2005 international symposium on pavement

Transcription

2005 INTERNATIONAL SYMPOSIUM ON
PAVEMENT RECYCLING
SÃO PAULO – SP – BRAZIL – MARCH 14 –16
PAVEMENT REHABILITATION THROUGH RECYCLING WITH
THE ADDITION OF PORTLAND CEMENT ON HIGHWAY SP-351
Paulo César Arrieiro de Oliveira M. Sc., Civil Engineer
Production Engineer
FRESAR Tecnologia de Pavimentos Ltda.
R. Adelino Teste,30 – Olhos d’agua
30.390-070 – Belo Horizonte – MG – BRAZIL
pcesar@gruposantanna.com.br
Fernando Márcio Guimarães Sant’Anna, Civil Engineer
Technical Director
30.390-070 – Belo Horizonte – MG - BRAZIL
fernando@gruposantanna.com.br
Firmino Sávio Vasconcellos de Souza, Civil Engineer
Technical Consultant
30.390-070 – Belo Horizonte – MG - BRAZIL
savio@gruposantanna.com.br
Paper 047-01
PAVEMENT RECYCLING
SÃO PAULO - SP – BRAZIL – MARCH 14 –16
1
ABSTRACT
This paper describes a successful case of a road pavement rehabilitation with the
reclamation of the materials from the original pavement structure (hot rolled asphalt
over a granular base) with the addition of Portland cement and crushed stone. The
pavement recycling operation was performed on a single lane Highway SP-351,
between the cities of Bebedouro and Palmares Paulista in the State of São Paulo, Brazil,
on a total extension of 21,916 Km. A total width of 7,0 m of the two traffic lanes was
recycled to a depth of 0,18 m. A total volume of 27.614,16 m3 of recycled material was
processed. The quality of the pavement recycling intervention is evident because of the
results acquired by the quality control system performed throughout the field works.
The methodology used for the technological control system, the test results obtained
from the recycled materials’ physical properties and the measured recycled pavement
structural deformations are summarized in this paper and analysed for the sake of
evaluating the likely service life of the highway. The pavement recycling activity was
performed by “Fresar Tecnologia de Pavimentos Ltda.” who, in its turn, hired “Solocap
– Tecnologia e Serviços de Engenharia Ltda.” to execute the technological control
procedures. This pavement recycling intervention was performed according to a
pavement rehabilitation program presently in effect for the highway network under the
responsibility of “Concessionária de Rodovias TEBE”. The design solution adopted by
“TEBE” to rehabilitate the pavement for a design period of 10 years, was to add 3,5 %
of Portland cement CP III – 40 RS and 10 % of crushed stone sizes 1 and 2, both by %
weight to the pulverized material reclaimed from the original pavement structure and
compact it with the energy equivalent to Modified Proctor to achieve maximum dry
density at its optimum moisture content.
KEY WORDS
Pavements, recycling, rehabilitation techniques, cement stabilization
1. Introduction
As the typical flexible pavement ages its ride quality and support capacity decreases
proportionally to the upspringing of its surface distress. This distress is caused mostly
by the evolving traffic and also by cumulative environmental effects on the pavement,
which, at a certain point, make the pavement unable to fulfill its functions, which are, to
promote safe and comfortable riding conditions to the road users under any prevailing
climatic condition.
As the pavement distress increases it becomes critical to be able to predict the optimum
moment for the maintenance interventions so that the pavement´s service life can be
enhanced and its serviceability restored. Nevertheless, the necessary funds to cope with
the growing demand for pavement maintenance are seldom available as to preserve its
good condition as it ages.
The limited budgets together with environmental restrictions imposed on the highway
construction activity have stimulated the adoption of new technologies such as
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PAVEMENT RECYCLING
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pavement recycling. Pavement recycling has permited the technical personnel involved
with highways to pursue better technical and economical results.
The objective of recycling a pavement is to reclaim the original material from the upper
portion of the pavement structure, which is distressed, turning it into a homogeneous
new layer, capable of coping with a new period of service life. We highlight pavement
recycling with the addition of Portland cement among the other various forms of
pavement recycling and reclaiming available.
