International Journal of Mining Science and Technology 23 (2013) 603–611

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International Journal of Mining Science and Technology

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Corrosion control in underground concrete structures using doublewaterproofing shield system (DWS)

2095-2686/$ - see front matter � 2013 Published by Elsevier B.V. on behalf of China University of Mining & Technology.http://dx.doi.org/10.1016/j.ijmst.2013.07.021

⇑ Tel.: +98 9121333954.E-mail address: nghafari@mymail.mapua.edu.ph

Nima Ghafari ⇑Mapua Institute of Technology, School of Civil, Environmental and Geological Engineering, Intramuros, Manila 1002, Philippines

a r t i c l e i n f o a b s t r a c t

Article history:Received 12 November 2012Received in revised form 12 December 2012Accepted 13 January 2013Available online 2 August 2013

Keywords:CorrosionFinal lining structureOrganic polymer concrete (OPC)Underground concrete structureWaterproofing shieldWater-resistant temporary support

High level of structural and waterproofing stability leads to long-term service life in underground infra-structures. Interaction between aggressive groundwater with tunnel causes corrosion and damage inconcrete structure due to steel reinforcement corrosion and concrete cracks. This study introduces a dou-ble waterproofing shield system (DWS) as an innovative solution to waterproofing and structural failuresin underground concrete structures. In this method, ordinary shotcrete mixture replaces by an organicpolymer concrete (OPC) to construct a water-resistant temporary support right after each partial excava-tion. Two groups of specimens including reference concrete and OPC specimens were provided and testedin accordance with ASTM C 642. Waterproofing parameters including porosity, pore volume, permeabil-ity and hydraulic conductivity have been determined. Results show a remarkable reduction in mentionedparameters for OPC compared with ordinary concrete. Improvement in waterproofing performance oftemporary support corresponds to a healthy final lining and increase in service life of the structure.

� 2013 Published by Elsevier B.V. on behalf of China University of Mining & Technology.

1. Introduction

Construction of tunnels and underground spaces has an old his-tory particularly in European countries. Basilica Cistern in Istanbul,constructed in the 6th century by the Romans, or the tunnel whichwas recently discovered at the archaeological site of Bertseko inLavrion, Greece, during archaeological excavations are just twoexamples of existing ancient tunnels in Europe [1,2].

From opening of the first underground railway system in Lon-don (1863) until the present time, underground transportation sys-tem has been one of the best solutions for control and reduction ofurban traffic and air pollution in most of the crowded cities inAmerica, Europe and Asia. Due to the nature of underground con-structions, these reinforced concrete structures are very time-con-suming and expensive to build and therefore, expected to have along-term service life. On the other hand, as one of the most essen-tial urban infrastructures they cannot become out of service, eventemporarily, for maintenance or repair purposes. For instance, aforced temporary suspension in London, Paris or Amsterdam metrooperations can immediately freeze the public transportation sys-tem in these large cities. Hence, to build underground concretestructures with a long-term service life and the lowest level of fail-ures, adequate considerations should be taken into design and con-struction of these expensive infrastructures from the first stages ofthe project.

However, the ground conditions such as soil type, soil structureand soil texture are not usually the same in different regions, pres-ence of corrosive materials in underground soil is a common factorin all regions around the world. Different types of aggressive soilscan be categorized into acidic soil, basic soil, acid sulfate soil andalso the soils which contain one or more of heavy metals such asiron and aluminum. While groundwater infiltrate through the soilthese corrosive materials dissolve in the water. Transmission ofcorrosive materials by groundwater to underground tunnel leadto contact and chemical interactions between these materials withstructural and waterproofing components of the tunnel includingtunnel’s temporary support (shotcreted structure), waterproofingmembrane and final lining (final reinforced concrete structure),respectively.

Acidic/basic conditions of the soil depend on the soil pH. In-crease in acidity of the environment in vicinity of tunnel (decreas-ing pH) increasingly corrode metal and concrete in undergroundstructures, and also generate increasing amounts of soluble alumi-num and iron [3,4].

It is known that the chloride corrosion of rebar in undergroundreinforced concrete structures is one of the major problems partic-ularly in cold regions where salt is applied to roads for de-icing.One of the most important issues in the corrosion of reinforcedsteel is the ingress of chloride ion into concrete. However, rein-forced steel embedded in hydrating cement paste forms a thin pas-sive film around the embedded steel that tightly adheres to thesteel and gives it complete protection from reaction with oxygenand water, unfortunately the chloride ion can destroy the passive

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film and initiate the corrosion of reinforced steel bar. Furthermore,concrete structures are periodically inspected in order to monitorpossible damage caused by chloride induced corrosion of the rein-forcement but the available drilling and visual inspections do notsupply sufficient spatial information or can only be assessed in ad-vanced stages of corrosion, respectively [5–7].

