Pavement Test Research Articles

Evaluation of moderate and high RAP mixtures at laboratory and pavement scales

The use of reclaimed asphalt pavement (RAP) to replace the virgin materials in asphalt mixtures can result in significant cost savings and provide environmental benefits. As part of the national efforts to support the increasing use of RAP without adversely affecting the long-term performance of asphalt mixtures, a field evaluation of six asphalt mixtures containing moderate and high RAP contents has been conducted on six test sections at the National Center for Asphalt Technology Pavement Test Track since the third research cycle started in 2006. The objective of this study was to present the latest field and laboratory evaluation results of these six RAP mixtures. The field performance evaluated included rutting, roughness, surface texture and cracking. Sections W4 and W3 were constructed with 20% RAP mixes using PG 67-22 and PG 76-22 base binders, respectively. The four other sections, W5, E5, E6 and E7, were paved with 45% RAP mixtures using four different base binder options, consisting of PG 52-28, PG 67-22, PG 76-22 and PG 76-22 + 1.5% Sasobit. The results of this study show that moderate (20%) and high (45%) RAP contents can be used to produce asphalt mixtures that provide good performance, and a softer base binder can be used to improve the performance of a high RAP mixture. In addition, the creep strain rate determined in the indirect tensile test at 10 °C closely matched the field performance ranking – the mix with a higher creep strain rate exhibited more cracking in the field. The difference between the laboratory and field rank order discussed in this study may be affected by the different laboratory and field specimens and testing conditions, illustrating challenges when one uses smaller scale specimens and/or tests to simulate the performance and results of much larger scale pavement sections.

Mechanistic-empirical approach to characterizing permanent deformation of reinforced soft soil subgrade

This study focuses on characterizing the permanent deformation of geogrid-reinforced soft soil subgrade by using the mechanistic-empirical (ME) approach based on both experimental measurements and results of numerical modeling. Two sets of small-scale pavement sections were built over two types of soft soil subgrade and subjected to cyclic moving loads by means of a reduced-scale accelerated pavement testing (APT) device. Each set of pavement sections included one control section and three sections reinforced by different geogrids placed at the base–subgrade interface. The pavement sections were instrumented to measure vertical deformation and vertical stresses at the top of the subgrade. Strains developed in the geogrids were also measured by strain gauges throughout the construction and accelerated testing. Simplified finite element (FE) models were created to simulate both the control and geogrid-reinforced pavement sections and to compute the pavement mechanistic responses. With the experimental measurements from the first set of tests and results of FE analysis, the permanent deformation model in NCHRP 1-37A for unbound layers was adapted and calibrated to model the permanent deformation of the geogrid-modified subgrade. The effects of geogrids on the subgrade permanent deformation were integrated into the ME performance model through both the mechanistic response modeling and the empirical calibration. Predictions from the permanent deformation model were then compared with the second set of measurements and found to underestimate the permanent deformation of the geogrid-modified subgrade. However, the model was able to distinguish the difference in performance among the sections, i.e. the predicted rank of the performance was consistent with the measurements.

INNOVATIVE ASPHALT RESEARCH USING ACCELERATED PAVEMENT TESTING

Accelerated pavement testing is one key for innovations in the field of road pavement structures and materials due to its power of assessing mechanical performance in close to reality situations. This paper discusses two types of mobile load simulators for applying unidirectional wheel loads at comparatively high frequencies, the MMLS3, a one third scale device, and the MLS10, a full-scale device. Through examples it is demonstrated that these devices are suitable for testing complex systems, such as mechanical resistance of light reflectors on pavements, traffic resistance of bituminous plug expansion joints for bridges, performance of grid reinforced pavements as well as water resistance of porous asphalt against traffic induced pumping effects. Moreover, an example of MLS10 ultimate bearing capacity tests on a real test section is shown focusing on the discussion of strain gauge, acceleration, rut depth and falling weight deflectometer (FWD) measurement results.

Numerical validation of viscoelastic responses of a pavement structure in a full-scale accelerated pavement test

This paper demonstrates the application of a generalised layered linear viscoelastic (LVE) analysis for estimating the structural response of flexible pavements. A comparison of the direct layered viscoelastic responses with approximate solutions based on the linear elastic (LE) and LVE collocation methods was also carried out. The different approaches were implemented by extending a layered elastic program with an improved computational performance. The LE and LVE collocation methods were further extended for analysis of pavements under moving loads. The methods were illustrated by analysing a pavement structure subjected to moving wheel loads of 30, 50, 60 and 80 kN using a Heavy Vehicle Simulator (HVS). The various responses (stresses and strains) in the pavement, at pavement temperatures of 0, 10 and 20°C, were measured using various types of sensors installed in the structure. It was shown that the approximated LVE solution based on the LE collocation method agreed very well with the measurements and is computationally the least expensive.

