Experimental investigation of eggshell powder and quarry dust for stabilizing subgrade soil

Abstract

This study investigates the potential of using eggshell powder and quarry dust as alternative stabilizing agents for improving the engineering properties of lean clay soil. The objective is to develop a sustainable and cost-effective solution for subgrade enhancement in road construction, particularly in regions with limited access to traditional materials like lime or cement. contributes to chemical stabilization by providing calcium for cementitious reactions and improving soil structure, while quarry dust improves mechanical interlock and particle gradation. A comprehensive experimental program was conducted to evaluate changes in Atterberg limits, compaction characteristics, California Bearing Ratio, unconfined compressive strength, swell potential, and durability under wet-dry and freeze-thaw conditions. The results showed a marked improvement in strength, compaction efficiency, and moisture resistance, with a significant reduction in plasticity and swell behavior. The optimal mix of 6% eggshell powder and 30% quarry dust achieved the highest UCS and CBR values while demonstrating excellent durability. These findings highlight the feasibility of utilizing agricultural and construction waste materials in soil stabilization, offering both engineering benefits and environmental advantages for sustainable infrastructure development.

Introduction

With growing urbanization and road network growth, there is an increasing need for safe, durable, and affordable infrastructure, especially in areas that have poor or problematic subgrade soils. These soils, which are widely distributed around the world, are usually clay-rich, have low shear strength, and are sensitive to changes in moisture content. They are prone to excessive swelling, shrinkage, and settling if they are not treated, which frequently leads to structural deformation, pavement cracking, and early road deterioration. In addition to interfering with transportation, these problems raise ongoing maintenance expenses and safety issues^1–3. In order to overcome those challenges, soil stabilization becomes an essential part of civil engineering project planning and design, particularly when it comes to road and embankment building.

Conventional stabilizing techniques use industrial chemicals like cement, lime, and other additions to improve the engineering behavior of soils by causing chemical or physical changes. Although these techniques are tried-and-true and efficient, there are economic and environmental costs associated with their use. High temperatures, a lot of energy, and a lot of greenhouse gas emissions are all part of the manufacture of cement and lime^4,5. Moreover, access to these materials may be limiting or economically not feasible in many rural or low-income areas⁶. In view of these issues, the search for locally accessible and ecologically suitable substitute soil stabilizers is becoming more and more important to the civil engineering community^7,8. A viable approach to long-term soil stabilization is provided by waste products from building and agricultural operations. Usually unused, these materials are disposed of in ways that may risk the environment. Due to their beneficial characteristics and accessibility, eggshell powder and quarry dust stand out among the many waste materials investigated for geotechnical applications^9,10. Calcium carbonate (CaCO3) makes up the majority of eggshells, which are frequently thrown away in significant amounts by households, restaurant chains, and food processing industries. They function similarly to lime when ground into a fine powder, and in clay-rich soils, they can initiate pozzolanic processes that increase the soils’ strength, stiffness, and deformation resistance¹¹. Another easily accessible material with potential for stabilizing soil is quarry dust, a fine residue created during the crushing of stones in quarry operations. Packed with silica and other mineral particles, quarry dust can fill in the spaces between soil grains and improve gradation, creating denser, more compacted soil structures; its angular particle shape also helps to improve inter-particle friction and mechanical stability. Although it is produced in massive amounts, quarry dust is frequently considered a waste product and dumped in landfills, which contributes to air pollution and land degradation through dust dispersion^12–14. Reusing eggshell powder and quarry dust in geotechnical applications has two advantages: it addresses the issue of weak soil and provides a practical waste management solution^15,16. The idea of turning construction and agricultural waste into materials with additional value aligns in effectively with the circular economy and sustainable development tenets. It decreases trash accumulation, lessens reliance on traditional stabilizers, and promotes ecologically friendly building methods¹⁷. According to this sustainability-driven purpose, prior studies have increasingly concentrated on assessing waste-derived stabilizers from both an environmental and quantifiable engineering aspect. Empirical research demonstrating that these waste products may substantially enhance soil strength, stiffness, bearing capacity, and resilience supports the switch from traditional materials to substitutes like eggshell powder and quarry dust. The material of research shows that environmentally friendly stabilizers are both technically feasible and comprehensible, offering scientific evidence that links sustainability concepts with useful geotechnical performance. Consequently, the literature that follows explores the behavior of such waste materials in actual soil systems and supports the logical connection between the engineering advancements revealed in the research and sustainable building practices.

