New Approach to Determine Standard Deviation and Precision Estimates for ASTM D4867/D4867M and AASHTO T283

Abstract

Abstract Moisture damage in asphalt pavements can be attributed to the incompatibility of the asphalt binder, aggregate, or the interaction of the asphalt binder and aggregate. Moisture damage can accelerate pavement distresses such as cracking and rutting. The most widely used test methods by state highway agencies are AASHTO T283-14, Standard Method of Test for Resistance of Compacted Asphalt Mixtures to Moisture-Induced Damage, and ASTM D4867/D4867M-09, Standard Test Method for Effect of Moisture on Asphalt Concrete Paving Mixtures. Some state highway agencies evaluate moisture resistance during production to ensure a quality asphalt mixture. Currently AASHTO T283-14 and ASTM D4867/D4867M-09 do not provide a method to calculate the standard deviation of the tensile strength ratio (TSR), nor does it provide precision estimates for the TSR. The objective of this paper is to show how one can calculate the variance (or standard deviation) of a variable when the value of interest (i.e., TSR) is calculated from two other random variables. The standard deviation of a random variable that is a quotient of two other variables can be calculated easily as long as the individual variables are random, independent, and the standard deviations are small relative to the mean. The novelty of this approach is in a statistics-based method for determining the standard deviation of the TSR based on using an approximation for the ratio variance using ASTM D4460-97, Standard Practice for Calculating Precision Limits Where Values Are Calculated from Other Test Methods. This new approach to calculate the standard deviation of the TSR will be used to develop a precision statement for AASHTO T283-14 and ASTM D4867/D4867M-09 following ASTM E691-19e1, Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method (Superseded).