Abstract: This article evaluates the behaviour and environmental impact of two recycled aggregates from selected construction and demolition waste (CDW) in field conditions. For this purpose, one experimental unpaved rural road with two sections was built in 2007. Sections were formed with an excellent subgrade (A-1-b) and two structural layers: the first section consisted of a base course and a surface built using a mixed recycled aggregate and a recycled concrete aggregate, respectively, and the second section consisted of crushed limestone aggregate as a reference. The materials were previously characterised in the laboratory. Control compaction ensured that the materials were correctly set in place, and the bearing capacity of each of the fill layers was measured. The structural performance of the pavement was determined using a Falling Weight Deflectometer, and changes over time in the International Roughness Index and the bearing capacity were studied. The results show that recycled aggregates from selected CDW can be used as an alternative to natural aggregates in unpaved rural road construction without risk of environmental impact. According to technical specifications, the soluble salt content can rise to 1.3% without reducing the quality of this type of road. This study is important for increasing recycling rates and creating a market for mixed recycled aggregates in Mediterranean countries such as Spain, which has one of the lowest recycling rates in Europe.

Abstract: The need to manage construction and demolition waste (CDW) has led to environmentally-friendly actions that promote the reuse and recycling of this type of waste and other forms of waste valorization. The main priority is to foment sustainable construction work, which has the advantage of avoiding the deposit of large quantities of construction waste at landfills and greatly reducing the use of borrow material in construction projects. In this sense, the reuse of CDW materials significantly lessens the impact of construction work on the surrounding environment. The aim of this research study is to verify the technical viability of using construction waste as material for the base pavement layers of road surfaces. For this purpose, a field study was carried out, which included testing the performance of pavement composed of concrete, asphalt mix, and ceramic waste aggregate. This was done by analyzing the characteristics of the recycled material on a section of an actual road under real vehicle traffic conditions. It was observed that the load-bearing capacity of the recycled artificial CDW aggregate was satisfactory.

Abstract: The advantages of utilizing recycled materials/byproducts in pavement construction are numerous. The reduction in landfilling resulting from the adoption of recycled materials in large quanitites primarily promotes their usage. Most of the recycled materials are used successfully throughout the world as embankment fill or subgrade foundation material. Although the utilization of the recycled materials/byproducts as pavement bases has been gaining increased acceptance, comprehensive geotechnical characterization of these materials is still lacking. In a research project, Limestone quarry fines (QF), which are a residue deposit produced from limestone quarries, and reclaimed asphalt pavement (RAP) aggregates, obtained from milling existing hot-mix asphalt (HMA) pavement layers, were characterized in both laboratory and field conditions. Before the usage of these materials as pavement bases, a series of laboratory tests were conducted to verify their engineering behavior and suitability. Shear strength and consolidation tests were performed to evaluate both strength and compressibility characteristics. Repeated load triaxial tests were conducted to obtain the resilient behavior of these recycled materials. Because the QF material exhibited both low strength and low moduli, cement stabilization was performed to enhance the material properties. The treated materials were then used as bases in test sections built as a part of the state highway. These test sections were instrumented and monitored for approximately 3 years. However, the long-term performance of the new materials is crucial for highways. Henceforth, numerical simulations were performed to predict the-performance of the test sections. This paper presents a summary of test results obtained from the laboratory, field, and numerical studies, and the results were analysed to evaluate the efficacy of these materials as pavement bases.

Abstract: The objective of this research is to predict rut depth in local flexible pavements. Predication model in pavement performance is the process that used to estimate the parameter values which related to pavement structure, environmental condition and traffic loading. The different local empirical models have been used to calculate permanent deformation which include environmental and traffic conditions. Finite element analysis through ANSYS computer software is used to analyze two dimensional linear elastic plane strain problem through (Plane 82) elements. Standard Axle Load (ESAL) of 18 kip (80 kN) loading on an axle with dual set of tires, the wheel spacing is 13.5 in (343 mm) with tire contact pressure of 87 psi (0.6 MPa) is used. The pavement system is assumed to be an elastic multi-layers system with each layer being isotropic, homogeneous with specified resilient modulus and Poisson ratio. Each layer is to extend to infinity in the horizontal direction and have a finite thickness except the bottom layer. The analysis of results show that, although, the stress level decrease 14% in the leveling course and 27% in the base course, the rut depth is increased by 12 and 28% in that layers respectively because the material properties is changed.

