Corrosion Science 52 (2010) 2958–2963

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Corrosion Science

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The effect of silane-based hydrophobic admixture on corrosion of galvanizedreinforcing steel in concrete

F. Tittarelli *, G. MoriconiDepartment of Materials and Environment Engineering and Physics, Polytechnic University of Marche, 60131 Ancona, Italy

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

Article history:Received 21 January 2010Accepted 6 May 2010Available online 12 May 2010

Keywords:A. ConcreteA. Steel reinforced concreteA. ZincB. PolarizationC. Passivity

0010-938X/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.corsci.2010.05.008

* Corresponding author. Tel.: +39 071 2204732; faxE-mail address: f.tittarelli@univpm.it (F. Tittarelli)

Sound or deliberately pre-cracked concrete specimens, with 0.5 or 1 mm wide crack, were manufacturedwith water to cement ratios (w/c) of 0.45 and 0.75, both in the presence and in the absence of a silaneadmixture. The specimens were exposed to wet–dry cycles in a 10% NaCl aqueous solution. The results,in terms of electrochemical measurements, and visual and metallographic observations carried out on thegalvanized steel reinforcement removed from the specimens, showed that the hydrophobic concrete isable to protect galvanized steel reinforcement from corrosion even in the presence of cracks in the con-crete cover, especially when a high w/c is used.

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1. Introduction

Static, dynamic and cyclic loading as well as shrinkage, creep andthermal stress or even, in precast concrete, mechanical shock andflexural stress induced during transportation, lifting and mounting,can cause concrete cover cracking. Cracks greatly increase the con-crete surface permeability since they represent preferential pathsfor penetration of aggressive agents such as chloride ions, whichpromote corrosion of steel [1]. After the initial induction period,the degradation process grows very rapidly, since the deteriorationmechanisms show a destructive expansive nature [2]. Since the costof repairing reinforced concrete structures during the induction per-iod of the corrosion process is generally much lower than the reha-bilitation cost during the propagation process [3], concretetechnology is continuously developing new methods to preventthe onset of deterioration in reinforced concrete structures.

In this respect, it is evident that steel corrosion would not occur ifwater, which acts as the main carrier for aggressive substances andthe medium where corrosion reactions develop, is permanently pre-vented from wetting the concrete porous structure. The water incontact with a porous material such as concrete penetrates thematerial by means of capillary forces following the Washburn equa-tion, p = (2c/rc) cos r, where c represents the liquid surface tension,rc is the capillary pore radius, and r is the contact angle. A waterdroplet, on a hydrophilic solid, wets the solid surface by spreadingitself and by absorption through the solid porosity. The contact angle

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becomes less than 90�, p becomes positive and the liquid fills thepore spontaneously. However the molecular attraction betweenwater and the concrete pore walls can be lowered by surface treat-ment based on impregnation with hydrophobic agents, such asthose currently named silanes and siloxanes [4–19]. Their alkoxylicgroups are chemically bound to the concrete hydrated silicates by acondensation reaction while their hydrophobic alkylic groups comeout on the pores surface [20]. Hydrophobic treatments hinder liquidwater to penetrate the structure when pressure is not excessivelyhigh. However, differently from waterproofing treatments, they al-low water vapour permeation, and in general gas permeation, lead-ing to water leakage from the structure.

To optimize the effectiveness and durability of hydrophobicagents [21–29], they have been recently introduced in the concretemixture in order to make both the surface and the whole concretebulk hydrophobic [30–38]. In this way, bulk hydrophobization couldcancel the detrimental effect, from a corrosion point of view, of con-crete cover cracking. However, experimental results have shownthat the silane admixture is able to protect steel reinforcement fromcorrosion only in sound concrete, while in cracked concrete it can in-duce a catastrophic corrosion [37]. This unexpected result has beenascribed to a greater oxygen diffusion through an unsaturatedhydrophobic cementitious matrix that, in this way, can feed morequickly the cathodic reaction controlling the corrosion process [38].

