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Potential application of geopolymers asprotection coatings for marine concrete III.

Field experiment

ARTICLE in APPLIED CLAY SCIENCE · JUNE 2010

Impact Factor: 2.47 · DOI: 10.1016/j.clay.2010.01.014

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University of Southern Queensland

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Xiao Yao

Nanjing University of Technology

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Author's personal copy

Potential application of geopolymers as protection coatings for marine concrete III.Field experiment

Zuhua Zhang a,b,⁎, Xiao Yao b, Hao Wang a

a Faculty of Engineering and Surveying, University of Southern Queensland, Toowoomba, QLD, 4350, Australiab College of Materials Science and Engineering, Nanjing University of Technology, Nanjing, 210009, China

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

Article history:

Received 19 May 2011

Received in revised form 27 April 2012

Accepted 26 May 2012

Available online xxxx

Keywords:

Marine concrete

Geopolymer

Coating

Field experiment

Integrity

Previous studies have shown a high potential of using geopolymers as new inorganic coatings in protecting

marine concrete. This article reports the results of the experiment on eld application. Geopolymer coatings

were in-situ applied on the surfaces of concrete accropodes along the coast. It was observed that the geo-

polymer coatings set within 4 hours, bound strongly with concrete and were able to resist the wave shock

in the rst tide rise. There was a modicum of calcite detected by X-ray diffraction (XRD) but no sulphate

was found in the coatings within 6 months. One issue raised during in-situ application is the large shrinkage

of the geopolymer paste under ambient condition. Micro-cracks on the surfaces were observed after 7 days

although the MgO-based expansion agent and polypropylene (PP)bers were added to withstand the shrink-

age. The humidity of the atmosphere and the thickness of the coating layer are the two signicant factors af-

fecting the integrity of coatings. It was noted that the coating with a thickness of 5 mm at the tidal area,

where contact with seawater periodically, exhibited the best integrity. To solve the problem of large shrink-

age, it is recommended to use suitable aggregates in coating paste and to develop appropriate shrinkage re-

ducing agents together with careful curing procedures.

© 2012 Elsevier B.V. All rights reserved.

1. Introduction

The concrete structures exposed to aggressive marine environ-

ment, especially the steel reinforced structures, readily deteriorate

with time. This is because the cement hydration products and the

reinforced steel bar in concrete react quickly with aggressive

mediums. The mechanisms are mainly due to the carbonation of the

cement hydration products Ca(OH)2 in wet environment with the

presence of Cl−, Mg2+ and SO42− ions. The carbonation products

CaCO3 may block the capillary pores at the beginning; however, it

can be further dissolved when contacting with water. Consequently,

the pores allow more corrosive ions to move in and meanwhile thedecreased alkalinity of cement matrix due to the loss of Ca(OH) 2 fur-

ther increases the potential of chloride corrosion. Chloride ion is one

of most dangerous ions for the reinforced concrete. It acts as a catalyst

to destroy the passive layer on steel and leads to a continuous corro-

sion once the pH of the pore water in concrete decreases to a critical

level. Besides, the reactions between the magnesium and sulfate ions

with the cement hydration products form expansive products and

further cause micro-cracks, which become the ingression channels

for outside aggressive mediums. These corrosion processes reduce

the life of concretes substantially.

Surface protection is applied to concrete structures to extend their

service life. Organic coatings, such as polyurethane coating, acrylic

coating, epoxy resin coating and chlorinated rubber coating, have

been applied on the surface of structures exposed to marine environ-

ment (Medeiros and Helene, 2009; Rodrigues et al., 2000). However,

since the aging under sunshine condition and the chemical and phys-

ical impacts of sea wave, the durability of the organic coatings is

doubtful. Using inorganic polymers, known as ‘geopolymer’, as pro-

tective coating materials may be an alternative choice. Geopolymers

are a family of alkali-activated cements with excellent resistance tosulfate and seawater attack (Bakharev, 2005; Fernández-Jiménez

and Palomo, 2009). Geopolymer concretes exhibit much lower chlo-

ride permeability than ordinary Portland cement (OPC) concrete

(Bernal et al., 2011). Moreover, the presence of chloride in geo-

polymer matrix does not seem to affect the strength of concrete in

the long term (Makaratat et al., 2011; Rattanasak et al., 2011). It

means that the geopolymer concretes can keep the integrity even

the diffused chloride ions reach a certain concentration.

