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Article

Waste Foundry Sand as an Alternative Material in Road Construction

by
Vivian Silveira dos Santos Bardini
1,
Luis Miguel Klinsky
2,
Antonio Albuquerque
3,*,
Luís Andrade Pais
3 and
Fabiana Alves Fiore
4,*
1
School of Technology, State University of Campinas, Pascoal Marmo St, 1888, Limeira 13484-332, Brazil
2
CCR Group, Professora Maria do Carmo Guimarães Pellegrini Avenue, 200, Jundiaí 13209-500, Brazil
3
GeoBioTec, Department of Civil Enginenering and Architecture, Universidade da Beira Interior, 6201-001 Covilhã, Portugal
4
Institute of Science and Technology, São Paulo State University, Presidente Dutra Road, km 138.5, São José dos Campos 12247-004, Brazil
*
Authors to whom correspondence should be addressed.
Sustainability 2025, 17(6), 2370; https://doi.org/10.3390/su17062370
Submission received: 27 December 2024 / Revised: 1 March 2025 / Accepted: 4 March 2025 / Published: 7 March 2025
(This article belongs to the Special Issue Sustainable Materials: Recycled Materials Toward Smart Future)
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Abstract

:
The generation of solid waste and the use of non-renewable natural resources in the foundry industry are environmental challenges that require the search for solutions that guarantee the application of circular economy and cleaner production principles. Studies on the reuse of Foundry Sand Waste (FSW) generated in this process can guarantee the minimization of the current environmental impact and contribute to the achievement of sustainability in the industrial sector. The objective of this study is to assess the feasibility of utilizing WFS in the construction of pavement bases and sub-bases, in combination with sandy soil and hydrated lime. The laboratory experimental program included the evaluation of compaction characteristics, California Bearing Ratio (CBR), compressive strength, and resilient modulus. The results indicate that the addition of 25% and 50% WFS yields predicted performance levels ranging from good to excellent. The inclusion of hydrated lime enables the mixtures to be employed in sub-bases and bases, while the increased WFS content further enhances load-bearing capacity by up to 60% and 75% for 25% and 50% WFS, respectively.