Yang et al. utilized eggshell waste to enhance the properties of subgrade material. Two types of Iowa soils were combined with up to 12% ESP in laboratory tests, and the results showed that calcination greatly improved the performance of ESP. When compared to the soil without ESP, the unconfined compressive strength increased by more than 10 times at the ideal addition rate of 6% to 8% ESP, and the soil’s California bearing ratio also improved¹⁸. Hamza, Muhammad, et al. investigated the possibility of reducing the geotechnical problems by utilizing eggshell food waste and molding it into eggshell powder (ESP) through calcination. In the current investigation, the plasticity index and liquid limit of the fat clay with 10% ESP concentration decreased by 62% and 17%, respectively. Meanwhile, the addition of ESP to the fat clay resulted in a notable rise in the CBR, elastic modulus (E50), and UCS¹⁹. Acharya, S., et al., Utilized egg shell powder to enhance the properties of high plastic soil. This study examined Atterberg’s limits, compaction properties, and unconfined compressive strength at different alkaline activator ratios (0.25, 0.45, and 0.65), curing times, and ESP levels (5–30% by weight of natural soil). Following treatment, the soil’s strength and stiffness also improved noticeably; when treated with 30% ESP at 56 days of the curing period, the unconfined compressive strength increased by about 18 times, or from 103 to 1833 kPa²⁰. U Arun Kumar and Kiran B. Biradar used quarry dust as industrial waste to improve the soft subgrade. After testing the LL and PI of untreated soil are decreased by 26.86% and 28.48%, respectively, by adding quarry dust. When the percentage of quarry dust increases, the soil’s ideal moisture content decreases by 36.71%. By adding 40% quarry dust, the maximum dry density of the soil is raised by 5.88%. Additionally, it has been found that adding 40% quarry dust results in a high CBR value²¹. Agapitus Ahamefule Amadi, in the current study, CBR, swell. Strength loss upon saturation was used to evaluate the durability of soil mixtures made with black cotton soil at 0%, 4%, 8%, 12%, and 16% CKD content and at a constant dosage of 10% quarry fines compacted at optimal moisture contents with compaction effort. Soil mixtures with 8–16% CKD met the CBR and swell requirements as well as the strength on immersion criterion; however, mixtures with 0 and 4% CKD failed the CBR test because of their low CBR value, comparatively large swell measurements, and insufficient strength on saturation^22,23.

Prior research has examined the impacts of quarry dust and eggshell powder separately on different types of soil, but there aren’t several studies that combine the two. It’s needed to investigate the possible benefits of combining a siliceous filler like quarry dust with a calcium-rich, chemically active substance like eggshell powder. Together, these substances may provide a balance of physical and chemical stabilization, enhancing treated soils’ performance over the short and long terms^24,25. This study focuses on lean clay soil, which is known for its low bearing capacity, high plasticity, and poor drainage characteristics^26–28. The soil was selected due to its widespread occurrence and relevance in many infrastructure projects requiring subgrade enhancement. The main objective of the research is to evaluate the combined effect of eggshell powder and quarry dust on the geotechnical properties of this soil type. Specific emphasis is placed on understanding changes in Atterberg limits, compaction parameters, California Bearing Ratio (CBR), unconfined compressive strength (UCS), and swell potential after stabilization^29,30.

Experimental materials

Eggshell powder, quarry dust, and natural lean clay soil were the materials utilized for this investigation. These materials were chosen since they are readily available, have the capacity to stabilize soil effectively, and are consistent with sustainable engineering methods. To ensure consistency and reliability throughout the testing program, all materials were gathered locally from Islamabad, Pakistan, and prepared in accordance with standard laboratory procedures.

Lean clay soil

The soil used in this study was acquired from an area outside of Islamabad, close to Bhara Kahu. The region is recognized for its fine-grained soil deposits, which frequently present problems for subgrade applications. Upon visual investigation, the soil was determined to be lean clay, smooth, and dark brown in color. It is an appropriate selection for stabilization because preliminary index testing verified its high plasticity and low bearing capacity. Before mixing with additives, the soil sample was sieved into a uniform size using a 4.75 mm sieve, air-dried to remove any remaining moisture, and then ground into a powder. Its classification as lean clay has been verified by the Unified Soil Classification System with a high liquid limit. The particle size distribution curve is shown in Fig. 1.

Fig. 1.

Particle size distribution curve.

The physical properties of soil is presented in Table 1.

Table 1.

Physical properties of soil.

45	LL (%)	Liquid limit
22	PL (%)	Plastic limit
23	PI (%)	Plasticity index
1.62	ɣd (g/cc)	Maximum dry density
18.5	OMC (%)	Optimum moisture content
2.7	Gs	Specific gravity
CL	USCS	Classification of soil
A-7-6	AASHTO	Classification of soil

Eggshell powder

Eggshells were sourced from various local food establishments and restaurants in Sector G-9, Islamabad. These establishments produce significant quantities of eggshell waste daily. The collected shells were cleaned thoroughly with water to remove organic residues and then sun-dried for several days. After drying, the shells were ground using a mechanical grinder and sieved through a 425-micron sieve to obtain a fine and uniform powder. The powder was stored in sealed plastic containers to prevent moisture absorption. Chemically, eggshells are rich in calcium carbonate (CaCO₃), which serves as a source of calcium and fine filler when mixed with clayey soils, enhancing strength and reducing plasticity through gradual cementation. Calcium hydroxide is created when quicklime (CaO) and water undergo an exothermic reaction. Calcium silicate hydrate and calcium aluminate hydrate are created when the Ca²⁺ ions from Ca(OH)₂ react with reactive silica and alumina in soil. The chemical composition of eggshell is presented in Table 2.

Table 2.

Chemical composition of Eggshell powder.

