Chris Abadie

Louisiana experience with crumb rubber-modified hot-mix asphalt pavement

A comparative study of laboratory and field performance of several applications of crumb rubber-modified (CRM) hot-mix asphalt in Louisiana is presented. Eight CRM asphalt pavement sections were constructed by eight different CRM processes or applications. These eight CRM sections were built at five state highway projects. A control section with conventional asphalt mixture was constructed at each project to compare with the performance of pavement sections built with CRM asphalt mixtures. To evaluate the mixture characteristics of the CRM and conventional mixes, laboratory tests of Marshall stability and flow, indirect tensile strength and strain, and indirect tensile resilient modulus were conducted on field compacted Marshall specimens. Comparisons of the field performances of the pavements were achieved through roadway core air void analysis, rut-depth measurement, international roughness index, pavement structure numbers measured through the Dynaflect (dynamic deflection determination) system, and visual inspections of cracks. The results indicated that the conventional mixtures exhibited higher laboratory strength characteristics than the CRM mixtures. The pavement sections constructed with CRM asphalt mixtures showed overall better performance indices (rut depth, fatigue cracks, and international roughness index numbers) than the corresponding control sections after 5 to 7 years of traffic.

LOUISIANA EXPERIENCE WITH FOAMED RECYCLED ASPHALT PAVEMENT BASE MATERIALS

Utilization of existing recyclable materials has always been key to more efficient and economical highway construction. Use of the foamed-asphalt (FA) technique to stabilize recycled asphalt pavement (RAP) is one strategy for an efficient use of salvaged construction materials. The main objective of this study is to investigate the potential use of FA-treated RAP as a base course material in lieu of a crushed-limestone base beneath a concrete pavement layer. Test sections were constructed at US-190 near Baton Rouge, Louisiana, and used for field evaluation of the FA RAP base. The laboratory mixture design of the FA RAP, the construction of the experimental base section, and the field evaluation of the stiffness of the FA RAP base layers using different in situ testing devices are presented. Preliminary results of both laboratory and field tests showed that the FA-treated RAP mixtures are very promising and can be used as an alternative to the traditional limestone base beneath a concrete pavement layer.

MECHANISTIC EVALUATION OF HYDRATED LIME IN HOT-MIX ASPHALT MIXTURES

Permanent deformation and moisture damage are common distresses found in pavements today. The use of mineral fillers such as hydrated lime is known to provide a decrease in moisture susceptibility. In many cases, mineral fillers will also increase the mixture stiffness. Conventional asphaltic concrete mixtures and mixtures modified with hydrated lime were evaluated for their fundamental engineering properties as defined by indirect tensile strength and strain, permanent deformation characteristics, resilient modulus, and fatigue resistance. A typical Louisiana low-volume dense-graded mixture was used. The test factorial included two aggregate types (limestone and gravel) and two asphalt cement types (a conventional AC-30 and one modified with styrene-butadiene polymer). The results indicated that the addition of hydrated lime as mineral filler improved the permanent deformation characteristics and fatigue endurance of the asphaltic concrete mixtures. This improvement was particularly apparent at higher testing temperatures with mixes containing polymer-modified asphalt and limestone aggregate.

Variability of Air Voids and Mechanistic Properties of Plant-Produced Asphalt Mixtures

The results of a laboratory and field evaluation of the variability of physical and mechanistic properties of plant-produced asphalt mixtures are presented. Three asphalt mixtures from two overlay rehabilitation projects were selected. Comparison analyses were conducted on density measurements between two laboratory (AASHTO T166 and ASTM D6752-02, or CoreLok) and one in situ (pavement quality indicator) test methods. In addition, two laboratory mechanistic tests—indirect tensile (IDT)-strength and frequency-sweep-at-constant-height tests—and two field nondestructive tests with falling weight deflectometer (FWD) and light falling weight deflectometer (LFWD) were performed to characterize the variability of the plant-produced mixtures evaluated in this study. Superpaver gyratory compactor (SGC) samples and field cores were used in the laboratory testing program. A strong correlation was observed between the two laboratory bulk specific gravity test methods: AASHTO T166 and CoreLok. The IDT strengths of SGC samples were higher than those of field cores. A good correlation was found between the complex shear moduli of SGC samples and field cores. Field test results indicated that the LFWD test may be used as an alternative to the FWD test in pavement structure evaluation.

