Corrosion control in underground concrete structures using double waterproofingshield system

9 Pages·2.748 MB·English

by  Ghafar Nima.

InternationalJournalofMiningScienceandTechnology23(2013)603–611
ContentslistsavailableatSciVerseScienceDirect
International Journal of Mining Science and Technology
journal homepage: www.elsevier.com/locate/ijmst
Corrosion control in underground concrete structures using double
waterproofing shield system (DWS)
⇑
Nima Ghafari
MapuaInstituteofTechnology,SchoolofCivil,EnvironmentalandGeologicalEngineering,Intramuros,Manila1002,Philippines
a r t i c l e i n f o a b s t r a c t
Articlehistory: Highlevelofstructuralandwaterproofingstabilityleadstolong-termservicelifeinundergroundinfra-
Received12November2012 structures. Interaction between aggressive groundwater with tunnel causes corrosion and damage in
Receivedinrevisedform12December2012 concretestructureduetosteelreinforcementcorrosionandconcretecracks.Thisstudyintroducesadou-
Accepted13January2013
blewaterproofingshieldsystem(DWS)asaninnovativesolutiontowaterproofingandstructuralfailures
Availableonline2August2013
inundergroundconcretestructures.Inthismethod,ordinaryshotcretemixturereplacesbyanorganic
polymerconcrete(OPC)toconstructawater-resistanttemporarysupportrightaftereachpartialexcava-
Keywords:
tion.TwogroupsofspecimensincludingreferenceconcreteandOPCspecimenswereprovidedandtested
Corrosion
inaccordancewithASTMC642.Waterproofingparametersincludingporosity,porevolume,permeabil-
Finalliningstructure
ityandhydraulicconductivityhavebeendetermined.Resultsshowaremarkablereductioninmentioned
Organicpolymerconcrete(OPC)
Undergroundconcretestructure parameters forOPCcomparedwithordinaryconcrete.Improvement inwaterproofingperformance of
Waterproofingshield temporarysupportcorrespondstoahealthyfinalliningandincreaseinservicelifeofthestructure.
Water-resistanttemporarysupport (cid:2)2013PublishedbyElsevierB.V.onbehalfofChinaUniversityofMining&Technology.
1.Introduction However,thegroundconditionssuchassoiltype,soilstructure
andsoiltexturearenotusuallythesameindifferentregions,pres-
Constructionoftunnelsandundergroundspaceshasanoldhis- enceofcorrosivematerialsinundergroundsoilisacommonfactor
toryparticularlyinEuropeancountries.BasilicaCisterninIstanbul, inallregionsaroundtheworld.Differenttypesofaggressivesoils
constructedinthe6thcenturybytheRomans,orthetunnelwhich canbecategorizedintoacidicsoil,basicsoil,acidsulfatesoiland
was recently discovered at the archaeological site of Bertseko in alsothesoilswhichcontainoneormoreofheavymetalssuchas
Lavrion, Greece, during archaeological excavations are just two ironandaluminum.Whilegroundwaterinfiltratethroughthesoil
examplesofexistingancienttunnelsinEurope[1,2]. these corrosive materials dissolve in the water. Transmission of
FromopeningofthefirstundergroundrailwaysysteminLon- corrosive materials by groundwater to underground tunnel lead
don(1863)untilthepresenttime,undergroundtransportationsys- tocontactandchemicalinteractionsbetweenthesematerialswith
temhasbeenoneofthebestsolutionsforcontrolandreductionof structuralandwaterproofingcomponentsofthetunnelincluding
urban traffic and air pollution in most of the crowded cities in tunnel’s temporary support (shotcreted structure), waterproofing
America,EuropeandAsia.Duetothenatureofundergroundcon- membrane and final lining (final reinforced concrete structure),
structions,thesereinforcedconcretestructuresareverytime-con- respectively.
sumingandexpensivetobuildand therefore,expectedtohavea Acidic/basic conditions of the soil depend on the soil pH. In-
long-termservicelife.Ontheotherhand,asoneofthemostessen- creaseinacidityoftheenvironmentinvicinityoftunnel(decreas-
tialurbaninfrastructurestheycannotbecomeoutofservice,even ing pH) increasingly corrode metal and concrete in underground
temporarily, for maintenance or repair purposes. For instance, a structures,andalsogenerateincreasingamountsofsolublealumi-
forcedtemporarysuspensioninLondon,ParisorAmsterdammetro numandiron[3,4].
operations can immediately freeze the public transportation sys- Itisknownthatthechloridecorrosionofrebarinunderground
tem in these large cities. Hence, to build underground concrete reinforcedconcretestructuresisoneofthemajorproblemspartic-
structureswithalong-termservicelifeandthelowestleveloffail- ularly in cold regions where salt is applied to roads for de-icing.