CaCO₃	MgCO3	Na₂O	K₂O	Other oxides
93.2%	1.1%	0.3%	0.2%	0.4%

Quarry dust

Quarry dust was obtained from Margalla Hills stone-crushing plants, located in the Taxila region, approximately 25 km northwest of Islamabad. The chemical composition of quarry dust obtained from Margalla hills is shown in Table 3. The material was collected in dry conditions and transported to the laboratory in sealed bags. It was then oven-dried at a moderate temperature to remove any residual moisture and passed through a 4.75 mm sieve to maintain consistency across test samples. Quarry dust is known for its fine, angular particles and siliceous composition, which help improve soil gradation and compaction properties. It also enhances mechanical interlocking, leading to better strength characteristics when mixed with cohesive soils.

Table 3.

Chemical composition of quarry dust from Margalla Hills.

LOI	CaO	SiO₂	`Al2O3	MgO	Fe₂O₃	K₂O	P₂O₅
36.1%	48.3%	7.9%	2.1%	2.0%	1.5%	0.8%	0.10%

Water

Clean tap water was used throughout the study for mixing and sample preparation. All water was sourced from the laboratory facility located at the Department of Civil and Environmental Engineering, ensuring consistency and purity across all tests. Water plays a key role in activating pozzolanic reactions and achieving optimal compaction in stabilized soil samples.

Methodology

The experimental program was developed to investigate the impact of eggshell powder and quarry dust on the strength and durability of lean clay soil. This methodology includes procedures for sample preparation, mix proportioning, laboratory testing, and curing. A comprehensive suite of geotechnical tests was performed, including consistency limits, compaction characteristics, bearing capacity, strength, swell potential, durability, and shear strength. All laboratory tests were conducted on three parallel specimens (n = 3) for each mix proportion and curing condition. The reported values correspond to the average of the replicate measurements, and the associated variability is presented in the form of error bars in the figures.

Sample preparation

Lean clay soil was obtained from Bhara Kahu, a semi-rural area near Islamabad, Pakistan. The soil was air-dried, crushed manually to eliminate lumps, and sieved through a 4.75 mm sieve. Eggshells, collected from commercial kitchens in Sector G-9, Islamabad, were cleaned, dried, ground into powder, and passed through a 425-micron sieve. Quarry dust was acquired from stone crushing units near the Margalla Hills, Taxila, and similarly sieved to ensure consistency.

Mix proportions

Four different soil mixtures were prepared and are demonstrated in Table 4.

Table 4.

Mix proportion of soil, eggshell powder and quarry dust.

Samples	Soil	Eggshell powder	Quarry dust
Sample 1	100%	0%	0%
Sample 2	88%	2%	10%
Sample 3	76%	4%	20%
Sample 4	64%	6%	30%

The percentages represent the proportion of each additive by dry weight of soil. These mixes were selected to study the influence of increasing stabilizer content.

Mixing and curing

Dry materials were first blended thoroughly to ensure uniform distribution, followed by gradual addition of water to reach optimum moisture content. Samples were mixed manually on a non-absorbent tray until uniformity in texture and color was achieved. For tests requiring curing, samples were stored in sealed plastic bags at room temperature and cured for 7, 14, and 28 days.

Laboratory testing

The following tests were conducted in accordance with ASTM and AASHTO standards:

Atterberg limits test

Liquid and plastic limits were measured to determine the plasticity index of both untreated and treated samples, indicating changes in soil consistency due to stabilization. The LL and PL tests were carried out in accordance with ASTM D4318 requirements.

Standard proctor compaction test

This test determined the optimum moisture content and maximum dry density of each mix, which are essential for evaluating field compaction behaviour, in accordance with ASTM D698-12 standards³¹.

California bearing ratio test

In accordance with the ASTM D1883 standard, the California Bearing Ratio (CBR) test was conducted. Both unsoaked and soaked CBR tests were conducted to evaluate the load-bearing capacity of the stabilized soil. This test simulates the strength behavior of subgrade under pavement loading³².

Unconfined compressive strength test

Cylindrical samples were prepared and tested after 7, 14, and 28 days of curing. The UCS test provided data on the short-term compressive strength gain due to the additives and test of the soil was conducted following the guidelines outlined in ASTM D2166 ³³.

Swell potential test

The swell potential test was conducted as per the guidelines of ASTM D4546-14. To assess the expansive behavior of the soil, treated and untreated samples were submerged in water, and volumetric changes were recorded. A reduction in swell potential indicated effective stabilization³⁴.

Wet-dry durability test

Durability was assessed through five cycles of alternate wetting and drying. Samples were soaked in water for 24 h, air-dried for 24 h, and weighed after each cycle to measure loss of mass. The purpose was to simulate environmental fluctuations and evaluate the resistance of the stabilized soil to weathering³⁵.

Freezing-thawing test

Cylindrical specimens were subjected to five cycles of freezing at -5 °C for 24 h, followed by thawing at room temperature for 24 h. After each cycle, visual changes, weight loss, and strength reduction were noted. This test simulated cold climate conditions and assessed the long-term durability of stabilized mixes under seasonal changes³⁶.

