Road Base Layer Research Articles

Optimizing aggregate grading and residual mortar coefficient in low-cement concrete by using crushed coal mine waste rock as base layers for low-traffic roads

In the context of depleting natural resources and environmental challenges posed by large-scale extraction and use of natural aggregates, this study investigates the use of crushed coal mine waste rock (CCMWR) as a sustainable alternative for low-cement concrete in the base layers of low-traffic roads. The primary goal is to optimize the aggregate grading and the residual mortar coefficient (RMC) to enhance the performance and durability of low-cement concrete. Utilizing the I-optimal design methodology and curve of Fuller for particle size distribution, this research evaluates the mechanical properties, workability, and environmental impact of incorporating CCMWR in low-cement concrete. The findings demonstrate that with the appropriate optimization, CCMWR can effectively replace natural aggregates, significantly reducing the ecological footprint and providing an effective solution for sustainable road construction. This research holds substantial engineering application significance by offering an innovative approach to classify and reuse waste from the coal mining industry while addressing the urgent need for sustainable infrastructure development.

Mechanical and Microstructural Analysis of Treated Tuff with Metakaolin Geopolymer Cement for Road Base layers Applications

Traditional road bases materials such as natural gravel and crushed stone are environmentally damaging, and there is a growing need for sustainable and eco-friendly alternatives. One such alternative is using geopolymer cement and tuff as aggregate materials. Geopolymer cement is an innovative and environmentally-friendly alternative to traditional Portland cement, and using locally-sourced tuff as an aggregate material can further reduce the environmental impact of road construction. This article discusses the importance of sustainable road construction practices, particularly in the use of eco-friendly materials for road base layers. It focuses on the treatment of tuff with alkali-activated metakaolin as the geopolymer precursor activated with a mixture of sodium hydroxide and sodium silicate. The effectiveness of treating tuff with metakaolin geopolymer cement is evaluated using several parameters, including dry density, California Bearing Ratio (CBR), shear strength, and microstructure analysis. These evaluations are performed with different NaOH dosages (8, 10, and 12 moles) to determine the optimal molarity for enhancing the material's performance.

Consequential life cycle assessment of demolition waste management in Germany

ContextBulk mineral waste materials such as construction and demolition waste are Germany’s largest waste stream. Despite the availability of high-quality recycling pathways such as road base layers, waste concrete is predominantly recycled into lower-quality recycling pathways like earthworks or unbound road construction. This is due to low demand for recycled aggregates in road base layers and frost protection layers, especially in public procurement.PurposeThis study assesses the environmental consequences of increasing high-quality recycling of waste concrete in the near future to provide decision support for public procurement in Germany. The focus lies on climate change due to its importance for decision-makers. However, 17 other impact categories were assessed to avoid problem shifting.MethodsLife cycle assessment (LCA) is applied with background data from ecoinvent 3.9.1. Impact assessment was conducted at midpoint level using IPCC 2021 and ReCiPe Midpoint (H). Foreground data were taken from literature and expert interviews. In line with the goal of this LCA, a consequential modeling approach was followed to account for changes in the material flow system. Substitution creates a cascade effect previously omitted in consequential LCA studies, in which lower quality recycling materials replace higher quality recycling materials in their respective utilization pathways.Results and discussionIncreasing the high-quality recycling of waste concrete into road base layers causes a reduction in environmental impacts for all 18 impact categories, as it replaces natural aggregate and avoids backfilling of mixed mineral waste and excavated earth through substitution effects. Transport distances and ferrous metal recovery were identified as hot spots. Sensitivity analyses show that only transport is a significant issue.ConclusionIncreasing the high-quality recycling of waste concrete in Germany is recommended in terms of environmental impacts. Lower-quality recycling is environmentally feasible only in cases where the avoided transport distances for natural aggregates and backfilling are significantly lower than the additional transport distances for high-quality recycling.

Long-Term Strength and Durability of Cement-Treated Coal Mine Overburden Materials in Subbase and Base Layers of Low-Volume Roads

Long-Term Strength and Durability of Cement-Treated Coal Mine Overburden Materials in Subbase and Base Layers of Low-Volume Roads

Preparation and Mechanism Analysis of Stainless Steel AOD Slag Mixture Base Materials.

