Airfield and Highway Pavements 2017: Testing and Characterization of Bound and Unbound Pavement Materials

The premature cracking of the asphalt concrete (AC) layer in flexible pavements highlights the importance of a simple cracking performance test that can be used for routine applications during the design process of AC mixes. The overlay tester (OT) can be used to evaluate the formation and propagation of a crack within the AC specimens. This paper explains an alternative methodology for assessing the cracking potential of AC mixes using the OT test. The proposed methodology consists of two main stages: crack initiation and propagation. The fracture properties of the AC specimens are estimated from the critical fracture energy computed from the first OT loading cycle. The resistance of the AC mix to crack propagation is estimated from the crack progression rate, the rate of reduction in load carrying capacity of the AC specimen with the number of cycles. The process of selecting the limits for the critical fracture energy and crack progression rate to delineate the well and poor performing mixes is discussed here. The proposed cracking methodology and acceptance limits may provide a more comprehensive approach to predict and design the cracking potential of AC mixes.

Permanent shear deformation is the main cause for rutting in asphalt concrete layers. The paper presents the development of a new test device to replicate similar loading conditions and constraints of the superpave shear tester (SST). The duplicate shear tester (DST) determines the mechanical average of the shear properties and responses of two specimens loaded simultaneously. The DST device is simple and inexpensive and can be used with any universal testing machine that can provide repeated dynamic and static axial loads in a temperature-controlled environment. The two most used SST tests, the frequency sweep test at constant height (FSCH) and the repeated shear test at constant height (RSCH) were performed with the DST device mounted inside of a UTM-25 test system.

In uniaxial fatigue testing, breaks near the loading platen away from the middle of the sample are still common despite different proposed solutions to avoid them. This paper presents finite element results used to develop dog-bone shape specimens for uniaxial tensile testing. A configuration was selected such that in the middle of the sample the strain distribution is substantially more uniform than those obtained with traditional cylindrical samples, and the maximum strain occurs in the middle of the sample instead of near the plate. The trimming procedure, challenges faced to avoid end failures, and the restoration of a smooth dog-bone shape of trimmed samples with epoxy are also explained. The simulation results were validated by testing eight specimens of four different mixes using a stress controlled tensile repeated load-recovery tests performed at 40°C. All the trimmed-epoxy smoothed samples tested broke consistently in the middle, thus validating the selected design.

Micro cracks healing property of asphalt concrete is considered as start for understanding its elastic behaviour. However, the impact of repeated micro crack healing cycles on deformation has not been investigated thoroughly. An attempt has been taken in this work to investigate the crack healing cycle’s phenomena on specimens of 100 mm diameter and 63 mm height, prepared using Marshall Method. Specimens were divided into two sets. The first set was subjected to repeated indirect tensile stresses, while the second set was subjected to the repeated double punch shear stresses (both at 25°C) to initiate micro cracks within the specimens using controlled stress mode of loading. After controlled number of stress application, Specimens were subjected to external heating in an oven at 60°C and allowed to heal for two hours, conditioned, then subjected to another two courses of repeated stresses and healing. The permanent deformation of the specimens was monitored through continuous video capture in the pneumatic repeated load system (PRLS). The impact of asphalt content, type of test, and healing cycles on the permanent deformation have been analysed.

Hot-in-place recycling (HIR) is an in-situ process that preserves asphalt pavements while minimizing use of virgin binder and aggregates. HIR mixture requires asphalt binder modification, which is commonly achieved by adding an asphalt rejuvenating agent (ARA) to the mixture. However, ARA potentially adversely affects rutting resistance of the final surface. The objective of this research was to investigate the effects of rejuvenation on HIR permanent deformation by conducting Hamburg wheel-tracking device and dynamic modulus tests. The samples were collected from three different HIR projects in KS and the test results showed that although the addition of ARA has a slight softening effect on HIR mixture performance, HIR mixtures with ARA could certainly meet the Kansas Department of Transportation permanent deformation requirement.