2. Double waterproofing shield system

In this paper, double waterproofing shield system (DWS) hasbeen introduced as a new construction method for execution oftunnel temporary support that leads to improvement in water-proofing stability of underground reinforced concrete structures.DWS construction method employs an organic polymer modifiedconcrete mixture which spray on to freshly excavated walls usingshotcrete operation to build up a water-resistant temporarystructure right after each partial excavation. At the next step,main waterproofing membrane and final lining will be executedrespectively to complete the DWS system. A comparison betweenthe DWS and current underground construction methods (tradi-tional methods) has been illustrated in Fig. 1. In Fig. 1a, differentparts of an underground concrete structure including temporarysupport, waterproofing membrane and final concrete structure(final lining) have been illustrated as well as the existing aggres-sive soil. Fig. 1b shows infiltration of water through the soil thatleads to dissolution of corrosive materials in the water. Also, inFig. 1b, the penetrations of corrosive water through the tradi-tional temporary support, waterproofing membrane and final lin-ing have been illustrated, respectively. Fig. 1c shows themechanism of the DWS.

As shown, in DWS waterproofing method, the water-resistanttemporary support constructed by organic polymer concrete(OPC) acts as a primary barrier to reduce the water seepage.Decrease in water penetration through the temporary supportcorresponds to decrease inflow of corrosive water into veryclose vicinity of waterproofing membrane and final concretestructure.

Execution of temporary structure is one of the main and indis-pensable parts of underground construction methods (except cut-and-cover tunneling method) to support the freshly excavatedwalls against falling of any debris and reduce the risk of settlementbefore execution of tunnel final lining. Hence, in DWS system, thewater-resistant temporary support will be constructed withoutany additional shotcrete operation costs (equipments, energy, la-bors, etc.), and this is exactly one of the main advantages of thisproposed waterproofing system.

Street level

Surface water

Waterproofing membrane

Heavy metals, sulfates, etc

Temporary support

Final lining

Surface soil

(a) Locations of the existing corrosive soil, temporary support, waterproofing membrane

and final concrete structure (final lining)

(b) Infiltration of wattraditional temporary su

membrane and

Fig. 1. Comparison between the DWS and cur

In methodology section of this study, OPC specimens have beenprovided and tested to investigate the effects of organic polymeron waterproofing features of hardened concrete structures.

Providing a practical solution to penetration of aggressivegroundwater through underground concrete structures leads tocorrosion control and as a result, increase in service life of thesevaluable infrastructures.

3. Material selection and preparation

Concrete mixture materials and admixture have been se-lected and prepared in accordance with ASTM standard specifi-cations including ASTM C 150 for portland cement, ASTM C 33for fine and coarse aggregates, ASTM C 1602 for water andASTM C 1141 and ASTM C 1438 for organic polymer as theonly concrete admixture used in the experimental part of thisstudy [8–12]. According to the mentioned ASTM specificationsportland cement type 1P, potable water, sand with passingsieve number of 12 (X 6 1.70 mm) and a typical cement basedorganic polymer as waterproofing admixture were providedand stored in a dry and suitable place in laboratory environ-ment before beginning of specimen preparation and concretetest.

4. Specimen preparation

Formulation and selection of concrete mixture proportionsincluding ratios of portland cement, sand, water, and organic poly-mer are established in accordance with ASTM C 1438, ASTM C 1439and ACI 506.5R [13,14] (Table 1).

Table 1, presents concrete mixture proportioning to showsthe amounts and ratios of mixture materials including: portlandcement, dry sand with passing sieve number of 12 (X 61.70 mm), potable water and organic polymer (componentA + component B) as well as the water–cementitious material ra-tio (w/cm). Moreover in Table 1, water–cementitious material ra-tio (w/cm) shows the ratio of the mass of water, excluding thatabsorbed by the aggregate, to the mass of cementitious materialin mixtures including the mass of Portland cement and the massof component B of organic polymer which is a cement basedmaterial.

The coverage ratio of organic polymer recommended by manu-facturer for an average coating thickness of 8.5 mm is approxi-mately 1.07 (107%) by mass of the concrete mixture(cement + sand + water). Hence, in production of concrete mixtureused for shotcrete of underground temporary support with an

Water infiltration

Material absorption

ContactWater penetration

Water penetration

Corrosion & damage of final lining

Corrosion & damage of waterproofing membrane

Street level

Surface water

Water infiltrationMaterial absorption

Contact

Reduction in water penetration

Healthy waterproofing membrane

Street level

Surface water

Healthy final lining

OPC

er through the soil, pport, waterproofing final lining

(c) Mechanism of the double waterproofing shield system (DWS)

rent underground construction methods.