“In situ” recycliong is defined by Álvarez & Marín [1]as a mixture of milled material
from an original betuminous wearing course with predetermined quantities of the base
material, cement, water and, eventually, imported granular material to be added to
compose a certain granular distribution.
This new recycled mix has enough strength to cope with traffic loads because of its low
deformation caharacteristics, its water resistant capacity and low thermal susceptibility.
All these characteristics together make the recycled layer, at one time, highly resistant
and thus capable of protecting the underlying subgrade and still cost worthy.
The Wirtgen Cold Recycling Manual [9] highlights the following advantages arising
from the adoption of recycling with the addition of Portland cement in pavement
rehabilitation projects:
-
Availability: Portland cement may be obtained practically anywhere in the world;
Cost: Portland cement is usually less expensive than asphalt;
Application: Portland cement may be spread manually in the absence of dry or wet
suspension spreaders;
Acceptability: The use of Portland cement is well known by the heavy construction
industry. Specifications and test methods are available;
Strength: Portland cement greatly enhances the axial compressive strength of most
pavement construction materials.
TEBE Concessionária Rodovias, a road Concessionary, chose the pavement recycling
technique because there was a need to rehabilitate the pavement with minimum traffic
disruptions and still attend a tight work schedule.
Pavement recycling is a sustainable process that makes it possible for the construction
material to be used over again. It has made it so feasible because of the reduction on
transportation costs with less material hauling altogether and less volume of material
dispensing along the road.
2. Road Information
The rehabilitated road stretch belongs to Highway SP 351named after Pedro
Monteleone and links the two towns of Bebedouro and Palmares Paulista, in the north
region of the State of São Paulo. The total recycled extension was 21.916 kilometers of
a single lane highway, 7,00 m wide with two shoulders 2.5 m wide on each side. The
recycling operation was performed on two separate extensions from km 157,656
through Km 173,772 and the other from km 185,200 through Km 191,000. The
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pavement recycling operation was performed by Fresar Tecnologia de Pavimentos Ltda.
The total volume of recycled material reached 27,614.16 m3, comprising the road width
(except shoulders) recycled to a depth of 0.18 m.
The average annual daily traffic on the highway is 22,134 vehicles, 29% of which are
heavy vehicles. The number of expected 8,2 tf Equivalent Standard Axle Loads
(ESAL’s) applications expected during a design life of 10 years is 4,36 x 106
determined by the United States Army Corp of Engineers (USACE) methodology.
The original pavement structure was a 6 cm thick on average of a betuminous wearing
course over a soil cement base with a depth of 15 cm, both layers being very constant in
terms of depth. The average original pavement structure is represented below.
Asphalt wearing course
6,0 cm
Soil cement base
15 cm
The subgrade is a sandy soil classified A-2-4 by the Highway Research Board (HRB)
method, with practically no expansion and a California Bearing Ratio (CBR) of 35%.
Although constant in depth, the betuminous layer was found to be made up of different
kinds of asphalt mixes, such as surface treatments, hot roled asphalt and micro surfacing
due to maintenace interventions performed with time. In fact, the original pavement was
very distressed by traffic and climate.
On some parts the soil cement base was very distressed, with cracks that propagated to
the pavement surface. The regular transversal profile was disrupted at points and there
were pot holes and patching in poor conditions.
Although the base being in such poor structural condition, there were no great surface
deflection readings that would justify a need for an intervention on the lower part of the
pavement structure. Benkelman beam deflections on the pavement surface averaged 45x
10-2 mm. A conclusion was reached that the surface distress was caused by the fractured
soil cement base.
3. Preliminary Studies
The preliminary studies were performed, basically, to verify the deformation of the
original pavement structure through the measuring of surface deflections with a
Benkelman beam.
Since the recycling rehabilitation intervention done previously in 2002 on the same road
has been a great success and the realization that the bituminous wearing course and base
layers were very similar to what is on the present road stretch, TEBE decided to
maintain the design parameters used before on the other road extension.
