Why Put Rebar in Concrete Driveway? Helps Increase Strength!
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Should I Put Rebar in My Concrete Driveway?
Yes, you should put rebar in your concrete driveway if it is 6” or thicker.
Why put rebar in concrete? A 6” thick concrete driveway reinforced with galvanized steel deformed rebars is extremely strong and durable. It will not sink, heave or crack even under heavy loads, freeze thaw cycles and ground movement.
Hot rolled carbon steel rebar (aka black bar) is most commonly used for reinforcing concrete driveways. Incorporating black bar in the concrete driveway will increase the tensile strength significantly.
A rebar that is made from corrosion resistant steel and has a deformed profile will result in additional benefits.
Hot rolled carbon steel rebar is popular because it’s the most affordable rebar. However, it is prone to corrosion. Stainless steel, epoxy coated and galvanized rebars are the corrosion resistant (albeit more expensive) alternatives.
Stainless steel rebars are fantastic but extremely expensive.
Epoxy coated rebars resist corrosion, but only as long as the coating does not get damaged. Even a slight hole or cut in the coating will result in corrosion which will creep under the epoxy coating.
Galvanized rebars are your best bet. They are coated with zinc and are 40 times more resistant to corrosion.
Make sure to use deformed rather than smooth rebars. Deformed rebars have ridges on the surface. The concrete bonds better with a deformed rebar. A deformed rebar becomes an integral part of the reinforced concrete slab.
Why Put Rebar in Concrete?
Concrete is an extremely strong construction material when it comes to compressive strength. Driveways typically use concrete with compressive strength between 3000 and 4000 psi.
On the other hand, steel has compressive strength of around 25,000 psi.
Unfortunately, concrete has a relatively poor tensile strength. Concrete with compressive strength of 3000 – 4000 psi may have a tensile strength of just 300 – 400 psi.
Steel rebars, on the other hand, have extremely high tensile strength. Steel rebar tensile strength is typically between 40,000 psi (Grade 40) to 60,000 psi (Grade 60). This is of immense value to concrete slabs & beams.
The effective strength of a concrete driveway more than doubles when it is reinforced with steel rebars.
It is not unusual for the grade below the concrete driveway to settle and move with changes in the water table level, mild seismic activity and growth of tree roots. A steel rebar reinforced concrete driveway is less likely to crack under such stress.
How Much Rebar Is Needed for a Driveway?
Contractors tend to use the 1/8 rule of thumb to determine the rebar diameter. The rebar diameter should not be more than ⅛ th the thickness of the concrete slab.
Based on this rule of thumb, # 3 or # 4 (⅜ “ or ½ “ diameter) rebars are generally used for 6” thick concrete driveways. The rebars are arranged in a grid, 18” – 24” apart.
The rebars should never extend all the way to the driveway edges. You do not want the rebars to be exposed after the concrete has been poured and the slab has cured.
Any exposed rebar will surely start corroding. Once corrosion starts it will eat its way even into the covered portion of the rebar!
The total number of rebars required for a driveway that is L feet long and W feet wide is calculated as under:
A = Number of rebars for driveway length = (W X 12 – 6)/18 + 1
B = Number of rebars for driveway width = (L X 12 – 6)/18 + 1
The total length of rebars required is then calculated as under:
Total rebar length in feet = A X (L – 0.5) + B X (W – 0.5)
EXAMPLE: Driveway length is 60’ and width is 20’
A = (20 X 12 – 6)/18 + 1 = 14
B = (60 X 12 – 6)/18 + 1 = 41
Total Rebar Length (in feet) = 14 X (60 – 0.5) + 41 X (20 – 0.5) = 833 + 800 = 1633
As standard rebar length available is 20’ you will need 82 (say 85) standard length rebars.
Assumptions made:
- Rebar spacing for the concrete slab is 18”.
- Rebars stay 3” away from any edge of the concrete driveway
- 1 is added while calculating A and B so as to get a closed grid
- A degree of rounding off and wastage can be expected, so buy a bit more than your calculations
Do’s and Don’ts of Rebar Grid Placement
Proper placement of the rebar grid is essential to maximize its effectiveness.
| Do’s | Don’ts |
|---|---|
| Place the rebar at the center of the concrete thickness | Don’t place the rebar too close to the surface |
| Securely tie the intersections of the rebar using tie wire | Don’t allow the rebar to touch the ground |
Here are the details of the key do’s and don’ts to keep in mind:
Do:
Ensure the Rebar is Placed at the Center of the Concrete Thickness
When placing the rebar, it is crucial to position it at the center of the concrete thickness.
This positioning provides balanced reinforcement throughout the structure and enhances the overall strength and load-bearing capacity of the driveway.
Securely Tie the Rebar Intersections
To prevent movement during the pouring process, it is important to securely tie the intersections of the rebar using tie wire.
This ensures that the rebar grid remains in its intended position and maintains its structural integrity as the concrete is poured.
Don’t:
Place the Rebar Too Close to the Surface
While it is vital to position the rebar at the center of the concrete thickness, it should not be placed too close to the surface.
When the rebar is too close to the top, there is a risk of it becoming exposed over time, which can compromise both the appearance and the integrity of the driveway.
Adhering to proper placement guidelines will help avoid this issue.
Allow the Rebar to Touch the Ground
It is important to prevent the rebar from coming into contact with the ground.
Allowing the rebar to touch the ground can result in corrosion over time, leading to structural degradation.
Proper elevation and support of the rebar grid are essential to ensure its long-term effectiveness. This is why I recommend the use of high quality Concrete Reinforcing Chairs.
TIP: For maximum slab strength, make sure that the rebars are not laid at the bottom of the concrete slab. Concrete Reinforcing Chairs ensure that rebars stay 1-1/2″ above the bottom.
Bottom Line
The bottom line is that the answer to the question “why put rebar in concrete” is that by doing so you create a composite building material that benefits from the high compressive strength of concrete and the high tensile strength of a steel rebar.
The resulting steel rebar reinforced concrete driveway has more than double the load bearing capacity. The lifespan goes up and the repair & maintenance costs come down.
Thank you very much for reading this post. I do hope you found it informative and helpful.