ures,adequateconsiderationsshouldbetakenintodesignandcon- One of the most important issues in the corrosion of reinforced
structionoftheseexpensiveinfrastructuresfromthefirststagesof steel is the ingress of chloride ion into concrete. However, rein-
theproject. forcedsteelembeddedinhydratingcementpasteformsathinpas-
sive film around the embedded steel that tightly adheres to the
⇑ steelandgivesitcompleteprotectionfromreactionwithoxygen
Tel.:[phone].
andwater,unfortunatelythechlorideioncandestroythepassive
E-mailaddress:[email protected]
2095-2686/$-seefrontmatter(cid:2)2013PublishedbyElsevierB.V.onbehalfofChinaUniversityofMining&Technology.
http://dx.doi.org/10.1016/j.ijmst.2013.07.021
604 N.Ghafari/InternationalJournalofMiningScienceandTechnology23(2013)603–611
filmandinitiatethecorrosionofreinforcedsteelbar.Furthermore, Inmethodologysectionofthisstudy,OPCspecimenshavebeen
concretestructuresareperiodicallyinspectedinordertomonitor provided and tested to investigate the effects of organic polymer
possibledamagecausedbychlorideinducedcorrosionoftherein- onwaterproofingfeaturesofhardenedconcretestructures.
forcementbuttheavailabledrillingandvisualinspectionsdonot Providing a practical solution to penetration of aggressive
supplysufficientspatialinformationorcanonlybeassessedinad- groundwater through underground concrete structures leads to
vancedstagesofcorrosion,respectively[5–7]. corrosion control and as a result, increase in service life of these
valuableinfrastructures.
2.Doublewaterproofingshieldsystem
3.Materialselectionandpreparation
In this paper, double waterproofing shield system (DWS) has
been introduced as a new construction method for execution of Concrete mixture materials and admixture have been se-
tunnel temporary support that leads to improvement in water- lected and prepared in accordance with ASTM standard specifi-
proofing stability of underground reinforced concrete structures. cations including ASTM C 150 for portland cement, ASTM C 33
DWS constructionmethod employs an organic polymer modified for fine and coarse aggregates, ASTM C 1602 for water and
concretemixturewhichsprayontofreshlyexcavatedwallsusing ASTM C 1141 and ASTM C 1438 for organic polymer as the
shotcrete operation to build up a water-resistant temporary only concrete admixture used in the experimental part of this
structure right after each partial excavation. At the next step, study [8–12]. According to the mentioned ASTM specifications
main waterproofing membrane and final lining will be executed portland cement type 1P, potable water, sand with passing
respectivelytocompletetheDWSsystem.Acomparisonbetween sieve number of 12 (X61.70mm) and a typical cement based
the DWS and current underground construction methods (tradi- organic polymer as waterproofing admixture were provided
tionalmethods)hasbeenillustratedinFig.1.InFig.1a,different and stored in a dry and suitable place in laboratory environ-
parts of an underground concrete structure including temporary ment before beginning of specimen preparation and concrete
support, waterproofing membrane and final concrete structure test.
(finallining)havebeenillustratedas wellastheexisting aggres-
sive soil. Fig. 1b shows infiltration of water through the soil that 4.Specimenpreparation
leads to dissolution of corrosive materials in the water. Also, in
Fig. 1b, the penetrations of corrosive water through the tradi- Formulation and selection of concrete mixture proportions
tionaltemporarysupport,waterproofingmembraneandfinallin- includingratiosofportlandcement,sand,water,andorganicpoly-
ing have been illustrated, respectively. Fig. 1c shows the merareestablishedinaccordancewithASTMC1438,ASTMC1439
mechanism of the DWS. andACI506.5R[13,14](Table1).
As shown, in DWS waterproofing method, the water-resistant Table 1, presents concrete mixture proportioning to shows
temporary support constructed by organic polymer concrete the amounts and ratios of mixture materials including: portland
(OPC) acts as a primary barrier to reduce the water seepage. cement, dry sand with passing sieve number of 12 (X6
Decrease in water penetration through the temporary support 1.70mm), potable water and organic polymer (component
corresponds to decrease inflow of corrosive water into very A+componentB) aswellas thewater–cementitiousmaterialra-
close vicinity of waterproofing membrane and final concrete tio(w/cm).MoreoverinTable1,water–cementitiousmaterialra-
structure. tio (w/cm) shows the ratio of the mass of water, excluding that
Executionoftemporarystructureisoneofthemainandindis- absorbed by the aggregate, to the mass of cementitious material
pensablepartsofundergroundconstructionmethods(exceptcut- in mixturesincludingthe mass of Portlandcementand themass
and-cover tunneling method) to support the freshly excavated of component B of organic polymer which is a cement based
wallsagainstfallingofanydebrisandreducetheriskofsettlement material.