Results and discussion

Atterberg limits

The results indicate an exceptional and progressive drop in the lean clay soil’s plasticity index (PI) as the eggshell powder and quarry dust content increases as shown in Fig. 2. The untreated soil had a liquid limit of 45% and a plastic limit of 22%, resulting in a plasticity index of 23%, indicating a moderately plastic soil with significant potential for volume change and low workability. When 10% quarry dust and 2% eggshell powder were added, the LL dropped to 41% and the PL marginally increased to 24%, resulting in a lower PI of 17%. With increasing dosages, this pattern stays the same: the PI decreased even more to 11% at 4% eggshell and 20% quarry dust, and it was considerably lowered to 7% at the maximum dosage. The observed drop in liquid limit as stabilizer concentration increases indicates that the soil’s ability to retain water is being lowered, most likely as a result of clay particle flocculation and aggregation carried on by calcium ions from the eggshell powder. These processes decrease the soil’s capacity to undergo plastic deformation and lower its affinity for water^37,38. Additionally, a slight increase in the plastic limit suggests better soil structure and workability, most likely attributable to quarry dust’s texture and frictional resistance. The combined application of quarry dust and eggshell powder significantly improves the soil’s structure, lowers its plastic behaviour, and improves its suitability for subgrade applications, as indicated by the overall decrease in the plasticity index. Lower PI soils perform better in working conditions, particularly when it comes to pavement and road construction, because they are less likely to swell and shrink. These results support the possibility of the chosen waste materials to function as economical and ecologically beneficial stabilizers.

Fig. 2.

Effect of eggshell powder and quarry dust on Atterberg limits of lean clay soil.

Compaction characteristics

The results shown in Table 5; Fig. 3 demonstrate how the compaction behavior of lean clay soil is affected by increasing amounts of quarry dust and eggshell powder. With increasing dosages of stabilizing materials a different pattern is seen where the optimum moisture content falls and the maximum dry density rises. The MDD of the untreated soil is 1.62 g/cc, and its OMC is 18.5%. When 10% quarry dust and 2% eggshell powder are added, the OMC slightly decreases to 17.8% and the MDD rises to 1.66 g/cc. The OMC is 17.2% and the MDD is 1.71 g/cc when the additive concentration is increased further to 4% eggshell and 20% quarry dust. At 6% eggshell and 30% quarry dust, optimal compaction results are seen, with the OMC falling to 16.5% and the MDD peaking at 1.75 g/cc. This improvement in dry density can be attributed to several factors. Quarry dust’s granular and angular texture improves soil particle packing by minimizing pore gaps and filling voids, raising the soil’s overall density. In the meantime, eggshell powder may help flocculate clay particles and bind them more successfully during compaction because of its tiny particle size and calcium content. Both additions work together to create denser soil matrices that require less moisture to achieve maximal compaction. The treated soil needs less water to reach its maximum density, as illustrated by the decrease in OMC with increasing stabilizer content. This can be explained by the fact that the addition of non-plastic elements, such as quarry dust and calcium-rich eggshell powder, changed the surface area and decreased the permeability of the soil particles. Therefore, the soil becomes more compactible and less sensitive to water, which is beneficial in the field, particularly in places where water is limited.

Table 5.

Optimum moisture content and maximum dry density of treated and untreated soils.

Mix	OMC (%)	MDD (g/cc)
Untreated soil	18.5	1.62
2% Eggshell + 10% quarry dust	17.8	1.66
4% Eggshell + 20% quarry dust	17.2	1.71
6% Eggshell + 30% quarry dust	16.5	1.75

Fig. 3.

Maximum dry density with optimum moisture content for different soil mixes.

The trends shown in Table 5 are further supported by the curve in Fig. 3. In comparison to the untreated soil, all treated mixes exhibit a steeper compaction curve and a shift to the right in dry density. The effectiveness of eggshell powder and quarry dust in improving the compaction properties of lean clay soil is confirmed by the improvements, which are gradual and consistent with an increase in stabilizer dosage.

California bearing ratio

The results of the California Bearing Ratio test presented in Fig. 4 demonstrate a consistent and significant improvement in the load-bearing capacity of the lean clay soil as the content of eggshell powder and quarry dust increases. The CBR test, which simulates the strength of subgrade material under loading, is critical for evaluating the suitability of soil for use in pavement and road construction. The untreated soil exhibits a relatively low unsoaked CBR value of 5.2% and a soaked value of 3.1%. These figures are below the typical minimum values required for subgrade layers in flexible pavements. This confirms that the natural soil, in its unstabilized form, lacks sufficient strength for supporting structural loads, particularly under wet conditions. With the incorporation of 2% eggshell powder and 10% quarry dust, both CBR values show a noticeable increase, rising to 8.9% (unsoaked) and 6.5% (soaked). This trend continues as the stabilizer dosage increases. At 4% eggshell powder and 20% quarry dust, the CBR values improve to 11.3% and 8.1% for unsoaked and soaked conditions, respectively. The highest performance is observed in the mix with 6% eggshell and 30% quarry dust, where the unsoaked CBR reaches 13.5%, and the soaked CBR improves to 9.8%. The rate of improvement starts to decline as the soil gets closer to its maximum feasible densification and chemical reaction capacity, even if the CBR values increase noticeably within the tested range of 2–6% eggshell powder and 10–30% quarry dust. Since the majority of the voids have already been filled and the available reactive clay surfaces are almost completely used, any additional stabilizer after this point only makes minor and incremental improvements. In light of this, further eggshell powder or quarry dust additions typically act as unnecessary filler than as active strength-enhancing ingredients. As a result, the strength enhancement that follows the ideal dosage is marginal it is still there but so slight that it is hardly noticeable and is incapable of reporting as a distinct, measurable gain. This explains why expected gains beyond the optimal ratio are negligible and fall below the threshold of significant engineering advantage, despite the trend appearing near linear within the measured range.

