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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.