Abstract: The objective of this project was to characterize the properties of crushed recycled concrete (RCA) and asphalt pavement (RAP) as unbound base without being stabilized, to assess how RCA and RAP behave in the field and to determine how pavements can be designed using RCA and RAP. Issues to be considered include variability in material properties, purity of material, climatic effects, how to identify and control material quality, and leaching characteristics. This project included laboratory specimen and large-scale model tests and evaluation of field data from the Minnesota Road Research facility (MnROAD) test sections constructed using recycled materials. To identify the characteristics of RAP and RCA typically available in different parts of the country, samples were obtained from eight states: California, Colorado, Michigan, Minnesota, New Jersey, Ohio, Texas, and Wisconsin covering a geographically diverse area. A conventional base course was used as a control material. The extensive investigation undertaken on RCA and RAP indicate that these materials are generally suitable for unbound base course applications and they show equal or superior performance characteristics compared to natural aggregates in terms of stiffness, freeze-thaw and wet-dry durability, and toughness. Their typical compositional and mechanical properties and their variability are defined in this study providing a basis for design considerations. Their relative differences from natural aggregate such as temperature sensitivity, plastic deformations, and water absorption and retention characteristics are also well established. It is noted that some RAP may be sensitive to temperature change that may lead to rutting. This aspect needs to be considered in design.

Abstract: The most common recycled construction materials used as unbound base course in pavement construction are recycled concrete aggregate (RCA) and recycled asphalt pavement (RAP). This study investigated the mechanical properties of RCA and RAP as unbound base, including the relationships between resilient modulus (Mr) and composition (e.g., particle shape, binder type, aggregate mineralogy, and contamination). The recycled materials were collected from a wide geographical area, covering eight states in the U.S. The Mr tests were conducted following National Cooperative Highway Research Program (NCHRP) protocol, which measures specimen deflections externally and internally. Power function and NCHRP models were applied to estimate Mr. The NCHRP model was more reliable in capturing Mr dependency on stress state in RCA and RAP. A multiple linear regression model was developed to predict the Mr of RCA (R=0.96) and RAP (R=0.97). There was a high degree of correlation between the predicted Mr and the physical properties of RCA (R=0.89) and RAP (R=0.99).

Abstract: Conventional pavements rely on stiff upper layers to spread traffic loads onto less rigid lower layers. In contrast, an inverted pavement system consists of an unbound aggregate base compacted on top of a stiff cement-treated base and covered by a relatively thin asphalt concrete layer. The unbound aggregate interlayer in an inverted pavement experiences high cyclic stresses that incite its inherently nonlinear granular media behavior. A physically sound, nonlinear elastoplastic material model is selected to capture the unbound granular base in a finite-element simulator developed to analyze the performance of inverted pavement structures. The simulation results show that an inverted pavement can deliver superior rutting resistance, as compared with a conventional flexible pavement structure with similar fatigue life.

Abstract: A full-sale test section was constructed and subjected to traffic loading at the U.S. Army Engineer Research and Development Center to evaluate the performance of a geogrid that was used for base reinforcement in a thin flexible pavement. Three test items—a geogrid-reinforced test item and two unreinforced control test items—were constructed under controlled conditions. The test pavements were subjected to accelerated traffic loading to evaluate the relative performance of the pavement structures. Pavement stiffness and permanent surface deformations were measured periodically throughout the testing. The study results showed that the geogrid-reinforced pavement performed better than the unreinforced control pavements did. The results were used to develop traffic benefit ratios and effective base course structural coefficients to enable comparison of the pavement structures.

Abstract: The use of recycled materials for construction is beneficial to both the environment and the economy. Reclaimed asphalt pavement (RAP) is one of the most commonly used recycled materials. State departments of transportation allow its use in unbound base materials at different percentages. The modulus and the permeability are recognized as important parameters for base course materials because of their effect on pavement service life. Determining the effects of the percentage of RAP on the modulus and permeability of base materials that contain RAP is important for proper pavement design. This study evaluates the effects of RAP percentage on the resilient modulus and the permeability of unbound base materials. Increasing the RAP percentage increased the resilient modulus. Constant-head permeability test results indicated that increasing the RAP percentage decreased the coefficient of permeability. High-resolution X-ray computed tomography was used to study the internal structure of the test specimens. RAP ...