The possibility of using geopolymer as a novel coating material for

protecting marine concretes has been studied recently (Zhang et al.,

2010a, 2010b). It was found that the setting time of metakaolin-based

geopolymer coating can be adjusted by adding slag at an amount

accordingly to experiment temperature. The adhesion of geopolymer

coating to cement mortar substrate was appreciated. The shrinkage

Applied Clay Science 67–68 (2012) 57–60

⁎ Corresponding author at: Faculty of Engineering and Surveying, University of

Southern Queensland, Toowoomba, QLD, 4350, Australia.

E-mail addresses: [email protected] (Z. Zhang), [email protected] (X. Yao),

[email protected] (H. Wang).

0169-1317/$ – see front matter © 2012 Elsevier B.V. All rights reserved.

doi:10.1016/j.clay.2012.05.008

Contents lists available at SciVerse ScienceDirect

Applied Clay Science

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c l a y

https://www.researchgate.net/publication/240402872_Durability_of_Geopolymer_Materials_in_Sodium_and_Magnesium_Sulfate_Solutions?el=1_x_8&enrichId=rgreq-61c5b734-cbfa-4ae1-b252-930b191040f9&enrichSource=Y292ZXJQYWdlOzI0ODUzNjc4NjtBUzoyMzQyNTkyNTIyNDg1NzZAMTQzMjg2MzE2NjIyOA==https://www.researchgate.net/publication/222298498_Effect_of_Binder_Content_on_the_Performance_of_Alkali-Activated_Slag_Concretes?el=1_x_8&enrichId=rgreq-61c5b734-cbfa-4ae1-b252-930b191040f9&enrichSource=Y292ZXJQYWdlOzI0ODUzNjc4NjtBUzoyMzQyNTkyNTIyNDg1NzZAMTQzMjg2MzE2NjIyOA==https://www.researchgate.net/publication/225759599_Effect_of_chemical_admixtures_on_properties_of_high-calcium_fly_ash_geopolymer?el=1_x_8&enrichId=rgreq-61c5b734-cbfa-4ae1-b252-930b191040f9&enrichSource=Y292ZXJQYWdlOzI0ODUzNjc4NjtBUzoyMzQyNTkyNTIyNDg1NzZAMTQzMjg2MzE2NjIyOA==https://www.researchgate.net/publication/225584414_Effectiveness_of_surface_coatings_to_protect_reinforced_concrete_in_marine_environments?el=1_x_8&enrichId=rgreq-61c5b734-cbfa-4ae1-b252-930b191040f9&enrichSource=Y292ZXJQYWdlOzI0ODUzNjc4NjtBUzoyMzQyNTkyNTIyNDg1NzZAMTQzMjg2MzE2NjIyOA==https://www.researchgate.net/publication/222769127_Surface_treatment_of_reinforced_concrete_in_marine_environment_Influence_on_chloride_diffusion_coefficient_and_capillary_water_absorption?el=1_x_8&enrichId=rgreq-61c5b734-cbfa-4ae1-b252-930b191040f9&enrichSource=Y292ZXJQYWdlOzI0ODUzNjc4NjtBUzoyMzQyNTkyNTIyNDg1NzZAMTQzMjg2MzE2NjIyOA==


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could be controlled by using MgO-based expansion agent and polypro-

pylene (PP) bers. However, since the experiments were performed at

the laboratory condition (Relative humidity=90±5%, 20±2 °C), it

was dif cult to conclude that the investigated geopolymer systems

were capable of providing a sustainable anticorrosion coating for con-

cretes exposed to natural marine environment. The primary purpose

of this technical paper is to update the research progress and to reportthe results from the eld experiment.