Table 1Concrete mixture proportioning table shows the amounts and ratios of mixture materials.

No. Organic polymer (g) Portland cement (g) Sand (g) Water (g) w/cm

S1 0 (0%) 460 (24.08%) 1265 (66.23%) 185 (66.23%) 0.40S2 19.15 (1%) 460 (23.78%) 1265 (65.40%) 190 (65.40%) 0.40S3 38.4 (2%) 460 (23.49%) 1265 (64.59%) 195(64.59%) 0.40S4 57.9 (3%) 460 (23.14%) 1265 (63.63%) 205 (63.63%) 0.40S5 77.4 (4%) 460 (22.86%) 1265 (62.86%) 210 (62.86%) 0.40S6 97 (5%) 460 (22.58%) 1265 (62.10%) 215 (62.10%) 0.40S7 117 (6%) 460 (22.25%) 1265 (61.20%) 225 (61.20%) 0.40S8 136.85 (7%) 460 (21.99%) 1265 (60.47%) 230 (60.47%) 0.40S9 156.8 (8%) 460 (21.73%) 1265 (59.76%) 235 (59.76%) 0.40S10 177.3 (9%) 460 (21.42%) 1265 (58.91%) 245 (58.91%) 0.40S11 197.5 (10%) 460 (21.17%) 1265 (58.23%) 250 (58.23%) 0.40S12 218.35 (11%) 460 (20.88%) 1265 (57.41%) 260 (57.41%) 0.40S13 238.8 (12%) 460 (20.64%) 1265 (56.76%) 265 (56.76%) 0.40S14 259.35 (13%) 460 (20.40%) 1265 (56.11%) 270 (56.11%) 0.40S15 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/cm is the water–cementitious material ratio, calculated by dividing the mass of water, excluding that absorbed by the aggregate, to the mass of cementitious materialincluding the mass of portland cement and the mass of component B of organic polymer.

(a) Organic polymer admixture preparation (b) Organic polymer concrete preparation.

Fig. 2. Admixture preparation and admixing process.

N. Ghafari / International Journal of Mining Science and Technology 23 (2013) 603–611 605

approximate coating thickness of 100 mm, the coverage ratio of or-ganic polymer will be 9.1%.

In this study, the amounts of organic polymer used in test con-crete specimen preparation were designed to cover all points be-low and above 9.1% to determine the best ratio of organicpolymer for thickness of 100 mm, practically. Fig. 2 shows admix-ture preparation and admixing process including weighting andmixing part A (form: liquid; color: white) and part B (form: pow-der; color: gray) to achieve a uniform cement based two compo-nent organic polymer admixture (A:B = 1:6) (Fig. 2a). Theprepared admixture was then added to concrete mixture to pro-duce a uniform OPC (Fig. 2b).

A number of three cylindrical specimens (5 cm diame-ter � 10 cm height) with the volume of 196.25 cm3 were producedfrom each sixteen batches of concrete mixture in accordance withASTM 192 [15]. Therefore, total number of 48 specimens in 16batches including 3 specimens form one batch of ordinary (refer-ence) concrete and 45 specimens from 15 batches of OPC with var-iable amounts of admixture were provided in laboratoryenvironment.

Production of cylindrical concrete specimens including: mold-ing, curing and specimen removal from the mold (Fig. 3) carriedout in accordance with ASTM C 642, ASTM C 192, and ASTM C470 [15–17].

5. Concrete test (ASTM C 642)

ASTM C 642, the standard test method for density, absorption,and voids in hardened concrete, estimates the volume of perme-

able pore space (pore volume) in a hardened concrete specimenby determining the hardened concrete’s density in different statesof oven dried, saturated, and saturated-boiled.

Conducting ASTM C 642 which recommended by NationalConcrete Pavement Technology Center at Iowa State Universityfollowing by required calculations lead to estimation of poros-ity (n) and pore volume (VP) for concrete specimens [18](Fig. 4).

5.1. Determination of oven-dry mass

After the first mass determination by a digital scale, all 28-day specimens were placed in the electrical oven with tempera-ture of 105 �C for oven drying process for 24 h (Fig. 5a). After thefirst 24 h, oven dried specimens were removed from the ovenand they were allowed to cool in room temperature of 25 �C.Then the mass of each specimen was determined and recorded(Fig. 5b). The recorded mass of specimens showed they were stillwet and need redrying because the differential in the deter-mined mass was more than 0.5% of the lesser value. Thereforethe specimens were returned to the oven for an additional24 h drying.