To promote resourceful utilization of argon oxygen decarburization (AOD) slag, this research developed a new three-ash stabilized recycled aggregate with AOD slag, cement, fly ash (FA), and recycled aggregate (RA) as raw materials. The AOD slag was adopted as an equal mass replacement for fly ash. The application of this aggregate in a road base layer was investigated in terms of its mechanical properties and mechanistic analysis. First, based on a cement: FA ratio of 1:4, 20 sets of mixed proportion schemes were designed for four kinds of cement dosage and AOD slag replacement rates (R/%). Through compaction tests and the 7-day unconfined compressive strength test, it was found that a 3% cement dosage met the engineering requirements. Then, the unconfined compressive strength test, indirect tensile strength test, compressive rebound modulus test, and expansion rate test were carried out at different age thresholds. The results showed that the mixture's strength, modulus, and expansion rate increased initially and then stabilized with age, while the strength and modulus initially increased and then decreased with increasing R. Secondly, based on X-ray diffraction (XRD) and scanning electron microscopy (SEM) used to analyze the mechanism, it was found that the strength, modulus, and expansion rate of the new material can be promoted by blending AOD slag, due to its ability to fully stimulate the hydration reaction and pozzolanic reaction of the binder. Finally, based on the strength and modulus results, R = 3% was identified as the optimal ratio, which provides a reference point for the effective application of AOD slag and RA in road base materials.

Geotechnical Properties of Sand-Asphalt for Use in Road Base Layer Instead of Conventional Materials

The study of the geotechnical properties of sand-asphalt for use in road base layer instead of conventional materials, for low to moderate traffic volume, is based on standardized laboratory tests. Sand samples were taken from Kayar, Darou Alpha and Keur Morry (Thies region, Senegal). Identification tests (particle size distribution and sand equivalent) made it possible to select Kayar and Darou Alpha sands which have respective sand equivalent (ES) values of 92 % and 62 %. These values are higher than the minimum required (40 %), for sand-asphalt, with different 35/50 bitumen dosages. The results of the Hubbard-Field test carried out showed that Darou Alpha sands are suitable, with an optimum dosage of 7 % bitumen : the stability at 18 °C, at dry conditions, is 2 732 kg and is greater than the minimum required value of 2 300 kg; the immersion/compression ratio is 85 % and is greater than the minimum required limit of 75 %; water absorption reaches 5.4 % and remains below the maximum required limit of 7 %; the volumetric swelling is 2.6 % and is below the maximum required limit of 5 %. The compactness is 84 % and is acceptable because it exceeds the minimum required limit of 80 %. The sizing carried out with the Alizé©3 software gives deformation values lower than the permissible values. The pavement structure that is placed on a PF3 type platform is therefore correctly sized to support a traffic of 150 heavy vehicles per day for a service life of 15 years. This roadway structure, which is devoid of a foundation layer, includes a 23 cm thick sand-asphalt base layer on which rests a 5 cm thick asphalt concrete. Keywords: sand-asphalt, Hubbard-Field test, Kayar, Darou Alpha, Keur Morry.

Evaluation of road performance and micro-mechanism analysis of bentonite plastic concrete subgrade

This study evaluated the performance of bentonite plasticized concrete with good deformation coordination as a road base material, to address the poor deformation coordination of rigid base layers in roads. Through tests such as slump, strength, permeability, and scanning electron microscopy (SEM) and x-ray diffraction (XRD), the study analyzed the variations in workability, mechanical properties, and durability of plastic concrete as a base material under different bentonite and cement contents, as well as the underlying micro-mechanisms. The results showed that plastic concrete exhibited good workability, which improved with increased bentonite and cement content. The 28-day mechanical properties of the plastic concrete met the design criteria for road base layers and had features of higher load-bearing capacity, good toughness, slow strength attenuation, and overall integrity. In durability, the increase of bentonite content enhanced the concrete’s permeability, but decreased abrasivenes and shrinkage. From economic, performance, and engineering perspectives, the optimal bentonite and cement contents for the plastic concrete base were in the ranges of 90 kg m−3 to 120 kg m−3 and 110 kg m−3 to 150 kg m−3, respectively.