Abstract: In this paper, the results of a series of cyclic plate load tests on geogrid base reinforced pavement sections were analyzed to incorporate the benefit of geogrid within the context of the new AASHTO Mechanistic-Empirical Pavement Design Guide (MEPDG). The structural contribution of geogrid reinforcement was quantified in terms of increasing the resilient modulus of base course layer and/or reducing the thickness of base aggregate layer in pavement structure. With regard to increase in resilient modulus, the effective resilient modulus of base course layer was backcalculated to account for the improvement in the performance in pavement section provided by the geogrid reinforcement. The increase in the base course resilient modulus was then quantified. The benefit of geogrid base reinforcement was also evaluated by the amount of reduction in the thickness of base aggregate layer of required performance defined in terms of Base Course Reduction (BCR) factor. The results show that the value of resilient modulus of the base course layer can be increased by 10-90 percent and that the thickness of base layer can be reduced by 12 to 49 percent for the geogrid reinforced pavement sections tested in this study. The results also indicated that the higher tensile modulus geogrids typically provide better performance.

Abstract: The objective of this study was to improve Reclaimed Asphalt Pavement (RAP) strength in base course applications while reducing creep to an acceptable level using compaction techniques, fractionating, blending with high quality base course aggregate, and/or by chemical stabilization with asphalt emulsion, Portland cement, or lime. RAP/limerock blends with and without chemical stabilization were compacted by modified Proctor, Marshall, or gyratory methods, cured, and tested for strength and creep. Strength tests included limerock bearing ratio (LBR), unconfined compression, Marshall compression, and indirect tensile tests. Strength specimens were tested dry and soaked to evaluate retained strength. Seven-day one-dimensional creep testing was performed. Gyratory compaction produced higher densities than modified Proctor or Marshall compaction. At the same density, gyratory compaction improved RAP strength by a factor of two to three over modified Proctor but had less effect on creep. Modified Proctor moisture-density plots followed an S-shape without a clear optimum; modified Proctor may not be the best method to predict RAP compaction behavior. Fractionating RAP did not improve strength or creep unless RAP was remixed to match a maximum density curve. Fractionating did not produce acceptable LBRs or creep. RAP blended with limerock, cemented coquina, or reclaimed concrete aggregates showed improved LBR and creep performance. RAP/aggregate blends have the potential to be used as Florida base course. As the amount of aggregate blended with RAP increased, LBR increased and creep decreased. Creep behavior of blends with 75% aggregate was similar to 100% aggregate. Unstabilized blends with 50% aggregate did not produce LBR values over 100. Blends of 50% RAP/50% limerock stabilized with 1% of either asphalt emulsion or cement attained soaked LBRs over 100 and acceptable creep. Blends of RAP with 75% limerock attained soaked LBRs close to 100 and low creep without any chemical stabilizer. Adding RAP to limerock blends generally increased the soaked retained strength and improved permeability compared to 100% limerock.

Abstract: Shortage of crushed rock as pavement base course for road construction and an increase in fuel cost have prompted the search for alternative materials. In this regard, improvements of the lateritic soil cement (LSC) have been investigated. Many researches have focused on study of the properties of the stabilized soil. However, more researches have to be done in order to explain how soil properties have improved. The production of crushed rock involves drilling, blasting, crushing and transportation, which are the cause of environmental problems. The objective is to use the improved lateritic soil instead of crushed rock as the base course material for highway pavement construction. In order to understand why the LSC has higher strength, microstructure of LSC composite was investigated by X-ray diffraction machine (XRD) and the Scanning Electron Microscope (SEM). The improvement of the unconfined compressive strength (UCS) of LSC composite was also evaluated. As regards the application aspect, the results show that cement mixed lateritic soils are suitable for base course construction. The investigation also shows that increase in UCS was attributed to the cement hydration within soil mass, resulting in the formation of reaction products as analyzed by XRD. It was also found that UCS was proportionally increased with the amount of the major reaction products such as calcium silicate hydrate (CSH).