Fig. 4.

Soaked and unsoaked CBR values for different samples.

The increase in CBR values with additive content is attributed to the synergistic effects of the stabilizers. Eggshell powder contributes calcium carbonate, which interacts chemically with the clay minerals in the soil, forming cementitious bonds that enhance cohesion and reduce plasticity. Meanwhile, the addition of quarry dust improves soil gradation, fills void spaces, and introduces angular particles that enhance interparticle friction and density. These effects collectively result in a denser, more rigid soil structure capable of withstanding higher loads^39,40. The improvement in soaked CBR is especially noteworthy. Soaked conditions simulate the worst-case field scenario where the subgrade is saturated due to water infiltration. The treated soils showed not only increased dry strength but also significant retention of strength when soaked, indicating improved water resistance and durability. This is a key advantage for road construction, particularly in areas subject to heavy rainfall or poor drainage.

Unconfined compressive strength (UCS)

The data presented in Table 6; Fig. 5 clearly demonstrate the positive influence of eggshell powder and quarry dust on the unconfined compressive strength of lean clay soil over different curing periods. As the curing time increases from 7 to 28 days, all treated mixes show significant strength gains, with greater improvements observed at higher percentages of stabilizing additives. The untreated soil exhibits minimal strength development over time, with UCS increasing only from 125 kPa at 7 days to 145 kPa at 28 days. This limited increase reflects the inherent weakness of the soil and the absence of any binding or pozzolanic agents to enhance strength. Furthermore, the minor increase in UCS for the untreated soil highlights the significance for extra stabilizing additives since natural healing is insufficient for significant structural improvement. The treated samples exhibit significantly improved performance when compared to this baseline. In contrast, the addition of 2% eggshell powder and 10% quarry dust leads to a UCS of 180 kPa at 7 days, which further improves to 240 kPa at 28 days an overall strength increases of 65.5% compared to the untreated sample. This indicates the early formation of cementitious bonds initiated by the calcium carbonate in the eggshell powder and the filler effect of quarry dust. It indicates that following the initial reaction peak, the improvement gradually turns toward a more marginal rate, which is usual once most reactive sites are occupied, despite the significant gain from 7 to 28 days. Despite its little size, this slight rise nevertheless promotes in the soil matrix’s internal reorganization and densification. The strength continues to improve with increased stabilizer content. At 4% eggshell and 20% quarry dust, the UCS reaches 290 kPa after 28 days, doubling the strength of untreated soil. The maximum strength is observed in the mix containing 6% eggshell powder and 30% quarry dust, where UCS increases from 245 kPa at 7 days to 340 kPa at 28 days reflecting a 134.5% improvement. However, the extra strength gain tends to fall off beyond this ideal range, suggesting that the soil is getting close to a point of diminishing returns. Even with long curing, this plateauing behavior is typical when the microstructure approaches near-maximum bonding efficiency, leaving fewer chances for improvement. The main component of eggshell powder is calcium carbonate. A reaction takes place when it is mixed with water, particularly when carbon dioxide or acidic conditions from the soil pore water are present. This reaction releases calcium ions and forms calcium hydroxide. Alumina and silica are abundant in quarry dust, and these are the important pozzolanic oxides. The silica and alumina molecules on the surface of the quarry dust and the native clay particles become activated and start to dissolve into the pore water in the high-pH environment produced by the released calcium hydroxide. This progressive strength gain can be attributed to the pozzolanic reaction between the free calcium ions in pore water that react with the dissolved silica and alumina ions. This reaction precipitates strong, stable, and insoluble gel-like crystals known as Calcium-Silicate-Hydrate. These compounds bind soil particles more effectively over time, contributing to higher UCS values. Additionally, the angular quarry dust particles improve mechanical interlock and packing density, further enhancing strength. The production of C-S-H compounds becomes more spatially limited as curing proceeds, resulting in relatively slight but detectable strength increases. In mature pozzolanic systems, when most bond formation has already taken place, this marginal development is typical. Longer times cause the microstructure to stabilize and the system to approach equilibrium, which accounts for the progressively declining gains in spite of continuous reactions.

Table 6.

Unconfined compressive strength (UCS) of soil samples at different curing periods.

Mix	UCS 7 days (kPa)	UCS 14 days (kPa)	UCS 28 days (kPa)	% Increase (28 days)
Untreated Soil	125	135	145	—
2% Eggshell + 10% Quarry Dust	180	210	240	65.5
4% Eggshell + 20% Quarry Dust	215	250	290	100
6% Eggshell + 30% Quarry Dust	245	290	340	134.5

Fig. 5.

Unconfined compressive strength (UCS) with curing time for treated and untreated soil mixes.