1. Introduction

The foundry industry has long used clean natural sand mixed with binders in the metal casting process. However, the use of this material is limited due to wear and the loss of sand properties during casting. As a result, the foundry industry disposes of its waste, including waste foundry sand (WFS), in licensed landfills or controlled areas, despite the sand retaining properties that make it suitable for specific civil engineering applications. In many regions, however, the existing landfills have reached capacity, and the costs of establishing new disposal sites are very high, compounded by increasingly strict environmental regulations. It is, therefore, ecologically and economically opportune to use such waste in building materials [1].
According to the Modern Casting Magazine [2], in 2019, more than 100 million tons of metal parts were produced by the foundry process all around the world, where China and the United States are the largest producers. American Foundry Society [3] estimates a WFS production of 100 million tons annually, of which almost 10% are discarded annually and are available to be reusable. In Brazil, 2289 thousand ton/month of cast metal was produced in 2019 according to the Brazilian Foundry Association [4]. Using 0.9 as the proportionality index for the relationship between cast metal production and WFS—which, according to Dantas [5], varies between 0.8 and 1.0 by weight—the estimated WFS generation for the period would be around 3 million tons in 2019 alone.
WFS refers to the byproduct of the metal casting process, specifically the used sand from foundries that can no longer be recycled or reused in casting molds. During metal casting, foundry sand is used to create molds for shaping molten metal. Over time, the sand degrades due to thermal and mechanical wear, impurities, and chemical changes, making it unsuitable for further use in mold-making. Once it reaches this point, it is discarded and considered waste. Although not classified as hazardous, WFS contains low levels of environmental toxins according to the U.S. Environmental Protection Agency [6], and present in their composition are some metals derived from the casting process. For the Brazilian Association of Technical Standards [7], the WFS is classified as Non-dangerous and non-inert waste.
Depending on the additives used in the sand, it can present low concentrations of heavy metals such as arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), nickel (Ni) and zinc (Zn), phenols, polycyclic aromatic hydrocarbons, nitrogen, and sulfur compounds [8,9,10]. Therefore, WFS should be disposed of in licensed landfills [11]. Brazilian environmental legislation requires that such waste be deposited in controlled industrial landfills or incinerated [12]. In European countries, depending on the chemical characteristics of this WFS, it may be classified as non-hazardous and can be reused, or as hazardous waste requiring landfill disposal [13].
Much research has been developed in recent years to reuse WFS in civil engineering constructions and proved to be technically viable. The sand has appropriate characteristics for its use as aggregate in asphalt concrete [14,15]; concrete products [16,17]; flowable fills [18]; pavement bases and sub-bases courses [19,20]; subgrade soil [21]; and road construction [22]. A key modern challenge is finding sustainable alternatives for solid waste valorization, especially those resulting from industrial activities, and given the resource-intensive nature of highway construction, WFS could partially or entirely replace the fine aggregates commonly used in the layers of pavement structures. Therefore, the reuse of WFS in pavement construction can be a sustainable alternative for the recovery of this waste while reducing the extraction of natural material.
Many studies highlight the potential of WFS for use in road construction, evaluating mechanical properties such as compaction behavior, compressive strength, and bearing capacity. However, the resilient modulus (MR) is one of the key properties used to characterize the mechanical behavior of soil materials for pavement design purposes. This is because the current mechanistic–empirical design procedures for structural design rely on this parameter to describe the mechanical behavior of the soil materials. Conceptually, MR is defined as the ratio between the applied deviator stress (σd) and the recoverable (resilient) strain (εR) under dynamic loading.
There are numerous studies on the use of waste foundry sand as a material in pavement construction. However, part of these studies focuses on the use in road embankments and research about the geotechnical and geomechanical behavior [23,24,25]. Also, many studies evaluate mechanical properties through tests that are not required in pavement design methods [26,27]. Finally, the proportions of WFS used in most research are small, around 10 to 30%, which represents a small volume of reuse of this material [28,29,30].
Many studies have focused on the environmental properties of WFS and demonstrated that the material does not cause groundwater or surface water contaminations according to the U.S. Environmental Protection Agency (EPA) limits [31,32,33]. According to Freber [34], the concentrations of metals in groundwater underlying highway embankments are comparable with those encountered in embankments constructed with natural materials. Guney et al. [35] affirm that if there is contact between the WFS and water that has been discharged directly into the environment, the quality of the water will not be affected by any metals leached from the WFS or WFS-based mixtures.
Therefore, there is a lack of information regarding the mechanical properties of the road engineering of the stabilized waste foundry sand (WFS) mixtures to enable its applications in high volume for pavement layers. It is essential to encourage the formulation of materials to build sustainable road infrastructures, combined with the increasing intensity of traffic, climate variations, and other impacts generated due to human action [36].
The reuse of WFS in pavement construction can be a sustainable alternative for the recovery of this waste while reducing the extraction of new natural resource. This activity is in line with the principles of sustainable development goals (SDGs), especially with SDG 12, which deals with responsible consumption and production, and SDG 9 which advocates sustainable industrialization and the promotion of innovation [37]. Financial budget is a specific issue [38]. With the high prices of conventional materials, the availability of pavement design options needs to be more comprehensive, and this can be achieved with a selection of alternative materials such as ADF.
The objective of this work was to evaluate the viability of using WFS in the construction of pavement bases and sub-bases, in combination with clayed sand soil and hydrated lime. Cementing additives, such as hydrated lime and Portland cement, are most commonly used to stabilize granular and non-cohesive pavement layers. In general, chemical soil stabilization refers to the procedure in which any chemical material is added to natural soil to improve one or more of its properties of interest to engineering.
To better understand the behavior of soil stabilization with WFS, a series of experiments was conducted using clayey soil mixed with varying amounts of WFS, ranging from 0% to 50%. This research primarily examines the effects of WFS addition on the compaction properties, CBR value, unconfined compressive strength, and resilient modulus of clayey soil to assess the suitability of WFS for base and sub-base layers of low-traffic highways.