beforeexecutionoftunnelfinallining.Hence,inDWSsystem,the Thecoverageratiooforganicpolymerrecommendedbymanu-
water-resistant temporary support will be constructed without facturer for an average coating thickness of 8.5mm is approxi-
any additional shotcrete operation costs (equipments, energy, la- mately 1.07 (107%) by mass of the concrete mixture
bors, etc.), and this is exactly one of the main advantages of this (cement+sand+water).Hence,inproductionofconcretemixture
proposedwaterproofingsystem. used for shotcrete of underground temporary support with an
Street level Street level Street level
Surface water Surface water Surface water
Surface soil Water Water
infiltration infiltration
Material Material
Heavy metals, absorption absorption
sulfates, etc
Contact Contact
Water
Temporary penetration Reduction in
support Corrosion & water penetration
damage of
waterproofing
Waterproofing membrane OPC
membrane Water Healthy
penetration waterproofing
membrane
Final lining Cdaomrraogseio onf &fi nal Healthy final
lining lining
(a) Locations of the existing corrosive soil, (b) Infiltration of water through the soil, (c) Mechanism of the double waterproofing
temporary support, waterproofing membrane traditional temporary support, waterproofing shield system (DWS)
and final concrete structure (final lining) membrane and final lining
Fig.1. ComparisonbetweentheDWSandcurrentundergroundconstructionmethods.
N.Ghafari/InternationalJournalofMiningScienceandTechnology23(2013)603–611 605
Table1
Concretemixtureproportioningtableshowstheamountsandratiosofmixturematerials.
No. Organicpolymer(g) Portlandcement(g) Sand(g) Water(g) w/cm
S1 0(0%) 460(24.08%) 1265(66.23%) 185(66.23%) 0.40
S2 19.15(1%) 460(23.78%) 1265(65.40%) 190(65.40%) 0.40
S3 38.4(2%) 460(23.49%) 1265(64.59%) 195(64.59%) 0.40
S4 57.9(3%) 460(23.14%) 1265(63.63%) 205(63.63%) 0.40
S5 77.4(4%) 460(22.86%) 1265(62.86%) 210(62.86%) 0.40
S6 97(5%) 460(22.58%) 1265(62.10%) 215(62.10%) 0.40
S7 117(6%) 460(22.25%) 1265(61.20%) 225(61.20%) 0.40
S8 136.85(7%) 460(21.99%) 1265(60.47%) 230(60.47%) 0.40
S9 156.8(8%) 460(21.73%) 1265(59.76%) 235(59.76%) 0.40
S10 177.3(9%) 460(21.42%) 1265(58.91%) 245(58.91%) 0.40
S11 197.5(10%) 460(21.17%) 1265(58.23%) 250(58.23%) 0.40
S12 218.35(11%) 460(20.88%) 1265(57.41%) 260(57.41%) 0.40
S13 238.8(12%) 460(20.64%) 1265(56.76%) 265(56.76%) 0.40
S14 259.35(13%) 460(20.40%) 1265(56.11%) 270(56.11%) 0.40
S15 280.7(14%) 460(20.13%) 1265(55.34%) 280(55.34%) 40%
S16 301.5(15%) 460(19.90%) 1265(54.73%) 285(54.73%) 40%
Note:w/cmisthewater–cementitiousmaterialratio,calculatedbydividingthemassofwater,excludingthatabsorbedbytheaggregate,tothemassofcementitiousmaterial
includingthemassofportlandcementandthemassofcomponentBoforganicpolymer.
(a) Organic polymer admixture preparation (b) Organic polymer concrete preparation.
Fig.2. Admixturepreparationandadmixingprocess.
approximatecoatingthicknessof100mm,thecoverageratioofor- able pore space (pore volume) in a hardened concrete specimen
ganicpolymerwillbe9.1%. bydeterminingthehardenedconcrete’sdensityindifferentstates
Inthisstudy,theamountsoforganicpolymerusedintestcon- ofovendried,saturated,andsaturated-boiled.
cretespecimenpreparationweredesignedtocoverallpointsbe- Conducting ASTM C 642 which recommended by National
low and above 9.1% to determine the best ratio of organic Concrete Pavement Technology Center at Iowa State University
polymerforthicknessof100mm,practically.Fig.2showsadmix- following by required calculations lead to estimation of poros-
ture preparation and admixing process including weighting and ity (n) and pore volume (V ) for concrete specimens [18]
P
mixingpartA(form:liquid;color:white)andpartB(form:pow- (Fig. 4).
der; color:gray) to achieveauniformcementbased two compo-
nent organic polymer admixture (A:B=1:6) (Fig. 2a). The
5.1.Determinationofoven-drymass
prepared admixture was then added to concrete mixture to pro-
duceauniformOPC(Fig.2b).
