Improving Bridge Concrete Overlay Performance

Abstract

Low slump concrete overlays have been widely utilized in the midwestern United States, including Wisconsin, to mitigate bridge deck deterioration and extend service life. However, concerns regarding their performance have necessitated investigations into optimal mix designs, placement procedures, and curing practices. This study focuses on assessing the cracking potential of seven overlay mixtures, including: Current Wisconsin Grade E concrete with Type I and IL cement, latex modified concrete, fly-ash modified Grade E concrete, Grade E with reduced cement content, and fiber reinforced concrete. The various concrete mixtures were tested for compressive strength, slump, and air content. Seven 8ft x 8ft x 6 in test slabs were subjected to field conditions with 3- and 7-day curing periods. The salt ponding test was conducted on 21 small slab specimens fabricated based on the seven mix designs to assess their chloride penetration resistance. A new dog bone test was developed to assess the restraint stress response of Grade E mix (type IL cement) under different curing conditions. The 7-day wet curing (with wet burlap) is recommended (based on the dog bone test results) to control and limit restraint of shrinkage stresses. A 15% reduction in cement content and addition of PVA fibers to the Wisconsin Grade E mix can potentially improve the performance of overlays with respect to cracking. Latex modified mix exhibited the lowest chloride permeability.