2. Experimental programs

2.1. Field location

The eld experiment was performed on Shanghai Jinshan coast

(Hangzhou Bay, N30.705239, E121.334724). The large temperature

change between summer (up to 38 °C) and winter (low to −10 °C)

is the reason to select this location for examining the weatherability

of the coating. The eld experiment started from 20th August 2010

(middle of summer) and the observation lasted for 6 months till

20th February 2011 (middle of winter). During this period, the ob-

served temperature varied from 38 °C (highest in summer) to−

4 °C(lowest in winter). A longer observation will be performed after this

stage when more eld information is obtained and taken into consid-

eration of geopolymer formulation and coating procedures.

Three accropodes on the coast were chosen as the concrete sub-

strates. The concrete accropodes are placed in the tide zone to absorb

the wave energy, therefore to reduce the impact of wave on seawall

(Fig. 1(a)). The deterioration of accropods is very fast. Fig. 1(b)

shows the damaged accropods after being in service for only

6 years. Fig. 1(c) shows the characteristics of the three selected sur-

faces (denoted as SI, SII and SIII respectively): SI does not contact

with seawater while SII and SIII are immersed in seawater periodically.

The difference is that SII is back to the wave shock while SIII is face to

the wave shock.

2.2. Preparation of geopolymer coating

Table 1 provides the composition of the geopolymer coating. The

chemical composition of metakaolin, slag and sodium-based activator

solution and the characteristics of MgO and PP were reported previ-

ously (Zhang et al., 2010a). The metakaolin, slag and MgO expansion

agent were dry mixed in a cement paste mixer for 10 min at a low

speed and then the activator solution with well distributed PP bers

was poured in and mixed together until homogeneous slurry was

achieved. This mixing procedure was developed to prevent the aggre-

gation of PP bers (Zhang et al., 2010a).

2.3. Coating procedure and examination

The coating work was performed in the afternoon of 20th August

2010, a cloudy and windy day. On the coast, the temperature was

26 °C, the wind reached to Grade 7 (13.9–17.1 m/s) and the relative

humidity was ~65%. After ebb tide, surfaces S II and SIII were scrubbed

with a wire brush to remove the sea shells and the loose mortar and

allowed to naturally dry for 30 min. The geopolymer slurry was man-

ually coated on SI, SII and SIII to a thickness of 3 mm, 3 mm and 5 mm

respectively with a putty brush. After the initial setting (about

30 min), the coatings were covered with wet straw mats. It was

noted thenal setting time under natural marine condition was with-

in 4 h, which is shorter than the half tidal cycle (6 h). After being so-

lidied for two tidal cycles (24 h), the straw mats were removed to

allow coatings to be hardened under ambient condition.

The coatings were daily observed during the rst month to recordthe change in appearance. To examine the possible phase change in

the hardened coatings due to the contact with seawater, XRD was

Table 1

Composition of geopolymer coating.

Metakaolin Slag Activator PP ber MgO

mass% 42.97 7.52 47.17 0.39 0.95

a

c

b

SIII: face to wave

SII: back to wave

SI: dry

Fig. 1. Field experiment location (a), the deteriorated accropodes (b), and the surfaces

to be coated (c).

58 Z. Zhang et al. / Applied Clay Science 67 –68 (2012) 57 –60

https://www.researchgate.net/publication/248536786_Potential_application_of_geopolymers_as_protection_coatings_for_marine_concrete_III_Field_experiment?el=1_x_8&enrichId=rgreq-61c5b734-cbfa-4ae1-b252-930b191040f9&enrichSource=Y292ZXJQYWdlOzI0ODUzNjc4NjtBUzoyMzQyNTkyNTIyNDg1NzZAMTQzMjg2MzE2NjIyOA==https://www.researchgate.net/publication/248536786_Potential_application_of_geopolymers_as_protection_coatings_for_marine_concrete_III_Field_experiment?el=1_x_8&enrichId=rgreq-61c5b734-cbfa-4ae1-b252-930b191040f9&enrichSource=Y292ZXJQYWdlOzI0ODUzNjc4NjtBUzoyMzQyNTkyNTIyNDg1NzZAMTQzMjg2MzE2NjIyOA==


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carried out. The sampling and testing procedures for XRD were de-

scribed elsewhere (Zhang et al., 2010b).

