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1 INTRODUCTION
National Road No. 7 starts in the city of BuenosAires and
developes from east to west- crossing the
provinces of Buenos Aires, Santa Fe, Crdoba, SanLuis and
Mendoza.The section under study starts in the Santa Fe Prov-
ince at Km 380.0 and continues around the floodingarea of the
Laguna La Picasa, ending at km 390.5.This lake is located in the
southwest of the provinceof Santa Fe and North of the Province of
BuenosAires and has basin of approximately 500,000 hec-tares
contribution, including SE of Cordoba, NW ofBuenos Aires and SW of
Santa Fe areas, on a stretchof 100 km long and 50 meters wide along
NationalRoute No. 7.
Figure 1. Level at the time of the work of the lagoon: IGN
104.00 (approximate).
The work, contracted by the Direccin Nacional de
Vialidad of Argentine, was officially started
01/02/2006 and ended on 15/06/2007. It gave conti-
nuity to the NR No. 7 interrupted from 1999 due to
the overflowing of the water. The track crosses the
La Picasa lagoon by the South West end. The gen-
eral morphology of the area has a typical landscape
of gently undulating plains, with alternation of very
flat hills and depressed sectors, where ponds and
temporary lows locate, incorporating a surface stor-
age capacity. Surface slopes are low, less than the
0004 m / m. The aim of the project was to rehabili-
tate the road through an embankment along the ex-
isting track and avoid disruption in the future.
Figure 2. View of the trace of the roadway when starting the
work
To achieve this, the following hydraulic and project
parameters have been considered:
Cement- treated soil: Experience in the work Rehabilitation of
NationalRoute No 7 Section: crossing La Picasa Lagoon through
existing road
F. Gerbaudo & J.E. Ramoneda & J. ViozziDireccin Nacional
de Vialidad, 7 Distrito- Divisin Obras. Santa Fe, Argentina
ABSTRACT: The paper presents the experience of using cement
treated soil to construct an embankment in
the Rehabilitation of National Route 7 Section: crossing La
Picasa Lagoon through existing road work,
located between Km 380.0 and Km 390.5 in the Santa Fe Province,
Argentine. The overflowing of La Picasa
Lagoon in 1999 interrupted the existing road. This work
rehabilitated the flood section. The project itself in-
cluded the construction of an embankment protected by stones on
the existing road. The chemical aggressive-
ness of water, caused by high content of salts, especially
sulfates, required the embankment to be neutralized
both physically and chemically. Consequently, a treatment with
low quantities of ARS Portland cement was
proposed. While in Argentina this technique is widely used in
soil stabilization, seeking to improve both phys-
ical characteristics and bearing capacity, it has never been
used to modify only the physical conditions.
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Level at the time of the work of the lagoon: IGN
104.00 (approximate). Maximum level of the lagoon at the
conclusion ofthe drainage works currently in progress: 102.50IGN.
Federal Plan of Flood Control administered bythe Secretary of Water
Resources of the Nation. Minimal height of grade project: 104.80
IGN.The typical profile of basic work also takes into ac-
count the following requirements, according to thelevel of
service to be provided along the way: Guideline Speed: 110 km / h
Roadway width: 7.44 m Crown width: 15.30 m Shoulder width: 3.00 mIt
was also built a bridge located in the progressive 6+759.13, with a
length of 60 m in three tranches of20m light each, a level beam
background of104.50m and a roadway width of 8.30m. The basicwork of
raising the embankment has its axis coinci-dent with the axis of
the existing pavement. It con-sists of a shoulder and core of
rockfill. The last oneis formed by a causeway to advance beyond the
levelof water hair with a rematch of 0.20 m. From thisbase causeway
lies layers of cement treated soil andafter that the main pavement
structure is found. It isthe result of the application of 1993
AASHTO De-sign Method for annual average daily traffic designof
1960 vehicles per day in 2007. The structure wasdesigned as a
semirigid pavement, trying to makerigid support layers decreasing
in depth. The finalstructure was formed as follows:
Subgrade soil treated with cement sub base of20cm thick. See
Figure 2 reference 6. Sub base granular treated with cement of
20cmthick. See Figure 2 reference 5. Base granular treated with
cement of 15cm thick.See Figure 2 reference 4. Asphalt concrete
layer of 7cm thick. See Figure 2reference 1.A geotextile membrane
resistance to puncture andtear was placed between the causeway and
the layersof soil cement.
