypsum-bearing kaolin treated with 20% lime alone and in combination with metakaolin. (Note: kaolinite–K, gypsum–G, ettringite–E, calcite–C1, portlandite–P, and calcium silicate hydrate–CSH).
Figure 7. X-ray diffraction diagrams of gypsum-bearing kaolin treated with 20% lime alone and in combination with metakaolin. (Note: kaolinite–K, gypsum–G, ettringite–E, calcite–C1, portlandite–P, and calcium silicate hydrate–CSH).
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Figure 8. The photomicrographs of kaolin specimens treated with lime and metakaolin: (a) specimen made with 20L and (b) specimen made with 7.5L–12.5MK.
Figure 8. The photomicrographs of kaolin specimens treated with lime and metakaolin: (a) specimen made with 20L and (b) specimen made with 7.5L–12.5MK.
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Table 1. Oxides and elements of kaolin, gypsum, lime, and metakaolin.
Table 1. Oxides and elements of kaolin, gypsum, lime, and metakaolin.
Oxides and ElementsCompositions as Weight Percentages (%)
KaolinGypsumLimeMetakaolin
CaO---0.2
Ca(OH)2--92-
MgO--3.50.1
SiO258-2.552
Al2O338-0.936
Ca2SO4-990.1-
Fe-0.0050.068
SO3----
LOI11–140.990.243.7
Table 2. Physical characteristics of kaolin, gypsum, lime, and metakaolin.
Table 2. Physical characteristics of kaolin, gypsum, lime, and metakaolin.
PropertiesKaolinLimeMetakaolin
Plasticity index (%)19.7
Swelling (%) 4.8
Specific gravity (mg/m3)2.52.22.3
pH5127
ColourWhiteWhiteWhite
Table 3. Mix design of kaolin soil treated with lime and metakaolin.
Table 3. Mix design of kaolin soil treated with lime and metakaolin.
Mix CodeMix Compositions (%)
Soil Material (%)Water (%)Stabiliser (%)Stabiliser in % by Soil
KaolinGypsumLimeMetakaolin
K10G–20L901029.42020-
K10G–2.5L–17.5MK901029202.517.5
K10G–5L–15MK901028.620515
K10G–7.5L–12.5MK901028207.512.5
Table 4. Compaction parameters.
Table 4. Compaction parameters.
Mix CodeCompaction Parameters
OMC (%)MDD (Mg/m3)
K–10G291.32
K10G–20L29.41.27
K10G–2.5L–17.5MK291.28
K10G–5L–15MK28.61.31
K10G–7.5L–12.5MK281.33
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Ebailila, M.; Ehwailat, K.; Oti, J. Swelling Behaviour of Sulfate Soil Treated with Lime–Metakaolin at Different Curing Ages. Ceramics 2025, 8, 133. https://doi.org/10.3390/ceramics8040133

AMA Style

Ebailila M, Ehwailat K, Oti J. Swelling Behaviour of Sulfate Soil Treated with Lime–Metakaolin at Different Curing Ages. Ceramics. 2025; 8(4):133. https://doi.org/10.3390/ceramics8040133

Chicago/Turabian Style

Ebailila, Mansour, Khaled Ehwailat, and Jonathan Oti. 2025. "Swelling Behaviour of Sulfate Soil Treated with Lime–Metakaolin at Different Curing Ages" Ceramics 8, no. 4: 133. https://doi.org/10.3390/ceramics8040133

APA Style

Ebailila, M., Ehwailat, K., & Oti, J. (2025). Swelling Behaviour of Sulfate Soil Treated with Lime–Metakaolin at Different Curing Ages. Ceramics, 8(4), 133. https://doi.org/10.3390/ceramics8040133

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