Feasibility of Non-Proprietary Ultra-High Performance Concrete (UHPC) for Use in Highway Bridges in Montana
Ultra-high performance concrete (UHPC) has mechanical and durability properties that far exceed those of conventional concrete. However, using UHPC in conventional concrete applications has been cost prohibitive with its price about 20 times the cost of conventional concrete. The overall objective of the Phase I 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 simply Type I/II Portland cement (from Trident, MT), class F fly ash (from North Dakota), fine masonry sand (from Billings, MT), silica fume, and high range water reducer. UHPC mixes were then developed/characterized/optimized using a statistical experimental design procedure (response surface methodology).
Research on UHPC has shown that batch size, mixing equipment, mixing method, and mixing energy can have a significant effect on the performance of the resulting UHPC mix. Therefore, further research should be conducted on the proposed UHPC mixes using the equipment that will be used in the field (most likely a high-shear mixer), under various mixing conditions (e.g., various temperatures, various aggregate moisture contents), and in larger batch sizes. Previous research on UHPC field cast joints has shown that UHPC can reduce development lengths of the reinforcing in the inter-element connection zone, and thus reduce spacing between decks. However, this research was conducted using only proprietary UHPC concrete mixes. Further research should be conducted on field cast joints using the newly developed non-proprietary mixes to ensure that these mixes behave as expected in this application (e.g., increased bond strength, decreased deck spacing).
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