3. Results and discussion

Fig. 2 shows the appearance of geopolymer coatings on SI, SII and SIII

at different ages. The coatings bound withconcrete substrates very well(Fig. 3a), although they have been exposed 6 h of wave shocking on S IIand SIII in the rst 12 h. The color change with time at early age and the

different shrinkage properties were two notable phenomena. After

being solidied for 24 h, the color of the coatings changed from soil-

red to azury, a typical color that usually appears in the product of alkali

activated slag at early age, and then gradually turned back to the origi-

nal soil-red after being exposed in the marine condition for 7 d. There

was no notable color change afterwards. The most concerned property

is the integrity of the coatings under natural marine environment. It

was observed that the coating on SI (Fig. 3b) exhibited the highest

shrinkage, and a few of micro-cracks appeared on the edges after

24 h. This is because of the fast loss of water under thewindy condition

(Lin and Ran, 2010) and may also partially be due to the chemical

shrinkage of geopolymer binder (Zhang et al., 2010a, 2010b). Althoughthe coating on SII (Fig. 3c) immersed in seawater for 12 h in the rst

24 h, it still had shrinkage, which lead to the micro-cracks (the white

line indicated in Fig. 3c (left)). The coating on SIII had the best integrity

and no micro-crackwas found in therst 24 h.However, after 7 d,a few

micro-cracks appeared on the coating but the size and concentration

were much smaller than those which appeared on SI and SII.

Fig. 3 shows a piece of 28 d-aged coating chip, which was forcedly

broken off from SIII. The coating chips being pounded down always

ripped off some concrete substrate, indicating that the bonding inter-

face was stronger than the substrate. Fig. 4 presents the XRD patterns

of the 28 and 180 d-aged coatings on SIII. Calcite was detectable in

both 28 d and 180 d products. However, sulphate was not found,

maybe due to the quantity is below the testing limitation of XRD.

From literatures, the magnesium and sulphate ions have been ob-

served in the

y-ash based geopolymer matrix when the specimensimmersed in seawater, although theses ions seem to have no signi-

cant inuence on the mechanical strength (Fernández-Jiménez and

Palomo, 2009). It is reported that the alkali activated slag/metakaolin

blends possess faster carbonation when more metakaolin is used

(Bernal et al., 2010). In this study, however, it should be noted that

the slag used in this system is 12 wt.% of the total solid content,

much less than those alkali activated slag or slag/metakaolin systems,

where the slag content is more than 80 wt.% (Bernal et al., 2010). In

return very limited amount of calcite silicate hydrates (C–S–H) was

formed. Therefore, the extremely slow ingression of ions and carbon-

ation are attributed to the compact structure of the coating and the

less C–S–H, which is one possible ingredient that may process

a b24 h 180 d 24 h 180 d

10 mm

c d

24 h 180 d 24 h 180 d

10 mm 10 mm

Fig. 2. Geopolymer coatings solidied for 24 h and aged 180 d: a whole view on accropods (a); cracks to micro-cracks appeared on coating surfaces on S I (b), SII (c) and SIII (d).

Arrows point to micro-cracks.

Geopolymercoating

Concretesubstrate

PP fibres

Fig. 3. Geopolymer coating forcedly broken off with cement substrate bound together.