However, if galvanized steel reinforcement is used, in whichcase it has been already demonstrated that passivation is mainlypromoted by oxygen [39], it is easy to predict that the hydrophobicadmixture could effectively counteract the corrosion process.Therefore, the present paper is aimed to verify the validity of thisintuition by monitoring the corrosion behavior of galvanized steel

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reinforcement embedded in sound or cracked hydrophobicconcrete exposed to chloride environment.

2. Experimental

2.1. Materials

Concrete mixtures with water to cement ratios (w/c) of 0.45 and0.75 were manufactured by using commercial Portland cementtype CEM II/A-L 42.5 R with and without silane as a hydrophobicadmixture. The silane admixture was used in form of 45% aqueousemulsion of butyl-ethoxy-silane at a dosage of 1% by cementweight. Natural sand and gravel with 6- and 11-mm maximumsize, respectively, were used as aggregate. The proportions of theconcrete mixtures are given in Table 1, where compressivestrengths at 2, 7, and 28 days are also reported. In the presenceof silane admixture, a reduction in the concrete compressivestrength of about 18% and 23% was recorded with respect to thatof non-hydrophobic concrete when w/c ratio of 0.45 and 0.75was used, respectively.

2.2. Specimens

For each concrete type, nine prismatic specimens (70 � 70 �280 mm in size) were produced (Fig. 1). These prismatic specimenswere reinforced with a hot dip galvanized steel plate (210 � 40 �1 mm) embedded at mid depth from a specimen side. The zinc coat-ing, obtained by immersion in molten zinc, was 100 lm thick withan outer pure zinc layer about 20 lm thick. An electric cable, isolatedthrough a PVC sheath, was connected to each steel plate by means ofspot welding. The weld was protected by epoxy resin before castingthe concrete mixture. Steel plates instead of usual rebars were usedin order to facilitate the cracking of specimens and to modulate thecrack width.

After casting, all the specimens were wet cured for 2 days andair dried for 1 month at room temperature. Then, six specimensfor each concrete type were deliberately cracked by a flexuralstress in order to open a crack 0.5 or 1 mm wide in the middlezone, with the crack apex reaching the steel reinforcement. In or-

Table 1Concrete mixture proportions (kg/m3) and related compressive strengths (MPa).

Mixtures w/c = 0.45 w/c = 0.45hydrophobic

w/c = 0.75 w/c = 0.75hydrophobic

Water 240 233 240 236Cement 533 533 320 320Silane – 11.8 – 7.1Sand 639 639 949 949Gravel 847 847 716 716Rc at 2 days 19.9 16.8 6.7 4.9Rc at 7 days 35.4 27.5 14.5 9.2Rc at 28 days 39.2 32.3 25.6 19.8

Fig. 1. Prismatic reinforced concrete specimens.

der to localize the crack formation at a predetermined point, a pre-formed V-notch, 10 mm deep and 14 mm wide, was produced onthese specimens by placing a plastic rod on the bottom surface ofthe mould. Once the crack of required width, measured by anextensometer, was obtained its opening was maintained after theelimination of the flexure load by the insertion of small elementsof hard polymeric material of suitable thickness. In order to makethe oxygen and chloride flow unidirectionally and perpendicularlydirected to the steel plate through the concrete cover, all the othersides of the specimens but the one containing the crack apex wereepoxy coated.

Subsequently, the specimens were exposed to wet–dry cycles(2 days wet followed by 5 days dry) in a 1.7 M NaCl aqueous solu-tion for 4 months.

2.3. Tests

The corrosion risk of the reinforced concrete specimens exposedto the chloride environment was evaluated by free corrosion po-tential measurements with respect to a saturated calomel elec-trode (SCE) as reference, while the kinetics of the corrosionprocess was followed by polarization measurements. The polariza-tion resistance, in inverse relation with the corrosion rate, wasmeasured through the galvanodynamic method, using an externalgraphite bar as counter-electrode, by calculating its average valuebetween the anodic and cathodic zones. The electrochemical val-ues reported in the graphs are averaged among the measurementscarried out on three specimens of each concrete type during theimmersion period.

