paulsharvey
Super Member
So, ChatGPT's answer, actually kinda says im right for where I am, and runner is right for for his area. In the end, driveways/sidewalks are not rocket science, and both approaches generally work. For Long runs, regardless of cold joint or a continuous pour, I would place expansion joint every 80-100 LF, to prevent "tenting" (where heat expands the concrete, and it has no where to go, so the joint pushes up, creating a "tent"
Great question — and it’s one that even a lot of contractors disagree on, depending on the project size, soil, and climate. Here’s a clear breakdown:
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1. Expansion Joints vs. Dowels — Different Purposes
Expansion Joints
Purpose: Allow movement (expansion/contraction) of concrete due to temperature and moisture changes.
Where used:
Between driveway and structures (house foundation, garage slab, sidewalk, etc.)
Occasionally between very large slabs or different pours if you expect significant temperature variation.
Material: Fiberboard, asphalt-impregnated board, rubber, or foam strips (½" thick typically).
Rule: You want an expansion joint where you want the slabs to move independently — not crack against each other.
Dowels / Rebar Connections
Purpose: Keep slabs level with each other while allowing some horizontal movement.
Used for:
Large driveways poured in multiple sections (cold joints between pours).
Transitions (like between driveway panels).
Slabs on grades that might shift slightly due to soil.
Typical setup: Smooth, greased dowels (⅝" or ¾") across the joint so one slab can slide without locking up.
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2. Best Practice for a Driveway
Situation Recommendation
Between driveway and house/garage Use an expansion joint (no dowels or rebar)
Between sections poured on different days Use dowels, not rebar or rigid tie — prevents uneven settling but still allows shrinkage
Within large driveway (over 20 ft long) Add control joints every ~10–12 ft to control cracking
Hot climates (like Florida) Use fewer rigid ties, allow for movement — concrete expands more
Cold climates (freeze-thaw) Dowels with expansion caps work well; allow sliding movement
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Example Setup
For a 30' x 40' driveway poured in two 15' x 40' sections:
At the joint between the two pours:
→ Place ⅝" smooth dowels, 12" long, spaced 12" apart, greased on one end (so slabs can move).
At the garage/sidewalk edge:
→ Use a ½" fiber expansion joint strip, no steel tying them together.
Within each section:
→ Saw-cut control joints every 10 feet (¼ the slab thickness deep).
---
Common Mistakes
Using rebar or welded wire mesh through an expansion joint — that defeats the purpose.
Skipping joints altogether — results in uncontrolled cracking.
Using ungreased dowels — causes restraint and cracks.
---
If you tell me your driveway size, region (for temperature swings), and whether you’re pouring it in one go or sections, I can give you an exact joint layout and dowel spacing plan. Would you like that?
Great question — and it’s one that even a lot of contractors disagree on, depending on the project size, soil, and climate. Here’s a clear breakdown:
---
1. Expansion Joints vs. Dowels — Different PurposesExpansion Joints
Purpose: Allow movement (expansion/contraction) of concrete due to temperature and moisture changes.
Where used:
Between driveway and structures (house foundation, garage slab, sidewalk, etc.)
Occasionally between very large slabs or different pours if you expect significant temperature variation.
Material: Fiberboard, asphalt-impregnated board, rubber, or foam strips (½" thick typically).
Rule: You want an expansion joint where you want the slabs to move independently — not crack against each other.
Dowels / Rebar Connections
Purpose: Keep slabs level with each other while allowing some horizontal movement.
Used for:
Large driveways poured in multiple sections (cold joints between pours).
Transitions (like between driveway panels).
Slabs on grades that might shift slightly due to soil.
Typical setup: Smooth, greased dowels (⅝" or ¾") across the joint so one slab can slide without locking up.
---
2. Best Practice for a DrivewaySituation Recommendation
Between driveway and house/garage Use an expansion joint (no dowels or rebar)
Between sections poured on different days Use dowels, not rebar or rigid tie — prevents uneven settling but still allows shrinkage
Within large driveway (over 20 ft long) Add control joints every ~10–12 ft to control cracking
Hot climates (like Florida) Use fewer rigid ties, allow for movement — concrete expands more
Cold climates (freeze-thaw) Dowels with expansion caps work well; allow sliding movement
---
Example SetupFor a 30' x 40' driveway poured in two 15' x 40' sections:
At the joint between the two pours:
→ Place ⅝" smooth dowels, 12" long, spaced 12" apart, greased on one end (so slabs can move).
At the garage/sidewalk edge:
→ Use a ½" fiber expansion joint strip, no steel tying them together.
Within each section:
→ Saw-cut control joints every 10 feet (¼ the slab thickness deep).
---
Common MistakesUsing rebar or welded wire mesh through an expansion joint — that defeats the purpose.
Skipping joints altogether — results in uncontrolled cracking.
Using ungreased dowels — causes restraint and cracks.
---
If you tell me your driveway size, region (for temperature swings), and whether you’re pouring it in one go or sections, I can give you an exact joint layout and dowel spacing plan. Would you like that?