The cracked chips are linked by PP bres.


https://www.researchgate.net/publication/222707195_Effect_of_Silicate_Modulus_and_Metakaolin_Incorporation_on_the_Carbonation_of_Alkali_Silicate-Activated_Slags?el=1_x_8&enrichId=rgreq-61c5b734-cbfa-4ae1-b252-930b191040f9&enrichSource=Y292ZXJQYWdlOzI0ODUzNjc4NjtBUzoyMzQyNTkyNTIyNDg1NzZAMTQzMjg2MzE2NjIyOA==https://www.researchgate.net/publication/222707195_Effect_of_Silicate_Modulus_and_Metakaolin_Incorporation_on_the_Carbonation_of_Alkali_Silicate-Activated_Slags?el=1_x_8&enrichId=rgreq-61c5b734-cbfa-4ae1-b252-930b191040f9&enrichSource=Y292ZXJQYWdlOzI0ODUzNjc4NjtBUzoyMzQyNTkyNTIyNDg1NzZAMTQzMjg2MzE2NjIyOA==https://www.researchgate.net/publication/225640883_Effect_of_viscosity_modifying_agent_on_plastic_shrinkage_cracking_of_cementitious_composites?el=1_x_8&enrichId=rgreq-61c5b734-cbfa-4ae1-b252-930b191040f9&enrichSource=Y292ZXJQYWdlOzI0ODUzNjc4NjtBUzoyMzQyNTkyNTIyNDg1NzZAMTQzMjg2MzE2NjIyOA==https://www.researchgate.net/publication/223829352_Potential_application_of_geopolymers_as_protection_coatings_for_marine_concrete_II_Microstructure_and_anticorrosion_mechanism?el=1_x_8&enrichId=rgreq-61c5b734-cbfa-4ae1-b252-930b191040f9&enrichSource=Y292ZXJQYWdlOzI0ODUzNjc4NjtBUzoyMzQyNTkyNTIyNDg1NzZAMTQzMjg2MzE2NjIyOA==https://www.researchgate.net/publication/248536786_Potential_application_of_geopolymers_as_protection_coatings_for_marine_concrete_III_Field_experiment?el=1_x_8&enrichId=rgreq-61c5b734-cbfa-4ae1-b252-930b191040f9&enrichSource=Y292ZXJQYWdlOzI0ODUzNjc4NjtBUzoyMzQyNTkyNTIyNDg1NzZAMTQzMjg2MzE2NjIyOA==


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carbonation. The white solid product(s) appeared on coatings in the

early age (7 d) could be CaCO3 or a mixture of CaCO3 and Na2CO3. Al-

though there is no detectable Na2CO3 in the 28 d and 180 d products,

it cannot exclude the possibility that the formation of Na2CO3. Na2CO3seems more possible because with the geopolymerization continuing,

the white product no longer appears as less sodium is available.

From the above observation it can be concluded that the geo-

polymer coating develops a high bonding strength within 6 h,

which is strong enough to resist the wave shock. The chemical stabil-

ity of the coating under marine condition is also sound. One potential

problem could be the water stability of fresh coating when contacts

with seawater (Temuujin et al., 2011). However, from the laboratory

and eld experiments in this investigation, the geopolymer coatings

exhibited good water stability. The only issue noticed is shrinkage,

which causes a high tension stress on surface, resulting in micro-

cracks. Small cracks may not affect the bonding strength and the

chemical stability. However, cracks would allow the aggressive ions

to reach and corrode the concrete inside, and thus invalidate the func-

tion of geopolymer coating.

The humidity of the atmosphere and the thickness of coating layer

are the two factors that have signicant impacts on the integrity of

geopolymer coating. The cracks appeared on SI are more and wider

than on SII. Since both coatings on SI and SII are of 3 mm thickness,

it is clear that periodical contact with seawater reduces the shrinkage

of coating. Applying geopolymer coating on the tidal concrete struc-

tures seems more preferred. The thickness factor can be seen by com-

paring the coatings on SII and SIII. Although they are suffered the same

tidal cycles, the thicker coating on SIII exhibits fewer cracks and better

integrity. It is concluded that increasing the thickness of the coatingfrom 3 mm to 5 mm is helpful in reducing the shrinkage of geo-

polymer coatings.