Comparing rutting of airfield pavements to simulations using Pavement Analysis Using Nonlinear Damage Approach (PANDA)

This study presents the rutting performance results of full-scale pavement test sections subjected to F-15E and C-17 aircraft wheels at two different temperatures. Pavement structures for the tests were constructed under shelter in the U.S. Army Engineer Research and Development Center's (ERDC) pavement test facility. The full-scale test results are used to validate viscoelastic, viscoplastic and hardening-relaxation constitutive relationships implemented in the Pavement Analysis Using Nonlinear Damage Approach (PANDA) model. PANDA is a mechanistic-based model which incorporates nonlinear viscoelastic, viscoplastic, hardening-relaxation, viscodamage, moisture-induced damage and ageing constitutive relationships. Results of dynamic modulus and different repeated creep-recovery laboratory tests are analysed to extract the parameters associated with viscoelastic, viscoplastic and hardening-relaxation constitutive relationships implemented in PANDA. Once calibrated, PANDA is used to predict the rutting performance observed in full-scale pavement test sections. The simulation results illustrate that PANDA is capable of predicting the rutting of airfield pavements subjected to heavy aircraft wheel loads at intermediate and high temperatures. It is shown that PANDA successfully predicts the effect of shear flow and upheaval at the edges of the wheel. The data from simulation suggested that PANDA, once calibrated, can provide insight into the critical locations of tensile and compressive stresses within the pavement structure. PANDA simulations not only provide a tool for evaluating existing structures, but also can be used in designing more sustainable pavement structures and materials.

Mechanical performance of pavement structures with paving slabs – Part II: Numerical simulation tool validated by means of full-scale accelerated tests

In recent years, pavement structures with paving slabs have gained importance, especially in urban trafficked areas, because they provide more design options and have great potential with regard to durability and low maintenance compared to flexible pavements. In order to exploit this potential, an accurate and reliable performance prediction by means of appropriate design concepts is necessary. Contributing to this topic, a numerical simulation tool was developed and its performance evaluated by means of full-scale accelerated pavement tests (APT).Within this paper (Part II of this work), a numerical simulation tool is proposed which is able to take into account the non-linear and plastic behavior between paving slabs (vertical joints) and between slabs and sandbed. The material parameters required for the paving concrete slabs, the vertical joints and the base courses are obtained by identification experiments. Finally, the main results from the APT could be reproduced very well with the numerical simulation tool without using phenomenological parameters.

Mechanical performance of pavement structures with paving slabs – Part I: Full-scale accelerated tests as validation for a numerical simulation tool

In recent years, pavement structures with paving slabs have gained importance, especially in urban trafficked areas, because they provide more design options and have great potential with regard to durability and low maintenance compared to flexible pavements. In order to exploit this potential, an accurate and reliable performance prediction by means of appropriate design concepts is necessary. Contributing to this topic, a numerical simulation tool was developed and its performance evaluated by means of full-scale accelerated pavement tests (APT).Within this paper (Part I of this work), the APT using the New Mobile Load Simulator (MLS10) is presented. The APT program was carried out by the Swiss Federal Laboratories of Material Science and Technology on four test sections with concrete slabs of different dimensions. Two of them were instrumented with soil pressure cells and horizontal strain gauges in order to assess the primary response under the 65kN wheel load. With a loading speed of 22km/h under a super single tire, up to 38,400 load passes per day could be simulated on the test sections. With a frequency of the measuring sensors of 100Hz, the stress peaks in the concrete slabs as well as at the top of the upper base course and the subgrade were recorded during the whole testing period. Overall, a very successful test execution has led to valuable and reliable data, which will be used to assess and validate the performance of a numerical simulation tool.

Utilization of Advanced Diagnostic Methods for Texture and Rut Depth Analysis on a Testing Pavement Section

Abstract Qualitative characteristics of pavement in wide range reflects the pavement serviceability, which is a summary of the characteristics of the pavement, providing a fast, smooth, economical and especially safe driving of motor-vehicles. The target factor of pavement serviceability and safety of roads represents the quality of their surface properties. In the framework of research activities performed in the Research Centre founded under the auspices of University of Žilina, individual parameters of pavement serviceability were monitored by pavement surface scanning. This paper describes the creation of a 3D - road surface model and its analysis and evaluation from the viewpoint of two pavement serviceability parameters - the rut depth and texture. Measurements were performed on an experimental pavement section used contemporary in an Accelerated Pavement Testing experiment. The long-term goal is to ascertain functions predicting degradation of these two pavement serviceability parameters.