2. Materials and Methods

2.1. Waste Foundry Sand

The WFS used in this research comes from an industrial waste landfill that is operated by a company specialized in the Integrated Environmental Management of industrial waste and the treatment and final disposal of waste. The WFS was collected from a cell of the industrial landfill of the company unit in the city of São José dos Campos (Brazil), which was grounded under a layer of 3 m of soil for approximately 30 years.
The collected WFS is a non-plastic material and can be classified as A-1-b according to AASHTO M-145 [39]. According to these Standards, this includes those materials consisting predominantly of coarse sand either with or without fine fill material, and these materials present satisfactory behavior as subgrade when properly drained and compacted for the traffic to be carried.
Figure 1 shows the particle size distribution of WFS. Dyer et al. [40] worked with the same WFS, and the properties are shown in Table 1, as well as Dyer et al. [41], and the semi-analytical elemental composition of the WFS and the probable oxides were also obtained by elementary balance, as presented in Table 2.

2.2. Soil

The soil incorporated in this study are samples from the southeast region of Brazil located near the industrial waste landfill where the WFS was collected. The particle size distribution of the soil is presented in Figure 2, and Table 3 shows the index characteristics, and the soil was classified according to AASHTO as clayey soil (A-2-7) and USCS systems as clayed sand (SC).

2.3. Additive

Hydrated lime-type CH-I was used in this research to stabilize the soil–sand mixes. This product has more than 50% soluble lime (CaO+CaOH2) as recommended by DNIT [24], and has calcite origin, with a high concentration of calcium hydroxide. The chemical composition of the hydrated lime used for the study is shown in Table 4, while Table 5 gives the physical properties of the material.

