March 6, 2025 · Education
Concrete's Hidden Weakness
Concrete is strong in compression but weak in tension. Soil movement, settling, and thermal expansion create tensile forces that would crack unreinforced concrete. That's where steel rebar comes in.
How Rebar Works
Steel rebar handles tensile and bending forces. The ribbed surface creates a mechanical bond with surrounding concrete, making them work as a composite unit.
Sizing and Spacing
Common sizes: #4 (1/2 inch) and #5 (5/8 inch). Size and spacing are determined by the structural engineer. Typical residential: #4 at 12 inches on center both ways.
Proper Placement
Rebar must be positioned at the correct depth. Too close to the surface — won't resist bending and may corrode. Too deep — won't resist surface tension. It's supported on wire chairs at the correct height.
What to Look For
Securely tied at intersections, correct height on chairs, free of excessive rust/mud/oil, and matching engineered plans.