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Utility Cut Restoration

DAVID

J HALPENNY

Portland Cement

Association

Skokie Illinois

INTRODUCTION

THE DESIGN LIFE of a c i t y str t i s

dependent

on

the

pavement th ickness

d e s i ~ n

and t he number and w ei gh t o f

loads t

rece ives

while it i s in se rv

i c e . One a s p e c t t h a t i s no t a ccoun t ed

fo r

in

pavement

design

i s

the a f f ec t of

u t i l i t y cu t s on pavement l i f e . U t i l i t y

cut r ep a i r s can d r a s t i c a l l y shor t en the

s e r v i c e lif i f t hey

a r e

no t c o n s t r u c t e d

proper ly

however.

a

proper r e s t o ra t i o n

wi l l

have no

e f f ec t

on

e i the r the des ign

l i f e

or r i de a b i l i t y

of

the pavement.

SIZE AND

SHAPE

The

shape and d i m ens i on

of

a r e p a i r

and i t s

pos i t i on in the pavement with

r e s p e c t

to j o i n t s and edges

have

a

d i r ec t r e l a t i o n s h i p with

i t s

a b i l i t y to

s tand up under t r a f f i c . U t i l i t y cut

r e s t o ra t i o n s

can be

c l a s s i f i e d in to

the

fo l lowing

f ive

types

as shown in

Fig. I .

4

Fig. 1. Resto ra t ion

fo r

pla in pavement.

1.

FtTLL PAVEMENT REPAIR

invo lves

a l l

lanes

of

the

pavement. These r e

p a i r s are usua l ly cons t ruc t ed one l ane

a t

a t ime and should

have

a minimum

width

of

6 - f t .

J o i n t s t h a t f ll with in

the l i m i t s of the r e s t o ra t i o n need not

be

rep laced . I f

the

u t i l i t y

cut

f a l l s

with in 2 - f t .

of a

j o in t .

the r e s to r a t ion

must

extend to the

j o i n t .

2. SINGLE LANE REPAIR involves

olily a s ing le

t r a f f i c

l ane and should be

a t

l e a s t 6 - f t . in

width. All j o i n t s

t h a t are

loca ted

wi th in

the

u t i l i t y Cllt

must be rep laced in t he i r o r i g i n a l 10-

r :a t ion .

3. EXTERIOR EDGE REPAIR a r ep a i r

with

a

l eng th l e s s than one

fu l l l ane

width. and a

width no l e s s

than

4 - f t .

One edge

l i e s

along the

out s ide edge of

the

pavement

and the

othe r

a

minimllm

di s t ance

of

2 - f t .

from the

nea res t

j o in t .

4 .

INTERIOR EDGE REPAIR a r ep a i r

with a iength l e s s

than

one fu l l l ane

width.

One edge l i e s

along an

i n t e r i o r

edge

or j o i n t of the

pavement

anci the

othe r

a

minimum

of

2 - f t . from

the

near

es t j o i n t or edge.

5 . INTERIOR REPAIR t h i s r ep a i r

has a

l eng th

l e s s

than

one fu l l l ane

width, and

i s l e ss than

one

fu l l

panel

wide, with no edge of

the

r ep a i r l y i n g

along

a j o i n t

or

pavement edge. The

minimum di s t ance of an edge to the

near

es t j o i n t or

edge

should be

2 - f t . I f

l e s s

than

2 - f t

. . the

r ep a i r

shu l l extend

to

the j o i n t

or

edge

and be

c l a s s i f i e d

as an

edge

r ep a i r .

In heav i ly t r a f f i ck ed roadways.

s t e e l dowels a re d r i l l e d

and

grouted

i n to

the

remain ing s l ab to improve

load

t r an s fe r

fo r

pla in

doweled

p a v e m e n t ~

Pavements

with

dowels

fol low the

same

ru l e s

and

dimens ions fo r

u t i l i t y

cu t s as

pavements without dowels . Two add i t ions

used in

t he i r

c o n s t r u c t i o n a re

the u t i

l i z a t i o n of t i eba r s

in a l l non-working

t r ansve rse j o in t s .

and

dowels in a l l

working t r ansve rse j o i n t s as

shown

in

Fig. 2.

- J oi nt s form ld

ond sealed

Fig.

2. Resto ra t ion fo r

doweled

pavement.