Figure 3. Cross Section
This paper will focus on the core layer of soil fill,the
subgrade and shoulders coating, all executed insoil treated with
cement.
2 TECHNICAL SOLUTION
The system of elements and materials that make up
the existing basic work respond to the demands re-quired by the
environment.The pier contains the nucleus and acts as
protection,containment and filter side together with
geotextilemembrane. The embankment forms a floor that isnot
affected in its stability by the presence of waterand eliminates
the phenomenon of capillary rise forthe high void ratio.The change
in the physical properties aims to pro-vide the fill water
insensitivity to the phenomena ofvolume changes (swelling,
shrinkage and consolida-tion) and embedding capillary absorption.
This em-bedding is a latent possibility in the work because ofits
proximity to high laggon level and exposure torain.Moreover, the
slight stiffening of cement brings anumber of advantages, among
others, constructiontechnology and also influences the attenuation
of thephysical phenomenon of consolidation.This series of
technological advantages are: Reduces lead times and costs for
using the equip-ment. A similar structural capacity as the bank
exe-cuted without cement requires significant mechani-
cal densification, which implies a considerableruntime and
greater use of compaction equipment (aswill be seen in the
development of constructionmethodology and equipment used for
distributionand preparation of material to be compacted is simi-lar
to that required for untreated soil with cement). At the same time
constitutes a less deformableseat base for the pavement structure
to improve itsperformance and durability. It also helps to mitigate
potential differential set-tlement between the sectors of basic
work that are
above the existing pavement structure and outside it,that is, on
shoulders verges and existing embank-ment slope.As a disadvantage,
the soil layers agglomerated withcement have a significant
potential for dryingshrinkage cracking, a problem that can be
solved byattending carefully curing task.Nevertheless the useof low
cement tenors in this case, presented no suchproblems.In order to
use cement as a treatment of soil we hadto pay special attention to
water of the lagoon. Thechemical analysis verified the presence of
important
contents of sulfate, 2.4g / l, a substance that is com-bined
with tricalcium aluminate hydrates (AC3) ex-pansive cement to form
compounds that cause crack-ing. We therefore had to use Portland
Cement ARS,highly resistant to sulfates. It is provided to give
an
C.Rasante Min.
C.RasanteMin. Exist.
ANCHO TOTAL DE CORONAMIENTO 14.65 m
Pavimento
Existente
4.0%2.0%4.0%2.0%
4321 85 79
12
11
10 6
2.60 2.60ANCHO DE CALZADA=7.44m
EJE
RAS
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order of magnitude that according to PETG Ref. [1]the maximum
sulfate content for mixing water forsoil cement is 1g / l.
3 SPECIFICATIONS
In this paper we mention some concepts of the speci-
fications related to soils treated with cement, whichcome from
the Special Technical Specifications(PETG) of the work. Ref
[1].Related to the materials, the most important re-quirement is
Cement, which must be of type ARSaccording to the IRAM Norms
1669-1:1984 PortlandCement highly sulphate-resistant, with no
additionsand/or IRAM Norms 1669-2:1987 Portland Cementhighly
sulphate-resistant, with additions. There wereno parameters to
control soil established exceptthose related to the presence of
organic matter, leav-ing the feasibility of using soil from
different sites
subject to the study of economic and technical feasi-bility for
mixture proportions.As for the soil-cement mixture did not set any
pa-rameter that has to do with the physical properties ofthe
material, grain size distribution and Atterberglimits, common
practice for the specification oflime-treated mixtures. Such
properties allow to di-rectly assess the effectiveness of
treatment. The lackof quantifiers of these properties in the
specificationsof soil treated with cement applied to this project
re-sponds to the tests required to obtain the mixture
should offer the possibility to break into particles.Because of
the cement, once the mixture was com-pacted or left aside for some
time uncompacted, thislast process is not easy to do. One could try
to makesome kind of characterization when uncompactedmixture is
young, hours or days after homogeniza-tion, but in this period the
reactions and chemicalchanges are substantial minute by minute and
thusthe time variable would introduce a large scatter inresults. It
should be further study in this regard.It was established as an
indirect control parameterfor evaluating the effectiveness of
treatment in an
indirect way the compressive strength according toStandard Test
VN - E33 - 67 Ref [2], except youhave to do with curing and molding
of the speci-mens. The test was due to perform after a
curingprocess of 48 hours at 50 degrees Celsius or 21 daysat room
temperature. The molding process took be-tween two and two and a
half hours after the mixingwas made.According to the current
standard specifications asoil stabilized with cement has a curing
period of 7days at 20 degrees Celsius; which serves to mitigate
the structural requirement for the mixture treated, incomparison
to the stabilized one, maintaining thevalues of compressive
strength environments com-monly demanded. This measure
substantially reduc-es the amount of cement into the soil.