After the first mass determination by a digital scale, all 28-
A number of three cylindrical specimens (5cm diame-
day specimens were placed in the electrical oven with tempera-
ter(cid:2)10cmheight)withthevolumeof196.25cm3wereproduced
tureof105(cid:3)Cforovendryingprocessfor24h(Fig.5a).Afterthe
fromeachsixteenbatchesofconcretemixtureinaccordancewith
first 24h, oven dried specimens were removed from the oven
ASTM 192 [15]. Therefore, total number of 48 specimens in 16
and they were allowed to cool in room temperature of 25(cid:3)C.
batchesincluding3specimensformonebatchofordinary(refer-
Then the mass of each specimen was determined and recorded
ence)concreteand45specimensfrom15batchesofOPCwithvar-
(Fig.5b).Therecordedmassofspecimensshowedtheywerestill
iable amounts of admixture were provided in laboratory
wet and need redrying because the differential in the deter-
environment.
mined mass was more than 0.5% of the lesser value. Therefore
Production of cylindrical concretespecimens including:mold-
the specimens were returned to the oven for an additional
ing, curing and specimen removal from the mold (Fig. 3) carried
24h drying.
out in accordance with ASTM C 642, ASTM C 192, and ASTM C
After the second 24h, oven dried specimens were removed
470[15–17].
fromtheovenandtheywereallowedtocoolindryairtoatemper-
ature of 25(cid:3)C. Then the mass of each specimen was determined
5.Concretetest(ASTMC642) and recorded. This time the differential in the determined mass
wasnotexceeding0.5%ofthelesservalue.Hence,thislastvalue
ASTMC642,thestandardtestmethodfordensity,absorption, was designated as ‘‘A’’ and the specimens were getting ready for
and voids in hardened concrete, estimates the volume of perme- thenextstepoftheconcretetest.
606 N.Ghafari/InternationalJournalofMiningScienceandTechnology23(2013)603–611
(a) Mold greasing and preparation (b) Concrete placing in cylindrical (c) Specimen removal from the mold
molds after 28 days curing period
Fig.3. Productionofcylindricalconcretespecimens.
was determined and recorded. The recorded mass of specimens
Start showed that, this time the increase in the determined mass was
notexceeding0.5%ofthelargervalue.Hence,thislastvaluewas
Concrete specimen preparation designated as ‘‘B’’ and the specimens were getting ready for the
nextstepoftheconcretetest.
Oven-drying the specimens
5.3.Determinationofsaturatedmassafterboiling
Specimen removal from oven and mass determination
After the last immersion, surface drying and mass determina-
If X 0.5% If X 0.5%
tion,thespecimenswereboiledusingboilingapparatus.Theboil-
ing apparatus was composed of a metal water container and an
Determined mass=A
electricalstove. All specimens placedin thecontainer and boiled
for5h(Fig.7).
Immersing the specimens
After 5h, boiled specimens were removed from the boiling
Specimen removal from water and mass determination apparatus and allowed to cool by natural loss of heat for 18h.
The surface moisture was removed and mass of each specimen
wasdetermined.ThisdeterminedmassdesignatedC.
If X 0.5% If X 0.5%
Determined mass=B
5.4.Determinationofimmersedapparentmass
Determination of saturated mass after boiling
After immersion and boiling, specimens were suspended in
(determined mass=C)
waterusingasuitablewiretodeterminetheapparentmassofeach
specimen.Toachievetheadequatevaluesofapparentmassespe-
Determination of apparent mass during
suspension in the water (determined mass=D) cial technique described below was used in this part of concrete
test. First a small deep bowl filled with tap water and placed on
Calculations the electronic scale and the scale was set on the zero. Then one
by one the specimens suspended in the water by a wire and
End weightswererecordedanddesignatedas‘‘W’’(Fig.8).
Eq.(1a)belowhasbeenusedtodeterminetheapparentmassfor
Fig. 4. Diagram shows the concrete test ASTM C 642 processes from specimen eachspecimen.
preparationtofinalcalculations.
