Resilient Modulus Research Articles

Dynamic Resilient Modulus and Microstructure Degradation of Compacted Loess under Wetting–Drying–Freezing–Thawing Cycles

Investigations on the fluidized solidified soil prepared by sand-washing sludge: Engineering properties, solidification mechanism, and environmental impact.

Subgrade soils form the foundation of pavement structures, and their mechanical properties play a crucial role in ensuring pavement durability and performance. Weak soils often result in deformation, low load-carrying capacity, and premature failure of pavements. Traditional stabilization methods, such as lime, cement, and fly ash, have limitations related to cost, carbon footprint, and sustainability. With the increasing accumulation of polymeric waste, researchers are exploring the use of recycled plastic materials (PET, PE, PP) as a sustainable soil stabilizer. This review critically examines 20 previous research studies on geotechnical enhancement of subgrade soils using polymeric waste. The analysis highlights improvements in strength, CBR, compaction, permeability, and resilient modulus, while identifying key limitations in current research. The study emphasizes the research gaps and proposes directions for future investigations to optimize polymer use for sustainable and durable subgrade soil improvement.

Waste tyre rubber (TR) from end-of-life tyres poses a major environmental challenge. Therefore, recycling this waste into useful applications contributes to sustainable waste management strategies and supports a circular economy. Rubber possesses properties that can enhance the flexibility and ductility of pavements, making it a feasible material for use in road infrastructure. This study investigates the mechanical and fatigue performance of recycled concrete aggregates (RCA) mixed with waste TR. RCA was partially replaced at three different levels: 5%, 10% and 15% by weight. To mitigate the loss in mechanical strength associated with rubber inclusion, the TR + RCA mixes were stabilised through geopolymerisation using slag as a precursor. The unconfined compressive strength (UCS) increased with higher binder content. For instance, the mix containing 15% TR and stabilised with 5% slag geopolymer achieved a UCS of only 0.7 MPa, whereas increasing the binder content to 15% raised the UCS to 2.2 MPa. Similarly, resilient modulus improved with increasing slag content. Results from the four-point bending fatigue test showed that replacing RCA with rubber particles enhanced the fatigue performance of the mixes. The initial fatigue modulus of 100% RCA mix stabilised with 15% binder was 13,690 MPa, which reduced to 9740 MPa when 10% TR was introduced. In contrast, the number of cycles to reach half the initial modulus increased by four times when the TR content was raised from 0% to 15%. Microstructural observations of the slag-stabilised TR + RCA mixes showed improved microstructure due to geopolymerisation. Only insignificant traces of arsenic (<0.0008 mg/L) and barium (<0.000208 mg/L) were present in the TR + RCA mixes, while all other concerning heavy metals, including mercury and lead, were not detected in the leaching test. This indicates that there is no potential risk of soil or groundwater contamination, confirming the environmental safety of using slag geopolymer-stabilised TR + RCA mixes in subbase applications.

