Herbert F. Southgate

TEMPERATURE DISTRIBUTION WITHIN ASPHALT PAVEMENTS AND ITS RELATIONSHIP TO PAVEMENT DEFLECTION

A METHOD HAS BEEN DEVELOPED TO ESTIMATE THE TEMPERATURES AT DEPTH IN AN ASPHALTIC CONCRETE PAVEMENT UTILIZING THE MEASURED SURFACE TEMPERATURE AND THE 5-DAY AVERAGE AIR TEMPERATURE HISTORY. TEMPERATURE PREDICTION NOMOGRAPHS WERE DEVELOPED FOR EACH HOUR BETWEEN 6 A.M. AND 5 P.M. THIS TEMPERATURE PREDICTION METHOD IS INDEPENDENT OF THE SEASON OF THE YEAR. A METHOD FOR ADJUSTING BENKELMAN BEAM DEFLECTIONS FOR TEMPERATURE EFFECTS HAS BEEN DEVELOPED AND IS PRESENTED. THIS ENABLES THE DEFLECTIONS TAKEN AT ANY TEMPERATURE TO BE ADJUSTED TO A REFERENCE TEMPERATURE, THUS MAKING POSSIBLE DIRECT COMPARISONS OF DEFLECTIONS. AN ANALYSIS OF AASHO ROAD TEST DATA WAS MADE USING THE BOUSSINESQ AND BURMISTER EQUATIONS AND CHARTS. THE RESULTS INDICATE THAT THE TEMPERATURE-MODULUS OF ELASTICITY RELATIONSHIP IS CURVILINEAR, HAS THE SAME BASIC SHAPES AS THE TEMPERATURE-DEFLECTION ADJUSTMENT FACTOR CURVE. THERE APPEARS TO BE A LINEAR RELATIONSHIP BETWEEN DEFLECTIONS ADJUSTMENT FACTORS AND MODULUS OF ELASTICITY. THEREFORE, THERE SEEMS TO BE A TEMPERATURE-DEFLECTION-MODULUS OF ELASTICITY CORRELATION BETWEEN FIELD TEST DATA AND THEORY. /AUTHOR/

EFFECTS OF LOAD DISTRIBUTIONS AND AXLE AND TIRE CONFIGURATIONS ON PAVEMENT FATIGUE

Damage factor relationships for axle and tire configurations are presented. Adjustment factors are provided to account for variations in load distributions within axle groups, distances between axles of a tandem, and variations in tire pressure for both dual and flotation tires. Properly accounting for accumulated fatigue of a pavement requires a reasonable measure of traffic volume, proportions of vehicle styles (classifications) within the traffic stream, dates of service, estimate of the average damage factor for each classification, and estimates of tire contact pressures. All adjustment factors presented are based on analyses of a limited number of structures and should be used with caution. The accuracy of these analyses is not in question, but the range of structures investigated was limited. They are intended to indicate the trend, shape, and sensitivity of various inter-relationships and their relative magnitudes. Modifications may have to be made upon the analyses of additional pavement structures. Kentucky traffic may differ from that in other areas, both in types of vehicles in the traffic stream and the type and direction that cargo is being transported.

Structural Capacity of In-Place Asphaltic Concrete Pavements from Dynamic Deflections

The proper design of asphaltic overlay thicknesses involves four major factors: the in-place modulus of the subgrade, an estimate of the structural capacity of the existing pavement, estimates of the future traffic expressed AS Equivalent axleloads and required or desired design levels, and a thickness design procedure. This paper deals with estimating the in-place subgrade modulus and the remaining load-carrying capacity of the existing pavement. The method presented herein is valid for any road rater or other dynamic tester such as the dynaflect. This procedure was based upon a 600-pound (272.4-kg) peak-to-peak dynamic load applied at a rate of 25 hz. The steady-state deflections have to be adjusted for load, dynamic frequency, and location of sensors. This method should be applied only to those testers that use a constant vibratory load.(a) for the covering abstract of the conference see IRRD 815640.

