This document provides general guidance for determining appropriate acceptance criteria for a prepared surface to receive a protection system. There are many techniques for preparation of a surface prior to installation of a protection system, and no single method is ideal for all situations. This guide discusses various preparation methods that can be used to achieve the intended surface condition.
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This document provides information on the evaluation of both dry-mix and wet-mix shotcrete. It is assumed throughout the document that shotcrete is a method of placing concrete. However, for the sake of readability, the word “shotcrete” is often used either to identify the shotcrete process (method) or the shotcrete mixture (product) in the present document.
Evaluation of in-place shotcrete requires experience, education, and engineering judgment. This document serves as a guide for engineers, inspectors, contractors, and others involved in accepting, rejecting, or evaluating in-place dry- or wet-mix shotcrete.
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The use of fiber-reinforced polymer (FRP) materials to strengthen concrete members is an accepted technology. In many applications, performance of FRP-strengthened members during exposure to fire remains a significant concern to design professionals, building officials, and owners. The objective of this TechNote is to provide a brief overview of key concepts, code provisions, and industry guidelines relating to the structural performance of FRP-strengthened members during a fire event.
Research findings regarding the performance of FRP-strengthened members during exposure to fire have been published by Williams et al. (2008). However, design examples and guidance regarding the performance of externally bonded FRP during exposure to fire are not widely available. In addition, differences in the design approaches and load combinations used by the steel and concrete industries, combined with the relatively recent emergence of FRP fire protection systems, have created challenges for practicing engineers tasked with assessing the structural fire resistance of FRP-strengthened members.
Keywords:
fiber-reinforced polymer; fire; fire protection; fireproofing; repair; strengthening.
Code:
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Embedded galvanic anodes reduce the corrosion activity of the reinforcing steel in the vicinity of the installed anode. Anodes are installed in areas of the concrete where there is a high likelihood of corrosion occurring or recurring. Type 1 anodes are installed to provide improved protection of uncoated reinforcing steel in the repair area and in adjacent chloride-contaminated or carbonated concrete surrounding the repair area. Type 2 anodes are used in sound chloride-contaminated or carbonated concrete to mitigate corrosion of the reinforcing steel and delay the onset of delamination or spalling of the concrete.
Code:
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Cracking can adversely affect the performance and service life of the repair, as cracks provide a more direct path for the ingress of deleterious elements into the repair, creating a durability concern. For structural repairs,
cracks may adversely affect the repair performance and the load-carrying capacity of the repaired structure. Additionally, cracking may be an aesthetic concern. In consideration of the aforementioned, the licensed design
professional should evaluate the cause(s) and consequences of cracks in the repair and, as needed, develop a remediation approach. If the cracks compromise the load-carrying capacity of the repaired structure, appropriate
measures should be taken. ACI 562 requires cracking mitigation to be considered in repair design.
Keywords:
cracking; cracks; durability; nonstructural repair; service life; shrinkage; structural repair.
Code:
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What is concrete “bruising,” how is it evaluated, and how can it be minimized?
Bruising refers to damage in a surface layer of remaining substrate concrete that is weakened by fine interconnected
cracks caused by the use of high-impact, mechanical methods for concrete removal and surface preparation. The bruised (or fractured) layer left by such surface preparation methods typically extends to a depth of 1/8 to 3/8 in. (3 to 10 mm) or more below the remaining substrate surface and, if not removed, generally results in lower repair bond strengths. Bruising, which can be detected through pulloff testing and petrographic examination, can be effectively minimized by selecting the most appropriate method and equipment for the given application.
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How important is the modulus of elasticity as a property of surface repair materials?
Modulus of elasticity is an important physical property of surface repair materials. For structural repairs, the modulus of elasticity of the repair materials should be similar to that of the substrate concrete, whereas in the case of nonstructural repairs, a lower modulus of elasticity may be beneficial.
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When a structural evaluation to determine capacity is to be performed, knowledge of member sizes, reinforcing details, and material properties is required. In cases where this information is not readily available through drawing document records, it needs to be obtained through in-place measurements and sampling.
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Rehabilitation projects often involve the need to increase the load-carrying capacity of members within existing concrete structures that are deficient due to increased load demand associated with change of use, deficiencies in the original design or construction, or deterioration. Such strengthening often includes increasing shear capacity.
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