All t i eb a r s are d r i l l e d

and

grouted

i n to the hardened

conc re t e .

and

a re

1/2-

in . diameter

by

24 in . in length . The

b ar s

a re

placed

a t

a

di s t ance

of 3D-in.

cen te r

to

cen te r fo r

the

purpose

of

t i e i n g

the

r e s t o r a t i o n to

the ex i s t i n g

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pavement and provid ing addi t iona l load

t r an s fe r . Dowels provide the

same

func

t i o n as

t i eb a r s by

inc reas ing

load

t r an s f e r with the excep t ion t ha t they

are p laced

a t working c o n t r o l j o in t s

and

a l low expans ion

and

cont rac t ion a t these

j o i n t s . The

s t ee l dowels

are

d r i l l e d

and grouted in place a t

1 2 - i n .

cen te rs

with

dowel

dimensions

shown

in Table 1 .

Spec ia l ca re

must

be

t aken

to

insure

al ignment

to

al low for movement a t the

j o in t .

Convent ional ly re in forced

concre te

pavements requ i re dowels

to e placed

in

the

same manner

and

dimensions as pla in

doweled pavements . There are no t i eb a r s

placed

a t

in te rmedia te

non-working

j o i n t s .

i ns t ead .

a f t e r sawcu t t ing the

ex i s t i n g

concre te pavement

care

i s

t aken

to remove the

concre te

by

jackhammer

to

r e t a in a minimum

of 12- in .

of

the

o r i g i

nal mesh r e i n f o r c i n g . During placement

of

the

new

concre te .

the r e s to r a t i o n i s

t i ed in to

the or ig ina l

pavement

by ex

tending the ex i s t i n g

r e i n f o r c i n g mesh

in to

the

r e p a i r

and

over l app ing

it

with

new

s t ee l .

Slab

Depth

in .

6

7

8

Table

1

Dowel

Diameter

in .

3/4

7 /8

Dowel bar s i z e

Tota l

Dowel

Length

in .

14

14

14

When excava t ing for

the

u t i l i t y ,

the t rench width must be a

minimum of

G-

In.

from

a l l edges of

the u t i l i t y cut

as

shown

in

Fig.

3. Care must

be

t aken

to

not undermine the ex i s t i n g

pavement

s

1

b.

Pig .

3.

Trench width for

u t i l i t y

cu t .

JOINT

DESIGN

Transver se

and

l ong i tud ina l con t ro l

j o in t s are sawed in concre te pavements

pr imar i ly to cont ro l

the format ion

of

shr inkage

cracks .

Shr inkage cracks

oc

cur shor t ly a f t e r placement

of

the

con

c r e t e due to the dry ing loss of mix

water . Shr inkage cracks are

c o n t r o l l e d

by

sawcut t ing t h ~ concre te {laVement 1/4

the depth of the

s l a b

and inducing the

26

crack

a t

the

l oca t ion

of the t r ansve rse

j o in t .

Unlike f r e sh l y placed concre te , the

purpose

of tbe

sawcut for u t i l i t y

cuts

i s

to provide a s t r a i g h t

v e r t i c a l

face

t h a t wil l not s p a l l and l a t e r become a

maintenance problem. The depth

of

the

sawcut should

be approximately 1-1 /2 to

2 inches

in

depth

rega rd less of s l a b

t h i ckness .

The

concre te

below

the

cut

i s removed

by

a

jackhammer

to prodllce

u

rough

face aga ins t which the concre t e

r e p a i r i s

placed (Fig. 3. .

This

method

provides load

t r an s fe r

across the r e s to

r a t i o n

by

agg rega te

i n t e r l o c k

as

shown

in

Fig.

4. To a id in concre te

removal .

an

a d d i t i o n a l

saw cu t fu l l

depth

can be

made approximately 12- in .

in

[rom and

p ar a l l e l to

the

cuts made

for

the re

pai r . This second cut

wil l

allow

the

ex i s t i n g

concre te

to be

l i f t e d

away

giv ing

an

edge pnd a

smal l

amount of

concre te

to

be jackhammered.

Trench

w ll

Fig.

4. Saw Cut t ing Concrete .

BACKFILLING

When b a c k f i l l l n ~ the u t i l i t y

t rench, every a t tempt should be mnde t o

r e s to r e the

or ig inHl un i formi ty o[

Lhf

subgrade This

normal ly involves

back

f i l l i n g with

mate r i a l

p r e v i o u ~ l y

removerl

and compacted to a proper dens i ty .

Backfi-l l

mater ia l

t ha t Is not of the

same type as

the r e s t

of

the roadway may

res l1 l t in d i f f f r en t i a l movement between

the

road

sur face

and

the r es to ra t ion .

This may be caused

by

the swel l ing

of

expansive

s o i l s

or

f r o s t ac t ion of

two

d i s s imi l a r ma te r i a l s .