In order to validate and to complete the evaluation of the elec-trochemical behavior, the galvanized steel plates were extracted bysplitting the concrete specimens after 16 wet–dry cycles in thechloride solution and the corrosion extent was assessed by visualobservation. Metallographic analysis was carried out on a crosssection of the galvanized steel plates in order to evaluate the de-crease in the zinc coating thickness due to the corrosive attack. Across section 1 cm from the crack apex was chosen in order to re-flect the effects of a real corrosive process, avoiding the extremesituation produced at the crack apex by a strongly accelerated cor-rosion process in order to reduce experimental times. Zinc corro-sion products were identified by X-ray diffraction. Additionally,the free chloride concentration derived by water extraction fromthe cement paste in contact with the steel reinforcement in thesame cross section was measured at the end of the exposure timeto the chloride environment by ion chromatography.

3. Results and discussion

3.1. Electrochemical measurements

Fig. 2 shows the free corrosion potential values of galvanizedsteel plates embedded in concrete specimens with** w/c = 0.75 asa function of wet–dry cycles in the aggressive environment. Innon-hydrophobic concrete they assume active values of about�1000 mV/SCE indicating that zinc is carrying out its prescribedfunction and reflecting a generally great corrosion risk; these val-ues keep constant for almost all the test time. On the other hand,in bulk hydrophobic concrete, just after the exposure to the aggres-sive environment the galvanized steel plates assume values of�800 mV/SCE in the presence of concrete cracks regardless of thecrack width, and �600 mV/SCE in sound specimens. Moreover,the free corrosion potentials move towards more passive values,indicating a very low corrosion risk, after a few wet–dry cycles.Cracks in the concrete cover do not significantly affect the rein-forcement potential.

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V/SC

E) sound hydrophobic0.5mm cracked hydrophobic1mm cracked hydrophobicsound non-hydrophobic0.5mm cracked non-hydrophobic1mm cracked non-hydrophobic

Fig. 2. Corrosion potential of the galvanized steel plates embedded in concretespecimens with w/c = 0.75, as a function of the test time.

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sound hydrophobic 0.5mm cracked hydrophobic1mm cracked hydrophobic sound non-hydrophobic0.5mm cracked non-hydrophobic 1mm cracked non-hydrophobic

Fig. 4. Corrosion potential of the galvanized steel plates embedded in concretespecimens with w/c = 0.45, as a function of the test time.

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Res

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nce

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sound hydrophobic 0.5mm cracked hydrophobic1mm cracked hydrophobic sound non-hydrophobic0.5mm cracked non-hydrophobic 1mm cracked non-hydrophobic

Fig. 5. Polarization resistance of the galvanized steel plates embedded in concretespecimens with w/c = 0.45, as a function of the test time.

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In the absence of concrete cracks, the polarization resistance(Fig. 3) of the steel reinforcement in hydrophobic concrete is even10 times higher with respect to that in non-hydrophobic concrete,indicating a very low corrosion rate; moreover, this value seems tofurther increase during the test time. In the presence of concretecracks, the difference between hydrophobic and non-hydrophobicconcrete is moderate, but the polarization resistance of steel rein-forcement in hydrophobic concrete remains at least three timeshigher with respect to that of non-hydrophobic concrete. More-over, in this case, cracked hydrophobic concrete behaves even bet-ter than sound non-hydrophobic concrete, whatever the crackwidth; therefore, bulk hydrophobization seems to cancel, from acorrosion point of view, the detrimental effect of concrete covercracking.

The two different crack widths considered do not affect the cor-rosion results in non-hydrophobic concrete specimens, due to thehigh porosity of the cement matrix, while, in the hydrophobic ones,just a little bit higher corrosion rate is detected in the presence ofthe wider crack.

A good quality concrete matrix with a w/c as low as 0.45 seemsto partially hide the beneficial effect of the hydrophobic admixture.The corrosion risk described by the free corrosion potential mea-surements (Fig. 4) is about the same regardless of the cement ma-trix. However, the polarization resistance of steel reinforcement(Fig. 5) is always higher in the hydrophobic concrete specimenswith respect to the corresponding non-hydrophobic ones, even ifthe difference is not as evident as observed in the more porous ce-ment matrix. In particular, in this case, the hydrophobic effect wasnot able to cancel, from a corrosion point of view, the detrimentaleffect of the concrete cover cracking as previously observed in con-cretes with w/c = 0.75. Moreover, due to the low porosity of the ce-

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Fig. 3. Polarization resistance of the galvanized steel plates embedded in concretespecimens with w/c = 0.75, as a function of the test time.

ment matrix, the crack width influenced the test results both in thepresence and in the absence of silane with corrosion risk and cor-rosion rates which increase with the crack width.

