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SPACI NG OF JOINTS AND LOAD TR ANSFER DEVICESI N CO NCRETE PAVEME NTS
Introduction
1. This technical instruction covers the spacing of joints in concr ete
pavements and intr oduction of dowel bars at expansion joints as a loadtransfer device. There is a sco pe f or increasing the spacing of ex pansion
joints in view of the experience gained and curr ent thinking. With theincr eased wheel loads and tyr e pr essur e, incorporation of load transf er device will prevent s palling at ex pansion joints.
S pacing of joints2. The spacing of joints of concrete pavements of thick ness of 200mm
, and above will be as follows :-
(a) Expansion joints
(b) Contr action (Dummy) joints
(c) Construction joints
36 m
4.5 m
3.75 m
3. Ther e will be only one ex pansion joint in the longitudinal dir ectioni.e. along the centr e-line of the runway.
Note: A r evised standard drawing incorporating these changeil is
under issue.
4. In case of overlays, the joints will have to be matched with the old pavement to avoid reflection cracking.
5. For new pavements, less than 200 mm . thick, the spacing of joints
will remain the same and existing standard drawings will be followed.
Load transfer devices
6. Load transfer devices in the form of dowel bars should be incor- porated at the expansion joints in pavements with thickness of 150 mmor mor e. These will transmit the load fr om one slab to the other more
efficiently and avoid excessive stresses along the edges of the expansion joint. This will protect the edges from spalling.
7. Dowel bars are provided as an integral part of expansion joints.
Theyare mild steel round bars of short length, whose half length is
bonded in concrete on one side of the joint and the other half is made to
slide in a sleeve with a recess at the end to accommodate the movementof slabs durini the expansion of concrete.
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8. A system of dowels should be pro per ly designed to transfer 40 to45 percent of the w heel load to the adjacent slab.
9. Indian Roads Congr ess r ecommendations on the use of dowel barsfor expansion joints in concrete roads are given in table No 1.
Table No.1
Dowel BarsThickness of slab
Diameter Length Spacing
mm mm mm mm
200 25 500 450200 20 380 360
150 25 5UO
450150 20 380 400
10. For airfield pavements, the dowels used range in size between20 mm and 75 mm round bars. Dowel spacing ranges between 300 mmto 450 mm. US Corps of Engineers recommendation on dowel sizerequirements are given in table No.2.
Table No.2
Dowel BarsThickness of slab
Diameter Length
I Spacing
mm mm mm mm
Less than 200 mm 20 400 300200 - 275 25 400 300300 - 375 32 500 375400 - 500 40 500 450525 - 625 50 600 450
Over 625 75 750 450
Conclusion
12. The reduction in the number of joints will improve the ridingquality of the surface and reduce the cost of maintenance and filling of
joints with sealing compound. Edge spalling is a hazard to flying and poses serious problems of repair s. The incorporation of load transfer devices will provide more efficient expansion joints and will reduce the
spalling to a large extent.
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