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Chemical resistance of epoxy and polyester polymer concrete to acids and salts

M.C.S. Ribeiro, C.M.L. Tavares, A. J.M. Ferreira

Instituto de Engenharia Mecânica e Gestão Industrial Faculdade de Engenharia da Universidade do Porto

Rua do Barroco, 174-214 4465-591 Leça do Balio

Abstract

The aim of this work is to analyse the chemical resistance of epoxy and polyester

concretes when exposed to acids and salts. The chemical resistance is evaluated through

the variation of bending strength and variation of mass, after exposure in acid and salted

solutions, for various periods of time.

The test solutions chosen were water solutions of sulphuric acid and sodium chloride.

The motivation for this research work is the increasing use of polymer concrete

structures near seawater and residual waters.

1 – INTRODUCTION

Polymer concrete is a mixture of mineral aggregate and a polymer binder in which the

polymeric resin replaces the Portland cement/water binder of conventional concrete [1].

In comparison with conventional Portland cement concrete, this unique composite

material offers a number of advantages, such as higher strength, better chemical

resistance, and lower permeability [2].

The applications of polymer concrete have developed quickly since the 1950s when it

was used initially to produce synthetic marble. Since then, its applications in structural

have increased tremendously because of its good workability, low-temperature curing

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and early high strength development. With the expansion of its applications, its

chemical resistance has been an important characteristic [3].

There have been several publications on deterioration of Portland cement concrete when

exposed to corrosive environment (Attiogbe and Rizkalla [4], Hendrik and Orbison [5],

Fattuhi and Hughes [6]). However, little information is available concerning the

resistance of polymer concrete to aggressive chemical agents.

Previous studies on polymer-metal composites, carried out by Kinloch [7], showed that

one of the most common aggressive environments is water.

Ohama [8] studied the resistance of polyester PC to hot water. Cylindrical PC

specimens were immersed in boiling water for up to 1 year before being tested in

compression and splitting tension. It was concluded that erosion depth in polyester PC

increased, with the immersion time, and the compressive and tensile strengths

decreased, with no appearance or weight change.

Yamamoto [9] immersed Portland cement mortar and polyester resin mortar in 10%

hydrochloric acid and 10% sulphuric acid for a period of 28 days. No loss in weight was

observed for the PC. However, Portland cement mortar specimens lost about 50% of its

initial weight.

Mebarkia and Vipullanandan [10] analysed the changes in compressive strength of

polyester PC, after a one-month immersion, in chemical solutions with various PH

levels. They concluded that the strength of PC decreased with the increase in PH level

of the chemical solutions.

Ohama and Kobayashi [3] also investigated the effect of 11 typical reagents in the

compressive strength of polymethyl methacrylate concrete. The test results showed that

this kind of material is seriously attacked by acetone and toluene and slightly attacked

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by acids. However it shows good resistance to tap water, alkali, salts, kerosene and

rapeseed oil.

Chawalwala [2] studied the application of vinyl and polyester polymer concrete as a

wear surface for a composite bridge deck. The behaviour of these PC, when exposed to

water and chemicals like motor oil and antifreeze solutions, was investigated. It was

concluded that the degradation rate of PC properties was primarily due to the weakness

of the interface between the aggregate and the polymer matrix phases, witch depends on

the absorbed water content.

Following these studies, the purpose of this work is to analyse the chemical resistance

of epoxy and unsaturated polyester polymer concrete to water solutions of sulphuric

acid and sodium chloride. The choice of these chemical reagents is justified by the

increasing use of polymer concrete structures near seawater and residual waters. The

concentration of both test solutions is 10% in order to simulate, as close as possible, the

exposure conditions. The chemical resistance is evaluated through the variation of

bending strength and variation of mass, after exposure in the test solutions for various

periods of time. The rate of degradation with exposure time is also evaluated.

2 – EXPERIMENTAL PROGRAM

2.1 Preparation of the specimens

PC with the binder formulations and mix proportions given in Table 1 was mixed and

moulded to prismatic specimens 40*40*160mm, according to RILEM PC2-“Method of

making polymer concrete and mortar” [11]. Early studies, using Taguchi method, did

permit to optimise these formulations [12 and 13].

