165 research outputs found
Anti-reflective cracking design of (reinforced) asphaltic overlays
No full textCivil Engineering and Geoscience
Characterization of Unbound Granular Materials for Pavements
No full textThis research is focused on the characterization of the mechanical behavior of unbound granular road base materials (UGMs). An extensive laboratory investigation is described, in which various methods for determination of the mechanical properties of granular materials are examined for their applicability, particularly in developing countries. Further, the mechanical behavior of unbound granular materials as a function of the moisture content and the degree of compaction is investigated. A study into the modeling of the stress dependent mechanical behavior of granular materials is presented. Finally, verification and validation of a relatively simple characterization technique, the repeated load CBR test (RL-CBR), by the results of cyclic load triaxial testing are provided and overall practical implications of the research are presented. The laboratory investigation involves a large range of granular materials, mainly (sub-)tropical road base and subbase materials. The performed tests yield fundamental parameters that describe the strength, stiffness and resistance to permanent deformation of the materials tested. In addition to the (sub-)tropical road base and subbase materials, a recycled mix-granulate widely used in pavement construction in the Netherlands and a base course and frost protection material from Austria are incorporated to a limited extent in the laboratory testing program. Most roads in developing countries are either unpaved or have a thin asphalt surfacing, and as a consequence the granular base and subbase layers provide the bulk of the bearing capacity. Although the important structural contribution of these unbound granular layers is understood, engineering practice still greatly relies on tests which mainly give index properties of these materials. Pavement structures are designed based on empirical design methods related to a single design chart, restricting the incorporation of marginal materials or new materials for which the empirical data sets are not available. The reasons that pavement design and construction in developing countries rely on empirical design procedures that are basically developed for completely different conditions are: - the affordability and complexity of the cyclic triaxial tests required to determine the stress dependent mechanical behavior of granular materials; - the perceived complexity and unfamiliarity with the computational tools (non-linear multilayer or finite element analysis) required to model the performance of pavements using this mechanical behavior despite the availability of powerful digital computers and their penetration even to remote places. In order to promote the introduction of Mechanistic-Empirical design methods in developing countries, this research was set up with two goals: i. to make the characterization technique for the mechanical behavior of granular road base materials more accessible to practice through the development of a simple and effective characterization technique; ii. to further develop the understanding of the stress dependent mechanical behavior of unbound (sub-)tropical base and subbase materials. To achieve the first aim an innovative and relatively simple testing procedure, the RL-CBR test, is developed to characterize the mechanical behavior of the UGMs. RL-CBR testing is performed on the various granular materials in steel moulds without and with strain gauges. With the strain gauges the confining condition and hence the stress state of the specimen is estimated through mould deformation measurements. The finite element method (FEM) is used to model the RL-CBR testing and interpret the test results into mechanical behavior. Due to the non-uniform complex stress distribution in the RL-CBR compared to the triaxial test, fundamental material properties such as the stiffness modulus are less easy to determine. Extensive triaxial testing on the various granular materials is performed to realize the second goal. The result of this investigation is also used to validate and verify the results of the RL-CBR tests. Moreover, the effect of influence factors such as moisture content, degree of compaction, material type etc. on the mechanical behavior is investigated. For the unbound granular road base materials, particularly the natural gravels, the effect of the moisture content on the mechanical behavior was found to be more significant than the effect of the degree of compaction. Relative to the failure and permanent deformation behavior the resilient deformation behavior is less affected by the moisture content and the degree of compaction. The RL-CBR testing serves well its purpose to get a good estimate of the fundamental mechanical properties of granular road base materials from a rather simple characterization technique. The practical accessibility of characterizing the mechanical behavior of UGMs can therefore be enhanced through RL-CBR testing. This is proven by the fact that good correlations have been found between the stiffness results of the two characterization techniques, i.e. the complex triaxial test and the newly developed repeated load CBR test.Design and ConstructionCivil Engineering and Geoscience
Performance related characterisation of the mechanical behaviour of asphalt mixtures
No full textAbstract not availableCivil Engineering and Geoscience
Design principles of surfacings on orthotropic steel bridge decks