Abstract: The vertical strain of an asphalt layer is essentially important when identifying rutting mechanisms or causes in asphalt pavement with a semi-rigid base course, which is a typical pavement structure in China. As a result, three directional strain measurements (longitudinal, transverse, and vertical strain) in the field, together with a pavement rutting survey and finite element simulation, were carried out in order to clarify the causes of rutting happening in Beijing heavy-duty expressways. First, the basic principal of a fiber Bragg grating sensor is explained, followed by the introduction of sensor installation in the field. Then, a three-dimensional finite element pavement model subjected to a non-uniform moving load was established to validate the dynamic response measurement on site. Finally, based on a comprehensive analysis including a pavement condition survey, numerical simulation, and strain measurement, the rutting mechanism of heavy-duty asphalt pavement in Beijing is discussed. The results show that the occurrence of shear deformation within asphalt layers results in the rutting development, in which material weakness, modulus mismatch of asphalt layers, and heavy-duty characteristics play important roles. Optimizing asphalt layers’ moduli, i.e., making them match, might make pavement bear the applied loading with integrity, thus averting the occurrence of excessive local strain, i.e., rutting.

Abstract: The invention relates to a pavement base course material prepared from brick mixed building rubbish regenerated aggregate and a construction method thereof. A regenerated inorganic binder stable material layer with the thickness of 180-800 mm is constructed above a lower bearing layer, and a road pavement layer is constructed above the regenerated inorganic binder stable material layer; the regenerated inorganic binder stable material layer is formed by mixing brick mixed building rubbish regenerated aggregate grains and common aggregate and base gelation power and is divided into one layer to four layers, and every small layer selects one of three mixture ratios. The invention adopts the brick mixed building rubbish regenerated aggregate as a main raw material. By applying the brick mixed building rubbish regenerated aggregate to pavement materials, the invention solves the problems of low utilization rate, narrow range of application, small application quantity and the like of the brick mixed building rubbish. The application performance of the pavement base course material not only can meet the prior standard and the practical application condition requirement of engineering, but also has relatively better durability and mechanical property by test comparison of freeze thawing, strength and the like.

Abstract: Challenges in finding high-quality sources of natural aggregate have led Saskatchewan, Canada, road agencies to explore alternative solutions to meet aggregate demands. The use of recycled materials, such as recycled portland cement concrete (PCC), though traditionally limited to low-quality applications such as subbase or backfill materials, shows promise as a technically viable solution that also offers economic and environmental advantages. In this study, mechanistic material testing was used to examine the effects of cement stabilization on traditional granular base and on two impact-crushed recycled PCC materials from different locations. The unstabilized PCC materials had substantially better mechanistic material properties than the unstabilized conventional granular base material; this result indicates that PCC materials could be suitable for use in high-quality applications, such as base course layers, rather than being limited to use in low-quality applications, such as utility and embankment fil...

Abstract: The objective of this study was to conduct a sensitivity analysis to identify the input parameters with the greatest effects on the predicted pavement performance from the Mechanistic-Empirical Pavement Design Guide (MEPDG). Three levels of analysis (low, medium, and high) with five input parameters (traffic level, hot-mix asphalt (HMA) thickness, E*, base course thickness, and subgrade type) were evaluated through a full factorial design. The main influence of each individual input parameter and the combinational interaction effects of the input parameters on the predicted distress response were quantified. It was determined that the traffic level input parameter was the main effect on all predicted pavement distresses in the MEPDG. The second main effect for international roughness index (IRI), fatigue cracking, and total pavement rutting was HMA thickness. For asphalt concrete (AC) rutting, the mixture dynamic modulus ranked second for the main effect followed by HMA thickness. For top-down cracking, it was observed that the base course thickness ranked second for the main effect followed by the HMA dynamic modulus. The influence of base thickness on top-down cracking was not expected but it may be due that the MEPDG adopted a traditional fatigue cracking model to describe this failure mechanism.