The polyester resin used was an orthophtalic one (NESTE-S226E), pre-accelerated, with

2% in mass of methyl ethyl ketone peroxide catalyst. The chosen epoxy resin (EPOSIL-

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551) has low viscosity (500-600 mPa.s), and flexural strength of 70+/-5 MPa. The

foundry sand used in this research has a very uniform grain and a d501 of 342 microns.

It was made, for each kind of polymer concrete, three batches with 18 specimens each

(3 control specimens + 15 test specimens). The third batch was necessary for the control

solution of distillate water.

All the specimens were allowed to cure for one day at room temperature and then at

80ºC for three hours (post-cure treatment).

[Insert TABLE 1]

2.2 Chemical resistance tests

The cured specimens were tested for chemical resistance at room temperature in

accordance with standard RILEM PC12- “Method of test for chemical resistance of

polymer concrete”[14]. The types of test solutions used were as follows: 10% sulphuric

acid (H2SO4), and 10% sodium chloride (NaCl). A control solution of distilled water

was also used according to [14].

The test specimens, after record of their weight, were soaked in solutions for periods of

time of 1, 7, 21, 56 and 84 days.

After each immersion period, the appearance of three test specimens was visually

checked, cleaned by running tap water, quickly dried by blotting it with a paper towel,

and their weight was measured.

After that, three-point bending tests, according to RILEM PCM8-“Method of test for

flexural strength and deflection of polymer-modified mortar”[15], were performed on

the test specimens. Test results were compared with those obtained from flexural tests

of the three control specimens.

1 d50 - 50% of sand particles are less than this size.

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Mass change and flexural strength change of the specimens after immersion for each

examination period were calculated by the following equations (rounded off to nearest

tenth):

Mass change = [ ( Mf – Mi ) / Mi ] * 100

where Mi is the mass (g) of the specimens before immersion, and Mf is the mass (g)

after test period.

Flexural strength change = [ ( Ff – Fi ) / Fi ] * 100

where Fi is the flexural strength (MPa) of the control specimens, and Ff is the flexural

strength (MPa) of the test specimens for each examination period.

Accordingly, it was calculated the relative mass change and relative flexural strength

change of the specimens after immersion for each examination period by the following

equations (rounded off to integer):

Relative mass change = ( Moi / Mow )*100

where Moi is the mass change of the specimens after immersion in each test solution for

each examination period (%), and Mow is the mass change of the specimens after

immersion in control solution of water for each examination period (%).

Relative flexural strength change = ( Foi / Fow )*100

where Foi is the flexural strength change of the specimens after immersion in each test

solution for each examination period (%), and Fow is the flexural strength change of the

specimens after immersion in control solution of water for each examination period (%).

3 – TEST RESULTS

The test results, mass change and flexural strength change, for each test solution and for

each kind of polymer concrete, as function of immersion period, are shown in figures 1

to 4. The relative change of these two parameters is represented in Table 2.

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[Insert Figure 1, 2 3, 4]

[Insert TABLE 2]

The change in appearance of test specimens immersed in the chemical solutions after

each examination period is described in Table 3. The more relevant changes, as well the

failure surface of PC specimens are illustrated in figures 5 to 7.

[Insert Table 3]

[Insert Figure 5,6,7]

By an X-Ray microanalysis (EDS/WDS) and a scanning electronic microscopy (SEM)

analysis, done on samples of attacked surface, it was possible to determine the chemical

nature of the incrustations that appeared in the surface of some epoxy PC specimens

immersed in NaCl solution.

The photographic record by scanning electronic microscopy, of the density map of an

affected sample is illustrated in figure 8.

Figure 9 shows the chemical spectres or elementary distribution profiles, obtained by X-

Ray microanalysis (EDS/WDS), of three different points of that sample:

I. one point corresponding to a smooth surface of the sample –Profile I-;

II. another point corresponding to an area where there was an detachment of the

concrete mass due to the demoulding, but without chemical attack signs –

Profile II-;

III. and finally, a third point in the border of this detachment area in which the

incrustations are located –Profile III-.