The investigation of the frost resistance of the aggregate-sand mixes

Problem. Recently there is a steady trend to the increase of the intensity of traffic and of the loads from the wheels of the rolling stock on the whole structure of the road pavement, therefore during the building of the road pavement layers the most important thing is a rational choice of the materials for the base layers and for the top layers which will provide the performance of the entire structure during the designed service life under the working conditions which are getting worse all the time. Nowadays the most widespread material for the road base layers is aggregate mix strengthened by cement. One of the ways of the base layers materials improving is the increase of their frost resistance. One of the ways to solve this problem can be the different additive and fibers usage as a reinforcing component of the aggregate mix. But until today the influence of the internal factors such as size of mineral grains, granulometric composition and binder content on the indexes of frost resistance is still not investigated.
 Goal. The aim of the research is the investigation of the maximum grain size and content and also mineral binder concentration influence on the indexes of frost resistance of the aggregate mixes strengthened by cement. Methodology. To achieve this goal in the laboratory of the Department of Highway Building and Maintenance named after O. Birulia the samples of sand, fine-grained, medium-grained and coarse-grained aggregate mixes with cement content from 2 to 10 % were prepared. Results. For the frost resistance indexes determination of the aggregate mixes of different compositions strengthened by cement according to the maximum grain size the cement concentration influence on the grade strength indexes was found. The research results have shown that: with the increase of cement content the compressive strength indexes in the fine, medium and coarse-grained mixes are increasing; the increase of the maximum grain size of the same cement concentration shows that compressive strength and tensile strength indexes are increasing. The repeated freezing and thawing is one of the main aggressive factors of the external environment influence which reduces strength and durability of the materials, therefore the influence of this factor on the compressive strength and tensile strength was evaluated. In Ukraine according to the current standard the frost resistance of the aggregate mixes is evaluated only in terms of compressive strength index of samples which were subjected to certain number of freeze-thaw cycles. It is determined that the aggregate mixes with the same cement content with larger mineral grains in its composition have higher indexes of the frost resistance coefficient. Also it was found that the influence of the freeze-thaw cycles is more informatively shown at the samples testing according to the split tensile test. Conclusions: 1. The increase of the binder content in the composition of strengthened aggregate mixes leads to the decrease of the freeze-thaw cycles influence on the compressive strength and splitting strength for all studied compositions of aggregate mixes. 2. The aggregate mixes strengthened by the same cement amount with the larger size of mineral grains in its composition have higher values of frost resistance coefficients in comparison with strengthened aggregate mixes with smaller maximum size of mineral grains in its composition. 3. The influence of the freeze-thaw cycles is showed more informatively by the split tensile scheme.

Assessment of Mechanical Characteristics of Crushed Rock Substituted with Tyre Crumb for the Application of Road Base or Subbase Layers of Road Pavement

Assessment of Mechanical Characteristics of Crushed Rock Substituted with Tyre Crumb for the Application of Road Base or Subbase Layers of Road Pavement

Experimental Study on Effect of Recycled Reinforced Concrete Waste on Mechanical Properties and Structural behaviour of the Sandy Soil

In recent years, constructing natural aggregates as a base layer for the roads has increased. Natural resources will run out as long as human consumption of them continues. Recycled concrete aggregate (RC) has thus emerged as a substitute material for the building of road base layers. Additionally, RC can be utilized to create interior city highways. The base layer for roads must have sufficient strength to support the working load on the pavement surface without damage deforming. As a result, the focus of this paper is on enhancing the structural performance of sandy soil reinforced with various RC percentages. The three key factors are relative soil density (Dr = 83 and 97%), recycled concrete aggregate reinforcing levels (RC = 0,5,10,15,20,25,30,40,50 and 100%), and reinforcement layer thickness (Rd = 0.0B, 0.5B, B, and 2B where B is the footing model width). Numerous laboratory experiments were conducted in order to examine the impact of important parameters on the properties of the mixtures. The plate bearing tests were carried out using a footing model (250 × 250 mm) inside a tank (1500 × 1500x1000 mm) to ascertain the stress–strain response, bearing capacity ratio (BCR), ultimate bearing capacity, and modulus of elasticity of the tested mixtures. It is clear that raising the RC has no effect on the diameters of the grains. It was found that as RC increased, the mixture's bulk density increased but specific gravity decreased. Maximum dry density rose as RC rose, whereas water content fell. It was noted that BCR unquestionably increased as RC increased for all RC levels and all values of settlement ratios. The appropriate reinforcing layer thickness is suggested to be no more than 2B. As the RC concentration in the sand and Rd increased, the difference between two pressure-settlement curves of densities 83% and 97% significantly decreased. Furthermore, when RC reaches 50%, two curves are roughly comparable. At RC = 50%, it is advised that the relative density of 83% is sufficient to produce the same behavior as the relative density of 97%. It was found that as RC and Rd grew, the tested mixtures' ultimate bearing capacity and elasticity modulus increased as well. A novel proposed formulas are developed to compute bearing capacity ratio, ultimate bearing capacity, and elasticity modulus of the tested mixtures taking into account the influence of RC, reinforcement layer depth, settlement ratio, and the relative density, and its results agree with the experimental results.