Abstract: The performance of typical thin flexible pavement systems depends on the quality of the granular base course. The granular base is responsible for mitigating strains on the subgrade, preventing fines pumping, and managing drainage. Field conditions including high water tables, increased precipitation, and poor subgrade conditions often lead to water pumping and fines migration into granular bases in urban areas. Furthermore, current construction practices favor the use of granular base materials with fines contents at the high end of the base course specifications, as higher fines base courses are thought to be more easily compacted. Additionally, the use of recycled materials is becoming more common, with the natural aggregate source depletion and waste reduction measures in many urban areas. This study examined the effects of increasing fines contents on a conventional City of Saskatoon (COS) granular base material as well as an impact-crushed recycled Portland cement concrete (PCC) aggregate. Gyratory compaction and rapid triaxial frequency sweep characterization were performed on samples with varying fines contents. The results of this study showed that increasing the fines content of the conventional COS granular base improved its compactibility. However, increasing the fines content of the PCC granular base material did not offer substantial improvements in compaction behavior. The mechanistic material results showed that the increased fines contents lessened the mechanistic material stiffness properties of both materials, although the effects of increased fines were often less pronounced with the PCC material.

Abstract: G1 Crushed Stone for base course is not the same thing as crusher-run and it is not only a matter of density. It was developed during the late 1950’s from single stage crusher-run material that complies with Fuller curve particle grading and very strict material and construction specifications. Closure on this development and its capabilities was achieved during the South African Heavy Vehicle Simulator (HVS) test program during the 1980’s, resulting in the conclusive proof that a properly constructed G1 Crushed Stone layer can be used for pavements with a bearing capacity up to 50 million standard axles (MISA) repetitions. This discussion sketches this development but concerns itself mainly with the slush-compaction construction process of a G1 layer and those aspects which directly monitor its success. 1. INTRODUCTION G1 Crushed Stone for base course is not the same thing as crusher-run, and it is not just a matter of density that makes the difference. G1 Crushed Stone was developed from single stage crusher-run material when during the late 1950’s some observant Engineers noticed that this material would sometimes, after a sudden downpour and towards the end of its compaction cycle, exhibit the tendency to expel some of its fines (minus 0.075mm material), resulting in the aggregate “locking up” into a hitherto unknown tightly knit matrix, instead of becoming unstable as do other gravels under similar circumstances. This phenomenon was investigated and the results and conclusions applied to various experimental test sections until it could be controllably replicated. Refer to Figures 1 and 2 for schematic illustrations of the evolution of G1 and the impact this has had on the road infrastructure industry (Jooste and Sampson, 2005) Closure on this development and its capabilities was achieved during the South African Heavy Vehicle Simulator (HVS) test program during the 1980’s by using in-service G1 base course roads. The conclusion was that a properly done Crushed Stone layer could be used for pavements with a bearing capacity of up to 50 million standard axles (MISA) repetitions. It is exceptionally water resistant and the only unbound road building material found to increase in bearing capacity (“make muscle”) to accommodate any increase in loading up to the point of rupture of the aggregate itself, without noticeable traffic moulding. However, this comes at a premium – it has to be produced and constructed to very tight specifications. Note that, while there are a number of aspects important to successful G1 Crushed Stone application, such as pavement composition, construction, maintenance and rehabilitation, this discussion will concern itself mainly with the construction process of a G1 layer and those aspects which directly monitor its success.

Abstract: A large-scale recycling and reuse application of scrap shingles would utilize an otherwise wasted resource while clearing landfill space and creating new business opportunities. One potential reuse application is the use of reclaimed asphalt shingles (RAS) as an additive or substitute for the earth materials typically used in the aggregate base (AB) and subbase (ASB) layers of roadway pavements. The purpose of this study was to determine the technical specifications of RAS, the effect of fly ash stabilization on RAS strength, and the practicality of the widespread implementation of RAS in the AB and ASB layers of roadway pavements. RAS, fly ash stabilized RAS (S-RAS), RAS-aggregate mixtures, and RAS-silt mixtures were evaluated for particle size characteristics, compaction characteristics, CA Bearing Ratio (CBR), unconfined compressive strength, and resilient modulus. According to the results of the testing protocol, unstabilized RAS is unsuitable as base material although RAS could potentially be used as subbase or general fill material. RAS-aggregate mixtures are suitable for use as subbase and are potentially suitable as base course in an unstabilized state; however, RAS-aggregate mixtures exhibited decreasing resilient modulus with increasing RAS content. Fly ash stabilized RAS (S-RAS) was less susceptible to penetrative deformation than unstabilized RAS, however, S-RAS was still highly susceptible to penetrative deformation when unpaved. Fly ash stabilization of RAS generally provided less improvement in resilient modulus compared to fly ash stabilized low-plasticity clays. This may be due to the high asphalt content of RAS particles and resulting diminishment in pozzolanic activity and/or the diminished particle interconnectedness for cementation. Other forms of stabilization, such as cold asphalt emulsion, may be more effective in strengthening RAS. Further evaluation of alternative stabilization methods and additional studies to evaluate the practicality of RAS in other geotechnical applications such as embankment fill, filter, and/or drainage material are recommended.