The addition of MgO-based expansion agent and PP bers can ef-

fectively reduce the shrinkage of geopolymer paste at high humidity

conditions, reported at laboratory condition with RH= 90± 5%

(Zhang et al., 2010a). However, this method is less effective in con-

trolling shrinkage of geopolymer coating under natural marine condi-

tion. The rst reason lies on the chemical shrinkage nature of

geopolymer binder, particularly for metakaolin-based geopolymer,

which requires a much higher liquid/solid ratio to achieve good

workability. The second reason is that the high speed wind on coast

accelerates the water evaporation during solidifying and causes a se-

rious shrinkage at plastic stage. The third reason is that the coating is

usually a relatively thin layer. The fast water loss of thin layer contrib-utes to the dry shrinkage after hardening. Several remedies may be

helpful to solve the problem. One is using sand or other aggregates

to reduce the binder content in coating. It has been noted that a

higher sand/binder ratio results in low shrinkage (Vasconcelos et al.,

2011). Spraying suitable shrinkage reducing agents (moisturizers)

on the surface of coating or using viscosity modifying agents to re-

duce water evaporation may also work (Lin and Ran, 2010). However,

those commercial agents are only reported workable for normal con-

crete. Very limited information about geopolymer additives has beendisclosed yet. Further investigations are needed in both the coating

composition design and the eld application procedure.

4. Summary

A novel geopolymeric coating material has been proposed with the

aim of protecting the concrete structures exposed to marine environ-

ment. The systematical experiments from laboratory and eld applica-

tion have demonstrated the coating possesses suitable setting time,

high bonding strength and excellent anti-corrosion properties. The

chemical stability under marine condition enables it to provide a sus-

tainable protection to concrete structures. The large shrinkage during

setting and hardening can be reduced by adding MgO-based expansion

agent and PP

bers but not satisfactory under naturalmarinecondition.Recommendations for solving this problem include: 1) to keep the coat-

ing thickness>5 mm; 2) to apply the coating at tidal area, where the

humidity is relatively high and the deterioration of concrete is more se-

rious; 3) to add suitable aggregates in coating paste and/or to develop

appropriate shrinkage reducing agents; 4) to apply careful curing pro-

duces at early age, such as cover wind shields.

Acknowledgements

The authors acknowledge the support of the Graduates Research &

Innovation Program (CX098_126Z) of Jiangsu province, China, the In-

ternational Postgraduate Research Scholarship provided by the Aus-

tralia government and the Halok Pty Ltd Research Scholarship.

References

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10 20 30 40 50 60 70 80

calcite

2-theta (degree)

28 d

180 d

α-Quartz

kaolinite

Fig. 4. XRD patterns of the geopolymer coating on SIII at ages of 28 d and 180 d.

https://www.researchgate.net/publication/225640883_Effect_of_viscosity_modifying_agent_on_plastic_shrinkage_cracking_of_cementitious_composites?el=1_x_8&enrichId=rgreq-61c5b734-cbfa-4ae1-b252-930b191040f9&enrichSource=Y292ZXJQYWdlOzI0ODUzNjc4NjtBUzoyMzQyNTkyNTIyNDg1NzZAMTQzMjg2MzE2NjIyOA==https://www.researchgate.net/publication/221987264_Preparation_and_Thermal_Properties_of_Fire_Resistant_Metakaolin-Based_Geopolymer-Type_Coatings?el=1_x_8&enrichId=rgreq-61c5b734-cbfa-4ae1-b252-930b191040f9&enrichSource=Y292ZXJQYWdlOzI0ODUzNjc4NjtBUzoyMzQyNTkyNTIyNDg1NzZAMTQzMjg2MzE2NjIyOA==https://www.researchgate.net/publication/248536786_Potential_application_of_geopolymers_as_protection_coatings_for_marine_concrete_III_Field_experiment?el=1_x_8&enrichId=rgreq-61c5b734-cbfa-4ae1-b252-930b191040f9&enrichSource=Y292ZXJQYWdlOzI0ODUzNjc4NjtBUzoyMzQyNTkyNTIyNDg1NzZAMTQzMjg2MzE2NjIyOA==

2012-applied clay science-z.zhang, et al.,-potential application of geopolymers

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