Monitoring concrete temperature during construction of the Confederation Bridge

A short-term monitoring project on the Confederation Bridge, crossing the Northumberland Strait in Atlantic Canada, was completed to collect data on the temperatures in high performance concrete during construction. High temperatures in the middle of the large concrete members were caused by cement hydration. The temperatures inside some members did not approach ambient levels until one month after pouring. The core temperature of the large concrete members was not significantly influenced by weather conditions or orientation. Temperature gradients existed between the middle of the concrete and the cooler outer surfaces. After the formwork was removed, the gradients suddenly increased, a phenomenon called thermal shock. The degree of thermal shock was a function of weather conditions, concrete location, concrete spatial orientation, and the temperature difference between the concrete and the surrounding air. When new concrete was cast against hardened concrete, a large thermal gradient was induced across the construction joint in both the new and hardened concrete. The temperature data collected during construction will be used to calibrate a finite element model that will predict three-dimensional heat flow in concrete, and cracking due to the heat of hydration and varying ambient and boundary conditions.