2.4. Methodology

The WFS was collected from an industrial landfill: A random location was selected and the first 4.5 m were removed and discarded. The WFS at this depth was removed and sieved (passing through a 12.7 mm sieve), forming a 1 m3 pile. Then, samples were obtained according to the procedures of NBR 10007 (ABNT, 2004). A sampler and a scale were used to remove 2 kg at a time until 50 kg of WFS-1 was obtained.
Soil and waste foundry sand were mixed in the laboratory to obtain mixes containing 0%, 25%, and 50% of WFS. Particle Size Analysis [42] and Atterberg Limit Tests [43] were performed to obtain the required parameters to classify the soil–sand mixtures, even though these classification systems were not idealized for soil mixtures [44]. The Atterberg Limits, namely the liquid limit and plastic limit, provide valuable information about their behavior under various moisture conditions. These limits allow evaluation of the plasticity of soils; this property consists of the greater or lesser ability to be molded without volume variation under certain conditions of moisture.
The optimum moisture content (OMC) and maximum dry density (MDD) of the soil–sand mixtures were obtained through the compaction test [45]. The Intermediate Effort was used in this research according to the recommendations of the ASTM D1557 (2012) [45] for the compaction of sub-bases and base courses of pavements with low-volume traffic.
The specimens were compacted at their their optimal points at intermediate Proctor energy and subjected to the California Bearing Ratio (CBR) test [46]. The unconfined undrained compression test [47] provided the unconfined and undrained compression strength (qu) of the mixtures of soil–WFS and soil–WFS–hydrated lime. The test was performed on the specimens after 48 h of wetting by capillarity and 24 h in contact with water on each side of the specimen and then applying static load. and This test it is used to evaluate the stabilizing effects of hydrated lime.
Pavement materials reacts at every traffic load, processing displacement and recovery. Part of the displacement is permanent, not recoverable, and part is resilient, recoverable when the traffic solicitation ceases. Laboratory evaluation uses the triaxil cclic test to determine the resilient modulus under dynamic loads. That is, elastic modulus, measured in cyclical conditions, represents the ability of the soil to resist deformation under repeated loads. The resilient modulus is internationally accepted for characterizing materials in pavement design and performance evaluation. It indicates a basic material property crucial for the mechanistic analysis of multiple layers.
The cyclic triaxial test was performed on the soil–WFS and soil–WFS–hydrated lime mixtures according to AASHTO [48]. The specimens, in dimensions of 100 mm in diameter and 200 mm in height, were statically molded into five layers, compacted with intermediate energy, and in the optimum moisture content obtained by the compaction test. Combinations of principal stress states are applied, with the deviator stress (q = σ1 − σ3) being cycled while the confining pressure (σ3) is kept constant using the recommended levels for base layers and sub-bases of pavement [47]. Loading cycles with a frequency of 1 Hz are applied with a load pulse of 0.1 s followed by a rest period of 0.9 s.
To remove the effects of initial permanent deformation, the specimens were conditioned at a deviator stress of 27.6 kPa and confining pressure of 41.4 kPa for 500 load repetitions. Next, 100 load repetitions were applied to the specimens for a loading sequence that ranged from 13.8 to 41.4 kPa for the confining stress and from 13.8 to 68.8 kPa for the deviator stress.
The results from the cyclic triaxial test provide the data necessary to estimate the resilient modulus (MR) using constitutive mathematical models. In this study, three mathematical models were used to represent the resilient modulus values as a function of stress, which are presented in Table 6. The model (I), as a function of the confining stress (σ3), was proposed by Dunlap [49]. It is best suited for materials that are strongly dependent on confinement stress, such as granular. Moosazadeh and Witczak [50] proposed model (II), which considers only the stress deviation (q) in the representation of the resilience module. For the authors, this model presents a regular performance in fine-grained soils with high clay content.
Model (III), known in Brazil as a composed model, is recommended by NCHRP 1-28 [51]. Several authors [52,53] consider that this model, which includes both the deviation stress (q) and the confining stress (σ3), presents a good adjustment in the representation of the resilient modulus, regardless of the particle size distribution of the evaluated material.

