pavement design class notes

8/12/2019 Pavement Design Class Notes

1/42


2/42

/

iirr

' 5

T ------------f -S, cC-

1 14

1.i

rU M

^ .sr ^^ 1 i 4

>'


3/42

Pnf'K

%^WV(^u. "J) siAtsa 5

$\*n' tA CijA. \st **-** .

)KK Wf^

T,(5a vw^ -

p

M i u H v A ^ n -^ 4 a > ^ v

(B*

Ofa)*cX;oi,

J : J L ^ 6v ^^:^^

(JU ^Ak v^

~ tUjA,

j p ,c ( f v '-

^ S^.>uu


4/42

^ ' - ^ l o ^ ^ , ^ A u-Wa J^^ ^

^ V W -- v 2 ^ 4 , ^>wmV^ , Ct* NiV\C \l .nA-v\fia .'t.

- y I ' f f\ ^oWvT^ ![W

U i't *^ ^*4g nk A.A v^ ^x(JUy^i( rtA^

*Ae


5/42

P ^w^:

t)

a j ^ w t a ^ ^ ^

(J) iy-e_

iRw nJ/iy /VwW.'*

( f ) PwOv-J SHiliA fi>i

{h}fu \ k i-

O)

fX* UlAiAlL.

P^iUraVi' i^vvJuV-^v S^'V^

(jA'f* f*A-N)t-w*A't CeL-t 6*vCt (jy

tii-cl\, 7v ' * \P-*"'g 1 l -**-

f f \^ ^

ft'-C '1 "M-aa ^v ' 'n^t J .~ll\c \-. p^


6/42

f oi ^

J)v

,-fW_ hdh oiv^ c i U f U t '^ '^

0 t' [^ '~ Q ^

() Ur [i^~^ O'CiX

^oXm^ 3) at)rkCNt^

3> = 5- i (f>^ - fj ^ -i)

,5 AC- W

'V

w~y',

^ y o - s t .

2- y z i ' 0f

^ y ' " f i ' 1 . - 0 4

2 vo'if I >'

i;r- ''>1r s f c i - O' O 5 -b 'o i r

^y'5'j *i:t>v iyitto''=')-=

a ri^-i t V

X)ct>-s- - r o ! O'

H' 0^- (-------------- j * V ''-

l-fc

> ^( f l - 11.> -r^bv)'^+ r'-2-^ -'^'0"^

1 -t(.( 9-5v-(-3


7/42

/>>

/

/

\y


8/42

AUiyAiWs C H i w W V ' j ;

^ S)'lIl Jl- te :> (ftcX'W\4*J_ tk.

* ^ i/M-

O' V iviu^Wt

dlajiC. fc w K i ^ I ajbui . * i*U\jL

k(W. wlojytpA

* (AhVuA (.tctAMA,VjA Jfcvy tv/-iCvs| f-tt>(jtni

\m V \Jjr~jL. * .*c

CtluK

6WJ l cAiLtkCi ;

A-ttii/FYwAiJt.C\a jAj /V l/tvi. /r'J ^UL

-U* P'O'vuai.ewW-

0(i^ AAAjLifb

.yvAJPiMy 6*0l/ 'J^ vAnVW. aXr ^

S'Sp

^ iW(f i C, __ ca^ b-

/S a.A*A- Wt ,

1-8CAjUT-eI 0>/s lY A*\iV i'vf/R.U_k ,.

Utrt*. kil 'K' Aa- ^K *L f-wv^Mi.-

j*i>fc nAdLjL_ (iAi-s-Aj


9/42

_- .

f ^ v ^ . x .jb xb is si^ ^

(3(,vY( **^- ;: ;

bjjU'J

^^ .t l/ A Y V JuA A ^^ bijUx-AATw ?>W. V- JlM-

J tco. c , la\3Luijrv-AA\.

'V'i^ .

M P '^ L ^ ---- 4 ^ teiiu-*. vv*w

CXx3ft4Vt' iw- 'JbVlA. ^P* dUAAiAj

i Pa p v m

WlW PT M y

VOt kv u ,c

^ i *W : ^ \ ; w v c C -\ A oi M

S' TV' eJ u ( A^ t*t.i ovJ ' t>v' ^ >a 4 ^ 1

v ^ -> v i-O L **.^ bi oaftA:4uJV

-ejc?cft-*>wiL Wa(dA*>.4 [ VJvAu' A^.'X^ iiy

t j )o Ai A ^ < V( J V^ Vfl J Uu.

. - . t-5:#vp'ttnv ^isjoA WAiN*x.j- f i U s r ^ ^ V ^ ^


10/42

V# 7VMiA )

^ w- ^


11/42

Is PCA/\Uirv.*v Ai VVr/ -/b\,

^ /U


12/42


13/42

| | J | H ig h w a y

74.7 JNTRODUCriON

An in-service pavement requires maintenance. The maintenance may be routine in

nature, or may be a major reconsiniction.

A pavement is designed against an assumed design period. After the expiry of the

design period, the pavement is likely to fail structurally and, therefore, it would require

a major renewal to extend its life furdier. Even within the service life of a pavement, the

top wearing course is likely to be subjected to considerable distress due to the movement

of vehicles on it. Thus, the wearing course needs some routine maimenance for smooth

movement of vehicles over the pavement.

The present chapter introduces the reader to the maintenance issues of a pavement.

The chapter is divided into five sections, apart from the introduction, of which the first

section discusses the various forms of disjsessts of pavement, their possible origin, and

their quantification in terms of distress indices. The next two consecutive sections deal

with the functional and structural evaluations of_pa^men_ttheir techniques, related

equipment, and analysis procedures. Remedial measures to extend the longevity of

pavement are discussed in the fourth section while the last section briefly mentions the

need for evolving maintenance strategies subjected to possible fund constraints.

14.2 DISTRESSES IN PAVEMENTS

In most of the ca.ses, the distresses in pavement are_measurp^ the_djjjH^er_miit_ares

^ t ^ jMvernent. For example, one may specify a pavement as M % ^rac ke d and 30%

corrugaied. In smne cases, the distresses are subjective, such as comer cracks, or are

expressed in some other units, such as rutting which is expressed us depression

measured by a 3 m straight edge, or aggregate polish which is expressed in terms of skid

resistance, and so on. According to the "code of practice for maintenance of biuiminous

surfaces of highways", 1RC:82 [39], thel^efecls of bituminous siirfacimi^cun be grouped.,448


14/42

iiinJcr four caicBories. as Niows:

! \ . Surfat f defeofs. For example, faii vutface*. huagry *rfces. simwihsurfaces, streaking, and so on. -- ------

j 2. Crudes. For exiunple. alJi|aior cracks, km(piudinal cracks, hairline crack*,' shrinkage cracks, edge cracks, refieetion crack's. W so on.