[Insert Figure 8]

[Insert Figure 9]

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Attempting to high pattern of iron (II) oxide presented in Profile III, it was concluded

that the formations dark chestnut were unequivocally little rust incrustations.

The appearance of these incrustations is probably related to the presence of iron trioxide

(0,1%) in foundry sand constituents. This compound, despite its little content, is

unstable in alkali environments, and is reduced to iron (II) oxide, the stable form when

pH increases.

The zones with slightly detachments were the elected places for the occurrence of this

phenomenon car in these zones, due the abrasion process, the sand grains are not totally

recovered with the polymer binder. The presence of free amine in those places,

proceeding from the epoxy resin hardener, created a favourable alkali environment to

oxidation process.

4 – RESULTS DISCUSSION

4.1 Mass variation

In all test solutions, the weight change of the epoxy PC specimens was very small and

always smaller than polyester PC specimens. The discrepancy of values was more

significant in relation to immersion in water: for 84 days immersion period, the average

mass change of epoxy concrete specimens was 0.088%, while the average mass change

of polyester concrete specimens was 0.443%. The higher mass change was verified,

precisely, for polyester PC immersed in water, which indicates that the chloride sodium

and sulphuric acid, with the concentrations used in test solutions, inhibit in part the

water absorption rate (the relative mass changes of polyester PC specimens for both test

solutions were, respectively, 36.3% and 56.7%).

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4.2 Flexural strength variation

For all the test solutions, the flexural strength change was clearly smaller for the epoxy

PC specimens. For the longest period of conditioning, the maximum flexural strength

decrease occurred in this kind of PC was approximately 8%, against 30% in the case of

polyester PC2.

The higher permeability of polyester PC, measured by weight uptake values after

immersion and indicated equally by the existing aureole in failure surface, could be an

explication for the bigger decrease of flexural resistance.

For both types of concrete, the specimens immersed in chloride sodium solution showed

the smallest flexural strength decreases. Inclusively, for the initial examination periods

(1, 7 and 21 days), it was verified an increase in the flexural strength3.

The rust incrustations, that appeared in the surface of some epoxy PC specimens

immersed in salt water, did not affected their flexural strength. It’s a located and

superficial phenomenon, and even to longer immersion periods, it is not expect it comes

to have any influence in the mechanical resistance of the concrete.

4.3 Correlation between mass and flexural strength variations

There is a positive correlation between mass change and flexural strength reduction.

This correlation is very clear in the case of the polyester PC specimens immersed in

water and sulphuric acid solution – the linear correlation coefficients obtained were,

respectively, 0.98 and 0.91. Relatively to epoxy PC specimens, the correlation is not so

strong: for the same test solutions, the coefficients obtained were 0.65 and 0.76.

2 Values referring to specimens immersed in sulphuric acid solution. 3 This increase could be irrelevant, but it also could be indicative of little representation of control specimens. The control specimens, chosen among all the specimens proceeding from the same batch, could be precisely those, which have smaller flexural resistance.

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This correlation between the two parameters was already expected, as mentioned in

previous works [2, 3 and 10].

It is very important in composite materials that good adhesion is maintained across the

interfacial region. This is because, in most multiphase composites, the load is

transferred from one phase to another via a shear mechanism at the interface. Previous

studies showed that the polymers did not react or dissolve in water, and its strength is

not affect by immersion up to 3 years in water [7, 16, 17 and 18]. So, it can be

concluded that the most predominant factor causing the reduction in strength is the

degradation of the interface due to water diffusion into PC.

In the case of the test specimens that have been immersed in chloride solution, it was no

possible to establish a positive correlation between water uptake and strength reduction

due to flexural strength increases in the first examination periods.

5 – CONCLUSIONS

The effect of chloride sodium and sulphuric acid chemical solutions on the bending

strength and mass of an epoxy and polyester polymer concretes was investigated in

various periods from 1 to 84 days. A comparative analysis with the effect of water

immersion was also done.

