There are many factors to consider before the actual construction commences during the planning stages of any building project. One of those considerations is the rebar that you are going to use. Rebar is short for steel reinforcement bars. Rebar performs well when subjected to tension. It is also an excellent material to reinforce concrete, which performs well under compression.

well Product Page

The quality of rebar chosen will determine your project's strength and durability; it will also ensure that the structure is safe for use and will last a long time even if subjected to the elements. Think of it as the skeleton in the human body but for buildings. It holds the concrete, so even if there is an earthquake, the building will still stand.

Installing an Access Panel like BA-CTR Flush Universal Access Door with Hidden Flange will also improve your structure's safety, as discussed in the article "Enhancing Your Safety Through Access Panels," which covers this topic more in-depth.

What You Should Look for in Rebar

Quality is #1. You must first assess if the steel's quality fits your project. It's essential to familiarize yourself with the standards for rebar in North America. The main standards outline the requirements for chemistry, corrosion resistance, magnetic permeability, surface finish, and mandatory corrosion tests. These standards will assist you in choosing the right product and help to ensure that the rebar passes the test for the following categories:

• Fatigue
• Compression
• Tensile strength
• Bending

Selecting the Right Size and Weight: Choosing the correct rebar size and weight is critical to safe building practices. As we've already discussed, concrete is weak against compression and will bend or fracture if not reinforced. This weakness is the reason you have to consider the correct size for your rebar.

The usual rebar diameter size used for bearing minimal loads is 6mm, 8mm, and 10mm. For columns and walls, the recommended size is 8mm or greater. Foundations and building footings commonly require a 10mm diameter rebar or greater. The bigger the structure, the thicker the rebar. 204-334-

Yield Strength: Tensile or yield strength is the measurement that indicates the overall strength of the steel. High yield steel is best used for heavy-duty rebar and has a grade of 500 Mpa (or N/mm2).

*Note that increasing the rebar's diameter size does not make it twice as strong. The grade of your steel determines the strength.

Kinds of Rebar

We omitted Epoxy-Coated Rebar because it is under a ban in Quebec, Canada, and some parts of the United States. Reevaluations and further studies regarding the material are in progress.

Some of the common types of rebar you might consider are:

Thermo Mechanically Treated Bars (TMT Rebar): Hot treated bars high in strength primarily used in reinforced cement concrete (RCC) work.

High Strength Deformed Bars (HSD Rebar): This steel bar has deformation or projection on the surface. It is a cold twisted bar primarily used for reinforcement purposes in construction.

Carbon Steel Rebar: It is known as 'black bar' due to its carbon color. It has an excellent tensile strength ratio at an affordable price. The drawback is that it may rust over time.

Galvanized Rebar: It is forty times more resistant to corrosion than black rebar but is also more expensive.

Glass-Fiber-Reinforced-Polymer (GFRP): This rebar mustn't bend because it is carbon fiber, making it costly. The upside is it's highly resistant to corrosion.

Stainless Steel Rebar: This is the best rebar, but it is also the most expensive. It is 1,500 times more resistant to corrosion compared to a black bar. You will need hydraulic rebar cutting tool to cut through this.

Taking your time to carefully plan your project and becoming familiar with safety and quality standards is well worth your while. It will ensure that your building is strong, durable, and withstands the test of time and exposure to the elements.

Standing the test of time

Stainless steel reinforcement (rebar) is increasingly being specified for its excellent corrosion resistance, long-term performance and economic benefits.

There are many advantages to using stainless steel rebar:

• Excellent durability, fire resistance and structural performance.

• Exceptional corrosion resistance in harsh marine environments, resisting chlorides and pitting corrosion.

  Are you interested in learning more about stainless steel reinforcing fibers? Contact us today to secure an expert consultation!

• Extended service life and reduced life cycle costs.

• Minimal maintenance costs and therefore less disruption of service for refurbishment 

  or replacement.

• Easy to cut and bend, good weldability.

• Cathodic protection is not required.

• Reduced concrete cover, minimising costs and delivering a more lightweight, higher tensile structure. Cracks are less critical and concrete surface treatments are not required.

• Supplied in accordance with ASTM A955 and 

  BS standards, both of which require confirmation of a generic corrosion resistance test by the manufacturer to meet specific strength levels.

Some history
Concrete is the most used material in infrastructure projects because of its properties, cost and availability. It has excellent compressive strength but very poor strength under tension. Cast iron and steel bars were incorporated into structures to form durable and strong reinforced concrete with the steel protected by the alkalinity of the concrete. Unfortunately, a combination of cost-cutting (poor quality concrete) and atmospheric CO2 carbonation led to the prevalence of concrete cancer with reduced service life and durability.

