M. Huurman

Research of Bituminous MortarFatigue Test Method Based on Dynamic Shear Rheometer

This paper presents a new test method that allows fatigue characterization on bituminous mortar by means of dynamic shear rheometer (DSR). The studied mortar is composed of bitumen, filler and fine sand at a mass ratio of 0.34:0.30:0.36. Dynamic shear rheometer instruments are widely used for bitumen testing by using parallel plate geometry. However, the parallel plate geometry is not suitable for mortar testing due to the fact that the mortar contains fine sand. To take good advantage of DSR instruments, mortar specimen and clamp system were specially designed so that mortar testing can be performed by using DSR instruments under parallel plate control mode. Due to the complex specimen geometry, finite element simulations were performed to translate the torque and deformation that the specimen was subjected into the real mortar stress and strain. An intensive experimental program indicated that the developed test method was capable to capture the shear fatigue behaviour of mortar at meso-scale by using DSR instruments.

Developments in 3D Surfacing Seals FE Modelling

A surfacing seal may not be considered a thin homogeneous bituminous layer and thus cannot be designed on the basis of material bulk properties. As a result, common design methodologies are of no value in seal design. Seals are thus designed on the basis of empirical methods or engineering judgement. The introduction of new tyre types, the increase in traffic loads and the introduction of new types of bitumen and modifiers ask for fundamental insight into seal behaviour. Hereto a 3D meso-mechanical FE model of a seal was developed. The model represents the seal as it is, i.e. aggregates sitting in a binder and partially worked into the base. Individual aggregates are loaded by forces that follow from a moving tyre. This paper shows that full insight into the stresses and strains that develop in the various relevant structural components of the seal is obtained. It is discussed how this insight may be used for seal design.

Characterisation of surfacing materials for orthotropic steel deck bridges. Part 1: experimental work

The life span of surfacing materials like mastic asphalt on orthotropic steel deck bridges is quite short when compared with those of ordinary road pavements. Several problems including cracking and rutting of the surfacing materials have been reported in many countries. In order to get an insight into these problems, it is deemed necessary to represent the behaviour of the different materials and the geometry of the bridge structure in a realistic way. For this purpose, an extensive experimental programme was carried out and a nonlinear finite element constitutive model was developed. This is the first part of two papers on characterisation of the behaviour of two typical surfacing materials for orthotropic steel deck bridges. Results of monotonic uniaxial compression and tension performed at different temperatures and strain rates will be presented. Furthermore, the response of the materials will be described using a Desai-type material model.

A Unified Model to Describe the Time-Temperature Dependency Characteristics of Several Bound Road Materials

ABSTRACT In this contribution the development of a unified model that describes the time-temperature dependency characteristics of several bound road materials will be presented. The model is based on observed physical trends of several engineering properties and the applicability of the time-temperature superposition principle to elastic as well as inelastic properties of several bound materials. The model has five parameters, two of which represent the temperature susceptibility of a bound material and three other parameters that describe individual properties of that material. Furthermore, it will be shown that the model has been used to successfully describe several properties of 18 bound road materials e.g. flexural stiffness, compressive, tensile and shear strength. The model has been validated by predicting values of properties outside the range of the data (extrapolation), for properties other than those used for estimation of the parameters of the model. Some apparent advantages of the unified model include: considerable reduction in testing programs, prediction of material properties which are impossible or difficult to determine experimentally, construction of master curves for different properties, logical material models and hence, numerically stable FE codes.

Nonlinear Response Characterization of Bituminous Mortar

In mesomechanics performance studies of porous asphalt concrete (PA), one of the crucial component materials influencing the raveling performance of the mixture is bituminous mortar. In relation fatigue performance, the viscoelastic response of the mortar for loads corresponding to the magnitude and frequency of the truck loading is important. In this paper, the mechanical response of a bituminous mortar material is investigated at various shear stress levels and loading frequencies. A dynamic shear rheometer setup with a specimen geometry specially developed for mortar testing is utilized. The mortar, which consists of bitumen, filler, and fine fractions of sand, is produced with a composition similar to that of a standard PA mixture. The tests were conducted at various temperatures in the frequency domain. The results show that the selected mortar test setup produces results with good repeatability. The results of high shear measurements show the presence of nonlinear behavior at shear stress levels in the range of 10 kPa for temperatures of 30°C and above. At temperatures of 0°C and below, the mortar exhibits linear viscoelastic behavior at shear stress levels of up to 1 MPa. The observed nonlinear viscoelastic behavior is described using Schapery nonlinear theory. The paper discusses the testing methods and the interpretation and description of results with the nonlinear theory. It also discusses the implications of the results for mechanistic based PA performance models.

Integrating Traditional Characterization Techniques in Mechanistic Pavement Design Approaches

Although widely applicable and useful, the traditional CBR test does not provide the mechanical behaviors such as resilient and permanent deformation characteristics of granular road materials. A relatively simple testing technique is developed to characterize the resilient modulus of granular materials based on the traditional CBR test using repeated load cycles. The Finite Element Method (FEM) analysis has been attempted for the purpose of modeling the Repeated Load CBR and derives an equivalent resilient modulus of the sample as a bulk. Strain gauges were used to measure the lateral deformation of the CBR mould from which the confining stress can be estimated to determine a stress dependent resilient modulus. Furthermore, a large scale cyclic load triaxial test was carried out to validate the result of the repeated load CBR on coarse granular materials from South Africa and Ethiopia. The repeated load CBR test is quite useful to estimate the resilient modulus of unbound granular materials that can be used as an input in mechanistic pavement design analysis in the absence of triaxial testing facilities.