Safeguarding historic structures, from Ellis Island masonry to the adobe churches of New Mexico, creates a challenge for historic preservation professionals. Research at the University of Nebraska-Lincoln College of Engineering is helping to define and refine best practices with funding from the National Center for Preservation Technology and Training (NCPTT), part of the National Park Service.
“The recent trend to rehabilitate and strengthen unreinforced masonry with fiber reinforced polymer laminates applied externally on masonry walls and arches, while effective, is unacceptable in historic buildings for aesthetic reasons,” said Ece Erdogmus, assistant professor of architectural engineering with The Charles W. Durham School of Architectural Engineering and Construction. “There is a need for an effective and aesthetically pleasing methodology.”
She focused on the use of fiber-reinforced-mortars, specifically sustainable organic fibers, for masonry rehabilitation in her work on the NCPTT grant, “Sustainable Fiber Reinforced Mortar (FRM) Mixtures for the Preservation of Unreinforced Masonry Architectural Heritage.” As principal investigator on the yearlong grant, valued at nearly $50,000, her research plan pursued a comprehensive experimental program and developed a database of material properties to be available online.
Erdogmus said the experimental program includes various materials and testing of several parameters to evaluate the strength, ductility, durability, and overall feasibility of the proposed FRMs, and the fiber reinforced epoxy surface treatment. Her work sought to optimize FRM mixtures based on fiber type and fiber volume in different situations.
The fibers Erdogmus selected for this study include sustainable options, such corn silk fibers prepared at the University of Nebraska, as well as horse-hair, goat-hair, "green" fiber by Nycon, and synthetic options, e.g. various types of polyvinyl alcohol (PVA) fibers. Mortar types ranged from cement-lime mortar to various lime mortar mixtures. She said specimens are being tested in different masonry unit types, with eight different experiment types to identify strength, durability and workability characteristics of each material combination.
“With all of the fiber types and varying volume fractions, different binding matrices and units,” said Erdogmus, “a test matrix of 80 mixtures is prepared for FRM, and a pilot study of 36 specimen types for the development of novel translucent fiber reinforced epoxy (FRE) treatments.”
The database, nearing completion, will include hundreds of entries for material characteristics to help users have information to make decisions for preserving varied and valued historical structures.
In historic preservation projects the compatibility of the repair material with the authentic mortar is key, and the knowledge Erdogmus acquired in past research on historical mortars (aging from 3rd century A.D. in Europe/Asia structures to 19th century monuments in the U.S.) provided the basis for the binding matrices represented in the database.
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