Direct tensile test to assess healing in asphalt

Asphalt concrete has the advantageous ability to heal. During rest periods, damage present in the material is restored to a certain extent. Healing of the material can be observed in its regaining of strength and stiffness after rest periods. In this paper, a new test method is presented. It was developed to increase the understanding of the healing phenomenon. The test method focused on asphalt as it was assumed to be the driver of the healing performance. The test method assessed the healing performance of asphalt in stiffness and strength by testing the bond strength in tensile mode of two pieces of asphalt that were assembled under controlled temperature and stress conditions. With the test method, healing tests were performed on one type of binder; the load level during healing and the healing time were varied. The test results showed that after a short healing time of only 6 min, a significant amount of healing could be detected. That finding indicates the importance of adhesion between two crack surfaces when the healing capacity is assessed. It was also found that the maximum tensile stress reached a plateau value after 24 h of healing; the finding indicates that full healing can be realized in short time periods for pure, unaged, soft binders. It was also shown that the load level perpendicular to the damage during healing had a significant effect on the observed healing

Het healingmechanisme van bitumen nader verklaard

Asfalt heeft de aantrekkelijke eigenschap dat het zichzelf kan herstellen na schade. Er is echter tot op heden geen betrouwbare methode om de healingcapaciteit van een asfaltmengsel te bepalen. Bij het healingproces van een discrete scheur spelen twee processen een rol, namelijk het in contact komen van de oppervlakken van de scheur; het zogenaamde bevochtigen, en het vermogen van deze oppervlakken in contact om kracht over te dragen; de intrinsieke healing. In dit artikel wordt een testmethode gepresenteerd welke in staat is om de verschillende parameters die een rol spelen gedurende de healing te variëren om zo het belang van de processen in healing bloot te leggen. Met behulp van deze testmethode is de mate van healing van bitumen in de tijd onderzocht en de invloed van normaalkracht gedurende healing. Op basis van de gepresenteerde resultaten kan worden geconcludeerd dat bevochtiging van het scheuroppervlak tenminste 50% van de macroscopisch geobserveerde healing bepaalt voor pure bitumen. Dit inzicht kan worden gebruikt om een materiaalmodel voor healing van asfalt te formuleren, op basis waarvan een relatief eenvoudige healingtest kan worden ontworpen waarmee de healingcapaciteit van asfaltmaterialen onderling kan worden vergeleken

Calibration and Validation of a Visco-Elasto-Plastic Constitutive Model for Bituminous Conglomerates

The paper presents and discusses the calibration and validation of a three-dimensional constitutive visco-elasto-plastic model developed for the analysis of the mechanical behaviour of bituminous mixes. The methodology, an inverse problem technique, uses a one-dimensional analytic formulation of the constitutive model and four different algorithms of non-linear constrained optimisation: the Conjugate Gradient, Montecarlo, Davidon-Fletcher-Powell and Simplex. On the basis of the creep recovery data obtained from an experiment in support of the model calibration, it was verified that the values of the constitutive parameters can be reliably identified, even starting from different initial guesses. A subsequent comparison between the experimental creep curves and numerical ones of the 3-D model demonstrated minimal shifts, confirming the robustness of the identification procedure for the parameters

On the use of rigid body modes in the deflated preconditioned conjugate gradient method

Large discontinuities in material properties, such as those encountered in composite materials, lead to ill-conditioned systems of linear equations. These discontinuities give rise to small eigenvalues that may negatively affect the convergence of iterative solution methods such as the preconditioned conjugate gradient method. This paper considers the deflated preconditioned conjugate gradient method for solving such systems. Our deflation technique uses as the deflation space the rigid body modes of sets of elements with homogeneous material properties. We show that in the deflated spectrum the small eigenvalues are mapped to zero and no longer negatively affect the convergence. We justify our approach through mathematical analysis and show with numerical experiments on both academic and realistic test problems that the convergence of our DPCG method is independent of discontinuities in the material properties.Structural EngineeringCivil Engineering and Geoscience

Study of Influence of Operating Parameters on Braking Distance

Stopping distance includes driver thinking distance and braking distance. Braking distance is one of the basic standards for road design and maintenance practices. Adequate tire–pavement skid resistance plays a significant role in reducing braking distance and consequently enhancing road safety. With technology such as the antilock braking system, the friction force is maximized by applying the brakes repeatedly, in an on-and-off pattern, such that the braking distance is shortened. Several studies have shown the effect that some parameters, such as water film thickness, tire inflation pressure, and wheel load, have on braking distance. Less discussed is the effect of slip ratio, temperature, and pavement surface characteristics. Measuring the braking distance in the field is energy-consuming and time-consuming, and there are uncertainties in the environmental conditions as well. General approaches to calculating braking distance are based on basic mechanics principles. To the authors’ knowledge, a model that can simulate the whole braking process is not available. The presented study proposes a way to predict braking distance by means of finite element modeling only. A model that can include the effect of parameters such as temperature, slip ratio, and pavement surface characteristics on the braking distance is introduced.Accepted Author ManuscriptPavement Engineerin