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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
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
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
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
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 • 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.