Engineering Geology 127 (2012) 75–80

Contents lists available at SciVerse ScienceDirect

Engineering Geology

j ourna l homepage: www.e lsev ie r .com/ locate /enggeo

Technical Note

A comparative investigation of the degradation of pyrite and pyrrhotite undersimulated laboratory conditions

S. Chinchón-Payá a,⁎, A. Aguado b, S. Chinchón a

a Departamento de Construcciones Arquitectónicas, Universidad de Alicante, Carretera de San Vicente del Raspeig s/n 03690 San Vicente del Raspeig, Alicante, Spainb Departamento de Ingeniería de la Construcción, Campus Nord, Edifici C1, C/Jordi Girona 1-3 08034, Barcelona, Spain

⁎ Corresponding author. Tel.: +34 965903677; fax: +E-mail address: s.chinchon@ua.es (S. Chinchón-Payá

0013-7952/$ – see front matter © 2011 Elsevier B.V. Alldoi:10.1016/j.enggeo.2011.12.003

a b s t r a c t

a r t i c l e i n f o

Article history:Received 23 August 2010Received in revised form 30 November 2011Accepted 3 December 2011Available online 5 January 2012

Keywords:PyritePyrrhotiteCarbonatesConcreteOxidation

The effect of the oxidation of iron sulfides contained in aggregates on concrete durability is well known. Themechanisms of formation of gypsum or ettringite have been well documented for a long time and also, forabout 15 years, the formation of thaumasite although there are some unanswered questions concerningthis compound, such as whether the ettringite is always needed as a precursor to thaumasite.However, there are few studies on behavioral differences of different oxidizable sulfides in the process of oxida-tion with more or less harming effects on concrete durability. As a result there is some confusion in the variousstandards of aggregates for concrete. The American Standard ASTMC294-05 (Section No. 13) does not make anydistinction between the different sulfide types: marcasite, pyrite or pyrrhotite. In contrast, the European stan-dard EN 12620:2008 specifically in paragraph 6.3.2 says that it is necessary to take special precautions if it detectsthe presence of pyrrhotite (an unstable form of iron sulfide FeS). Once confirmed of their presence the maximum totalsulfur content is less than 0.1%. This amount is 10 times lower than would be permitted for aggregates containingother iron sulfides. This fact is exaggerated from the point of view of many engineers and could result that inpractice, suitable aggregates have been rejected unnecessarily on some sites.This technical note presents the findings of a first experimental set-up that serves to analyze the products of anaqueous solutionwith constant oxygen supply in twopyrite andpyrrhotite samples aswell as the physicochemicalpH and electrical potential values of the solutions. The results show the existence of significant differences regard-ing the nature of the alteration products proving that the pyrrhotite is degraded more than the pyrite. In a secondexperimental set-up, the oxidation of both iron sulfides has been analyzed but three aggregate types coming fromthree different rocks were added: a marlstone, a limestone and a shale. In all three cases reveal that pyrrhotite isdegraded more than pyrite.Despite the limitations in the representativity of this study in such a huge context, the results of this study permitsome first reflections to be made about the normative that rules the characterization and quantification of sulfurcompounds in concrete aggregates.

© 2011 Elsevier B.V. All rights reserved.

1. Introduction

1.1. Pyrite and pyrrhotite oxidation

Pyrite (FeS2) and pyrrhotite (Fe1−xS) are commonly referred to asoxidizable iron sulfides because they can react relatively quickly inthe presence of water and oxygen. Due to the degradation productsresulting from this process, it is problematic in two ways. Firstlyfrom an environmental point of view, there is an enormous supplyof protons which can result in the pore solutions becoming highlyacid. Neutralization of this acidity can mobilize metals into solution,thus leading to groundwater contamination (Ziemkiewicz et al.,1997; Gravotta and Trahan, 1999; Santomartino and Webb, 2007).Secondly, from the engineering point of view, as a result of the oxidation

34 965903702.).

rights reserved.

of these sulfides, acid and sulfate attacks can be produced that affectconcrete structures very much.

The pyrite dissolution can occur as a direct oxidation. The main oxi-dant agent is oxygen dissolved inwater. Ferric ions can act as catalysers.The reactions taking place are (Moses et al., 1987):

FeS2 þ 7=2O2 þ H2O→Fe2þ þ 2SO

2−4 þ 2H

þ ð1Þ

Fe2þ þ 1=4O2 þ H

þ→Fe3þ þ 1=2H2O ð2Þ

FeS2 þ 14Fe3þ þ 8H2O→15Fe

2þ þ 2SO2−4 þ 16H

þ ð3ÞReaction (2) is extremely low but in natural environments it is

strongly conditioned by temperature and relative humidity (Steguer,

Fig. 1. SEM image shows ettringite crystals in fractures and pores.