After the second 24 h, oven dried specimens were removedfrom the oven and they were allowed to cool in dry air to a temper-ature of 25 �C. Then the mass of each specimen was determinedand recorded. This time the differential in the determined masswas not exceeding 0.5% of the lesser value. Hence, this last valuewas designated as ‘‘A’’ and the specimens were getting ready forthe next step of the concrete test.

(a) Mold greasing and preparation (b) Concrete placing in cylindrical molds

(c) Specimen removal from the mold after 28 days curing period

Fig. 3. Production of cylindrical concrete specimens.

Concrete specimen preparation

Oven-drying the specimens

Specimen removal from oven and mass determination

Determined mass=A

If X 0.5% If X 0.5%

Immersing the specimens

Specimen removal from water and mass determination

Determination of saturated mass after boiling (determined mass=C)

Determination of apparent mass during suspension in the water (determined mass=D)

Calculations

Determined mass=B

If X 0.5% If X 0.5%

Start

End

Fig. 4. Diagram shows the concrete test ASTM C 642 processes from specimenpreparation to final calculations.

606 N. Ghafari / International Journal of Mining Science and Technology 23 (2013) 603–611

5.2. Determination of saturated mass after immersion

In this part of the test, all specimens were immersed in potablewater at approximately 21 �C for 48 h (Fig. 6).

The temperature of water measured before beginning ofimmersion using a suitable thermometer. After the first 48 h, im-mersed specimens were removed from the container and thenthe mass of each specimen was determined and recorded. Thespecimens were placed in the water container for immersion foran additional 24 h to become fully saturated. After 24 h (totally72 h), immersed specimens were removed from the containerand after drying the surface by a towel, the mass of each specimen

was determined and recorded. The recorded mass of specimensshowed that, this time the increase in the determined mass wasnot exceeding 0.5% of the larger value. Hence, this last value wasdesignated as ‘‘B’’ and the specimens were getting ready for thenext step of the concrete test.

5.3. Determination of saturated mass after boiling

After the last immersion, surface drying and mass determina-tion, the specimens were boiled using boiling apparatus. The boil-ing apparatus was composed of a metal water container and anelectrical stove. All specimens placed in the container and boiledfor 5 h (Fig. 7).

After 5 h, boiled specimens were removed from the boilingapparatus and allowed to cool by natural loss of heat for 18 h.The surface moisture was removed and mass of each specimenwas determined. This determined mass designated C.

5.4. Determination of immersed apparent mass

After immersion and boiling, specimens were suspended inwater using a suitable wire to determine the apparent mass of eachspecimen. To achieve the adequate values of apparent mass espe-cial technique described below was used in this part of concretetest. First a small deep bowl filled with tap water and placed onthe electronic scale and the scale was set on the zero. Then oneby one the specimens suspended in the water by a wire andweights were recorded and designated as ‘‘W’’ (Fig. 8).

Eq.(1a) below has been used to determine the apparent mass foreach specimen.

D ¼ C �W ð1aÞ

where D is the apparent mass of sample in water after immersionand boiling; C the recorded weight of each specimen after boiling;and W the recorded weight during suspension of specimens in thewater.For example for specimen number 1-1 (S1-1) Eq.(1a) can bewritten in form of Eq.(1b).

D1�1 ¼ C1�1 �W1�1 ð1bÞ

where D1-1 is the apparent mass of S1-1 in water after immersionand boiling; C1-1 the recorded weight of S1-1 after boiling; W1-1

the recorded weight during suspension of S1-1 in the water.

(a) Oven-drying of specimens using an electrical oven in temperature of 105 for 48 hours

(b) Prior to and after each oven-drying process, mass of specimens were determining by a digital scale and recording

Fig. 5. Oven-drying of specimens and mass of specimens were determining and recording.

Fig. 6. Specimens were immersed in potable water at approximately 21 �C for 72 h.

N. Ghafari / International Journal of Mining Science and Technology 23 (2013) 603–611 607

6. Calculations

6.1. Calculation of porosity (n)

Below are the Eqs.(2–8) that have been used in calculations ofthe concrete test to determine the porosity and pore volume ofconcrete specimens [10]. Complete details on the results of thesecalculations are provided in the form of tables and charts in ‘‘Sec-tion 7’’ of this study (chapter 7).