Finally, by comparing the results obtained in concrete speci-mens with w/c = 0.45 and 0.75, it is evident that the hydrophobicadmixture, even in the presence of concrete cracks, decreases thecorrosion rate monitored in very porous concrete, as that manufac-tured with w/c = 0.75, to values comparable with those obtained ingood quality concrete, as that manufactured with w/c = 0.45. Inother words, silane cancels the detrimental effect, at least fromthe corrosion point of view, of a large porosity of the cementmatrix.

As reported in Table 2, the hydrophobic admixture is able to re-duce chloride penetration both in sound and cracked concretes ofabout 60%, especially when in the concrete cover narrower cracks(0.5 mm) are present.

3.2. Visual evaluation

Visual and metallographic observations carried out on the gal-vanized steel plates removed from the specimens after the aggres-sive exposure confirmed the electrochemical measurements.

Table 2Chloride ion concentration (% by cement mass).

Concrete type No crack 0.5 mm crack 1 mm crack

w/c = 0.45 0.8 1.1 1.8w/c = 0.45 hydrophobic 0.2 0.4 0.5w/c = 0.75 3.4 3.9 4.5w/c = 0.75 hydrophobic 1.4 1.5 1.9

Fig. 6a. Visual observation of the galvanized steel plate embedded in concretespecimens with w/c = 0.45 in the absence of the hydrophobic admixture (up: nocrack; middle: 0.5 mm crack; down: 1 mm crack).

Fig. 6b. Metallographic section of the galvanized steel plate embedded in cracked(1 mm wide) concrete specimens with w/c = 0.45 in the absence of the hydrophobicadmixture.

Fig. 7a. Visual observation of the galvanized steel plate embedded in concretespecimens with w/c = 0.45 in the presence of the hydrophobic admixture (up: nocrack; middle: 0.5 mm crack; down: 1 mm crack).

Fig. 7b. Metallographic section of the galvanized steel plate embedded in cracked(1 mm wide) concrete specimens with w/c = 0.45 in the presence of the hydropho-bic admixture.

Fig. 8. X-ray Diffraction analysis of white zinc corrosion products.

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Fig. 10a. Visual observation of the galvanized steel plate embedded in concretespecimens with w/c = 0.75 in the presence of the hydrophobic admixture (up: nocrack; middle: 0.5 mm crack; down: 1 mm crack).

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The galvanized steel plates embedded in non-hydrophobic con-crete with w/c = 0.45 (Fig. 6a) showed a general corrosion state,where dark Fe–Zn alloys appeared on the plate surface, meaningthat total consumption of the pure zinc layer due to the corrosiveattack occurred, as also confirmed by metallographic analysis(Fig. 6b).

On the other hand, for the galvanized steel plates embedded inhydrophobic concrete (Fig. 7a), zinc grains were still well visible onthe galvanized plate surface and close to the crack apex a whitesurface deposit of adherent and compact zinc corrosion products,later identified by X-ray diffraction as zinc oxides, hydroxidesand calcium hydroxyzincate (Fig. 8), appeared. In particular cal-cium hydroxyzincate is a well known passivating zinc corrosionproduct [40–44] that, once formed, protects the underlying purezinc layer from further corrosion as metallographic analysis haswell demonstrated (Fig. 7b).

Also the visual evaluations, in agreement with the electrochem-ical measurements, confirm that the hydrophobic admixture isable to counteract galvanized reinforcement corrosion especiallyin concrete with w/c = 0.75.

As a matter of fact, the galvanized steel plates extracted fromnon-hydrophobic concrete (Fig. 9a) showed a very deep generalcorrosive attack with red rust appearing on the surface indicatingthat total consumption of the protective zinc layer had occurred(Fig. 9b).