76 S. Chinchón-Payá et al. / Engineering Geology 127 (2012) 75–80

1982; Dehaan, 1991) and it is catalyzed by the presence of sulfur-reducing bacteria (Colmer and Hinkle, 1947; Dehaan, 1991).

The pyrrhotite reactions and products are difficult to identify.Thomas et al. (2001) add to the oxidative mechanism of pyrrhotite,a non-oxidative dissolving process. The first element to interveneduring the oxidative process is the dissolved O2 but, as in the caseof pyrite, oxidative force is also provided by Fe3+ ions, which arethen reduced to Fe2+ (Thomas et al., 1998; Thomas et al., 2000;Thomas et al., 2001). In this respect, the presence of Fe3+ can main-tain a cyclic reaction where it acts as an oxidant (Belzile et al.,2004), according to the reaction stated below:

Fe1−xS þ ð8−2ñÞFe3þ þ 4H2O→ð9−3ñÞFe2þ þ SO2−4 þ 8H

þ ð4ÞIn the non-oxidative process there is a consumption of protons

with formation of H2S.Chiriţă et al. (2008) also say that while FeS2 dissolves only in the

presence of an oxidant, FeS does so with or without those in oxidativeand non-oxidative processes.

1.2. Expansive reactions in concrete

There is abundant documentation on the expansive reactions thatoccur in concrete as a result of the reaction between the sulfates gen-erated in the oxidation of sulfides and hydrated portland cementcomponents:

• In the case of concrete made with low-aluminate content cements(sulfate resistant cement), gypsum is formed as a result of thereaction between sulfates and portlandite (reaction 5) or with thecalcite resulting from the carbonation of portlandite process(reaction 6).

2X þ SO2−4 þ CaðOHÞ2 þ 2H2O→CaSO4·2H2O þ 2OH

− þ 2X ð5Þ

2X þ SO2−4 þ CaCO3 þ 2H2O→CaSO4·2H2O þ CO

2−3 þ 2X ð6Þ

Where X=Na+, K+ or 1/2 Mg2+

• When using ordinary portland cement in concrete (non sulfate resis-tant cement), secondary and strongly expansive ettringite is formedas a result of the reaction between sulfate and aluminate cements.This reaction is the most widely documented (Taylor, 1997; Ayoraet al., 1998; Aguado et al., 2003; Neville, 2004; Araújo et al., 2008)and it is considered that the ettringite can be formed from gypsum(reaction 7) or monosulfate (reaction 8)

3CaSO4·2H2O þ ðCaOÞ3ðAl2O3Þþ 26H2O→ðCaOÞ3ðAl2O3ÞðCaSO4Þ3·32H2O ð7Þ

ðCaOÞ3ðAl2O3ÞðCaSO4Þ·12H2O þ 2CaSO4·2H2Oþ 16H2O→ðCaOÞ3ðAl2O3ÞðCaSO4Þ3·32H2O ð8Þ

Aswith any crystallization, this will commence in existing voids, poresand cracks in the cement paste. If degradation continues, the increasedvolume of this new solid leads to tensions and microfissurations(Figure 1).

• In certain circumstances, thaumasite can even be formed causingmore damage to the structure because the phase that reacts withthe sulfate is the C–S–H (reaction 9).

C–S–H þ H2O þ SO2−4 þ CO

2−3

þ 4X→½Ca3SiðOHÞ6�ðSO4ÞðCO3Þ·26H2O ð9Þ

Where X=Na+, K+, 1/2 Mg2+ or 1/2Ca2+

The acicular appearance of thaumasite and ettringite and the fact thatthe X-ray diffraction (XRD) patterns are similar, have led to in the past,that some samples of thaumasite have been mistaken with ettringite.In 2003 a monographic International Congress about thaumasite tookplace in UK and an interesting thematic volume of Cement and ConcreteComposites wheremore than 50 articles appeared (Cement and ConcreteComposites, 2003). It perfectly describes all topics about thaumasite andconditions to be formed under. We think it is interesting to highlightthe idea supported by some authors about the possibility of formationof thaumasite in concrete made with sulfate resisting portland cement(The UK Government Thaumasite Expert Group, 1999; Crammond,2002; Crammond, 2003; Torres et al., 2004; Zhou et al., 2007) This is anissuewe are working on and our results seem to indicate that thaumasitealways needs ettringite as a precursor as stated by many other authors(Taylor, 1997; Barnett et al., 2002; Barnett et al., 2003; Bensted, 2003;Macphee and Barnett, 2004; Köhler et al., 2006). (Figure 2).

