Thin Asphalt Research Articles

Fast Nondestructive Field Test Method to Determine Stiffness of Subsurface Layer in Thin Surface Hot-Mix Asphalt Pavement

The determination of the moduli of subsurface stabilized layers in pavements with unknown and variable layers and thin asphalt layers is a challenging problem. Reliable estimation of moduli cannot be obtained from backcalculation of falling weight deflectometer data. In addition, for many stabilized layers, full-depth intact cores cannot be obtained from the field, and hence, laboratory determination of the moduli is not possible. Analysis of the seismic property of a pavement is a well-known method for estimation of the surface modulus of the pavement. This paper proposes a simple methodology on how seismic data acquired on the pavement surface can be effectively used to estimate the modulus of the surface layer as well as those of the subsequent subsurface layers of a flexible pavement. A research study was conducted on three hot-mix asphalt pavements with a foamed asphalt (FA) stabilized base in Maine. These three pavements were tested with both portable seismic and falling weight deflectometer equipment. Cores were taken from the same locations and tested in the laboratory for their resilient moduli. The modulus values obtained from different tests were compared, the effect of temperature on the modulus of the FA was evaluated, and the deflections computed from layered elastic analysis by use of the predicted modulus of the FA layer were compared with the observed deflections. It is concluded that the portable seismic equipment can be used to determine accurate moduli of subsurface stabilized layers. The practical advantages of using such equipment warrant further study for refinement of the method.

Fast Nondestructive Field Test Method to Determine Stiffness of Subsurface Layer in Thin Surface Hot-Mix Asphalt Pavement

The determination of the moduli of subsurface stabilized layers in pavements with unknown and variable layers and thin asphalt layers is a challenging problem. Reliable estimation of moduli cannot be obtained from backcalculation of falling weight deflectometer data. In addition, for many stabilized layers, full-depth intact cores cannot be obtained from the field, and hence, laboratory determination of the moduli is not possible. Analysis of the seismic property of a pavement is a well-known method for estimation of the surface modulus of the pavement. This paper proposes a simple methodology on how seismic data acquired on the pavement surface can be effectively used to estimate the modulus of the surface layer as well as those of the subsequent subsurface layers of a flexible pavement. A research study was conducted on three hot-mix asphalt pavements with a foamed asphalt (FA) stabilized base in Maine. These three pavements were tested with both portable seismic and falling weight deflectometer equipment. Cores were taken from the same locations and tested in the laboratory for their resilient moduli. The modulus values obtained from different tests were compared, the effect of temperature on the modulus of the FA was evaluated, and the deflections computed from layered elastic analysis by use of the predicted modulus of the FA layer were compared with the observed deflections. It is concluded that the portable seismic equipment can be used to determine accurate moduli of subsurface stabilized layers. The practical advantages of using such equipment warrant further study for refinement of the method.

New Criterion for Superpave High-Temperature Binder Specification

The results of a study conducted to determine a new binder parameter that might replace the existing Superpave® high-temperature specification parameter ( G*/sin δ) are described. The current parameter ( G*/sin δ) is inadequate because of increasing concerns about its applicability to polymer and other modified asphalt binders. In this study, several parameters were calculated from rheological test data generated on four asphalt binders of different grades at four test temperatures. Two of the binders were unmodified binders, and the other two were modified binders. Laboratory hot-mix rutting tests also were conducted at three temperatures on the asphalt pavement analyzer (APA) and the dry Hamburg rut testers. APA overestimated the rutting potential of modified binders used in this study. Dry Hamburg produced reasonable results. From the correlation between the dry Hamburg data and binder parameters, the storage viscosity, η', was found to be the most promising binder parameter that could adequately characterize the rutting resistance of both unmodified and modified asphalt binders. Of all of the parameters, it was the easiest to measure with minimal change in existing instrumentation and software. A specification criterion for η' was determined. According to the new criterion, the temperature at which the η' has a value of 220 Pa-s for rolling thin film oven-aged asphalt binders is the high-performance grade (PG grade) temperature that may reasonably replace the current Superpave high-PG grade temperature obtained using G*/sinδ.