Green Thermal Aggregates: Influence of the Physical Properties of Recycled Aggregates with Phase Change Materials.

Increasing construction and demolition waste (CDW) and the large amount of energy consumption in the building operation process are high-profile issues at present. In the construction industry, recycled aggregated (RA) from CDW can be reutilized in construction, along with green materials, for example, as a road base layer, as aggregate in concrete, etc. Phase change materials (PCM) are often used as building materials due to their good latent heat storage properties. With the use of RA as a matrix to absorb PCM, a thermal performance aggregate can be obtained. This work studied the physical properties of RA from Portugal and combined PCM with RA to prepare a green thermal aggregate through two methodologies using a vacuum and atmospheric pressure. The green aggregate was used in concrete to observe its effect on the compressive strength of concrete. The results showed that the amount of PCM absorbed by the RA mainly depends on the porosity of the matrix material. At the same time, the volume expansion coefficient of PCM was 2.7%, which was not enough to destroy the RA. Ultimately, as the amount of green thermal aggregate increases, the compressive strength of concrete decreases. Green thermal aggregate prepared under vacuum conditions has a greater negative impact on the compressive strength of concrete.

Geotechnical and engineering properties of expansive clayey soil stabilized with biomass ash and nanomaterials for its application in structural road layers

Clayey soils often pose issues such as swelling, high plasticity, low permeability, and low bearing capacity, particularly in regions with seasonal rainfall. Consequently, soil improvement techniques are necessary for constructing road base layers. Currently, the most used method for road stabilization involves the application of traditional binders such as lime and cement. However, the production of cement and lime has negative environmental impacts and depletes natural resources.In this study, new stabilizing materials based on waste and by-products, as well as a new generation of nanomaterials, are investigated for stabilizing highly plastic and expansive soils. The geotechnical and mechanical properties of soils stabilized with waste materials like biomass ashes from electricity generation, along with small amounts of a silica-based nanotechnological stabilizer, are examined. The obtained results suggest the potential reduction in the use of traditional binders by incorporating by-products, while still maintaining soil properties, and even improving the properties through the application of nano-sized additives.

Performance assessment of recycled waste materials for use in unbound pavement Layers: A case study from Turkey

Construction and demolition wastes (CDW) have become uncontrollable due to population expansion, fast urbanization, ongoing technological advancements, and changing building materials throughout time, as well as the storage of these wastes and the environmental degradation they create. In addition, recently, the depletion of natural resources and rising expense of waste disposal have increased the importance of recycling and reuse of waste. Recycling and reuse of CDW can reduce the rate of depletion of natural aggregate resources, landfill area and carbon footprint. However, the lack of knowledge about parent concrete's qualities, such as compressive strength, is one of the most significant barriers to using these waste materials. In addition, further research is needed on the use of high-strength building waste that was devastated by earthquakes and floods as aggregates. The study aimed to investigate the quality of waste concrete and assess the usability of mixtures prepared using recycled aggregates obtained from waste concrete with a predetermined strength of 35–40 MPa in combination with crushed limestone aggregate in granular road base and sub-base layers. The engineering performance of RCA will be evaluated, along with a comparison to natural aggregate, and its compliance with the limit values given in the Turkey Highways Technical Specifications (THTS) will be examined. 5 different mixes were created by replacing RCA with LA at 0%, 25%, 50%, 50%, 75%, and 100%. The strength, durability and hydraulic properties of the prepared mixtures were investigated. It was concluded that the use of RCA had no negative effects on the mixture's properties, with the exception of permeability, and even outperformed natural aggregate in terms of soaked and unsoaked CBR, CBR strength after a freeze–thaw cycle, and modulus of elasticity. Additionally, it was established that RCA satisfies the standards set in the THTS for the materials to be used in granular road base and sub-base layers.