Road infrastructure is a key indicator of a country's development. Traditionally, hot dense asphalt mixtures (HMA) have been used due to their ability to withstand traffic loads and adverse weather conditions. However, a growing emphasis on sustainability in road construction drives the search for technologies that reduce environmental impact without compromising durability and safety. One solution is the incorporation of recycled rubber crumb (RRC) into asphalt mixtures, reusing tire waste and enhancing performance. This study evaluates the impact of RRC on HMA through an experimental process developed in four phases. In Phase 1, the materials used (aggregates, asphalt binder, and RRC) were collected and characterized according to INVIAS 2022 specifications. Tests were conducted on the aggregates to assess hardness, durability, cleanliness, and gradation; the asphalt binder was evaluated in terms of viscosity, penetration, and softening point. The RRC was characterized based on particle size distribution, and moisture, and fiber content. In Phase 2, conventional and RRC-modified asphalt mixture briquettes were designed and fabricated with RRC proportions of 1%, 2%, and 3% (dry process), compacted according to current regulations. Phase 3 involved the characterization of the briquettes testing rutting (INV E 756-13), moisture susceptibility (INV E 725-13), the resilient modulus (INV E 749-13), and fatigue resistance. Finally, in Phase 4, a technical and statistical analysis of the results was conducted, comparing the mechanical and functional performance of the mixtures in terms of durability, structural resistance, and behavior under environmental and load-related factors. The results indicate that the addition of 1% RRC significantly improves fatigue resistance, structural stability, and safety under wet conditions, surpassing the performance of conventional mixtures. The environmental and economic impact assessment demonstrates that the use of RRC not only extends pavement service life but also reduces tire waste and CO₂ emissions associated with virgin asphalt production, contributing to the circular economy and sustainable development. It is important to recognize some limitations in this study. The tests were carried out under controlled conditions which do not fully replicate the real conditions of the variables already mentioned. The granular material used was obtained from a quarry in the region of Tunja, Boyacá, which limits the applicability compared to material obtained from other regions with different climatic, geotechnical, or traffic characteristics. Other modification techniques besides RRC, which could offer variations in the mechanical and environmental performance of the mixtures, were not evaluated. This research did not directly quantify the environmental impact of the use of RRC through each stage of the life cycle of an asphalt pavement: it does not include an experimental or quantitative environmental evaluation. Finally, the sustainability component was developed through a referential review of updated scientific literature. This study provides scientific and applied evidence for the implementation of more sustainable technologies in road construction, establishing RRC as an effective and environmentally responsible modifier. Its alignment with international standards and its potential to optimize waste management position it as a viable strategy for modernizing flexible pavements on a global scale.

Abstract To overcome the limitations of conventional single‐factor analysis, this study proposed a framework for investigating interaction effects of influencing factors on the resilient modulus (Mr) of stabilized aggregate base. First, cross‐validation was utilized to compare the predictive accuracy and generalization capability of gradient boosting (GB) and random forest (RF) in predicting the Mr. The grid search algorithm was used to optimize hyperparameters. After optimization, the coefficient of determination for GB reached 0.99 on the training set and 0.96 on the test set, while those for RF were 0.98 and 0.94, respectively. The results indicated that GB demonstrated higher predictive accuracy for the Mr. Finally, the importance analysis, univariate sensitivity analysis, and bivariate interaction sensitivity analysis of influencing factors were systematically conducted using partial dependence plots (PDP) and Shapley additive explanations (SHAP). The research results showed that the importance of influencing factors on the Mr decreases in the order of maximum dry density to optimum moisture content ratio, wet–dry cycles (WDC), deviator stress, confining pressure, and ratio of oxide compounds in the cementitious materials. The bivariate interaction sensitivity analysis of the WDC, deviator stress, confining pressure, and ratio of oxide compounds in the cementitious materials did not disrupt their single‐variable sensitivity relationships with the Mr. The variation of the WDC would destroy the single variable sensitivity relationship between the optimum moisture content ratio and Mr.

In this paper, we use recycled glass powder (RGP) as a replacement of the soil to enhance the mechanical characteristics of the Mashhad clayey soil. For this purpose, a total of 60 unconfined compression tests and microstructural analyses including scanning electron microscopy (SEM) and x-ray diffraction (XRD) have been carried out on both of the unstabilized/stabilized RGP clayey soil specimens. The RGP contents used for replacing in the soil were 3% to 25% and the curing time were of 7 and 28 days, respectively. The results indicated that replacing RGP in clayey soil led to an increase in soil stiffness, unconfined compressive strength (UCS), maximum strain energy or energy absorption capacity (Eu), secant modulus (E50), resilient modulus (MR) and a decrease in the failure strain (εf) of the clayey soil mixture. The effect of increasing in the soil strength was more pronounced with RGP = 15% (optimum content) and more amount of curing times. The results obtained from the microstructural analysis were in full agreement with the findings obtained from UCS tests. The XRD tests indicated that the replacing of RGP = 15% with amorphous structure to the clays soil caused reduced the concentration of crystalline phases in the unstabilized soil specimens, leading to reduce in the intensity of the peaks. SEM results further emphasized that the microstructure of the clayey soil stabilized with RGP = 15% became more consolidated, with a noticeable reduction in the number and size of pores.

