Joints in Concrete Construction Matt Mettler, P.E. DOWL HKM

Joint Definition Isolation Joints Construction Joints Contraction Joints Expansion Joints

Joint Construction Doweled Tied Keyed Tooled Insert (zip strips) Butt Joints

Isolation 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

Isolation Joint

Construction Joints 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

Construction Joint

Contraction Joint 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

Contraction Joints

Expansion Joints 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

Expansion Joint

Joint Spacing 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

Joint Spacing

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

Recommendations for Hydraulic Structures 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.

References 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.