Based on experimental results, the following conclusions are proposed:

♦ The flexural strength of epoxy PC is slightly affect by the immersion in the

solutions of sulphuric acid and chloride sodium, which is an indicator of the

good chemical resistance of this kind of concrete to these aggressive agents. The

natural heterogeneity among specimens is, probably, the main cause of the small

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differences recorded for flexural strengths obtained for the consecutive

examination periods.

♦ The flexural strength decrease of polyester PC with the immersion time in the

test solutions is not irrelevant, specially in the sulphuric acid solution, and it

cannot be justified by the natural variability among specimens proceeding from

the same batch. It will be necessary a deeper study, with longer immersion

times, to evaluate the significance and the level of strength reduction.

♦ Taking into account the positive correlation between water uptake and flexural

strength decrease4, the different behaviour of the two kinds of concrete, can be

related to the matrix permeability characteristics of each resin used in this

research, which is one of the factors which influence the most the integrity of the

aggregate-resin binder interface.

For a better understanding of the unexpected increase of the flexural resistance, in the

initial immersion times, of both PC specimens immersed in chloride sodium solution,

another study is foreseen.

6 – REFERENCES

[1] Walters, D.G., Polymer Concrete, 1993, Detroit: American Concrete Institute, SP

137.

[2] Arif J. Chawalwala, Material characteristics of Polymer Concrete, 1999, Technical

Report, University of Delaware Center of Composite Materials.

4 Except for the first immersions periods in the case of the specimens immersed in chloride sodium.

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[3] Y. Ohama, T. Kobayashi, K. Takeuchi and K. Nawata, Chemical resistance of

polymethyl methacrylate concrete, May 1986, International Journal of Cement

Composites and Lightweight Concrete, p.86-91.

[4] E. Stooge and S. Rizkalla, Response of concrete to sulphuric acid attack, 1988, ACI

Journal, 85, p.109-118.

[5] L. Hendrik and J. Orbison, Concrete deterioration due to acid precipitation, 1987,

ACI Journal, 84, p.110-116.

[6] N. Fattuhi and B. Hughes, Ordinary Portland cement mixes with selected admixture

subjected to sulphuric acid attack, 1988, ACI Journal, 85, p.512-518.

[7] A.J. Kinloch, Environmental attack at metal-adhesive interfaces, 1987, Elsevier

Applied Science, New York.

[8] Y. Ohama, Hot water resistance of polyester resin concrete, 1977, Proceedings of

20th Japan Congress on Materials Resistance, Tokyo, Japan, p.176-178.

[9] T. Yamamoto, The production performance and potential of polymers in concrete,

Proceedings of 5th International Congress on Polymer in Concrete, p.395-398.

[10] S. Mebarkia and C. Vipulanandan, Mechanical Properties and Water Diffusion in

Polyester Polymer Concrete, December 1995, Journal of Engineering Mechanics,

p.1359-1365.

[11] RILEM PC-2, Method of making polymer concrete and mortar specimens,

Technical Committee TC-113, Symposium on Properties and Test Methods for

Concrete-Polymer Composites.

[12] C. Tavares, C. Ribeiro, A. Ferreira and A. Fernandes, Influence of Material

Parameters in the Mechanical Behaviour of Polymer Concrete, 2000, Proceedings

of Mechanical and Materials in Design, Orlando, USA.

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[13] A.J.M. Ferreira, C. Tavares and C. Ribeiro, Flexural properties of polyester resin

concretes, 2000, Journal of Polymer Engineering, Freund Publishing House, v.20,

nº6, p.459-468.

[14] RILEM PC-12, Method of test for chemical resistance of polymer concrete and

mortar, Technical Committee TC-113, Symposium on Properties and Test Methods

for Concrete-Polymer Composites.

[15] RILEM PCM-8, Method of test for flexural strength and deflection of polymer-

modified concrete, Technical Committee TC-113, Symposium on Properties and

Test Methods for Concrete-Polymer Composites.

[16] D. Feldman, Polymeric building materials, 1989, Elsevier Applied Science,New

York.

