Norbert J. Delatte

Bond Strength Development with Maturity of High-Early-Strength Bonded Concrete Overlays

The development of concrete-to-concrete bond is important for performance of bonded concrete overlays and bridge deck overlays. Bond development is also important for repairs of concrete structures with cementitious repair materials. The test methods used, along with their difficulty and relative reliability, is also of interest to other researchers investigating concrete-to-concrete bond. Methods presented in this study may be used to estimate the bond development between a bonded concrete overlay and its underlying substrate, at early ages, on the basis of concrete maturity. Compressive, splitting tensile, tension bond, and shear bond strength development of concrete are related to mixture proportioning and curing temperature. For a given concrete, they may be predicted by the maturity method, provided curing is adequate and that the effects of other variables can be controlled. Shear bond strength was found to be approximately twice the value of tension bond strength.

FULL-SCALE TEST OF HIGH EARLY STRENGTH BONDED CONCRETE OVERLAY DESIGN AND CONSTRUCTION METHODS

For rehabilitation of concrete pavements, resurfacing with a bonded concrete overlay (BCO) may provide significantly longer life and reduced maintenance costs. Two important issues are bonding and rapid reopening of resurfaced sections. The project objectives were to determine a method of constructing a BCO under extreme weather conditions in El Paso, Texas, that would ensure early opening to traffic and achieve design requirements for long-term performance, and to investigate methods of detecting and mapping delaminations nondestructively. A BCO test slab that was designed and constructed for a full-scale test of feasible design and construction alternatives is reported. The month of June was selected for the test because severe environmental conditions were expected. The experimental variables encompassed in eight test sections were reinforcement of concrete (plain, polypropylene fiber-reinforced, and steel fiber-reinforced), use of shear connectors (nails and anchors), reinforcement, surface preparation, and day or night construction. A weather station was used to record air temperature, relative humidity, and wind speed. By combining these data with concrete temperatures, evaporation rates could be calculated. Several nondestructive testing methods were used to attempt to detect and map delaminations. The results developed from the test are presented in terms of observations during construction, weather and slab temperatures, coring and pull-off testing, delamination detection, cracking, and slab loading. Recommendations are made for construction and quality control of BCOs for early opening to traffic.

CRITERIA FOR OPENING EXPEDITED BONDED CONCRETE OVERLAYS TO TRAFFIC

For rehabilitation of concrete pavements, resurfacing with a bonded concrete overlay (BCO) may provide significantly longer life and reduced maintenance costs. Two important issues to consider in rehabilitation are bonding and rapid reopening of resurfaced sections. The purpose of accelerated or expedited concrete paving is to limit the duration of lane closure and inconvenience to the public. Expedited BCOs offer an economical method for substantially extending rigid pavement life. Research for expedited BCOs in El Paso and Fort Worth, Texas, has been carried out for the Texas Department of Transportation by the Center for Transportation Research at the University of Texas. Results of previous expedited BCO construction are reviewed. Laboratory testing for this project included a high-early-strength mix design, bond development of that mix design, and early-age fatigue strength of half-scale BCO models. A 122-m-long test strip was cast with eight different expedited BCO designs, and accelerated traffic loading was imposed at 12 hr. Recommendations are made for construction and quality control of BCOs for early opening to traffic.