Device and method for testing paving materials

#The present invention relates generally to devices for testing the characteristics of construction materials such as asphalt and concrete and specifically to a circular metal device and associated method for characterizing the failure modes of asphalt binders.

#Asphalt is a general term that refers to the various bituminous substances that are used extensively for paving and road-making. Asphalt binders function as adhesion promoters for asphalt mixtures or aggregates and are typically comprised of naturally occurring hydrocarbons or petroleum distillate residue with or without polymer or chemical modifiers. In the paving industry, the term “aggregate” is used for a mass of crushed or uncrushed stone, gravel, sand, etc., predominantly composed of individual particles, but in some cases including clays and silts. The performance characteristics of asphalt binders are of particular importance in roadway construction. Understanding the limitations of the materials used for roadway construction permits the design and construction of roadways that are more stable, durable, and that offer greater safety to the user of the roadway.

#Low temperature thermal shrinkage cracking is one of four major failure modes in asphalt pavement, together with rutting, fatigue cracking, and moisture damage. Thermal shrinkage cracking in asphalt pavement occurs when the thermal tensile stress within the asphalt pavement that results from temperature drop exceeds the strength at that temperature. Thermal cracks typically appear as transverse cracks (pavement cracks perpendicular to the direction of traffic) at regular intervals in the field pavements.

#The accompanying drawings, which are incorporated into and form a part of the specification, schematically illustrate one or more exemplary embodiments of the invention and, together with the general description given above and detailed description of the preferred embodiments given below, serve to explain the principles of the invention.

#FIG. 1 is an exploded, perspective view of the mold and ring portion of the system of the present invention.

#FIG. 2 is a perspective view of the mold and ring portion of the system of the present invention.

#Reference Numerals

#10 materials testing device 12 ring 14 strain gauge 15 thermocouple 16 lead wires 18 test specimen 20 mold 22 base plate 24 centering plate 26 first specimen support 28 second specimen support 30 shoulder bolts 31 washer/nut combination 32 dowel pins 40 signal amplifier 50 processor 60 environmental chamber 70 materials testing system I. Overview

#The present invention provides a device and method for inducing a thermal crack in a test specimen in a manner that simulates the conditions experienced by asphalt binder found in the field. This device can be used to measure the cracking temperature and the thermal stress experienced by the test specimen under experimental conditions. The present invention directly measures the critical temperatures for thermal cracking of asphalt binders by using the dissimilar coefficients of thermal expansion for asphalt binders and common metals, such as aluminum. Aluminum has a modulus of elasticity that is about one third of steel and consequently shows three times larger strain response, i.e., better resolution, for the same stress development.