Stabilized Base Layer Research Articles

Erosion Potential of Stabilized Support Layers for Concrete Pavements and Overlays

The performance of concrete pavements and overlays is highly dependent on the uniformity, durability, and stability of the underlying support layers. Erosion of support layers can lead to pavement distresses and a reduction in pavement life. A review of existing erodibility performance tests that assessed stabilized support layers was first conducted to identify and evaluate their suitability for adaptation. The Hamburg wheel tracking device (HWTD) test was selected to assess the erosion potential of asphalt and cement stabilized support layers. Field testing with distress surveys, falling weight deflectometer, and coring was completed to obtain HWTD specimens and link laboratory results to pavement performance. The HWTD test was performed on cores obtained from in-service cement and asphalt stabilized support layers, a cold in-place recycling (CIR) mixture, and cement stabilized laboratory mixtures. As expected, an increase in cement content within cement stabilized mixtures decreases the likelihood of erosion with the HWTD. Additionally, conventional asphalt stabilized base layers were highly erosion resistant. Erosion resistant cement stabilized bases (including full-depth reclamation) should target an average HWTD erosion depth ≤2 to 4 mm (0.08 to 0.16 in.) after 10,000 load cycles based on the functional classification and expected traffic volume of the pavement section. Likewise, asphalt stabilized bases (including CIR and support layers for concrete overlays) should target an average HWTD erosion depth ≤12.5 mm (0.5 in.) after 7,500 load cycles with performance grade 64 binder.

A comparative study on rutting behavior of unbound and cement stabilized base layers in flexible pavements

Rutting distress, a phenomenon characterized by formation of ruts in high-stress areas of flexible pavements, necessitates material enhancements due to increased vehicular loads resulting from national and international trade via highways, highlighting the need for revised prediction methods utilizing laboratory tests with standardized protocols to evaluate asphalt mixtures before field application. While pavement construction consumes substantial non-renewable resources, there's an increasing emphasis on sustainability over initial costs in government decision-making, underscoring the importance of sustainable development to reduce investments and preserve natural resources. Notably, cement-treated bases are effective in extending the fatigue life and reducing cracking in flexible pavements. Various testing devices, such as the Georgia loaded-wheel tester, French wheel tracking tester, Hamburg wheel-tracking device, and asphalt pavement analyser, assess asphalt mixture properties, but mainly target bound bituminous layers. This study's primary goal is to compare the rutting performance of two pavement sections using a novel device called the 'Roller compactor cum rut analyser' (RCRA), capable of compacting and analysing all layers of flexible pavement. By applying the RCRA model, the research demonstrates that the section with cement-stabilized layers displays enhanced resistance to rutting and deformation, providing valuable insights for the construction of durable road infrastructure.

Establishment of best practices for laboratory evaluation of stabilized base layers and comparative study on influence of different types of stabilizers

The stabilization of pavement layers is nowadays widely accepted across the globe due to several issues like scarcity of good quality aggregates, weak subgrade, presence of undesirable material, heavy loadings, and many more. The present study envisaged the suitability of different stabilizers available commercially for the stabilization of the base layer. The primary objective of the study is to ascertain the stabilizer which will aid in attaining the required strength with a minimum curing period while keeping the other characteristics of the stabilized mix under permissible limits. Three different types of cementitious stabilizers were incorporated in the study, namely polymer-based cementitious material (Commercial Chemical Stabilzer-1 or CCS-1), fiber-based cementitious material (CCS-2), and Ordinary Portland Cement (OPC) Grade-53. The microstructure analysis of the three stabilizers was also conducted to understand their mineralogical compositions. The desired level of compaction was achieved through the vibratory hammer approach after adopting different compaction methods during the laboratory study. The optimum content of stabilizers was determined by a trial-and-error approach, and the corresponding moisture-density relationship was utilized further for sample preparation. Moreover, several sets of samples were prepared, which were subjected to different curing periods. The samples were prepared in different shapes and sizes as required for conducting tests such as Unconfined Compressive Strength (UCS), flexural strength, Indirect Tensile Strength (ITS), and durability. For a detailed investigation of the stabilizer effect on the stabilized mix, the micro-structure analysis through X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) was performed. The laboratory study concluded that the minimum requisite UCS strength of 4.5 MPa was achieved by adding only 4% of CCS-1 in comparison to 4.5% of the other two stabilizers, i.e., CCS-2 and OPC-53. Moreover, the strength gains by stabilized mix prepared by the addition of CCS-1 are relatively fast, and the requisite strength was attained after 3-days curing only. The other test results also demonstrated the superiority of CCS-1 over the other two stabilizers. The microstructure analysis depicted that the formation of hydration products influencing the mix strength was relatively more for CCS-1.