No full textThis dissertation describes the research into surfacings of orthotropic steel bridge decks. The motive for this research is the frequently reported problems of this type of structures including cracking and rutting of surfacing materials and fatigue related cracks in the steel plate. An intensive experimental program was carried out on three wearing course materials, namely mastic asphalt, guss asphalt and an open synthetic material. The program also included on a bituminous based membrane material. The results of the experimental program were analysed to characterise the complex mechanical behaviour of the different materials. Within the framework of this research, models that describe the response of the surfacing materials were developed, including a newly developed unified model that describes the time-temperature characteristics of many road materials. Furthermore, constitutive relations for elastic as well as inelastic response of the materials were developed. All the developed models were implemented in the Finite Element System CAPA-3D. For verification of the different models results of laboratory tests and full-scale experiments in the LINTRACK APT facility were used. Furthermore, a scientific approach in which the non-linear response of the materials, the geometry and the load are well presented, was used to give an insight into the interaction between the different components of the structure and the vehicle at different temperatures. Because this scientific approach is too sophisticated and expensive for routine analyses and design of the structure, a practical design concept is proposed. In this concept, the geometry and the load are well presented, but the material behaviour is simplifiedCivil Engineering and Geoscience
Development of an Evaluation Protocol for Self-Cementing Secondary Road Base Materials
No full textIn congested areas around the world, traffic has significantly grown beyond expectation in terms of both volume and weight. Any hinder to the traffic causes severe delays resulting not only in economic loss but also in extra pollution of the environment. Therefore, the number of times maintenance work have to be performed should be reduced as much as possible. Application of self-cementing, secondary materials such as Blast Furnace Slag (BFS) for base courses is one of the methods to reduce the need for maintenance, since such base courses can provide an increase of the stiffness and the strength of the pavement structure. The long-term performance of this type of self-cementing, secondary material is however not fully understood. Because this type of stabilization appears to be associated with undesired deformations and distresses such as heaves formation and cracking. These undesired defects, which appear at random in terms of severity and moment of occurring, requires an assessment of the long-term physical and mechanical performance of these materials. However, long-term behaviour is often difficult to predict. In general, field-scale trials monitored over a long period of time, are needed to provide information whether these materials can be used without significant risk or not. As an alternative to field trials, which are time consuming and expensive, reliable methodologies are needed to estimate the long-term physical and mechanical performance within a short period of time. In this research, a protocol is proposed as a means of exploring the long-term mechanical and physical performance of secondary materials. A slag mixture which is routinely used in the Netherlands in road (sub-)bases was selected as study material. The slag mixture consisted of fresh Air-cooled Blast Furnace Slag (AC-BFS), steel slag and Granulated Blast Furnace Slag (GBFS) sand. The A32 motorway in the Netherlands was used as a source of field aged Blast Furnace Slag and steel slag materials. The pavement structure of this motorway experienced serious failure after about 20 years of service life and the base layer material caused this failure. In order to prevent similar problems to occur in the future, this research suggests different methods to detect at an early stage potential poor material performance. The first step of exploring the long-term performance of self-cementing materials in road applications implies obtaining a better understanding of the physical, mechanical and microstructural features of the materials when used as road base material and to analysis its possible effects on the pavement performance. Consequently, the influence of different potential degradation conditions, which can be mimicked in the laboratory was investigated. Numerous failure mechanisms have been hypothesized, including chemical reactions and increased stresses due to obstructed deformations. Additionally, other physical failure mechanisms including frost action damage were investigated. The results show that there is a linkage between the secondary material performance and temperature, moisture, chemical composition and time. The measured data indicate a relationship between some major chemical compositions and the mechanical properties of slags. The response of the laboratory prepared samples to the proposed tests were similar to the A32 base material failure, suggesting that the evaluation method did a reasonable job of producing in an accelerated way in the laboratory a material which behaves similar as the A32 material. The developed procedure (protocol) suggests that it is possible on the basis of material characterization, steam aging tests and freezing – thawing tests to trace in a rather short period of time materials which may attribute to the failure process of base layers in pavements.Structural EngineeringCivil Engineering and Geoscience
The effect of aging on binder proporties of porous asphalt concrete
No full textIn this dissertation, the results of a research on the effects of aging on the binder properties of porous asphalt concrete (PAC) are described. The research has been done on laboratory and field aged specimens. In addition to the conventional aging methods for short and long term aging of the binder in the laboratory, a new mixture aging protocol in a 'weatherometer' was proposed that combines the main environmental factors influencing field aging, i.e. temperature, UV light, and humidity/moisture. The field binders were recovered from specimens taken from road sections immediately after construction and after 1, 3, 7, and 12 years service life. Rheological, mechanical, and chemical characterization of the binders was conducted on the laboratory and field binders to understand the effects of aging. To this end, the determination of fundamental rheological binder properties was performed in addition to conventional empirical properties such as penetration and softening point. Low temperature tensile and stiffness properties of the binder/mastic were determined using the Direct Tensile Test (DTT) and