Whenever the construction methodology adopted forthe execution
is the indicated in this paper, the delaybetween mixing and
compaction of the specimens iscommon practice in laboratories in
order to adjustsample conditions to the real compaction in
thework.It was also introduced the alternative to cure thespecimens
at a higher temperature than standard 50
degrees Celsius during 48 hours to control the mix-ture in order
to verify the correct execution of layersin a reasonable time
according to work deadlines.The temperature acts as a catalyst
accelerating thehydration of cement in a direct analogy with
thesteam-cured concrete, a technology that is used whentrying to
obtain mechanical strength at early ages.The compression strength
both for the bank, the sub-base coating and the coating should be
betweenshoulders 18 and 25 kg/cm2.Another condition of approval of
the layers is com-paction which has been one of the most discussed.
In
accordance with the Particular Specification of theWork the
finished layer must be inspected compar-ing the result of
compaction control test by the sandmethod according to standard VN
- E8 - 66 Ref [2]with the obtained using the technique of
compactiontest of soil-cement mixtures and soil-lime VN - E19- 66
Ref [2]. The last one was performed on a mixedspecimen obtained in
the road prior to compaction,but using the compaction energy
corresponding toeach layer as set out in the PETG Ref. [1].
Thiscombination of standards specifications for the com-
paction test required taking an approach during
thework.According to the test VN- E19 66, specific com-paction
energy of 6.05 kg cm/cm3 should be appliedto the specimen, which
coincides with the lowest testspecified in VN E5 - 93, Type I Ref
[2]. That ener-gy depends on soil classification to be used in
theformation of the embankment or coatings, in accord-ance with the
PETG. The identification of soil test-ing is done according to the
grain size distributionVN - E1 - 65, Liquid limit VN - E2 - 65,
Plastic lim-it, Plasticity index VN - E3 - 65, Soil
classification
VN- E4 - 84 Ref. [2]. As stated above, these
physicalcharacterizations are not applied to soil with
cement.Beyond that if we take as a starting point that A4type soils
treated with cement to improve them areused, we can speculate about
obtaining a higher orequal quality, A4, A3, A2 or A1. For these
types ofsoil compaction test correspond the VN E5 - 93Type II or V,
both specific energy of 27.3 kgcm/cm3 compaction, the maxims
contained therein.Given this uncertainty and following the
technicaland economic criteria to reduce the compaction en-
ergy applied, that supported the use of cement treat-ed soil,
energy compaction test adopted was VN E5 - 93 of 6.05 kg cm/cm3 .In
order to improve the slenderness of the specimenfor the simple
compression test, the using of speci-
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mens of greater height and larger diameter was pro-posed in the
particular specifications of the work. Toachieve this, larger molds
to setting the standard andalternative methods of compaction of the
specimenswere indicated to keep the specific energy of com-paction.
On one hand the increased number of layersand another ram using a
drop of greater height andweight.
TEST MOLD
Noflayers
RamWeight(kg)
LayerHeight
(cm)
Nofhits
Compaction
Energy
(kgcm/cm
3)
VN-E5-93
AASTHO
(cm)
H
(cm)
I T 99 10.2 11.7 3 2.5 3.89 25 6.05
V T 180 15.2 11.7 5 4.5 2.33 56 27.25
Alternative proposal
I T 99 15.2 17.8 5 2.5 3.56 52 6.11
V T 180 15.2 17.8 5 4.5 3.56 86 27.45
Table 1. Alternative proposal modified compaction test.
Both proposed techniques were tested and discardedbecause we
found no consistent results regarding thedensity achieved compared
with specimens testedaccording to National Highway standards. In
general,the density at optimum moisture content was higherin the
range 3% - 7%. Without further analysis, tointroduce variations of
this type should take into ac-
count not only energy but also compaction specificbulbs caused
by ram pressure and the thickness ofthe layers, but this was not
the case.For coatings and the 0.30m at the top of the em-bankment
was required to reach 100% of the densityobtained in this test, and
for the 0.30m below theembankment above 95%.As regards the
implementation, it was establishedthat the mixing of the materials
should not exceed2.5 hours from the time the water either for
irrigationor contained in the soil, contact with cement. In
turn,the distribution and compaction process should not
exceed a period of 6 hours.For soil stabilization with cement is
generally re-quired that the latter term is less than 3 hours.