3. Analysis of Results

3.1. Characterization

Figure 3 shows the particle size distribution of the samples containing 100% soil and 3% hydrated lime (HL), 75% soil + 25% WFS + 3% HL, and 50% soil + 50% WFS + 3%HL. As expected, high percentages of WFS reduce the content of particles smaller than 0.075 mm.
Table 7 shows the values of the index properties for all the samples. As WFS increases, the LL and PI are reduced, and non-plastic mixes are obtained when 50% is added to the mix, characterizing a non-plastic composition when the maximum content residue is reached in the study.
The hydrated lime was added to the samples just before use. The short time prior to the run of the tests may not have been sufficient for the additive to react with the soil particles significantly, resulting in more noticeable changes in the Atterberg Limits. The National Lime Association (NLA) [54] affirms that the modification effects of HL take place within typically 1 to 48 h after the lime is introduced.
Regarding the effect of the addition of 3% hydrated lime, it was observed that the values presented are very similar to those obtained without the addition of hydrated lime. There was only a small decrease in the values of LL and PI and an increase in the value of PL to the soil without WFS addition.
Although the results agree with those reported by several authors, the LL and PI reductions were not as expressive. For Thompson [55] and Yunus [56], the change in the consistency of soils stabilized with hydrated lime occurs a few hours after mixing but may extend for days. As the hydrated lime had been added to the samples just prior to use, this time was probably not sufficient to elicit the reactions needed to obtain more significant reductions in the Plasticity Indices of the mixtures.
The compaction test results are presented in a summarized way in Table 8. Figure 4 shows the curves of the Proctor compaction for the soil + WFS and soil + WFS + HL samples. All samples show a typical compaction behavior: increasing WFS content increases MDD as expected, and reduces moisture. Abichou et al. [57] compacted WFS at Proctor Standard and Modified Effort, and the MDD values varied from 17 to 19 kN/m3, with OMC values between 5 and 15%.
According to the Road Research Center (Centro de Pesquisas Rodoviarias—CPR) [58], the compaction curves of the HL mixtures presented a flatter shape compared to natural soils, as occurred in the research. This format indicates the facility of reaching the maximum dry density, in a wider range of humidity. Furthermore, this change in the slope and peak of the compaction curve can represent significant savings in time, effort, and energy. Other studies, reported by the American Society of Foundry [59], also show that the addition of WFS to clayey soils raises the value of MDD.
With the addition of WFS, for samples with HL and for those without the additive, the curves move up and to the left; that is, the samples have characteristics of sandy soils while increasing the percentage of WFS in their composition. This trend was also observed by the authors Sharma et al. [60] and Behak [61].
In the previous items it was shown that as the WFS content increases in the soils, the mixtures show a behavior like that of sandy soils. Several authors [62,63] argue that sandy soils have a lower specific surface area than clay soils and therefore require lower water content to achieve maximum densification. According to Klinsky et al. [53], clayey soils have a higher specific surface area than sandy soils, demanding higher water contents to reach the MDD, which can explain the reduction in the optimal moisture of the samples with the increase in WFS.
The addition of hydrated lime causes changes in the particle size distribution of the materials, thus changing the compaction characteristics of the soils, as several authors have noticed a decrease in the MDD compared to soils without HL for the same compaction energy [58]. Thus, when hydrated lime is added, the effect is a reduction in the MDD, as found by several authors [64,65,66], such as the reduction in the OMC (except sample 5), a characteristic that did not follow the same pattern by CPR [58] and Klinsky et al. [53].