Bending Beam Rheometer (BBR). The Dynamic Shear Rheometer (DSR) was used to determine the viscoelastic properties (complex modulus and phase angle) of the binders in a wide range of temperatures. Furthermore, the DSR was used to determine the fatigue properties of the binders using strain controlled repeated loading at different strain levels. Chemical characterization using Infrared spectroscopy (IR) and Gel-Permeation Chromatography (GPC) were performed to determine, respectively, the development of the functional groups responsible for aging and the Molecular Weight Distribution (MWD). All the test results have provided insight into laboratory and field aging simulations, the impact of the filler, and at the same time has provided material properties for constitutive modelling. An important finding in this research signifies that aging greatly influences the low temperature performance of the binding material leading to a higher rate of damage accumulation (fatigue) and ultimately ravelling of PA. To illustrate the implications of the research results, a limited number of finite element calculations have been made to determine the stress conditions in the binder/mortar due to traffic loads. Because aging has a negative influence on the fatigue resistance and relaxation behaviour of the binder, aging negatively influences the performance of PAC.Civil Engineering and Geoscience
Accelerated testing and surface cracking of asphaltic concrete pavements
No full textCivil Engineering and Geoscience
Response Modelling of Bitumen, Bituminous Mastic and Mortar
No full textThis research focuses on testing and modelling the viscoelastic response of bituminous binders. The main goal is to find an appropriate response model for bituminous binders. The desired model should allow implementation into numerical environments such as ABAQUS. On the basis of such numerical environment, Delft University of Technology (TU) is developing mechanistic asphalt mixture design tools. These tools are based on Meso scale mechanics. For Porous Asphalt (PA) performance, such a tool is readily available in ABAQUS. Implementation of an accurate viscoelastic response model for bituminous mortar will improve the tool’s capability in explaining PA performance at various temperatures and it is therefore a primary goal of this research. In addition the response model is also thought to be of equal importance for other meso mechanics tools for asphalt concrete mixtures that will be developed in the near future. To realise the main objective of the study, first an extensive Dynamic Shear Rheometer (DSR) testing program was carried out on bituminous binder, mastic and mortar. The program was carried out to get a better understanding of the response behaviour of binders for various loading conditions. For the pure binder and mastic testing, a cone and plate setup was developed. For the mortar testing, a specially designed mortar column setup was utilized. The frequency and time domain response of the binders was first analysed in the linear viscoelastic range. Hereafter the frequency domain response of the binders beyond the linear range response was investigated. The results showed that binders exhibit nonlinear behaviour at higher levels of shear stress. At relatively high temperatures, in the range of 30°C and above, mortar and mastic show nonlinear behaviour at shear stresses as low as 10 kPa. At low temperatures of 0°C and below, high shear stresses in the range of 1 MPa were observed to cause nonlinear behaviour. The second part of the study covers extensive modelling work. After a literature survey, two response models were first selected as a basis for further research; i.e. the Huet-Sayegh (HS) and the Burgers’ model. These models were then utilised to describe the frequency domain response data. It was observed that the Burgers’ model requires a number of Kelvin-Voigt elements to accurately describe experimental data. The HS model on the other hand presented an accurate description of response data. However, the HS model lacks the capability of explaining viscous deformation. For this reason the HS model was extended by adding a linear dashpot in series. The modified Huet-Sayegh (MHS) and the generalized Burgers’ model were then used to describe the frequency domain response of various materials. Results have shown that the MHS description of the response data excels that of the generalized Burgers’ model. For time domain use in numerical environments, incremental formulations of the response models were obtained. The formulations were coded and the numerical outputs were then validated by performing various simulations. The formulations were used to simulate time domain response tests. In this process parameter determination was first performed on the basis of frequency domain data. The parameters were then used to simulate time domain creep and relaxation tests. The simulation results showed that the frequency domain master curve data provided accurate material information for simulating the time domain response. The result further underlines the fact that binder’s behaviour is intrinsic, and as such their behaviour in frequency and time domain is related. It is this intrinsic behaviour of the binders that was described by the generalized Burgers’ and the MHS models. Hereafter the models were finally implemented into ABAQUS, and they are made available for use in the meso mechanics PA design tool. The results from the PA design tool showed that both models lead to comparable results. The pros and cons of the models for practical application were evaluated. For relatively small numerical models, the MHS model is suggested because of its simplicity in the number of model parameters and its high accuracy in describing material response. However, for computationally intensive numerical models, the use of the generalized Burgers’ model is suggested because of its high computational efficiency in numerical environments. Finally, the nonlinear response of binders was analyzed using Schapery’s nonlinear theory. Numerical formulation of the theory that incorporates the generalized Burgers’ model was adopted. The formulation was coded into a User Subroutine Material code (UMAT) for use in ABAQUS. In the UMAT code an iterative scheme for obtaining correct stress state was incorporated at the material level. Results from the code were verified by performing various simulations. Application of the Schapery’s nonlinear theory in the PA design tool showed that the effects of nonlinear behaviour are negligible at temperatures of 10°C and below. However, at 20°C and above, distinct and significant differences between linear and nonlinear simulations are observed. From the results it is concluded that common binders may be modelled as being linear viscoelastic for temperatures of 10°C and below. At 20°C and above nonlinear response becomes significant and, it needs to be considered in meso mechanistic computations.Road and Railway EngineeringCivil Engineering and Geoscience
