Concrete Construction Tips -- Joints_tcm45-344519.pdf
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TYPES The basic types of joints are: construction joints (occur b et ween concrete lif ts of slabs in which one part is al- lowed to harden before the next is placed); contraction joints (us ed to permit shrinkage without r andom cra cks being formed); connection detail joints (between stru c- tural members); and isolation joints (to prevent random cracking of slabs of different thicknesses or shapes). Use an isolation joint between concrete slabs of diff erent shapes or thicknesses and around all columns, footings and peri pheries of buildings. Consider the use of skewed joints to reduce impact at the joint. PLACEM ENT Mark the exact loca tion of all j oints on plans and indi- cate the means of forming them. Remember that placement of contraction joints va ries with such fa ctors as a ggregate used, tempe ratu re and humidity range experienced, sub-base restraint and to- tal water content of the mix. Floor joints should not be placed too far apart. When in doubt, place joints 15 feet apart when using siliceous gravel or slag, 20 feet apart when using calcareous gra v- el or crushed limestone, and 25 feet apart when using crushed granite. Place joints at the inside point of V-shaped rust icat ion strips and at the top edge of the inner face of rectangular rustication strips. Make joints exactly horizontal or vertical in walls. WATERSTOPS Use waterstops for joints subject to hydrostatic pressure. Fa miliarize yourself with the several types of waterstops on the market. Le a rn how w aterstops should be inst alled. Poor instal- lation can undermine their functioning. Remember t hat waterstops w ill not be eff ective if ra n- dom cracks occur in places other than the joint across which they a re instal led. FILLERS Clean all joints before inserting joint filler materi als. Consider the use of lead as a join t fille r in industri a l floors because it reduces maintenance considera bl y . Consider the use of the new extruded lead joint filler ma- terials. Don’t allow workers to handle hot lead for joints with- out first instructing them in its p roper use and handling. When using pre-molde d joint fill er mate ri a l s, use an edging tool with a maximum rad ius of 1 ⁄ 8 inch. Fill sawed joints immediately to pre vent debris from be- coming lodged in them. SAWING The time to saw a joint is crucial. If sawed too early, the concrete will ra vel badly at the joint; if sawed too late, blade wear will be excess i ve and/or random cra c k s might form. The time to saw joints will va ry from 4 to 12 hours after casting. Concrete cast in the morning should be sawed the same afternoon, but evening concrete may be sawe d the next morning. Saw as early as possible when using silicon carbon blades and as late as possible when using diamond blades. When postpo ning s awing, use rel ief joint s eve ry 6 0 to 100 feet. Don’t saw a joint deeper than necessary. A 1 1 ⁄ 2-inch cut has been found to be successful in most states. Remember that sawed joints in large floor jobs can effect a considerable saving over other jointing methods. CONCRETE CONSTRUCTION TIPS j oints
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Transcript of Concrete Construction Tips -- Joints_tcm45-344519.pdf
7/27/2019 Concrete Construction Tips -- Joints_tcm45-344519.pdf
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TYPES
The basic types of joints are: construction joints (occurb e t ween concrete lifts of slabs in which one part is al-lowed to harden before the next is placed); contraction joints (used to permit shrinkage without random crack sbeing formed); connection detail joints (between struc-tural members); and isolation joints (to prevent randomcracking of slabs of different thicknesses or shapes).
Use an isolation joint between concrete slabs of differentshapes or thicknesses and around all columns, footings
and peripheries of buildings.
Consider the use of skewed joints to reduce impact atthe joint.
PLACEM ENT
Ma rk the exact location of all joints on plans and indi-cate the means of forming them.
Remember that placement of contraction joints vari es with such factors as aggregate used, tempera t u re andhumidity range experienced, sub-base restraint and to-
tal water content of the mix.
Floor joints should not be placed too far apart. When indoubt, place joints 15 feet apart when using siliceousg ravel or slag, 20 feet apart when using calcareous grav-el or crushed limestone, and 25 feet apart when using crushed granite.
Place joints at the inside point of V-shaped rust icat ionstrips and at the top edge of the inner face of re ctang ularrustication strips.
Make joints exactly horizontal or vertical in walls.
WATERSTOPS
Use waterstops for joints subject to hydrostatic pressure.
Familiarize yourself with the several types of waterstopson the mark et.
Le a rn how waterstops should be installed. Poor instal-lation can undermine their functioning.
Remember that waterstops will not be effective if ra n-dom cracks occur in places other than the joint across which they are installed.
FILLERS
Clean all joints before inserting joint filler materials.
Consider the use of lead as a joint filler in industri a lfloors because it reduces maintenance considerabl y.
Consider the use of the new extruded lead joint filler ma-terials.
D on’t allow workers to handle hot lead for joints with-out first instructing them in its proper use and handling.
When using pre-molded joint filler materi a l s, use anedging tool with a maximum radius of 1 ⁄ 8 inch.
Fill sawed joints immediately to prevent debris from be-coming lodged in them.
SAWING
The time to saw a joint is crucial. If sawed too early, thec o n crete will ra vel badly at the joint; if sawed too late,blade wear will be exc e s s i ve and/or random cra c k smight form.
The time to saw joints will vary from 4 to 12 hours aftercasting. Concrete cast in the morning should be sawedthe same afternoon, but evening concrete may be sawedthe next morning .
Saw as early as possible when using silicon carbonblades and as late as possible when using diamond
blades.
When postponing sawing, use relief joints eve ry 60 to100 feet.
D on’t saw a joint deeper than necessary. A 11 ⁄ 2-inch cuthas been found to be successful in most states.
Remember that sawed joints in large floor jobs can effecta considerable saving over other jointing methods.
CONCRETE CONSTRUCTION TIPS joints
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CONSTRUCTION PRACTICES
Use a mix with the amount of coarse aggregate reducedby one-half for the first 5 inches of a lift at construction joints.
D on’t lap rei nf o rcement at joints. Cut eve ry other wire when using wire mesh at a joint.
Remember that concrete on either side of a construction
joint must be tightly bonded, and concrete on either sideof a contraction or expansion joint must be pre ven t e df rom bonding.
Position formed joint materials securely in place.
Avoid bleeding at a construction joint.Don’t permit leaks in forms at a construction joint sincethey will result in staining of the concrete below the joint.
Don’t position dowels at joints at an angle. This will pre-vent proper functioning of the joint. Make sure they are
p e rfectly level and are secured fi rmly in place beforecommencing placing operations.
Remember that slabs-on-ground placed on a poors u b g rade re q u i re more joints to allow for differentialsettlement.
Bef ore placing the top layer of concrete at a construction joint, always clean the top surface and provide a cushionof mortar.
For more deta iled information o n this s ubject refer to the fol-lowing earlier articles in Concrete Construction:
Sa wed J oints; Ja n., 1958.
Expansion Jo ints; J an., 1958.
Lead J oints; Aug., 1958.
Wa terstop s In Review ; Dec ., 1959.
Insta lla tion Of Wa terstop s; Feb ., 1960.
Full-Depth Control J oints For Conc rete Highwa y P avements;Oct., 1960.
PUBLICATION#C630219
Copyright © 1963, The Aberdeen GroupAll rights reserved
