Lucas F. de A. L. Babadopulos

Softening and local self-heating of bituminous mixtures during cyclic loading

Bituminous materials are heterogeneous media composed of aggregate particles and bituminous binder. The repetition of loading cycles on such materials induces stiffness changes. Those changes are measured during cyclic tension–compression tests by tracking the evolution of the norm and of the phase angle of the complex modulus. Different phenomena may be responsible for the stiffness changes. Some of those phenomena are completely reversible, for example, self-heating, recoverable nonlinearity (complex modulus dependency on stress/strain amplitude) and another bulk phenomenon, which is hypothesised as thixotropy. Another one, known as damage, is irreversible. All stiffness change in bituminous materials is frequently considered as caused by damage. This is not realistic, as careful analysis shows that the other phenomena are responsible for a major part of the stiffness decrease in most fatigue tests. Local self-heating could be a physical explanation for a large part of the observed reversible stiffness decrease. This paper proposes three simplified coupled thermomechanical analytical calculations in order to model the observed stiffness decrease due to local self-heating. The last calculation considers a heterogeneous structure of bituminous mixtures, composed of rigid monodisperse spherical particles and a mastic phase. The model allows calculating the initial slopes of the curves’ “norm of complex modulus” and “phase angle” versus “number of cycles”. Aggregate gradation of the mixture, mastic film thickness, volume fraction of binder and thermophysical properties of aggregate particles and binder are taken into account. Simulated and experimental results for one bituminous mixture were compared for tests at different temperatures and frequencies. Results show that local effects could explain the observed initial decrease in the norm of complex modulus during cyclic tests.

Aggregate Maximum Nominal Sizes’ Influence on Fatigue Damage Performance Using Different Scales

AbstractSome researchers have used the fine aggregates matrix (FAM) as a means to evaluate the influence of material properties on the expected changes in the performance of hot mix asphalt (HMA). ...

Evaluation of Fatigue Behavior of Aged Asphalt Mixtures Using the Simplified Viscoelastic Continuum Damage Model

Aging of asphalt mixtures might play an important role in pavement structural behavior. That should be evaluated using mechanical models. This work aims at identifying the effects of aging on linear viscoelastic and damage behavior of asphalt mixtures, properties that influence the fatigue life of asphalt pavements. That is performed by characterizing a Hot Mix Asphalt (HMA) at four different aging states. The aged materials were obtained by heating loose asphalt mixture in oven at two different temperatures (85 and 135 °C) and aging times (2 and 45 days). Prony series were fitted to complex modulus results. For damage characterization, the Simplified Viscoelastic Continuum Damage (S-VECD) model was adopted. Damage characteristic curves and G R versus N f failure envelopes were obtained from controlled crosshead tension-compression test results at 19 °C. It was concluded that aging produces materials that fail for less evolved damage states. However, depending on pavement conditions and layer geometry, and considering the HMA hardening, aging does not necessarily reduce the fatigue life.

Resistance to Moisture-Induced Damage of Asphalt Mixtures and Aggregate-Binder Interfaces

The aggregate-asphalt binder adhesiveness is considerably affected by moisture. This property may accelerate distresses in asphalt pavement surface courses when aggregate-binder compatibility is not adequate. Numerous tests have been developed to measure this property, such as the Moisture-Induced Damage test (AASHTO T283) and the Asphalt Bond Strength test (AASTHO TP 91). The former measures the indirect tensile strength of dry and moisture-conditioned asphalt mixtures. The latter measures the tension stress needed to remove a pullout stub with asphalt binder from a solid substrate. Although these are distinct tests, both may be used as a means to analyze how moisture affects a certain combination of mineral aggregate and asphalt binder. The objective of this work is to correlate the results of these two tests and to analyze if the tested combinations of materials follow the same trend under both circumstances. Chemical compositions of the tested aggregates are also investigated. Results from Moisture-Induced Damage tests show that the use of an antistripping agent may reduce the impact of moisture-damage on tensile strength and that the aggregate with a higher content of calcium oxide performed better. The 12 h moisture conditioning in the Asphalt Bond Strength test had a strong correlation with the dry mixes, which was not noticed for the mixtures conditioned for 3 and 6 h. Asphalt mixture’s moisture sensitivity results correlated well to the loss of adhesion in the aggregate-binder interface.

Fatigue cracking simulation of aged asphalt pavements using a viscoelastic continuum damage model

Few information in the literature indicates how aging affects the service life of asphalt pavements. This work presents linear viscoelasticity and damage characterisation of an asphalt mixture at four aging states, and simulation of pavements fatigue performance. E* tests were performed in sinusoidal compression. Controlled crosshead tension-compression testing was used for damage characterisation. Aged materials were obtained by heating loose asphalt mixture at two temperatures (85°C and 135°C) and aging times (2 and 45 days). Two simulated pavements were studied for comparing behaviour at different ages using Layered Viscoelastic Pavement Analysis for Critical Distresses (LVECD). Results showed that the effect of aging seems to improve service life. It was also observed that simulating the asphalt layer as composed by two half-layers (aged at the top and unaged at the bottom) did not lead to significantly different results with respect to fatigue performance of an evenly aged layer.