STRAIN ENERGY ANALYSIS OF PAVEMENT DESIGNS FOR HEAVY TRUCKS

Classical concepts of work, or strain energy, as applied to the analysis of stresses, strains, and deflections under various vehicular load configurations on pavement systems are summarized and controlling equations for strain energy density are presented. When considering strain energy density, strain energy, or work, all components of stresses or strains must be taken into account so that total internal behavior can be evaluated. Previously, pavement thickness design systems have been developed using only one component of strain, typically at the bottom of the asphaltic concrete layer or at the top of the subgrade. Strain energy concepts permit modifications to thickness design systems to account for the net effect of all components of strains or stresses. Effects of loads and distribution of loads on vehicles are summarized. One startling result shows the large increase in fatigue rate due to unequal distribution of loads between the two axles of a tandem group relative to the fatigue rate caused by an equal load distribution. Damage factors and pavement thickness designs for heavily loaded trucks exceeding legal load limits are also discussed. The effects of those vehicles on Interstate pavements are compared to the effects of more normally loaded vehicles. (Author)

DEVELOPMENT OF A THICKNESS DESIGN SYSTEM FOR PORTLAND CEMENT CONCRETE PAVEMENTS

This report covers the merger of criteria used in the Portland Cement Associations and AASHTOs pavement thickness design systems. The combined criteria is coupled witht heprinciple of equal work as defined in classical physics to produce thickness design curves for portland cement concrete pavements. The thickness of portland cement concrete varied by approximately 0.15 inches for the same CBR and design EAL when the thickness of crushed-stone base varied from 3 to 6 inches. Therefore, the design thickness of the portland cement concrete is relatively insensitive to change in thickness of the crushed stone base. (Author) base. (Author)

Temperature Distributions in Asphaltic Concrete Pavements

The straight-line relationship derived from Maryland data between temperatures at a given depth and the surface temperatures plus 5-day average air temperatures is as valid for upper New York State and Arizona as for Maryland. The main differences were in the annual ranges and annual mean temperatures. The concept for estimating pavement temperature distributions appears to be valid and may be used with confidence for estimating pavement temperatures at all latitudes and longitudes.

Deflection Behavior of Asphaltic Concrete Pavements

Deflection responses of a series of experimental test sections were obtained layer by layer during construction, upon completion of construction, and subsequent to construction. Deflections were obtained by use of Benkelman beams, the Road Rater, and the Dynaflect. Test results from one location within each test section were analyzed to determine which relationships were, or were not, meaningful. This was done as a pilot study and as a preliminary step toward final analysis of the data bank. The analyses are presented in this report.

Non destructive evaluation of rigid pavements using road rater deflections

The aim of this paper is to summarize and document research and developments relating to the use and application of dynamic deflection measurements (specifically Road Rater deflections) for evaluation of rigid pavements in Kentucky. Procedures have been developed to theoretically simulate measured Road Rater deflections and associated stresses and strains using elastic theory as expressed in the Chevron N-layer computer program.

Variations of Fatigue Due to Unevenly Loaded Axles within Tridem Groups

The effect of unevenly distributed loads on the axles within a tridem has been shown to be very significant. Equations are presented that enable the equivalent load effect for equal load distribution to be adjusted for uneven loading. Considering the relative increase and the relatively small volume of trucks currently using tridems, the equation for all tridems without regard to locations on the vehicle is recommended at this time. Consideration should be give to using equations for individual load patterns as the volume of trucks using tridems increases and more weight data become available. (Author)

THICKNESS DESIGN CURVES FOR PORTLAND CEMENT CONCRETE PAVEMENTS

Past experience indicates that thickness designs using portland cement concrete best agree with criterion used in the Portland Cement Associations design method for 18-kip EAL of 2 to 3 million or less. For EALs greater than 2 to 3 million, past experience best agrees with criterion developed from the AASHO Road Test. Research herein indicates the two criterion become asymptotic to each other at approximately 2.5 million EAL. For a variation in thickness and elastic moduli in portland cement concrete, dense-graded aggregate, and subgrade elastic modulus, research indicates that a general conic equation (included herein) very closely 18-kip single axleload. The transition from a tensile strain to a work criterion is presented. Decreasing the thickness of dense-graded aggregate base caused a maximum increase of 0.15 inches in the thickness of portland cement concrete. Thus, the design curves are presented for a concrete elastic modulus of 4.2 million psi (Kentucky concrete strength). (Author)