Umme Amina Mannan

Effects of Reclaimed Asphalt Pavement on Hot-mix Asphalt

This study examined the effects of reclaimed asphalt pavement (RAP) on the structural properties and performance of hot-mix asphalt (HMA) and the rheological properties of asphalt binder in the laboratory. As a first step, dynamic modulus (|E*|) and indirect tensile strength (ITS) tests were conducted on a set of HMA samples prepared with RAP and a set of HMA samples without RAP. The moisture susceptibility of samples with and without RAP was evaluated based on the |E*| ratio of wet to dry conditioned samples. Bending beam rheometer tests and direct tension tests were conducted on virgin binder, extracted binder, and RAP and aggregate mastics (mixture of binder and RAP and aggregate passing #200 to #50 sieves) to evaluate the low-temperature cracking. The results show that RAP materials caused an increase in |E*| and a decrease in ITS and had a negligible effect on moisture susceptibility. The RAP samples produced 15 % less permanent strain in |E*| testing than samples without RAP, which means that the RAP mixes were less susceptible to rutting. However, RAP mixed binder was more susceptible to low-temperature cracking as measured by the m-value (slope of the curve of stiffness versus time) and brittleness.

Chemical and mechanical changes in asphalt binder due to moisture conditioning

This study evaluates the effects of moisture conditioning on changes in chemical composition and mechanical properties of asphalt binder. Moisture conditioning is conducted using the AASHTO T 283 procedure and the recently developed moisture-induced sensitivity testing (MIST) device. Chemical analysis is performed using the Fourier transform infrared device and the mechanical testing is performed by a dynamic shear rheometer. Results show that ageing as well as other chemical changes occurred during moisture conditioning. Changes in binder fatigue life and damaged modulus are observed. Undamaged modulus and cohesive damage due to moisture conditioning were synthesised from this damaged modulus. It is found that undamaged moduli for both MIST- and T283-conditioned samples are almost the same; however more damage occurs in MIST-conditioned samples. Two regression models were developed to correlate physical properties with chemical changes.

Tribological and rheological characterisation of asphalt binders at different temperatures

Asphalt binder works as a binding by creating a thin film around the aggregate in asphalt pavement. Binder lubricity reduces the friction between aggregate particles and provides a better wear protection. Better wear protection prevents the degradation of pavement materials that occurs because of the traffic loading. Therefore, both proper compaction and surface interaction between the aggregates and asphalt binder are essential for enhanced long-term performance of the pavement. To explain surface interaction and rheology, the variation in friction coefficient and viscosity of three asphalt binders were tested at three different temperatures (135°C, 50°C and 25°C) that an asphalt pavement is likely to withstand during its service life. While all binders show similar trends and the viscosity and Stribeck curves are similar at 135°C and 50°C, at 25°C asphalt binders behave more like solids at lower sliding speed resulting in a different trend. Results show that rheological tests only provide the flow behaviour, whereas tribological tests provide a better understanding of friction and surface interaction between the aggregates and asphalt binder.

Evaluation of Long-Term Pavement Performance Based on New Mexico LTPP SPS5 Data

The Long Term Pavement Performance (LTPP) program has Specific Pavement Studies 5 (SPS-5), which study the effects of overlay rehabilitation on typical distresses. Each SPS-5 site has eight sections with two overlay thicknesses (50 mm and 125 mm), two overlay types (virgin asphalt mix and 30% recycled asphalt (RAP) mix), and surface preparation prior to rehabilitation (milling or not milling). The New Mexico SPS-5 sections were constructed in the eastbound Interstate 10 (I-10) in 1995. In this study, five distress parameters from these test sections are analyzed including International Roughness Index (IRI), rutting, fatigue cracking, longitudinal cracking, and transverse cracking. Analyses are conducted to determine which overlay factors affected the pavement performance more. Also statistical analysis is conducted to compare the performance of the No RAP and RAP mix. Analyses show that overlay age has the strongest impact on the overall pavement performance. Overlays with RAP showed more distress and roughness than the no RAP overlays, although this difference is not significant for rutting and IRI. Also thick overlays perform better than the thin overlays except for rutting. Milling prior to the rehabilitation decreases IRI and transverse cracking, but does not have any effect on longitudinal cracking.