Long life asphalt pavement, also known as “Perpetual Pavement”, is a pavement with design life more than 50 years and needs only periodic surface renewal. It works on the concept of controlling horizontal tensile strain at the bottom of the asphalt layer and vertical compressive strain at the top of the subgrade to a particular limit. This can be achieved by increasing the binder content of the mix over the optimum binder content (OBC) and by increasing the overall pavement thickness. In the present study two Superpave mixes were prepared using conventional binder at OBC (optimum binder mixture [OBM]) and also at 0.5 % extra binder over OBC (rich binder mixture [RBM]) which can be used in Perpetual Pavements. The mixes were tested for indirect tensile (IDT) strength, moisture susceptibility, fatigue and rutting resistance. From the results it was observed that, OBM performed well as compared to RBM. However the fatigue life of RBM was more compared to the OBM and this helps in reducing the horizontal tensile strain at the bottom of the asphalt layer which in turn increases the life of the pavement.

In this study, five CCPs (coal combustion products) are used in asphalt mixtures such that 10% of the asphalt binder is replaced with the CCP without changing the mix design. The study used laboratory testing to monitor any change in performance compared to a control blend. Testing focused on aging related distresses, such as fatigue, and low temperature performance. Mixture samples are exposed to long term aging before conducting the performance related tests. The results show that mixture volumeetrics, mechanical performance, and aging related performance show significant improvement when 10% of the binder is replaced by the CCPS. Statistical analysis show that the improved performance is correlated to the CCP physiochemical properties.

The use of recycled asphalt pavement (RAP) has significantly increased in construction and rehabilitation of flexible pavements to ensure proper utilization of limited natural resources and for environmental benefits. Performance measures of asphalt pavement like cracking and rutting resistance under repetitive traffic and environment induced load are important criteria to assess the viability of the use of RAP in hot-mix asphalt (HMA). This research was conducted to evaluate the effect of RAP on cracking and rutting resistance of HMA mixes. Three different mixtures, Control (0% RAP), 20% RAP, and 24% RAP mixtures were considered for the study. Nominal maximum aggregate size (NMAS) used for all mixes was 12.5 mm. Eight specimens (150 mm diameter and 75 mm high each) were compacted at a target 7% air void content using gyratory compactor. Six of the specimens were tested with the asphalt pavement analyzer (APA) to determine their rutting resistance. While other two specimens were tested using disc-shaped compact tension (DCT) to determine the cracking resistance at 10°C higher than low-temperature grade of the binder in the mixes. The cracking resistance was evaluated in terms of fracture energy. The results showed that mixes with RAP performed better than virgin mixes in terms of rutting and worse in terms of cracking resistance. 20% RAP, not 24% RAP mix was the most rut resistant mix.

The rutting susceptibility of asphalt mixes containing high amounts of reclaimed asphalt pavement (RAP) was evaluated through a laboratory testing program. A commonly used PG 64-22 asphalt binder, RAP, aggregates and mix design sheets required for the production of an asphalt mix with a nominal maximum aggregate size of 19 mm containing 35% RAP were collected from a local asphalt plant in Oklahoma. The rutting susceptibility of the laboratory-produced asphalt mix was determined using the Hamburg Wheel Tracking test. The asphalt mix with 35% RAP content was found to exhibit satisfactory rutting resistance. Also, asphalt binder was extracted from the collected RAP and blended with the PG 64-22 binder at a rate of 40% by the weight of binder. The rheological characterization of the asphalt binders was conducted using multiple stress creep and recovery (MSCR) and Superpave methods. The continuous high temperature PG grade of asphalt binder was found to increase and the non-recoverable creep compliance (J_nr) value was found to decrease with the addition of RAP binder to the neat binder. The findings of this study are expected to help pavement engineers in Oklahoma to understand the performance properties of asphalt mix with high RAP content.

Curing of emulsion in cold recycling process is one of the important factors affecting performance of the recycled mix. In the study here, the effect of curing time and temperature on emulsified RAP cold mixes is evaluated using ultrasonic pulse velocity (UPV) test. The UPV test was also employed to evaluate its effectiveness in discerning rutting potential of the mixes. A series of 100% cold milled RAP mixes were prepared with conventional emulsion and polymer modified emulsion, with and without treatment with 1% cement. The specimens were tested with UPV at curing temperatures at a defined set time intervals, up to 14 days after compaction. The rutting potential of the specimens cured for three days was evaluated using the Superpave Shear Tester. Results indicate that the UPV test is able to discern and capture expected stiffness trend among the mixes with variations in temperature and curing time. Results also indicate that the UPV test, as a simple and quick method, has the ability to properly rank the rutting potential of cold mixes.