Swell potential

The findings in Fig. 6 show that adding more eggshell powder and quarry dust to lean clay soil significantly lowers the swell potential. With a swell percentage of 9.2%, the untreated soil demonstrated great expansiveness and a strong tendency to alter volumetrically in response to moisture. For subgrade materials, this tendency is problematic because it can lead to pavement and foundation heaving, cracking, and structural damage. The swell potential significantly improved to 6.8% with the addition of 10% quarry dust and 2% eggshell powder. As the dose increased, this pattern remained constant: the greatest dosage (6% eggshell + 30% quarry dust) reduced the swell to just 2.6%, which is more than 70% less than the untreated soil, while 4% eggshell + 20% quarry dust lowered it to 4.1%. There are several factors responsible for the decrease in swell behavior. Cementitious chemicals are created when the calcium carbonate in eggshell powder combines with clay particles to cause flocculation. The clay particles’ water affinity and surface activity are decreased by this process. A denser soil structure that is resistant to moisture-induced volume changes is achieved by filling in gaps and replacing expansive clay fractions with quarry dust, which is made up of inert and angular siliceous material. These findings show that adding quarry dust and eggshell powder together improves the soil’s strength and bearing capacity while also considerably reducing swelling behavior. Due to this, the stabilized soil is more dimensionally stable and more appropriate for uses like building foundations and road subgrades where volume stability is essential.

Fig. 6.

Swell potential of treated and untreated soil samples.

Wet-dry durability test

After five wet-dry cycles as shown in Fig. 7, the untreated soil showed the largest cumulative mass loss of 18.4%, indicating inadequate durability and notable decline under alternating moisture conditions. High-plasticity soils, which soften and lose cohesion when repeatedly wetted and dried, exhibit this tendency. The soil’s resistance to weathering was greatly increased by the addition of quarry dust and eggshell powder. With 2% eggshell and 10% quarry dust, the mass loss decreased to 12.6%; with 4% eggshell and 20% quarry dust, it further decreased to 7.9%. With only 4.2% mass loss, the best results were obtained with 6% eggshell and 30% quarry dust, suggesting an effective, durable soil structure. The formation of cementitious compounds as a result of the pozzolanic reaction between calcium from eggshell powder and the siliceous component of the soil and quarry dust is responsible for the decrease in mass loss. These substances improve resistance to deterioration brought on by moisture by strengthening interparticle interactions. Quarry dust also enhances packing and lowers permeability, which limits water infiltration and related degradation.

Fig. 7.

Cumulative mass loss after wet-dry cycles.

Freeze-thawing test

Cylindrical specimens were subjected to five cycles of freezing at -5 °C and thawing at room temperature. The test assessed visual integrity, mass loss, and reduction in UCS after the fifth cycle. The results are summarized in Table 7.

Table 7.

Performance of samples after five freezing-thawing cycles.

Mix	Mass loss (%)	UCS reduction (%)
Untreated soil	15.3	24.1
2% Eggshell + 10% quarry dust	10.2	17.6
4% Eggshell + 20% quarry dust	6.5	11.3
6% Eggshell + 30% quarry dust	3.1	6.8

Untreated lean clay soil demonstrated a 15.3% mass loss and a 24.1% decrease in unconfined compressive strength, making it extremely vulnerable to freeze-thaw cycles. The structure was significantly broken down and its strength reduced as a result of the ice repeatedly forming and melting inside the soil pores. The use of quarry dust and eggshell powder for stabilization significantly increased the resistance to freeze-thaw. The mass loss decreased to 10.2% and the UCS loss decreased to 17.6% at 2% eggshell and 10% quarry dust as shown in Fig. 8. The soil performed significantly better when the dosages were increased. After five cycles, the sample containing 6% eggshells and 30% quarry dust had only 3.1% mass loss and 6.8% UCS reduction, demonstrating negligible cracking or disintegration. These enhancements result from the stabilizers’ creation of a denser matrix, which minimizes pore gaps and restricts water infiltration. Additionally, the pozzolanic binding strengthens the soil against temperature stress and inhibits the formation of ice lenses. This demonstrates to the treated soil’s suitability for long-term environmental exposure and applications in cold climates^41,42.

Fig. 8.

Performance of samples after five freezing-thawing cycles.

Microstructure analysis

The soil stabilized using eggshell powder and quarry dust shows notable microstructural improvements, increasing soil strength and stability, according to scanning electron microscopy study. As seen in Fig. 9 (a), the SEM images usually demonstrate that untreated soil has a loose, flaky structure with large spaces, which results in low load-bearing capacity. When eggshell powder (rich in calcium carbonate) is added, it fills these voids and reacts with clay particles, forming cementitious compounds that bind soil grains together, as seen in the denser, more compacted microstructure as shown in Fig. 9 (b-c). Meanwhile, quarry dust, being angular and granular, interlocks with soil particles, reducing pore spaces and improving shear strength. The combined use of ESP and QD further enhances stabilization, ESP contributes to pozzolanic reactions, while QD provides mechanical reinforcement. SEM analysis confirms that the stabilized soil exhibits a more homogeneous and tightly packed matrix, reducing permeability and increasing durability. Furthermore, secondary pozzolanic reactions between the calcium ions released from eggshell powder and the silica/alumina content of the soil can be seen in the matrix through the formation of cementitious gels like calcium silicate hydrate and calcium aluminate hydrate. Stronger interparticle bonds and reduced microcracks result from these hydration products coating the soil particles and filling the micro-voids. This is further improved by the angular shape of quarry dust, which increases the frictional resistance between grains and improves particle interlocking. Water penetration is efficiently prevented and the soil is strengthened against shear deformation by the resulting microstructure, which has a solid, cemented fabric with little pore continuity. This makes the blend of eggshell powder and quarry dust an effective, eco-friendly solution for subgrade stabilization in road construction.