DYNAMIC STRUCTURAL EVALUATION OF PAVEMENT AND INFLUENCE OF SEED VALUES

Generally, backcalculation analysis based on FWD test data is an unstable procedure greatly influenced by several types of errors. These errors may be categorized by accuracy of forward analysis, measurement error, instability of backcalculation analysis, etc. Due to instability of the backcalculation algorithm, seed values of layer moduli highly influence backcalculation results, especially in case of thin asphalt concrete layer. In this paper, following verification of the accuracy of forward analysis, importance of dynamic backcalculation analysis will be explained and the use of Monte Carlo simulation for seed values of layer moduli to accurately backcalculate layer moduli will be presented.

Typical properties of proprietary thin asphalt surfacing systems

Thin asphalt surfacing systems have been laid in the UK for ten years. Therefore, it has become possible to examine the typical values for various properties that are achieved with different categories of thin surfacing systems. The categories are defined and the longevity, texture depth, skid resistance and visual, together with limited data for some other properties, are reviewed.

Typical properties of proprietary thin asphalt surfacing systems

Thin asphalt surfacing systems have been laid in the UK for ten years. Therefore, it has become possible to examine the typical values for various properties that are achieved with different categories of thin surfacing systems. The categories are defined and the longevity, texture depth, skid resistance and visual, together with limited data for some other properties, are reviewed.

Modelling short-term aging of asphalt binders using the rolling thin film oven test

Simulation of short-term aging of asphalt binders is a widely used procedure in asphalt binder characterization for predicting the binder response to plant mixing and paving under controlled laboratory conditions. There are two laboratory test methods for evaluating the short-term aging of asphalt binders: (i) a method using rotating pans filled with a thin asphalt film termed thin film oven test (TFOT) and (ii) a method using rolling cylindrical asphalt containers termed rolling thin film oven test (RTFOT). In this paper, an attempt is made to develop generalized models for short-term aging effects using the RTFOT aging time as a benchmark. Six binder types representing two PG grades and three source suppliers are conditioned to varying levels of RTFOT aging and tested using the dynamic shear rheometer (DSR). Aging effects are modelled using independent temperature shift models for the shear modulus and phase angle. The paper discusses the sources of errors in producing generalized models and some potential applications of aging models. The research revealed that it is possible to develop and implement such models for unmodified binders.Key words: asphalt, aging, RTFOT, DSR, binder rheology, shear modulus, phase angle.

Minimizing Distress on Flexible Pavements Using Variable Tire Pressure

The potential of variable tire pressure technology to minimize distress on flexible pavements with thin asphalt surfacing layers and peat soil subgrade was evaluated using in-situ stress-strain data. Pavement interfacial strains and corresponding subgrade stresses imposed by a three-axle truck were measured and used to estimate the fatigue life of the surfacing layer. Three levels of truck wheel loads in combination with four tire inflation pressures (350, 490, 630, and 770 kPa) were used to evaluate the potential distress by the single steering wheel and rear dual wheels in tandem. Results suggest that lateral strain due to the single steering wheel is the most critical to fatigue failure, which is influenced by the viscoelastic nature of asphalt, and therefore truck speed and axle configuration are important. Lower tire pressures increased the fatigue life of the surfacing layer with respect to the rear dual wheels and the steering wheel by up to 200 and 300%, respectively. Haulage trucks with systems for managing variable tire pressure such as the central tire inflation systems may therefore enhance the serviceability of pavements overlying peat or other soft soil foundations.