I f

the

o r ig in a l

excavated

mater ia l

i s used.

the

mate r i a l mllst

be

frlle

of

f rozen

lumps of ea r th

and

of

rocks

l a rge r than 6- in . in diameter . Uniform

i t y

i s

accomplis lled

by

proper choice

of

b ack f i l l i n g

m a t e r i a l s

and

by

compilctlnR

these

mate r i a l s in

6- in .

l ayer s a t

a

proper

moisture conten t

and

dens i ty .

To

insure proper compaction and dens i ty ,

the

mater ia l

should be

a t

optimum

mois

t u re

conten t as

determined

by

AASHO T99.

or i f

f i n e - g r a i n e d

or expansive Sil i is

a re being used . compaction a t 1 to 3

percent above

optimum moisture

con ten t

is recommended.

In some cases when

proper

compac

t ion i s d i f f i c u l t

or expensive to

achieve, i t may be

d e s i r e a b l e

to place H

cont rOl l ed-dens i ty

b ack f i l l unshr ink-

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a b l e fill Unshr inkab le fill mix d e s i g n

shou ld have

a

maximum c o a r s e

agg r ega t e

s i z e of 1 to 1- 1 / 2 i n . i n d i ame t e r , and

a minimum 24 hour compres s ive s t r e n g t h

of 10

p s i . and a 28 day maximum

cqmpres

s i v e s t r e n g t h

of

60 p s i .

As

d i s cus s ed p r e v i o u s l y , subgrade

u n i f o r m i t y i s a key f a c t o r in

pavement

pe r fo rmance . When u n s h r i n k a b l e fill i s

used a s

b a c k f i l l

m a t e r i a l , the t r ench

shou ld

be b a c k f i l l e d to

a maximum h e i g h t

of

1 8 - i n . below the bo t tom

of the s l a b .

The

r ema inde r of the subgrade shou ld

be

b a c k f i l l e d wi th

m a t e r i a l

s i m i l a r to t h a t

used benea th the pavement to

i n s u r e

u n i f o r m i t y

-and e l i m i n a t e d i f f e r e n t i a l

movement of the r e s t o r a t i o n wi th r e s p e c t

to the roadway .

CONCRETE MIX DESIGN

The

mix

des ign

f o r a p o r t l a n d

cemen t conc r e t e

r e s t o r a t i o n

i s nor ma l l y

the

same

s t r e n g t h and mix as used in the

ma i n l i ne pavemen t . However t oday agen

c i e s a r e p l a c i n g

r e s t r i c t i o n s

on

when

t he work

w i l l

be per formed and how l ong

the

roadway wi l l be c l o s ed to

traffic

On h e a v i l y

t r a v e l l e d

urban f r eeways . the

c o n t r a c t o r may be

p e r m i t t e d to c l o s e t he

roads down

dur i ng

the n i g h t and

make

the

utility c u t ,

per form the

work r e p l a c e

the

c o n c r e t e ,

and

open

the road to

traf-

f i c . all between t he

hour s

o f 8 :00

p.m.

and 6:00 a .m. Thi s

type

of work sched

u l e m e ~ n s t h a t the

c o n t r a c t o r

must

com

p l e t e

the work in 8

to

10 hour s . a l l ow

i ng

the

new c o n c r e t e on l y 3 to 5 hours

to s e t , cu r e ,

and

ga in adequa t e s t r e n g t h

to c a r r y traffic

Many s t a t e s

and m u n i c i p a l i t i e s

a r e

s p e c i f y i n g

h i g h - e a r l y - s t r e n g t h c o n c r e t e

fo r

utility

r e s t o r a t i o n s

which a r e capa

b l e of

o b t a i n i n g

a c c e p t a b l e compres s ive

s t r e n g t h s

to c a r r y traffic in as

little

as 4 hour s . These

m i x t u r e s

no rma l ly

c o n t a i n 600 to 750 pounds of p o r t l a n d

cement pe r cub i c yard of c o n c r e t e .

H i g h - e a r l y - s t r e n g t h

cement ,

Type

r I I .

may

be

used when a v a i l a ~ l e The w a t e r

cemen t r a t i o should be kep t a s low as

p o s s i b l e

t o speed

e a r l y

s t r e n g t h

ga i n .

An a c c e l e r a t i n g

admix tu re can a l s o

be

added t o t he mix to a c h i e v e h i g h e r e a r l y

s t r e n g t h s .

The

most commonly used a c

c e l e r a t i n g

admix tu re used which meets

ASTM C494

r equ i r emen t s

i s ca l c ium

c h l o

r i d e .

Calcium c h l o r i d e

shou ld no t be

added i n exces s of 2 by weigh t of the

cement .