^ 3- Deformations. For example, ratting comtgaiion. shoving, shallow

* depressions. scu|e_ ment, heaving.aid on.

^ 4. Disiniegralionj^For example, s^giging. km of aggiepre*, ravelling,potholes, and so on.

Subsequent subsections present a brief discusion on some of the major forms ofdistresses of both bituminous and concrete pavemenis.

: i

14.2.1 Alligator Cracking or Fatigue Cracking

Bituminous pavement surfaces can exhibit distress due to flexural faigae as a resoh ofipeiUive applications of vehicular loads. The oacks on the biiumiiwus sutfree allowthe

surftice water to percolate into the basie and subgrade of the pavements which ftirtlier

accelerates the deterioration process. Yne fatl^e'cSks are like hexagons, joined

together one after another, and hence, also known as oMigotor emdUng. The foUowrng

photograph (Figure 14.1) shows a typical fatigue crading

i ;

Figure 14.t A typical fatigue crackeig.

T4.2.2 Block Cracking

Block cracks are the ajiproxiin.nc rectangular cracks formed i t ^ surface of ^

bi^nin oiis pavement- Thc.


15/42

4S0 Pnnfifilfi t f TraTiiperUtm E n g n ^ n f

of suitable bituminous layer, or lecycling binimen. can serve as a remedy to prevemVock (racking J2).

14.2.3 Corner Break and Spall

Comer break and spall are the cracks developed it) the concrete pavement at the comers

ol the concrete slabs. Spalling is not generally extended (hrougli the whole slab thickness

(2]. These failures are due to the combined effect of mud pumping, heavy repetitive

loadif^ poor load transfer across the joinu. and thermal curling.

14.2.4 Corrugation

Corrugation is the plastic deformatK}n._rir tl)e iot> bituminous surface of the pavement

along the horiaontal direction, Its manifestation is in the form of undulations or ripple

formations on the top suf^ce of the pavement. Corrugation Kcurs due to lack of

stability ^ asphalt nuys jn warm weather. It is mostly observed whoe vehicles exert

a greater horizontal force to sun or stop, such as in the intersection l ^ s where brakesare applied. If the corrugated surface i$_thin. it can be scarified and material can be relaid.

The e k v a ^ spots are cut with a medianical Made, widi or wilhMt heating. The surface

can be roiled afteswards.

14.2.S Depression

DepresstM. as the name suggests, is the localized area where the pavement surface s i i ^

a lin k jniih fafetcnce ir> the lu ii sM si^ace. Depression in a pavement occurs d jp yp

differenti.al. seiilemeni of inadequately c^^acted subgrade (or other layers) due to

baffle loading.. Water accumulates on the depre.ssed zone after rainfall, which percolates

u d causes further damage lolHTpavement in that area. Depression can also be due to

inappropriate mix design or settlement of the lower pavement layers. Depressions can

be removed by fiUing the de(uessed part with premix aggregates, followed by ada}ual

compacting.

14.2.6 (any Surface or Bleeding

This is a surface defect associated with tucuminous pavements only. It is the

accumulation of bitumen on the sw fac^ of the pavement which occurs at h i ^

wnqteTUures during the dayiiine Bitumen at a li ii ^ temperature, sedeens and occupies

the available void space in the aggregates. If the space is inadequare. bitumen expands

out omo the surface and forms a sticky, shiny surface over the pavemem, called bleeding

o rfany su ifact. It is an irreversible process, that is. the bitumen does not go back to the

void space during the winter season Proper mix design which includes the selection of


16/42

appropriate g rad e -of bitum en, and provision of requisite void s pa ec cart co o tro i th is

Weeding pheiKunenon. Loss of cover aggregates, heavy prime or uck coat. ioi-unforro

ipplication o f b ind er can be the o ther possible reasons o f bteerling, there fore , th ese

should be pro pe rly de signe d and contiolted during construction. If the b leed ing is

nisifomi and w ith ou t surfa ce irregularities, small siie, clean , angular sa nd, o r sm all

aggregates can be used over the surface. This i$ called sand htoiiing or sand blituiing [3?]. If the Wed surface has irregularities, it is advisable to remove the affected portion,

end relay it w ith a prop erly d esigned mix.

14.2.7 H airlin e C rac k on Bituminous Pavement Surface

Haitine cracks are small and fine cracks over the surface of the bituminous pavetnent.

these cracks develop due to insufftcieni bitumen content, excessive ftller at the surface,

or improper co m pa ctio n (i.e. over-compaction, coinpaction when the base is unsta ble,

or compaction at a high temperature).

14.2.B H uirg ry Su rfac e

Hungry surface is a situation just reverse of the fatty surface. If the bitumen distribution

rate is lower than the designed value, sntall cracks develop on the surface, and low of

aggregates may start taking place from (he surface due to tiafnc. On the oibei hand, a

hungry surface may also develop if the aggregates have a strong absoqitton afTmity

toward bitumen. Fog seal or slurry seal can be used as requisiie measures to take care

of the hungry surfac e situation.

14.2.9 Lane/ ShouM er D rop o ff o r Heave

Shoulder drop-off is a si tuation when the shoulder elevation becomes lower than the

level of the pavement lane. This occurs due to the followisg teasonv.

(a) G radu al consol idat ioa of the shoulder

(b) E ros ion o f shoulder maieiials due to rain or weaihet

Heaving nf shoulder may occur due to frost heaving of die shoulder sml.

14.2.10 Lo ss o f Aggregates

Loss of aggregates occurs subsequent to stripping or ravelling- The possible leasons for

the loss of aggregates an:

(a) Im prop er m ix des ign

(b) Im pro pe r des ign of surface dress ing

(c) Inade quate ro l l ing


17/42

fill

4 5 2 Priudptts 9f Tnn spoH o^ E^tfynt^ng

(d) TraffK allowed lo flow before proper f il in g Surface ha$ become hungry due to absorption of bitumen unaccounted in mix

dej ign.

The treatment needed to prevent loss of a^regates depends on specific reasons.

A layer of slurry seal, or fog seal, or relaying of surface dressing, or complete

replacement of the disintegrated layer can be used as some of the possible solutions.

14.2.11 Map Cracking in Concrete Pavements

Map cracking refers to the small map-like cracks which are superficially located over the

lop surface of the concrete pavemenl. Such cracks are caused due lo improper finish ofthe top surface, or due to the reinforcemeni bars being too close to the surface (2J.

14.2.12 Patch

)t is the repair work dore on the existing potholes, depressions, or the corrugated

pavement surface. Generally, patch work is a visually distinguishable featu re of die

pavement surface.

14.2.13 Polished Aggregate or Smooth Surface

Smooth surface or polished aggregate, as the name suggests, is a situation which arises

due to repetitive passage of traffic on the aggregates of road, whose polished stone value

(or the abrasive strength) is less. The skid resistance of the pavement therefore decreases,

and this requires replacement of the top course with fresh angular aggregates, having a

higher abrasive resistance.