On the other hand, the zinc layer on steel reinforcement embed-ded in hydrophobic concrete (Fig. 10a) appeared thicker, as shown

Fig. 9b. Metallographic section of the galvanized steel plate embedded in cracked(1 mm wide) concrete specimens with w/c = 0.75 in the absence of the hydrophobicadmixture.

Fig. 9a. Visual observation of the galvanized steel plate embedded in concretespecimens with w/c = 0.75 in the absence of the hydrophobic admixture (up: nocrack; middle: 0.5 mm crack; down: 1 mm crack).

Fig. 10b. Metallographic section of the galvanized steel plate embedded in cracked(1 mm wide) concrete specimens with w/c = 0.75 in the presence of the hydropho-bic admixture.

by the metallographic section (Fig. 10b), in spite of an apparentlystronger corrosive attack with respect to that observed in hydro-phobic concrete with lower w/c ratio (Fig. 7b), indicating that thecorrosive attack is weaker.

It must be pointed out that this behavior was observed regardlessof the chloride concentration. This was measured close to the platesembedded in hydrophobic concrete with w/c = 0.75 and it resultedin a concentration four times higher with respect to that measuredwith w/c = 0.45 (Table 2). Such an observation confirms greateroxygen diffusion, as that assured by more porous hydrophobiccementitious matrix manufactured with higher w/c [37,38], canreally favour galvanized reinforcement passivation [39].

4. Conclusions

The use of hydrophobic admixture can improve the corrosionresistance of galvanized steel reinforcement in concrete specimensexposed to wet–dry cycles in a chloride aqueous solution, even inthe presence of concrete cracks, especially when a high w/c is used.Bulk hydrophobization cancels the detrimental effect of a largeporosity of the cement matrix as well as, in high porous concretes,of concrete cover cracking.

Galvanized steel in hydrophobic concrete not only assures theconcurrence of the benefits derived from the use of either steel gal-vanization or concrete hydrophobization, but it could further pro-vide a useful synergistic effect. As a matter of fact, hydrophobic

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concrete in repelling water, not only hinders the penetration ofaggressive agents inducing the corrosion process, but also favoursfaster oxygen diffusion through concrete, thus making galvanizedreinforcement passivation faster and easier, particularly when ahigh w/c is used.

Therefore, it is concluded that the use of galvanized steel rein-forcement in hydrophobic concrete could be an optimal, innovative,relatively cheap and effective method against corrosion of rein-forced concrete structures even in the presence of concrete cracks.

References

[1] C.L. Page, K.W.J. Treadaway, Aspects of the electrochemistry of steel inconcrete, Nature 297 (1982) 109–115.

[2] K. Tuutti, Corrosion of Steel in Concrete, Report CBI 10.4.82, Swedish Cementand Concrete Research Institute, Stockholm, 1982, p. 468.

[3] W.R. de Sitter Jr., Costs for service life optimization, the law of fives, durability ofconcrete structures, in: Proceedings of CEB-RILEM International Workshop,Copenhagen, Denmark, CEB Bulletin d’Information, No. 152, 1983, pp. 131–134.

[4] L. Basheer, D.J. Cleland, A.E. Long, Protection provided by surface treatmentsagainst chloride induced corrosion, Materials and Structures 31 (211) (1998)459–464.

[5] A. Frattolillo, G. Giovinco, M.C. Mascolo, A. Vitale, Effects of hydrophobictreatment on thermophysical properties of lightweight mortars, ExperimentalThermal and Fluid Science 29 (6) (2005) 733–741.

[6] J. de Vries, R.B. Polder, Hydrophobic treatment of concrete, Construction Repair9 (5) (1995) 42–47.

[7] J. de Vries, R.B. Polder, Hydrophobic treatment of concrete, Construction andBuilding Materials 11 (4) (1997) 259–265.

[8] T. Zhang, S. Shang, F. Yin, A. Aishah, A. Salmiah, T.L. Ooi, Adsorptive behaviourof surfactants on surface of portland cement, Cement and Concrete Research31 (7) (2001) 1009–1015.