At that occasion samples were collected from the original pavement’s wearing course
and base course layers when a Reclaimer/Mixer machine Caterpillar RM 350, the same
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machine that performed the pavement recycling afterwards, was applied. A total depth
of 0.18m was cut from the pavement surface, the same depth that was cut in 2002.
The Reclaimer/Mixer machine was used at a speed of 7 to 8 meters per minute, with a
rotary speed of 215 rotations per minute of the milling drum. That was enough to
guarantee a homogeneous recycled material grading curve which fit into material’s
standard specifications DNER ME 080/94.
The recycled mixes were moulded at optimum moisture content and tested for resistance
to axial compression according to the standard specification DNER ME 201/94. The
compaction energy prescribed was that of the Modified Proctor (AASHTO) test, 55
blows per layer, as referred in specification DNER ME 162/94.
4. Recycled Mix Design
It was established that the recycled mix stabilized with Portland cement should endure
2,5 Mpa of compressive axial strength on the seventh day after moulding. This
compressive strength was only achieved in the laboratory when a percentage of cement
greater than 5% by weight was added to the mixture.
As it is known that one of the factors responsible for the cracking of materials treated
with cement is the excess content of this stabilizing agent in the mixture [12], the
possibility of adding crushed stone to the recycled mix was considered in order to
maintain the strength although reducing the cement content. This was done in order to
safeguard the pavement performance from the undesired effects of the shrinkage and
stiffness caused by the addition of excessive quantities of Portland cement.
Various mixtures composed of the milled material from the original betuminous
wearing course and soil cement base layers, crushed stone and Portland cement were
tested. Based on test results, the mix that showed the highest compressive strength when
varying the Portland cement addition rate had the following characteristics:
• 3.5 % of Portland cement by weight;
• 10% of crushed stone (sizes 1 and 2) by weight;
• 30% of Residual Asphalt Pavement (RAP) by weight ;
• 56.5% of milled soil cement base by weight;
• Compressive axial strength seven days after moulding: 2.9 MPa and 4.2 Mpa after 28
days.
This recycled mix was designed with the RAP obtained from a cut depth of 0.18 m for
the entire recycled length of the road, for both the base and the betuminous wearing
course were very homogeneous all along.
5. Recycling and Compaction Equipment
The pavement recycling process was executed and controlled by Fresar Tecnologia de
Pavimentos Ltda, when a total volume of 27.614,16 m3 of recycled material was
processed in 75 days.
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The pavement rehabilitation was performed on a half road width with the traffic
detoured to the contiguous lane. An average extension of 800 meters of this half road
section was recycled per day using the equipments described in the following table:
OCCUPATION
RATE
Reclaimer/Mixer Caterpillar RM 350
1
0,90
Motor grader Fiat Allis FG 200
1
0,95
Tamping Roller – Operational weight 11 ton.
3
0,65
Static Steel Drum Roller–Op. Weight 11 ton.
1
0,22
Tanker Truck
2
0,50
Wheel Loader Caterpillar 930 R
1
0,75
Dump Truck - Capacity 5.0 m3
2
0,40
Hauling Truck - Capacity 10 Ton.
1
0,50
Table 1 – Equipments employed on the recycling works
RECYCLING EQUIPMENT
QUANTITY
The work shifts were planned regularly according to the equipment availability, the
existing traffic and the desirable charcteristics of the recycled mix. The trial test section
held at the start of the recycling work was very useful for optimizing the equipment
allocation and the furnishing of other resources to allow continuity throughout the work
shifts.
6. Trial Test Section
On the first day of work a trial test section was held to allow the operational and
technical people involved to be more intimately familiarized with the execution process
and the material characteristics without the natural typical haste when production is at
its normal pace. All production phases were closely observed by everyone and thus it
became possible to develop ideal adequacy of the equipments to prevailing conditions at
the work site.