14.2.14 Potholes

Potholes are bowl-shaped holes, caused by localized disintegration of materials, ofvarying sizes on Che surface of the bituminous pavement, sometimes extending to the

base course [39]. Due to variation in a large number of parameters involved, during

highway consiniccion. it may not be possible to maintain the same level of homogeneity

althrough. The localized disintegration scans occurring from those places, which are the

weakest spots on the pavement stretch, Potholes may occur due to a number of causes,

such as:

fa) Inadequate construction quality control

(b) ingress o f water and subsequent damage

(c) Ravelling


18/42

MuffUfnance A55

p oth o les are tep aired by paicbwotk; a good bwxi n w etsa fy beiweco ibe e a sin g

pav etn eti t a o d t h e p a tc h w o rk

^4 .2 1 S P u m p i n g o r M u d Pum pm g

pumping a failu re generally observed in coocreie pavcmetitt. When traff>c moves on

(be craeVed surface, or over the concrete pints, aecunwtaied water along whh subgrade

m I Cor s u b -b a se par tic les ) e p c ls out. th is pKenomenoa u called pumping or mewf

pumping and it i s m ore prorntnemly observed in respect ot Ibe cades where the concrete

pavement is put direc tly on the subgrede layer, l i e fotlowieg sinuiKms Wad to (heoccurrence o f th e pum ping phenomenon

(a ) M ate ria l under the concrete dab saturated with water

lb ) Fr eq ue nt p ass es of heavy wheel loads

(c ) M a te r ia l un der the concrete pavemeal i$ crodaMe in naiute with low

permeabi l i ty .

The m ec h an ism o f mu d pumping can be explained as follows.

(a ) A v o id is fu st formed below the concrete sUh This ci happen ei te r due to

posl'Constfuciion plastic defennaiion of soil or due lo warpiog of (he conciete

slab.

V /a te r ac cum ulate s in (he void Water raay come from the surface infilttaiion. or

fr o m oth er groundwater sources.

D u e to re pet u iv e applka iion of heavy vehicles, soil suspension in water is

fo r m e d w h ic h is ejected out through cracks/joints at each pass of (he heavy

v e h ic le . I f the ma teoal below the conoete slab is granuiar. the pumping may

n o t o ccu r becau se qtuck drainage take^ place through this maieriat

Gradual removal


19/42

t

4S4 h'tncipUs of Tmnspofioihn E^gin*tri>^

14.2.16 Reflection Cracking

When a pavement (concrete or biiuminous) is overlaid with a bituminous layer,

sometimes, the same pattern of cracks as was in the existing pavement surface

propagates upwards and comes Up to the top surface a f the new overlay. This is culled

r^ection cracking because it appears, as if the cracks on the existing surface have been

reflected onto the top overlaid surface. Reflection cracks occur due to the relative

movcxnenc of the existing crocks of (he onginal pavement. If the original cracks in the

pavement are controlled, reflection cracks aie auiomatically checked. To prevent

reneciioa cracks, stress relief layers, geotextiles, or overly reinforcement are provided

as interlayers between the existing pavement and the overlay. Stress relief layers are the

open graded a^regate specification which do not allow the cracks to propagateupwards. Geotextifes or overlay reinforcement, on the other hand, bear the teosion

rtiemselves. and do not allow the cracks to prop^^aie further.

14.2.17 RaveUing

Ravellingis the gradual wearing of the top surface, mainly due to weathering of bitumen.

Tl>e binder becomes hard due to weather action, looses its binding property, and the

aggregate panicles are dislodged horn the pavement surfoce, as the trank moves over

it. This form of pavement distress is termed ravelling. If the extent of ravelling is not

severe, it can be rectified with one coat of slurry seal, or fog seal Otherwise, a renewalcoat may be necessary.

14.2.18 Rutting

As already discussed in Section 12.3.6, accumulation of permanent deform ation along

the maximum travelled wheel path is called rutiing.The extent of rutting depends on the

traffic repetitions the pavement has undergone, properties of the materials used in

coDstniction of the pavement, densillcalion achieved during constructioii, average

temperature of the pavement surface, and so on. If rutting is due to compaction of thelayers, it can be rectified by applying a profile corrective course. A ao$$-section of the

profile correc ting course is shown in Figure 14.3.

Profile corieciive course

P)0ur 14.3 A croaa-aecHon of the profile cofrective course 1215).


20/42

1 4 , 2 . 1 9 S l i p p a g e

SiipiHige ts a re lative movem ent between tfie top wearii>g co im c and the laye r b elow Italong the horizontal direction. Slippage occurs when a horizomai fhmsc c applied by (hevehicles, s pecia lly by the braking vehiefev Ii occurs in the abseivce o f adequate b ond ingbetween the layers, that is, when che tack coat or the prime coat is either missmg orinadequate. S lip p ag e i& associated with the creseetU'Shaped cracks on (he p ave m emfxirTace. For repair work, the wearing course of the affected area may be removed, andreUtd ensuring proper interlayer bonding (39].

14.2.20 Streaking

S:reaking is (he appearan ce o f alternate lean and heavy lines o f bitame o. alotig the(ongitudicia! or tra nsve rse directions. This is dw result of Bon^DOtform application o fbinder during construction (391.

14.2.21 Stripping

Si ripping is a phenomenon in which the segregation of biUinien and aggregates takesplace in the presence of moisture. The loss of bonding between the aggregates andbitumen c au se s lo ss o f aggregates, further infihraiioa of water. loss o f stieogih , m dsubsequent fa ilure o f the pavement. The stripping phesomenon is caused due to thefollowing (391*.

(a) U se o f hydrophilic aggregates

(b) Imp roper mix design with excess of fines

(c ) Cofuim iou s exposure to moisture or accunnilated water

(d> O pe nin g the road to n f f ic before proper setting o f the binder

(e) A gin g o f the binder

As a preventive measure, the stripping potential of the aggregate-^nder should bechecked before laying the pavement If necessary, an anti*stripping agent can be usedduring the mixing process. The arras affected by senppiog need cr-taying with the fresh mix.

14.2.2 2 Ssvell and Blow Up

Swelling and blow up of the pavemeni occur due to expansion of the subgrade soil. Theaxponsiofi could be either due to expansive aaiure of soil used in subgrade. or due tofrost action. Such a failure is called swell aiid blow up in bituminous and concretepavements respectively. Blow up also occurs due to tnfilmtion of certain materials into(be joints of the concrete pavement, which expand doling the rummer season. caenUngenough pressure to cause bU>w up of the carvrete paveiuems (2J.


