Reinforcing bars used in structural concrete has raised deformations on it, which helps keep the reinforcing bars locked inside the concrete.
Special care needs to be taken to make sure the reinforcing bars are clean of any debris (such as caked-on mud or rust) to allow them to function properly.
View attachment 543037
_______________________________________________________________________________________________________________________
Q.: If reinforcing bars have been stored outside and have a coating of rust, how much rust is acceptable?
A.: Section 12 of ASTM A 615-96a, "Standard Specification for Deformed and Plain Billet Steel Bars for Concrete Reinforcement," says that rust shall not be cause for rejection provided the weight, dimensions, cross-sectional area, and tensile properties of a hand-wire-brushed test specimen aren't less than the ASTM specification requires.
Section 7.4.2 of ACI 318-95, "Building Code Requirements for Structural Concrete," has a similar statement indicating that reinforcement with rust shall be considered satisfactory, provided the minimum dimensions (including height of deformations) and weight of a hand-wire-brushed test specimen aren't less than applicable ASTM specification requirements.
_______________________________________________________________________________________________________________________
CAN YOU USE RUSTY REBAR IN CONCRETE?
It’s perfectly fine using “rusty” rebar that is coated in mill-scale and is not genuinely rusted. Mill-scale has even been shown to improve the adhesion between rebar and concrete.
Section 12 of the ASTM A 615-96a, “Standard Specification for Deformed and Plain Billet Steel Bars for Concrete Reinforcement,” states explicitly that rust is not a cause to reject a piece of rebar so long as it otherwise meets ASTM specifications.
When Rusty Rebar Can Become Problematic
Given certain conditions, rusty rebar can be an issue.
First, the rebar must be exposed to corrosive elements. Perhaps the concrete around the rebar has cracked, and saltwater has made its way to the exposed steel. Road salt and seawater can provide enough chloride ions. However, that steel rebar can be affected even if the concrete remains whole.
Corroding steel presents a couple of problems. First, the more steel rusts, the weaker it becomes as the metal is replaced by flakes and powder. Second, rusting steel expands.
As the steel expands, it places more stress on the surrounding concrete in a process called “oxide jacking.” This process causes the concrete to fail faster than it would have otherwise.
Mid Continent Steel and Wire is a leading steel and wire manufacturer headquartered in Houston, TX. Our brands include Magnum, Rangemaster, Stay-Tuff, & more.
www.dwreinforcing.com
_______________________________________________________________________________________________________________________
Generally speaking, rust on your reinforcing steel isn't a problem where it's formed by fresh water and research has demonstrated that a light coating of rust may actually help to increase the bond with concrete. The Australian Standard makes this clear:
AS 3600, Clause 19.2.4 states: “At the time concrete is placed, the surface condition of reinforcement shall be such as not to impair its bond to the concrete or its performance in the member. The presence of millscale or surface rust shall not be cause for rejection of reinforcement under this Clause.”
When rust might be a problem
There are a few instances where rusting of reinforcing steel may create structural or aesthetic issues:
Rain may wash rust off reinforcing steel laid in formwork such that it stains visible concrete. In this instance, the SRIA recommends removing loose rusted material prior to pouring your concrete or for more significant applications, using galvanised steel
Salt water can cause a more serious corrosion issue that may render the rebar or mesh structurally unsuitable. Where you have reinforcing steel that's been subjected to salt water and has visible rust it is important to treat it by using high-pressure washing to remove salt and loose corrosion and in severe cases the steel may need to be replaced. If in doubt, conduct strength and cross-sectional area limitation tests.
Reinforcing bar and mesh often arrives on site with some rust on it. This is quite normal: hot-rolled bars and coil have a layer of what's called mill-scale on the surface when they leave the mill. This mill-scale provides a protective layer in the right conditions but if stored externally or if...
www.materialslink.com.au
_______________________________________________________________________________________________________________________