The use of reclaimed asphalt pavement (RAP) has become relatively common practice in all over the world because it is an environmentally and economically attractive proposition. The primary reason for limited use is the uncertainty and variability of the RAP material performance. Understanding the response of RAP source and its variability are important to the selection of virgin and RAP material. Five different percentages (0, 15, 25, 35, and 40%) of RAP included asphalt concrete (AC) were designed to compare the effects of two RAP source on hot mix asphalt (HMA). Gradation of all the HMA were remained fixed and checked for volumetric requirements. To assess the effect of RAP source on AC, the samples were tested for dynamic modulus characterization, rutting characterization and beam fatigue characterization. Results show RAP in HMA material increases the complex modulus of all the samples irrespective of RAP sources. In addition, rutting resistance of the material increases with increase in RAP percentage in HMA. However, high RAP in HMA materials show lower fatigue life compared to low percentage RAP in HMA.

This study serves as proof of concept for using mixture micro indentation and relaxation (MIR) and possible means of capturing mastic rheological properties in place without binder extraction and recovery. This is achieved via analysis of stress relaxation behavior of samples under constant indentation depth on laboratory fabricated mixture samples. For laboratory compacted samples, indentation is applied on mastic within the mix in the radial direction to explore the aging gradient. The results show significant difference in stiffness of mastic depending on location from the surface. Air content in the mix also appears to be a key factor influencing aging diffusion. The results prove the ability of this testing approach to capture rheological properties of asphalt binders within the mix directly. Testing mastic samples in the laboratory using dynamic shear rheometer (DSR) was conducted to validate the results obtained from the mixture samples. The significant contribution of this study is that it provides direct testing of the material rather than rely on chemical extraction and recovery.

This study evaluates changes in viscoelastic properties of asphalt concrete and its binder due to aging. In essence, field collected asphalt mixes were used to prepare cylindrical asphalt concrete specimens using a Superpave gyratory compactor and were subjected to five different aging levels: unaged, Level 1, Level 2, Level 3, and Level 4. Next, the aged samples were tested for viscoelastic material functions such as complex modulus, relaxation modulus, and creep compliance in the laboratory. Using the test data, mastercurves of related viscoelastic material functions were determined. Results show that aging affects these viscoelastic materials functions significantly. In addition, liquid asphalt binders corresponding to the asphalt mixtures were tested for complex shear modulus using dynamic shear rheometer. It is shown that aging affects binder’s shear modulus and viscosity significantly. Toward the end, contribution of binder aging to the overall aging of AC is assessed.

Proper characterization of asphalt concrete mixtures with respect to the changes in dynamic modulus (DM) with the applied loading frequency and test temperature is a key task for pavement structural design. This phenomenon is generally described through the use of a modulus master curve, which is an important input for mechanistic empirical pavement design tools. In the current abbreviated DM testing protocol, given in AASHTO TP-79-09, the limiting maximum modulus value, estimated through Hirsch model, is used to constrain the upper portion of the modulus master curve function. However, the predicted modulus values of higher shelf region can become an artifact of the presumed upper asymptote due to any inaccuracies in estimation of the limiting maximum modulus value. In this study, DM tests were coupled with a series of ultrasonic pulse velocity (UPV) tests to investigate the validity of the current limiting maximum modulus assumption. Three hot mix asphalt mixtures prepared using different binder performance grades, i.e. 52-28, 64-22, and 76-16, were investigated. Experimental program consisted of DM and UPV testing of the specimens at 4, 10, 25, and 40°C along with a series of additional UPV tests at -10°C. Polynomial shift factor function was used to construct the modulus master curves. It was concluded that the Hirsch model can result in underpredicting the actual limiting maximum modulus. Results indicate the potential advantages of using higher frequency-range nondestructive tests along with the conventional modulus tests to improve the prediction accuracy of higher shelf of modulus master curve.

Viscoelastic material functions such as time-dependent relaxation modulus or creep compliance, and frequency-dependent complex modulus can be used to characterize the linear viscoelastic behavior of asphalt concrete in advanced modeling and pavement design. Among these, complex or dynamic modulus has been adopted in the new mechanistic-empirical (M-E) pavement design method. In this study, a procedure is documented to interconvert one material function from another. In essence, cylindrical AC specimens were tested for complex modulus as a function of loading frequency and temperature and hence, the time-temperature superposition principle was used to generate mastercurve. The complex modulus function is then converted to relaxation modulus and creep compliance by a numerical method. These converted material functions were then compared to the tested material functions. A good agreement was found between the measured and the converted material functions. The mastercurves were used to study aging in asphalt concrete sample. It is shown that various linear viscoelastic material functions of aged asphalt concrete sample vary significantly from those of unaged sample.