The following aspects, as recommended by Oliveira [10], were accounted for during the
trial test section:
• Cut depth;
• Cut width;
• Recycled mix granular distribution control;
• Recycled mix humidity;
• Cement and aggregate percentual addition control;
• Recycled mix homogeneousness.
Once the basic working conditions were known through the trial test section
implementation, segments of 150 m in extension with a half road width were adopted.
This was the ideal working length for the maximum number of equipment working
simultaneously which optimized equipment occupation and enhanced productivity.
7. Executive Process
The pavement recycling executive process can be divided into the following tasks:
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• Milling of existing pavement;
• Portland cement application;
• Recycled mix stabilization;
• Longitudinal and transversal profile shaping and final compaction;
• Surface grooming;
• Prime coat application;
• Sand spreading.
Operation begins with the reclaimer milling the surface of the original pavement to a
pre-determined granular distribution, after which the Portland cement will be added.
The pre-determined quantity of cement to be added to the calculated volume of RAP
was distributed evenly over the measured milled surface, which gave great precision to
the stabilizing agent application rate. One single pass of the reclaimer was sufficient for
granting homogeneouness and stability to the recycled mix. This was very positive as it
allowed maximum density to be reached with the least effort of the rolling equipment.
When this was accomplished, the recycled surface was prime coated with diluted
asphalt applied at a rate of 0.8 liters per square meter. After the curing of the prime coat
a very fine layer of sand was manually evenly spread over the surface to prevent
skidding and consequent raveling of the surface which could be caused by immediate
liberation of traffic.
Among published papers which deal with traffic liberation after recycling operations
with Portland cement addition, the one by Jofré [8] where this practice is recommended
for low volume traffic roads. According to the author, allowing traffic to run on a newly
recycled pavement surface is possible because the stability is acquired by the mineral
structure of the recycled mix and thus traffic generated deformations are not sufficient
to break the cimentitious bonds generated. This way the progressive gain in
compressive strength is not interrupted and the recycled mix maintains its good
behavior as a supporting material in the long run.
Stresses generated by traffic loads, thermal variations (or a combination of both) or
simply retraction cracks, acting upon cement stabilized (stiffer) materials, may lead to
little fractures on the pavement structures. It is also common for small fractures to form
along longitudinal and transversal joints due to insufficient bonding of adjacent mats.
According to Paul & Simões [11] the fracturing of the Portland cement recycled mixture
layer makes it easy for the water to enter the pavement structure and accelerate the
fatigue generated process of the pavement deterioration. In order to eliminate or to
mitigate this cracking effect a double layer of polymer modified surface treatment was
devised to be laid onto the recycled material surface. The application of this more
elastic betuminous layer was an attempt to postpone the propagation of cracks arising
from the recycled layer. The application of the surface treatment layer allows more time
for most of the cracks to evolve in the cement treated layer before the final base and
wearing course betuminous layers are built. This may result in the occurrence of smaller
and less significant fractures on the asphalt bound layers [10].
The final pavement layer, composed of a 75 mm thick hot rolled asphalt mix “C” by
DNER specification, was laid 15 days after the application of the surface treatment.
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Traditional execution procedures were followed for the conventional hot rolled asphalt
layer construction.
8. Quality Control
A very good productivity level was reached during the recycled layer construction and
still high quality standards were achieved. Mostly, this was possible because a
systematic procedure was established to monitor the following items in order to
guarantee a satisfactory performance for the recycled layer and the pavement as a
whole:
• Recycled layer depth;
• Recycled mix granular distribution;
• Percentage of added material;
• Recycled mix optimum moisture content;
• Recycled mix homogeneousness;
• Recycled mix compaction;
• Recycled mix surface finishing;
• Axial compressive strength;
• Surface deflection.
The recycled layer thickness was measured with a ruler on both sides of the cut made by
the reclaimer at regular intervals. The recycled mix granular distribution was checked
periodically against the one devised in standard specification method DNER-ES 303/97.
Proper care was taken to avoid the presence of big chunks of the original aspahlt
pavement either by really breaking everything up or picking up after the reclaimer.
