utility cut restoration
TRANSCRIPT
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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 .
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