In recent years, the use of additional binder parameters such as ΔT_c and the Glover-Rowe parameter have been used to assess the propensity for a binder to show early life durability, non-load associated and thermal cracking. This paper will provide a background on how these parameters were developed based on studies conducted on materials from Newark Airport and others. The inter-relationship that these parameters have with other binder tests and mixture tests will be given. In particular, the parameters used for assessment of mixture master curves can be shown to be related to the binder parameters (R-value, cross-over frequency and temperature susceptibility) as determined by the Christensen Anderson model will be explained using various samples of both binder and mix. The importance for pavement design of binder selection and concepts regarding application of rejuvenating oils to restore properties have also been evaluated using this approach and will be presented in the paper.

Among different warm mix asphalt (WMA) technologies, chemical WMA additives are being widely used by the asphalt industry. In the present study, the effect of using two different types of chemical additives, referred to as CHM1 and CHM2, on the performance grade (PG) and moisture-induced damage potential of a PG 58-28 asphalt binder was evaluated. For this purpose, the asphalt binder was modified by adding 0.5% of CHM1 and CHM2. The dynamic shear rheometer, rotational viscometer and bending beam rheometer tests were conducted on binder blends to determine their PG and dynamic viscosity. The surface free energy (SFE) parameters of the binder blends were also determined in order to evaluate their moisture-induced damage potential with limestone and granite aggregates. Test results indicated that adding chemical additives to the asphalt binder did not significantly affect the high-temperature PG grade and dynamic viscosity of the asphalt binder. While the use of the chemical additives did not alter the PG grade of the asphalt binder, an increase of 3°C was observed in the low-temperature continuous grade of the binder blended with both additives. Based on the SFE results, it was found that binder blends without any additive and those containing CHM1 and CHM2 showed higher adhesion with granite aggregate than limestone aggregate. Therefore, it is expected that the asphalt mixes containing granite aggregate may exhibit a higher resistance to the moisture-induced damage potential than the one containing limestone aggregate.

Hot in-place recycling (HIR) preserves distressed asphalt pavements while minimizing use of virgin binder and aggregates. The final quality of an HIR mixture depends on characteristics of the original binder, aging of the pavement surface during service, and whether or not new binder or rejuvenator was added to the mixture. An HIR mixture should maintain desired properties for additional service periods, making asphalt binder modification inevitable. Asphalt binder modifications in HIR are commonly done by adding an asphalt rejuvenating agent (ARA). However, ARA may adversely affect the qualities of new HIR and potentially fail to improve the quality of the final surface. The objective of this research was to investigate the effects of rejuvenation on HIR performance by assessing critical performance indicators such as cracking resistance, moisture susceptibility, and low temperature cracking. An experimental program was designed that included mechanical property measurements of the HIR mixture by conducting Texas overlay, thermal stress restrained specimen, and moisture susceptibility tests. HIR Samples were obtained from three Kansas Department of Transportation projects and tests were conducted on HIR mixtures with and without ARA. Study results showed significant variability in the mechanical performance of HIR mixtures, which was attributed to the variability of binders.

This study proposes new regression-based predictive models to estimate dynamic modulus and phase angle of asphalt concrete from the dynamic shear modulus and phase angle of the asphalt binder used in the asphalt mixture. Other parameters related to the aggregate gradation and mixture volumetric are also incorporated in these models. A total of 10 asphalt concrete mixes with 4 asphalt binders having different performance grades and sources were used in this study. The loose asphalt-aggregate mixtures were compacted and cored to cylindrical specimens. Three cylindrical specimens from each of the asphalt-aggregate mixtures were prepared and tested in the laboratory for dynamic modulus and phase angle at different test temperatures and loading frequencies. For all the test specimens, dynamic modulus and phase angle mastercurves at 70°F reference temperature were generated by applying time-temperature superposition principle. The collected binders were tested for dynamic shear modulus and binder phase angle using dynamic shear rheometer. Also for the binder, the dynamic shear modulus and phase angle mastercurves were generated by applying time-temperature superposition principle. Non-linear optimization process was used to evaluate the model parameters. Statistical analysis showed that a fairly accurate estimation of dynamic modulus as well as phase angle of asphalt concrete as a function of temperature and loading frequency can be found by using these new predictive models.