An innovative technique for using polymer composites in airport pavement rehabilitation

A new design of a fiberglass composite overlay with a granite riding surface to eliminate reflective cracking on jointed rigid airport pavements is presented, together with an analytical solution for the stresses and deflection in the overlay. The stresses and deflection are obtained from fracture mechanics using the relationship between the deflection and the stress intensity factor for a crack or joint. All modes of cracking are analyzed rationally. The thermal, bending and shear stresses together with the number of cycles of repeated loading for the occurrence of the first sign of reflective cracking are presented. A 15 mm thick E-glass mat-reinforced polyester (0/90° woven fabric, 18.3% volume fraction) is used over the joints covering a length of 20 cm on either side. This laminate has the strength and flexibility to carry very heavy gear loads and tire pressures across the joints. Within a distance of 50 cm from the joint, the thickness of the fiberglass/polyester laminate is decreased gradually to 1.9 mm and formed a hybrid composite with a thin asphalt concrete (AC) layer. The overlay is designed to withstand the thermal and vehicular stresses for about one million cycles of loading. The new design is considerably more economical than the conventional AC overlay.

Study of Steric Hardening Effect of Thin Asphalt Films in Presence of Aggregate Surface

The interaction between asphalt and aggregate surfaces before and after low-temperature storage (reversible, irreversible, or both) at various film thicknesses was investigated by means of the sliding plate geometry with standard Pyrex glass plates and machined aggregate plates. The study of storage and setting in thin films of asphalts on aggregate surfaces indicates that asphalts interact differently and unpredictably with aggregate surfaces. The phenomenon of steric hardening in thin films appears to be retarded (compared with the same phenomenon in bulk asphalts) during short storage times but is enhanced in contact with aggregate surfaces after several weeks’ storage.

Three-dimensional finite element analysis of flexible pavements with an (open joint in the) EPS sub-base

The behaviour of pavement structures with an expanded polystyrene (EPS) sub-base and a relatively thin asphalt top layer to a 50-kN falling weight load is analyzed by means of a three-dimensional finite element model with a single vertical interface layer. The position of the vertical interface layer was chosen next to the loading area. In this way, an open joint between the EPS blocks at the most critical position with respect to the loading area can be modelled, and the effect of such a joint on the structural pavement behaviour can be determined. Calculations have been carried out for pavement structures with only unbound base layers on the top of the EPS sub-base and for pavements with a cement-treated load-spreading layer above the EPS. Finally, the calculated deformations, asphalt strains and vertical stresses in the EPS sub-base are presented.

Framework for Selecting Effective Preventive Maintenance Treatments for Flexible Pavements

Preventive maintenance techniques are considered useful in extending the life of a pavement if applied at the right time. Discussed here is a framework for a process that can be used to select the proper maintenance strategies for different distress types in asphalt pavements, depending on traffic level and environment. Maintenance treatments addressed include only crack seals, fog seals, slurry seals, microsurfacings, chip seals, thin asphalt concrete overlays, and other thin surface treatments. Types of distress considered include roughness, rutting, fatigue cracking, longitudinal cracking, raveling, weathering, and bleeding. Decision trees, based on the authors' experiences, are presented to illustrate the process in selecting appropriate maintenance treatments. A framework for evaluating the cost-effectiveness of the various maintenance treatments is presented. Existing methods for evaluating cost-effectiveness of maintenance are discussed together with their strengths and weaknesses. An example of cost-effectiveness for different maintenance treatments is also briefly presented.

Fracture Morphology and Fracture Toughness Measurement of Polymer-Modified Asphalt Concrete

Pavement distress occurs through a variety of mechanisms, but it is always controlled by the adhesive and cohesive performance of the asphalt binder. Although the causes of pavement failures are known, the precise mechanisms by which they occur remain to be understood. Observation of the fracture morphology of asphalt concrete can provide some information in this respect. The fracture morphology of asphalt concrete is dependent on the morphology of the binder. A network structure was observed in thin asphalt binder films and the fracture morphology and engineering properties of asphalt concrete were found to be dependent on the network morphology of the asphalt binder. Addition of polymers to asphalt binders causes changes in the nature of the network structure, and its effect can be qualitatively determined by characterizing the fracture morphology. Styrene butadiene styrene (SBS), styrene ethylene butylene styrene (SEBS), styrene butadiene rubber (SBR) latex and an epoxy-terminated reacting polyolefin (Elvaloy AM) were used in this study. A quantitative method to determine the effect of polymer modification on the fracture properties of asphalt concrete is the J-contour integral fracture toughness measurement. An experimental protocol to measure the critical J-integral fracture toughness ( J1 c) was developed and the low temperature (-10°C) J1 c values were determined for SEBS and Elvaloy AM-modified asphalt concrete at three different concentrations.