3.2. Mechanical Behavior

The results of the CBR test and expansion are shown in Figure 5a,b, respectively. The samples composed only of soil and WFS, without hydrated lime, show the same CBR values as 0 and 25% of WFS, but with 50% WFS, a significant CBR increase is observed.
In the samples containing hydrated lime, higher CBR values were observed in comparison with the samples without the additive, as well as the gain of a significant support index with the increase in WFS.
The increase in WFS significantly reduces the expansion of the specimens, but samples without hydrated lime remain with expansion above 1%. These values meet the Pavement Manual of the Brazilian Standards [31] to be used as a base material for pavements with low traffic levels (Equivalent Single Axle Load—ESALs ≤ 5 × 106 applications of standard axle load of 80 kN). On the other hand, the samples containing 3% of hydrated lime show expansion values lower than 1% and it is observed that the expansion tends to zero with high levels of WFS.
According to the American Association of State Highway and Transportation Officials (AASHTO) [66], the subgrade material must have a CBR value ofat least 10%, so, all the samples containing WFS and 3% of hydrated lime can be employed. However, only the sample containing 50% of WFS and hydrated lime could be used as base pavement material with low volume traffic, since it has a CBR ≥ 60% and expansion ≤ 0.5%, according to the Pavement Manual of the Brazilian Standards [31].
According to CPR [58], the CBR value increases when HL is added, and the expansion reduces. The same behavior was observed in this study, but in some cases hydrated lime increases CBR by over 100%, making them unsuitable for the design of pavement structures in the methodologies that use the CBR as a parameter. Therefore, it is recommended to replace the CBR test with the cyclic triaxial test to obtain the resilient modulus (RM) to better characterize these materials.
The unconfined compression test permitted to obtain the unconfined compression strength (qu), of the mixtures soil–WFS and soil–WFS–HL, presented in Figure 6. It can be noted that higher WFS contents increase the UCS (unconfined compression strength) values and the addition of 3% hydrated lime provided mixtures with higher UCS values.
The minimum values established for this parameter vary according to the agencies responsible for the design and construction of roads. For example, Transportation Research Board (TRB) [66] establishes a minimum UCS value of 1030 kPa for base layers of pavements after 28 days of curing, and for sub-bases recommends UCS values above 690 kPa. For the National Lime Association [54], the sub-bases must have resistance to simple compression greater than 700 kPa, and the bases must have UCS greater than 1400 kPa, after 28 days of cure.
Considering only the mixtures containing HL, according to TRB [66] and NLA [54], both mixtures containing 25 and 50% WFS could be used as a sub-base. However, the cure time for this research was only 48 h, and these limits are set for 28 days of cure, so the UCS values of mixtures containing WFS are likely to be higher.
To represent the resilient modulus of the mixtures, the results obtained from the cyclic triaxialtests were modeled using three mathematical equations, the model according to the deviation stress; the model according to the confining stress; and the composed model. The criterion used to evaluate these models was the determination coefficient R2 since this parameter is adequate to estimate the accuracy of the statistical adjustment achieved by the model with respect to the data obtained in the test. According to the AASHTO Pavement Design Guide [66], R2 values greater than 0.90 indicate adequate adjustments to represent the resilient modulus.
To obtain the models, at least 11 of the 15 stress pairs applied to the specimens were used during the cyclic triaxial test, as recommended by AASHTO T 307 [48]. Thus, for each model studied, R2 was determined in the prediction of the resilient modulus (MR), depending on the WFS content and the presence of hydrated lime in the mixture. Figure 7 presents the results for mixtures, for each model. Note that the worst performance was obtained for the model as a function of the deviator stress (σd). The composed model was the one with the highest R2 values, but these values were not close to the recommended by AASHTO [66], 0.90.
Given that the composed model was the one that presented the best fit in the representation of the resilient modulus of the mixtures, as was also noticed by other authors [35,36], it was used to perform the analyses presented in the next items.
Table 9 shows the maximum and minimum MR values obtained in the test for the 15 sequences used in the cyclic triaxial compression test in the mixtures. In these tables the value of the resilience modulus calculated with the composite model is also presented, considering the tensions of σd = 41.34 kPa and σ3 = 13.78 kPa. According to Little [65] and Solanki et al. [52], these stresses are common at the top of the road subgrades.
To better understand the behavior of the influence of the WFS content and the hydrated lime content used in the mixtures, the maximum and minimum values of MR (Table 9) were used in the construction of the ranges of RM values presented in Figure 8. It can be observed that samples without the addition of lime have a resilience modulus value ranging from 150 MPa to 300 MPa. The addition of 3% hydrated lime increased the RM values ranging from 200 MPa to about 400 MPa.
The MR value calculated for the mixtures is shown in Figure 9. For the non-lime mixtures, the highest RM value was reached with 0% of WFS, but for the mixtures with 3% hydrated lime, the highest resilient modulus value was obtained with 25% of WFS; the highest RM values were reached with mixtures containing hydrated lime. Tanyu [67] reports that in the United States, residues from the foundry industry without stabilization have RM that fall in the range of 600 to 700 MPa.

4. Conclusions

The study evaluated the addition of 0, 25, and 50% WFS into clay soils chemically stabilized with lime (3%) and showed that the consistency limit and granulometric analysis tests allowed the mixtures to be classified according to the USCS and AASHTO methods, but these classifications did not provide sufficient parameters to assess the feasibility of using the waste in paving. It was also found that the addition of hydrated lime and WFS reduced the optimum moisture and maximum dr density of the clayed soil samples evaluated.
The mixtures containing 50% soil + 50% WFS + 3% HL had a CBR ≥ 60% and expansion ≤ 0.5% and can be used as a base and sub-base material for flexible pavements with low traffic levels (N ≤ 5 × 106 standard axle load applications of 80 kN), which meets the Brazilian requirements. The mixes with 25% and 50% WFS showed an MR between 150 and 250 MPa, higher than the values previously reported by other authors.
The study did not evaluate the environmental and economic viability of reusing WFS. However, it can be said that the reuse of WFS helps to prevent pollution and minimize the costs associated with landfills and the use of natural resource. For future research, further studies could focus on large-scale application, long-term durability, and the effects of weathering or moisture on the WFS mix, as widening the scope of the research would help to explore the wider applicability of this material in different contexts.