D¼C(cid:3)W ð1aÞ
5.2.Determinationofsaturatedmassafterimmersion
whereDistheapparentmassofsampleinwaterafterimmersion
Inthispartofthetest,allspecimenswereimmersedinpotable
andboiling;Ctherecordedweightofeachspecimenafterboiling;
wateratapproximately21(cid:3)Cfor48h(Fig.6).
andWtherecordedweightduringsuspensionofspecimensinthe
The temperature of water measured before beginning of
water.For example for specimen number 1-1 (S ) Eq.(1a) can be
1-1
immersionusingasuitablethermometer.Afterthefirst48h,im-
writteninformofEq.(1b).
mersed specimens were removed from the container and then
the mass of each specimen was determined and recorded. The D ¼C (cid:3)W ð1bÞ
1(cid:3)1 1(cid:3)1 1(cid:3)1
specimens were placed in the water container for immersion for
an additional 24h to become fully saturated. After 24h (totally where D is the apparent mass of S in water after immersion
1-1 1-1
72h), immersed specimens were removed from the container and boiling; C the recorded weight of S after boiling; W
1-1 1-1 1-1
andafterdryingthesurfacebyatowel,themassofeachspecimen therecordedweightduringsuspensionofS inthewater.
1-1
N.Ghafari/InternationalJournalofMiningScienceandTechnology23(2013)603–611 607
(a) Oven-drying of specimens using an electrical oven in (b) Prior to and after each oven-drying process, mass of
temperature of 105 for 48 hours specimens were determining by a digital scale and recording
Fig.5. Oven-dryingofspecimensandmassofspecimensweredeterminingandrecording.
inairafterimmersion;Cthemassofsurface-drysampleinairafter
immersion and boiling; D the apparent mass of sample in water
afterimmersionandboiling;g thebulkdensity,dry;g theappar-
1 2
entdensity;andqthedensityofthefluid.Since,inthistestwater
hasbeenusedasthefluid,thereforethevalueofqhereisequalto
1Mg/m3 or 1g/cm3. Note that, in these calculations the units of
‘‘mass’’and‘‘density’’areingram(g)andMg/m3,respectively.
6.2.Calculationofvolumeofpermeableporespace(V )
P
Thetotalvolumeofeachcylindricalconcretespecimenaswell
as the volume of permeable pore space can be calculated from
porosityusingEqs.(9)–(11).
V ¼pr2(cid:2)h¼p(cid:2)2:52(cid:2)10¼196:25 ð9Þ
Fig.6. Specimenswereimmersedinpotablewateratapproximately21(cid:3)Cfor72h. T
V ¼n(cid:2)V ð10Þ
P T
6.Calculations
V ¼n(cid:2)196:25 ð11Þ
P
6.1.Calculationofporosity(n)
whereV isthetotalvolumeofconcretespecimen,cm3;V thevol-
T P
umeofpermeableporespaceofeachspecimen,cm3;pr2theareaof
BelowaretheEqs.(2–8)thathavebeenusedincalculationsof
crosssectionofspecimen;andhtheheightofeachspecimen.
the concrete test to determine the porosity and pore volume of
concretespecimens[10].Completedetailsontheresultsofthese
calculationsareprovidedintheformoftablesandchartsin‘‘Sec- 6.3.Calculationofpermeability(k)
tion7’’ofthisstudy(chapter7).
Todeterminethepermeability(k)ofconcretefromtheporosity
A ¼½ðB(cid:3)AÞ=A(cid:4)(cid:2)100 ð2Þ
i (n)percentagesachievedintheconcretetest,arelationshipneeded
tobefoundbetweenpermeabilityandporosityinordertowritean
A ¼½ðC(cid:3)DÞ=A(cid:4)(cid:2)100 ð3Þ
ib equationbetweenthesetwoparameters.
Eq.(12) below recommended by Bourbie and Zinsner in 1985,
qb¼½A=ðC(cid:3)DÞ(cid:4):q¼g1 ð4Þ shows this relationship between porosity and permeability and
hasbeenusedtoevaluatetherateofpermeabilityofconcretespec-
qbi¼½B=ðC(cid:3)DÞ(cid:4):q ð5Þ imens[19]:
q ¼½C=ðC(cid:3)DÞ(cid:4):q ð6Þ k¼303ð100nÞ3:05ðnmÞ2ðforn>0:08Þ ð12Þ
bib
wherekisthepermeabilityandntheporosityofconcrete.
