by The use of hot surface treatment to rehabilitate cracked asphaltic concrete surfacings in Malaysi

C Jones

Colin Jones

Ir. Moharned

J Emby

Johari Emiby

M S Mustafa

Shaffi Mustafa

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TRANSPORT RESEARCH LABORATORY
TITLE
by
The  use  of  hot  surface  treatment  to
rehabilitate  cracked  asphaltic  concrete
surfacings in Malaysia
J  Emby, C Jones  and  M S Mustafa'
Oversea's  Centre
Transport Research  Labo'ratory  ,-
Crowtho~rne  Berkshire  U~nite'd  ~Kingdom
￿IA
. X
101  -
1 -
11  AEmby,J,  C  R  Jones  and  M  S Mustafa,  1992.  The  use  of hot  surface  treatment  to  rehabilitate
cracked  asphaltic  concrete  surfacings  in  Malaysia.  In:  Proceedings  of  the  Seventh  REAAAA
Conference,  Singapore,  22-26  June  1992.THE USE  OF HOT SURFACE  TREATMENT TO
REHABILITATE  CRACKED  ASPHALTIC  CONCREUE
SURFACIN4GS  IN  MAlAYSIA,
Johari  Emiby
Training and  Research  Institute,
JK  Malaysia
Colin  Jones
Transport  and  Road Research  L-aboratory
UK
Ir.  Moharned  Shaffi  Mustafa
Training  and Research  Institute,
JKR  Malaysia
ABSTRACT
In tropical climates the binder in the top few millimetres of dense bituminous surfacings suffers from rapid age
hardening causing the viscosity of the bitumen to  increase.  The material becomes brittle and this results  in
premature cracking starting at the surface caused by environmental or traffic induced strains.  If left untreated
these cracks will propagate down  through the bituminous layer  decreasing its effective  modulus and allowing
the  ingress of water  resulting in more serious  pavement  deterioration.
One meth  od of arresting this type of cracking before  more serious failure occurs is  to heat the surfacing and
then either remove  or recycle  the cracked layer  before the cracks  can reach any substantial depth.
This paper describes the first two  years performance of a full-scale hot surface treatment  trial on a heavily
trafficked  urban highway  in Malaysia.  The performance of the trial was monitored  under a joint research
programme  between the Training and Research Institute of the Jabatan Kerja Raya  (JKR), Malaysia  and the
Transport and Road Research Laboratory  (TRRL)  of the  UK-
Three  different  hot  surface techniques were used in  the  trial and their performance  compared  to  that of a
control section.  The results  showed  that although these techniques have been designed to  treat only shallow
surface cracking, minor modfification  to one of the methods may make it suitable for solving the more serious
problem  of reflection  cracking in  thin overlays.
538
11.0  INTRODUCTI'ON
The  primary  cause  of failure  of  thin  asphaltic  concrete  overlays  used  to  maintain  flexible  road
pavements  in  Malaysia  is the  occurrence  of  reflection  cracking  which  is  initiated  by  cracks  in  the
previous  surfacing.  These  cracks  can  occur  as soon  as  2-3  months after  the construction  Of 40mmn
thick overlays, their rate of propagation  being dependent  upon the severity of cracking before overlay,
the  pavement  deflection  and the commercial  traffic  volume.
Viljoen et  al,  1987, have reported  that the rate of propagation of reflection cracks  in asphalt surfacings
is dependent  on  the number of load  repetitions and  the movement  of the crack  due to  the deflection
of the  road pavement  under the  load.  As shown  in Figure  1 the movement  at the crack will  impose
a localised  strain  on  a  layer placed  above, eventually  causing  the  material  to fracture  and  a crack to
propagate  upwards  through  thernew  overlay.
Rolt  et al,  1986,  have  shown  that  another common  mode  of  -failure  of both  new  asphaltic concrete
surfacings  and  overlays  in  tropical -environments is cracking which starts  at the top of the surfacing
and  propagates  downwards.  This  type  of cracking  is  induced  by  the  oxidation  and  consequent
hardening of the  bitumen  in  the top  2-3mmn of the  material  (Smith  et al,  1990) making  it  brittle  and
thus susceptible to  'top-down'  cracking.  This type of cracking, although  exacerbated  by  the material
properties of the top  2-3mm,  can be caused  by  a  variety  of stresses.
Hot surface  treatment,  a technique recently  introduced  into Malaysia,  can  be used to rehabilitate  road