Ai ¼ ½ðB� AÞ=A� � 100 ð2Þ

Aib ¼ ½ðC � DÞ=A� � 100 ð3Þ

qb ¼ ½A=ðC � DÞ�:q ¼ g1 ð4Þ

qbi ¼ ½B=ðC � DÞ�:q ð5Þ

qbib ¼ ½C=ðC � DÞ�:q ð6Þ

qa ¼ ½A=ðA� DÞ�:q ¼ g2 ð7Þ

n ¼ ½ðg2 � g1Þ=g2� � 100 ð8aÞ

Or : n ¼ ½ðC � AÞ=ðC � DÞ� � 100 ð8bÞ

where Ai is the absorption after immersion; Aib the absorption afterimmersion and boiling; qb the bulk density, dry; qbi the bulk densityafter immersion; qbib the bulk density after immersion and boiling;qa the apparent density; n the porosity (percentage of voids); A themass of oven-dried sample in air; B the mass of surface-dry sample

in air after immersion; C the mass of surface-dry sample in air afterimmersion and boiling; D the apparent mass of sample in waterafter immersion and boiling; g1 the bulk density, dry; g2 the appar-ent density; and q the density of the fluid. Since, in this test waterhas been used as the fluid, therefore the value of q here is equal to1 Mg/m3 or 1 g/cm3. Note that, in these calculations the units of‘‘mass’’ and ‘‘density’’ are in gram (g) and Mg/m3, respectively.

6.2. Calculation of volume of permeable pore space (VP)

The total volume of each cylindrical concrete specimen as wellas the volume of permeable pore space can be calculated fromporosity using Eqs.(9)–(11).

VT ¼ pr2 � h ¼ p� 2:52 � 10 ¼ 196:25 ð9Þ

VP ¼ n� VT ð10Þ

VP ¼ n� 196:25 ð11Þ

where VT is the total volume of concrete specimen, cm3; VP the vol-ume of permeable pore space of each specimen, cm3; pr2 the area ofcross section of specimen; and h the height of each specimen.

6.3. Calculation of permeability (k)

To determine the permeability (k) of concrete from the porosity(n) percentages achieved in the concrete test, a relationship neededto be found between permeability and porosity in order to write anequation between these two parameters.

Eq.(12) below recommended by Bourbie and Zinsner in 1985,shows this relationship between porosity and permeability andhas been used to evaluate the rate of permeability of concrete spec-imens [19]:

k ¼ 303ð100nÞ3:05ðnmÞ2 ðfor n > 0:08Þ ð12Þ

where k is the permeability and n the porosity of concrete.

6.4. Calculation of hydraulic conductivity (K)

Since one of the most important parameters used to quantifywater seepage is hydraulic conductivity; hence, after determina-tion of permeability, the next step was to determine the rate ofwater transmissivity in ordinary and acrylic polymer concrete todemonstrate the positive effects of organic polymer admixtureon reduction of hydraulic conductivity of tunnel temporary sup-port [20].

608 N. Ghafari / International Journal of Mining Science and Technology 23 (2013) 603–611

Eqs.(13) and (14) below recommended by Garboczi in 1990,show the relation between permeability (k) and hydraulic conduc-tivity (K) of concrete [21].

K ¼ kðqg=lÞ ð13Þ

where K is the hydraulic conductivity, m/s; k the permeability; qthe density of the fluid; g the acceleration due to gravity; l the dy-namic viscosity of the fluid. For water flowing through the pore sys-tem, Eq.(14) can be simplified as:

Fig. 7. Specimens were placed in a steel contain

Fig. 8. Specimens were suspended in the water using a suitable wire and a deep bowl

Table 2Values of mass of specimens in different states during concrete test and calculated values f

No. A (g) B (g) C (g) D (g) Ai

S1 406.74 448.97 437.19 224.34 10.38S2 407.67 448.61 437.20 224.35 10.04S3 409.01 448.11 437.22 224.35 9.56S4 410.28 447.70 437.28 224.39 9.12S5 411.38 447.35 437.34 224.43 8.74S6 412.40 447.08 437.42 224.48 8.41S7 413.43 446.82 437.52 224.54 8.08S8 414.35 446.64 437.66 224.63 7.79S9 415.15 446.49 437.78 224.71 7.55S10 415.97 446.30 437.88 224.77 7.29S11 416.72 446.15 437.98 224.83 7.06S12 417.17 446.03 438.02 224.86 6.92S13 417.39 446.01 438.07 224.89 6.86S14 417.35 446.01 438.06 224.88 6.87S15 417.31 446.00 438.04 224.87 6.88S16 417.22 445.96 437.99 224.84 6.89

Note: A is the mass of oven-dried sample in air; B the mass of surface-dry sample in air aftthe apparent mass of sample in water after immersion and boiling; Ai the absorption afterqbi the bulk density after immersion; qbib the bulk density after immersion and boiling;

K ¼ k� 107 ð14Þ

where K is the hydraulic conductivity, m/s and k the permeability ofconcrete specimen.

7. Results and discussion

A summary of recorded values during concrete test includingdetermined mass of specimens in four different states (A, B, C

er above an electrical stove to boil for 5 h.

filled by tape water to determine the immersed apparent mass for each specimen.

or absorptions and densities, lead to calculation of porosity (n) of concrete specimens.