Dynamic Properties of Reclaimed Asphalt Pavement–Green Cement Blends for Road Base Layer

Dynamic Properties of Reclaimed Asphalt Pavement–Green Cement Blends for Road Base Layer

Use of Marble Waste as A Road Base Material in Different Size Ranges

Along with the economic loss caused by the non-use of waste worldwide, uncontrolled storage also brings an additional cost. Today, the rapid increase in the population and the rapid depletion of natural resources in nature lead us to research the recycling possibilities of waste materials. In this context, using marble waste in road pavements is one of the best areas of use. This study investigated the suitability of substituting the marble waste obtained from a marble quarry in Bilecik, Turkey, in the road base layer instead of the aggregate, which was used all the time in the base layer in highway construction at different intervals. The physical tests carried out in this context have met the base material limit conditions of the Turkish Highways Technical Specification (THTS). Mixtures obtained in modified Proctor experiments, and optimum water contents (wopt) and maximum dry unit volume weight (rdmax) were determined for each mixture. California bearing ratio (CBR) values remained above the limit value of all mixtures for 0 days and 7 days of curing according to the specifications for THTS. In addition, CBR values were obtained after freezing-thawing at 4, 12, and 20 cycle numbers. According to the freeze-thaw test results, there was an increase in CBR values in the first 4 cycles and a decrease in the following cycles. Still, all the test results obtained remained above the limit value according to the specifications for THTS. Aggregate unit cost constitutes approximately twice the unit cost of marble waste. Besides, this difference has created an economic equality distance of 18.9 km. Therefore, a marble quarry, a road construction site within the calculated economic equality distance and marble waste material will provide a financial gain for our country. With the evaluation of quarry waste all over the world, we can leave a liveable world with rich raw material resources and a strong economy for future generations.

Validation and improvement of a punching test to ensure excavatability of cement-based materials used as pavement subbase

Cement-based materials, regularly used in urban road base layers, must be sufficiently resistant to traffic but above all, easily excavated, even with a pick, to allow easy access to the underlying networks during maintenance operations. Unfortunately, bibliography shows that there is no satisfactory method for determining the ease of excavation. This paper presents the results of a large campaign in which manual excavations and Charpy tests carried out on scale 1 trenches were analyzed with an original laboratory punching test. It proposes a rational definition of an excavation difficulty scale by linking the feeling of workers and excavated volume per pick impact. The latter can be calculated from punching test thanks a classic soil failure model. A complete methodology to determine at the laboratory stage the excavation difficulty with a pick is finally proposed, opening the way of rational optimization of excavation ease, while keeping the bearing capacity constant..

Alternative Fillers in Asphalt Concrete Mixtures: Laboratory Investigation and Machine Learning Modeling towards Mechanical Performance Prediction.

In recent years, due to the reduction in available natural resources, the attention of many researchers has been focused on the reuse of recycled materials and industrial waste in common engineering applications. This paper discusses the feasibility of using seven different materials as alternative fillers instead of ordinary Portland cement (OPC) in road pavement base layers: namely rice husk ash (RHA), brick dust (BD), marble dust (MD), stone dust (SD), fly ash (FA), limestone dust (LD), and silica fume (SF). To exclusively evaluate the effect that selected fillers had on the mechanical performance of asphalt mixtures, we carried out Marshall, indirect tensile strength, moisture susceptibility, and Cantabro abrasion loss tests on specimens in which only the filler type and its percentage varied while keeping constant all the remaining design parameters. Experimental findings showed that all mixtures, except those prepared with 4% RHA or MD, met the requirements of Indian standards with respect to air voids, Marshall stability and quotient. LD and SF mixtures provided slightly better mechanical strength and durability than OPC ones, proving they can be successfully recycled as filler in asphalt mixtures. Furthermore, a Machine Learning methodology based on laboratory results was developed. A decision tree Categorical Boosting approach allowed the main mechanical properties of the investigated mixtures to be predicted on the basis of the main compositional variables, with a mean Pearson correlation and a mean coefficient of determination equal to 0.9724 and 0.9374, respectively.