[9] P.A.M. Basheer, Surface treatments for concrete, in: C. Andrade, R. Cox, B. Pukl(Eds.), Proceedings of COST 509 Workshop on Corrosion and Protection ofMetals in Concrete, Sevilla, Spain, 1995.

[10] E. McGettigan, Silicon-based weatherproofing materials, ConcreteInternational 14 (6) (1992) 52–56.

[11] P.A.M. Basheer, L. Basheer, D.J. Cleland, A.E. Long, Surface treatments forconcrete: assessment methods and reported performance, Construction andBuilding Materials 11 (7–8) (1997) 413–429.

[12] G. Moriconi, F. Tittarelli, V. Corinaldesi, Review of silicone-based hydrophobictreatment and admixtures for concrete, The Indian Concrete Journal 76 (10)(2002) 637–642.

[13] A. Chowdhury, A. Gillies, P.J. McDonald, M. Mulheron, Vapour phaseapplication of hydrophobic coatings to cement-based materials, Magazine ofConcrete Research 53 (5) (2001) 347–352.

[14] CIRIA, Protection of reinforced concrete by surface treatments, Technical Note130, Construction Industry Research and Information Association, UK, 1987.

[15] ACI Committee 515, A Guide to the Use of Waterproofing, DamproofingProtective and Decorative Barrier Systems for Concrete, ACI, 1985.

[16] E. McGettigan, Application mechanism of silane weatherproofers, ConcreteInternational 12 (10) (1990) 66–68.

[17] R.B. Polder, H. Borsje, Hydrophobic treatment of concrete against chloridepenetration, in: C.L. Page, P.B. Bamforth, J.W. Figg (Eds.), Corrosion ofReinforcement in Concrete Construction, SCI Special Publication n. 183,Berlin, 1996, pp. 546–555.

[18] T. Kamile, B. Felekoglu, B. Baradan, Effectiveness of alkyl alkoxy silanetreatment in mitigating alkali-silica reaction, ACI Materials Journal 105 (1)(2008) 20–27.

[19] M.H.F. Medeiros, P. Helene, Surface treatment of reinforced concrete in marineenvironment: influence on chloride diffusion coefficient and capillary waterabsorption, Construction and Building Materials 23 (3) (2009) 1476–1484.

[20] K.H. Wong, E. Weyers, P.D. Cady, The retardation of reinforcing steel corrosionby alkyl-alkoxy silane, Cement and Concrete Research 13 (6) (1983) 778–788.

[21] M. Medeiros, P. Helene, Efficacy of surface hydrophobic agents in reducingwater and chloride ion penetration in concrete, Materials and Structures/Materiaux et Constructions 41 (1) (2008) 59–71.

[22] Folker H. Wittmann, Tie-Jun Zhao, Zhao-Jun Ren, Ping-Gong Guo, Influence ofsurface impregnation with silane on penetration of chloride into cracked

concrete and on corrosion of steel reinforcement, International Journal ofModelling, Identification and Control 7 (2) (2009) 135–141.

[23] Jian-Guo Dai, Y. Akira, F.H. Wittmann, H. Yokota, Peng. Zhang, Water repellentsurface impregnation for extension of service life of reinforced concretestructures in marine environments: the role of cracks, Cement and ConcreteComposites 32 (2) (2010) 101–109.

[24] P. Zhang, Jian-Guo Dai, Tie-Jun Zhao, Folker H. Wittmann, S. Hartmann, Waterrepellent treatment on surface of cracked concrete under seawater exposureenvironment, Jianzhu Cailiao Xuebao/Journal of Building Materials 12 (2)(2009) 214–218.

[25] L. Schueremans, D. Van Gemert, S. Giessler, Chloride penetration in RC-structures in marine environment – long term assessment of a preventivehydrophobic treatment, Construction and Building Materials 21 (6) (2007)1238–1249.

[26] O.T. De Rincón, M. Aboulhosn, C. Morales, J. Bravo, M. Sánchez, D. Contreras, Y.Hernández, V. Millano, Evaluation of hydrophobic concrete coatings in tropicalmarine environments, NACE – International Corrosion Conference Series,Corrosion 2008, pp. 083171–0831723.