21/42

14.3 F U N C T IO N A L E V A L U A T I O N O F P A V E M E N T

Varioiis types and I'orms of pavement disoesses have been discussed in the previous section,

In a pas'cmcnt. in fact, a number ofdistresses may occur simultaneously, because many of the

distres.ses are interrelated, and the occurrence of one may as well initiate the other. Inditddual

assessment and quantification of (he distresses may not therefore be very useful. Rather, there

is a need to assess die functional condition of the pavement as a whole. Table 14.1 illustrates

the recommendations as per the Indian specification for classifying pavement condition based

on visual a.ssessment [74]. Two terms for the functional assessment of pavement, were

developed from the AASHO [I] testPresent Serviceability Rating (PSR) and the Presem

Serv iceability Index (PSD,

TabI* 14.1 Criteria for classification of pavement sections [74]

456 ^ Tmnspmiatitm

CfassMeabon Pa ve nw it cond it ion

Good No cracking, njtting less than 10 mm

Fair No cracking, or cracking confined lo a single

crack in the wheel Uack with rutting between 10 mm

and 20 mm

Poor ExtansFve cracking and/or rutting greater man 20 mm and

cracking exceeding 201i

AsapancdthefunctionalpavemeolevaluaiioacnAASHOfl I road test, people were askedto drive on the pavement stretch with a vehicle of their choice, and they were asked to rate the

pavement surface in a scale ranging from 0 to S- Later. PSI was developed which statistically

correlated the physical measuremenis on pavement conditions to the subjective judgement of

human rating (i.e. PSR). Thus, PSI is an empirical equation containing terms such as, cracked

area, patched area, cut depth, and slope variance. PSI. as the functional index o f pavement

condition, has somedeficicDCies. For example, it was developed from the evaluation of a panel

of experts in the AASHO test, and therefore, may not hold good in the presem comexi. Also,

the kind of profilometers dial were used in the test are not in vogue [266] today.

Likewise, various other indices have been evolved to quantify pavement distress as a

whole. Automatic equipment has been developed which can be driven over the road to acquire

continuous data of functional condition of the pavement. The acquired data is analyzed in the

laboratory to extract the desired infonnation. In this section, two basic functional surface

characteristics of pavement, namely paventeni toughness and skid resistance o f pavement have

been discussed.

14.3.1 Pavement Roughness

The objective o f roughness measuramem is to obtain a single or a num ber o f parameters

characterizing the level of roughness of a given stretch. A road profile is a two-


22/42

dimensional sl ice o f th e roa d surface taken along any imaginary long itvdinal siraigb*

line: and the p ro fi le m eas ure m en t is a series of numbers lepicseming elevaiwm s relal ive

to some referen ce lev el . T he problem l ies in reducing these huge da ia-points to a

Ttpresentative i n d e x c a l l e d roughness [234j.

lb ob ta in rou gh ne ss infonnatioTi f rom a measured prof ile, two b as k requi remen ts

on {VXt\-1. T he p ro fi le r m us t be ca pab le o f sensing the relevant infonnation preseiM in the

true profile of th e ro ad .

2 . A su i table a lg or i thm nrasi be able to process the measured va lues to ext rac t the

denred info rm at io n a s the sum m ary roughness utdex.

Aprofiltr i s an ins t rum en t used to produce a ser ies of numbers to represent a prof ile .

Fallowing co n ta in s a b r ie f d iscussion on profi le rs .

Various ty p es o f p ro ti le r s

A profi le r w o rk s by co m bin ing the fol lowing Ihtee mgiedients:

(i) A r e f e r e n c e e l e v a t i o n

( ii ) A h eig h t re la t iv e to the reference


23/42

average of a given base length, lo remove local irregularities. T hen , the resp onse of

a quarter car model, in (he form of vertical vibration is added which on divid ing Iqr

Ibe length o f the profile yields . IRI [201],

A quarter car consists of a .spning ma.ss and an unsprung mass, with spring

and dashpol configuration as shot i in Figure 14.4, Ratios between masses,

spring coasiaots and damping coefficients ate fixed for a standard q ua iier car.

The stmulaiion model generates vibration response caused to the moving

quarter car (at a fixed speed of 80 kmph) 1^ the roughness of road profile. TTie

analysis of the response of a model vehicle (quarter car. in this case) due to toad

roughness is. however, beyond the scope of this book.

IMnripIn oj Tia'ispmlithtm

(ii) Mean Pane! Rating(MPR). The concept of Mean Panel R ating (M PR ) ev olved out

o f AASH O road test. It is the average o f ratings given by a p anel o f pav em ent experts

while driving ove r a given road stretch. These ratings are pro cessed statistically to

yield a single rating, for the panel as a whole, which is called Mean Panel Rating

(MPR). Thus, MPR gives an idea about the average degree o f disco m fort o f riding

due to roughness o ver a given stretch o f road. Panel ratings d ep end strongly on theinstructions given to the mem bers of the panel to define as to wh ich p hysical property

or quality is to be judged. Thus. MPR is a subjective judg em ent o f roa d roughttess.

(iii) Profile Index (Pt>. Th is index is calculated in a sim ilar fash ion as th e qu arter car

simulation used in IRI computation. However, the ratios between the mas.ses.

spring constants, damping coefficients are chosen different in this case. The

root mean square value o f the response profile o f the qua rter ca r norm alised to

the scale between S (perfectly smooth) to 0 (maximum possible toughness), is

referre d as PI f200].

( iv) Root Mean Square Vertical Acceleration (RMSVA). Th e rale o f cha nge o f slope

o fthe m easured profile is the spatial veitical acceleration. T he tool m ean square

o f this spatial ac ce lm iion is the RMSVA,


24/42

l i tg h u f t y M a t t iU n a n c t 4 5 9

(v) Wiivrbtind fnJices. A road profile is assumed to be comprised of sh on . med ium,

and long vvaveieng;lhs. The Power Spectral Density fPSO) distribution plotted

against th e w av e number {the number o f waves m unit length) give s so m e

quantitative idea of the roughness level. The nature o f this plot remains the

same for various roads and (he area enclosed is observed lo be linearly

piopoitional to IRf

Closing remar ks

AiMinber of profilers s^e used to measure roughness and also a number of indices have

been proposed, m os t o f th em are apparently uncotTclated to each other. Roughness

information can be derived from the true profile of ifae road, as well as from the vibration

response o f the ve hic le p ly ing on it. It may be argued that the study on the v ehicle

vibtation reisponse could act as a better roughness index compared to that on the true

profile of the surface, because it is the vehicle vibration and the related discomfort which

a road user is more concerned with. Different vehicles would show different vibr^ ion

tsj>onses, and that is why a quarter car model (with fixed ratios of mass, damping

coefficient and spring constants) is chosen as a standard vehicle for the roughness suxly.

For this reason , IR l. a s th e roughness index, is gaining acceptance in most o f the

countries.