1.3. Iron sulfides in aggregates for concrete

There are different standards concerning the characterization andquantification of iron sulfides contained in aggregates for concrete.

Article No. 28 of the Spanish Regulation on Structural Concrete —

EHE — (EHE, 1999), in force between 1999 and July 2008, prohibitsthe use of coarse aggregates which contain oxidizable sulfur com-pounds. An important clarification is made in the Comments sectionwhere it states that: oxidizable sulfurs (e.g. pyrrhotite, marcasite andsome forms of pyrite), even in small quantities are very damaging to con-crete since, as through oxidation and hydration, they form sulfuric acidand iron oxide/hydroxide minerals.

It is important to highlight that in 1998 there was no obligatory Euro-pean standard — EN — with which the EHE could be compared. In anycase the text is similar to that found in the American standard (still inforce) Section No. 13 of ASTM C294-05 (ASTM C294-05, 2005) whichstates: Marcasite and certain forms of pyrite and pyrrhotite are reactive inmortar and concrete, producing a brown stain accompanied by an increasein volume that has been reported as a source of popouts in concrete.

Finally, Section 28.7.3 of the new EHE-08 (EHE-08, 2008) makes thefollowing statement: Should the presence of oxidizable iron sulfides in theform of pyrrhotite be detected, the sulfur content provided by them,expressed in S, will be lower than 0.1%. That paragraph is the same that ap-pears in Section 6.3.2 of EN 12620:2008 (EN 12620, 2008) and it

Fig. 4. XRD spectra and XRF analysis of Fe and S compositions of the pyrite (lower) andpyrrhotite (upper) samples.

Fig. 2. SEM image shows thaumasite (EDX microanalysis with Si) and ettringite (EDXmicroanalysis with Al).

77S. Chinchón-Payá et al. / Engineering Geology 127 (2012) 75–80

appeared exactly as in Section 6.3.2 of EN 12620:2002 (EN 12620, 2002).Thus it is implied, that of the various iron sulfide minerals, pyrrhotite isthe only one really harmful to concrete.

It should be added that neither the EN 12620:2008 nor any othernormative of aggregates for concrete consulted, refer to the impor-tance of host rock in the process of degradation of the sulfurs. In theabsence of this regulatory vacuum it is worth quoting a recent study(Reid and Avery, 2009) that proposes a test to measure the potentialreactivity of sulfides in the aggregate and contains important reflec-tions. However, in this work it is also clear that many gaps remainto be resolved in the field of characterization and quantification ofsulfur compounds in the aggregates.

The authors of this article are part of a Research Group that has beenworking for 20 years on dam concretes in which the coarse aggregatesvery often contain oxidizable iron sulfides, usually in the formof pyrrho-tite in a metamorphic shale host rock. It has been observed in practicethat this combination produces conditions more harmful to concretethan other situations such as for example limestones with pyrite.

The work exposed here is the first step to a more extended studyon the role of different iron sulfides when they form part of aggre-gates used in concrete dams, and has a twofold objective: firstly, tostudy the oxidation of pyrite and pyrrhotite samples under thesame experimental conditions, seeking to differentiate their

Fig. 3. Image showing the sacks which contain shales with pyrrhotite. It could be seenthat the aggregates already have a certain degree of weathering.

respective behaviors; and secondly, to investigate the effects of add-ing different aggregates to solutions containing pyrite and pyrrhotitein order to check the effect that the host rock has on the speed of re-action and the nature of the reaction products.

The experiences shown here are intended to reproduce the weath-ering process of the aggregates since the aggregates used in concreteextracted near the dams under construction always have a certain de-gree of weathering (Figure 3) which means that the concrete directlyincorporates iron hydroxides and sulfates and will do so in differentamounts if they influence the nature of sulfur and the type of host rock.

2. Experimental

2.1. Sample characterization

Two pyrite and pyrrhotite samples from the Catalonian Pyrenees(Spain) were obtained, in an area located near some of the damsthat we have studied (Ayora et al., 1998). Approximately 500 g ofeach sulfide was obtained in a laborious process of separation of therock. XRD spectra and their chemical composition indicate that theyare two practically pure pyrite and pyrrhotite samples (Figure 4).