Effects of using screening materials in the graded aggregate base layer of flexible pavements

In this paper, the potential use of screening materials in Graded Aggregate Base (GAB) layer of pavements was investigated using aggregate sources in Georgia. Three content levels of screening materials in GAB, i.e. 0%, 25% and 50%, were studied. Morphological analysis of aggregates and Proctor test were conducted to reveal the characteristics of the modified GAB materials, followed by the California Bearing Ratio (CBR) test and Mechanistic-Empirical Pavement Design Guide software simulation to evaluate how the GAB strength and overall pavement performance change with varying amount of screening materials in the GAB layer. The results indicated that the effect of using screening materials in GAB varies and depends on the amount of screening materials used, which changes gradation, and the aggregate types and sources, which exhibit significantly different morphological properties.

Long term monitoring of full scale pavement test section with eight different asphalt wearing courses

With the collapse of Soviet Union the traffic loads and available materials significantly changed in Latvia. When joining European Union the situation altered again with new requirements for test methods, road design, and increased traffic flow. Entirely new road construction and pavement design specifications had to be implemented. Largely these were adopted from existing foreign norms albeit in many cases pavements still exhibited premature failure, mostly in form of rutting. To improve the National specifications for asphalt mix design an experimental section consisting of six asphalt concrete and two stone matrix asphalt wearing course sections was paved on Riga bypass in 2001 and monitored until 2012. The experiment was designed to evaluate the use of different mix designs and various types of mineral aggregates, including granite, diabase, and dolomite for the use in high traffic intensity roads. The sections were continuously monitored for bearing capacity, skid resistance, roughness, rutting, and cracking. It was found that the use of dolomite significantly reduces skid resistance, and the use of natural sand increases plastic deformations. Based on these conclusions, changes in the National road specifications were introduced, including flow coefficient test for sand, abrasion and fracture resistance requirements for stone, rutting resistance requirement for mix design and minimum skid resistance requirement for newly constructed pavements.

4.75 mm SMA Performance and Cost-Effectiveness for Asphalt Thin Overlays

This paper presents the design of stone matrix asphalt (SMA) with 4.75-mm nominal maximum aggregate size (NMAS) and alternative surfacing cross-section for an asphalt wearing course that may improve pavement performances while controlling costs by using locally available aggregates. The 4.75 -mm NMAS dense-graded mix was previously used in several states to reduce layer thickness and cost. Because of its poor friction and limited performance, however, it was generally used as levelling binder and placed on low-volume roads. The 4.75-mm SMA is proposed for thinner asphalt overlays in this study to improve its performance as well as surface texture. The ultimate goal of this study is to develop the 4.75-mm SMA and evaluate its performance and engineering benefits as a wearing course under laboratory and field conditions. Test pavement sections were constructed in Northern Illinois and on-site performance tests were conducted to evaluate its performance under actual traffic loading. The engineering cost-benefit analysis with respect to performances from both laboratory and field studies suggests the proper application of 4.75-mm SMA as an efficient and cost-effective wearing course for asphalt thin overlays.

Laboratory evaluation of flexible pavement structures containing geocomposite drainage layers using light weight deflectometer

The behaviour of flexible pavement structures in wet environments is significantly influenced by the infiltration of excess water. The use of geocomposite drainage layers is an alternative to promote rapid removal of any infiltration of excess water. Using four small-scale flexible pavement test sections, this laboratory study focused on measuring the effectiveness of the different configurations of geocomposite drainage layers in terms of reduction in water content and improvement of mechanical properties during a drainage period. The experiment allowed measuring the significant effects of each drainage configuration on pavement structural strength in the short-term and long-term drainage behaviour of each experimental pavement structure. The shallow drainage blanket, as well as the vertical drain, showed a more pronounced effect in the top layer of the structures, while the deep drainage blanket showed a limited effect. From the results obtained, a drainage configuration combining a shallow drainage blanket with a vertical drain may be optimal.

