Matt Mettler, P.E.

DOWL HKM

Isolation Joints Construction Joints Contraction Joints Expansion Joints

Doweled Tied Keyed Tooled Insert (zip strips) Butt Joints

Type of control joint Allows for drying shrinkage and other

movements Provides no vertical or horizontal restraint May act as an expansion joint if needed

Can be constructed of multiple types of joints: Doweled Tied Keyed Butt Joint

Are spaced and or located to facilitate construction Concrete quantity limitation Sequencing of construction tasks

Also known as control joints Controls cracking due to drying shrinkage May be constructed from a variety of

methods: Hand tooled Saw Cut (my preference) Inserts

Used primarily in exterior conditions Can be doweled but not keyed or tied Allows for un-restrained movements due to

temperature gradients Can be sealed

Function of concrete thickness, coarse aggregate size and concrete slump

PCA recommends the joint spacing be 2 to 3 times (in feet) the concrete thickness (inches) Example: a 5 inch slab would have joints

spaced 10 to 15 feet It is good practice to maintain a square

shape in so much as practical

Slab Slump, 4 to 6 inches SlumpThicknessMCA<3/4" MCA>3/4" < 4"

(in.) (ft.) (ft.) (ft.)5 10 13 156 12 15 187 14 18 218 16 20 249 18 23 2710 20 25 30

Structure geometry and other elements such as interior walls, columns and piers may dictate layout.

Contraction joints: Should be doweled or tied Saw cut floors Formed with chamfer strips for walls Try to maintain a square shape between joints May need waterstop and or joint sealant

Construction joints: Should be doweled or tied and keyed Use chamfer strips for adequate consolidation May need special attention regarding drainage

because of hydraulic loading.

Bureau of Reclamation, “Concrete Manual,” 8th Edition Revised, 1981

Ringo & Anderson, “Designing Floor Slabs on Grade,” 1992

Spears & Panarese, Concrete Floors on Ground, EB075.2D, Portland Cement Association, Skokie, IL, second edition 1983; revised 1990.

Young & Paxson, Undermining of Spillway Chutes, Safety of Dams Conference, Seattle, WA, Fall 2010.