Ternary and Multivariate Quality Control Charts of Aggregate Gradation for Hot Mix Asphalt

Several statistical methods for controlling the quality of aggregate gradation are proposed, based on a multivariate model that describes compositional data. First, ternary quality control charts are developed to control a three-part gradation such as that given by the restricted zone method, with both hexagonal and elliptical acceptance regions. Second, multivariate quality control charts are developed with multiple category and T2 acceptance regions. Hexagonal and multiple category regions use fixed lower and upper control limits for each category and are easier to interpret by a visual plot, whereas elliptical and T2 regions account for the correlations among the categories and are more accurate and efficient. The control charts may be used to show the dynamic status of consecutive average values and can easily be applied with spreadsheet software such as Microsoft Excel.