Fig. 9.

SEM analysis (a) untreated soil, (b,c) soil treated with eggshell powder and quarry dust.

XRD analysis and cementation mechanism

X-ray diffraction analysis was performed on stabilized soil samples containing 4% eggshell powder + 20% quarry dust and 6% eggshell powder + 30% quarry dust to verify the formation of cementing products responsible for strength enhancement. As shown in Fig. 10, prominent diffraction peaks corresponding to calcite are observed, confirming calcium carbonate formation resulting from the calcium-rich eggshell powder and subsequent carbonation reactions. Additionally, peaks associated with ettringite (3CaO·Al₂O₃·3CaSO₄·32 H₂O) are detected, indicating the formation of calcium–aluminate hydration products. These phases are known to contribute to interparticle bonding and strength development in stabilized soils. Quartz peaks are also present, reflecting the siliceous nature of quarry dust, which primarily contributes through mechanical interlocking and improved gradation. The combined presence of calcite and ettringite confirms that both chemical cementation and physical reinforcement mechanisms are responsible for the observed increase in unconfined compressive strength.

Fig. 10.

X-ray diffraction patterns of stabilized soil samples containing 4% eggshell + 20% quarry dust and 6% eggshell + 30% quarry dust, showing the presence of ettringite (A), calcite (B), and quartz (C), confirming the formation of cementing and filler phases responsible for strength enhancement.

Discussion

This study investigated the effectiveness of eggshell powder and quarry dust as stabilizing agents for lean clay soil, with a focus on improving strength, durability, and volumetric stability. Based on the experimental findings, using these materials together greatly improves the engineering performance of weak subgrade soil, making it more appropriate for foundation and pavement applications.

The plasticity index clearly decreased as the stabilizer content increased, according to the Atterberg limits results. The untreated soil exhibited high plasticity, which poses challenges in compaction and stability. However, the addition of quarry dust and eggshell powder caused the liquid limit to gradually decline and the plastic limit to moderately increase, which resulted in a significant drop in the plasticity index. This phenomenon is explained by the calcium carbonate in the eggshell powder, which causes the clay particles to flocculate, and the quarry dust, which enhances the gradation and structural stability.

The use of stabilizers resulted in an improvement in the compact properties. With higher percentages of eggshell powder and quarry dust, the optimum moisture content dropped, and the maximum dry density rose. The granular and angular shape of quarry dust, which increases the packing density of the soil, is directly responsible for this enhancement. By combining soil particles into a denser structure, eggshell powder’s pozzolanic reactivity additionally contributes to a part. According to these findings, the stabilized soil has greater in-place densities and uses less water for compaction, two properties that are advantageous for building.

The strength improvement achieved by stabilization was further validated by the California Bearing Ratio data. The addition of stabilizers led to a considerable rise in both unsoaked and soaked CBR values. The treated mixes showed more than double the strength under soaking conditions, with the 6% eggshell + 30% quarry dust mix obtaining the highest values, because the untreated soil had a rather low bearing capacity. Due to improved resistance to moisture penetration and degradation is a crucial component of pavement construction, the improvement in soaking CBR is especially significant.

The findings for Unconfined Compressive Strength after 7, 14, and 28 days of curing showed that all treated samples had a steady and significant increase in strength. The 6% eggshell and 30% quarry dust mixture produced the highest UCS and, after 28 days, demonstrated a strength enhancement of almost 130% above untreated soil. This behavior is explained by the formation of cementitious products, such as calcium silicate hydrates, which are the result of the reaction between the siliceous elements in the soil and quarry dust and the calcium in eggshell powder. The method’s potential for field applications and long-term stabilizing effect are confirmed by the steady strength growth with curing time^43–45.

The additives combined action greatly decreased swelling potential, which is an important issue in clay-rich soils. The untreated soil’s expansive nature was successfully managed, with the highest dosage mix showing the greatest reduction. Due to quarry dust replaced active clay minerals and minimized voids, the stabilization decreased the soil’s capacity to absorb water and swell. Their swelling behavior was further reduced by the chemical interaction between the eggshell powder and the clay particles^46,47.

In addition to conventional and waste-derived stabilizers, recent advances in biogeotechnical methods such as microbially induced calcium carbonate precipitation have gained attention for soil improvement. Studies employing MICP demonstrate that calcium carbonate precipitation enhances particle bonding and reduces pore spaces, producing substantial gains in strength and durability. For example, CT scanning analyses of microbial solidified sand have revealed that bio cementation leads to the formation of denser, interconnected microstructures with improved mechanical stability. Similarly, investigations on biostimulation treatments have shown that controlled microbial activity can significantly increase the unconfined compressive strength and stiffness of sandy soils, while simultaneously improving freeze-thaw resistance and long-term performance. These findings highlight the effectiveness of biologically driven cementation processes in achieving durable stabilization outcomes^48–50.

