When do I need to use dowels for load transfer across transverse, sawed, contraction joints, and how big should they be?
Rule of Thumb | Size of Dowels
Rule of Thumb
If a pavement is properly designed using an accepted thickness design procedure, and the design is 8 inches or more, use dowels at all transverse joints. If the design is less than 7 inches, dowels are most likely not needed at transverse contraction joints, because there is not enough truck traffic to cause faulting. Between 7 and 8 inches, you are in a gray zone, and the use of dowels depends on the amount of trucks, the traffic patterns (channelized or non channelized), speed, etc.
Another rule of thumb for the use of dowels is truck traffic. If the design lane (most heavily trafficked lane) of the roadway has less than 80 trucks per day, dowels are probably not needed. However, if the design lane has more than 120 trucks per day, dowels are most likely needed. If the truck traffic is 80 to 120 trucks per day, then the use of dowels is up to engineering judgement.
However, transverse construction joints (headers) are typically formed, butt joints, so they do not have any load transfer. Dowels are needed at these locations for all pavements, regardless of thickness or truck traffic.
Size
The rule of thumb for dowel size is: Dowel Diameter = 1/8 of the Pavement Thickness.
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Lengths from 15-18 inches (380-460 mm)
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6.0 inches (150 mm) minimum embedment length on each side of the joint
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1.0-1.50 in. (25-40 mm) diameter typical for roads
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1.50-2.0 in. (40-50 mm) diameter typical for airfields
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Epoxy or other coating for corrosion protection
Table 1. Dowel Requirements Based On Pavement Thickness or Truck Traffic
Concrete Pavement Thickness
in. (mm) |
Truck Traffic
trucks/day |
Dowel Diameter
in. (mm) |
< 7.0 (175) |
< 80 |
not necessary* |
7.0 - 8.0
(175 - 200) |
80 - 100 |
? |
8.0 - 10.0
(200 - 250) |
> 100 |
1.25 (32) |
> 10.0 (250) |
> 100 |
1.5 (38) |
* Except at construction joints
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Load Transfer Fundamentals
