| Stone Matrix Asphalt has been used in Europe and Scandinavia for over twenty years. It was originally designed to withstand the wear of studded tires. However, it was quickly found to be very resistant to rutting. The majority of this rut resistance is provided by the coarse aggregate skeleton component of the mixture. However, the second component, a high asphalt binder content mortar, also plays a role.; Stone Matrix Asphalt technology was brought to the United States in 1990, and in 1991, several trial projects were completed. Today, it is widely used in some states even though no standard design procedure exists. To remedy this lack of a mixture design method, the National Cooperative Highway Research Program initiated Project 9-8, Designing Stone Matrix Asphalt Mixtures. The overall goal of the project was to develop a simple, straightforward mixture design method for Stone Matrix Asphalt. As part of this, an extensive investigation of Stone Matrix Asphalt mortars was conducted. The results of the mortar study are presented in this report.; The objectives of the study reported herein were to develop test methods and protocols for use in characterizing Stone Matrix Asphalt mortars. These tests were then to be used to examine a wide range of mortars to enhance the understanding of their behavior. The final objective was to use the test results to establish specification criteria that could be used to accept or reject mortars during the design of Stone Matrix Asphalt mixtures.; Several tests were initially used including resilient modulus, indirect tensile strength, Rotational Viscometer, Dynamic Shear Rheometer, Bending Beam Rheometer, and the Direct Tension Tester. It was found that the Dynamic Shear and Bending Beam Rheometers could be used to adequately characterize mortars at high and low temperatures. Specification limits for these tests were recommended to be five times higher than the limits currently specified for performance graded binders. Testing is completed at temperatures representative of the expected in-service climate.; Limited testing of Stone Matrix Asphalt mixtures containing various mortar combinations was also undertaken in an attempt to determine how the mortar affects the mixture as a whole. The findings indicate that if the mortar is not designed correctly, the mixture cannot perform as intended. |