Aib qb qbi qbib qa n (%)

7.49 1.91 2.11 2.05 2.23 14.317.24 1.92 2.11 2.05 2.22 13.876.90 1.92 2.11 2.05 2.21 13.256.58 1.93 2.10 2.05 2.21 12.686.31 1.93 2.10 2.05 2.20 12.196.07 1.94 2.10 2.05 2.19 11.755.83 1.94 2.10 2.05 2.19 11.315.63 1.95 2.10 2.05 2.18 10.945.45 1.95 2.10 2.05 2.18 10.625.27 1.95 2.09 2.05 2.18 10.285.10 1.96 2.09 2.05 2.17 9.975.00 1.96 2.09 2.05 2.17 9.784.95 1.96 2.09 2.05 2.17 9.704.96 1.96 2.09 2.05 2.17 9.714.97 1.96 2.09 2.05 2.17 9.724.98 1.96 2.09 2.05 2.17 9.74

er immersion; C the mass of surface-dry sample in air after immersion and boiling; Dimmersion; Aib the absorption after immersion and boiling; qb the bulk density, dry;qa the apparent density; and n the porosity (percentage of voids).

N. Ghafari / International Journal of Mining Science and Technology 23 (2013) 603–611 609

and D), as well as the calculated values for absorption after immer-sion (Ai), absorption after immersion and boiling (Aib), bulk density,dry (qb), bulk density after immersion (qbi), bulk density afterimmersion and boiling (qbib), apparent density (qa) and porosity(n) are listed in Table 2.

Also, a summary of estimated pore volume (VP) and porosity (n)as well as the calculated rates of permeability (k) and hydraulicconductivity (K) for all sixteen series of specimens are providedand listed in Table 3.

Moreover, analysis of the mentioned waterproofing parametersare illustrated in the form of charts and presented in Fig. 9.

As presented in Fig. 9, considerable reductions in porosity (n),pore volume (VP), permeability (k) and hydraulic conductivity (K)

Table 3A list of calculated porosity (n), volume of permeable pore space (Vp), permeability (k) an

No. Porosity (%) Pore volume (cm3)

S1 14.31 28.08S2 13.87 27.22S3 13.25 26.00S4 12.68 24.88S5 12.19 23.92S6 11.75 23.06S7 11.31 22.20S8 10.94 21.47S9 10.62 20.84S10 10.28 20.17S11 9.97 19.57S12 9.78 19.19S13 9.70 19.04S14 9.71 19.06S15 9.72 19.08S16 9.74 19.11

14

16

10

12

6

8

2

4

0S1 S3 S5 S7 S9 S11 S13 S15Specimen

Poro

sity

(%

)

1000

1200

600

800

200

400

0S1 S3 S5 S7 S9 S11 S13 S15Specimen

Perm

eabi

lity

(mD

)

%OP=12%k =309.81

%OP=12%n =9.70%

(a) Porosity

(c) Rate of permeability (d) Hydr

Fig. 9. Analysis of the mentioned

of organic polymer concrete specimens have demonstrated the po-sitive effects of using organic polymer as a concrete admixture toimprove waterproofing stability of underground concrete struc-tures. As shown in these charts the lowest values for the abovementioned concrete waterproofing parameters (n, VP, k, K) havebeen achieved for S13 which was contained 12% organic polymeradmixture.

The maximum reduction from S1 which was the reference con-crete specimen with 0% organic polymer to S13 which has shownthe best waterproofing features, have been listed below in formof Eqs.(15)–(18).

Dnmax ¼ nðS1Þ � nðS13Þ ¼ 14:31%� 9:70 ¼ 4:61% ð15Þ

d hydraulic conductivity (K) for all sixteen specimens are stated.

Permeability (10�13 m2) Hydraulic conductivity (lm/s)

10.10 10.109.22 9.228.02 8.027.01 7.016.22 6.225.56 5.564.95 4.954.47 4.474.08 4.083.70 3.703.37 3.373.18 3.183.10 3.103.11 3.113.12 3.123.14 3.14

25

30

15

20

5

10

0S1 S3 S5 S7 S9 S11 S13 S15Specimen

Pore

vol

ume

(m3 )

%OP=12%Vp=19.04 m3

%OP=12%K =3.1×10-6

3.1×10-6

1.01×10-5

0S1 S3 S5 S7 S9 S11 S13 S15Specimen

10

12

6

8

2

4

Hyd

raul

ic c

ondu

ctiv

ity (

µm/s

)

(b) Volume of permeable pore space

aulic conductivity of hardened concrete specimens from S1 to S16

waterproofing parameters.

