Development of high-performance fiber-reinforced link slabs for jointless bridge decks

Abstract

The purpose of this study of high-performance fiber-reinforced cementitious composite (HPFRCC) reinforced with glass fiber reinforced polymer (GFRP) bars was to investigate its use as link slabs to replace the expansion joints commonly found in bridge decks. Numerous small scale test specimens and a full scale specimen test were conducted. The small scale test specimens consisted of 3 inch by 3 inch by 3 foot long and 6 inch by 3 inch by 3 foot long HPFRCC rectangular cuboids with single GFRP bars placed in the center of the specimens. These specimens were tested in direct tension until failure to determine the maximum strain while maintaining uniform micro-cracking. Following the direct tension tests, the specimens were subjected to cyclic loading to determine the reinforcement bar's and concrete's ability to re-contract, durability, and determine its resultant equilibrium state. After the small scale tests were completed, a full scale bridge expansion joint specimen was constructed to test the strain capabilities of the HPFRCC as a link slab. The full scale bridge expansion joint specimen emulated an expansion joint condition of a composite steel girder to concrete deck slab section. The link slab was 90 inches wide by 3 inches thick with an unbonded length of 6 feet and was recessed into the top 3 inches of a 9 inch thick deck slab. #3 GFRP reinforcement bars were placed at mid-depth of the link slab at 6 inches on center and the ends were cast in to the cast-in-place concrete deck. The slab was then subjected to cyclic axial strains in both tension and compression and later in direct tension until failure. The link slab's strain capabilities and distribution of microcracking were the primary focus of the full scale test. It was found that the cast-in-place link slab had the advantage of providing good continuity with the bridge deck, but had no compressive strain capacity. Microcracking was observed in the specimen, however, numerous localized cracks appeared throughout the entire specimen for various reasons. Shear lag caused localized diagonal cracks at the top of the slab in the transition areas between the bonded and unbonded zones, and numerous areas of localized debonding of the GFRP rebar in the HPFRCC allowing cracks to localize over the debonded zones. A different HPFRCC mix design in combination with different GFRP reinforcement bars, resembling typical steel reinforcement bars, may better control crack localization. The concept shows promise, however, further study of the materials and their performance issues is required. The link slab may be a suitable replacement for expansion joints, but due to their high force demands to achieve such deformations, not all bridges may be eligible for their application at this time.