Investigation of Shear Strength of Subbase-Subgrade Interface with Geosynthetics Reinforcement Utilizing A Large-Scale Direct Shear Test

Geosynthetics are being used to strengthen road pavement. Geosynthetic inclusions improve pavement carrying capacity, maintenance costs, highway service life, reflective cracks, and undesirable large lateral and vertical deformations. The primary purpose of this research is to determine the effectiveness of geosynthetics (geogrids and geotextiles) in stabilizing the subgrade and reinforcing the base course layers in unpaved test sections. Determine the mechanical interaction of subgrade soils (clay and sand) and aggregate road base layers (subbase) with and without reinforcement. Compute the shear strength parameters (cohesion, friction angle, and interface coefficient factor). Therefore, Large-scale direct shear experiments in the laboratory were performed on subbase-subgrade materials with and without geosynthetics, under the applying normal of stresses (25, 50, 75, and 100) kPa, indicating the quantity overburden the pressure in paving. The present research uses a large-scale direct shear apparatus with an up square box (200 mm×200 mm×100 mm) and a bottom rectangular box (200 mm×250 mm×100 mm). A direct shear test was implemented by manufacturing this equipment. The results obtained from experiments showed that biaxial geogrid G1 has the best behavior for both (subbase-clay) and (subbase-sand) and has an interface shear coefficient factor more significant than unity and equal to 1.05 and 1.02, respectively.

Durability and mechanical long-term performance of reclaimed asphalt pavement stabilized by alkali-activation

The application of alkali-activated industrial by-products for the stabilization of reclaimed asphalt pavement (RAP), can become a sustainable solution to reduce the carbon footprint of road construction and maintenance activities. Furthermore, this approach can also reduce the increasing depletion of natural resources. Thus, the durability and long-term mechanical performance of RAP stabilized with alkali-activated fly ash were assessed in this study. The alkaline activator was a solution composed of sodium hydroxide and sodium silicate. To this extent, unconfined compressive strength (UCS) and durability tests were conducted in this research. The proposed alkali-activated binder significantly increased the UCS of RAP mixtures, with long-term (365 days) results reaching values up to 32 MPa; fulfilling the strength requirements for cement-stabilized soil mixtures and even stable inorganic binder materials for road base and sub-base layers of pavements. These results indicate that when stabilized with an alkali-activated fly ash binder, RAP presents several applications for road engineering; even when subjected to seasonal variations in humidity and temperature, as shown by the durability tests.

Investigating the Relationship Between Moisture Content and Dry Density on Different Gradations for Road Base Granular Materials

California Bearing Ratio (CBR)in granular materials is the key technical characteristic of layers in flexible pavement. The CBR value is a way to measure the material stiffness used in the pavement design procedure for the road base layer depending on the aggregate types. Road base layers’ ultimate role in the flexible pavement is to spread loading evenly over the sub-grade from the loading of vehicles throughout the design life. Among the factors affecting the material's bearing capacity, aggregate gradations are one of the most important parameters that give a considerable result. This study was carried to evaluate the effects of different aggregate gradations using granite, basalt, and quartzite aggregates on the bearing capacity of the granular materials. Further analysis on the base course layer’s upper and lower gradation limit were conducted to identify the bearing capacity of the layer, through a series of aggregates physical tests and strength tests. The results indicated that physical properties of the selected aggregates complied to the Public Works Department (PWD) Specifications (2008) for soaked and un-soaked condition. For both soaked and un-soaked conditions, the samples with lower limit gradations showed higher stress values compared to upper limit gradations for all three types of aggregates. Granite showed higher CBR values for both, soaked, and un-soaked conditions, followed by basalt and quartzite at upper and lower limit gradation. Un-soaked granite samples with lower limit gradation showed 60.5% increment in strength compared to un-soaked upper limit gradation, followed by quartzite 53.6% and basalt 9.94% respectively. The results indicated that strength is highest in the lower limit gradations where the use of coarse-grained aggregates could significantly increase the strength.