Laboratory and Field Asphalt Fatigue Performance, Matching Theory with Practice
No full textThis thesis investigates the relationship between predicted and observed fatigue life of asphalt. This study also investigates the positive effects of modifying bitumen with Retona, a bitumen modifier produced in Indonesia from natural asphalt rock sources, on pavement performance in terms of increased resistance to fatigue and permanent deformation. Classical pavement fatigue analysis assumes cracking to initiate from the bottom of the pavement and propagates to the top. However, when relating ‘predicted’ pavement fatigue life to ‘observed’ fatigue life, one immediately encounters a ‘conflict’ with theory because in practice cracks are also initiated at the pavement surface. This thesis also attempts to explain the phenomenon of surface or top-down cracking. In the past, many studies were made to validate design procedures by matching predicted performance with field performance. However, this project, only takes into account the studies that were carried out in the Netherlands and by Dutch researchers elsewhere. Test results performed in the 1990’s on three pavement sections on the accelerated pavement testing facility Lintrack, then owned by the Section of Road and Railway Engineering, Department of Civil Engineering Delft University of Technology, have therefore been used in this study. The Lintrack research provided a large amount of valuable data with respect to pavement performance and was therefore perfectly suited for a study to match theory with practice. To achieve these goals, several steps were taken. Firstly, the data obtained from observations made on the Lintrack accelerated pavement test sections (built in 1990) were studied. The sections were simple two-layered pavement systems consisting of a gravel asphalt concrete (GAC) layer overlying a sand subgrade. The data consisted of information on the geometry and material characteristics of the test pavements, loading and environmental conditions, deflection test results and visual condition data in terms of cracking and permanent deformation. Secondly, a fatigue cracking prediction model was developed based on laboratory data obtained from four point bending (4PB) tests on the same material type. To more accurately simulate the fatigue behaviour of a real pavement in the laboratory, a new test setup termed as the “beam on elastic foundation” (BOEF) test was developed. Since the GAC pavement sections built in 1990 had been removed, the GAC (GAC 1990) material was not available anymore. Therefore, a new GAC (GAC 2010) mixture needed to be produced and considerable efforts were made to produce the GAC 2010 mixture such that it truly replicated the GAC 1990 mixture. Material characterization tests performed to understand better the GAC 2010 mixture included, in addition to the two mentioned fatigue tests; monotonic uniaxial tension and compression tests, indirect tension tests, mastic healing tests and tests on the recovered bitumen such as penetration and Dynamic Shear Rheometer tests. The analysis of the Lintrack APT sections was carried out by determining; (1) the pavement life based on the back calculated modulus of the asphalt layer for different probability of survival levels, and (2) the magnitude of damage that was initiated at the bottom of the asphalt layer expressed by means of Miner’s damage ratio. The cumulative damage ratio, ni/Nfi (Miner’s ratio), was calculated based on the tensile strain at the bottom of the asphalt layer at different temperatures that occurred during the Lintrack tests and the fatigue relationships that were obtained from 4PB and BOEF fatigue laboratory tests. It is shown that the observed pavement life based on the back-calculated asphalt modulus from deflection measurements is longer than the pavement life calculated on the basis of damage initiation at the bottom of the asphalt layer. The results showed that for all three Lintrack sections, the BOEF based predictions exhibited a better agreement as evidenced from the smaller shift factor between “field stiffness reduction” lifetime and the lifetime based on “fatigue” predictions. Therefore, BOEF test based fatigue models are highly recommended to be used for predicting pavement life in practice. This study has shown that it is very difficult to relate cracking visible at the surface of the pavement to the initiation of fatigue damage at the bottom of the asphalt layer. Finite element simulations using detailed tyre–pavement contact pressure modelling have been carried out. The results showed that significant tensile strains had developed at the pavement surface. The magnitude of these tensile strains was such that they can be held responsible for the development of surface cracking. It should be noted however that surface cracking cannot be explained using a stress based analysis. This study clearly showed that permanent deformation (in this study this was permanent deformation of the subgrade) exhibits significant effects on the formation of longitudinal cracks at the edges of the wheel paths. The study on modifying GAC with Retona showed that the GAC+Retona mixture exhibits better mechanical properties compared to the reference GAC mixture. The Retona modified mixture showed a higher fatigue life and higher resistance to permanent deformation compared to the reference GAC mixture.Structural EngineeringCivil Engineering and Geoscience
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