Experience with end-result specifications for granular base aggregates in Ontario

Abstract

In 1982, the Ontario Ministry of Transportation (MTO) introduced end-result specifications (ERS) for the acceptance of granular base and subbase aggregates with respect to lot-by-lot statistical testing for grading and percentage of crushed particles. Under ERS, the mean and range of four test results (sublots) were used to determine the payment for specific production quantities (lots). Quality assurance (QA) sampling and testing were conducted at the aggregate source by the MTO. Materials within a lot that were, on average, marginally outside the specification limits or exhibited a wide range would be paid at a reduced contract price. Materials significantly exceeding these requirements would be rejected. In 1997, MTO introduced quality control (QC) requirements that made the contractor responsible for sampling and testing at the source. Quality assurance testing was based on a reduced number of samples taken from materials delivered to the worksite. Price adjustments, if any, were determined solely on QA test results (subject to a referee process). This paper describes in detail the steps taken to introduce these various ERS schemes. Acceptance for granular base materials at full price in 2002 has not changed significantly from 1994 and earlier years; the quantity of rejected materials has also not changed significantly over the years. It is concluded that the introduction of contractor QC testing has not significantly improved the quality of materials supplied, but neither has it had a detrimental effect.Key words: aggregate, construction, end-result specification, granular base, pavement, quality assurance, quality control, statistics, testing.