14.3.2 Skid R es ista n ce

The skid resistance is the retarding force generated due to ioteraciion between thepavemerit and locked tyre when the vehicle is moving. Skid number is defined as tOOtimes the frictional coefficient between the wheel tyre and the pavement surface.

Skid number = 100 x coefficient of friction (1 4.1)

factors a f f^ c i in g s k idresistance

The following are the factors affecting the skid resistance of pavement surface:

Ci) Aggregate qu ality . Aggregate polish reduces the skid resistance. Hardaggregates, which are fine grained, sometimes show tendency to get polished quickly, compared to softer and coarse-grained aggregates 1187). Thus, a compromise needs to be made between the durability and the desired skidresistance.


25/42

situation, lyre tread and the surface texture may not be sufficient to drive away

(he water and (he tyre may start slipping on the water film. This phenomenon

is called hydroplaning.

Meawremeftr of diid rtsisUnct

Skid resistance can be measured by a portable skid tester, known as the British Pendulum

Tesier. Figure 14.5 shows the photograph of a portable skid tester developed by

Transpon Road Research Laboratory (TRRL). UK. The test uses a pendulum, as a spring

loaded rubber slid^. The pendulum is released from horizontal position, and it slides

over the specimen whose skid resistance is to be measured. The scale attached to the

pendulum measures the energy lost, and the friction coefficient of the object is estimated

by the following formula (111]:

/= " ' - ^ 1 ^ x100

460 Piitififtlfs ef IraaspnrUthm Engiilfering

(14.2)

where

/ is the coelTicienl of friclimi ( e t^ s se d as percentage)

IF is the weight of the swing arm

X is the distance of effective centre of gravity of the swinging arm from the centre

ofoscillation

Z is the vertical distance of Ihe edge of (he scale below the zero of the scale

P is the load on the slider0 is Che sliding distance

p is the length of the arm of the pointer.

Figure 14.$ A portable skid tesier


26/42

High-way MutrU^narw.e 4 6 1

T he p e n d u l u m s k i d t e s t e r c a n m e a s u r e th e s k id r es is ta n ce f n r s m a l l a r ea s o n l y , a n d i t ta k e n

uioe f ur e a c h m e a s u r e m e n t , t h e n i t m a y b e d i f fi c u lt t o u s e fo r n e tw o r k l e v e l e v a l u a t i o n o f s k i d

tesisiance- A l s o , i t r e q u i r e s r e g u l a t c a l i b r a t io n . O t h e r d e v i c e s a i e a l s o a v a i l a b l e , s u c h a s l o c k e d

Vi'heel t r a i le r an d y a w m o d e t ra i l e r , w h ich c an m easu re the sk id re s i s tance o f a lon g s t re tch o f

road, m o u n t e d o n a v e h i c l e m o v i n g a t n o n n a i t ra f fi c sp e e d . I n a l o c k e d w h e e l t r a i l e r , a t w o -

wheel t ra i le r w h o s e w h e e l s a r e l o ^ e d , i s pu l le d i n th e fo r w a r d d i re c t io n . T h e l o c k i n g f o r c e i s

measured a n d t h e s k i d n u m b e r i s o b t a in e d . I n t h e y a w m o d e e q u ip m e n t , th e l o c k e d w h e e l s o f

ihe tTdiler a r e t u r n e d a t a s p e c i f i c a n g l e t o s im u l a t e t h e e f fe c t o f tu r n i n g . M u - m c t e r is a s k i d

testing e q u i p m e n t b a s e d o n t h i s p r i n c i p l e . Sk i d r e s i ^a n c e c a n a l s o b e m ea.


27/42

(a> in dc-tiruclive rvaluaiiMi. samples are retrieved froni the pavement and

analyzed tn (he laboratory. The ptis dug in the pavement give a measure of the

thickness o f various l^ e rs o f the exisirng pavement, w hich is turn gives an idea

about the f ie ld compacted thkkness compared to the thickness which was

originally laid.

Bitumen extraction is generally employed to ch eck the bitumen content and

aggregate gradation used in a pavement construction. The sample taken out (by

core cutter or from pits) from the in-service pavement, is broken into pieces,and pul into a centrifuge bitumen extractor, where bitumen is dissolved in a

solvent (tricholoroethylene. benzene, methylene chloride, and so on) and is

separated out from the mix by the action of centrifugal force. The quantity of

bitum en is m easure d afte r the so lv ent is evaporate d, and th is g ives an idea

ab ou t the quan tity o f bitumen used in the actual construction. The aggregate

proporti ons are a lso checked by sieve analy sis . C orrec tions a re m ade fo r the

amount of fines which goes out along with the dissolved bitumen during the

extraction process. Also, necessary corrections are made for the water content,

if presen t, in the m ix. For concrete pavements, the be am sam ples taken are

tested for the ir flexural strength and cra shin g strength 1230).

The phys ica l propei l ies of bi tumen and a^rega les a re tes ted i f required,

such as estimating the suitability of recycling-

(b) A num ber o f ND T devices have been developed for the s truc tura l evalua tion

o f pavem ent. T he ND T equipment is used to dM ermine the


28/42

.s te ad y s ta te d ef le ci to n devices- Ih e NtTp devices tliaf fall in this calegeiry.

m ea su re ih c de flec tion response nf the pavement w> a low frequeacy

oscillatory load. The Road Rater and Dynaflcci arc the (wo such devicea.

T h e b a sic op era ting principte of these devices U to impart a vibratory

loading by means of some eccentnc loading mechanism and to metnure the

d efle ctio n ca us ed to th e pavement at a series of points through velocity sensors.

T h e fix ed p o in t referencing prablem, as in the static creep method, is taken care

b y th is e q u ip m en t w ith th e u se o f inet tial reference (veloc ky se nso rt). H ow ever,

th e ste ad y stale load ing applied to the pavement does rtot correspond to the actual

fo rm o f lo ad in g applied by the vehicles [266). Figure 14.6 presents a schematic

d iag ram of a R oad Rate r.

Bridge and elevainr asteinirty

W ave propagaiMR devices. The vibrations propagate through layered media tt

various speeds. Individual waves have different reflectivity cbaractetistics. The

sensors, like, geophone or acceleromeuts. placed at a distance, senae the arrival

of various waves, and the elastic moduli of (he respective layers cao be estintdedtherefrom. Among the various available analysis methods, the Spectra) Analysis

o f Surface Waves (SASW> is popularly used for pavement evaloaiion.