Abstract: The Giroud-Han (G-H) design method provides a design tool that is used to determine the thicknesses of unreinforced and geosynthetic-reinforced aggregate bases for unpaved roads over soft subgrade. Unpaved roads typically consist of an aggregate layer (often called base course) resting on the subgrade. When a geosynthetic is used in an unpaved road, it is generally placed at the base/subgrade interface. The use of geosynthetics in unpaved roads is a mechanical stabilization technique that is different from chemical stabilization. In mechanical stabilization, the base is improved via the inclusion of a geosynthetic layer (or layers) and the aggregate remains unbound. Chemical stabilization involves inclusion of chemicals (e.g., lime, cement, binders) to bind aggregate materials or the subgrade soils. It is important to distinguish between aggregate that is bound (as a result of chemical stabilization) and aggregate that is unbound. In this article, only unpaved roads constructed with unbound aggregate are considered. These roads can be either unreinforced or reinforced using geosynthetics. The term reinforced is equivalent to mechanically stabilized throughout this article. The use of the terms reinforced and reinforcement in the context of unpaved roads does not imply that the geosynthetic simply adds force (i.e., simply adds its strength) to the unpaved road structure. A geosynthetic improves an unpaved road through complex mechanisms that mostly do not involve the strength of the geosynthetic per se. The basic equation developed in this article for the required thickness of unreinforced and/or geosynthetic-reinforced bases is generic. Therefore, this equation can be used for unpaved roads reinforced with any type of geosynthetic, provided it is calibrated for the specific type of geosynthetic considered. This article has discussed the calibration of the G-H method in detail. In particular, it has been indicated that the aperture stability modulus, which is an appropriate property to calibrate the G-H method for some specific biaxial geogrids, may not be appropriate for other types of geogrids.

Abstract: This paper examines the effects of freezing and thawing on the mechanical behavior of granular base under unsaturated conditions through the long-term field measurement and falling weight deflectometers (FWD) tests for pavement structure subjected to freeze-thaw actions, and by performing California bearing ratio (CBR) tests for freeze-thawed base course material using a newly developed test apparatus. The authors also evaluate the influences of the change in the bearing capacity of granular base due to freeze-thawing on the fatigue life of pavement structures by applying the theoretical design method for pavement structures in consideration of the effects found in the above-mentioned experiments. As the results, it was revealed that the bearing capacity of granular base increases in freezing season and decreases due to increment of the water content in thawing season. This indicates that the freeze-thaw of granular base has a strong influence on the fatigue life of pavement structure in cold regions.

Abstract: Cracking deterioration was observed on a motorway after only few years after construction. The motorway pavement was semi-rigid with a relatively thin thickness: 4 cm wearing layer, 11 cm asphalt base course, 20 cm lean concrete base course, 20 cm cement stabilized base course, 20 cm drainage layer, subgrade. lean concrete base course was cut in spacing 2,5 m to reduce the reflective cracking in asphalt layers. Testing program included: coring and materials composition testing, FWD testing to evaluate pavement layers stiffness modulus, radar testing to measure layer thickness, and to detect water presence in pavement layers, evaluation of cracks type and spacing, interlayer bond testing, low temperature resistance of asphalt wearing course. Testing results led to following conclusions: extremely low winter temperature in combination with relatively thin pavements thickness and semi-rigid pavement type was the reason of transverse cracking, longitudinal cracking observed on one of the sections were evaluated as top-down fatigue type cracking, low interlayer bond between asphalt base layers was one of the main reason of lower fatigue resistance of the pavement, lack of drainage in motorway median caused the presence of water in the pavement layers, and increased the danger of premature pavement deterioration, unpredicted increase in road traffic caused longitudinal top-down fatigue cracking.

