Search Results (17)

The road construction sector urgently requires environmentally friendly, low-carbon, and high-performance base materials. Traditional materials exhibit issues of high energy consumption and carbon emissions, making it difficult for them to align with sustainable development requirements. While slag- and fly ash-based geopolymers demonstrate promising application potential in civil engineering, research on their application in road-stabilized soils remains insufficient. To address the high energy consumption and carbon emissions associated with conventional road base materials and to fill this research gap, this study investigated the utilization of industrial solid wastes through slag-based geopolymer and fly ash as stabilizers, systematically evaluating the pavement performance of two distinct soil types. Unconfined compressive strength tests and freeze–thaw cycling tests were conducted to elucidate the effects of stabilizer dosage, fly ash co-stabilization, and compaction degree on mechanical properties. The results demonstrated that the compressive strength of both stabilized soils increased significantly with higher slag-based geopolymer content, achieving peak values of 5.2 MPa (soil sample 1) and 4.5 MPa (soil sample 2), representing a 30% improvement over cement-stabilized soils with identical mix proportions. Fly ash co-stabilization exhibited more pronounced reinforcement effects on soil sample 2. At a 98% compaction degree, soil sample 1 maintained a stable 50% strength enhancement, whereas soil sample 2 displayed a dose-dependent exponential strength increase. Freeze–thaw resistance tests revealed the superior performance of soil sample 1, showing a loss of compressive strength (BDR) of 78% with 8% geopolymer stabilization alone, which improved to 90% after fly ash co-stabilization. For soil sample 2, the BDR increased from 64% to 80% through composite stabilization. This study confirms that slag/fly ash-based geopolymer-stabilized soils not only meet the strength requirements for heavy-traffic subbases and light-traffic base courses, but also demonstrates its great potential as a low-carbon and environmentally friendly material to replace traditional road base materials. Full article

High-modulus asphalt concrete (HMAC) has been widely used in the surface coating of high-grade pavement. Due to HMAC’s modulus being significantly higher than traditional asphalt concrete, the mechanical responses of a pavement structure using an HMAC coating must be notably different from those of a traditional asphalt pavement structure. Moreover, when asphalt surface coating is fixed, the selection of base-course combinations will determine the mechanical response of the whole pavement structure. However, previous studies usually analyzed the mechanical response of pavement structures at limited combinations of base-courses, resulting in difficulties comprehensively understanding the laws of mechanics and effectively optimizing the HMAC pavement structure. Hence, in this study, a total of 108 groups of numerical experiments under six working conditions of base-course combinations are carried out using orthogonal experimental design to investigate the mechanical response of pavement structures using HMAC coatings using the PR MODULE high-modulus additive. The effects of pavement thickness, material modulus, and structural combination on mechanical responses are analyzed for the 108 groups to determine the optimal pavement combinations based on the balance of mechanical response and economic efficiency. The results show the following: The effect of the base layer type on mechanical response is more significant than that of the subbase layer type. Surface and undersurface layer thickness for the granular material base layer; surface and base layer thickness for the asphalt mixture base layer; and base layer thickness, subbase layer modulus, and base layer modulus for the inorganic binder mixture base layer are the key factors for mechanical response. Finally, six recommended HMAC pavement structure configurations for various base-courses are proposed. Full article

The design of flexible road pavements is a complex process as a result of the multiple variables that influence and interact in the models that allow the design of each layer. In recent years, a particular interest has been raised to ensure that climate is considered in pavement design due to temperature and precipitation that influence the deterioration of pavements, impacting their service life. This paper presents a critical review of flexible pavement design methods, from the first ones based on experience, such as empirical methods, to the most recent ones on mechanical–empirical methodologies, where, based on different principles, they determine the thicknesses of the layers that integrate the structure of a pavement to identify how these methods have included climate variables within their methodology. Through this review, it was identified that temperature is incorporated in the dynamic modulus of the asphalt mix, and precipitation and moisture are incorporated through the resilient modulus in the granular layers (base, subbase, and foundation soil or subgrade courses). As a result, it was identified that the most holistic way of integrating climate is through the Enhanced Integrated Climatic Model (EICM) from the Mechanistic–Empirical Pavement Design Guide (MEPDG). In many cases, climate is incorporated through parameters whose behavior is associated with temperature and precipitation but does not use the data of these climate variables directly from the project site. The practical incorporation of climate into design methods allows an increase in the certainty of results, ensuring additional climate-resilient pavement structures and increasing their durability and sustainability during their service life. Full article