Impulsive loading devices. ITie impuistve loading type NDT devices apply

an impulsive load to the pavement and record the resulting pavement

deflections at several radial distances from the load applkatioii point. Awing

a short loading time. The Juratioa and the impulsive nature of loading

clo sely simulate the nature of loading irapaned to the pavement the


29/42

vehicles. The enamples of impulsive loading devices arc Dynaiesl. Phoenix,

and KUAB FWDs. These devices generate impulsive load through rapid

decelerolion of Ihe falling mass. The defteciions caused to ihc pavemcnl are

measured with the help of velocity sensors, that is, geophones. The peak

deflections at each measurement location constitute the deflection basin. In

a multidepih deflectomeler, deflections at various depths are measured by

installing .sensors at various depths.

14.4.T Benitelman Beam

Benkelman beam was devised by A.C. Benkelman as a deflection measurement test

bituminous pavement for Ihe WASHO road test in 1953 f74]. The Benkelman Beam

Deflection (BBD) technique is a popular test all over the world for estimating the

required overlay thickness. The popularity is possibly because of its simplicity and lowcost. The permissible maximum allowable Benkelman Beam deflection for satisfactory

performance of a road stretch depends upon the trafTic. material o f construction, and the

environmental factors. This forms the basis of Ihe BBD study. Benkelman deflection

more than the allowable deflection suggests that the pavement may require an overlay.

In India, the earlier guidelines [73] on strengthening by overlay using the BBD

method, have been revised, and the present guidelines [74] have evolved from a broader

perspective of experience gained through research and practice [61] in India and in other

countries.

Principle o f BBD study

A conceptual working ctf a Benkelman beam is depicted in Figure 14.7. A 'B ' represents

the position of a Benkelman beam when the probe A' is placed between the dual wheel

of a loaded truck. The poim A ' touches the maximum deflected point of the deflected

bowl. When the truck moves forward by a given distance (from F to P). the deflection

bowl also moves forward, and the probe point A ' comes back to a point position A. This

f'rm iplrt a f TrantporUthoH EnpurariHg

Eaitierwhedposjllon

Rebound

deneaion


30/42

deflection i& called th e re bo und deflection,and is UKd f


31/42

for IIS ftrs- iihofiw m . Tho inick liii'o i i* ska1 to slowly movf 2,7 m from ilio

pinm mikI slop. The .lial gaujje iviulinf! foi Ihc conv.spondins dt-floclion is nolod when

the rts.o\er> of Ihc |ni\emoiu is less ihiiii or iH|iial lo 0.025 mm/inimile; thi.s wading is

s'alieti the it/erme^i.Me iroiiiMg- The irm-k is niosed I'orwunl by luiother m. iimJ Ihe

fiMl reading is laken. I'aveim'ni leniperainre is alsi> rn-ordcd every hour by inserting a

iheniH'iiwier in ihe stniulnixl hole filled with glyceixil, Tho diffewiice Iviwoen the final

and the initial dial tradings ami alst> the difference between tho inlcnncdiulo and iniiial

readings, are both calrnloRd. If the difference of values lies within 0.025 mni. then the

actu.il imveiiwm deticciion is iwico tho final diffowniiiil reiiding. If ii is noi so. Ihen. aterm


32/42

P rinc iple o i r w r ^

In FWn ttudy, the deflection of the paventerw suffoce i menwred at a oMinber o f pointsat different disinnccs situated radially umwards from the centre of the falling weight. Thegererated response is tisttally measured by velocity rmnsducert fgeophones) and afterthe velocity time response is integntted. the values of inMantaneous pavement Jeflectinnat a mimher of points are obtained. The tc.st is repeated several times at a panictilarlocntittn nnd the results are averaged to reduce random errors. If required, the test may also he done with different loads to evaluate the stress dependence of the layermodulus 1210V Figure 14.10 shows a photograph of the FWD test being carried out inihc field.

F i gu r e S 4 . 1 0 F VUO testin g tn p r o gm a N M o n a t H i g iv w a v 1

Back-calcutation o f layer nvoduh from the ftVO deffeefson profi ts

In the F W D les t, six o r seven discrete surface deflectioo readings rep resen t th e defW ctkM

basin . I f th e b eh a v io u r o f th e pav ement tinder im pact lo adin g is as.\um ed to beefaecse.the pitveinent response can be described by knowing only the elastic modulus ff and thePo is son s r a t io p o f each lay er S onw siandaid M values may toe assu m ed from th eliteTiiiure. sin ce the se hav e little effect im ihe stress analys is 6 a c h layer is thu s,repres ented by only one unknown, that is. the elastic modulus of the la y er The porpvvseof the F W D stud y is to find out the in-sitw elastic h k h Iu Iu s o f the l aye r s , when thedeflec tion hu sin is known from FW D testing. The pn.xes.s o f estim ating unkno w n etaMicmoduli from known deflection bastn is known as b*H'k-cah'ultnu*n. Therefore , theintniiuu in num bei o f surface dcllectis 'ii leadings ncciled in toac k-cak 'ulaiioa proc essm ust b e at lea st cijual to the luimbcr of layers lo avoid non-unHtue v..dution (.^7| B eca useof the roimding o f f and iniiu'acion errors iiuivxluccd during b ac k'c ak 'ula tion . u may not

be p ossib le to rcpivn luce exac tly the origina l layer nKxtuh from a basin gerreraU'sl by alinear elastic solution. ,Mo. Ixn the devianoii of material behavirnir fmm the htx'ac clastic


33/42

model no solution may exist which matches the measured basin perfectly [37j. The divisiono fa pavement structure into many layers may produce a non-uni|Uc solution whereas assumingfewer layers may not be able to reach a >loikm which matches the measured deflections. Someresearchers have reported that there is no unique solution to the set of moduli that would produceexactly a given deflection basin (96]. The thicknesses of the different layers also form an

important input to the back-calculation, otherwise a realistic match may not be achieved [210].Thicknesses may be measured accurately by coring, boring, ground penetration radar, and

seismic tests (2S8] treated as unknown parameters.As meniicoed. the basic philosophy of back-calculation is that when the computed surface

deflections match the measured deflections, the resulting layer moduli are considered to be themost appropriate material tnodult for the pavement structure [37]. The process is initiated by

assuming 'seed values' for elastic moduli of the pavement layers and comparing the lesullingdeflections (through a pavement analysis, i.e. forward calculation routine] with the measured

ones. Adjustments of the elastic moduli are made until the difference between the two deflectionprofiles is within a given tolerance. Algorithms forconvogence should be carefully adopted,

otherwise convergence may not even be adueved. or it may take an unnecessarily long limeto atiivC at a reliable re.suli [145]. Hiere are several back-calculation algorithms (such as,

equivalent half-space method, regression method, database search method, optimization

method, and so on) suggested by a number of researchers. The methods are inevitably

complex and not unique. Figure 14.11 presents a simple back-calculation scheme.

