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2015FallShotcreteEMag

Technical Tip Rapidly Deployable Shotcrete System for the Structural Stabilization of Shock-Damaged Structures By Anne Oberlink and Robert Jewell Tattacks on September 11, 2001. The protec- bilization of damaged structures requires mater --construction practices due to the critical time issueand the nature of the damaged structure. The stahe Department of Homeland Security wasformed as a consequence of the terrorist tion of the nation’s critical infrastructure was ials and equipment that can be rapidly deployed made part of their mandate, and included in their to place materials that have very rapid-strength mandate is the rapid repair and stabilization of development. These materials need to be place- shock-damaged structures. In response, the able at a distance to provide some degree of safety National Institute for Hometown Security, a sub- to the responders. In addition, the materials must contractor of the Department of Homeland Secu- be able to adhere to structural surfaces that have rity, awarded a contract to the University of not been properly prepared and conditioned, and Kentucky Center for Applied Energy Research may also be highly fractured, dusty, wet, and very (UK CAER) and Minova USA Inc. This contract possibly hot or extremely cold. called for development of a material that gains The technology for the rapid delivery of large structural strengths very rapidly, as well as the volumes of cementitious materials to vertical or development of a corresponding deployment even overhead surfaces currently exists. Pneumatic system to stabilize and repair shock-damaged delivery (shotcreting) has been used in construc- structures to avoid catastrophic failure. A fast- tion for over 100 years. Shotcreting has played a setting material is imperative to an emergency major role in structures such as the Washington situation because the faster first responders can DC Metro subway system and the England to stabilize a collapsed structure, the safer they make France undersea rail connector (the Chunnel). it for themselves, and for the people that are Numerous rapid-setting cements are commer- potentially inside the structure that may need help. cially available. They are used for rapid repair of The system and material developed by the surfaces such as bridge decks, pavements, and UK CAER and Minova USA Inc. consists of a commercial floors, as well as structural repairs of delivery vehicle capable of shotcreting prepack- vertical and overhead surfaces. Few of these aged, rapid-setting, fiber-reinforced dry-mix shot- products are specifically marketed for use in crete material. Tekcrete Fast® is a material that shotcrete applications. was developed for this process, and is a specially The majority of rapid-setting cements are based designed, rapid-setting, and high-performance on, or at least contain, portland cement as a prin- dry-mix shotcrete. This system will stabilize cipal component. Other components are added that structures such as airport runways, tunnels, help provide early strength, such as high-alumina bridges, and dams that have been shocked and cement (HAC), organic polymers, chemical accel- damaged by explosives, or seismic activity, before erators (which can also be added during concrete they fail. Tekcrete Fast M®, a low-dust version for batching), and calcium sulfate hemihydrate (for underground mining, has also been developed by example, gypsum plaster). Mortars prepared with Minova USA Inc. Both Tekcrete Fast and Tekcrete some of these cements can achieve compressive Fast M are available at Minova USA Inc. strengths of 6.8 to 13.8 MPa (1000 to 2000 psi) within 1 hour. However, portland cement mortar Introduction and concrete typically require many weeks of The rapid stabilization of shock-damaged proper curing to reach significant levels of their structures falls outside the purview of normal ultimate strengths, even when used with set accel- 38 Shotcrete • Fall 2015


2015FallShotcreteEMag
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