In

a d d i t i o n . an a i r - e n t r a i n i n g

admix tu re i s norma l ly

added

to

the

mix

t u r e to i n c r e a s e t he f r e e z e - t h a w d u r a

bility

of

the c o n c r e t e . and

to

improve

w o r k a b i l i t y and

c o n s o l i d a t i o n of

the

r e p a i r .

Prope r c u r i n g of t he

c o n c r e t e

re

p a i r

i s a l s o

very

critical

t o the

s t r e n g t h ga i n . A

whi t e - p i gmen t ed ,

mem-

br ane - f o r mi ng

a p p l i e d as

c u r i n g

compound shou ld

be

soon

as

p o s s i b l e a f t e r

f i n i s h i n g . Some

agenc i e s

have

p laced a

l ayer

of p o l y e t h y l e n e

ove r

the cu r i ng

compound

t hen

p laced

a l - i n . - t h i c k

i n s u l a t i o n board on

t op .

The I n s u l a t i o n

board r e t a i n s

the

h i gh

t empe r a t u r e s

gene r a t ed du r i ng t he

chemical

hydr a t i on

of the

cement . The h igh

t empe r a t u r e

he lps a c c e l e r a t e

the

s t r e n g t h

ga in .

CONCRET.E PLACEMENT

In p r e p a r a t i o n f o r c o n c r e t e p l a c e

ment

t he subgrade and edges of the

o ld

conc r e t e shou ld be

dampened wi t hou t

l eav i ng any

s t a n d i n g

wate r on the sub

g rade . A l l t i e b a r s .

dowe l s .

and

r e i n

fo rc ing

mesh shou ld be s t r a i g h t e n e d and

r e a l i g n e d

as

n e c e s s a r y . A t h i n

coa t

of

gr ea s e shou ld be

a p p l i e d

to

the p r o t r u d

ing

end

of smooth dowel ba r s but

no t

to

de fo rmed

t i e b a r s .

Any o r i g i n a l

r e i n

fo rc ing

mesh shou ld be

s uppor t ed in the

r e s t o r a t i o n a t

the

prope r h e i g h t .

The t h i c k n e s s of the r e s t o r a t i o n

shou ld

be

the

dep th

of

the

e x i s t i n g

s l a b

p l us

an a d d i t i o n a l

2- i nches

of c o n c r e t e

(

Fi g . 3 ) .

The

c o n c r e t e

ShOllld

be p laced

on the

subgrade and v i b r a t e d

wi t h i n t e r n a l

v i b r a t i o n .

Care shou ld

be

t aken to

ob t a i n

adequa t e c o n s o l i d a t i o n

a round

t i e b a r s

and

dowe l s .

F ~ r a smoothe r

r i d e . t he

c o n c r e t e

should be s t r u c k - o f f

in the d i r e c t i o n

p a r a l i e l

to traffic

When p l a c i n g

mesh

r e i n f o r c e d conc r e t e

r e p a i r s , t h e c o n c r e t e shou ld

be p laced

and s t r u c k - o f f a t t he dep th of the r e i n

fo rc ing

mesh. the

mesh c a r e f u l l y

p laced

on t he c o n c r e t e . and the top

c o u r s e

of

conc r e t e pour e d

and

f i n i s h e d .

The s u r f a c e

of

the

r e p a i r

should

r e c e i v e

t he

same

s u r f a c e t e x t u r e as t h a t

of

the a d j a c e n t

s l a b .

Tr ans ve r s e and

l o n g i t u d i n a l

j o i n t s

shou ld

be

p l aced

as

d e s c r i b e d in

the

j o i n t des i gn

s e c t i o n .

Non-work ing

j o i n t s a t the edges of the r e p a i r can

be

f i n j s h e d f l u s h

a g a i n s t

the

e x i s t i n g

c o n c r e t e ,

or

if a

s e a l a n t i s

r e q u i r e d . a

r e s e r v o i r

f o r

p l a c i n g

j o i n t

s e a l e r s

can

e i t h e r

be

t oo l ed i n t o the p l a s t i c

c on

c r e t e . or

s a w c ~ t a f t e r the c o n c r e t e

has

ha rdened .

Whi t e -p igmen ted c u r i n g

membranes .

wet

bur l ap ,

or p o l y e t h y l e n e s h e e t s may

be

used

to

cu r e t he c o n c r e t e r e s t o r a

t i o n . The l eng th

of

c u r i n g

t ime

i s

de pe nde n t

on the t ype of

c o n c r e t e

and

wea the r .

OPENING TO TRAFFIC

The

c o n c r e t e r e s t o r a t i o n shou ld no t

be opened to traffic u n t i l the

c o n c r e t e

has a t t a i n e d 75 of the des i gn f l e x u r a l

s t r e n g t h .

27