q ¼½A=ðA(cid:3)DÞ(cid:4):q¼g ð7Þ
a 2
6.4.Calculationofhydraulicconductivity(K)
n¼½ðg (cid:3)g Þ=g (cid:4)(cid:2)100 ð8aÞ
2 1 2
Since one of the most important parameters used to quantify
Or:n¼½ðC(cid:3)AÞ=ðC(cid:3)DÞ(cid:4)(cid:2)100 ð8bÞ
water seepage is hydraulic conductivity; hence, after determina-
whereA istheabsorptionafterimmersion;A theabsorptionafter tion of permeability, the next step was to determine the rate of
i ib
immersionandboiling;q thebulkdensity,dry;q thebulkdensity water transmissivity in ordinary and acrylic polymer concrete to
b bi
afterimmersion;q thebulkdensityafterimmersionandboiling; demonstrate the positive effects of organic polymer admixture
bib
q theapparentdensity;ntheporosity(percentageofvoids);Athe on reduction of hydraulic conductivity of tunnel temporary sup-
a
massofoven-driedsampleinair;Bthemassofsurface-drysample port[20].
608 N.Ghafari/InternationalJournalofMiningScienceandTechnology23(2013)603–611
Eqs.(13) and (14) below recommended by Garboczi in 1990, K¼k(cid:2)107 ð14Þ
showtherelationbetweenpermeability(k)andhydraulicconduc-
tivity(K)ofconcrete[21]. whereKisthehydraulicconductivity,m/sandkthepermeabilityof
concretespecimen.
K¼kðqg=lÞ ð13Þ
where K is the hydraulic conductivity, m/s; k the permeability; q 7.Resultsanddiscussion
thedensityofthefluid;gtheaccelerationduetogravity;lthedy-
namicviscosityofthefluid.Forwaterflowingthroughtheporesys- A summary of recorded values during concrete test including
tem,Eq.(14)canbesimplifiedas: determined mass of specimens in four different states (A, B, C
Fig.7. Specimenswereplacedinasteelcontaineraboveanelectricalstovetoboilfor5h.
Fig.8. Specimensweresuspendedinthewaterusingasuitablewireandadeepbowlfilledbytapewatertodeterminetheimmersedapparentmassforeachspecimen.
Table2
Valuesofmassofspecimensindifferentstatesduringconcretetestandcalculatedvaluesforabsorptionsanddensities,leadtocalculationofporosity(n)ofconcretespecimens.
No. A(g) B(g) C(g) D(g) Ai Aib qb qbi qbib qa n(%)
S1 406.74 448.97 437.19 224.34 10.38 7.49 1.91 2.11 2.05 2.23 14.31
S2 407.67 448.61 437.20 224.35 10.04 7.24 1.92 2.11 2.05 2.22 13.87
S3 409.01 448.11 437.22 224.35 9.56 6.90 1.92 2.11 2.05 2.21 13.25
S4 410.28 447.70 437.28 224.39 9.12 6.58 1.93 2.10 2.05 2.21 12.68
S5 411.38 447.35 437.34 224.43 8.74 6.31 1.93 2.10 2.05 2.20 12.19
S6 412.40 447.08 437.42 224.48 8.41 6.07 1.94 2.10 2.05 2.19 11.75
S7 413.43 446.82 437.52 224.54 8.08 5.83 1.94 2.10 2.05 2.19 11.31
S8 414.35 446.64 437.66 224.63 7.79 5.63 1.95 2.10 2.05 2.18 10.94
S9 415.15 446.49 437.78 224.71 7.55 5.45 1.95 2.10 2.05 2.18 10.62
S10 415.97 446.30 437.88 224.77 7.29 5.27 1.95 2.09 2.05 2.18 10.28
S11 416.72 446.15 437.98 224.83 7.06 5.10 1.96 2.09 2.05 2.17 9.97
S12 417.17 446.03 438.02 224.86 6.92 5.00 1.96 2.09 2.05 2.17 9.78
S13 417.39 446.01 438.07 224.89 6.86 4.95 1.96 2.09 2.05 2.17 9.70
S14 417.35 446.01 438.06 224.88 6.87 4.96 1.96 2.09 2.05 2.17 9.71
S15 417.31 446.00 438.04 224.87 6.88 4.97 1.96 2.09 2.05 2.17 9.72
S16 417.22 445.96 437.99 224.84 6.89 4.98 1.96 2.09 2.05 2.17 9.74
Note:Aisthemassofoven-driedsampleinair;Bthemassofsurface-drysampleinairafterimmersion;Cthemassofsurface-drysampleinairafterimmersionandboiling;D
theapparentmassofsampleinwaterafterimmersionandboiling;Aitheabsorptionafterimmersion;Aibtheabsorptionafterimmersionandboiling;qbthebulkdensity,dry;
qbithebulkdensityafterimmersion;qbibthebulkdensityafterimmersionandboiling;qatheapparentdensity;andntheporosity(percentageofvoids).
