Alternate approach slab reinforcement.

Alternate approach slab reinforcement.

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  • Abstract:
    The upper mat of reinforcing steel, in exposed concrete bridge approach slabs, is prone to corrosion damage. Chlorides applied to the highways for winter maintenance can penetrate this concrete layer. Eventually chlorides reach the steel and begin the corrosion process. The objective of this research project was to investigate the performance of approach slabs constructed with structural fibers to replace the top mat of reinforcing steel. The research studied whether the performance of approach slabs reinforced with structural fibers would be equivalent to traditionally reinforced approach slabs. NHDOT Materials & Research Bureau technicians performed standard quality acceptance tests on the fresh concrete at the time of placement. Technicians also fabricated three freeze/thaw prisms for each mix. The specimens survived freeze/thaw testing with only minor physical deterioration, consisting of slight scaling and pitting. The Civil Engineering Department of the University of New Hampshire (UNH) was contracted to perform laboratory testing. The beam samples were tested for First Crack Strength and Average Residual Strength in accordance with ASTM C 1018 and C 1399, respectively. An independent testing laboratory extracted two cores from each approach slab to evaluate the air matrix within the concrete. Comparisons of the laboratory test results show that compressive and flexural strengths are similar for both mixes. The plots resulting from the residual strength testing show that the fiber-mix had greater strength after cracking than the normal mix. Periodic visual observations of the approach slabs were made to evaluate field performance by comparing crack size, frequency and scaling. After more than three and half years in service, the two approach slabs have performed similarly and well. The expected advantages of a thicker concrete cover over steel reinforcement will not be seen for many years. The epoxy-coated steel in the conventional slab construction should also delay damage from corrosion. Based on the performance observations to date, fiber-reinforced concrete is recommended for use in this and other applications where delaying the effects of steel corrosion is of interest. The NHDOT has implemented the use of fiber-reinforced concrete for all approach slabs as a result of this study.
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