The use of recycled tire rubber in a portland cement concrete (PCC) mixture is investigated as a possible alternative for nonconventional PCC mixtures. This study is focused on the determination of the practicality of producing such mixes and evaluating their engineering properties. An experimental program was developed to use two types of tire rubber (fine crumb rubber and coarse tire chips) in PCC mixtures. A control PCC mix is designed using American Concrete Institute mix design methods, and three groups of rubberized PCC mixes were developed by partially replacing the aggregate with rubber. Eight tire rubber contents were used in each group. Mixes were tested in compressive and flexural strength in accordance to ASTM standards. Results show that rubberized PCC mixes can be made and are workable to a certain degree with the tire rubber content being as much as 57% of the total aggregate volume. However, strength results show that large reductions in strength would prohibit the use of such a high rubbe...

The mechanistic-empirical pavement design guide (MEPDG) is the research version of the newly released DARWin-ME software by AASHTO. MEPDG includes two models for Levels 2 and 3 hot-mix asphalt (HMA) dynamic modulus (E*) predictions. The two models are NCHRP 1-37A and NCHRP 1-40D. The primary difference between the two is the binder stiffness parameter; viscosity or shear modulus. Moreover, MEPDG includes three levels for binder stiffness characterization: viscosity for Level 1 conventional binders, shear modulus for Level 1 superpave binders, and default values for Level 3. The influence of the binder characterization input level on the performance of the MEPDG E* predictive models is evaluated in this paper. To calibrate the models for Idaho, 27 HMA mixtures commonly used in Idaho were investigated. Results showed that the performance of the investigated models varied based on the temperature and the binder characterization method. The NCHRP1-37A E* model with MEPDG Level 3 binder inputs yielded ...

Many pavement distresses, including rutting, fatigue cracking and low-temperature cracking, are influenced by the air void distribution in hot mix asphalt (HMA). This study investigated the influence of the type of Superpave gyratory compactors (SGCs) and specimen preparation/geometry on air void distribution and its manifestation on mechanical response. X-ray computed tomography along with image analysis techniques was used to capture and characterise the air void distribution within HMA microstructure. The mechanical response was characterised using the dynamic modulus test and static creep test. An index called heterogeneity index was developed to quantify the air void distribution in vertical and lateral directions. The study revealed that laboratory compacted specimens are heterogeneous and there is a need to prepare laboratory specimens with homogeneous air void distribution for accurate interpretation of results. In addition, the study revealed that the type of the SGC used influenced the dynamic modulus of compacted HMA specimens.

This paper addresses the development and evaluation of a mix stability index referred to as the gyratory stability (GS). GS is calculated from the compaction data by summing the cumulative energies dissipated in the compaction of a gyratory sample. A wide range of commonly used mixes in the State of Idaho were selected for evaluation. Mixes were tested for dynamic modulus (E*) and flow number (F _N); rutting was measured with the asphalt pavement analyser (APA). Furthermore, E* test results were used in the AASHTO Mechanistic–Empirical Pavement Design Guide (MEPDG) as level 1 inputs, to predict rutting for these mixes; GS ranked mixes similarly to the APA and F _N tests and MEPDG results. Furthermore, results indicated that the GS has the potential to be used as a screening tool for asphalt mix design, especially to decide upon the acceptance of the mix aggregate structure, and as a quality control tool.

Several monotonic performance indicators that use one or more elements of the load–displacement curve (e.g., area under the curve, curve peak) are used to assess the resistance of asphalt mix to cracking. While these indicators have their own merits, they lack the full description of the load–displacement curve. This study developed a new performance indicator called the Weibull cracking resistance index (${\mathrm{Weibull}}_{\mathrm{CRI}}$ ), which describes the entire load–displacement curve. The study performed an extensive laboratory evaluation of 16 different asphalt mixes tested in two different testing protocols [i.e., indirect tension (IDT) test and semicircular bending (SCB) test] to evaluate the proposed indicator. The findings of this study demonstrated that ${\mathrm{Weibull}}_{\mathrm{CRI}}$ results are sensitive to the variation in binder content and binder performance grade (PG) and were in good agreement with expected cracking resistance based on the composition of the studied mixes. In addition, ${\mathrm{Weibull}}_{\mathrm{CRI}}$ had low variability and provided a good statistical grouping of mix resistance to cracking. The study recommended IDT to determine ${\mathrm{Weibull}}_{\mathrm{CRI}}$ in order to assess asphalt mix resistance to cracking.

Several in service pavements located in different regions of Idaho that have been designed according to the ITD design method were redesigned using the AASHTO 1993 as well as the Mechanistic-Empirical Pavement Design Guide (MEPDG) procedures. All designs were conducted at a 50% reliability level. The nationally calibrated MEPDG (version 1.1) was used to predict the performance of the three design methods. Level 2 subgrade material characterization inputs were used in the MEPDG analysis. All other MEPDG inputs were level 3. Performance indicators predicted using MEPDG related to the three design methods were compared to each other. Results showed that, relative to AASHTO 1993 and MEPDG procedures, ITD design method significantly overestimates the thickness of the pavement structure, and particularly the thickness(s) of the unbound layer(s). On the other hand, the AASHTO 1993 and MEPDG guides show reasonable agreement on the resulting pavement structure.