Reinforced concrete: Difference between revisions

Because the actual bond stress varies along the length of a bar anchored in a zone of tension, current international codes of specifications use the concept of development length rather than bond stress. The main requirement for safety against bond failure is to provide a sufficient extension of the length of the bar beyond the point where the steel is required to develop its yield stress and this length must be at least equal to its development length. However, if the actual available length is inadequate for full development, special anchorages must be provided, such as cogs or hooks or mechanical end plates. The same concept applies to lap splice length <ref>{{Cite journal|title=Monotonic and Cyclic Seismic Analyses of Old-Type RC Columns with Short Lap Splices|journal=Construction Materials|date=31 March 2024|volume=4|issue=2|pages=329-341329–341|last1=Megalooikonomou|first1=Konstantinos G.|doi=10.3390/constrmater4020018 |doi-access=free }}</ref> mentioned in the codes where splices (overlapping) provided between two adjacent bars in order to maintain the required continuity of stress in the splice zone.

In wet and cold climates, reinforced concrete for roads, bridges, parking structures and other structures that may be exposed to [[deicing]] salt may benefit from use of corrosion-resistant reinforcement such as uncoated, low carbon/chromium (micro composite), epoxy-coated, hot dip galvanized or [[stainless steel]] rebar. Good design and a well-chosen concrete mix will provide additional protection for many applications.

Uncoated, low carbon/chromium rebar looks similar to standard carbon steel rebar due to its lack of a coating; its highly corrosion-resistant features are inherent in the steel microstructure. It can be identified by the unique ASTM specified mill marking on its smooth, dark charcoal finish. Epoxy -coated rebar can easily be identified by the light green color of its epoxy coating. Hot dip galvanized rebar may be bright or dull gray depending on length of exposure, and stainless rebar exhibits a typical white metallic sheen that is readily distinguishable from carbon steel reinforcing bar. Reference ASTM standard specifications '''A1035/A1035M''' Standard Specification for Deformed and Plain Low-carbon, Chromium, Steel Bars for Concrete Reinforcement, '''A767''' Standard Specification for Hot Dip Galvanized Reinforcing Bars, '''A775''' Standard Specification for Epoxy Coated Steel Reinforcing Bars and '''A955''' Standard Specification for Deformed and Plain Stainless Bars for Concrete Reinforcement.<!-- [[American Concrete Institute|ACI]] 440 provides information about properties and design of FRP reinforced concrete structures. The Canadian [[Canadian Standards Association|CSA]] 806 and 807 providing the same information in form of a real standard. In addition the Canadian Highway Design Code is the first standard allowing for composites in bridge construction. -->

{{Main|Fiber -reinforced concrete}}

Concrete reinforced with fibers (which are usually steel, [[glass]], [[Fiber-reinforced plastic|plastic fibers]]) or cellulose polymer fiber is less expensive than hand-tied rebar.{{Citation needed|date=December 2017}} The shape, dimension, and length of the fiber are important. A thin and short fiber, for example short, hair-shaped glass fiber, is only effective during the first hours after pouring the concrete (its function is to reduce cracking while the concrete is stiffening), but it will not increase the concrete tensile strength. A normal-size fiber for European shotcrete (1&nbsp;mm diameter, 45&nbsp;mm length—steel or plastic) will increase the concrete's tensile strength. Fiber reinforcement is most often used to supplement or partially replace primary rebar, and in some cases it can be designed to fully replace rebar.<ref>Fiber Concrete in Construction , Wietek B. , Springer 2021 , pages 268 ; ISBN 978-3-658-34480-1</ref>