Post-tensioned (PT) concrete bridges can be very durable if properly constructed with high performance materials. Problems were found in grouted post-tensioned ducts in Florida during the late 1990s and early 2000s that indicated a change in grouting materials and construction practices were necessary. Since that time, materials and practices have been significantly improved. States that have investigated older PT bridges have found widely varying levels of deterioration depending on climate, construction practices, structure type and other variables. In the case of bridges built prior to approximately 2003, voided areas in the grouted tendons are fairly common (after 2003 specifications governing materials use and construction practices were in place).
This thesis focuses on PT bridges built in Minnesota prior to 2003. The scope is limited to providing a targeted check of bridges that are most likely to have grouting related corrosion problems based on a review of plans and inspection notes. The project consisted of three phases: 1) review of plans and inspection reports of 40 post-tensioned bridges constructed prior to 2003; 2) selection of 10 bridges for a limited on site inspection of the exterior of the bridge; 3) invasive inspection of 3 select bridges. The bridges selected were chosen to represent different bridge construction types and to provide a spot check of the PT bridge inventory in Minnesota. One of the three bridges has corrosion and voids due to poor grouting, one has a major corrosion problem related to construction issues (but appears to have good grout), and one showed no tendon corrosion or grouting problems during the invasive spot checks.