Biopolymers have recently been introduced as eco-friendly alternatives to other chemical cementitious additives for sandy soil stabilization, especially in pavement construction. The resilient modulus (MR) is a key metric considered in the mechanistic design of pavement layers that ensures a safe and economic design based on guaranteed accurate values. This study investigated the effects of dehydration on the MR of biopolymer-treated sand. Prepared specimens were subjected to two different curing conditions. The first set underwent closed-system curing (CSC) for periods of 7, 14, and 28 days. The second set of specimens was cured at different levels of suction by controlling relative humidity (RH) using different salt solutions (0.27, 1.0, 9.7, 21.0, 54.6, 113.7, and 294 MPa), referred to as dehydration curing (DC). The soil water retention curve (SWRC) was measured over the entire suction range to evaluate the dehydration curing and to link the results of suction levels and dehydration regime. MR tests were conducted on both sets of specimens using a dynamic triaxial system to simulate different confining, traffic, and dynamic stresses. The results showed a significant increase in MR (i.e., up to eight times) for specimens cured under DC conditions that was proportional to the suction level across different zones of the SWRC. Scanning electron microscopy revealed a phase change from hydrogel to film, which enhanced cementation and bonding between particles. in addition, CSC treatment resulted in a 10–30% reduction in MR. A new regression model is proposed to predict the MR of biopolymer-treated sand as a function of confining stresses, dynamic stresses, and suction. These findings will assist pavement engineers and designers in achieving safe, sustainable, and economic designs.

To address the challenge of long-term stiffness retention of subgrades in humid–hot climates, this study evaluates expansive soil stabilized with construction and demolition waste (CDW), focusing on the resilient modulus (Mr) under coupled stress states and wetting–drying histories. Basic physical and swelling tests identified an optimal CDW incorporation of about 40%, which was then used to prepare specimens subjected to controlled. Wetting–drying cycles (0, 1, 3, 6, 10) and multistage cyclic triaxial loading across confining and deviatoric stress combinations. Mr increased monotonically with both stresses, with stronger confinement hardening at higher deviatoric levels; with cycling, Mr exhibited a rapid then gradual degradation, and for most stress combinations, the ten-cycle loss was 20%–30%, slightly mitigated by higher confinement. Grey relational analysis ranked influence as follows: the number of wetting–drying cycles > deviatoric stress > confining pressure. A Lytton model, based on a modified prediction method, accurately predicted Mr across conditions (R2 ≈ 0.95–0.98). These results integrate stress dependence with environmental degradation, offering guidance on material selection (approximately 40% incorporation), construction (adequate compaction), and maintenance (priority control of early moisture fluctuations), and provide theoretical support for durable expansive soil subgrades in humid–hot regions.

The effect of polyurethane treatment depth on the behavior of geogrid-polyurethane composite-stabilized ballast (CSB) was evaluated based on large-scale cyclic tests. The geogrid was placed at the ballast–subballast interface, and polyurethane treatment depth of 76 and 152 mm from the sleeper soffit was considered for tests. The test results show that the vertical settlement of CSB decreased from 20.2 to 16.1 mm as the polyurethane treatment depth increased from 76 to 152 mm. Further, the stabilization efficiency factor ( S ef , cyc ), track stiffness ( k ), and resilient modulus ( M r ) of the CSB increased from 0.36 to 0.56, 55.9 to 66.1 MN/m, and 269.7 to 275.7 MPa, respectively, with the increase in treatment depth from 76 to 152 mm. The results from the current study were critically compared with those available in literature for treatment depths of 228 mm and fully treated polyurethane-stabilized ballast. It was seen that the improvement in S ef , cyc and k per unit of polyurethane was highest for treatment depth of 76 mm. Further, the track life enhancement factor ( L ef ), the ratio of the number of load cycles to reach 2% vertical strain by stabilized and unstabilized ballast, was determined to be 15.7. Although the lowest, the obtained L ef would imply an ~16 times increment in load cycles to cause 2% vertical strain. Thus, CSB with geogrid at the ballast–subballast interface and polyurethane treatment depth of 76 mm below the sleeper soffit was found to be an economically viable and practically feasible approach to stabilize the ballasted track.