The aggregates used were a Miocene marlstone, a Cretaceouslimestone and an Ordovician shale. Table 1 shows their chemicalcomposition. We have chosen three aggregates with insignificantsulfur content and sulfates generated in the oxidation process ofthe mixed sulfide-aggregates would be due solely to those providedby pyrite and pyrrhotite. Iron sulfide and aggregate samples wereground in an agate mortar and fractions between 1 mm and 500 μmwere used in experiments.

The solid sampleswere analyzed using a JSO-DEBYEFLEX 2002modelSeifert X-ray diffraction equipment, provided with a copper anode and anickel filter to check their mineralogy, and a Philips PW1480 fluores-cence spectrometer to determine their chemical composition.

2.2. Experimental set-up

Two iron sulfide solution experiments have been carried out withand without the addition of coarse aggregates. In the experiment with-out the addition of aggregates, 10 g of pyrite and 10 g of pyrrhotitewereimmersed in two 500 ml precipitation vessels with a volume of 200 ml

Table 1Chemical composition of the aggregates in%.

CaO SiO2 Al2O3 MgO Na2O K2O Fe2O3 SO3

Marlstone 26.12 53.81 3.21 0.46 0.61 0.36 2.0 0.14Limestone 52.57 2.21 0.75 1.24 0.28 0.15 0.57 –

Shale 3.44 68.81 8.61 0.69 0.28 2.51 4.83 0.07

Fig. 5. View of the experimental design.

Eh vs time

time (days)

Eh

(m

V)

pyrite pyrrhotite0

50

100

150

200

250

300

0 10 20 30 40 50

Fig. 6. Electric potential during the oxidation of pyrite and pyrrhotite samples.

78 S. Chinchón-Payá et al. / Engineering Geology 127 (2012) 75–80

of water. Next, a constant air flow was applied to the suspension bymeans of a pump with a pressure of ca. 120 mbar (Figure 5). Fromthen onward, pH and solution potential (Eh) values were taken dailywith a Crisol pH-meter. After allowing some time to elapse until thepH values obtained were stabilized — approximately two months later— the solution products were analyzed. The previously filtered liquidswere examined using a DIONEX DX5OO ionic chromatographer (IC)with chemical self-suppression seeking to determine the sulfate con-tent, and using a Perkin Elmer 4300 optical emission Spectrometerwith inductive coupling plasma (ICP-OES) to determine the total Fecontent.

In the second experimental set-up, binary samples of aggregate andiron sulfide were prepared in proportions of 95% and 5% respectively.The exact proportions of the components are reflected in Table 2. Thesolids were immersed in 500 ml precipitation vessels with a volumeof 200 ml of water and a similar experiment to that of sulfides withoutaggregates was conducted (Figure 5).

3. Results and discussion

3.1. Dissolving the iron sulfides

Figs. 6 and 7 show the Eh and pH results after monitoring the oxida-tion of pyrite and pyrrhotite samples in water with constant oxygensupply, and Table 2 provides Fe2+ and SO4

2− concentrations. There areno analyses of the solids at the end of the experiment. Due to the excessof sulfides added neither XRD spectra or X ray fluorescence (XRF) anal-ysis could be useful to identify newly formed solids.

The red-ox potential during the experiments is almost constant.One can only notice an initial significant increase in the case of pyriteup to a constant value that was reached a few days after commencing

Table 2Proportions of the components of experimental set-up and Fe2+ and SO4

2− concentra-tions of solution: M. — Marlstone, L. — Limestone, S. — Shale, py. — pyrite, po. —pyrrhotite.

Sample Sulfur g Aggregate g % S % Fe SO42− ppm Fe2+ ppm

Po 10 – 35.18 61.12 1517.8 455Py 10 – 49.03 46.37 1238.7 270M–Po 0.757 14.261 1.77 5.91 36.36 0M–Py 0.769 14.251 2.50 5.17 24.74 0L–Po 0.752 14.298 1.76 3.87 36.61 0L–Py 0.759 14.260 2.48 3.13 23.31 0S–Po 0.751 14.260 1.77 10.71 37.89 0S–Py 0.753 14.300 2.45 9.97 20.43 0

the experiment. Both solutions present positive potential values andoxidation conditions, though to a higher extent in the pyrite solution(see Figure 6).

