Efficacy of a Ternary Blend in Improving Bridge Deck Concrete Durability in Tennessee

A study related to the durability of bridge deck concrete in the state of Tennessee has been ongoing at the University of Tennessee (UT) for the past decade. The most recent phase of this research was begun in the fall of 2009 with a focus on developing assessment criteria and methodology to assess the durability of bridge deck concrete in the state of Tennessee. The methodology that was used to assess the durability of Tennessee bridge deck concrete was to determine the concrete’s resistance to chloride ion penetration by way of two test methods, the Surface Resistivity (SR) test and the Rapid Chloride Ion Penetration (RCP) test. Current guidelines set forth by the Tennessee Department of Transportation (TDOT) require that the “Class D” concrete mixture be placed on all bridge deck applications in the state of Tennessee. SR and RCP tests have been performed on “Class D” concrete cylinders from various bridge deck placements across the state for the past two and a half years. Results from the tests indicate that the current “Class D” concrete mixture is not adequate in resisting chloride ion penetration at satisfactory levels. Thus, it was decided to propose a ternary blended concrete mixture for use on Tennessee bridge decks in order to better resist chloride ion penetration and, as a result, improve the durability of bridge deck concrete in Tennessee. Ternary concrete mixtures have been found to offer many benefits to both the strength and durability properties of concrete. A concrete mixture is classified as “ternary” when it contains three different types of cementitious materials. While TDOT’s current specifications do not specifically prohibit the use of a ternary “Class D” mixture, the “Class D” concrete mixtures currently being placed on bridge decks are typically 100% portland cement mixtures or are binary mixtures containing mostly vii portland cement with a relatively small amount of fly ash. Ternary blended laboratory samples were created to compare SR and RCP values to the typical “Class D” mixtures. Results from the tests, as well as results reported in technical literature, indicate that ternary mixtures have significantly better resistance to chloride ion penetration as compared to the typical “Class D” mixtures.