N.Ghafari/InternationalJournalofMiningScienceandTechnology23(2013)603–611 609
andD),aswellasthecalculatedvaluesforabsorptionafterimmer- oforganicpolymerconcretespecimenshavedemonstratedthepo-
sion(A),absorptionafterimmersionandboiling(A ),bulkdensity, sitiveeffectsofusingorganicpolymerasaconcreteadmixtureto
i ib
dry (q ), bulk density after immersion (q ), bulk density after improve waterproofing stability of underground concrete struc-
b bi
immersion and boiling (q ), apparent density (q ) and porosity tures. As shown in these charts the lowest values for the above
bib a
(n)arelistedinTable2. mentioned concrete waterproofing parameters (n, V , k, K) have
P
Also,asummaryofestimatedporevolume(V )andporosity(n) been achieved for S which was contained 12% organic polymer
P 13
as well as the calculated rates of permeability (k) and hydraulic admixture.
conductivity (K) for all sixteen series of specimens are provided ThemaximumreductionfromS whichwasthereferencecon-
1
andlistedinTable3. cretespecimenwith0%organicpolymertoS whichhasshown
13
Moreover,analysisofthementionedwaterproofingparameters the best waterproofing features, have been listed below in form
areillustratedintheformofchartsandpresentedinFig.9. ofEqs.(15)–(18).
Aspresented in Fig.9, considerablereductionsinporosity(n),
porevolume(VP),permeability(k)andhydraulicconductivity(K) Dnmax¼nðS1Þ(cid:3)nðS13Þ¼14:31%(cid:3)9:70¼4:61% ð15Þ
Table3
Alistofcalculatedporosity(n),volumeofpermeableporespace(Vp),permeability(k)andhydraulicconductivity(K)forallsixteenspecimensarestated.
No. Porosity(%) Porevolume(cm3) Permeability(10(cid:3)13m2) Hydraulicconductivity(lm/s)
S1 14.31 28.08 10.10 10.10
S2 13.87 27.22 9.22 9.22
S3 13.25 26.00 8.02 8.02
S4 12.68 24.88 7.01 7.01
S5 12.19 23.92 6.22 6.22
S6 11.75 23.06 5.56 5.56
S7 11.31 22.20 4.95 4.95
S8 10.94 21.47 4.47 4.47
S9 10.62 20.84 4.08 4.08
S10 10.28 20.17 3.70 3.70
S11 9.97 19.57 3.37 3.37
S12 9.78 19.19 3.18 3.18
S13 9.70 19.04 3.10 3.10
S14 9.71 19.06 3.11 3.11
S15 9.72 19.08 3.12 3.12
S16 9.74 19.11 3.14 3.14
16 30
14 %OP=12%
%OP=12% 25 Vp=19.04 m3
)%( ytisoroP1120864 n =9.70% 3)m( emulov eroP 121500
2 5
0 0
S1 S3 S5 SSp7ecimS9en S11 S13 S15 S1 S3 S5 SSp7ecimS9en S11 S13 S15
(a) Porosity (b) Volume of permeable pore space
1200 12
s) 1.01×10-5
1000 m/10
µ
)D ( y
m( ytilibaemreP 846000000 %kO =3P0=91.821% tivitcudnoc cilua 864 %K =O3P.1=×1120%-6 3.1×10-6
200 rd 2
y
H
0 0
S1 S3 S5 SSp7ecimS9en S11 S13 S15 S1 S3 S5 SS7peciSm9enS11 S13 S15
(c) Rate of permeability (d) Hydraulic conductivity of hardened concrete specimens from S1 to S16
Fig.9. Analysisofthementionedwaterproofingparameters.
610 N.Ghafari/InternationalJournalofMiningScienceandTechnology23(2013)603–611
DVPmax¼VPðS1Þ(cid:3)VðS13Þ¼28:08(cid:3)19:04¼9:05 ð16Þ DWSwaterproofingsystem,inthisstudy,bothtechnicalandeco-
nomicalfactorswereconsideredindeterminationofthebestratio
Dk ¼kðS Þ(cid:3)kðS Þ¼10:10(cid:2)10(cid:3)13(cid:3)3:10(cid:2)10(cid:3)13 oforganicpolymeradmixtureinshotcrete/concretemixture.