Author Contributions

Conceptualization, V.S.d.S.B. and F.A.F.; methodology, V.S.d.S.B.; validation, L.M.K., L.A.P. and F.A.F.; formal analysis, V.S.d.S.B.; investigation, V.S.d.S.B. and L.M.K.; data curation, L.M.K.; writing—original draft preparation, V.S.d.S.B.; writing—review and editing, A.A., L.A.P. and F.A.F.; supervision, F.A.F.; funding acquisition, V.S.d.S.B. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the GeoBioTec Research Unit, through the strategic projects UIDB/04035/2020 (https://doi.org/10.54499/UIDB/04035/2020) and UIDP/04035/2020 (https://doi.org/10.54499/UIDP/04035/2020) funded by the Fundação para a Ciência e a Tecnologia (FCT), IP/MCTES through national funds (PIDDAC). Also, was supported by the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) (Process Number 2015/24936-0).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in the study are included in the article; further inquiries can be directed to the corresponding author.

Acknowledgments

The authors would like to acknowledge the Road Research Center (Centro de Pesquisas Rodoviarias—CPR) for the availability of carrying out the tests.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

WFSwaste foundry sand
AASHTOAmerican Association of State Highway and Transportation Officials
USCSUnified Soil Classification System
SC clayed sand
OMCoptimum moisture content
MDD maximum dry density
CBRCalifornia Bearing Ratio
RMresilient modulus
HL hydrated lime
LL liquid limit
PIplasticity index
NLA National Lime Association
UCS unconfined compression strength
TRB Transportation Research Board