Bitumen stabilized materials as pavement overlay: Laboratory and field study

Bitumen stabilized materials applied as base courses have been used in many countries. In the southern Brazilian State of Rio Grande do Sul, two test sections were built using such mixes (in 2011 and 2015) as overlay asphalt emulsion base courses and have been under monitoring since then. In 2019, a new test section was built to evaluate mixes of granular materials and reclaimed asphalt pavement stabilized with emulsion and Portland cement as overlay base courses. The main objective of the research reported here was to evaluate the mechanical behavior of such materials and to assess their performance in the field during the years after construction. Indirect tensile strength, monotonic triaxial, and repeated load triaxial tests were carried out to obtain the necessary mechanical parameters. The data collected during the monitoring of the test sections were used to analyze the field performance in terms of permanent deformation. Besides, in situ moduli were obtained using backanalysis of deflection basins. The number of equivalent single axle loads (ESALs) for the analysis period was computed using data collected in toll plazas near the test sections. Using field and laboratory results and the South African TG2 performance model, it was possible to estimate the life of the studied pavements regarding permanent deformation. The TG2 model seems to underestimate the life of pavements with thick (>40 mm) asphalt layers. A model relating rutting to the number of ESALs was obtained, allowing the prediction of rutting of asphalt pavements overlaid by a bitumen stabilized base layer and asphalt wearing courses. Considering the test sections’ performances, the mixes proved to be efficient to improve structural capacity, also reducing the influence of the water level variation on pavement performance.

Laboratory Study of the Effect of Zeolite and Cement Compound on the Unconfined Compressive Strength of a Stabilized Base Layer of Road Pavement.

Soil stabilization using cement is regarded as one of the conventional methods to improve the engineering properties of soil used in infrastructure and road bodies. Considering the environmental problems caused by the production and consumption of cement, finding a suitable replacement for cement is necessary. The present study aims to experimentally evaluate the effect of using zeolite instead of cement in the stabilization of pavement layers. In this research, only 5% of cement was used in the control sample, while zeolite was used instead of cement in other samples by 20, 30, 40, and 60 wt.% of cement. According to the analysis, the highest unconfined compressive strength was obtained in the sample containing 30% (wt.% of cement) of zeolite instead of cement (equivalent to 1.5% of the total stabilizing materials) after 28 days of treatment, which was 29% more than that of the sample without zeolite. Evaluating the fracture strains reveals that using zeolite instead of cement increases the fracture strain by 33%, and in other words, changes the behavior of the sample from brittle mode to soft mode.

Design and sustainability analyses of road base layers stabilized with traditional and nontraditional additives

Base course is an important structural layer of a road pavement which plays a vital role in transferring and distributing the traffic loadings to the subgrade. The base usually comprises unbound materials, which can be stabilized to enhance the mechanical properties when necessary. This study evaluates all the various types of stabilization products suitable for a coarse-graded base, which can be grouped as traditional solutions (cement and bitumen) and nontraditional solutions (brine salt, clay, organic non-petroleum, organic petroleum and synthetic polymer). The research presented here addresses four major objectives. First, the effect of the stabilizers is evaluated via cyclic triaxial tests both before and after the exposure of the samples to ten freeze-thaw cycles. Second, the potential to reduce the thickness of a base course is evaluated for each stabilizer according to the Norwegian pavement design code. Third, the study appraises the associated reductions in carbon dioxide emissions during the operations for road construction in Norway and, finally, the related economic costs are derived. The freeze-thaw actions exert almost no effect on the samples stabilized with cement, bitumen, organic petroleum and synthetic polymer. These stabilizers seem to display an aging effect, which is responsible for the improvement of the mechanical properties over time. The required thickness of a stabilized base layer is at least halved compared to a traditional unbound course and this remarkably lowers the carbon footprint of the construction operations. The application of most of the stabilizers is cost-effective, whereas their market price and the transport distance of aggregates are two crucial factors for the determination of their economic competitiveness.