max 1 13
Therefore,specimennumber13(S )with12%organicpolymer
¼7:04(cid:2)10(cid:3)13 ð17Þ 13
is determined as the favorite concrete specimen since it possess
lowestporosity(n),porevolume(V ),permeability(k)andhydrau-
DKmax¼KðS1Þ(cid:3)KðS13Þ¼10:10(cid:2)10(cid:3)6(cid:3)3:10(cid:2)10(cid:3)6 licconductivity(K).NotethatdurinPgtheconcretetestandcalcula-
¼7:04(cid:2)10(cid:3)6 ð18Þ tions,highervaluesofmentionedparameters(n,VP,k,K)havebeen
recordedforS , S andS comparedwithS ,whiletheywere
14 15 16 13
where Dnmax is the maximum reduction of porosity; n(S1) the containedthehigherorganicpolymerratiosof13%,14%and15%,
porosityofspecimennumberone;n(S13)theporosityofspecimen respectively.
numberthirteen;DVPmaxthemaximumreductioninvolumeofper- Improvementinwaterproofingperformanceofconcretecorre-
meableporespace(porevolume);VP(S1)theporevolumeofspeci- spondstoimprovementinwaterproofingstabilityoftunnel’stem-
men number one; VP(S13) the pore volume of specimen number porary support and lead to construction of DWS by adding
thirteen;Dkmaxthemaximumreductionofpermeability;k(S1)the appropriateamountsoforganicpolymertoshotcretemixture.
permeability of specimen number one; k(S13) the permeability of Since,executionofundergroundtemporarysupportaftereach
specimen number thirteen; DKmax the maximum reduction of partialexcavationisanessentialandindispensablepartofunder-
hydraulic conductivity; K(S1) the hydraulic conductivity of speci- ground construction (except cut-and-cover tunneling method);
men number one; K(S13) the hydraulic conductivity of specimen therefore, a water-resistant temporary support could be con-
numberthirteen. structed without additional shotcrete operation costs including
equipments,energy,labors,etc.
7.1.Technical–economicalconsiderationsinDWSconstruction Constructionofa water-resistanttemporarystructure, instead
method of a traditional temporary support, could be a practical solution
to the flow of groundwater in the close vicinity of underground
Asdiscussedpreviouslyinabstractandintroductionofthispa- tunnels. This water-resistant temporary support can act as a pri-
per,undergroundconcretestructuresarethemostexpensivecon- mary waterproofing shield against infiltration of groundwater to
structionprojects.Hencethecostsoftheseprojectsarealwaysone control and decrease the volume of this aggressive water before
ofthemostimportantfactorsforbothownerand contractorand contact and chemical interaction with the main waterproofing
affecttheirdecisionsonmethodandmaterialselection.Thetotal membraneandfinalconcretestructureofthetunnel(finallining).
costofaconstructionprojectisacombinationofoperationalcosts Reductionincontactsandchemicalinteractionsbetweenexisting
andcostsofmaterials. corrosive materials in groundwater with tunnel’s main water-
Avoidingunnecessaryuseofmaterialssuchasconcreteadmix- proofingmembraneandfinalliningimprovesbothwaterproofing
turescorrespondstoreductioninthecostofmaterialsandthetotal and structural stability of tunnel by means of the prevention of
costofproject.Therefore,tobecomeclosertoapracticalmodelfor concretecracksandreinforcementcorrosions.
thewater-resistanttemporarystructureinproposedDWS,inthis
study, both technical and economical factors were considered in
9.Recommendation
determinationofthebestratiooforganicpolymertobeaddedto
shotcrete/concrete mixture. Hence, according to the final results,
Inthis study,organicpolymerhas beenused asthe onlycon-
specimennumber13(S )with12%organicpolymerisdetermined
13 crete admixture to improve the waterproofing features of hard-
asthefavoriteconcretespecimenasitpossesslowestporosity(n),
ened concrete specimens while, there are a large number of
porevolume(V ),permeability(k)andhydraulicconductivity(K).
P additiveswhichcanimprovetheundergroundreinforcedconcrete
Notethatduringtheconcretetestandcalculations,highervalues
structures.Therefore,furtherinvestigationsareneededtobecon-
ofmentionedparameters(n,V ,k,K)havebeenrecordedforspec-
P ductedtofindotherconcreteadmixtureswhichmayplayaposi-
imens number 14 to 16 (S , S , S ) while they were contained
14 15 16 tiveroleinwaterproofinganddurabilityimprovementsoftunnel
the higher organic polymer ratios of 13%, 14% and 15%,
temporarysupportandfinallining.
respectively.
Furthermore, construction of an underground temporary sup-
portaftereachpartialexcavationisanessentialandindispensable Acknowledgments
partofundergroundconstructionandtunneling(exceptcut-and-
coverconstructionmethod).Hence,addinganappropriateamount The author would like to acknowledge the financial support
oforganicpolymertoshotcretemixturecorrespondstoconstruc- providedbyhisfamilyduringthisstudy.
tion of a water-resistant temporary support without additional
shotcreteoperationcostsincludingequipments,energy,labors,etc. References
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