[27] R.S. Gaislon, Water repellents: protection of facades of concrete in a wet climate,Internationale-Zeitschhrift-fuer-Bauinstandsetzen 5 (3) (1999) 251–272.

[28] K. Sandin, Influence of cracks on moisture conditions in facades with water-repellent treatments, Internationale-Zeitschhrift-fuer-Bauinstandsetzen-und-Baudenkmalpflege 5 (5) (1999) 499–521.

[29] M. Sauder, Damage caused by water repellent agents – reasons and counter-measures, Internationale-Zeitschhrift-fuer-Bauinstandsetzen 5 (3) (1999)311–321.

[30] H.E. Vivian, Some chemical additions and admixtures in cement paste andconcrete, in: Proceedings of the Fourth International Symposium on theChemistry of Cement, vol. 2, Washington, USA, 1960, pp. 909–926.

[31] N.P. Mailvaganam, Miscellaneous admixtures, in: V.S. Ramachandran (Ed.),Concrete Admixtures Handbook, Noyes Publications, Park Ridge, New Jersey,USA, 1984, pp. 518–524.

[32] A.M. Alshamsi, K.I. Alhosani, K.M. Yousri, Hydrophobic materials,superplasticizers and microsilica effects on setting of cement pastes at varioustemperatures, Magazine of Concrete Research 79 (179) (1997) 111–115.

[33] J.M. Aldred, S. Swaddiwudhipong, S.L. Lee, T.H. Wee, The effect of initialmoisture content on water transport in concrete containing a hydrophobicadmixture, Magazine of Concrete Research 53 (2) (2001) 127–134.

[34] E.E. Hekal, M. Abd. El-Khalek, G.M. El-Shafey, F.S. Hashem, Mechanical andphysico-chemical properties of hardened portland cement pastes containinghydrophobic admixtures. Part 1: compressive strength and hydration kinetics,ZKG International 52 (12) (1999) 697–700.

[35] E.E. Hekal, M. Abd. El-Khalek, G.M. El-Shafey, F.S. Hashem, Mechanical andphysico-chemical properties of hardened portland cement pastes containinghydrophobic admixtures. Part 2: physical properties and microstructure, ZKGInternational 53 (3) (2000) 152–158.

[36] G. Moriconi, F. Tittarelli, Use of hydrophobic agents as concrete admixtures, in:V.M. Malhotra (Ed.), Proceedings of the Sixth CANMET/ACI InternationalConference on Durability of Concrete, Thessaloniki, Greece, Farmington Hills,Michigan, USA, ACI Publication SP-212, 2003, p. 2.

[37] F. Tittarelli, G. Moriconi, The effect of silane-based hydrophobic admixture oncorrosion of reinforcing steel in concrete, Cement and Concrete Research 38(11) (2008) 1354–1357.

[38] F. Tittarelli, Oxygen diffusion through hydrophobic cement-based materials,Cement and Concrete Research 39 (10) (2009) 924–928.

[39] F. Tittarelli, T. Bellezze, Investigation of the major reduction reaction occurringduring the passivation of galvanized steel rebars, Corrosion Science 52 (3)(2010) 978–983.

[40] S.R. Yeomans, Performance of black, galvanized, and epoxy-coated reinforcingsteels in chloride-contaminated concrete, Corrosion Engineering January(1994) 72.

[41] G. Arliguie, J.P. Ollivier, J. Grandet, Study on the retarding effect of zinc onhydration of portland cement paste, Cement and Concrete Research 12 (1)(1982) 79.

[42] A. Macias, C. Andrade, Corrosion of galvanized steel in dilute Ca(OH)2 solutions(pH 11), British Corrosion Journal 22 (3) (1987) 162.

[43] A. Macias, C. Andrade, The behaviour of galvanized steel in chloride containingalkaline solution. I. The influence of cation, Corrosion Science 30 (4/5) (1990) 393.

[44] Z.Q. Tan, C.M. Hansson, Effect of surface condition on the initial corrosion ofgalvanized reinforcing steel embedded in concrete, Corrosion Science 50 (9)(2008) 2512.