Sustainable pavement construction has become increasingly important in India due to rapid infrastructure growth and the depletion of natural aggregates. This study investigates the performance of Dense Bituminous Macadam (DBM-II) mixes incorporating Reclaimed Asphalt Pavement (RAP) at 10%, 20%, and 30% replacement levels, with different fillers (stone dust, fly ash, and Ground Granulated Blast Furnace Slag) and bitumen VG-30 as binders. Laboratory investigations were carried out to evaluate the mechanical and durability characteristics of the mixes through Marshall Stability, Retained Marshall Stability (RMS), Indirect Tensile Strength (ITS), Tensile Strength Ratio (TSR) and Cantabro Abrasion Loss (CAL) and Resilient Modulus (MR). Results indicated that virgin binder demand reduced with RAP incorporation, although Marshall Stability decreased slightly due to the stiff aged binder in RAP. GGBS mixes consistently demonstrated superior stability, tensile strength, moisture resistance, and abrasion resistance compared to stone dust and fly ash mixes. All mixes satisfied MoRTH requirements for stability (>900 kg), RMS (>80%), TSR (>80%) and abrasion loss confirming their suitability for field applications. Overall, the findings establish that DBM-II mixes with up to 30% RAP, particularly when combined with GGBS filler, can deliver durable and environmentally sustainable pavement solutions.

ABSTRACT This study investigated the mechanical, microstructural, and environmental performance of recycled asphalt pavement materials stabilised with ordinary Portland cement (OPC) and cement kiln dust (CKD) as sustainable alternatives for full-depth reclamation (FDR) applications. Unconfined compressive strength (UCS), indirect tensile strength (ITS), flexural strength (FS), resilient modulus (MR), and wet–dry durability were evaluated for various reclaimed asphalt pavement (RAP) blends. Results showed that CKD at 15% maximised strength, the UCS increased up to 9.7 times compared to unstabilised blends and matched 3% OPC in up to 80% RAP blends, with similar ITS, FS, and MR trends before declining at higher dosages. However, CKD mixtures exhibited greater strength loss under wet–dry cycles than OPC mixes. Microstructural analysis revealed cementitious product formation, microstructural densification, elevated chloride/alkali content, and chloro-aluminate hydrates that explain CKD's performance limits. Lifecycle assessment showed CKD can cut CO₂ emissions by up to 89% and reduced costs by 36% versus OPC, supporting its use as a sustainable stabiliser in low- to medium-traffic FDR designs when properly dosed.

ABSTRACT In the Brazilian road sector, the use of materials derived from recycling asphalt pavements has become increasingly prominent. Milling typically involves removing a portion of the deteriorated surface layer, with the resulting waste known as reclaimed asphalt pavement (RAP). Reusing this material in paving has become a highly viable technique worldwide. This study presents laboratory results of cold-recycled asphalt mixtures containing high levels of RAP (50%, 60%, 70%, 80%, 90% and 100% residue), compared to a conventional mixture used as a control. The mixtures tested in the laboratory were designed and moulded according to the Marshall method. Resilient modulus and fatigue tests were conducted to evaluate the performance of each mixture, using the modelling proposed in the Brazilian mechanistic-empirical method (MeDiNa). The results indicated a reduction in asphalt binder consumption by incorporating RAP. The recycled mixtures exhibited higher values of resilient modulus and indirect tensile strength, more than 100% and approximately 26%, respectively compared to the control mixture. Furthermore, a clear reduction in cracked area (CA) was observed over the 10-year design period, with decreases reaching up to approximately 94% as the RAP content increased.

ABSTRACT Micaceous sand exhibits problematic geotechnical behaviour characterised by high compressibility, low shear strength, and progressive particle degradation under repeated loading. This study evaluated the efficacy of xanthan gum, a natural biopolymer, in stabilising micaceous sand subjected to varying degrees of particle crushing. Laboratory experiments, including one-dimensional consolidation, direct shear, and cyclic California Bearing Ratio tests, were conducted on micaceous sand treated with 0–1.5% xanthan gum by dry weight and cured for 1, 3, and 7 days, under varying degrees of particle crushing. The results demonstrated that xanthan gum enhanced the shear strength of micaceous sand, with cohesion increasing by 30–113% and the internal friction angle improving by 2–9.5%. Compressibility was consistently reduced, as reflected by the lower void ratios and compression indices. Under cyclic loading, the treated specimens showed marked improvements, with axial stress and CBR increasing by 95–386%, resilient deformation by 29–78%, and resilient modulus by 17–171%, indicating enhanced load-bearing and deformation resistance. Scanning electron microscopy confirmed the formation of a dense, gel-like matrix with improved particle bonding and reduced pores, correlating well with the observed macro-scale mechanical improvement. A 1% xanthan gum dosage with 7-day curing emerged as the optimal sustainable dosage for enhancing micaceous sand performance under static and cyclic loading.