The production of bitumen in Indian refineries is carried out by air blowing and component blending. In the component blending process, a highly viscous propane deasphalted (PDA) pitch is blended with a less viscous flux. The choice of the proportion of these two components is normally arrived at to meet the required technical specification such as penetration at 25°C and viscosity at 60 and 135°C. However, it is not clear at this point in time, the influence of constituent materials on the rheological response of the binder. In this investigation, two ratios of PDA pitch and Flux (75:25, 80:20) were blended in the laboratory. The rheological characterization of constituents and the final blend were carried out using a rotational viscometer at temperatures of 120, 140 and 160°C. Four viscosity mixing ‘rules’ were used to estimate the final blend viscosity from the individual constituent viscosities. The predictions varied with a wide range of errors.

Till now, the Iraqi specifications for asphalt binders depend on two methods for asphalt grading system, either based on penetration or viscosity. To overcome this shortage, the Super-pave method was invented in USA. The method evaluates asphalt binders through performance grade and this method is used in this research to reach the desired goals. Samples of asphalt with penetration grades of (40-50) and (60-70) were taken from three (3) different refineries, being equivalent to PG (70-28), PG (70-22) and PG (64-22). In this research, Polymer modification technique were used to achieve the required performance grade depending on different four (4) zones of PG in Kurdistan Region of Iraq, namely; {(64-22), (64-16), (70-10) and (76-10)}, to meet the required specifications for each zone. In the experimental work, local asphalt binders were used and have been modified with Polymer Elastomer type (SBS; Kraton and Iterprene SBS G-L) and Polymer Plastomer type (Iterplast 1806 brand). The results showed that both Polymers are helpful for local asphalt modification. The results showed that 2% of Kraton/Elastomer yields PG (82-28), and 2% of Iterprene/Elastomer yields PG (82-22) for Lanaz asphalt and those are applicable for all zones of Kurdistan Region of Iraq. On the other hand, 2% of Plastomer yields PG (82-22) for both Lanaz and Kat asphalts, this also is applicable for all zones of Kurdistan Region of Iraq.

Recycled asphalt pavement (RAP) was introduced to the transportation industry to build economical and sustainable pavements. However, thermal cracking at low temperature can increase with the use of RAP in the hot mix asphalt (HMA). Therefore, it is necessary to study the change in creep stiffness (S), which is a measure of the thermal stresses due to the thermal contraction. Higher creep stiffness value indicates higher thermal stresses resulting in higher susceptibility to cracking. Conventional Superpave low-temperature criteria for binder requires only one creep stiffness value from bending beam rheometer (BBR) at 60 sec. The objective of this study is to construct creep stiffness master curve using BBR test data and characterize the low-temperature behavior of the binder due to the addition of RAP. A Superpave PG 58-22 binder was used as the control binder and four RAP percentages in the HMA (15, 25, 35, and 40%) were studied at different temperatures and two aging condition were evaluated. Creep stiffness master curves were developed at −12°C. Results show that increasing RAP percentages and further aging conditions contribute to the increased stiffness of RAP binder blends at low-temperature. Furthermore, the rate of stiffness increase due to aging decreases with the addition of higher RAP in binder. Therefore, aging has less effect on binder with higher percentage of RAP than binder with no RAP.

Water injected foamed warm mix asphalt (WMA) accounts for about 90% of all WMA produced in last several years in the United States. This study aims for a documentation of recently developed asphalt foaming parameters and their correlation with foamed binder and mixture characteristics based on existing foamed WMA research. Incorporation of 1–3% water into hot binder stream at 141–171°C results in foamed asphalt binder through binder volume expansion and viscosity reduction, which is intended to improved coatability and workability. Foaming parameters: expansion ratio (ER), half-life (HL), surface area index (SAI), foamability index (FI), and collapse rate of semi-stable bubbles (k-value), together with foamed binder and mixture properties have been synthesized. Foaming water content (FWC) is found as a key parameter of foamed WMA practices. Optimization of FWC and subsequent evaluation of mixture properties shows that foamed asphalt mixtures exhibits equivalent or better performance as conventional hot mix asphalt (HMA).