4 M Pmtriplti t f Tntn^ ertation Enginefring


34/42

Highway Maintnvtiu.f 4 6 9

Ivalualion o f toad transfer fffici ^ncy of a foint

The ^oad transfer efficiency of a joint can be determmed by FWD (or any other impact devices). The tocation of fall of weight is so adjusted that it is close to the joints of thepavement slabs. The defiection.s measured in the two slabs cloae to the joint give the value of load transfer efficiency of the joint. Figure 14 12 showa a diagram o f two idealistic extreme situations where the efficiency of the joint is 0% and 100%.respectively. If due to the application of load close to the joint, both the adjacent stabs deflect by the same amount, the joint efficiency is 100%. and similarly, if the ocher slab(whkh is not loaded) does not deflect at all. its joint efficiency is 0%.

FWD tAiCing

Lq ad iransfer effielency of the Joint =

FWD Loading;

Load bv isf er eHkicAcy f the iMM iOQW

n g u ra 1 4 . 12 J oW e lBc ieney iM t t)y FW O

14.5 PAVEM ENT MAINTENANCE

A distressed pavement requires maintenance. Maintenance measures consti tute freshinvestment on the exist ing roads. There are two considerations which are of in^onance

in this regard:

1. Th e m aintenance expenditure can be reduced through prop er planning, design,construction, and quali ty control . If the causes of possible distresses arerem ove d, o r judiciously taken care of during design, the expenditure du e wmaintenance measures on in-service roads reduces. For example, if thedrainage provisions are designed properly, or. overloadtitg beyond the legallimit is stricily prevented, the premature pavement distresses can be avoided.

2. It is advisable to implement the necessary' mainten ance mea sures at an earlystage whe n the distresses have just started showing up. It is seen that properpavem ent maintenanc e tneasures at the early onset o f dis tress es, can obvta iemajor maintenance expetidiiure in future. This is because, in general, the raleof deterioration increases with time.


35/42

Thi section hricfly introduces various pavement maintenance measures under two categories,

namely maintenance measures other than overlay, and maintenance with overlay.

470 I'linrifilf' of Transpomlion Engiiiffriitg

14.5.1 Pavement M aintenance Measures O the r than Overlay

The pavement maintenance measures other than overlay are the minor m aintenance or repair

works ts'hich are performed on the pavement. These works do not enhance the structural strengthof the pavement, but can improve the functional .standards and check the rate o f deterioration.

These maintenance measures can be of routine type or periodic in nature. A br ief explanaticm

of surface repair and drainage maintenance measures is given below.

Surfan repairs

Surface repairs are effective when discrete damaged patches (say. potholes, local depressions)exist on a pavement surface which need immediate repair. For surface repairs, if needed, the

existing bituminous layers of the specified area are carefully scarified without caus ing any

disturbance to the other layers. Tack coat is applied to ensure good adherence. G ran ular layer

and bituminous layer, as the situation demands, are laid and compacted (see Figure 14.3).

Table 14.2 briefly presents the various repair works recommended against variou s forms

of distresses. Some of them have already been discussed while introducing the various forms

of distresses. Hie reader may note that the table is neither exhaustive nor does it express the

only available solutions. The actual repair technique needs to be evolved on a case to cases basis.

Also, T ^ le I4.2|esenisonly(herepairtechniques. not (be preventive measures, which have

already been covered in Section 14.2.

Table 14.2 Possible surface maintenance measures for some pavement distresses

T y p e c fd is tm ss Mbntenance measuras

Block cracking AMilication of new biluminous coat recycling

Heedng Sand bloflingfsand blinding

Corrugation Scarification of elevated part by mechanical blades and rolling

Depression Application of profile corrective course

Fatty surfaces Application of hot, dry, small aggregates, and roiling

Hungry surface Application of fog seal, slurry seal

Lo ss of aggregates Appllcatior of seal coat, fog coat, or surface dressing

Polished stone Surface dressing or other suitable form of wearkig coat

Pothole Patching and partial reconstruefloo

Ravefling Seal coat, fog coal, or laying of renewal coat

Rutting falure Milling of protruded portion, profile corrective course recycling

Sfippage Replacement of top wearing coal with proper tack coatStripping Replacemem o f affected layer with fresh mix

Swell and blow up Milling of protruded portion, construction of drainage facility


36/42

Drainage mainlenance

The draina ge sy stem provided in the road need* loui tne (or periodic) a t lent ion to check

(he i r proper func t ioning. The camber and the shoulder s lopes need to be mainta ined

p roperly fo r s a tis fa c to ry functi on in g o f su rface drain age. D epressto os, p o tho les, a n d

rut ting sh ou ld b e repaired imm ediate ly with premix aggregates to che ck the

accum ula t ion o f w a te r and subsequent damage to the pavement . Clogg ing of openlongitudinal drains due to debris accumulation needs regular checking. The sub'SurCKe

drainage n etw o rk sho uld a lso be inspected regularly for c logging.

1 4 .S .2 P a v e m e n t M a i n te n a n c e w i th O v e rla y

The overlay is the extra thickness provided on the pavement surface winch strengthens

the p av em en t s t ructural ly, and thereby enhances i ts loogevi ty. The overlay d e s i^

com prises th e determ inat ion of thickness and the type of materia l to be la id over (he

existing pa ve m en t s urface so as to extend its longevity by a given period. Earlier (prior

to I9 60 ), the ov erlay design used to be based on judgment and experience (266). There

are various overlay design methodolc^ies in vogue now and among which at least three

basic a p p ro a c h es m ay be id enti fie d as fo llows:

(a) E ffec t ive thickness approach

(b) D ef lec t ion approach

(c ) M ech anis t ic approach

The principle of effective thickness approach has already been covered with the stage

construction considerations in Section 12.8-2. The overlay design by the BB method is

ba .sed on d ef le c tio n approach, and that by FWD is based on m echanis tic approach .

Th ese t w o ap pr oa che s are now discussed in the subsequent parag raphs o f this section.

Se/ecfion o f homogeneous sectionsWhen the BBD survey data is collected over a long stretch of road, there is a need to

sub divid e the stretch into a number of (possibly unequal) parts, w here the de flecuon

reco rds are som ew hat the same in their order o f magnitude. T her e is no specificmethodology suggested in Indian guidelines 189. 74] for this segmentation, except doing

it by visu al o bserv ation of kilometre-wise plotted data How ever, it is sugg ested that the

minimum length of the section should be at least one kilometre 174J, otherwise itb eco m es in convenie nt from the co nstruction poin t o f vie w if th e overlay th ic kness

recommendation changes even for a fractional length of a kilometre.A simple method suggested by ASSHTO (2] can be adopted for such a situauoi*.

According to this method, (he cumulative data points are plotted on a kilometre scale,

as sh ow n in F igure 14.13. The best fit straight line is draw n through all the data po intsW he rev er th e da ta points change their location from one side o f the best fit line to the


37/42

4 7 2 P n n r ^ U s ^ T ra m pc ria tio n E n g tn ^ m n g

Other, it cAn be marked as the start o f another hom ogeneous section'. Thus, the BBD data

points observed from km 4 38 to km 4 74 o f a particuJar road stretch have been delineated

into three pans by this method as shown in Figure 14.13. These three stretches can

further b e referred for overlay design, individually.