Climate Change Adaptation Strategies for Canadian Asphalt Pavements; Part 1: Adaptation strategies

There is strong evidence for climate change leading to a rise in temperatures and a change in precipitation trends. These environmental changes pose a threat to pavement infrastructure worldwide. Therefore, it is necessary to modify pavement design procedures to consider climate change. In addition, it is necessary to consider suitable pavement materials for future climate. The objective of this study is to develop a framework for selecting an appropriate adaptation strategy to mitigate climate change impact. To fulfill this, the influence of climate change on long-term pavement performance in Canada has been quantified over sixteen Canadian pavement sections located over various provinces in Canada. In addition, the fundamental causes of pavement deterioration due to climate change were determined using ten different climate change models. Various adaptation strategies such as upgrading asphalt binder grade, increasing the thickness of asphaltic concrete layer, increasing the base layer thickness, and using stabilized base layers were analyzed to reduce pavement deterioration and to extend the service life of the pavement. Unlike the other studies, pavement temperatures were determined using Enhanced Integrated Climate Model (EICM) to determine the change in binder grade for the future climate in the adaptation process. The study found that by 2070 all examined locations will require an upgrade in binder grade and the majority will require an upgrade in mixture gradation. Furthermore, the east and west coast will be more vulnerable to climate change and require additional measures in comparison to Central Canada. Newfoundland and Prince Edward Island are the only locations that will need to consider a change in asphalt thickness while British Columbia is the only location eventually requiring a stabilized base. This study emphasizes the necessity of climate change adaptation strategies for Canadian asphaltic concrete pavements.

Performance Evaluation of Stabilized Reclaimed Asphalt Pavement as Base Layer in Flexible Pavement

The increased scarcity of natural quarry material has resulted in increases in the cost and burden on the environment. Pavement materials comprising asphalt coated aggregates that can be reused are called reclaimed asphalt pavement (RAP). RAP is crushed and screened, and then blended with one or more stabilization agents to produce a stabilized base or subbase aggregate. In the present study, the influences of fly ash dosage, lime dosage, and curing period on the strength, stiffness, and durability characteristics of RAP fly ash–lime (RFL) mixes were studied for utilization as a base layer material in flexible pavements. The dry density and moisture content relationship were determined by conducting a modified proctor test on all RFL mixes. Unconfined compression tests were conducted on specimens with different dry weight percentages of fly ash (10%–25%) and lime (5%–10%) content for different curing periods (0, 7, and 28 days). The optimum mix obtained as RFL2 had the proportions 70% RAP:22.5% fly ash:7.5% lime. A resilient modulus of 540 MPa at 28 days was observed for RFL2. The durability of RFL2 tested using the resistance index and a wet–dry cycle (weight loss) was observed to be 0.88% and 7.3%, respectively. Pavement analyses were performed for a pavement system with three layers using the KENLAYER program. The RFL2 mix as the base layer material was found to be superior to conventional wet mix macadam, hence the service life of an RFL2 pavement would be higher. Trial sections of the stabilized base and conventional pavement were constructed on a major district road. The falling weight deflectometer showed a better modulus (286 MPa) in RFL2. An RFL mix could therefore be used in a stabilized base layer to replace a conventional base layer.

The Latest Research in Mongolia on the Utilization of Coal Combustion By-Products

With a geological reserve of over 170 billion tons, coal is the most abundant energy source in Mongolia with six operating thermal power stations. Moreover, in Ulaanbaatar city over 210000 families live in the Ger district and use over 800000 tons of coal as a fuel. The three thermal power plants in Ulaanbaatar burn about 5 million tons of coal, resulting in more than 500000 tons of coal combustion by-products per year. Globally, the ashes produced by thermal power plants, boilers, and single ovens pose serious environmental problems. The utilization of various types of waste is one of the factors determining the sustainability of cities. Therefore, the processing of wastes for re-use or disposal is a critical topic in waste management and materials research. According to research, the Mongolian capital city's air and soil quality has reached a disastrous level. The main reasons for air pollution in Ulaanbaatar are reported as being coal-fired stoves of the Ger residential district, thermal power stations, small and medium-sized low-pressure furnaces, and motor vehicles. Previously, coal ashes have been used to prepare advanced materials such as glass-ceramics with the hardness of 6.35 GPa, geopolymer concrete with compressive strength of over 30 MPa and zeolite A with a Cr (III) removal capacity of 35.8 mg/g. Here we discuss our latest results on the utilization of fly ash for preparation of a cement stabilized base layer for paved roads, mechanically activated fly ash for use in concrete production, and coal ash from the Ger district for preparation of an adsorbent. An addition of 20% fly ash to 5-8% cement made from a mixture of road base gave a compressive strength of ~ 4MPa, which exceeds the standard. Using coal ashes from Ger district prepared a new type of adsorbent material capable of removing various organic pollutants from tannery water was developed. This ash also showed weak leaching characteristics in water and acidic environment, which opens up an excellent opportunity to utilize.

