Development of High Performance Grouts for Bonded Post-Tensioned Structures

The use of post-tensioning in bridges can provide durability and structural benefits to the system while expediting the construction process. When post-tensioning is combined with precast elements, traffic interference can be greatly reduced through rapid construction. Post-tensioned concrete substructure elements such as bridge piers, hammerhead bents, and straddle bents have become more prevalent in recent years. Chloride-induced corrosion of steel in concrete is one of the most costly forms of corrosion each year. Coastal substructure elements are exposed to seawater by immersion or spray, and inland bridges may also be at risk due to the application of deicing salts. Corrosion protection of the post-tensioning system is vital to the integrity of the structure because loss of post-tensioning can result in catastrophic failure.

In bonded post-tensioned construction, the portland cement grout acts as a “last line of defense” for preventing chlorides from reaching the steel and initiating corrosion. Documentation for durability design of grout used in bonded post-tensioning is very limited. The purpose of the research is to develop a high performance grout for post-tensioning tendon injection. An optimum grout combines a high level of corrosion protection and desirable fresh properties such as fluidity and resistance to bleed. The recommended grouts were developed through a series of fresh property tests, accelerated corrosion tests, and a large-scale pumping test to simulate field conditions. Variables included water to cement ratio and numerous admixtures such as superplasticizer, anti-bleed chemicals, silica fume, fly ash, and corrosion inhibitors.

One high performance fly ash grout was developed for applications with small vertical rises, and a second high performance anti-bleed grout was developed for applications involving large vertical rises such as tall bridge piers.