surfacings which  suffer from  this  latter  type of 'top-down'  cracking.
This paper  compares  the first two years performance  of three different forms of hot surface  treatment
with  that of a control section  on a  heavily  trafficked  urban  highway in Kuiala  Lumpur,  Malaysia.
2.0  EXPERIMENTAL  DESIGN
The  four trial  sections  are  located  adjacent  to one another  in the slow lane  of a  three  lane highway.
Each  section  is  approximately  180  metres  long and all  four were overlaid  with a  common  thickness
of 60mm of asphaltic concrete  after the surface  treatment  was completed.  The  layout of the sections
and the  method  of treatment  prior  to  overlay are  shown in Figure  2.
2.1  Surface  Treatment
The  different  methods of surface  treatment  are described  below:
Section  1:  Heat,  scarify  and  recompact.
In  this section  the  road surface  was  heated to  approximately  140C, then scarified
to  a depth of 25mm  and immediately  recompacted.
Section  2:  Heat,  remove and  patch.
In  this section  the  road  surface  was  heated to  approximately  1400C  scarified  and
removed,  and  then  a  new  25mm  layer of  nominal  13mmn  asphaltic  concrete  was
layed.
Section  3:  Control section.
The  surface of this  section was untreated  prior  to overlay.
Section  4:  Heat and  pave.
In  this  section  the  surface  was  heated  to  approximately  1400C  and  immediately
paved  with  a  20mm  layer of a  nominal  13mmn  asphaltic concrete.
539
￿11
i3.0  PRECONSTRUCTION  MEASUREMENT.
The  site  was  marked  out  by  10  metre  chainages  and  the  measurement  of rutting,  deflection  and
cracking  made with reference  to these  chainages.
3.1  Rutting
Rut depth  measurements  were taken  using a  2 metre straight edge  and calibrated  wedge.  The values
given  in  Table  1 show  that  all  four  sections  were structurally  strong  with  only low  values  having
developed, with the exception of one chainage  in section  2, since its construction  15 years previously.
The  only exception  to this was  one chainage  in  section  2 which  showed  a rut depth  of 19 mm.
3.2  Deflection
Deflection  measu  rements  were made  with  the  Falling  Weight Deflectometer  (FWD)  and  the  results
corrected  to a standard  pressure of 700  N/in  . The results given  in Table  1 show that sections  1 and
4 had similar values  to the control  section  (Section  3).  'Section 2  had slightly higher  values.
Table  1:  Rutting  and Deflection  Values Prior  to  Construction
3.3  Cracking
The  cracking  in  each  10  metre  length  was  assessed  by  its  intensity  and
assessed  visually using  the following  classification:-
Intensity
area.  The  intensity  was
o  - No cracking
1 - Single crack
2 - Two or more cracks  - not connected
3  - Two or more cracks  - interconnected
4  - Crocodile cracking
5 -Crocodile  cracking  with spa lng
The longitudinal  extent  and  the transverse  location of  the cracking  was also  recorded  and  from  this
its area  calculated.
Table 2 gives  the total area of pavement  that was cracked prior  to construction  and its distribution  by
intensity.
540
Section  No.  ______Rutting  (mm)  Deflection  (mm  x  10O3)
No.  of tests  Mean  Range  No. of tests  Mean  Range
1  12  7  4-11  12  389  283-494
2  22  7  3-19  22  526  288-866
3  18  5  3-8  18  40825-7
4  16  -S3-6  - 16  41739-2Table 2:  Cracking  Prior to  Construction
Section No  Area cracked  -Crack  intensity distribution  (per cent)  ______
(per cent)  1  2  3  4
1  35.4  0  0  75  12.5  12.5
2  27.7  0  2.3  57.3  40.4  0
3  21.7  0  11.4  88.6  0  0
4  23.1  0  2.3  84.1  6.8  6.8
The  results  show  that  the  majority  of cracking  at  the site  was  intensity  3  and  this  was  common
throughout  all four sections.  It was also  noted that  by the time  the cracks had progressed  to intensity
3  they were  becoming  badly  spalled.
3.4  Crack  Depth
After recording the  intensity and area of the cracking a series of 100mm  cores were taken  to establish
the depth  of  the cracks.  The results  from  these tests  are shown  in  Figure 3.  The  Figure  illustrates
that  although intensity  1 cracks were confined to the top 35mm  of the surfacing,  by the time they had
progressed  to  intensity  3  they  had  propagated  down  through  the surfacing  to  an  average  depth  of