Thereason of this is both to maximize the binding powerof the first
products generated by cement hydrationand to avoid the negative
consequences of fragmen-tation phenomenon beginning in the
compactionprocess.In the present work this matter was not neglected
butwas given a minor importance allowing longerterms, as not
intended to substantially increase the
bearing capacity of the layer.
4 DOSAGE
For the different layers the dosage used were thesame as those
obtained as a result of a series of de-posits of soil and
laboratory tests.Field studies showed that two sites had adequate
andsimilar technical characteristics, operating powerand convenient
transport distance to the section.
Both showed a mantle composed of soil exploitableA4, composed
mainly of silt, moderate or smallamount of coarse material and only
small amount ofclay. The prevalence of silt makes it require
lessamount of cement due to the smaller surface areacompared to the
clays, and the presence of the latter,although to a lesser extent,
gives you extra cementlong term because of their long-term
reactions to hy-droxides binder.Once the type of soil to use was
set, we began withthe laboratory research stage to determine
theamount of cement that meets the requirements of the
Technical Specifications of the Contract.To this end, the
compaction test was performed withdifferent contents of cement,
2.5%, 3%, 3.5% and4%. Based on this, series of 6 specimen each
weremolded, with such content of cement and compac-tion optimum
moisture. From each set of samples, 3samples were cured for 21 days
at 20 degrees Celsi-us and the remaining 3 for 48 hours at 50
degreesCelsius.The results obtained using both types of
curingshowed little dispersion, although in all cases
showed that the average compressive strength result-ing from
accelerated curing was lower for all the dif-ferent cement
contents.It was also found that the compressive strength re-quired,
among 18 to 25 kg/cm2, is achieved withless than 3% cement, which
is why the expected costin the item has not been changed.As an
extra information, we also performed test onsoil-cement mixtures of
durability by wetting (VN -E21 66) and durability by freezing and
thawing(VN - E22 66).As expected, results were above the specified
limits
of 10% loss for soils A-4 treated with cement set bythe General
Specifications Technical Specifications(1998) of Vialidad Nacional
(VN).The levels needed to achieve favorable results in thistest,
according to the experience of VN and the lit-erature, are in a
range from 7% to 12%. The percent-age of cement used is
significantly below that range.
5 CONSTRUCTION METHODOLOGY
Although the methodology employed is very tradi-tional, today is
being replaced by mixing plants thatensure quality and reduced lead
times.Nevertheless, the technology adopted for this workwas adapted
properly to the generous period of 6
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difficult to repeat every day. This directly affects thequality
of the mix and it is reflected in the results.After the work was
finished, which happened onJune 2007, auscultation was performed at
open skyor pit in shoulder during the month of December ofthat year
in order to verify the presence of water inthe core landfill due to
the phenomenon of capillaryrise. By that time the lake level
remained similar to
that which led to the interruption of National RoadNo. 7.
Moisture percentages were found rangingfrom 23.5% to a depth of
0.60m at 26% to 1.3m. Inaddition to these values indicating that no
saturationof pores occurred, there were no visual symptomsthat
demonstrated embedding.We also performed a new visit to the site in
January2010 to make an expeditious visual assessment inwhich we
have not detected longitudinal corruga-tions, rutting significant
-less than 3mm-, pavementcracks or defects in the shoulders, that
suggested abad response of the layers studied in this work.
7 CONCLUSION
The experience developed with cement treated soil issuccessful
and valuable. On the one hand by the re-sults obtained, which had
their difficulties during thework but were within the expected and
reasonable,supported it by the current performance of the work.On
the other hand it represented a complete successfrom the
technological innovation point of view.
While we should not ignore that this is a techniquewhich derives
from other soil stabilization with ce-ment, which has significant
experience and devel-opment not only scientifically but also
technological-ly, it has served as direct input for sustaining
thework performed.The future also will have a bench-scale testing
thathas already borne fruit and will continue throughoutlife. This
is of particular importance in overall de-velopment of new
research.
Figure 6. View of the completed road. Vialidad Nacional of
Argentine. National Route No 7.
8 REFERENCES
[1] Direccin Nacional de Vialidad, 1998. Pliegode
Especificaciones Tcnicas Generales. Publicacin101/102.[2] Direccin
Nacional de Vialidad. Normas de En-sayo.
