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ASA Graduate Student Scholarship properties of in-place materials. Additionally, by furthering the Over the last decade, this has often put structural engineers understanding of the parameters that allow a nozzle to be effi- in a difficult position who, in view of a lack of fundamental cient, it would be possible to understand how to improve comprehension of the phenomenon, have developed tools for shotcrete equipment, especially nozzles, and mixtures to the acceptance of shotcrete structures using CIP concrete minimize rebound. specifications. The visual examination of the encapsulation quality of reinforcing bars (void size and contact perimeter with reinforcing bars) of extracted cores from structures is one of them.25 Nevertheless, the acceptance criteria have been Pasquale Basso Trujillo graduated from selected empirically—that is, based on experience rather than Universidad Panamericana in Guadala- by a scientific and reliable assessment of the steel­concrete jara, México, in 2014, where he worked as bond reduction whenever voids are present at their interface. In a structural engineer apprentice, designing fact, the parameters that most affect bond with their presence are reinforced concrete and masonry low-rise still not fully understood. Thus, the influence of encapsulation buildings. He is now a PhD Candidate at quality on reinforcement development length makes this subject Laval University working under Marc a critical and much-needed research project to create durable Jolin’s supervision on the “Development and safe criteria for the design of reinforced shotcrete structures. Length of Reinforcing Bars in Shotcrete.” There, he also teaches a workshop on reinforced concrete design for under- Objectives graduate students. The specific objectives of this research are enumerated as follows: Research: Development Length of 1. Understand the steel-concrete bond phenomenon (failure Reinforcing Bars in Shotcrete Structures mode, stress-slip relationship, and ultimate bond force of Background and Industry Problem Adequate encasement of reinforcing bars and other obsta- cles using shotcrete has always been a point of interest in the industry.5-12 Achieving proper and complete encapsulation is strongly influenced by the selection of equipment and mixture design, but also to a great extent by nozzlemen experience and their skills; voids and/or sand pockets may be created behind obstacles if an improper placement technique is used.5,8,11 This raises concerns when engineers design rein- forced shotcrete structures, particularly when the development length of reinforcing bars in tension is calculated. Develop- ment length is defined as the additional length a reinforcing bar should be anchored in a given concrete member so it can develop its yield limit, assuring the concrete element’s ductility.13 In practice, engineers refer to standards such as ACI 318-1414 or CSA A23.3-04,15 which provide assessment and specific equations to calculate this extra reinforcement length. Moreover, modification factors have been added to the equation by other researchers over the years to account for conditions it originally did not consider, such as the reinforcing bar size16,17 and use of epoxy-coated reinforcing bars.18-20 However, both the equation and the modification factors have been formulated for cast-in-place (CIP) concrete only,21-24 where defects located specifically behind reinforcing bars as sometimes found in shotcrete are believed to be unique to this method of placement. Despite its potentially significant impact on structural behavior and safety, the complexity and vari- ability of steel-concrete bond in the presence of defects is the main reason this parameter has received very little attention. Thus, shotcrete as a method of concrete placement is not explicitly accounted for in the design codes for the develop- ment length calculation. Shotcrete • Spring 2015 55


2015SpringShotcreteEMag
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