Rut Resistant Asphalt Pavements
The author of this article examines the causes and potential cures of asphalt pavement rutting. He explains that rutting on the asphalt pavement surface commonly is the result of an unstable asphalt mix, heavy vehicle traffic, and high pavement temperatures. He notes that this type of rutting is often observed at intersections, bus stops, freeway off ramps, or under extreme loading situations on airport runways or dock loading facilities. He explains how an engineer can determine if rutting in the asphalt pavement surface is due to distress throughout the entire pavement structure or due to failure in the asphalt layer only. He suggests that asphalt mixes can be designed to resist rutting with the proper selection of materials, good construction practices, and use of appropriate mix design methods. Good compaction practices during construction will improve rut resistance by increasing the interlock of aggregate particles in the mix.
EARLY RUTTING OF ASPHALT CONCRETE PAVEMENT UNDER HEAVY AXLE LOADS IN HOT DESERT ENVIRONMENT: CASE HISTORY
A case study of early rutting of an asphalt concrete pavement under heavy axle loads in a hot desert environment is presented. A section of four-lane divided Dubai-Hatta Highway in the Dubai Municipality of the United Arab Emirates experienced a 13-mm (0.51-in.) rutting in a mere 10-month period. Review of the project documents indicated that the pavement section under consideration was properly designed and constructed by a mix design procedure that used the Marshall test equipment applicable to heavy-duty asphalt pavements. By this procedure a design asphalt content of 4.3% by the weight of mix was selected. During the course of the investigation the design asphalt content was confirmed by the Hveem mix design procedure. However, neither of these conventional mix design methods indicated any potential for rutting; moreover, the method of laboratory test specimen fabrication did not produce compaction levels representative of those obtained in situ under the actual traffic loading. On the basis of the results of this investigation the most probable cause for premature rutting was attributed to axle loadings that exceeded the loading conditions for which the Marshall and Hveem mix design criteria have empirically been developed. Creep testing appeared to better characterize asphalt concrete in a more fundamental manner with a potential use in mechanistic analysis to estimate the propensity of the mix for rutting. Its limited use in the study confirmed that the rutting that did occur was to be expected for the existing unconventional loading conditions for the environment in which the pavement was located. Although not performed in the present study, an improved analysis method developed by Strategic Highway Research Program Project A-003A researchers to evaluate rutting is briefly described.
A New Vacuum Pressure Infiltration CFRP Method and Preparation Experimental Study of Composite
In order to prepare a carbon-fiber-reinforced polymer composite (CFRP) with ideal microstructure and properties, a new vacuum pressure infiltration CFRP method is proposed based on an analysis of existing CFRP preparation process methods. Research on composite material preparation systems was carried out by using this new method principle. The system mainly includes a fiber pre-forming module, a vacuum heating infiltration module, a hot-press curing molding module, and a data acquisition control module. Under the conditions of natural curing at 0 MPa + 6 h + 25 °C, vacuum heating curing at –0.05 MPa + 30 min + 80 °C, and hot-press curing at 0.7 MPa + 5 min + 50 °C, a two-dimensional (2D) CFRP with excellent microstructure and properties was successfully prepared. Observing the microstructure of the prepared composite material, it can be found that the inside of the composite material was sufficiently and uniformly infiltrated, and common preparation defects such as holes and delamination were effectively controlled. Through the performance test, the bending strength of the material reached 790 MPa.