Development of Design Procedure to Predict Asphalt Pavement Skid Resistance

A laboratory design procedure was developed to evaluate the skid resistance of asphalt pavement with laboratory test results. For the development of the procedure, twelve typical asphalt wearing course mixtures with different combinations of aggregate sources and mix types were considered. The frictional performance of asphalt mixtures was evaluated with an accelerated polishing and testing procedure developed at the National Center for Asphalt Technology. The circular texture meter and the dynamic friction tester at various predetermined polishing cycles were used to evaluate the variations in surface texture and friction characteristics of asphalt testing slabs during accelerated polishing. The skid resistance of asphalt mixtures attributable to accelerated polishing was quantified with the international friction index number F60, which was computed with the friction numbers measured with the dynamic friction tester at 20 km/h and the obtained mean profile depth values. The analysis of F60 results led to the development of a set of friction prediction models and a laboratory friction-resistant mix design procedure. The developed procedure, which allows estimation of asphalt pavement skid resistance based on laboratory measured micro- and macrotexture results, is a useful tool for laboratory evaluation of a mixtures friction resistance. The procedure can also facilitate the use of locally available aggregates with lower skid resistance in a wearing course mix design and thereby produce both cost-effective and skid-resistant surface mixtures.

Variability of in-situ HMA volumetric and mechanistic characteristics using non-destructive test (NDT): case study

This paper discusses the variability of in-situ physical and mechanistic characteristics of three construction projects using non-destructive test (NDT). Six sites from each project in the state of Louisiana were selected. Three NDT tests – falling weight deflectometer (FWD), light falling weight deflectometer (LFWD) and pavement quality indicator (PQI) – were carried out during and after construction. The deflection data from FWD and LFWD were utilised to backcalculate in-situ layer moduli and composite moduli, respectively. ELMOD and MICHBACK backcalculation softwares were used to calculate and compare the hot mix asphalt (HMA) layer moduli. The in-situ density of the HMA layer was obtained from the PQI device. Project variability in the in-situ measurements of the HMA layer was attributed to HMA layer thickness, temperature and seasonal variations. It was found that there was a good relationship between the HMA composite moduli calculated using the FWD deflection and Bossinesqs equation and moduli from the LFWD. The results also indicated that there was no strong relationship between the in-situ moduli and in-situ PQI voids.

Developing Field Skid Resistance Prediction Procedure for Louisiana Pavements

Research shows that by improving pavement surface friction resistance, wet pavement crashes can be reduced or prevented. However, the current asphalt mixture design procedure does not directly consider friction as a design requirement. The main objective of this study was to develop a procedure to predict the pavement field skid resistance based on design traffic input, aggregate polishing, and mixture properties commonly available during a mix design. Twenty-two asphalt pavement test sections were considered in this study. The selected asphalt mixtures consisted of eight commonly used aggregates and four typical mix types: 12.5-mm Superpave®, 19-mm Superpave, stone mastic asphalt, and open-graded friction course. Field measurements were conducted with the dynamic friction tester, circular texture meter, and locked-wheel skid tester devices, while the coarse aggregate’s polished stone values were determined by using the accelerated polishing test in the laboratory. Statistical analysis of various field and lab test results led to the development of a procedure for predicting pavement end-of-life skid resistance based on the aggregate blend’s polished stone values, gradation parameters, and design traffic input. In addition, a new aggregate friction rating table was developed so that new aggregate sources can be certified by laboratory dynamic friction tester measurements to fulfill the required mixture friction requirements. The new procedure will allow engineers to check whether a mix design with a selected blend of aggregates would meet field friction requirements during the mix design stage.

Equivalency of Using the Binder or the Mastic Modulus to Estimate the Mixture Modulus

This paper presents an investigation in applying the Hirsch model to predict the mixture modulus through using the binder modulus and the mastic modulus and their corresponding volume compositions. By comparing the model predictions using the two different methods with the experimental results, it is found that the two methods are equivalent.

Estimation of the Stiffness of Asphalt Mastics Using Hirsch Model

Mastic properties are very important to the performance of asphalt concrete. Fine and coarse aggregates are usually not directly interacting with asphalt binder but with mastics. Permanent deformation and fatigue cracking tend to occur in the mastics and the interfaces between mastic and aggregate. Mastics demonstrate much more complicated behavior than asphalt binder including permanent deformation, non-linearity, and temperature sensitivity. Two important mastic properties include its shear modulus and permanent deformation. Too low stiffness may lead to high potential of rutting while too high stiffness may lead to cracking. This study targets at estimating the shear stiffness of mastics using the complex shear modulus of binder and the Hirsch model based on binder modulus and the volumetric composition of filler. Predictions of the mastics shear moduli using Hirsch model were compared with experimental measurements at different temperatures and frequencies and show very good agreement. The study also indicates that Time-Temperature superposition algorithms are applicable to mastics for different volume fractions of mineral fillers.