Simplified Thermal Stress Model to Predict Low Temperature Cracks in Flexible Pavement

Thermal stress due to a decrease in temperature is usually considered the product of modulus of Hot-Mix Asphalt (HMA), coefficient of thermal contraction (CTC) of HMA and the decrease in temperature. The effects of viscoelasticity, nonlinear temperature profile and stress history on the modulus of asphalt concrete were widely explored in the literature. However, the nonlinear behavior of CTC was neglected in all thermal stress models. This study incorporates the temperature-dependent CTC in a simplified thermal stress model and validates the results comparing with the field observations. As the first step, this study measures the dynamic modulus at low frequency and low temperature. The CTC of asphalt concrete is then determined in the laboratory at different temperatures and validates the results using the data from an instrumentation pavement section. Then, the thermal stress model has been developed using the low temperature CTC, temperature and frequency dependent stiffness and the decrease in temperature. Finally, these models are used to predict transverse crack spacing and are compared with two field observations. In addition, the critical temperature of asphalt concrete is predicted with age of pavement by intersecting tensile strength and developed tensile stress curves. Results show that the simplified viscoelastic model - without considering stress history and nonlinear temperature profile - predicts the crack spacing accurately. In addition, the critical temperature of asphalt concrete is not a constant value. It increases with the age of the pavement.

Predicting Dynamic Modulus of Asphalt Concrete From Binder Rheological Properties

This study proposes a completely new regression-based predictive model to estimate dynamic modulus (|E*|) of asphalt concrete (AC) from the dynamic shear modulus (|Gb*|) and binder phase angle (δb) of the asphalt binder used in the AC mix. Other parameters related to the aggregate gradation and volumetrics are also incorporated in the model. In this study, a total of ten AC mixes with four binders having different Performance Grades (PG) and sources were collected from the manufacturing plants. The AC mixes were compacted and cored to cylindrical specimens. After that, the samples were tested in the laboratory for |E*| and AC phase angle (ϕ) at different temperatures and loading frequencies. The collected binders were tested for |Gb*| and δb using dynamic shear rheometer (DSR). The statistical assessment showed that a fairly accurate estimation of |E*| and ϕ can be obtained by using these new predictive models.

Cluster Analysis of LTPP Data to Estimate MEPDG Traffic Input for NM State and Perform a Sensitivity Analysis

Mechanistic-empirical pavement design guide (MEPDG) uses vehicle type, load spectra and number of axle to characterize traffic inputs for the pavement designs, as an alternate of the previously used equivalent single axle load (ESAL). Long term pavement performance (LTPP) study has 8 sites in New Mexico (NM) which collects the weigh-in-motion (WIM) data all over the year. In this study, the LTPP traffic data were extracted and then clustering technique was used to find out the similarities between different sites. Then, the traffic data from different cluster was compared to the default values in the MEPDG software. The effect of these differences on the pavement performance for New Mexico conditions was established through a sensitivity analysis. It was found that the alligator cracking and rutting are sensitive to axle load distribution. However, IRI was not significantly affected.

Cluster Analysis of the LTPP Data of NM State to Estimate MEPDG Traffic Input and Sensitivity Analysis

Mechanistic-Empirical Pavement Design Guide (MEPDG) uses vehicle type, load spectra and number of axle to characterize traffic inputs for the pavement designs, as an alternate of the previously used equivalent single axle load (ESAL). Long term pavement performance (LTPP) study has 8 sites in New Mexico (NM) which collects the weigh-in-motion (WIM) data all over the year. These WIM collected data can be used as the traffic inputs for a reliable pavement design using the MEPDG. In this study the LTPP traffic data were extracted and then clustering technique was used to find out the similarities between different sites. Then the traffic data from different cluster was compared to the default values in the MEPDG software. The monthly adjustment factors (MAF), vehicle class distribution (VCD) and axle load distributions for different cluster deviated from the MEPDG’s default values. The effect of these differences on the pavement performance for New Mexico conditions was established through a sensitivity analysis. It was found that longitudinal cracking is mostly sensitive to MAF. Alligator cracking is found sensitive to axle load distribution. Whereas rutting was found sensitive to all the variables studied, however international roughness index (IRI) was not significantly affected by any of the variables in this study.