Abstract: BCS is short for blended calcium sulfate, a recycled fluorogypsum mixture that has been used in Louisiana as a roadway base for more than a decade. Without further chemical stabilization, the major concern of using raw BCS as a pavement structural layer is its moisture susceptibility. In order to verify the efficiency of laboratory-derived BCS stabilization schemes and further assess related field performance and potential cost benefits, an accelerated pavement testing (APT) experiment was recently conducted at Louisiana Transportation Research Center (LTRC) using the Accelerated Loading Facility (ALF). The APT experiment included three different base test sections: the first one contained a granulated ground blast furnace slag stabilized BCS base course (called BCS/Slag), the second used a fly ash stabilized BCS base course (called BCS/Flyash), and the third had a crushed limestone base. Except for using different base materials, the three APT sections shared a common pavement structure: a 2-in. asphalt wearing course, an 8.5-in. base course, and a 12-in. lime-treated working table layer over an A-6 soil subgrade. Each section was instrumented with one multi-depth deflectometer and two pressure cells for measuring ALF moving load induced pavement responses (i.e., deflections and vertical stresses). The instrumentation data were collected at approximately every 8,500 ALF load repetitions; whereas, non-destructive deflection tests and surface distress surveys (for surface rutting and cracking) were performed at every 25,000 ALF load passes. The accelerated loading results generally indicated that the test section with a BCS/Slag base course outperformed the other two APT sections (i.e., the BCS/Flyash and the crushed stone sections) by a large margin. This was evidenced by all measurements in surface deflection, vertical compressive stress, rutting resistance, and pavement life. Post-mortem trench results revealed that the BCS/Slag base performed just like a lean concrete layer inside the pavement without any moisture-induced damage issues. The backcalculated layer moduli of the BCS/Slag base ranged from 1,190 ksi to 2,730 ksi, much higher than that of an asphalt concrete layer. In addition, the BCS/Flyash test section performed significantly better than the crushed stone test section in terms of the load carrying capacity, rutting resistance, and pavement life. However, post-mortem trench results showed a shear failure initialized inside the BCS/Flyash base layer on a failed station of the corresponding test section. Whether or not such a shear failure is indicative of a long-term moisture susceptibility problem for the BCS/Flyash base layer, especially under a constantly wet environment, remains a concern due to the relatively short loading period associated with any APT experiment. Based on APT results, it was estimated that structural layer coefficients for the BCS/Slag and BCS/Flyash base courses used in this APT study would be 0.34 and 0.29, respectively. A cost-benefit analysis showed that the implementation of a slag stabilized BCS base in lieu of a crushed stone base will lead to a thinner asphalt pavement design, which can result in an initial construction cost reduction up to 16 percent without compromising future pavement performance. On the other hand, a 30-year life cycle cost analysis (LCCA) based on a typical Louisiana low volume road pavement structure indicated that using an 8.5-in. slag stabilized or 8.5-in. fly ash stabilized BCS base course, in lieu of a 8.5-in. crushed stone base, will potentially result in an LCCA cost savings up to 62 percent and 56 percent per lane mile, respectively. Overall, it is concluded that both the slag and fly ash stabilized BCS materials evaluated in the study should be a good base material candidate for a flexible pavement design in Louisiana. However, caution should be made when using a fly ash stabilized BCS base under a constantly wet environment.

Abstract: According to actual axle load data and the measured mechanical parameters of cement stabilized macadam material with different cement dosages, the bottom tensile stresses of different subbase structures are calculated and the results show that: to graded gravel subbase, the weight of construction vehicle is inadvisable to be more than 35t and the cement dosage of base course shall be more than 3.0%; and, the maximum bottom tensile stress of graded gravel subbase shall be much more than that of lime-flyash soil subbase. According to the measured dry shrinkage strain and dry shrinkage coefficient, the dry shrinkage crack space of base course is analyzed and the results show that: under the same cement dosage, the crack space of the base course with graded gravel subbase is smaller than that of lime-flyash soil subbase; with the increase of cement dosage, the crack space of base course increase first and then decrease, and when the cement dosage is 3.5%, the dry shrinkage strain and dry shrinkage coefficient is minimum and the crack space of base course is maximum.

