Over the past decade, the Texas Department of Transportation (TxDOT) focused research efforts on improving mixture design to preclude rutting in the early life of the pavement. However, these rut resistant stiff mixtures may be susceptible to long-term fatigue cracking in the pavement structure as the binder stiffens due to oxidative aging. To address this concern, TxDOT initiated a research study with the primary goal of evaluating and recommending a hot mix asphalt concrete (HMAC) mixture fatigue design and analysis system to ensure adequate mixture fatigue performance in a particular pavement structure under specific environmental and traffic loading conditions. A secondary goal of the research was to compare the fatigue resistance of commonly used TxDOT HMAC mixtures including investigating the effects of binder aging on fatigue performance.

Hot-mix asphalt concrete (HMAC) mixture fatigue characterization constitutes a fundamental component of HMAC pavement structural design and analysis to ensure adequate field fatigue performance. HMAC is a heterogeneous complex composite material of air, binder, and aggregate that behaves in a non-linear elasto-viscoplastic manner, exhibits anisotropic behavior, ages with time, and heals during traffic loading rest periods and changing environmental conditions. Comprehensive HMAC mixture fatigue analysis approaches that take into account this complex nature of HMAC are thus needed to ensure adequate field fatigue performance. In this study, four fatigue analysis approaches; the mechanistic empirical (ME), the calibrated mechanistic with (CMSE) and without (CM) surface energy measurements, and the proposed NCHRP 1-37A 2002 Pavement Design Guide (MEPDG) were comparatively evaluated and utilized to characterize the fatigue resistance of two Texas HMAC mixtures in the laboratory, including investigating the effects of binder oxidative aging. Although the results were comparable, the CMSE/CM approaches exhibited greater flexibility and potential to discretely account for most of the fundamental material properties (including fracture, aging, healing, visco-elasticity, and anisotropy) that affect HMAC pavement fatigue performance. Compared to the other approaches, which are mechanistic-empirically based, the CMSE/CM approaches are based on the fundamental concepts of continuum micromechanics and energy theory.

Over the past decade, the Texas Department of Transportation (TxDOT) focused research efforts on improving mixture design to preclude rutting in the early life of the pavement, which also offered increased resistance to moisture damage, but fatigue cracking may surface in the long term particularly if the binder stiffens excessively due to aging. The primary goal of this project is to evaluate and recommend a fatigue analysis system for TxDOT designs to ensure adequate mixture fatigue performance in a particular pavement structure under specific environmental and loading conditions. A secondary goal of comparing fatigue resistance of commonly used TxDOT mixtures including investigating the effects of aging will also be realized.

Fatigue cracking is one of the fundamental distresses that occur in the life of a Hot Mix Asphalt Concrete (HMAC) pavement. This load induced distress leads to structural collapse of the entire pavement ultimately and can only be remedied by rehabilitation. There is the need, therefore, for a total understanding of the phenomenon to be able to counter its occurrence. The fatigue resistance of hot mix asphalt concrete (HMAC) has been estimated using approaches ranging from empirical methods to mechanistic-empirical methods to purely mechanistic methods. A continuum mechanics based approach called the Calibrated Mechanistic with Surface Energy (CMSE) measurements was developed at Texas A & M University and recommended after comparison with other approaches in predicting fatigue lives of two Texas HMAC mixtures. The CMSE approach which includes fundamental material properties such as fracture, aging, healing, and anisotropy has been shown to effectively model the parameters that affect the performance of HMAC pavements exposed to repetitive traffic loads. Polymer modified asphalt (PMA) improves pavement performance by providing additional resistance to the primary distresses in flexible pavements, including permanent deformation or rutting, thermal cracking, and fatigue cracking. In this research, the CMSE approach was utilized to estimate the fatigue resistance of HMAC fabricated with asphalts modified with Styrene-butadiene-Styrene (SBS) co-block polymer. These HMAC mixtures were fabricated from materials used on three different road sections in Texas and one test pavement in Minnesota. The CMSE approach was validated as an effective approach for estimating the fatigue resistance of HMAC mixtures with PMA. The effect of oxidative aging on the fatigue resistance of the HMAC mixtures was also verified. Oxidative aging of the mixtures resulted in a corresponding decrease in mixture fatigue resistance. In addition, for two HMAC mixtures with the same binder content and aggregate gradation, the mixture with the softer of the two Performance Grade (PG) binders exhibited greater fatigue resistance. The use of the Utility Theory revealed the possible effects of aggregate geometric properties on the HMAC mixture properties and consequently on their fatigue resistance.

The work contained in this report constitutes Phase II of Texas Department of Transportation (TxDOT) Project 0-4468. The primary objective of Phase II was to provide additional laboratory validation and sensitivity analysis of the calibrated mechanistic with (CMSE) and without (CM) surface energy measurements fatigue analysis approaches recommended in Report 0-4468-2. The second objective was to provide a better understanding of the binder-mixture relationships and effects of binder oxidative aging on both mixture fracture properties and fatigue life (N sub f). The third objective was to explore the possibility of establishing a surrogate fatigue test protocol based on the CMSE approach. These objectives were achieved through fatigue characterization of additional hot-mix asphalt concrete (HMAC) mixtures with different mix-design parameters and materials under varying laboratory aging exposure conditions.

Bearing Capacity of Roads, Railways and Airfields includes the contributions to the 10th International Conference on the Bearing Capacity of Roads, Railways and Airfields (BCRRA 2017, 28-30 June 2017, Athens, Greece). The papers cover aspects related to materials, laboratory testing, design, construction, maintenance and management systems of transport infrastructure, and focus on roads, railways and airfields. Additional aspects that concern new materials and characterization, alternative rehabilitation techniques, technological advances as well as pavement and railway track substructure sustainability are included. The contributions discuss new concepts and innovative solutions, and are concentrated but not limited on the following topics: · Unbound aggregate materials and soil properties · Bound materials characteritics, mechanical properties and testing · Effect of traffic loading · In-situ measurements techniques and monitoring · Structural evaluation · Pavement serviceability condition · Rehabilitation and maintenance issues · Geophysical assessment · Stabilization and reinforcement · Performance modeling · Environmental challenges · Life cycle assessment and sustainability Bearing Capacity of Roads, Railways and Airfields is essential reading for academics and professionals involved or interested in transport infrastructure systems, in particular roads, railways and airfields.