Deflection characteristics of Unbound Base Course During a Large Scale Model Experiment

This paper evaluates de deflections (measured at the surface and/or at the top of the subgrade) of unbound pavement materials under cyclic loading. Deflections of three base course materials (Bakel Red Quartzite, Bakel Black Quartzite and Diack Basalt) were investigated using a large-scale model experiment (LSME). The LSME is a prototype-scale pavement test apparatus where cyclic loading is applied and deflections are measured. The LSME replicates field conditions and accounts for scale effects. The LSME results showed that the total, plastic and net plastic deflections of a pavement increase progressively as the number of loading cycles increases. The total deflection decreases as the thickness of the base layer increases. Plastics deflections at the top of the subgrade decrease progressively as the thickness of the base layer is increased. The elastic deflections of the surface and of the base layer decrease gradually with the increasing loading cycles. The elastic deflection at the top of the subgrade decreases with increasing thickness of the base layer. So, rutting can be limited by limiting the elastic deflection at the top of the subgrade. However, this criterion does not account for the rutting caused by the unbound base layers and that of the asphalt concrete.

Evaluation of the effects of gyratory and field compaction on asphalt mix internal structure

This study investigates the effect of gyratory and field compaction on the internal structure of asphalt mixtures. For this purpose, three new full-scale pavement test sections with different HMA mixes were selected for sampling loose material and field cores. Loose material was compacted using the gyratory compactor and adjusting several parameters, namely the gyration angle, compaction temperature and specimen geometry. Internal structure of the gyratory and field compacted specimens was quantified in terms of the aggregate contact points, orientation and segregation by means of 2-D image analysis. From the laboratory investigation it was demonstrated that the gyration angle and specimen geometry significantly affected the internal structure. The results also indicated that the field compaction produced similar internal structure in asphalt pavements and, especially, compaction with gyration angle of 1.45o best simulated the internal structure of field cores.

Impact of dynamic loading on backcalculated stiffness of rigid airfield pavements

The objective of this paper was to evaluate the deterioration of Portland Cement Concrete (PCC) slabs throughout trafficking. A full-scale accelerated pavement testing at the National Airport Pavement Test Facility (NAPTF) was conducted on Construction Cycle 6 (CC6) on rigid pavements with low, medium and high flexural strengths on both a concrete and asphalt stabilised base. Heavy Weight Deflectometer (HWD) testing was conducted on the test sections to backcalculate the stiffness of the layers. The majority of PCC deterioration occurred roughly within the first 1500–2000 passes of trafficking. On average, the MRS-1 (low flexural strength) PCC elastic modulus was found to decrease by 20%, from 5.0–.4 × 106 (34.5–37.2 GPa) to 4.0–4.3 × 106 psi (27.6–29.7 GPa), whereas the PCC elastic modulus of MRS-2 and MRS-3 was found to decrease by 17% and 22%, respectively. However, neither the MRS-2 nor MRS-3 elastic modulus was found to drop below 5.0 × 106 psi (34.5 GPa) after 15,000 passes.

Strain response of a semi-rigid base asphalt pavement based on heavy-load full-scale accelerated pavement testing with fibre Bragg grating sensors

Full-scale accelerated pavement testing with a mobile load simulator 66 (MLS66) was conducted on a semi-rigid base asphalt pavement on a highway in Chongming Island, Shanghai, China. The goal was to investigate performance behaviour of an asphalt pavement with fine-sand subgrade in the river bed. Chongming is the terminal of G40 highway where fine sand is abundant. Although commonly found, there are little published data on its performance in a pavement structure. If found reliable in the accelerated test, the design would be used for the construction of G40 highway, which can lower the construction costs greatly and provide an engineering practice for follow-up research. Performance of the pavement structure was evaluated under high-frequency heavy trafficking while being subject to high-temperature and ambient environmental impact. This included monitoring of strains, temperature, modulus, rutting deformation, pavement depth and water level. This paper discusses the cumulative and instantaneous three-dimensional strain at the bottom of each layer in the semi-rigid base asphalt pavement. Generally good agreement was reached between the measured and calculated strains with back-calculation resilient modulus considering modulus reduction of asphalt layers because of temperature. A fatigue equation of the asphalt layer was established between loading applications, strain and seismic modulus, a small-strain value of Young's modulus. Conclusions regarding the spatial distribution, time-history change of three-dimensional dynamic strain response and the relationships between influencing factors and strains are presented.