Abstract: Contractors are looking for ways to incorporate sustainable business practices into their daily operations that reduce cost. Diverting waste from the landfill is one way that contractors can reduce the environmental impact of construction. Construction is the largest contributor to landfill waste and concrete accounts for a significant portion of that waste. In turn, concrete waste can easily be recycled and reused as aggregate base course under roadway pavements and building slabs. Using recycled concrete in this manner reduces the environmental impact of construction by diverting waste and limiting the amount of virgin aggregate required for construction. Since aggregate is a finite resource, recycling and using recycled concrete limits the quantity of natural resources needed to support construction activity. This research identified barriers and drivers associated with recycling concrete and using the recycled material in new construction in the Phoenix metropolitan area. Data was collected through interviews with general contractors, demolition contractors, concrete recyclers, and engineers, as well as observation of jobsite activities. The results of this research revealed that the infrastructure for recycling and reusing concrete material is in place but there is a need to establish that recycled concrete is an acceptable material for use as base material in the Phoenix area, and there is a need for education and awareness among the stakeholders. Factors impacting the decision to recycle versus sending concrete debris to a landfill were not cost and proximity as expected but were the result of existing relationships contractors have with disposal locations. The factors impacting whether or not to utilize recycled material were lack of enabling standard specifications, perception of risk, and the regulatory environment of the municipality where the construction takes place.

Abstract: Geosynthetic-reinforced base course is potentially a cost-effective solution for flexible pavement construction. With the recent advance in the mechanistic-empirical pavement design in the United States, there is a need to develop the next generation design method for geosynthetic-reinforced bases in flexible pavements. To develop such a design method requires an improved understanding about the mechanistic behavior, especially the in-plane elastic behavior, of geosynthetics. In this paper, the geometry effect of geosynthetics was discussed. The author first reviewed recent experimental and numerical studies. Analytical equations based on cellular material mechanics were presented for determining the in-plane elastic properties of geosynthetics. The analytical equations were used to evaluate a few geosynthetics with typical geometries. The results showed that, with the same polymeric material and typical product geometries, the geocell has a better confinement effect than geogrids, and the triaxial geogrid with a triangular aperture has a better confinement effect than the biaxial geogrid with a rectangular aperture. It was also demonstrated that the traditional uniaxial tensile modulus may be a poor indicator of the effectiveness of geosynthetics for base course reinforcements.

Abstract: Roller compacted concrete is a zero-slump concrete, low water content, dense mix consisting of coarse aggregate, sand, cementitious materials, and water. By using conventional vibrators, it is very difficult to compact for larger thicknesses. There is a chance of getting honey combing and inconsistency with respect to laboratory values. To rectify this, roller compacted concrete technique is proposed by preparation of samples. In this an attempt is made to prepare M15 and M20 mixes at their optimum moisture content and tested for compressive and split tensile strengths for various time periods (i.e., 3days, 7days, 14 days and 28 days). From these results, it is observed that higher strengths at early periods are obtained. When cylinders were tested, the compressive strength for M15 and M20 mixes at 28 days are 25Mpa and 31Mpa respectively. Similarly, for M15 and M20 mixes at 28 days, the split tensile strengths are 1.7Mpa and 1.9Mpa respectively. Since high strengths are obtained in compression and tension, it can be used as base course and sub-base course for flexible and rigid pavements.

Abstract: The current American Association of State Highway and Transportation Officials standard on crushed concrete in base applications (M 319-02) allows up to 5 % brick by mass, and more with the approval of the engineer; however, in some regions the brick content may be greater than 10 %. More than 41 states allow the use of crushed concrete in highway applications, but only a handful allow the use of building derived concrete (BDC) or mixed stream crushed concrete. Barriers to increasing the appropriate use of BDC in highway applications include a lack of data comparing BDC properties and performance to natural aggregates, as well as data that pavement engineers can use for design. This research has focused on characterizing BDC that was screened to meet New Hampshire Department of Transportation specifications. The gradation, optimum water content, unit weight, and resilient modulus were measured for the BDC and for the control materials, which were a crushed stone and a sand. The resilient modulus was measured using both a laboratory triaxial cell, and a light falling weight deflectometer (LWD) in a test pit. The resilient modulus of the BDC exceeded that of the control materials as measured in the laboratory and using the LWD. In addition, the laboratory resilient modulus showed good correlation with the LWD stiffness. These results suggest that BDC would perform as well as natural aggregates in base course applications.