Sustainable development has become a major focus for engineers and planners as part of collective efforts in developing and integrating environmental-friendly solutions for material recycling and waste management into design and construction of civil engineering infrastructure. Significant growth in automobile manufacturing and increasing rubber tire production along with the growing concerns for protecting the environment and preserving natural resources have led the efforts in applying recycled tire particles in concrete, as environmental-friendly and cost-effective solution, to minimize the ecological footprint of such waste. Previous research has shown that introduction of rubber tire particles, as partial replacement for fine and coarse aggregates, reduces the brittleness of the concrete and provides more flexible aggregate bonding which ultimately improves the dynamic resistance of concrete. In this experimental study, various percentages of fine and coarse aggregates are replaced with fine and coarse rubber particles, respectively. The compressive and tensile strength characteristic are studied and investigated to propose a Quality Management Plan for rubberized tire applications in highway and airfield pavements. In this regard, as part of the Quality Assurance initiative, relevant quality standards for rubber-concrete mix designs and testing processes are identified to evaluate the specimens’ conformance. Moreover, through acquisition and analysis of the experimental data, this paper studies the results and identifies areas of improvement to eliminate the causes for unsatisfactory performance for Quality Control purposes. It applies the Project Management Body of Knowledge (PMBOK) Quality Management and Controls Tools to achieve these objectives.

The good quality of the bond between the substrate and the overlay is a key factor for providing composite or monolithic action in ultra-thin whitetopping (UTW) by shifting the neutral axis from middle of the UTW slab to the bottom of UTW slab. This will reduce the bending stresses, however, shear stress will remain maximum at the interface. The shear stress at the interface will increase with the increase in repeated application of traffic load which creates an accumulation of strain at the interface resulting in failure of the monolithic action and finally affects the long-term performance of UTW. In this study, a strategic test apparatus and procedure are used to evaluate the decrease in bond strength caused by cyclic loading with respect to different interface treatment. The direct shear test was performed at 7 and 28 days and parameters like interface bond strength, tangential stiffness (k-modulus) and a number of cycles at failure for different stress ratios were collected through the experiments of different interface conditions. Through comparison of test results of different interface treatment with different loading rate and interface shear fatigue, it proved that this test method and the device can evaluate interface bond strength of UTW under static and repeated loading conditions effectively.

There is a need for the development of Eco friendly and cost effective material for the rigid pavement construction. High volume fly ash concrete suits the pavement concrete due to its many advantages. The knowledge of fatigue behavior is essential for the design of concrete pavements. This paper describes the probabilistic analysis of flexural fatigue behavior of high volume fly ash concrete. High volume fly ash concrete mixtures, satisfying the criteria of pavement concrete, were proportioned using low calcium fly ash. A total number of 225 beam specimens at three cement replacement levels (0, 50, and 60%) were tested under non reversed cyclic wave loading. Lognormal model was found to be satisfactory for the fatigue life distribution in all the cases. The parameters of the log normal distribution model were found to be dependent on the stress level. Fatigue model was developed in the form of relation between the stress level (S) and the fatigue life (N). S-N relations were established for high volume fly ash and reference concrete mixes at different reliability levels.

The in-situ asphalt stiffness master curve is a critical input for flexible pavement design. The master curve can be established directly by performing dynamic modulus testing on field cores, predicted using the volumetrics of the mixture, binder grade and aggregate gradation established using field cores, or backcalculated using falling weight deflectometer testing. There can be significant differences between the master curves established using these three different methods. The effects of these differences on design were compared using distress predicted by the asphalt pavement design module in Pavement ME. It was found that the method used to determine the in-situ asphalt stiffness can have a significant effect on the predicted distress.

Strain energy method is a novel approach that can be utilized to better understand the cyclic behavior of geomaterials subjected to repeated loading in triaxial tests. In order to characterize the dissipation of the energy in the particulate systems, it is necessary to mechanistically identify the factors that influence the energy stored and restored in each loading application. The main motivation for this study was to successfully understand the manner in which the generated hysteresis loops are affected by moisture state, fines content, and constant confining pressure stress paths. A comprehensive laboratory experiment consisted of two different gradations of a limestone source molded at two different moisture states were considered in this study. The specimen were subjected to two series of constant confining pressure stress path tests, which were aimed to capture the hardening and softening behavior of geomaterials. Analysis of the cyclic test demonstrated that moisture and fines content both act in a synergistic manner.

