Thermal Coefficient of Expansion Test for Aggregates Using Dilatometry (7-4926-S)

The low durability of concrete is often attributed to the incompatibility between the thermal properties of mortar and aggregate. The coefficient of thermal expansion (CoTE) of aggregates determines the thermal expansion of concrete to a considerable extent. It also governs the degree of physical compatibility of the components and hence affects the durability of concrete. Proper characterization of thermal properties of aggregate allows us to predict the behavior of concrete with greater confidence. A test apparatus referred to as the dilatometer for determining CoTE of both fine and coarse aggregates was developed under Texas Department of Transportation (TxDOT) Project 7-2992 (1996-1997). The dilatometer is also suitable for determining CoTE of crushed mortar and concrete. The dilatometer originally devised by Verbeck and Haas in 1951 to measure CoTE of aggregate consisted of a I-liter flask to which was attached a capillary bulb containing electrical contacts. The flask was filled with aggregate and water, and the apparatus was allowed to equilibrate at one of the controlling electric contacts. The equilibrium temperature was observed by means of a Beckman thermometer. In Project 7-2992 the design of the apparatus was improved to obtain stable conditions, and the measuring device was fully automated. The objective of this project was to develop a test method to measure the thermal characteristics of concrete aggregates that could be used to create a database of aggregate thermal properties.