One of the main types of distress in pavement structures is rutting, which may also reduce serviceability significantly. Most design methods typically attribute rutting to the asphalt layer alone, proposing that it can be managed by controlling vertical deformation or stress at the subgrade’s top. Furthermore, these methods frequently lack precise measurements for rut depth. On-site measurements show that the majority of permanent deformation occurs in the unbound layers beneath the asphalt; attention should be directed towards these layers. In recent literature, there are calculation methods that account for accumulating strains in soils. However, further investigation is needed regarding the effect of soil properties and the significance of the pavement cross-section. The literature is also somewhat contractionary regarding the origin of permanent deformations. In this research, the residual settlement of soils (base, subbase, and subgrade) under flexible pavement systems was analyzed due to the repeated traffic loads. Rut depths were calculated and analyzed using the High-Cycle Accumulation (HCA) model. The different behaviour in each course of the pavement system is discussed to reveal their contribution to total ruts. The effect of the grain size distribution of the subgrade was analyzed, and its significance on the rutting depths was demonstrated. Standardized pavement cross-sections with different asphalt thicknesses were evaluated, and the calculated settlements of the pavement originating from the ground during the design lifetime are also presented. It is shown that, with the same number of repetitions, the settlements calculated in each traffic load class are proportional to the thickness of the asphalt course. The contribution of the base, subbase, and subgrade courses to the total settlement is also presented for different subgrade types and traffic load classes. Full article

Large-particle-size graded crushed stone mixtures (LPS-GCSMs) can improve the shortcomings of conventional graded crushed stone, such as low strength, high deformation, and a low modulus of resilience. At present, there is no systematic research on the gradation design and field evaluation of the LPS-GCSMs. In this study, compaction and California bearing ratio (CBR) tests and field construction conditions were combined to design six kinds of gradation of LPS-GCSM, and the optimum gradation was revealed. In order to improve the mechanical properties of LPS-GCSM, 2.5% cement was added to the mixture to prepare a low-content cement-modified LPS-GCSM (LCC-LPS-GCSM) based on the suggested gradation. The mechanical properties of the LCC-LPS-GCSM were investigated through unconfined compression strength (UCS) and compression rebound modulus (CRM) tests. Moreover, the compaction and deflection properties of LPS-GCSM and LCC-LPS-GCSM were examined through the test battery. The results showed that the optimum gradation of LPS-GCSM can be achieved with a combination of aggregate sizes of 20–40 mm, 10–20 mm, 5–10 mm, and 0–5 mm at a ratio of 44:20:10:26. The passing rates of 19 mm and 4.75 mm should be approximately at the median value of the gradation in view of field construction uniformity and a coarse aggregate interlocking effect. The UCS and CRM values of LCC-LPS-GCSM increased rapidly from 0 day to 28 days while they slowed after 28 days, which was similar to those of cement-stabilized materials. The field detection suggested that LPS-GCSM exhibited favorable compaction and that the addition of cement improved the stability of the field compaction of the mixture. Adding a subbase course of LPS-GCSM between the old pavement and the LCC-LPS-GCSM base can lead to more uniform stress on the base. The results of this study provide a reference for the gradation design of LPS-GCSM and optimization of the design indicators. Full article

The aim of the present study was to evaluate the technical feasibility of using a calcined aggregate with mining residue in different pavement layers, including the base, subbase, and wearing course layers. For this purpose, physical characterizations of the residue and clay and the production of calcined aggregates at temperatures ranging from 800 °C to 1100 °C were performed. Additionally, the suitability levels of these aggregates in pavement layers were assessed, considering the present standards. The physical characterization results indicated that the studied clay was suitable for manufacturing calcined clay aggregates since the particle size distribution showed ceramic potential according to the Winkler diagram, and it presented a plasticity index (PI) higher than 15%. In the tests of boiling-induced mass loss and unit mass, the values obtained were within the limits established by the standards, being lower than 10% and 0.88 g/cm³, respectively. Regarding the abrasion loss test, the M1100 aggregate showed Los Angeles abrasion values lower than the limit established by the standard, demonstrating its potential as an artificial aggregate in pavement applications. Full article