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Figure 1. Particle size distribution of the WFS.
Figure 1. Particle size distribution of the WFS.
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Figure 2. Particle size distribution of the soil.
Figure 2. Particle size distribution of the soil.
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Figure 3. Particle size distribution of the materials.
Figure 3. Particle size distribution of the materials.
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Figure 4. Compaction curves of the mixes containing WFS and HL.
Figure 4. Compaction curves of the mixes containing WFS and HL.
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Figure 5. Behavior of (a) CBR and (b) expansion of all the samples as a function of the WFS content.
Figure 5. Behavior of (a) CBR and (b) expansion of all the samples as a function of the WFS content.
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Figure 6. Behavior of the UCS in the mixes containing WFS and HL.
Figure 6. Behavior of the UCS in the mixes containing WFS and HL.
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Figure 7. R2 of the mixtures for the models studied according to the WFS content and the presence of hydrated lime.
Figure 7. R2 of the mixtures for the models studied according to the WFS content and the presence of hydrated lime.
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Figure 8. Range of RM values.
Figure 8. Range of RM values.
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Figure 9. RM values calculated by the composed model and σd = 41.34 kPa and σ3 = 13.78 kPa.
Figure 9. RM values calculated by the composed model and σd = 41.34 kPa and σ3 = 13.78 kPa.
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Table 1. Particle size distribution of the WFS [40].
Table 1. Particle size distribution of the WFS [40].
Characteristics
Bulk Density (kg/m3)1398
Specific Gravity (g/cm3)2.2
Absorption (%)1.6
Equivalent Sand (%)38
pH7.5
Lightweight particles (%)2.9
Organic impurity (ppm)<300
Petrographic analysisinoculant
SphericityHigh
RoundingRounded
SurfacePolished
Classificationinert
Table 2. Elemental composition and probable substances present in WFS obtained by EDS in % by weight [41].
Table 2. Elemental composition and probable substances present in WFS obtained by EDS in % by weight [41].
Element Composition%
O36.5
C15.0
Fe19.8
Si24.3
Al4.1
N0.0
Mg0.3
Na0.0
K0.0
Probable Oxides Content%
SiO251.77
Fe(OH)231.75
Al22.1
Al2O30.0
Na2SiO30.0
Na2O0.0
NO30.0
MgO0.0
Organic impurity10.0
Trace elements4.38
Table 3. Index properties of the soil.
Table 3. Index properties of the soil.
Liquid LimitPlastic LimitPlastic Index
(%)(%)(%)
421725
Table 4. Chemical composition of hydrated lime.
Table 4. Chemical composition of hydrated lime.
Constituents(%)
Calcium Hidroxide [Ca(OH)2]85
Magnesium Oxide (MgO)5
Carbon Dioxide (CO2)5
Silicon Oxide (SiO2)1
Table 5. Physical properties of hydrated lime.
Table 5. Physical properties of hydrated lime.
PropertyResult
Specific Gravity0.5 g/cm3
Accumulated retained #30 (0.60 mm)≤0.5%
Accumulated retained #200 (0.075 mm≤10.00%
Table 6. Mathematical models utilized to represent the resilient modulus.
Table 6. Mathematical models utilized to represent the resilient modulus.
ModelNameEquation
1Model as a function of deviation stress M R = k 1 σ d k 2
2Model as a function of confining stress M R = k 1 σ 3 k 2
3Composed model M R = k 1 σ 3 k 2 σ d k 3
Table 7. Index properties of the materials.
Table 7. Index properties of the materials.
WFSHLLLPLPI
(%)(%)(%)(%)(%)
00421725
2531238
5021NPNP
03421923
2530237
5020NPNP
Table 8. Results of the MDD and OMC in the mixes of soil–WSF and soil–WFS + HL.
Table 8. Results of the MDD and OMC in the mixes of soil–WSF and soil–WFS + HL.
WFS
(%)		HL
(%)		MDD
(kg/m3)		OMC
(%)
00179516.0
25192113.5
50196911.0
03176615.1
25189313.5
50195210.8
Table 9. Maximum and minimum RM values and RM values calculated by the composed model.
Table 9. Maximum and minimum RM values and RM values calculated by the composed model.
Waste Foundry Sand
(%)		Hydrated Lime
(%)		Cyclic Triaxial Test at OMC
Min RM
(MPa)		Max RM
(MPa)		RM
(MPa)
00180287216
25166249149
50146205138
03187327178
25309404316
50299389306
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Bardini, V.S.d.S.; Klinsky, L.M.; Albuquerque, A.; Andrade Pais, L.; Fiore, F.A. Waste Foundry Sand as an Alternative Material in Road Construction. Sustainability 2025, 17, 2370. https://doi.org/10.3390/su17062370

AMA Style

Bardini VSdS, Klinsky LM, Albuquerque A, Andrade Pais L, Fiore FA. Waste Foundry Sand as an Alternative Material in Road Construction. Sustainability. 2025; 17(6):2370. https://doi.org/10.3390/su17062370

Chicago/Turabian Style

Bardini, Vivian Silveira dos Santos, Luis Miguel Klinsky, Antonio Albuquerque, Luís Andrade Pais, and Fabiana Alves Fiore. 2025. "Waste Foundry Sand as an Alternative Material in Road Construction" Sustainability 17, no. 6: 2370. https://doi.org/10.3390/su17062370

APA Style

Bardini, V. S. d. S., Klinsky, L. M., Albuquerque, A., Andrade Pais, L., & Fiore, F. A. (2025). Waste Foundry Sand as an Alternative Material in Road Construction. Sustainability, 17(6), 2370. https://doi.org/10.3390/su17062370

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