This research provides useful insights into sustainable and cost-effective pavement rehabilitation by evaluating the combined effects of both Reclaimed Asphalt Pavement (RAP) and Crumb Rubber (CR) modification on flexible pavement performance using actual motorway sections. Pavement rehabilitation and maintenance can enhance the design and serviceable life of the pavement. Additionally, modification of asphalt with Crumb Rubber (CR) and Reclaimed Asphalt Pavement (RAP) not only proves to be economical but can also increase the resistance of flexible pavement concerning rutting, fatigue, and moisture damage. Four different pavement sections were selected, which were rehabilitated and modified with Reclaimed Asphalt Pavement (RAP), Crumb Rubber (CR), and a combination of both, along the Islamabad-Lahore motorway (M-2), Pakistan. The first pavement section consists of Asphalt Concrete Wearing Course (ACWC) with 60/70 grade bitumen as a binder (RAP 0%, CR 0%), the second pavement section was a mixture of asphalt concrete with crumb rubber modified bitumen as a binder (RAP0%, CR7%), the third pavement section was a blend of 15% RAP with 60/70 grade bitumen as a binder (RAP15%, CR 0%), the fourth section was a mixture of 15% RAP and 7% crumb rubber modified bitumen (RAP 15%, CR 7%). Pavement cores were extracted from the selected four pavement sections, which were experimentally explored in the laboratory to find the impact on the performance of highway pavement employing Reclaimed Asphalt Pavement (RAP) and Crumb Rubber (CR), partially replacing bituminous binder in the asphalt. The results show notable improvements in rutting resistance, tensile strength, and resilience. It was concluded that the performance of the section employing either RAP, CR or combined RAP and CR modified bitumen better enhanced the performance of pavement in terms of rut depth, indirect tensile strength and modulus of resilience. For instance, rutting depth was reduced by 41.35% and indirect tensile strength of pavement was increased by 17.93% by employing 15% RAP and 7% CR in modified bitumen binder for asphaltic mix. Likewise, the modulus of resilience was increased by 38.23% for the section employing 15% RAP and 7% CR in pavement.

The Life Cycle Assessment (LCA) of asphalt pavements is an essential tool for reducing environmental impacts. The definition of the functional unit (FU) within LCA can significantly influence the results, affecting the assessment of greenhouse gas (GHG) emissions and, consequently, the selection of asphalt mixtures. In this context, this study aims to analyze the impact of different functional units on the selection of asphalt mixtures for road pavements, considering the phases of raw material extraction, material production, mixing, and construction. To this end, the mechanical behavior of two distinct asphalt mixtures was evaluated under two different loading conditions, and their contributions to climate change were assessed using three functional units: t CO₂ eq/km of roadway, kg CO₂ eq/t of HMA, and kg CO₂ eq/m³ of HMA. The results indicated that asphalt mixtures with a higher resilient modulus require thinner pavement layers, leading to lower GHG emissions. However, when asphalt mixtures are analyzed individually and compared, no clear pattern in GHG emissions is observed, reflecting the specific characteristics of each production process. Additionally, it was found that the environmental impact varied according to the adopted functional unit, demonstrating that this choice can significantly influence decision-making regarding the selection of asphalt mixtures in terms of their contributions to climate change. It was concluded that the selection of the FU in pavement LCA should be aligned with the study's objective and the context of the analysis, as an inadequate choice may compromise the selection of asphalt mixtures.