Layer Composition of Continuously Reinforced Concrete Pavement Optimized Using a Regression Analysis Method

A procedure for determining the optimized composition of layer properties for a continuously reinforced concrete pavement (CRCP) system was constructed using field tests, finite element (FE) analysis, and regression analysis methods. The field support characteristics of a rigid pavement system were investigated using a falling weight deflectometer (FWD), dynamic cone penetrometer (DCP), and a static plate load test. The subgrade layer exhibited a more uniform condition than the aggregate base, and the modulus of the subgrade reaction of the aggregate base and subgrade combination (effective k-value) was improved by about 1.5 times by introducing a 2 inch (50.8 mm) asphalt stabilized base (ASB) layer. Thereafter, FE support models describing the actual field conditions were studied. The effects of the thickness of the stabilized base layer, the elastic modulus of the stabilized base material, and the effective k-value on the composite k-value of the support system were identified using a regression analysis method, and the results showed that the variables had a similar effect when determining the composite k-value. Afterward, a procedure for selecting the layer properties for producing a suitable composite k-value was constructed, and we identified that the maximum stress in the concrete slab was induced at different levels, even with identical composite k-values. Lastly, regression relationships were derived to estimate the maximum stress in the concrete slab by considering both the support layer properties and the concrete slab. Subsequently, an algorithm for selecting an optimized layer composition of the CRCP structure was construction considering the economical aspect.

Effects of construction time on the performance of cement treated base

Cement treated base (CTB) has been widely used as a stabilized base layer in pavement for highways, roads, airports, parking areas and some storage areas. CTB comprises mainly three components, namely, cement, water and either natural soil or aggregates. The mixture will become strong and durable after proper compaction and curing. CTB can be produced in central plant, haul to the laying area by dump trucks or can be mixed in-placed using proper materials and equipment. One of the key factors which can affect the performance of CTB is the construction time which consists of mixing to transportation, laying and compaction. This paper describes a study that was conducted to analyse the effects of construction time on the performance properties of CTB. Laboratory tests were conducted for various CTB mixtures. The CTB mixtures were compacted at different time frames and then tested for dry density and unconfined compressive strength. The results were then analysed to study the effects of construction time.

Mechanical property and microstructure characteristics of geopolymer stabilized aggregate base

With its potential to replace ordinary Portland cement, geopolymer has been receiving more and more attention in cement industry as well as geotechnical engineering. However, research is mainly focused on use of geopolymer to make geopolymer concrete or masonry bricks, little has been done about its application as a stabilizing agent in pavement base materials. This study explores the feasibility of using geopolymer-stabilized base material in pavement base layer. Two industrial wastes, class F fly ash and red mud, were utilized to synthesize the geopolymer stabilized aggregate base, and two conventional stabilizing agents, cement-fly ash and lime-fly ash, were also included for comparison purpose. Three curing conditions were adopted to investigate two key factors in the geopolymerization process, temperature and water. Test results show that a standard curing condition was adequate for strength development of geopolymer base samples with a compressive strength close to that of the cement-fly ash base sample. An increase in temperature from 20 °C to 38 °C accelerated the strength development of both geopolymer base samples, whereas a decrease in relative humidity from 98% to 45% significantly impaired the strengths of all conventional and geopolymer base specimens, indicating that a wet condition was still necessary for geopolymer stabilized base layer. According to the test results, geopolymer stabilized aggregate bases showed promise to be used as a stabilizing agent in flexible pavement applications.

Measuring the effects of styrene butadiene copolymer latex-Portland cement additives on properties of stabilized soil-aggregate base

The fundamental objective of this research is to study the behavior and properties of the traditional and non-traditional additives and to characterize the cementitious stabilized base layer. This research presents experimental results on the improvement of short-term road base performance by the addition of carboxylated styrene butadiene emulsion (Tylac® 4190); Portland cement and Tylac® 4190-Portland cement mixture. To evaluate the short-term performance, the specimens were molded, cured for 7, 28, and 60 days, and subjected to different stress sequences to study the unconfined compressive strength (UCS), indirect tensile strength (ITS), indirect tensile resilient modulus (ITRM), flexural strength (FS) and un-soaked California bearing ratio (U-CBR). The results indicate that the additives improved the strength and the stiffness of the specimens, which has been found to be an important quality indicator of mechanical properties of road base. The flexural strength tests showed that the addition of a 4% Portland cement–8% Tylac® 4190 mixture resulted in improvement of 81.5% of modulus of rupture as compared to the sample with 4% cement. Therefore, this research nominates a new polymer additive having outstanding engineering properties.

