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This research investigated the use of locally produced, non-proprietary ultra-high-performance concrete (UHPC) as a grouting material to repair deteriorated shear keys. Shear keys are used in adjacent girder superstructures to produce monolithic behavior and load transfer across the structure. Shear key degradation can jeopardize the integrity of the structure. Transportation agencies have reported that 75% of distress in adjacent girder bridges is because of cracking and de-bonding along shear keys. Previous research has shown that locally produced UHPC has excellent mechanical and durability properties. UHPC has also been shown to have good bonding characteristics that are desirable in a potential grouting material. Bond strength between UHPC grout and substrate concrete was evaluated using slant-shear and direct tension tests. Results showed that adequate bond was achieved at 7 days. Low strengths at 28 days were observed because of low strength of the substrate concrete. Shrinkage of UHPC grout was also investigated. Shrinkage at 28 days was less than 600 µstrain which is acceptable for repair practices. Full-scale testing was used to evaluate load-deflection behavior of channel girder assemblages with grouted shear keys. Results showed that UHPC grout and non-shrink grout had similar mechanical performance. Excellent bond was achieved with all grouts, even with minimal surface preparation. The similar performances of the non-shrink grout and the UHPC grout indicates that UHPC grout does not provide a mechanical benefit over the non-shrink grout.

This project focused on field implementation of an ultra-high performance concrete (UHPC) overlay during rehabilitation of an existing concrete bridge (No. 7032) deck in Socorro, New Mexico, USA. Bridge 7032 is a two-lane bridge that is approximately 300 ft. (91.4 m) long and 54 ft. (16.5 m) in width. Rehabilitation of bridge 7032 included removal of deteriorated concrete from the existing deck, installation of a high-performance deck (HPD) leveling course, and installation of a 1 in. (25 mm) UHPC overlay. An UHPC mixture with a 19.5 ksi (134 MPa) compressive strength developed in previous research was selected for this project. This mixture was revised at the beginning of the project, highlighting the need for robust mixtures that can accommodate constituent material substitutions. Prior to placement of the UHPC overlay, the HPD substrate was ceramic bead blasted to remove surface paste and partially expose fine aggregate, thoroughly cleaned, and maintained saturated for 24 hours prior to UHPC placement. The non-proprietary UHPC overlay was successfully placed in four sections between April 10, 2021 and April 27, 2021. During construction of the UHPC overlay, a total of 105 batches were placed. The average direct tensile bond strength of the UHPC overlaid bridge deck was 239 psi (1.65 MPa), which is conservative since several of the tests had fractures that occurred at the epoxy-UHPC interface. Strain gauges and thermocouples were used to monitor the UHPC overlay and existing deck through initial, early-age, and longer-term monitoring programs. Temperature and strain monitoring showed that daily and multi-day strain trends coincided well with daily temperature trends. Major observations during this field implementation project were that four small areas of possible delamination were identified using non-destructive testing, the bond strength was good since the 239 psi (1.65 MPa) average was conservative, preliminary monitoring results were consistent with expectations based on temperature measurements and restraint provided by the concrete superstructure, and relative strains from the monitoring data are being used for detailed analysis of the bridge and overlay behaviors for an ongoing NMDOT project that runs for another two years., Tran-SET Project: 19CNMS01

Direct tension tests were conducted to investigate the effects of substrate moisture conditions and texture on ultra-high performance concrete (UHPC) overlay bond strengths. Improper substrate surface preparation can result in inadequate bond strengths and, in severe cases, lack of bond. To demonstrate the importance of surface preparation, pull-off tests were performed on overlaid slabs that had two extreme substrate surface moisture conditions (saturated and dried) prior to overlay application. Saturated slabs had a tined, tined-light sand blasted, or tined-medium sand blasted substrate surface texture. Dried slabs had either a tined or an exposed aggregate surface texture. Saturated specimens with tined, tined-light sand blasted, and tined-medium sand blasted surface textures achieved average bond strengths of 0.924, 1.45, and 1.95 MPa, respectively. Dried substrate surfaced specimens had zero bond strength. Surface moisture conditions that ranged from saturated to dry were also investigated by allowing the substrate surfaces to dry for 15, 30, 45, and 60 minutes prior to application of an UHPC overlay. Tined-light sand blasted specimens with surfaces that dried for 15, 30, 45, and 60 minutes achieved average bond strengths of 2.86, 2.01, 1.59, and 0.165 MPa, respectively. Results showed tined-light sand blasted specimens with proper saturating achieved adequate bond strengths, and properly saturated, tined-medium sand blasted specimens produced excellent bond strengths. Results also exposed the drastic consequences of not maintaining a saturated substrate surface prior to overlay application and delaying overlay application up to 60 minutes can drastically reduce bond strength.

This paper investigates the shrinkage and thermal effects of an ultra-high performance concrete (UHPC) mixture proposed for use as an overlay material for concrete bridge decks. In this study, early-age and longer-term shrinkage tests were performed on the locally produced UHPC. Thermal and shrinkage effects in normal strength concrete slabs overlaid with UHPC were also observed. Early-age shrinkage testing showed that approximately 55% of the strain occurred in the plastic state and may not contribute to bond stresses since the elastic modulus of the UHPC should be small at such early ages. Thickness of the substrate and amount of reinforcing steel were important factors for shrinkage in the slabs. The thickest slab experienced greater shrinkage than thinner slabs. Comparing this slab to a thinner slab with the same reinforcement indicated that reinforcement ratio is more important than the area of steel.

With much of the world's infrastructure needing rehabilitation, new and more effective methods of repair are required to ensure that concrete structures can continue to perform adequately. This work investigates the potential for using locally produced ultra-high performance concrete (UHPC) as an overlay material to rehabilitate existing normal strength concrete (NSC) bridge decks. Bond strength tests were conducted using NSC substrate with four different textures seven days after casting the UHPC overlay. Depths of the different textures determined in accordance with ASTM E965 were 0.05, 0.90, 1.6, and 2.8 mm. Results from slant shear, split cylinder, and split prism tests indicate good bond even when inadequate texturing was provided. Average shear strengths from slant shear (ASTM C882) specimens increased from 7.1 MPa for the 0.05 mm texture to 19.8 MPa for the 2.8 mm texture. Similarly, bond strengths from split cylinders (ASTM C496) increased from 1.8 MPa for the 0.05 mm texture to 2.4 MPa for the 2.8 mm texture. Bond strength testing of split prisms specimens was conducted using a modified version of ASTM C496 and produced results of 1.5 MPa for the 0.05 mm texture and 3.7 MPa for the rough texture. Direct tensile strength testing was performed in accordance with ASTM C1583 and produced a bond strength of 1.08 MPa for chipped texture with a depth of 1.00 mm. Testing of chloride permeability (ASTM C1202) of the UHPC indicated negligible charge passing through the specimens. Free shrinkage measurements initiated 90 minutes after placement resulted in a total shrinkage of 1800 micro-strain in the UHPC after seven days. Results from these tests indicate the potential of locally produced UHPC to serve as an alternative to traditional overlay materials.