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.
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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:
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. 204-334-0909
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.
Advantages
Drawbacks
Epoxy coating
Lower initial costs
Cannot be bent without cracking
Galvanizing
Lower initial costs
Cannot be bent without cracking
Fiber-reinforced Polymers
Lower initial costs
Light
Low modulus (low stifffness)
Cathodic protection
Lower initial costs
Requires careful design for overall protection
Membranes
Lower initial costs?
Require careful installation
STAINLESS STEEL
Low Life Cycle cost:
Design similar to C-steels
Removes corrosion, hence corrosion-induced concrete cracking
Higher initial cost….but limited to a few percent of the cost of the structure
Recommendations of the Technical Center on Consulting for Cement and Concrete, Switzerland [17]:
Material of the reinforcement
Pitting
Resistance
1)
Corrosion
Resistance
Class
Carbonation of concrete
No
Yes
No
Yes
Yes
2)
Yes
2)
Chloride content 3)
Zero
Zero
Low
Low
Mid
High
Ordinary black rebar
0
0
+
-
+/-
(-)
-
-
Epoxy-coated rebar
0
?
4)
Galvanised rebar
0
0/1
+
+
(+)
-
-
-
Chromium-Steels 5)
10-16
1
+
+
+
(+/-)
(+/-)
-
Chromium-Nickel-Steels and Chromium-Nickel-Molybdenum-Steels
17-22
2
+
+
+
+
+
(+)
Chromium-Nickel-Molybdenum-Steels
23-30
3
+
+
+
+
+
+
Chromium-Nickel-Molybdenum-Steels
>31
4
For special cases e.g.:
1) WS: Pitting resistance equivalent calculated according to: WS=%Cr+3.3%Mo+0%N.
The minimum content of chromium and molybdenum according to EN 10088 and Stahlschlüssel (Germany) was used for the calculation. The nitrogen content was not taken into account.
2) The influence of the chloride content dominates. Carbonation is of minor importance since the rate of carbonation is low or the concrete cover is high
3) Chloride content:
low:
≤0.6 M.% in respect to cement content
middle:
≥0.6, but ≤1.5M.% in respect to the cement content
high:
≥1.5, but ≤5 M.% in respect to the cement content
very high:
>5 M.% in respect to the cement content
4) The classification is uncertain/controversial. Comparative considerations and judgement: see Chapter 4.7.
5) The susceptibility to pitting corrosion of chromium steels with a low chromium content increases rapidly with decreasing pH. Depending on the concrete cover the carbonation of the concrete is, therefore, more or less important
BSSA (British Stainless Steel Association) Special report (2003) [18]
Selection of material Grade for given exposure condition
Exposure condition
Material Grade
Stainless steel embedded in concrete with normal exposure to chlorides in soffits, edge beams, diaphragm walls, joints and structures
1.4301
As above but where design for durability requirements are relaxed in accordance with table 3.7.
1.4301
As above but where additional relaxation of design for durability is required for specific reasons on a given structure or component i.e. where waterproofing integrity cannot be guaranteed over the whole life of the structure
1.4436
Direct exposure to chlorides and chloride bearing waters for example dowel bars, holding down bolts and other components protruding from the concrete
1.4429
well supply professional and honest service.
1.4436
Specific structural requirements for the use of higher strength reinforcement and suitable for all exposure conditions
1.4462
1.4429
Please note, however, that since then lean Duplex grades gained acceptance and are now widely used (please go to stainless properties)
Example 1 [19]
ECONOMIC EXAMPLE:*
Total construction costs of a road bridge
Solution
Total bridge cost indications
100%
Carbon Steel Rebar
100
10%
Stainless Steel Rebar
103
25%
Stainless Steel Rebar
107.5
50%
Stainless Steel Rebar
115
100%
Stainless Steel Rebar
130
(*) The calculations are taken from a publication by the French information centre for cementeous materials, CIMbéton. The stainless steel used is grade 304. The numbers will vary with market prices and grade selection. Nevertheless, the indications represent typical road bridge construction experience.
Example 2 The Progreso pier was built in 1941, using stainless steel rebar. The LCA /LCC comparisons were made with an hypothetical alternative of C-steel rebar. They show that stainless rebar results in a lower Life Cycle Cost and a lower Global Warming Potential.“The advantage of stainless steel is the extremely slow rate at which it corrodes in a concrete/chloride environment. Minimal corrosion damage is anticipated during a service life of 75 years. Although it is much more expensive to purchase than black or epoxy-coated reinforcing steel, it is more cost-effective over the long term because the corrosion-induced damage typically seen with black steel and coated steel will not occur.”
