Investigation of Ontario’s Fine Aggregate Sources for use in Exposed Concrete Pavements

Pavement friction is an integral component in the design process of large volume, high speed roads. Research has shown that the fine aggregate of exposed Portland cement concrete (PCC) pavements is a significant contributor to pavement friction for these types of wearing surfaces. Acid insoluble residue (IR) testing that restricts the carbonate content of fine aggregate is used by many transportation agencies as an indicator of aggregate suitability for pavement frictional performance. Until recently, the Ontario Ministry of Transportation (MTO) restricted the use of manufactured sands for PCC pavements obtained from carbonate bedrock deposits, which underlay a majority of the heavily trafficked portion of the province. Natural sands from surficial deposits had no restriction, meaning these pavements could still contain an undesirable amount of carbonate fine aggregates. In an effort to improve frictional properties of Ontario highways and standardize requirements, MTO recently implemented new IR specifications that apply to all fine aggregates used in concrete pavement surfaces. The new specification also allows suppliers to blend material to meet the insoluble residue targets, which was traditionally not allowed.

Since insoluble residue test data of Ontario fine aggregate sources are not readily available, this project aims to provide representative test data of available natural sands in the context of Ontario and MTO needs. Specifically, the project examines Ontario concrete sand supplier material in relation to the new insoluble residue requirements to show current product availability. Furthermore, the project investigates how production methods affect an aggregate’s ability to meet these requirements and correlates various test methods used for assessing durability, silicate rock content, mineral content, and other properties of concrete fine aggregate. The results of this project may be used to support exposed concrete pavement frictional performance in Ontario.

The project has shown that at least 23% of sources currently producing concrete fine aggregate for the southern Ontario market are capable of successfully meeting a minimum 60% IRR75 requirement. An additional 18% of current suppliers are capable of achieving 50 to 60% IRR75 results. These suppliers that fall just short of the 60% IRR75 target may benefit from adjustment of their processing operations and/or a minor amount of blending. An IRR75 range of 40-50% was achievable for 32% of the currently producing concrete fine aggregate sources. These suppliers are also within reach of the specification limit and may benefit from the new blending allowance, which. will provide many suppliers the opportunity to produce material for future exposed PCC pavement contracts.

Material processing has shown to have a noticeable impact on the final insoluble residue content. Over half of the sources showed a beneficial impact in relation to insoluble residue targets, with a noticeable beneficial trend for ice contact sources. This effect allows some suppliers to increase insoluble residue results simply by using current processing techniques. This trend should be investigated further to optimize this advantage.