Quarry byproducts (QBs), usually less than 6 mm in size, are a major environmental and economic challenge for quarries as they accumulate in large quantities. Recent research at the Illinois Center for Transportation has evaluated new sustainable applications to utilize QB in pavement construction. Four full scale test sections were constructed to evaluate performances of pavement working platforms over a weak subgrade with an engineered strength of unsoaked California bearing ratio (CBR) of less than 1%. Two of the test sections utilized QBs packed into the voids of large-size aggregates, commonly referred to aggregate subgrade in Illinois and used as rockfill for building construction platforms over soft subgrade. To study the packing and percolation of the QBs through the large aggregates, and determine the optimum quantities of QBs to be mixed with the large-size aggregates, an extensive lab study was carried out to assess the packing of the two materials in a steel box. The large aggregates were added in one or two equal lifts, and the QB materials were evenly spread on the surface and then compacted with a laboratory-sized roller compactor. These applications were then replicated in full-scale test sections. The other two construction platform test sections studied the modification of soft subgrade by using aggregate subgrade materials with higher fines contents (up to 15% plastic and nonplastic fines, i.e. passing No. 200 sieve materials) than what is permitted in Illinois. This paper will present results of field rutting performance evaluations of these four construction platform test sections studied through accelerated pavement testing.

In asphalt plants, the real-time moisture content of a virgin aggregate mix can be used to optimize the production process and improve the product quality. The moisture information can be used for controlling the aggregate drying and asphalt binder addition processes, resulting in savings from energy and asphalt binder usage. For decades, nuclear gauges have been used in the road construction industry for measuring density, moisture, and asphalt content of materials. Recently, a system that utilizes nuclear techniques for real-time measurement of moisture in aggregate mixes moving on a conveyor belt has been developed. This system uses low-activity radioisotope sources and a safety-conscious design, placing minimal regulatory burden on plants in the United States. This paper presents the design features and measurement properties of this new moisture measurement system. Comparison of this system and the oven-drying method for the determination of moisture in aggregate mixes at four asphalt plants in Wisconsin, Utah, New Jersey, and Pennsylvania is also included.

Because of enormous construction activities scarcity of natural stone aggregate resources has resulted in a significant concern for engineers in many countries including in India. In the present laboratory study, an attempt has been made to explore possible utilisation of locally and abundantly available lateritic soil called moorum that fits to some extent to gravel, in the sub-base and base courses of a pavement. Conventional stone aggregates have also been used in combination with moorum to satisfy the desired grading as per the specifications. The optimum percentage of moorum that can be used in base or sub-base layer is found to be around 50%. Because of the relatively high plasticity index of moorum, ordinary Portland cement has been used for modification as well as stabilisation. The unconfined compressive strength test was conducted for the cement treated moorum-aggregate blends as per relevant specifications. It has been observed that the locally available moorum used in conjunction with normal stone aggregates modified/stabilised with cement has satisfactory engineering properties and hence can be used in the road base and sub-base applications.

Unbound aggregate layer (FAA specification P154) is an essential component of airfield pavement. For airport pavement design, P154 modulus is estimated as a function of subgrade CBR and subbase thickness. In this study the Precision Unbound Material Analyzer (PUMA) was used to characterize the resilient behavior of P-154 subbase material used at FAA’s National Airport Pavement Test Facility (NAPTF). A series of PUMA tests were conducted on two types of P154 subbase materials. Statistical analysis was performed to evaluate the effect of loading frequency on subbase resilient modulus. The correlation between vertical stress and horizontal stress was investigated. Triaxial tests were also conducted on these subbase materials. Resilient Modulus values measured from PUMA and triaxial tests are presented.

Design of flexible pavements incorporates mechanistic empirical approach pertaining to limiting stresses and strains at critical locations. In order to properly characterize the resilient behaviour of pavement foundations, non-linear stress dependent modulus models need to be incorporated in the analysis. The study conducted here focuses on employing non linear behaviour of subgrade in KENLAYER software for mechanistic pavement analysis. Road network being a major and preferential communication system draws attention towards an urgent need for sustainable construction of new roads. Pond ash produced by coal based thermal power plants takes huge disposal area and creates environmental problems like leaching and dusting. The present study investigates the effect of non-linearity on clayey subgrade stabilized with pond ash. Geotechnical studies were conducted by blending pond ash with 10, 20, 30, and 40% by mass of soil. The improvement in the characteristics of stabilized soils was assessed by evaluating the changes in the physical and strength parameters namely, the California bearing ratio (CBR) and compaction parameters. Significant improvement in geotechnical properties was observed leading to remarkable reduction in pavement thicknesses. It was observed that the assumption of linearity in the material behaviour gives a conservative design approach in terms of critical failure due to passes and critical strains. The critical pavement response reported with pond ash stabilization shows considerable improvement in increasing the rutting and fatigue life of pavement. At low CBR percentages, the critical strains were found to be high emphasizing the fact that benefit of pond ash stabilization will be prominent.