This study investigates the strength and microstructural evolution of SRX-stabilized aeolian sand-gravel mixtures for flexible base applications in desert roads. CBR, UPS (uniaxial penetration strength), and compressive resilient modulus tests were conducted under varying SRX dosages (0.4-1.0%) and aeolian sand contents (30-50%). The results show that increasing the SRX dosage significantly improves all three indices, with the 0.5% SRX and 30% aeolian sand mixture yielding the CBR (385.89%) and UPS (0.938 MPa) and achieving a compressive resilient modulus that meets the requirements for graded aggregate base layers. XRD FTIR and SEM-EDS analyses reveal that the SRX enhances material structure primarily through physical mechanisms, forming dense films and bonding networks without inducing significant chemical reactions. Extended curing improves structural integrity, while excessive aeolian sand reduces compactness. SRX-stabilized aeolian sand gravel is a viable base and subbase material for desert highways.

The high carbon footprint of ordinary Portland cement (OPC) has driven interest in sustainable pavement construction alternatives. This study explored the effectiveness of enhancing OPC with a nanotechnology-based additive, RoadCem (RC), in full-depth reclamation (FDR) applications. Extensive laboratory analysis evaluated compressive, tensile, and flexural strengths, resilient modulus, durability of FDR mixtures, and the microstructure of raw materials. Results showed a 39% increase in unconfined compressive strength (UCS) with the OPC/RC combination. ANOVA tests indicated statistically significant individual and interactive effects of FDR components on UCS (p-values < 0.0001). Increasing RC content at 3%OPC notably improved tensile and flexural strengths and modulus by up to 44%, 47%, and 39%, respectively. Microstructure analysis revealed the potential of RC to modify OPC hydration chemistry by promoting longer needle-like crystals, enhancing interfacial bonding and matrix density. A cost analysis revealed 37% savings when using OPC/RC combination, highlighting the sustainability and cost-effectiveness of RC modifier.

The generation of waste is inherent to production systems, necessitating proper management to mitigate environmental and economic impacts. In the mining sector, bauxite residue (BR), a byproduct from alumina production, presents significant environmental challenges due to its contaminant potential but also offers opportunities for reuse. This study evaluates the incorporation of BR in asphalt mixtures as a partial replacement for fine aggregates, assessing mechanical performance, environmental aspects, and economic impact. The methodology involved three stages: (i) physical, chemical, and environmental characterization of BR and aggregates; (ii) production of asphalt mixtures with 5%, 10%, and 15% BR, and mechanical characterization before and after long-term thermal aging (LTOA), including indirect tensile strength (ITS), moisture-induced damage, resilient modulus (RM), dynamic modulus (DM), fatigue life, and permanent deformation resistance; and (iii) economic and environmental evaluation, including leaching tests to assess the mobility of soluble metals and cost analysis for storage and disposal by the mining company. Results indicated that BR incorporation increased fine content, improving stiffness and performance in ITS, RM, DM, and permanent deformation resistance, both before and after LTOA. However, soluble metals in BR led to higher moisture susceptibility, requiring mitigation strategies. From an environmental perspective, BR reduced soluble metal mobility, indicating potential for residue encapsulation. Economically, partial BR substitution reduced storage and disposal costs for the mining company. These findings suggest that using bauxite residue in asphalt mixtures can be a sustainable, economically viable solution for the mining industry.

This study investigates the partial replacement of Ordinary Portland Cement (OPC) with nano co-additives to stabilize organic peat soil for subgrade stabilization. Nano Silica (NS) and a Zycobond-Terrasil (Zy-Te) solution were combined with 43-grade OPC (10% NS + 90% OPC and 15% Zy-Te + 85% OPC) to evaluate sustainability and strength. Notable improvement observed in UCS, CBR, Triaxial, Permeability, Resilient modulus, and microstructural test results. Stabilized peat showed up to a tenfold increase in cohesion, ∼2 × reduction in permeability, 18.2%-36.4% improvement in resilient modulus, and ∼10% reduction in permanent strain compared to untreated soil. SEM and EDX analysis indicated the formation of calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH) products binding the peat matrix. A hypothetical IITPAVE analysis demonstrated that stabilized peat could significantly reduce pavement thickness and cost for increased traffic loading (20 MSA to 50 MSA).