Abstract: The performance of experimental pavements at the Pennsylvania Transportation Research Facility was evaluated. These pavements contained five different types of base course: bituminous concrete, aggregate bituminous, aggregate cement, aggregate-lime-pozzolan, and crushed stone. Most of the pavements had been subjected to about 2.4 million 18-kip equivalent axle loads (EALs), which is equivalent to approximately 40-years service life. Data analyzed were pavement serviceability index and three distress manifestations--roughness, rutting, and cracking. Some existing pavement performance models were also evaluated by using the performance data. The performance data indicate that the trend of serviceability index loss with increasing EAL follows the power function developed at the American Association of State Highway Officials (AASHO) Road Test. Of the performance models evaluated--AASHO, modified Highway Research Board (HRB), and Painter's models--the AASHO model appears to predict best, although it overpredicts pavement service life. By using a curve-fitting process and regression analysis, equations that relate pavement performance indicators and structural number are formulated. These equations permit prediction of the rate of serviceability loss and pavement life required to reach a certain present serviceability index drop. Also developed are equations that relate distress with structural number and critical pavement response with pavement service life. These equations may be used to predict various distress intensities from structural numbers and also used to predict pavement life from critical response. According to the results of the analysis, the maximum compressive strain at the top of the subgrade appears to be a better factor than the maximum surface deflection for predicting pavement service life. (Author)

Abstract: 1. Composite structure for roadways and surfaced areas, based on bituminous mixtures comprising various superposed courses of materials bonded with a bituminous binder from a base course (6) in contact either with the foundation or with the roadway or area to be surfaced and a surfacing course (2), the said structure being characterised in that at least its base course (6) consists of a bituminous material capable of withstanding an alternating flexure fatigue test lasting for 10**6 cycles while being subjected to relative deformations greater than 1,5 10**-4 , and in that the thickness of the said base course is restricted to at least a part of the zone subjected to tensile stresses (5) under the effect of a single moment acting on the composite structure.

Abstract: The method of new pavement design developed at esso has been adapted to provide an overlay design system. The basic idea is to model the old pavement in order to be able to calculate stresses and strains, considering the traffic and climate conditions. It is then possible to define design criteria, corresponding to the requirements of an overlay: - the old pavement must be relieved. -the overlay itself must work under acceptable conditions. The modelling is achieved through the old pavement analysis, while the mechanical properties of the mixes considered are assessed: dynamic modulus, resistances to permanent deformations and to fatigue. The minimum thickness of the overlay is computed for each mix considered in order to match the design criteria. A selection between the various solutions is made from technical and economic considerations, to find out the most suitable one for the work. An example of application of the system is presented. The problem was to find out a suitable mix and to compute the required thickness of an overlay for a ring road in northern Ireland. Ruts and cracks in the temporary wearing surface made it compulsory to overlay the structure, the analysis of the old pavement (visual inspection, borings and deflection measurements) showed that it was very weak. Analysis of deflection values permitted modelling, and the selection of design criteria: reduction of horizontal tensile strain at the bottom of the old pavement, overlay fatigue index, and acceptable resistance to permanent deformations of the overlay mix. Six mixes altogether were envisioned for the study: 2 hot rolled asphalts, 2 asphalt concretes and 2 dense bitumen macadams for wearing courses. In a first step, a single course overlay was considered, and the minimum thickness for each mix computed. Because of the high values obtained, a two-course overlay was then envisaged: a wearing course made of 40 mm of hot rolled asphalt, and a base course to be determined. The minimum thickness of the base course for each mix was computed to match the design criteria, which led, together with considerations on the resistance to permanent deformations of the mixes, to selecting the asphalt concrete with the lower binder content in a 100 mm layer. This solution was retained and the pavement overlaid without any particular problem. A deflection follow-up was carried out: the overlay considerably reduced the deflection values, down to the level computed with the esso overlay design system, pointing out the validity of the procedure. For the covering abstract of the conference see IRRD 815640.

Abstract: When properly designed and constructed, the Asphalt Institute full-depth pavement concept can be a viable design alternative for seasonal frost areas The Corps of Engineers reduced subgrade strength frost design proved to be an upper bound or conservative design under these test conditions For each design, two different thicknesses were studied in test sections placed over 12 in of prepared subgrade and tested under light traffic conditions in Hanover, New Hampshire After design traffic loading was exceeded, pavement failure occurred as expected in the thinner full-depth section The thinner reduced subgrade strength section was still in good condition after experiencing twice its design loading Frost penetrations, pavement n-factors (surface transfer coefficients), Benkelman Beam deflections, and the spring subgrade moisture contents are also compared for the two designs