At Nashville International Airport, Taxiway S is a parallel taxiway to Runway 2C-20C constructed in concrete and asphalt and divided in 8 different sections. The asphalt sections between Taxiway N and S5 were the most deteriorated and required rehabilitation due to the amount of distresses recorded. Distresses included load and climate related cracking, weathering and raveling. The pavement was estimated to be more than 40 years old with the last recorded mill and overlay rehabilitation conducted in 1983. The pavement investigation revealed that the asphalt sections did not have the structural capacity to carry the anticipated traffic operations. Replacement was initially considered as the only alternative since a structural overlay was not feasible due to violations to the runway’s primary surface. Removing the entire pavement full-depth was an expensive alternative; therefore, other alternatives such as stabilizing the existing aggregate base to provide a stronger base over the soft clayey subgrade were considered. The initial plan was to stabilize 10 inches of aggregate base in-place to avoid exposing the underlying clayey soil. After the base was completed a 9-inch asphalt layer was to be constructed. In theory, the approach was feasible but the limited number of subcontractors in the area was a challenge. After a detailed evaluation that included life cycle cost analysis, risk assessment, sustainability and availability of contractors, the in-place stabilization of the existing aggregate base was selected. The Federal Aviation Administration P-304 specification was modified for the in-place stabilization process. This paper briefly discusses the planning, design and construction considerations conducted for the completion of this project.

In this pilot study, a new polymer binder based on carbamate linkages was evaluated for use with unbound aggregates to create a stable mixture for roadways, parking lots, and airport pavements. The binder is trade named “G5.” An extensive laboratory evaluation of the mechanical properties of the G5-stabilized aggregate mixture was conducted using the latest advancements in materials testing. The designed mixture was evaluated for stiffness using the dynamic modulus (E*) test and for its resistance to rutting using the flow number (FN) test, reflective cracking using the overlay tester (OT), thermal cracking using the uniaxial thermal stress and strain tester (UTSST), and fatigue cracking using the flexural beam fatigue test. In summary, the evaluated G5-stabilized aggregate mixture exhibited unique characteristics with superior performance at high, intermediate, and low temperatures suggesting a very good performance in the field when used as a surface course layer. The data showed that the evaluated G5-stabilized mixture may offer excellent alternatives when used as a surface layer in hot climate areas with heavy traffic and/or braking actions. The mixture is also anticipated to perform very well when used in cold climates and/or on top of a cracked asphalt pavement due to its high resistance to reflective and thermal cracking.

In recent years, the need to increase pavement service life and guarantee high performance has turned a greater attention on the use of pavement reinforcements. In this paper, the effectiveness of geogrids as reinforcement of flexible pavements has been investigated. This study focuses on the performance of pavement reinforced with geogrids, in term of reducing of rutting, under traffic loads. Analyses on numerical models of different road have been performed by using the finite element method. The results obtained show that the glass fiber grids can be used to improve the performance of flexible pavements and can provide a relevant contribution to the resistance to crack propagation and to the reduction of permanent deformations.

The advent of interlayer reinforcements with a wide range of stiffness properties has provided the opportunity to produce a specially-designed composite material that can enhance pavement performance in various aspects (e.g., rutting, fatigue cracking, reflective cracking). However, reinforcements may negatively affect the bonding between asphalt layers. The objective of this paper is to evaluate experimentally the interlayer de-bonding effect. In particular, reinforced and unreinforced asphalt specimens were tested in a direct shear test setup and their interlayer bond strength was characterized. The reinforcement inclusions used in the testing program involved synthetic materials made from various polymers, including polyester, polyvinyl alcohol, and glass fiber. Results of the experimental program indicated that the de-bonding effect impacts not only the maximum bond strength, but also the stiffness and the average interlayer shear strain at the maximum bond strength. Moreover, coverage ratio and the thickness of the reinforcement yarns were identified as additional important parameters in characterization of the interlayer de-bonding effect.