Special Topic: Pavement Engineering

Description

In this graduate course a number of topics which are relevant for the New Zealand pavement community will be discussed. Special emphasis will be placed on the following topics:
a. Design of pavements with thin surfaces such as sealcoats.
b. Re-use, recycling of construction demolition materials.
c. Characterization of asphalt mixtures.
d. Variability in pavement life caused by construction.
e. Deflection tests, remaining life analyses and design of maintenance strategies
In order to be able to fully understand the topics to be discussed, a good knowledge of the stress conditions in pavements is required as well as a good knowledge on material behavior. Therefore also lectures on these subjects will be given.

Course Content
Topic 1: How do pavements fail
The course will start with a discussion session with the students on how pavements will fail and how they look like if they are failed. The students will be asked to comment on the pictures of failed pavements and to present their ideas about the reasons for those failures.

Time needed: 1 hour Total time: 1 hour

Topic 2: Behavior of soils and granular materials
Then we will discuss the design of pavements, mainly consisting of granular layers and covered with only a thin surfacing being either a seal coat or a thin asphalt layer. After a short introduction on this topic a presentation will be given on the behavior of soils and unbound materials. Ample attention will be given to the stress dependent nature of granular materials and soils and it will be discussed how this stress dependent behavior and its dependency on moisture content and degree of compaction can be modelled. Relationships between this stress dependent behavior and the results one gets from simple, practical tests such as the CBR test will be discussed. Equations to predict stress dependent behavior will be presented as well as equations that allow soil moisture profiles to be estimated.

Time needed: 3 hours  Total time: 4 hours

Topic 3: Refresher stresses and strains
Using an advanced program like CIRCLY for the analysis of stresses, strains and displacements in multi-layered pavement systems, as the students will have to do during the course, doesn’t make sense if the user doesn’t have sufficient knowledge of these basic structural mechanics principles as well as failure models based on them. Therefore a 1 hour refresher course on this subject will be given.

Time needed: 1 hour Total time: 5 hours

Topic 4: Introduction to CIRCLY
For the analysis of stresses and strains in pavements, a computer program is needed which allows this nonlinear, stress dependent behavior into account. The best way to do this is to use a finite element program but linear elastic multi-layer programs like CIRCLY or BISAR can also be used for such purposes be it that the granular layers are divided into sublayers. Since CIRCLY is the program that is used in New Zealand, an introduction on how to use this program will be given. This introduction will be given by prof. Saleh.

Time needed: 1 hour Total time: 6 hours

Topic 5: Workshop on stress dependent analyses
In this workshop the students have to use CIRCLY in combination with the information on the stress dependent behavior of granular materials, to analyze the stress conditions in the unbound layers of a pavement with a thin surfacing. By means of an iteration process they have to determine the stiffness modulus to be used for the unbound layers and they have to determine whether or not shear failure is likely to occur.

Time needed: 2 hours    Total time: 8 hours

Topic 6: Overview of design of seals
It is not intended to give in depth lectures about designing seal coats. Nevertheless a short overview on what a seal coat is, its design, and the problems that may occur after several times of re-sealing will be given. Emphasis will be placed on the design on the granular layers below the thin surface course. Results of finite element analyses performed on pavements with a thin surfacing and granular base and sub-base layers will be presented showing that it is possible to design such pavements using advanced modelling techniques.
Time needed: 2 hour Total time: 10 hours

Topic 7: Re-use, recycling of construction demolition materials; how to build good quality granular layers with them
Especially in urban areas, millions of tons of construction demolition materials are produced. One way to get rid of it is simply by dumping it as landfill. This is a not so smart solution because much of the demolition waste consist of precious material which can easily be used again when selective demolition and sorting techniques are used. In the 3 hours to be spent on this topic, it will be shown that high quality base courses can be built using mixtures of crushed concrete and masonry coming from demolished houses, buildings and structures. It will also be shown that adding only a few percentage cement results in high quality materials which can very well be used as base course and certainly as sub-base course in pavements for roads, airfields and harbor areas.
Time needed: 3 hours Total time: 13 hours

Topic 8: Stabilized materials
A short introduction will be given about which type of stabilizing material should preferably be used for which type of material. This will be followed with a discussion on the complexities of testing such materials and why, because of that, the properties of cement stabilized materials are commonly estimated from equations correlating e.g. compressive strength on one hand and the flexural strength and stiffness on the other. Furthermore, it will be discussed how stabilized materials can effectively be used as capping layers. Also, the problem of reflective cracking in pavements with cement stabilized base and sub-base layers will be treated.

Time needed: 3 hours  Total time: 16 hours

Topic 9: Workshop cement treated layers
The students have to analyse the same pavement as was analysed in the previous workshop on stress dependent behaviour but now a cement treated layer is added. They have to analyse the effect of a cement stabilized base layer between the surface layer and the granular sub-base layer and the effect of a cement stabilization below the granular base course.

Time needed: 2 hours Total time: 18 hours

Topic 10: Characteristics of the bituminous binder used for asphalt mixtures
In this lecture the determination of the rheological characteristics of the bituminous binder will be discussed. Attention will be paid to the importance of determining the stiffness master curve by means of testing. Also equations will be presented that allow the prediction of the bitumen stiffness in relation to loading time and temperature as well as type of bitumen.

Time needed: 2 hours / Total time: 20 hours

Topic 11: Characterization of the mechanical properties of asphalt mixtures
In this block ample attention will be paid to the stiffness, fatigue resistance and resistance to permanent deformation of asphalt mixtures in relation to the characteristics of the bituminous binder, the volumetric mixture composition, loading time and temperature. It will be shown that the fatigue characteristics are dependent on the type of test and specimen size. It will be shown that laboratory fatigue testing results cannot straightforwardly be used for pavement life predictions and that all kind of corrections are needed in order to be able to do so. The nature and size of these corrections will be discussed. With respect to the resistance to permanent deformation it will be shown that depending on the type of mixture, the stone skeleton or the bituminous mortar play the most important role in the resistance of the mixture to permanent deformation. Furthermore, it will be shown that crack growth resistance and fatigue are highly related to the dependency of the asphalt mixture stiffness on loading time and temperature.
Since testing is not always possible, the above-mentioned characteristics are often estimated by using charts etc. Such estimation procedures will be presented.

Time needed: 4 hours / Total time: 24 hours

Topic 12: Production of asphalt mixtures, variations in mixture composition and bitumen characteristics caused by production and laying, effects of these variations on pavement life
In this lecture the different ways in which hot mix asphalt mixtures are produced and laid will be discussed. Attention will be paid to the variations in the mixing and laying procedures causing variations in asphalt mixture quality. The effect of these variations on pavement life will be analysed.

Time needed: 2 hours Total time: 26 hours

Topic 13: Workshop on quantifying variations in asphalt mix production on pavement life
In this workshop the students have to analyze/calculate the effects of variations in mixture composition on pavement life. They have to estimate how mechanical characteristics will change due to given changes in mixture composition, degree of compaction etc. They have to determine which type of variation causes the biggest variation in pavement life. Analyses have to be made using CIRCLY.
Time needed: 3 hours Total time: 29 hours

Topic 14: Deflection measurements and remaining life analyses
In a set of lectures the students will be informed about how to perform an evaluation of the remaining life of pavements using a falling weight deflectometer. Attention will be paid to: setting up a measurement plan, statistical treatment of the data, importance of visual condition assessment, importance of determining the surface modulus from the deflection data, back calculation of layer moduli, determination of the maintenance strategy. This subject will be taught by means of a real life example being the pavement of a container terminal in Western Europe.

Time needed: 6 hours / Total time: 35 hours