610 N. Ghafari / International Journal of Mining Science and Technology 23 (2013) 603–611

DVP max ¼ VPðS1Þ � VðS13Þ ¼ 28:08� 19:04 ¼ 9:05 ð16Þ

Dkmax ¼ kðS1Þ � kðS13Þ ¼ 10:10� 10�13 � 3:10� 10�13

¼ 7:04� 10�13 ð17Þ

DKmax ¼ KðS1Þ � KðS13Þ ¼ 10:10� 10�6 � 3:10� 10�6

¼ 7:04� 10�6 ð18Þ

where Dnmax is the maximum reduction of porosity; n(S1) theporosity of specimen number one; n(S13) the porosity of specimennumber thirteen; DVPmax the maximum reduction in volume of per-meable pore space (pore volume); VP(S1) the pore volume of speci-men number one; VP(S13) the pore volume of specimen numberthirteen; Dkmax the maximum reduction of permeability; k(S1) thepermeability of specimen number one; k(S13) the permeability ofspecimen number thirteen; DKmax the maximum reduction ofhydraulic conductivity; K(S1) the hydraulic conductivity of speci-men number one; K(S13) the hydraulic conductivity of specimennumber thirteen.

7.1. Technical–economical considerations in DWS constructionmethod

As discussed previously in abstract and introduction of this pa-per, underground concrete structures are the most expensive con-struction projects. Hence the costs of these projects are always oneof the most important factors for both owner and contractor andaffect their decisions on method and material selection. The totalcost of a construction project is a combination of operational costsand costs of materials.

Avoiding unnecessary use of materials such as concrete admix-tures corresponds to reduction in the cost of materials and the totalcost of project. Therefore, to become closer to a practical model forthe water-resistant temporary structure in proposed DWS, in thisstudy, both technical and economical factors were considered indetermination of the best ratio of organic polymer to be added toshotcrete/concrete mixture. Hence, according to the final results,specimen number 13 (S13) with 12% organic polymer is determinedas the favorite concrete specimen as it possess lowest porosity (n),pore volume (VP), permeability (k) and hydraulic conductivity (K).Note that during the concrete test and calculations, higher valuesof mentioned parameters (n, VP, k, K) have been recorded for spec-imens number 14 to 16 (S14, S15, S16) while they were containedthe higher organic polymer ratios of 13%, 14% and 15%,respectively.

Furthermore, construction of an underground temporary sup-port after each partial excavation is an essential and indispensablepart of underground construction and tunneling (except cut-and-cover construction method). Hence, adding an appropriate amountof organic polymer to shotcrete mixture corresponds to construc-tion of a water-resistant temporary support without additionalshotcrete operation costs including equipments, energy, labors, etc.

8. Conclusions

According to the final results discussed in chapter 6, porosity (n)less than 10%, pore volume (VP) less than 20 cm3 (while the totalvolume of each specimen was approximately 196.25 cm3), perme-ability (k) less than 3.37 � 10�13 m2 (337 mD) and hydraulic con-ductivity (K) less than 3.37 � 10�6 m/s, were achieved forspecimens which were contained 10–15% organic polymer (S11,S12, S13, S14, S15 and S16).

Avoiding unnecessary use of materials such as concrete admix-tures corresponds to reduction in the cost of materials and the totalcost of project. Hence, to become closer to a practical model for

DWS waterproofing system, in this study, both technical and eco-nomical factors were considered in determination of the best ratioof organic polymer admixture in shotcrete/concrete mixture.

Therefore, specimen number 13 (S13) with 12% organic polymeris determined as the favorite concrete specimen since it possesslowest porosity (n), pore volume (VP), permeability (k) and hydrau-lic conductivity (K). Note that during the concrete test and calcula-tions, higher values of mentioned parameters (n, VP, k, K) have beenrecorded for S14, S15 and S16 compared with S13, while they werecontained the higher organic polymer ratios of 13%, 14% and 15%,respectively.

Improvement in waterproofing performance of concrete corre-sponds to improvement in waterproofing stability of tunnel’s tem-porary support and lead to construction of DWS by addingappropriate amounts of organic polymer to shotcrete mixture.

Since, execution of underground temporary support after eachpartial excavation is an essential and indispensable part of under-ground construction (except cut-and-cover tunneling method);therefore, a water-resistant temporary support could be con-structed without additional shotcrete operation costs includingequipments, energy, labors, etc.