Rutting is one of the most common types of distress in flexible pavement structures. There are two fundamental methods of designing pavement structures: conventional empirical methods and analytical approaches. Many analytical and empirical design procedures assume that rutting is mostly of asphalt origin and can be reduced by limiting the vertical deformation or stress at the top of the subgrade, but they do not quantify the rutting depth itself. Mechanistic–empirical models to predict the permanent deformations of unbound pavement layers have been well investigated and are rather common in North America; however, they are not widely utilized in the rest of the world. To date, there is no generally accepted, widely recognized, and documented procedure for calculating permanent deformations and thus for determining the rutting depth in flexible pavement courses originating from the unbound granular layers. This paper presents a layered calculation method with which the deformation of soil layers (base, subbase, and subgrade courses) under flexible pavements due to repeated traffic load can be determined. In the first step, the cyclic strain amplitude is calculated using a nonlinear material model that is based on particle size distribution parameters (d₅₀ and C_U) and dependent on the mean normal stress, relative density, and actual strain level. In the second step, the HCA (High Cycle Accumulation) model is used to calculate the residual settlement of each sublayer as a function of the number of cycles. It is shown that the developed model is suitable for describing different types of subgrades and pavement cross-sections. It is also demonstrated with finite element calculations that the developed model describes both the elastic and plastic strains sufficiently accurately. The developed model can predict the settlement and rutting of pavement structures with sufficient accuracy based on easily available particle size distribution parameters without the need for complex laboratory and finite element tests. Full article

Metal manufacturing produces various types of byproducts and metal waste that have been growing exponentially. The increasing amounts of metal waste are usually disposed of in landfills, which causes soil and water pollution and increases the amount of gas emissions. On the other hand, in the field of pavement construction, the demand for natural materials is increasing rather rapidly. Many studies have suggested utilizing aggregate-like waste material in pavement construction, but there is little to no literature documenting the use of metal strips of different types. The aim of this study is to investigate utilizing the metal waste produced by the Intag Sohar company in layers of flexible pavement. Selected types of metal waste were utilized in the construction of the material used for base and subbase road layers. Three main parameters were studied: the number of layers, the distance between strips, and the direction of the strips. The effect of the metal waste on the pavement material is evaluated using the standard California Bearing Ratio test (CBR), which is the most important indication of the strength of the pavement material. Results show that the highest-quality mix consisted of four layers of metal waste with 1 cm spacing in one direction with CBR% values equal to 118.807%. Full article

A considerable amount of literature has been published on municipal solid waste incinerator (MSWI) bottom ash as a substitute for natural road materials. However, most studies are conducted in the laboratory, and as a result, very little is known about the construction of pavement structural layers from MSWI bottom ash mixtures and their performance under real conditions. Therefore, the main objective of this paper is to evaluate the bearing capacity and compaction level of the unbound base and sub-base course constructed from the MSWI bottom ash mixtures. For this purpose, three MSWI bottom ash mixtures (70–100% of MSWI bottom ash) and reference mixtures only from natural aggregates were designed and used to construct the unbound base and sub-base courses on a regional road in Lithuania. In total, five different pavement structures with MSWI bottom ash mixtures and a reference one with natural aggregates were constructed and tested. The results from this study showed that unbound mixtures with 70–100% of MSWI bottom ash are suitable to construct the unbound base and sub-base courses since the bearing capacity of those layers met the requirements (≥80 MPa for the sub-base course and ≥120 MPa for the base course) and was similar to that of the reference pavement (161 MPa for sub-base course and 212 MPa for base course). Full article

High calcium waste dust from asphalt concrete manufacturing was utilized to stabilize low-quality lateritic soil as a subbase course material in road structures. Asphalt waste dust up to 30 percent by weight (wt%) was incorporated into the solely lateritic soil and the mixture of lateritic soil containing 5 wt% Portland cement. The asphalt waste dust was successfully used as a subbase course material in road structures according to the standard specifications of pavement materials issued by the Thailand Department of Highways. The minimum 20 wt% asphalt waste dust induced a sufficiently high California bearing ratio, optimized plastic index, liquid limit, and swelling index of soil above the minimum standard requirements for a subbase course material. The fine particles of asphalt waste dust showed filler-like properties to reduce the voids and generated a very dense surface in the stabilized lateritic soil samples. With the small content of cement mixes, a decrease in the calcite phase in the soil stabilized with asphalt waste dust indicated a partial promotion of CaCO₃ from the asphalt waste dust in the cement hydration reaction. The very high strength (CBR > 250%) of these stabilized soil samples approached the standard for base course material (CBR ≥ 80%), which was beyond the expectation for the subbase material (CBR ≥ 25%). Thus, recycling-waste dust from asphalt concrete manufacturing can be used as an effectively sustainable subbase course and base course materials in further generation for road construction purposes. Full article