Example 4 Comparison of initial cost and life cycle costs of new bridges with various types of deck reinforcingReinforcing Type
ECR, Galvanized
MMFX 2
FRP
Solid Stainless
EnduraMet© 32 Stainless
Deck cost (compared to total initial cost of “base” structure)
38.00%
39.14%
39.90%
42.18%
39.90%
Steel cost (compared to total initial cost of “base” structure)
31.00%
31.00%
30.50%
30.50%
30.50%
Foundation cost (compared to total initial cost of “base” structure)
25.00%
25.00%
24.00%
24.00%
24.00%
Earthwork, etc. cost (compared to total initial cost of “base” structure)
6.00%
6.00%
6.00%
6.00%
6.00%
Total initial cost of structure
100.00%
101.14%
100.40%
102.68%
100.40%
Estimated Life (Years)
40
50
65
100
100
Present worth of deck replacement at end of life
9.89%
6.88%
3.93%
1.05%
1.00%
100-year life cycle cost as a percentage of initial cost of “base” structure
111.48%
108.02%
103.88%
103.74%
101.40%
[22]The Schaffhausen bridge across the river Rhine was completed in 1995. The bridge is required to resist to atmospheric corrosion and de-icing salts. The bridge is expected to last 80 years without loss of structural integrity and without significant maintenance.
Three options were considered for the rebar reinforcement:
The comparative costs of the three alternatives are shown below.
Proper use of stainless steel leads to an extra cost of only 0.5%, paid back 30 times by the savings achieved over the lifetime of the bridge!
LIFE CYCLE COST SUMMARY OF A RIVER CROSSING HIGHWAY BRIDGE:
Description
Carbon Steel
Epoxy C.S.
Stainless Steel
Material costs
Fabrication costs
Other installation costs
8,197
0
15,611,354
31,420
0
15,611,354
88,646
0
15,611,354
Initial cost (CHF)
15,619,551
15,642,774
15,700,000
Maintenance
Replacement
Lost production
Material related
0
256,239
2,218,524
0
0
76,872
2,218,524
0
0
-141
0
0
Operating costs (CHF)
2,474,763
2,295,396
-141
Total LCC (CHF)
18,094,314
17,938,170
15,699,859
Example 6 [Reference 26 Chapter 11]
It describes the repair of the facade of an 18-storey apartment building in Alicante, Spain.(see front view, below) The 30 year-old building is located close to the sea. Cracks in the façade panels were observed and required replacement by new ones reinforced with stainless steel.
Example 7 [Reference 27 Chapter 12]Compares the costs of two concrete structures ( i.e. apartment building and underground car park) reinforced with C-steel or with stainless steel. The use of stainless steel on the most exposed areas only leads to an increase of the construction cost of about 9€/m2 (about 2,5%) for the apartment building. A full replacement of C-steel by stainless steel would increase the cost by about 6%. This is not much in view of the longer life of the construction without major maintenance.
Building codes demand that structures should meet a proper level of fire resistance, usually 2 hours minimum, before collapse. One of the key parameters for reinforced concrete beams is the concrete cover (over the reinforcing bar).
Increasing the concrete cover will be efficient, however, only if the concrete does not exhibit large cracks or is deteriorated. This may occur over time as a result of corrosion.
Another problem, for thick concrete covers is that of "spalling", i.e. concrete cover cracking and flaking in case of fire. Ways to avoid this are enforced, but they add to the cost.
An efficient way to improve the fire resistance of reinforced concrete is to use stainless steel rebar. Stainless steels retain their mechanical properties better than carbon steel at elevated temperatures.
Note: EN 1.4311 (AISI 304N): stainless rebar data from worldstainless, EN 1.4301 (AISI 304) Eurocode data
Computer simulations show that the fire resistance of Stainless reinforced beams is much better than that of carbon steel reinforced ones.
The curve below obtained by computer simulation illustrates how a concrete beam reinforced with either C-steel or stainless steel (grade EN 1.4311 - AISI 304N) bends under load in case of fire (ISO 834 standard - cellulosic fire). Beam deflection increases with time (and beam temperature) until it cannot anymore bear the load.
Stainless steel almost doubles the time before the beam collapses. In addition, the high elongation provides a progressive onset of beam failure and therefore warns of imminent danger.
The increase in time before collapse brought by stainless steel reinforcement is an attractive alternative to the increase of concrete cover:
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