Sustainable nHPC Mixtures for Durable Overlay of Concrete Bridge Decks in Cold Regions: Proof of Concept
The higher cement content in UHPC increases the energy and CO2 footprints, and the use of supplementary cementitious materials (SCMs) to replace cement has been limited in the current design. Besides, the high compressive strength (> 150 MPa) of UHPC might be over-design for bridge deck overlay application. The combined use of very low w/b ratio (~ 0.2) and high dosage of fibers presents a great challenge for the construction of UHPC overlays in the field. In this context, the overarching goal of this project is to design sustainable nHPC mixtures for durable overlay of concrete bridge decks in cold regions through lowering initial cost of UHPC overlays and improving the workability and construction tolerance of UHPC for on-site application while maintaining dense microstructure and superior durability. The “n” before the HPC denotes for nano-engineering as well as the fact the durability of these mixtures will be a few times that of conventional UHPC. To achieve this goal, this study aims to: 1) identify and optimize eco-efficient mix designs for nHPC overlay, greatly reducing the use of cement, steel fiber and superplasticizer while tailoring the particle size gradation; 2) evaluate the engineering performance and durability of selected nHPC mixtures for cold-climate concrete deck overlay application; 3) enhance the thixotropy to ensure that fresh nHPC mix can hold the specified slope on the bridge deck; 4) conduct multiscale characterization of selected nHPC mixtures, to elucidate the role of individual constituents on the macroscopic behavior and performance.