The application rates for the cement and for the crushed stone were determined through
the calculation of the average rate deducted from volume of both for a corresponding
pavement area. The optimum moisture content for the recycled mix was determined at
the work site by weighing a sample before and after drying it on a gas stove. No
significant failures on homogeneousness of the recycled mix were detected. This
homogeneousness was guaranteed by the number of times the reclaimer went over the
same surface, the rotation speed of the milling drum and the translation speed of the
reclaimer, aside from the break bar presence. The recycled mix compaction is by far the
most important isolated item to affect the long term pavement performance. The
compaction rate for the recycled mix was contrlolled through the sand flask test as
prescribed by DNER ME 092/94. The recycled surface was kept always even, with no
loose particles and geometrically conformed according to the contractor demands. The
transversal profile was leveled against the original pavement grade.
Six samples of the recycled material were collected daily and tested for axial
compressive strength. The results were always positive, with a general average value of
28,4 kg/cm2 after 7 days.
A surface maximum deflection survey with a Benkelman beam was performed
throughout the recycled segment according to standard method DNER ME 061/94 as
part of the technological control applied. The measured values of the pavement´s elastic
deformation may be used as a reference for monitoring the long term pavement
performance.
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The next two pages contain representations of statistical data regarding the main
characteristics of the recycled pavement as it is next explained.
On page 10 there is a table containing average values of the destructive tests performed
on the recycled materials and average values of non-destructive testing on the recycled
pavemnt structure during its construction.
Five of the most significant mechanical and physical characteristics of the recycled
pavement and its constituing materials are plotted on page 11. These graphical
representations are important for the general view of the whole length of the recycled
pavement extension.
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9. Pavement Performance After Recycling
Two illustrations are next presented to demonstrate the maximum pavement deflections
reduction on the two traffic lanes (east and west bound). The surveys were done by a
Falling Weight Deflectometer in 2002 (before recycling) and in December 2004 (after
recycling). The reduced deformation of the recycled layer is a means to prolong the
pavement’s service life due to the reduction of the fatigue effects on the pavement
structure.
Next, on page 13, there is a table showing the recycled pavement calculated remaining
service life and the necessary betuminous overlay thickness for the design life of 10
years, considered the actual traffic and pavement structure, through back calculation.
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10. Conclusions
Many conclusions can be reached through this paper regarding the appropriateness of
recycling road construction materials; all of them being positive. Although, a pavement
rehabilitation project through recycling can only be successful if it is well conceived,
designed, executed and controlled. Thus, this paper is very concerned with highlighting
the most important peculiar aspects of pavement recycling so the positive results
obatained at SP-351 can be reproduced elsewhere.
For this matter, the authors have made a point of showing the prevailing conditions on
which TEBE´s executives based themselves to adopt the same solution that was used for
the previous intervention, though not before checking the equivalence of the
performance indicators and of the occurring traffic. The logistics involved in having all
supplies timely fetched to the construction site has also been emphasized as a basic
requirement for the pavement recycling job to be on schedule. The importance of the
trial test section was also highlighted along with the strategic planing of the size and
number of equipments involved in the recycling operation, mainly the compaction
equipment. The importance of the conduction of a trustworthy technological control
procedure lies in the fact that recycled materials do acquire new characteristics and thus
make up a brand new pavement layer with renewed functions. To monitor the
development of such new characteristics is important as a means of developing the
confidence of agents in charge of pavement maintenance everywhere. Also, the paper
makes it evident how productive the pavement recycling process is, when more than
1000 meters of traffic lane extension was recycled per day.
The main conclusion, though, about the pavement rehabilitation on Highway SP-351 is
that the recyccling intervention is economical and, above all, ecological.
Economical because, beyond the fact that the direct cost of the intervention is highly
feasible, there is an additional gain in the bearing capacity of the recycled mix layer
which prolongs the pavement´s service life considerably and enhances the pavement´s
functional performance. This bearing capacity gain is caused by the reduction in
pavement deformation and the consequent profit in the pavement’s capacity to resist to
fatigue effects as becomes evident by the back calculation exercise here presented.