積雪寒冷地における中温化舗装技術の適用方法に関する研究

Warm-mix asphalt technology helps reduce CO₂ emissions. In snowy cold regions, however, it is unclear what times of year it is feasible to use warm-mix asphalt for paving to help reduce CO₂ emissions, and quality control techniques for warm-mix asphalt have not been established. In light of the above, a test pavement was installed by using warm-mix asphalt technology in the cold-weather period, in order to contribute to CO₂ emissions reduction. Toward applying this technology, the asphalt mixing temperature was kept lower than the conventional asphalt mixing temperature. The test pavement was used for evaluating the conditions under which warm-mix technology is applicable. It was confirmed that warm-mix asphalt was unsuitable for the cold-weather period, because the degree of compaction was reduced due to the drops in asphalt mixture temperature during transport, laying, leveling and compaction. However, it was found that applying warm-mix asphalt materials at a temperature that is typically used for conventional asphalt materials improves the work efficiency and the quality of pavement compared with warm-mix asphalt. 積雪寒冷地では，CO₂排出量の削減を目的とした中温化舗装技術の適用可能な時期が明確ではなく，品質管理手法についても確立されていない．そこで，寒冷期におけるCO₂排出量の削減を目的して，中温化舗装技術を用い混合温度を低減した舗装の試験施工を行い，適用可能な条件を評価した．その結果，寒冷期に混合温度を低減した使用方法では，運搬時，敷均し時，転圧時の温度低下による締固め度の低下が見られ，このような使用方法は適さないことを明らかにした．さらに，寒冷期施工においては中温化舗装技術の低温下における施工性改善および品質低下防止効果の特長を生かし，温度低減を行わない使用方法で品質の向上が図られることを確認した．

Overlay Thickness Design for Low-Volume Roads

Identifying the appropriate overlay thicknesses is critical to a local transportation agency's ability to maintain its pavement network. Local agencies often use empirical approaches for designing the overlay thickness for low-volume pavements. For example, overlay design for low-volume roads in Illinois is currently carried out using assumed layer coefficients for a limited number of material types. Although such empirical approaches are fairly simple to use, they are often not suitable for considering the effects of recycled and nontraditional construction materials that are more commonly considered in current-day sustainable pavement applications. The lack of mechanical testing for evaluating the pavement structural condition often leads to uneconomical practices in the rehabilitation of low-volume roads. This paper presents a mechanistic–empirical approach for overlay thickness designs of low-volume pavements through a combination of nondestructive deflection testing and preestablished pavement damage models. Five pavement sections, with varying structural and traffic characteristics, were selected from two counties in Illinois. Three sets of falling weight deflectometer tests were conducted over a period of one year to monitor changes in pavement deflection responses. Structural conditions of the pavement sections in their original configuration were evaluated first. Then, the corresponding required overlay thicknesses were determined by using two methods currently used by local agencies. The inability of the currently available methods to properly account for current pavement structural conditions was highlighted. A new mechanistic–empirical overlay thickness design method introduced in this study successfully identified structural deficiencies in the original pavement configurations.

Comparison of Low-Volume Road Pavement Performance with Results of Accelerated Pavement Testing

Weathered basalts are polygonal fragments of various dimensions generally spread in a wide grading envelope. They are found in high-volume portions of basaltic spills where the rock is extremely fractured and where degradation processes prevail over decomposition. This material was used as base and subbase layers of experimental pavement sections tested with a heavy traffic simulator. The same material was used as the base and subbase of a pavement on a low-volume road in Rio Grande do Sul state, Brazil, that was monitored for 10 years. The main conclusion from the study is that the low-volume road pavement presented different forms of surface degradation in comparison with the experimental road tested with the traffic simulator. The design model obtained in the traffic simulator study was used to identify the point at which the pavement started to deteriorate and thereby identify when a maintenance program was needed rather than to predict when the pavement had already fully deteriorated.

Airfield Pavement Response Caused by Heavy Aircraft Takeoff

The effect of wheel configuration on critical airfield pavement responses during takeoff was calculated, and variables, usually omitted in conventional pavement analysis, were considered. The numerical analysis matrix consisted of two takeoff speeds, two inflation pressures, two pavement structures, and four wheel configurations. One of the pavement structures was built at the National Airport Pavement Test Facility and had been previously described in the literature. The method used in this study advanced current knowledge in two respects. First, the study examined not only the tensile strains at the bottom of the asphalt concrete (AC) layer (fatigue cracking) and vertical strain on top of the subgrade (rutting) but also the transverse surface strain (surface cracking) and vertical shear strains (near-surface cracking and rutting). Second, several assumptions about existing methods were advanced. These assumptions included (a) nonuniform three-dimensional contact stresses instead of uniform one-dimensional vertical stresses over a circular contact area, (b) viscoelastic and nonlinear material characterization for AC and granular material under high stress levels in lieu of a linear elastic model, and (c) load variation with time to reflect takeoff. Transverse surface strain and vertical shear strain in the subgrade were most affected by wheel configuration. In addition, the variables had varying influence on pavement responses and wheel interaction. For instance, takeoff speed affected vertical strain on top of the subgrade but did not affect transverse surface strain. Tire inflation pressure modified wheel interaction for shear strain in the AC but not in the subgrade.