Maciej Maliszewski

Advanced shear tester for evaluation of asphalt concrete under constant normal stiffness conditions

This paper presents motivation and details on the development of an advanced shear tester (AST) device capable of investigating the response of 150-mm cylindrical specimens under constant normal stiffness (CNS) conditions. Based on the laboratory experience and field observations from the soil and rock engineering, CNS conditions are particularly desirable when the normal stress changes considerably during the shearing process. Such situations occur in asphalt pavement structures especially under certain loading configurations. The CNS conditions are complementary to the constant normal load conditions that are applied in the current shear-mode devices incorporated in testing of asphalt concrete (AC) and pavement interface properties. This paper demonstrates the complex state of stress in the upper AC layer of a typical pavement under moving truck wheel and shows the need for the CNS device. In addition to outlining unique AST design features, this paper presents also the verification effort conducted on the solid Ultra-High Molecular Weight Polyethylene specimens. The AST results matched very well the reference data that were obtained under the elastic regime in the stress-controlled mode from the unconfined uniaxial compression and indirect tension tests. Finally, this paper demonstrates the example results collected on the solid AC specimens prepared with two different nominal maximum aggregate sizes. The analysis confirmed the ability of the AST device to capture both practical and fundamental phenomena occurring during the shearing process in the AC. It is believed that AST-type devices that are rather simple in design yet allow to induce complex state of stress in the AC specimens should be more recognised in the future research efforts.

Alternative Approach for Interpreting Traffic Speed Deflectometer Results

This paper presents an alternative approach for interpreting data collected with the traffic speed deflectometer (TSD). Although the idea of measuring pavement deflections at traffic speeds in a continuous manner is not new, worldwide interest is recent, in part because of the availability of a commercial TSD device. As with any new device, there is a need for robust, scientifically sound, yet practical interpretation procedures. This paper describes the details of such a procedure recently developed at the Road and Bridge Research Institute in Poland. In addition to a detailed description of the proposed algorithm and its unique features, this study demonstrates an example application that uses data collected by the TSD operated by the Road and Bridge Research Institute. The proposed approach can be successfully applied to the TSD data and allows for deep customization for a users and customers needs and applications.

Glass and carbon geogrid reinforcement of asphalt mixtures

Application of geogrids for asphalt layers in road and airport pavements has been studied since early 1980s. This type of geosynthetics is feasible to mitigate reflective cracking and to prolong fatigue life, that is, to reinforce asphalt layers within pavement structure. Up to now, many laboratory and field studies demonstrated significant benefits of using geogrids but still several aspects of their working mechanism within adjacent asphalt layers remain not fully understood and need to be further explored. This paper presents an initial part of the long-term study initiated in Poland in order to fully assess the benefits of using geogrids within asphalt layers. The first part of this paper presents the state-of-the-art review on geogrid applications in asphalt layers. The next part demonstrates and discusses the results obtained on the geogrid-reinforced beams under monotonic and cyclic loading conditions. Three types of large beams were prepared in the laboratory conditions. One group comprises reference beams without any reinforcement and the other two were reinforced, respectively, with glass and carbon geogrids. Specimens were evaluated in a custom-made 3PB/4PB fixture at 13°C in order to observe their behaviour under force-controlled fatigue test and displacement-controlled fracture test. Results demonstrated a beneficial impact of fibre reinforcement on the development of beam deflections in the fatigue tests and significantly higher fracture energy in the post-peak softening region. These results will be used to prepare a new experimental campaign to closely investigate the reinforcement mechanism of geogrids within asphalt layers. The paper concludes with short- and long-term plans necessary to develop an official design procedure for the pavements with geogrid-reinforced asphalt layers in Poland.

Microwave Applicator for Thermal Treatment of Bituminous Surfaces

A comprehensive study of a microwave applicator for thermal treatment of bituminous surface is presented in this paper. The applicator consists of a customized rectangular waveguide horn surrounded with a hexagonal lattice of cylindrical chokes preventing hazardous leakage of microwave radiation beyond an exposure area. Electromagnetic simulations based on a finite-difference time-domain method are applied in a design process and afterward, the prototype is manufactured with the aid of computerized numerical control machining. Eventually, the applicator is applied for experimental testing of microwave-assisted thermal treatment of the trial bituminous surface, which demonstrates that microwave energy may be a viable alternative to typical thermal bonding techniques used in road construction and maintenance processes if appropriate conditions are met.

Asphalt Mixture Sensitivity to Water and Frost

This paper presents recent study on the moisture susceptibility of asphalt mixtures under various water and frost conditioning. Moisture susceptibility of asphalt mixture is a very important property influencing significantly pavement durability. In particular, asphalt layers are subjected to a deterioration factor which is traffic independent—water and frost/thaw cycles. It is a common practice that during the mix design process qualitative experiments are conducted in order to assess the moisture resistance of trial mixes. Therefore there is a need for a suitable, validated and generally accepted method. This paper presents the results of the extensive research study conducted recently in Poland to compare several different testing protocols and associated requirements for the moisture sensitivity. Different aspects of the asphalt mixtures were investigated, in particular aggregate type, anti-stripping agent and bitumen type. Specimens for the moisture susceptibility were conditioned using four methods including an original method comprising the frost/thaw cycles as well as AASHTO T-283 protocol. In addition to the standard evaluation of the indirect tensile strength, there were several performance based tests conducted in the laboratory on the specimens before and after the conditioning procedures. The analysis shown in this paper lead to the development of the alternative specifications for the moisture susceptibility in Poland.