Construction of a water-resistant temporary structure, insteadof a traditional temporary support, could be a practical solutionto the flow of groundwater in the close vicinity of undergroundtunnels. This water-resistant temporary support can act as a pri-mary waterproofing shield against infiltration of groundwater tocontrol and decrease the volume of this aggressive water beforecontact and chemical interaction with the main waterproofingmembrane and final concrete structure of the tunnel (final lining).Reduction in contacts and chemical interactions between existingcorrosive materials in groundwater with tunnel’s main water-proofing membrane and final lining improves both waterproofingand structural stability of tunnel by means of the prevention ofconcrete cracks and reinforcement corrosions.

9. Recommendation

In this study, organic polymer has been used as the only con-crete admixture to improve the waterproofing features of hard-ened concrete specimens while, there are a large number ofadditives which can improve the underground reinforced concretestructures. Therefore, further investigations are needed to be con-ducted to find other concrete admixtures which may play a posi-tive role in waterproofing and durability improvements of tunneltemporary support and final lining.

Acknowledgments

The author would like to acknowledge the financial supportprovided by his family during this study.

References

[1] Novotny V, Brown P. Cities of the future: towards integrated sustainable waterand landscape management. London: IWA Publishing; 2007.

[2] Orfanos C, Apostolopoulos G. 2D–3D resistivity and microgravitymeasurements for the detection of an ancient tunnel in the Lavrion area,Greece. Near Surf Geophys 2011;9(5):449–57.

[3] Xia HC, Zhou GQ, Du ZC. Experimental study of the soil underground structureinterfacial layer effect. J China Univ Min Technol 2011;40(6):846–51.

[4] Lu ZL, Qian JS, Li LD. Gradient based restoration of coal mine images obtainedby underground wireless transmissions. Min Sci Technol 2011;21(6):809–13.

[5] Neville AM. Properties of concrete. London: John Wiley & Sons; 2003.[6] Wang K, Wang QP, Jiang D, Xu Q. A routing and positioning algorithm based on

a K-barrier for use in an underground wireless sensor network. Min SciTechnol 2011;21(6):773–9.

[7] Kalogeropoulos A, Kruk J, Hugenschmidt J, Busch S, Merz K. Chlorides andmoisture assessment in concrete by GPR full waveform inversion. Near SurfGeophys 2011;9(3):277–85.

N. Ghafari / International Journal of Mining Science and Technology 23 (2013) 603–611 611

[8] ASTM C150-05. Standard specification for portland cement. American societyof testing and materials year book. West Conshohocken: ASTM International;2009.

[9] ASTM C33-01. Standard specification for concrete aggregates. Americansociety of testing and materials year book. West Conshohocken: ASTMInternational; 2009.

[10] ASTM C1602-06. Standard specification for mixing water used in theproduction of hydraulic cement concrete. American society of testing andmaterials year book. West Conshohocken: ASTM International; 2009.

[11] ASTM C1141/C1141M-08. Standard specification for admixtures for shotcrete.American society of testing and materials year book. West Conshohocken:ASTM International; 2009.

[12] ASTM C1438-99. Standard specification for latex and powder polymermodifiers for hydraulic cement concrete and mortar. American society oftesting and materials year book. West Conshohocken: ASTM International;2009.

[13] ASTM C1439-08. Standard test methods for evaluating polymer modifiers inmortar and concrete. American society of testing and materials yearbook. West Conshohocken: ASTM International; 2009.

[14] Zhang DS, Fan GW, Wang XF. Characteristics and stability of slope movementresponse to underground mining of shallow coal seams away from gullies. Int JMin Sci Technol 2012;22(1):47–50.

[15] ASTM C192/C192M-07. Standard practice of making and curing concrete testspecimens in the laboratory. American society of testing and materials yearbook. West Conshohocken: ASTM International; 2009.

[16] ASTM C642-06. Standard test method for density, absorption, and voids inhardened concrete. American society of testing and materials year book. WestConshohocken: ASTM International; 2009.

[17] ASTM C470/C470M-09. Standard specification for molds for forming concretetest cylinders vertically. American society of testing and materials yearbook. West Conshohocken: ASTM International; 2009.

[18] Luo JA, Wang LG, Tang FR, He Y, Zheng L. Variation in the temperature field ofrocks overlying a high-temperature cavity during underground coalgasification. Min Sci Technol 2011;21(5):709–13.

[19] Bourbie T, Zinszner B. Hydraulic and acoustic properties as a function ofporosity in Fontainebleau sandstone. J Geophys 1985;90(11):524–32.

[20] Khalil MA, Ramalho EC, Monteiro Santos FA. Using resistivity logs to estimatehydraulic conductivity of a Nubian sandstone aquifer in southern Egypt. NearSurf Geophys 2011;9(4):349–55.

[21] Marilena C, Mauricio D, Jacopo S. Complexity analysis of blast-inducedvibrations in underground mining: a case study. Int J Min Sci Technol 2012;22(1):125–32.