[17] A. Davids and D. Simns, Weathering process for polymer composites, 1983,

Applied Science Publishers Ltd., New York.

[18] S. Mebarkia, Mechanical and Fracture Properties of High Strength Polymer

Concrete under Various Loading Conditions and Corrosive Environments, 1993,

Doctoral Dissertation, Faculty of the Department of Civil and Environmental

Engineering, University of Houston.

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Table 1 – PC formulations and mix proportions.

PC formulations PPC EPC

Resin Polyester Epoxy

Sand Foundry Foundry

Resin content 20 % 20 %

Charge content 0 % 0%

Table 2 – Relative mass change and relative flexural strength change.

POLYESTER EPOXY Test Sol.

R. Mass C.(%) R. Fl.St. C.(%) R. Mass C.(%) R. Fl.St. C.(%)

H2 SO4 56.66 95.36 243.18 591.09

Na Cl 36.34 51.38 118.18 -114.38

Table 3 – Appearance change of PC specimens immersed in test solutions.

Immersion period (days)

Test Sol. 1 7 21 56 84

H2O No change No change Marked

aureole in FS – 1mm -

Marked aureole in FS

– 3mm -

Marked aureole in FS

– 5mm -

H2SO4 No change No change Slight aureole

in FS – 2mm -

Marked aureole in FS

– 3mm -

Marked aureole in FS

– 4mm -

Pol

yest

er P

C

NaCl No change No change Slight aureole

in FS - 1mm -

Slight aureole in FS

- 2mm -

Fair whitening Slight aureole

in FS

H2O No change No change No change No change No change

H2SO4 No change No change Slight whitening

Slight whitening

Slight whitening

Epo

xy P

C

NaCl

Small incrustations chestnut in

prompt zones

Idem Idem Idem Idem

FS – Failure surface

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Fig.1 – Mass change (%) of polyester PC specimens as function of the immersion period and test solution.

Fig.2 – Mass change (%) of epoxy PC specimens as function of the immersion period and test solution.

- Epoxy polymer concrete -

0

0.1

0.2

0.3

0.4

0 20 40 60 80 100 Immersion period (days)

Mas

s ch

ang

e (%

)

Water Solution H2SO4 Solution NaCl Solution

- Polyester polymer concrete -

0

0.1

0.2

0.3

0.4

0.5

0 20 40 60 80 100 Immersion period (days)

Mas

s ch

ang

e (%

)

Water Solution H2SO4 Solution NaCl Solution

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Fig.3 – Flexural strength change (%) of polyester PC specimens as function of immersion time and test solution.

Fig.4 - Flexural strength change (%) of epoxy PC specimens as function of immersion time and test solution.

- Polyester polymer concrete -

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

0 20 40 60 80 100

Immersion (days)

Fle

xura

l str

eng

th c

han

ge

(%)

Water Solution H2SO4 Solution NaCl Solution

- Epoxy polymer concrete -

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

0 20 40 60 80 100

Immersion period (days)

Fle

xura

l str

eng

th c

han

ge

(%)

Water Solution H2SO4 Solution NaCl Solution

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Fig.5 – Failure surface of the control and test specimens for the successive immersion

periods in the test solutions.

a), b) Polyester and epoxy PC specimens, respectively, immersed in water solution; c), d) Polyester and epoxy PC specimens, respectively, immersed in sulphuric acid solution; e), f) Polyester and epoxy PC specimens, respectively, immersed in chloride sodium solution;

0

84 56 21

7 1

a) b)

Control 1 d 7 d

21 d 56 d 84 d

c) d)

e) f)

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≅ 5 mm

Fig.6 – Detail of failure surface of polyester PC specimen immersed in water for 84

days.

Fig.7 – Incrustations dark chestnut that had appeared in the surface of some epoxy PC specimens immersed in chloride sodium solution.

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Fig.8 – Density map (scanning electronic microscopy) of an affected sample of epoxy

PC specimen immersed in chloride sodium solution.

Fig.9 – Elementary distribution profiles of three different points of an affected sample,

obtained by spectroscopy.

I

II

III

Profile II Profile III Profile I