Evaluation of Structural Fillers for “Steel Grouting” in Steel Bridge Preventive Maintenance and Repairs

About the report:

In some instances, steel bridges can contain gaps between steel plates in bolted connections or between steel and concrete surfaces. In new bridges, these gaps may result from fabrication or assembly errors. In existing structures, the gaps often arise because of corrosion-related section loss. These gaps can also cause durability concerns because they are a place for water and salt to collect, leading to crevice corrosion. In concrete bridges, such gaps are commonly filled with cementitious grouts, but no widely accepted method exists for filling the gaps in steel bridges. Structural fillers, such as epoxies, offer a preventive maintenance solution for filling these gaps to alleviate future crevice corrosion concerns. However, despite the wide range of structural fillers used across various industries, information is limited on the selection and performance of structural fillers for steel bridge preventive maintenance applications.

This study investigated the performance of “steel grouting,” which is structural fillers for filling gaps in steel bridges, through laboratory testing and field evaluations. First, the research team developed a list of potential structural fillers and their key properties. Three fluid (injectable) and three putty structural fillers were selected for experimental testing of material and structural properties. Material tests of selected structural fillers included compressive strength testing at different curing temperatures and creep testing under sustained compressive loads at elevated curing temperatures. Results from these tests were used to narrow down the selection of structural fillers for structural component testing with slip-critical bolted connections. For these tests, fluid structural fillers were injected into a 1/8-inch thickness, and putty structural fillers were placed in a 1/2-inch thickness between steel plates. Compressive slip and tensile creep tests were conducted according to standard test procedures on specimens with both blast-cleaned and organic zinc faying surfaces. Lastly, field evaluations were conducted on previous Virginia Department of Transportation (VDOT) applications that used structural fillers for preventive maintenance, including bolted beam end repairs and bearing corrective actions, to evaluate their performances after multiple years of service.

The study concluded that structural fillers possess sufficient strength and stiffness to remain intact under compressive service loads when used for filling gaps, or steel grouting, in preventive maintenance of steel bridges. Because of their sufficient strength and stiffness, structural fillers can improve the constructability of bolted plate repairs by preventing deformation of the existing structure or repair plates during tensioning of bolted assemblies. Based on the structural component testing performed in this study, structural fillers cannot be considered incompressible, so pretensioned bolts with structural fillers within their grip length should not be considered slip-critical. Structural fillers can experience compressive creep when cured at high temperatures. This issue can be alleviated by casting and curing structural fillers within the manufacturer’s recommendations. In addition, field evaluations found that previous VDOT applications using structural fillers for preventive maintenance appeared to be performing well after multiple years of service. The study recommends that the Virginia Transportation Research Council develop guidance for using structural fillers to fill gaps to provide constructable and durable steel bridge preventive maintenance and repairs and implement this guidance into VDOT specifications.

Supplemental materials can be found at https://library.vdot.virginia.gov/vtrc/supplements.

_{Disclaimer Statement:The contents of this report reflect the views of the author(s), who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Virginia Department of Transportation, the Commonwealth Transportation Board, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. Any inclusion of manufacturer names, trade names, or trademarks is for identification purposes only and is not to be considered an endorsement.}

Authors