In the USA, multiple reinforced slab highway bridges suffered severe reinforcement corrosion and state authorities explored galvanising, epoxy coatings and cathodic protection in refurbishment and new programs. The UK Government had similar concrete corrosion problems at Birmingham's Spaghetti Junction and research led to the s revision of their BA 84/02 Design Manual for Roads and Bridges. The new code required stainless steel reinforcement around slab penetrations, in splash zones or wherever severe disruption would occur if carbon steel repairs would be required. It also permitted lower cover and wider cracks if stainless steel was used compared to the carbon steel requirements. In addition, it removed the requirement for surface diffusion barriers such as silane treatments.

Over the following decades this philosophy migrated into commercial buildings and non-government infrastructure. 

Why stainless steel?
When carbon steel corrodes, the oxides are up to 10 times the volume. This expansion will start cracks in the concrete and possibly surface stains. This allows more water, oxygen and chlorides to accelerate the steel attack, cause concrete spalling, further corrosion and potentially, structural failure. Stainless steel is inherently resistant to corrosion and, even if it is exposed to overwhelming chlorides in concrete, the pitting attack does not generate sufficient localised corrosion product to fracture the concrete. Despite the short-term attack of galvanised coatings in fresh concrete, galvanised reinforcement was trialled but did not offer sufficient long-term durability. Epoxy coated steel reinforcement suffered from handling and installation damage leading to concentrated attack at coating holidays. 

The solutions of cathodic protection (CP) and sacrificial anodes for carbon steel reinforcement can be effective. However, the reinforcement must be electrically continuous, the operation of the system must be regularly monitored, and periodic surveys are required to monitor the distribution and effectiveness of the CP. In a bridge designed for a 300-year service life, the monitoring costs would be significant.

The unfounded barriers to using stainless steel
Galvanic acceleration of corrosion?
Early on, there was significant resistance to specifying stainless steel due to the perception of the need for complete replacement of carbon steel. Connecting stainless steel to carbon steel corrodes the carbon steel but that assumes a near-neutral pH, i.e. about 7. Concrete is quite alkaline, i.e., pH>9.4, and in those conditions, the galvanic potential of carbon steel and stainless steel is about the same. Multiple laboratory and real-life tests have shown no galvanic acceleration of the carbon steel corrosion, even with quite significant levels of chloride contamination. Hence stainless steel can be used around joins in slabs, penetrations, at surfaces where diffusing water can evaporate and concentrate aggressive salts or where road or marine salts accumulate.

The Schaffhausen Bridge in Switzerland used about 15 tonnes of stainless steel rebar in areas subject to road salt, about 5% of the total steel use. This added less than 1% to the capital cost and delivered a 13% life cycle cost advantage over simple carbon steel for an 80-year life cycle.

Nearer to home, the McGee Bridge over the inlet in Hobart uses stainless steel rebar in the tidal zone (where the tides act  as a chloride pump) and carbon steel in the superstructure where chloride risk is low.

Misunderstanding of the chloride resistance of stainless vs. carbon steel
The widely accepted chloride limits for common stainless steels in near-neutral water are not relevant to the highly alkaline interior of a concrete structure. Figure 1 shows the results of multiple laboratory tests and uses chloride as a percentage of cement as a measure of corrosivity. The limited use of carbon steel in poorly cast (higher chloride penetration) and lower cement content (lower pH) is evident. What is surprising is that austenitic 304 or 316 (or their 'equivalent corrosion resistance' lean or low alloy duplex grades) provide useful service in a wide range of conditions.

However, duplex grades provide double the 0.2% proof stress than their austenitic equivalent and the worldwide trend is to specify reinforcement at the higher end of the alloy grade strength.

Product forms and inspection
Bar, and bar with defined deformations, are specified with recommended sizes that do not always match hard metric dimensions. Stocked sizes depend on the specific supplier. It is typical that bars above about 20mm diameter are supplied in duplex grades to utilise the superior strength compared to austenitic grades. 

Bars are often coupled by screwed fittings or can be welded provided the heat tint is removed, preferably by pickling. It is essential that stainless rebar is protected during delivery and site storage. If adjacent carbon or galvanised steel requires cutting, the debris must not settle on the stainless steel. Figure 2 of four bars is for quality assurance of bar delivered after pickling to remove contamination and passivate the surface. The upper two bars have different levels of pickling but are acceptable. The lower two are not acceptable because of iron residue from the rinse water (C) and insufficient pickling time (D).

Pre- and post-tensioned cables have been mainly austenitic but the strength advantages of duplex grades mean they are increasingly being used. Stainless steel mesh is often used to control shrinkage cracking and deliver tensile strength. A further product form for inclusion in concrete (and refractory) are wire fibres which are either undulating or with end hooks and aspect ratios in the range 35 to 60:1. 

 

This article is featured in Australian Stainless Magazine issue 74, . 

Want more information on refractory stainless steel fiber? Feel free to contact us.