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.
Mix Design and Analysis and Structural Section Design for Full Depth Pavement for Interstate Route 710
Note: This electronic version does not contain the appendices. The test data contained therein are available from: 1.0 INTRODUCTION This report summarizes the results of an investigation to design both a suitable asphalt concrete mix and a full-depth asphalt concrete structural section containing the mix, or mixes for a " Long Life Pavement " for a portion of Interstate 710 in Southern California. A companion report (Technical Memorandum, TM UCB PRC-99-3) desribes the asphalt concrete section for use as an overlay on the existing portland cement concrete pavement. Interstate 710 is located in Southern California, in Los Angeles County, Figure 1. Rehabilitation is scheduled for the summer 2000 and the project has been selected for a long-life pavement design, with a design life of 30 to 40 years. The freeway is a heavily trafficked route and carries traffic in and out of the Port of Long Beach. The specific section of Interstate Route 710 selected for this project is between the Pacific Coast Highway and the 405 Freeway, Figure 2. The current maximum number of trucks per day in the design lane is 9,650. An estimate of the design traffic for this period is 100×10 6 to 200×10 6 equivalent single axle loads (ESALs). The existing pavement structural section consists of 200 mm of portland cement concrete (PCC), 100 mm of cement treated subbase, 100 mm of aggregate base and 200 mm of imported subbase material. Two rehabilitation strategies are planned, one for the majority of the section and the other for under the structures. On the sections where the overhead clearance is not limiting, the existing PCC will be cracked and seated and overlaid with asphalt concrete. Under the structures where minimum clearance requirements do not allow an overlay, full depth asphalt concrete sections are will be utilized. 2 1.2 Design Concepts The design methodology is illustrated schematically in Figure 3. For Interstate Route 710 the performance tests and associated analyses have been limited to rutting and fatigue cracking. For rutting, the Hveem stabilometer has been used to select the range of binder contents required for the initial mix design process shown in Figure 3. To select the final mix design an accelerated performance test, the repeated load simple shear test at constant height (RSST-CH) has been utilized. Figure 4 illustrates the framework for the selection of the design binder content using the RSST-CH. Essentially the mix design consists …
The role of dissolved oxygen in supercritical water in the oxidation of ferritic–martensitic steel
Abstract To assess the role of dissolved oxygen in supercritical water on the growth processes of oxide scales, a marker experiment of ferritic–martensitic steel was performed by exposing to supercritical water (H 2 16 O) containing marked 18 O 2 at 600 °C under 25 MPa. The oxide scale was analysed by using Secondary Ion Mass Spectrometry (SIMS). The oxygen isotope profile shows that dissolved oxygen and supercritical water react with metals simultaneously. Dissolved oxygen changes the oxidation/reduction potential of supercritical water leading to an increase in the oxidation rate. The oxidation rate increases with increase in dissolved oxygen content in supercritical water. The mechanism of the effect of dissolved oxygen on oxidation is discussed.