115mm.
3:5  Traffic
The site  is situated  in the slow  lane  of a  particularly  heavily  trafficked  three  lane  highway in  Kuala
Lumpur.  A  classified  traffic  count  showed  that  the  commercial  vehicle  flow  in  the  slow  lane  was
6100  vehicles  per day.
4.0  CONSTRUCTION
The  heating  of  the  road  surface  was by  direct  flame  using  propane  burners.  The  average  surface
temperature  achieved  was  140'C decreasing  to 650C at  a  depth of 25mm.
The  relevant  construction  details  for each  of the sections  is given  in  Table  3.
Table  3:  Construction  Details
Section  Surface  Temp.  at  Pen.  of  Depth of  Thickness  of
No  temp.  after  rolling/  recovered  recompacted/pat  overlay  above
heating  before  paving  bitumen  chi  layer  road surface
_________  (OC)  (OC)  (mm  X 10,1)  (mm)  (mm)
1  136  110'  37'  25  60
2  - - - 25  60
3  - - - 60
4  144  78  -- 20+402. 3
I.
2
3
Recompacted  layer
20mm  of  13mm  nominal  A.C.  plus 40mm  of 20mm  nominal  A.C.
No  tack  coat  was applied  prior  to the  20mm  layer.
541Wheel  moement .
Opening  of cracks  doClosing  of cracks  O-J-  Opening of cracks
Fig. 1  Crack  movement  caused by the position of the crack  in the deflection  bowl
(after Villoen et  al.  1987)
Section 1  Section  2  Section 3  Section 4  i
2SmT~~~i..j  ,..2  Recampacted  aye  ~~~~~~~3  Patch..layer.
s  Qmy  jj
Fig.2  Schematic  cross section of experimental site
180
160
Mean thickness of bituminous surfacing
140
120
.v100
f  80
CL
2  3  4
Crack  intensity
Fig.3  Relation between crack depth  and intensity
'5425.0  PERFORMA&NCE
The  rutting  and  cracking of  the  sections -has  now  been  monitored -for a period  of two  years.  The
increase  in  rutting  has  been  small  with  the  mean  values  for  the  sections  ranging  between  2-4mm.
There  has however  been  a differential  progression  in  the development  of cracking.
5.1  Cracking
Cracking was noted in  the new overlay  as early  as 6 months after construction  and cores taken at that
time showed them  to be reflection cracks caused by cracks in the underlying layer.  Figure 4 illustrates
the increase in the area of cracking  of the different sections since construction.  The analysis has been
restricted  to those areas which  had  an  initial crack intensity  3  because this  type of cracking  was the
most extensive  and  common  to all  the four sections <see Table 2).
The  Figure  shows  that  in  Section  2,  92 per cent  of the  area  of intensity  3  cracking  had  reflected
through  after  2  years  trafficking  in  comparison  to  Section  1 where, only  24  per  cent  was  recorded.
The  control  section  and  Section  4  had  levels of cracking  midway between  these  extremes.
6.0  DISCUSSION
In the following discussion the performance  of each section is compared to that of the control (Section
3).
Section  1
The  improved  performance  of  this  section.(see figure  4)  is believed  to  be due  to  the  fact  that  the
25mm  recompacted  layer has  a high  void  content.  These voids  effectively dissipate  the strain 'above
the crack  in  the lower layer  and  thus prevent  the cracks  propagating  through  the recompacted  layer
and into the new  overlay.  This is  shown diagrammatically  in Figure 5.  This hypothesis  is supported
by the  fact that cores  taken  from  this section  after two years  showed  that  the recompacted  layer had
a  void  content  over  three  per  cent  higher  than  the  equivalent  material  prior  to  scarification  and
recompaction,  sampled  from  the untreated  surface  in the control section.
Section  2
The  performance  of this  section  is  significantly  inferior  than  the control  section,  despite  having  a
greater  thickness of new  material-'(see  Figures 4 & 5).  This is believed  to be because  the removal  of
the  top  25mm  of the  original  surfacing  decreases  the, effective  width  of intensity  3  cracks  by  the
removal  of the  spalled  area  at  the  top of the  cracks,  as indicated  in Figure  5.  Thus  for  the same
hodrizotal  movement  across  the  cracks,  dx,  caused  by  the deflection  of the  road  pavement  under
traffic,  the  strain at  the  top  of treated  crack,  dx/L,  is  significantly  greater  than  that at  the  top of a
