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Module 11: Introduction to Concrete

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Concrete Reinforcement Materials

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Concrete has good compressive strength, but is relatively weak in tension or if it is subjected to lateral or shearing forces.

Many kinds of proprietary reinforcement have been used for concrete in the past. Today, steel is the material that is generally used. This is because it has nearly the same temperature-expansion and -contraction rate as concrete.

Additionally, modern reinforcement conforms to ASTM -- American Society for Testing and Materials -- standards that govern both its form and the types of steel used.

As an alternative to steel reinforcement, fibers made from steel, fiberglass, or plastics, such as nylon, are sometimes added to concrete mixes to provide reinforcement.

a. Reinforcing Bars:
Reinforcing bars (rebars), sometimes referred to as rerods, are available in several grades. These grades vary in yield strength, ultimate strength, percentage of elongation, bend-test requirements, and chemical composition.

The standard configuration for reinforcing bars is the deformed bar. Different patterns may be impressed upon the bars depending on which mill manufactured them, but all are rolled to conform to ASTM specifications.
a. Reinforcing Bars (continued):

The deformation improves the bond between the concrete and the bar and prevents the bar from moving in the concrete.

Plain bars are smooth and round without deformations on them and are used for special purposes, such as for dowels at expansion joints where the bars must slide in a sleeve.

Deformed bars are designated by a number in eleven standard sizes (metric or inch-pound).

b. Bar Supports:

Bar supports are used to support, hold, and space reinforcing bars and mats or wire fabric before and during concrete placement.

Bar supports are made from steel, concrete, or plastic. When used with coated reinforcement steel, the supports should also be coated with the same material or made of concrete or plastic to prevent corrosion.

c. Splicing Reinforcing Bars:
Because in most situations it is impossible to provide full-length bars that run continuously throughout a structure, making splices in reinforcing bars in a common occurrence.

The placing drawings will show the location and type of splice to use.

d. Welded-wire Fabric:
When reinforcement is required for concrete pavement, parking lots, driveways, floor slabs, etc., welded-wire fabric (WWF) can be used instead of individual rebars.

WWF consists of longitudinal and transverse steel wires electrically welded together to form a square or rectangular mesh or mat.