Bond Behavior of Epoxy-Coated Reinforcing Bars in Non-Proprietary UHPC

Abstract

Non-proprietary ultra-high-performance concrete (UHPC) mixtures were developed for use in closure strips between precast members on reinforced concrete bridges. The mixtures contained ODOT approved Type I portland cement, slag cement, silica fume, graded fine aggregate, two high-range water-reducers (HRWRs), one of which incorporated a viscosity modifying admixture, and 2% by volume of 0.5-in. steel fibers. Several HRWRs of each type were included in the evaluations. Mixtures were evaluated based on flow, fiber distribution, flexural properties, compressive strength, and effect on bond strength using a modified pullout test and the ASTM A944 beam-end test for No. 5 uncoated, ASTM A755 epoxy-coated, and ASTM A1124 textured-epoxy-coated reinforcing bars. The UHPC mixture with the best properties was used to cast a closure strip between two precast sections to determine the splice strength of No. 4, No. 5, and No. 8 uncoated, epoxy-coated, and textured-epoxy-coated reinforcing bars with minimum clear covers ranging from 1.00 to 2.63 in. The results of the splice test were used to develop design recommendations. The study showed that UHPC can be made using ODOT approved materials. The splice strength of reinforcing bars in UHPC is two times the value in conventional concrete. The negative effects of epoxy coating on bond strength are lower in UHPC than in conventional concrete. ASTM A1124 textured epoxy-coated bars have the same bond strength as uncoated bars. The design procedures described in this report are based on UHPC with a minimum compressive strength at the time of load application of not less than 12 ksi, with a flow between 8 and 10 in. and good fiber distribution.