Single-Measurement Estimation of In Situ Asphalt-Layer Moduli with Portable Falling Weight Deflectometer

The portable falling weight deflectometer (FWD) was introduced some time ago. The use of this measuring device in Israel was stimulated by the contradictory results of various studies described in the technical literature. These studies indicated that significant deviations may exist between the in situ FWD-backcalculated asphalt-layer moduli and the expected true moduli values from laboratory testing. In addition to these deviations, it is known that uncertainties associated with the backcalculation procedure do not allow the backcalculation of moduli for thin asphalt layers less than 75 to 100 mm thick. Therefore, the need for an additional in situ testing device that would produce reasonable results for the in situ asphalt-layer moduli became obvious. In Israel, the portable FWD was considered to be a promising testing device to serve this need. In situ tests showed that the new device required additional testing on the asphalt surface after coring the asphalt layers to their bottom. This type of double-testing enabled the derivation of the in situ asphalt-layer modulus using a straightforward backcalculating technique. It was also thought, however, that the double-testing procedure may be sometimes too clumsy and costly. Therefore, it was decided to examine the possibility of conducting a single measurement to obtain a good estimate of the asphalt-layer modulus. The current study led to a proposed procedure for estimating the in situ asphalt-layer modulus after only one run.

Effects of tire – pavement contact pressure distributions on the response of asphalt concrete pavements

The paper presents the development of a computer program VIEM for the elastic analysis of multilayered elastic pavements under the action of arbitrary tire–pavement contact pressure distributions. The techniques adapted in VIEM primarily involves the use of a two-dimensional numerical integration to integrate point load solutions over the distributed pressure after discretizing the contact area into a finite number of triangular or quadrilateral elements. Values of contact pressure are inputted at the node points of discretized area. Numerical verification of VIEM indicates that numerical solution of high accuracy can be efficiently calculated for the elastic response of multilayered asphalt pavements. As a result, the determination of displacements and stresses (strains) can be achieved using a personal computer. With the use of VIEM, a theoretical investigation is further performed to illustrate the effects of tire–pavement contact pressure distributions on the response of asphalt concrete pavements. An in situ measured tire–pavement contact pressure distribution is utilized in the investigation. The response of asphalt concrete pavements due to the action of this measured contact pressure distribution is examined and compared with that due to the action of a uniform and circular contact pressure distribution by taking into account the influences of moduli and thicknesses of structural layers. The results of this investigation confirm theoretically a general consensus that details of the contact pressure distribution affect stresses and strains near the surface of the pavement, whereas the response in the lower layers depends mainly on the overall load. In particular, the contact pressure distributions have a significant effect on the horizontal tensile strains at the bottom of thin asphalt concrete layer which control the fatigue failure of asphalt pavements. Key words: tire–pavevment interaction, three-dimensional stress analysis, asphalt concrete pavements, numerical integration, multilayered elastic solids, point load solution.

Evaluation of nondestructive test equipment for airfield pavements. Phase 1. Calibration test results and field data collection : Bentsen, R.A.; Bush, A.J.; Harrison, J.A. Army Engineer Waterways Experimental Station, Vicksburg, Mississippi, (United States), AD-A207 159/5/GAR, 331pp. (Jan. 1989)

Abstract : This study evaluates seven nondestructive testing devices for use on airfield pavements. Four falling weight deflectometers and three vibrators were evaluated for accuracy, repeatability, and reliability. Deflection data were collected on 12 pavements consisting of thick and thin asphalt concrete, portland cement concrete, and composite (asphalt concrete over portland cement concrete) pavements over fine and coarse grain subgrades. This report describes the test program, presents results of accuracy and repeatability tests, and presents the deflection data collected on the 12 pavements.