The study aims to evaluate the change in the behavior of sub-base materials being used in road pavements through blending fines of different types in different amounts. Fines are added in aggregate samples as part of gradations proposed by the American Association for State and Highway Transportation Official (AASHTO). Composite samples conforming to AASHTO gradations B and C were prepared by mixing coarse aggregates in varying proportions, ranging from 0 to 15%. Laboratory tests—including aggregate quality tests (abrasion test, flakiness index and elongation Index), physical tests (particle size analysis and specific gravity), and strength test (modified Proctor, California bearing ratio, and permeability test)—were performed on the control as well as the modified samples. It was observed that the material with 0% fines yielded the highest CBR values (greater than 98%) and coefficient of permeability of 4.4 × 10⁻⁴ cm/s. However, with the increasing of the fines up to 15%, a substantial reduction in CBR value up to 10% and coefficient of permeability to 1.62 × 10⁻⁷ cm/s was noticed. Based on these results, the modulus of rigidity (M_R) and the corresponding structural numbers were determined for each layer. Conclusively, the required thickness of the base course was increased from 11 cm for the samples with 0% fines to 24 cm (118%) for the samples with the addition of 15% fines according to the AASHTO Design method. Full article

Growing demand for road infrastructures and accompanying environmental footprint calls for the replacement of pavement materials with recycled options. The complexities in real-world usability are dependent upon project-specific characteristics and are affected by budgetary constraints of local governmental agencies, material applicability, and climatical conditions. This study conducts a comprehensive lifecycle cost analysis (LCCA) of an urban highway section “E10” in the hot Middle Eastern climate of Abu Dhabi, where virgin asphalt usage is dominant, using actual cost data under multiple scenarios and recycled construction waste (RCW) usage across aggregate layers and recycled asphalt pavement (RAP) across wearing, binder, and asphalt base courses. Blast furnace slag as partial cement replacement for road concrete works is also analysed. Impacts across all lifecycle stages from initial earthworks and construction to routine maintenance and operation were compared. Results found that cost of sustainable construction is lower. Cost reduction was highest for RAP and RCW usage, particularly when the usage was accumulated. The optimum cost scenario used 25% RCW in the sub-base, 80% RCW in the unbound base, 25% warm-mix asphalt (WMA) RAP in the asphalt base, 15% warm-mix RAP in the binder and wearing courses, and 65% slag for concrete roadworks and resulted in USD 2.6 million (15%) cost reduction over 30 years from 2015 to 2045. Full article

During breast cancer therapy, paclitaxel and trastuzumab are both associated with adverse effects such as chemotherapy-induced peripheral neuropathy and other systemic side effects including ocular complications. Corneal nerves are considered part of the peripheral nervous system and can be imaged non-invasively by confocal laser scanning microscopy (CLSM) on the cellular level. Thus, in vivo CLSM imaging of structures of the corneal subbasal nerve plexus (SNP) such as sensory nerves or dendritic cells (DCs) can be a powerful tool for the assessment of corneal complications during cancer treatment. During the present study, the SNP of a breast cancer patient was analyzed over time by using large-scale in vivo CLSM in the course of paclitaxel and trastuzumab therapy. The same corneal regions could be re-identified over time. While the subbasal nerve morphology did not alter significantly, a change in dendritic cell density and an additional local burst within the first 11 weeks of therapy was detected, indicating treatment-mediated corneal inflammatory processes. Ocular structures such as nerves and dendritic cells could represent useful biomarkers for the assessment of ocular adverse effects during cancer therapy and their management, leading to a better visual prognosis. Full article

The paper presents the results of tests of the impact of hydraulic and bituminous binders on the properties of the cold-recycled mixture (CRM). The composition of the cold-recycled mixture includes two types of different binders, i.e., bituminous binder in the form of foamed bitumen and bitumen emulsion, as well as Portland cement (CEM I 32.5R) and hydraulic binder. The hydraulic binder was produced by mixing three base ingredients in the following ratio: 40% CEM I 32.5R; 20% Ca(OH)₂ and 40% CBD (cement bypass dust). The cold-recycled mixtures were produced under industrial conditions on a test section. The prepared CRM with bitumen emulsion (MCE) and foamed bitumen (MCAS) was collected from the test section and compacted under laboratory conditions. The impact of the type and kind of the binder was assessed in terms of physical properties, mechanical properties and deformation modulus (bearing capacity of subbase) of the recycled base course after 1, 7 and 28 days. It was found that the use of hydraulic binder in the recycled base course, regardless of the type of bituminous binder, reduced cohesion without reducing the remaining parameters. Full article

The mechanistic design of a concrete block pavement (CBP) can be very complicated and often requires the use of computer programs. This paper presents a new mechanistic-empirical method, which is implemented in a computer program (DesignPave) that calculates base course/sub-base thicknesses for a range of design inputs such as traffic load, interlocking properties, and material stiffness. A range of virgin and recycled unbound granular materials were also experimentally tested to characterize them for possible use as base course or sub-base materials. Combining the new mechanistic-empirical method and the range of base course/sub-base course materials (virgin and recycled aggregates), it was found that while a CBP containing recycled aggregates did not offer a significant direct financial benefit based on the characteristics or material costs, the associated environmental benefits were very high. Full article