spalled crack, dx/L,. It is this increased strain, compared  to that  in the control section that is believed
to have  caused  the differential  performance.
Section  4
As shown  in  Table  2  the temperature  of the surface  prior  to laying  the  first  layer. of overlay  had
decreased  from  a maximum  of 1440C after  heating to 780C on  paving.  As there was  also  no  visual
evidence  that the  preheating of the surface  had changed  the nature  of the cracks  there  is no  apparent
reason  why  this  section  should  perform  significantly  differently  from  the control  section.  This  is
substantiated  by  the crack  progression  illustrated  in Figure  4  which shows  the performance  of this
section  to be slightly  worse than  the control.
5435  10  15  20
Time (months)
Fig.4  Relation between cracking and time
(a) Heat  and recompact (b)  Heat and  patch
ws￿  ￿
Fig.5  Crack propagation
544
z
2i
'a
1
2
25
(c) Control7.0  CONCLUSIONS
1.  The  heat,  remove  and  patch technique  used  on  Section  2  has  not  been successful  in  preventing  the
propagation  of reflection  cracks  at  deflection  levels  of 500  x 10- 3mfm  and  daily commercial  vehicle
flows  of over 6000  vehicles.  Removing  the top layer of a  cracked  asphalt  surface prior  to patching
can only be-re~commended  when the cracks are confined to the top 20-25mm  of the existing surfacing.
2.  Heating the  surface prior  to paving was shown  to be ineffective  and  is  not  recommended  for further
Use.
3.  The coeation of an  initerlayer having a high void content,  in this case by heating the surface, scarifying
and  recompacting,  has been  shown to  be effective  in  redlucing  the  rate of propagation  of reflection
cracking.  The successful  ~compaction  of this  layer depends  upon the  viscosity  of the  binder  in the
surfacing and a rej'uvenatinig agent may have to be used with some material's  to obtain a 'tight'  surface.
4.  The use of alternative  'high  void'  interlayers to prevent reflection cracking  is being  considered by the
Training  and Research  Ihstitute.  At  present interlayers  of crushed stone, porous macadam  and large
stone surface dressings  are being investigated.  These  methods would  enable a more predictable void
content  to  be obtained and  avoid -processing of the existing surfacing.
8.0  ACKNOWLEDGEMENTS
This study was carried  out under a joint cooperative  research  programme between  the Jabatan  kerja
Raya (JKR)  of Malaysia  and  the  Transport  and  Road  Research  Laboratory  (TRRL)  of the  United
Kingdom.
The authors would like  to  thanik  the Director-General  of Public Works, JKR  Malaysia  for permission
to publish  the paper.
The work  described  in this paper  forms  part of the  research  programme  of the  Overseas  Unit  (Unit
Head:  Mr  J  S  Yerrell)  of  the  TRRL--  carried  out  on  behalf  of  the  Overseas  Development
Administration.  Any views expressed are not  necessarily  those of the Administration,  the Department
of Transport  or the JKR.  The paper  is published by permission  of the Chief Executive  of the TRRL--.
9.0  REFERENCES
Rolt  J,  H  R  Smith  and  C R  Jones  (1986).  The design  and  performance  of bituminous  overlays  in
tropical environments.  2nd  Tnt.  Conif. The Bearing Capacity of Roads and Airfields (Plymouth,  1986).
Smith  H R, J Rolt and J Wambura (1990).  Thedurability of bituminous overlays and wearing courses
in  tropical  environments.  3rd  Int.  Conif. The  Bearing  Capacity  of Roads  and Airfields  (Trondheim,
1990).
Vi1Joen  A  W,  C  R  Freeme,  V  P  Servas  and  F  C  Rust  (1987).  Heavy  vehicle  simulator  aided
evaluation  of overlays  on  pavements  with  active  cracks.  6th  Int  Conf. Structural  Design  of Asphalt
Pavements  (Ann  Arbor,  Michigan,  1987).
Crown  Copyright
The views expresse  in this Paper are  not necessarily  those of the Department  of Transport.  Extracts
from  the  text  may  be  reproduced,  except  for  commercial  purposes,  provided  the  source  is
acknowledged.
545

THE USE OF HOT SURFACE TREATMENT TO REHABILITATE CRACKED ASPHALTIC CONCREUE SURFACIN4GS IN MAlAYSIA,

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THE USE OF HOT SURFACE TREATMENT TO REHABILITATE CRACKED ASPHALTIC CONCREUE SURFACIN4GS IN MAlAYSIA,

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