Flexible Pavement Strains Caused by Auto Tires

This paper includes the results of an analytical study of the effects of automobile tire loads on thin asphalt pavements over granular bases. Two different methods of calculating the tire contact pressure are used and the strains induced in the pavement structure are evaluated. The uniform pressure tire model assumes that the tire contact pressure is equal to the tire inflation pressure. The Tielking tire model is a finite element computer program that models the tire as a shell of revolution and calculates the contact pressure distribution by using the tire carcass properties and the tire load. The contact pressure distributions are used in ILLIPAVE to calculate the strains at various locations in a pavement having a surface of thickness ranging from 2.54 to 10.16 cm (1 to 4 in.) and moduli ranging from 345 to 5,516 MPa (50 to 800 ksi). A granular base 20.32-cm (8-in.) thick with two different moduli is over a subgrade soil with a modulus of 34.5 MPa (5 ksi). The results are analyzed and the findings indicate that automobile tire loads can produce high pavement strains for certain combinations of surface thickness moduli over weak bases. The best performance occurs when stiff bases are used.

ON THE DYNAMIC CHARACTERISTICS OF ASPHALT MIXTURES

Dynamical properties of asphalt mixtures were studied by vibrating the cantilever beams of the mixtures. We found that the properties of actual mixture are so complicated that we cannot approximate by the simple linear viscoelastic models such as Voigt type and Maxwell type. When the vector locus of complex elastic modulus E* (iω) for asphalt mixtures was plotted with the dynamic elastic modulus as abscissa and loss modulus as ordinate, it forms a wing shape locus and is not so simple as the semicircle (Maxwell) or straight half line (Voigt).We proposed a new index which shows the mechanical properties of mixtures. It was defined by the length between the intersection of two asymptotes and frequency characteristic curve of mixture on E* (iω) and frequency plane at which the phase difference between stress and strain was 45°. From the vertical location of both ends of the line, we can estimate the resistance to deformation of mixtures as a function of frequency, since the top end shows the elastic characteristic at infinitive frequency and the bottom end shows the actual stiffness of the mixture. The horizontal location of the line shows the frequency at which the phase difference between stress and strain is 45°, when the viscous and elastic resistance is equal at this frequency. The length of the line shows the rate of change from viscous to elastic state when frequency increases, for example, the longer the length, the more gradual the change will be.Some of the test results are discussed, applying the characteristic line concept, and we found that the thin asphalt film with less than about 5 micron thickness has different properties from thicker ones. And also the mixing effect of mineral particles to asphalt are discussed.

Measuring the density of thin asphalt or concrete layers with a gamma-ray back-scatter apparatus

One drawback of radioactive back-scatter apparatus for measuring density is the difficulty of defining adequately the depth-sampling characteristic. In this paper the concept of the mean depth to which useful gammas penetrate is introduced. Provided the instrument has been designed to measure the absorption of back-scattered gamma radiation, the density determined in the presence of small density gradients will be the average density of the layer lying above the mean depth. The derived density of this shallow layer may be slightly erratic due to the presence of layers with a different density at depths between one and three times the mean depth to which the gamma rays penetrate. Allowances are calculated for such errors for a particular instrument used in the experiments described. For this particular apparatus with a radium 226 source, the mean depth of penetration of the useful gamma radiation was found to be between 1.2 and 1.8 in. for materials with densities ranging from 150 to 100 lb/ft 3. This apparatus was found useful for measuring the increase of density during compaction of a 2 1 2 - in. asphalt base-course, and for measuring the density variation near to the surface across layers of bituminous-bound materials.