Ultra-high-performance concrete (UHPC) retrofits for increased blast protection of concrete and masonry structures

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Recent bomb attacks around the world have demonstrated the vulnerability of existing buildings to blast loads. Events such as the Lac-Mégantic disaster and Toronto Propane Explosion also highlight the vulnerability of Canada's built infrastructure to accidental and industrial explosions. Bridges are also vulnerable to blast threats, and pose unique design challenges due to their open access. In addition, unlike buildings, key structural components in bridges are directly loaded and therefore may be exposed to large blast loads at low standoff. Until recently, blast-resistant design was not common in the design of buildings and bridges in Canada; thus, a large inventory of existing buildings and bridges are in need of retrofits to increase blast resilience and ensure safety and security of Canadians. Previous blast incidents such as the Oklahoma City Bombing have raised awareness of the need for retrofitting columns to increase the survivability of concrete buildings and bridges. Masonry walls are another vulnerable structural type found in many older buildings in Canada, either as infill or structural walls. Modern codes require minimum steel in masonry construction, but older buildings had no such requirement; thus unreinforced masonry (URM) walls in existing buildings are vulnerable to collapse under very low out-of-plane blast loads. Such walls can fail dramatically, with high speed projectiles that can injure building occupants. Ultra High Performance Concrete (UHPC) is a new class of advanced cement-based composite with remarkable strength, tensile resistance, toughness and damage tolerance. These unique features make UHPC an ideal material for blast-resistant design applications. This material's high bond capacity, coupled with its ability to be cast in very thin yet strong layers also make it an ideal material to retrofit vulnerable structures against blasts. The long term goal of the proposed research program is to develop novel blast retrofit strategies using advanced cement-based composite materials for critical Canadian infrastructure. The long term objectives include the development of retrofit methodologies, analytical tools and design procedures that can capture dynamic response of retrofitted elements. The short-term objective is to develop novel UHPC-retrofits for the protection of structural and non-structural elements in concrete and masonry structures. The scope will consist of four main tasks; i) materials research to investigate the high-strain behavior and bond response of the UHPC retrofits, ii) application of UHPC-jacketing in concrete building/bridge columns, iii) application of UHPC-overlays to masonry walls; iv) development of analytical models for predicting the blast response of the UHPC-retrofits. It is envisioned that the research program will result in the development of best practice guidelines and provisions for CSA Standards for the benefit of the Canadian construction industry.