Adaptation of NCHRP Project 1-41 Reflection Cracking Models for Semirigid Pavement Design in AASHTOWare Pavement ME Design

Semirigid pavements are composite pavements that comprise a surface asphalt concrete (AC) layer overlying a cement stabilized base, granular subbase, and subgrade foundation. When subjected to traffic and climate loading, semirigid pavements provide good performance through resistance to rutting or deformation of base and subgrade, moisture damage, and AC fatigue. However, semirigid pavements can develop fatigue and transverse shrinkage cracks in the underlying cement stabilized base layer, which ultimately propagates through the surface AC thickness with repeated applications of axle loads and temperature cycles (i.e., reflection cracking). Although new semirigid pavements have been designed and constructed in the United States since the 1960s, a new semirigid pavement design methodology was not included in Version 1.0 of AASHTOWare Pavement ME Design software. This methodology was omitted because developers and researchers at that time concluded that there were no suitable existing mechanistic-based fatigue or transverse reflection cracking models available to be adapted and included in the design procedure. Under NCHRP Project 1-41—Models for Predicting Reflection Cracking of Hot-Mix Asphalt Overlays, mechanistic-based AC fatigue and transverse reflection cracking models were developed. The models were developed to be compatible and thus easily adaptable into the AASHTOWare Pavement ME Design framework. Work done to adapt the NCHRP Project 1-41 reflection cracking models for the design of new semirigid pavement in AASHTOWare Pavement ME Design is presented.

Influence of Layer Interface Condition on Modulus Backcalculation Results of Semi-Rigid Asphalt Pavement

To make appropriate rehabilitation decisions, determining structural layer moduli of the existing semi-rigid asphalt pavements is a crucial task for highway engineers. The objective of this study was to analyze the errors in layer moduli backcalculation due to modeling of layer interface condition. Firstly, according to the full bonding hypothesis, a dynamic finite element analysis model was established to generate a synthetic surface deflection database of the semi-rigid asphalt pavements. Then, the regression functions between deflections basin parameters and layer moduli were created and used to backcalculate layer moduli. Secondly, different friction coefficient values between asphalt layer and stabilized base layer were introduced into dynamic finite element model, accordingly, deflection basin parameters were calculated and layer moduli are determined based on the established regression functions. Finally, the backcalculated layer moduli and the original moduli values were compared. The analysis results demonstrate that assuming full bonding, instead of actual interface conditions of asphalt-stabilized base layer, moduli of stabilized base layers is underestimated, up to 2.5 times smaller than the original values. The improper interface condition of the binder-stabilized base layer has little influence on moduli of asphalt and subgrade layer.

Comprehensive Monitoring Systems for Measuring Subgrade Moisture Conditions

Subgrade resilient modulus is highly dependent on water content, which can vary significantly with a number of environmental factors. Four sites across the state of Tennessee were instrumented with comprehensive monitoring systems that collect meteorologic, subgrade water content, infiltration, and temperature data. These data will be used to develop a rational method to account for environmental effects, such as seasonal changes in subgrade water content in flexible pavement design. Multiple-segment time domain reflectometry (TDR) probes were placed horizontally in the soil subgrade, in the stone subgrade, and in the asphalt stabilized base, and single-segment probes were placed in the asphaltic concrete of the roadway sections. Tension-free pan lysimeters were installed at three of the test sites to measure infiltration through the pavement layers. Temperature sensors were installed in the soil subgrade and in the stone base at the same elevations as the TDR probes, and at three elevations in the top 200 mm of the pavement. Each site was instrumented with a weather station that monitors relative humidity, air temperature, rainfall, wind speed, and solar radiation. The preliminary data indicate changes in water content in the stone base layer that correlate with rainfall, and a small seasonal change in subgrade water content. Data from a test site where the pavement surface layer is not in place indicate that the asphaltic layers below the surface layer are permeable during significant rainfall events and that water appears to move freely through the asphalt stabilized base layer.