Michael Berry, Richard Snidarich, Camylle Wood
Montana DOT; FHWA
Concrete overlays, Ultra high performance concrete (UHPC)
Ultra High Performance Concrete (UHPC) has mechanical and durability properties that far exceed those of conventional concrete. Specifically, UHPC has compressive and post-cracking tensile strengths of around 20 ksi and 0.72 ksi, respectively. Thus, elements made with UHPC are thinner/lighter than elements made with conventional concrete. The enhanced durability properties of UHPC also allow for longer service lives and decreased maintenance costs. However, using UHPC in conventional concrete applications has been cost prohibitive, with commercially available/proprietary mixes costing over 20 times more than conventional concrete mixes.The overall objective of this research was to develop and characterize economical non-proprietary UHPC mixes made with materials readily available in Montana. This objective was achieved by first identifying and obtaining suitable, economical materials to be used in UHPC. Specifically, the materials identified and used in this research were Type I/II portland cement, class F fly ash, fine masonry sand, silica fume, and high-range water reducer. UHPC mixes were then developed, characterized, and optimized by using a statistical experimental design procedure (response surface methodology). An optimal mix that provided desired workability and strength was selected for further evaluation through a suite of mechanical and durability tests. The mixes developed as part of this research obtained compressive strengths of approximately 20 ksi with flows of 8-11 inches. The mechanical properties tested in this research were compressive and tensile strength, elastic modulus, and shrinkage. Durability tests included alkali-silica reactivity, absorption, abrasion, chloride permeability, freeze thaw resistance, and scaling.