When compared to MICP-based stabilization, the use of eggshell powder and quarry dust in the present study provides a parallel pathway for generating calcium carbonate cementation, but through a chemical rather than biological route. The calcium-rich eggshell powder reacts with silica and alumina from quarry dust and soil minerals, producing cementitious compounds that bind soil particles, while quarry dust improves gradation and interlocking. Although MICP may offer superior microstructural refinement and sustainability by harnessing natural microbial processes, its field implementation often faces challenges such as cost, scalability, and environmental sensitivity. By contrast, eggshell powder and quarry dust are widely available, low-cost waste materials that achieve comparable improvements in UCS, CBR, and durability, as shown in this study. Thus, while MICP represents a promising frontier for sustainable geotechnics, the present approach offers a practical and accessible alternative for subgrade stabilization, particularly in resource-constrained regions^51–53.

Evaluations of durability using freeze-thaw and wet-dry cycles showed that stabilized soil was more resilient to changes in the environment. Low resilience to weathering and moisture fluctuation was indicated by the untreated soil’s substantial mass loss and obvious disintegration during both experiments. On the other hand, stabilized samples showed greater strength preservation, little weight loss, and very little cracking, especially at larger dosages. The stabilizers’ denser, more chemically linked structure, which prevents physical disintegration over time and restricts moisture infiltration, is what gives this increased durability^54–56.

In recent years, bio-mediated soil improvement techniques such as Microbially Induced Calcite Precipitation (MICP) have gained considerable attention as sustainable alternatives to conventional soil stabilization methods. MICP enhances soil strength through biologically driven precipitation of calcium carbonate, which binds soil particles and reduces pore spaces. Recent studies, including investigations on the undrained cyclic behavior of biocemented calcareous silty sands, have demonstrated significant improvements in strength, stiffness, and durability due to calcite cementation. The stabilization mechanism observed in the present study exhibits conceptual similarities to MICP, as both approaches rely on calcium carbonate–based cementation to enhance soil performance. However, unlike MICP, which depends on microbial activity, nutrient supply, and controlled environmental conditions, the ESP-QD composite stabilization method achieves cementation through a chemically driven pathway, utilizing calcium-rich eggshell powder and siliceous quarry dust. This approach offers practical advantages in terms of material availability, cost-effectiveness, and ease of implementation, particularly for large-scale subgrade applications in resource-constrained regions. The comparison underscores that environmentally friendly cementation can be achieved through both biological and waste-derived chemical routes, broadening the range of sustainable ground improvement strategies⁵⁷.

In field implementation, the density contrast between eggshell powder and quarry dust can promote segregation and layering if conventional loader-based mixing is used. To ensure uniformity, controlled moisture conditioning, staged premixing, calibrated mechanical spreading, and full-depth rotary mixing using a reclaimer/stabilizer are recommended. Mixing quality should be verified through grid-based sampling across the treated area and depth, supported by rapid indicators such as pH or CaCO₃ content and variability limits to ensure consistent spatial distribution of stabilizers prior to compaction.

Conclusion

With an emphasis on strength enhancement, decreased plasticity and swell potential, and long-term durability under environmental pressures, this study assessed the potential of eggshell powder and quarry dust as sustainable stabilizing agents for lean clay soil. The combined use of these materials greatly improves the engineering performance of weak subgrade soils, according to the experimental results.

The addition of eggshell powder reduced the plasticity of the soil through flocculation and pozzolanic reactions, while quarry dust improved the gradation and dry density through its angular, granular structure. The maximum dry density, unconfined compressive strength, and California Bearing Ratio all showed appreciable increases as a result of these impacts, especially when stabilizer concentration rose. With the greatest strength gains and the least amount of swell potential, an optimal mixture of 30% quarry dust and 6% eggshell powder was found.

The treated soil’s resistance to external conditions was further confirmed by durability evaluations using wet-dry and freeze-thaw testing, which revealed less mass loss and strength deterioration in comparison to untreated samples. These results demonstrate the practical value of eggshell powder and quarry dust as economical and environmentally beneficial substitutes for conventional stabilizers.

Author contributions

Conceptualization, Zaid Alajlan and Nabeel Liaqat ; methodology, Nabeel Liaqat, Zaid Alajlan, and Muhammad Waleed; software, Zaid Alajlan and Nabeel Liaqat; validation, Nabeel Liaqat and Zaid Alajlan; formal analysis, Nabeel Liaqat; investigation, Zaid Alajlan and Nabeel Liaqat; resources, Nabeel Liaqat; data curation, Nabeel Liaqat and Zaid Alajlan; writing original draft preparation, Zaid Alajlan, Nabeel Liaqat and Muhammad Waleed; writing review and editing, Zaid Alajlan and Muhammad Waleed; visualization, Nabeel Liaqat; supervision, Zaid Alajlan; project administration, Zaid Alajlan; funding acquisition, Zaid Alajlan. All authors have read and agreed to the published version of the manuscript.

Data availability

The data presented in this study are available on request from the corresponding author. The data are not publicly available due to institutional restrictions and the inclusion of experimental records that are part of ongoing research.

Declarations

Competing interests

The authors declare no competing interests.