B B D m e t h o d

The following example illustrates the overlay design method as per the IRC:8I>I997

[74] guidelines.

E X A M P L E 14.2

T h e fo llo w in g arc the BB D. Held moisture content, and temperature readings at

eq uid ista nt po ints obtained along a stretch o f a major road. If the pavement is to sustain

furth er 2 0 m sa o f irafitc repetitions, design an overlay thickness for the stretch. The

av er ag e ann ual rainfall o f the area is found to be 1200 mm, and the soil is o f clayey

nature, with average plasticity index I2.

'Xn fac t. Uie req uir em en t o f delineation of points into homogeneous stretches may arise, not only

fctf B B D su rvey , bu t a lso , in various param eurs uso cioie d with pavement design, such as, roughnessd ate . C B R data , pta le load teal data, and so on. A good reliability of the ovenll design, subjected to

a g iv e n fwrsd co m ira in t. ca/i be achieved depending on hoiv successhtlJy the delineation has been lione.


38/42

Sofu f todi

The actual pavemeni denectioas ate cakulated according to the IRC:81-1997recommendations. Temperature and moisture eorreciioAs (data given inTable 14.3) are applied and the finai corrected deflections are found out as shown inTable 14.4.

Table 14.3 Data to find temperature and moisture oorrectiorvs

Sr . P a ve m e n f Mo/sture plat sa u ga read ing (mm)

no. tempe/afi/re content miliai inUrmmaiate Pinal

rc>


39/42

A JM PnneipUs of TraniportaHoti Enginetring

F tg u r* 14.14 M oisture correction factor for da ye y subgrade with low plasticity (PI < 15) for lowrainfall areas (annual ra


40/42

Highu'aj Mahti^nniir^ 4 7 5

146 mm o f BM . This thickness can be converted to equivalent thickness of other layersby the empirical relationship, or by equivalency (see Eq. (12 I8,

n V D method

The overlay design by the FWD method is a three-stage process involving:

(i) FWD study

(ii) Back-calculation of layer moduli

(iii) Estimation of overlay thickness

The first two stages have been discussed in Section 14.4.2. Now, after the layer moduli are obtained, the mechanistic pavement design principles are applied to find out the necessary overlay thickness. For example, as shown in Figure 14.16. the existingpavement structure is o f three layers, and it is analyzed as a four-layered structure whenthe overlay is put for enhancement of hs lo i^viiy by a given 'msa' level. The overlayrequirements in terms o f extra bituminous concrete thickness are determined for varioustraffic levels, and the existing granular layer thickness is evaluated from fatigue and

rutting considerations.

200 400 600

Cianular thickness (mm)SCO

F igu ra 14.10 An over lay des ign chart obta ined f rom FW O study.

C los in g rem ark s

It is not always the maximum deflection but curvature, too. is ano ther im po na mparam eter required for determinat ion o f th e overla y th ic kness. Pavem enrs

which have the same design life with different pavement compositioins andsubgrade CBR. yield different deflections under the standard axle load. The


41/42

mfl]iiiuni H dcllcttion value, fhcrefw. cannoi alway be the righJ eritcfitw tot

overlay desi|{n. TTie cTc/Iected pnifikof the owtJ fcbouid alao be lakcn into account/orrrverlay dcMgn.

Thuv. ntudtpntbe Hcnkelnm Beam equipment hav been evotved, in which(k-ricciion ai variouv poiniv iv alao mraMired i derive some in fonnaiion about

the curvature of the deflection bowi. b'or example, in Auviroailv | IH2) me(hrd, a

parameter / ! ' W w '' forcHimating the overlay thteknexs. where / ^ a n d / ia ^are the maximum deflection and the deflection at 2fi0 mm rexpeciively. radially

outwards from the point of maximum deflection.T V BBD melliod is popular because of id low cosa and easy lest procedure, hut

the static loading nature and the dirficuliy in getting a fixed reference point fordeneetion mea.surcmenl are the shortcomings associated with this method,

a In a separate study, the overlay thicknesses derived fnim the BBD mcthrKf and the

mechanistic method arc compared 147) for various points of some selected stretchesin India, as shosvn in Figure 14.17. It it interesting to note that though the basicapproaches of the BBI) and the mechanistic method of overlay design arc difTerent.the final overlay recommendations are comparable Ui each other,

476 of ItantpMhilKm f^uginforinji

Figure 14.17 Comperiaon of overlay tfuckneu obtained from 6B0 P4] and mechaniaiiepavement detign method [47],

ffverlay is discuMied here as the Mruciural rchabiliialiofl procedure. In overlay,

extra thickness is laid on the existing pavement to extend its longevity.


42/42

However, nveitay conMnKiwM mcreswv the heigtu of the pavemeni. This

problem is porticuUdy acute in city weeis where toad level keeps on risw |

causing tneonverticnee to the toadvde ewabltdimeus. Tl* best driuiini in ibis

case is to recycle liic materials o( ibe existing pavement and use them for

overlay conshuclion. Recycling is a better itkibiVnatKin method than puniiif

new overlay on the existing surface, as it conserves aggregates, binder

and energy, preserves the environment and road gcomelrics 12). A brief

discussion cm bituminous pavonem recycling has alteady been pteseMed in

Section 13.10.3.

477

14.6 MAINTENANCE MANAGEMENr

Figure 14.18 shows a schematic diagram of vahaiion of pavement conditwa (siructwai.

or func tional, o r combined; with respect to time. If no rehabiliiaiKm measures ae taAen.the pavem ent gradually deteriorates and fails at a certain tuge, as shown in the figure.

Rehab ilita tion improves the condition of pavement, extends Hs life, and thus, prevents

its failure after the expiry of initial design period. 'These can be ahemiuive cthalnlitaiian

measures (in terms of their extent and ftequency;. shown in the figwe. Depending

upon the frequency and type of rehabilitation, pavemeni continues to serve satisfactorily

for an ex tend ed period. The designer has to jodtcionly recommend suitable

rehabilitation measures, chosen from various possible aUemuives. such that the fund

utilim iion is op tim al and the condilioa of pavemeiu at any given pouu of time icmaiitt

satisfactory. This may be Kferrcd as optimal maiatCMAce requiremem of a paniculat

stretch.

Tum(ycxrl

Figure 14.1$ SetiemaiK diapram sliowing lam e n t eomWIon aends tor attamawerehaMitation measufes.

^iriifiarly the fTuiinirniim;c requirementv uf vaniius individual pavement seirm s of

pavement design class notes

Documents