Highway SP-351 design life of 10 years will certainly be accomplished.
The process is ecological because it diminishes the environmental impact through a
sustainable action which helps to prevent the exploitation of natural resources that will
grant a healthier life to our descendants on earth in the future.
11.
[1]
[2]
Bibliography
Álvarez, M. G.; Marín, C. B. Reciclado In Situ com Cemento. Futuras
Prescripciones Técnicas de la Dirección General de Carreteras del
Ministerio de Fomento de España. 1º Simposio Internacional sobre
Estabilización de Explanadas y Reciclado In Situ de Firmes com Cemento.
Salamanca, España, .2001.
DNER ES 303/97. Departamento Nacional de Estradas de Rodagem.
Pavimentação – Base de Solo Estabilizada Granulometricamente. Rio de
Janeiro, Brasil,. 1997.
Paper 047-01
PAVEMENT RECYCLING
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[3]
DNER ME 061/94. Departamento Nacional de Estradas de Rodagem.
Pavimento – Delineamento da Linha de Influência Longitudinal da Bacia de
Deformação por Intermédio da Viga Benkelman. Rio de Janeiro, Brasil, 1994.
[4]
DNER ME 080/94. Departamento Nacional de Estradas de Rodagem. Solos
– Análise Granulométrica por Peneiramento. Rio de Janeiro, Brasil. 1994.
[5]
DNER ME 092/94. Departamento Nacional de Estradas de Rodagem. Solo –
Determinação da Massa Específica Aparente “In Situ”, com o emprego do
Frasco de Areia. Rio de Janeiro, Brasil, 1994.
[6]
DNER ME 162/94. Departamento Nacional de Estradas de Rodagem. Solos
– Ensaio de Compactação Utilizando Amostras Trabalhadas. Rio de Janeiro,
Brasil, 1994.
[7]
DNER ME 201/94. Departamento Nacional de Estradas de Rodagem. Solo
Cimento– Compressão Axial de Corpos-de-Prova Cilíndricos. Rio de Janeiro,
Brasil, 1994.
[8]
Jofré, C. La Técnica del Reciclado de Firmes com Cemento 1º Simposio
Internacional sobre Estabilización de Explanadas y Reciclado In Situ de
Firmes com Cemento. Salamanca, Espana, 2001.
[9]
Manual de Reciclagem a Frio. Wirtgen, 2ª Edição Revisada. Wirtgen GmbH.
ISBN 3-00-003577-X. Windhagen, Alemanha, 2001.
[10]
Oliveira, P C A. Contribuição ao Estudo da Técnica de Reciclagem Profunda
na Recuperação de Pavimentos Flexíveis. Dissertação (Mestrado) – Depto. de
Geotecnia e Transportes - UNICAMP – Universidade Estadual de Campinas.
Campinas, Brasil, 2003.
[11]
Paul, I., Simões R. Aplicação da Técnica de Reciclagem de Pavimentos “In
Situ” com Cimento, na Beneficiação da EN 383 – Canhestros/Aljustrel. II
Jornadas Técnicas de Pavimentos Rodoviários – Reciclagem de Pavimentos.
FEUP. Porto, Portugal, 2003.
[12]
P C A – Portland Cement Association. Soil-Cement Information: Reflective
Cracking in Cement Stabilized Pavement. Disponível para download em:
<http://www.cement..org/pavements /pv_sc_fdr_resources.asp/IS537{1}pdf>
ACKNOWLEDGEMENTS
The authors wish to thank the following persons and institutions for the help provided,
which was invaluable in the exercise of pavement performance prediction of the
recycled pavement.
• Henrique Borges da Cunha, Concessionária de Rodovias TEBE;
• Rui Alves Margarido, Dynatest Engenharia Ltda.;
• Anselmo Dias da Silva, Copavel Consultoria de Engenharia Ltda;
• Petrúcio Lima e Silva, Strata Engenharia Rodoviária Ltda.
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2005 international symposium on pavement

Transcription

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