As for pHmonitoring, Fig. 7 shows its course in both sulfides; a fastdecrease is observed at the moment of placing them in contact withwater, and a slight gradual decrease, until they reach constant values50 days after beginning the experiment. According to the results, itseems clear that the pyrite dissolution leads to an environment withmore protons than the pyrrhotite dissolution. This can be explainedconsidering the reactions that take place as discussed in the introduc-tory paragraphs.

Fig. 8 shows the Pourbaix diagram for iron, in which the pointscorresponding to the pyrite and pyrrhotite solutions are indicated.Both points are the pH and Eh values of the solutions after 50 days,the moment in which they are considered to be completely stable.

It becomes apparent that the points corresponding to each one ofthe sulfurs are situated in a different area, which suggests differentiron species: whereas in the case of pyrite, the iron is in solution, withpyrrhotite, the iron is also partly in a solid state in the form of a hydrox-ide. This hydroxide has a brownish-gray color and its presence is easy toidentify. The image in Fig. 9 shows the containers where each samplewas dissolved, the yellowish color of the container for the pyrrhotitesolution being caused by the iron hydroxide adhered to the sides ofthe precipitation vessel.

All of the above provides further confirmation that the solution ofboth sulfides is different, since the reaction products are not the same.And, in addition to that, as reflected in Table 2, the quantity of Fe2+ inpyrite solution is nearly twice as much in the pyrrhotite solution.

Regarding the other component generated in the alteration of ironsulfides, as shown in the chemical analyses by ion chromatography ofthe waters in both solutions (Table 2), the results obtained indicate thatpyrrhotite generates more sulfates than pyrite, whichmeans that the ox-idation of the pyrrhotite can lead, to a greater extent than in the case of alater formation of expansive secondary ettringites and/or thaumasites tobe harmful to concrete.

Themole ratio between Fe2+ and SO42− in both solutions indicates an

iron deficiency, as the pyrite is 0.37 instead of 0.5, and 0.45 instead of 1 inthe case of pyrrhotite sample. This could corroborate the appearance of

pH vs time

time (days)

pH

pyrite pyrrhotite0123456

0 10 20 30 40 50

Fig. 7. pH during the oxidation of the pyrite and pyrrhotite samples.

Fig. 8. Pourbaix diagram of iron. The points show the properties of the solutions withpyrite and pyrrhotite after reaching stability (50 days of reaction).

pH marlstone

0 10 20 30 40 50

time (days)

pH

Pyrite Pyrrhotite0

2

4

6

8

10

Fig. 10. pH evolution during solution of pyrite and pyrrhotite with marlstone aggregate.

2

4

6

8

10

0 10 20 30 40 50

pH

time (days)

pH limestone

pyrite pyrrhotite

Fig. 11. pH evolution during solution of pyrite and pyrrhotite with limestone aggregate.

79S. Chinchón-Payá et al. / Engineering Geology 127 (2012) 75–80

oxide–hydroxide (goethite) in both, although there is more quantity inpyrrhotite, hence the yellow coloration.

3.2. Dissolving the iron sufides with aggregates

Figs. 10, 11 and 12 show pH evolution in iron sulfide solutions withthe addition of marlstone M, limestone L and shale S type aggregates,respectively. In the three cases a noticeable increase of pH is observedcompared to those obtained in pure sulfide oxidation. In the case ofthe iron sulfides with marlstone and limestone there is a buffer effectdue to carbonates. In the iron sulfides with shale case, the pH is con-trolled by the solution of feldspars and micas.

The Fe2+ and SO42− concentrations of the solutions at the end of

the experiment are shown in Table 2. The results show no existenceof Fe2+ in solution which concords with the Pourbaix diagram.According to this, Fe has precipitated in the form of a hydroxide.

Fig. 9. View of pyrite and pyrrhotite solutions after 50 days of oxidation in water withconstant oxygen supply.

Regarding the SO42− concentration, in all three cases, the values are

much higher with pyrrhotite than with pyrite.As a resume of this section, results confirm that aggregates con-

taining pyrrhotite donate more sulfates to the solution in oxidationprocess than those with pyrite. Even more so when considering thatfor the same amount of iron sulfide, sulfur content in pyrite (53.4%)is higher than in pyrrhotite (36.4%).

4. Conclusions

An experience with a simple methodology for measuring potentialreactivity of oxidizable iron sulfides is presented herein. It has been con-firmed that iron sulfides, pyrites aswell as pyrrhotites, become oxidizedin the presence of water generating iron and sulfates. But pyrrhotiteprovides a larger quantity of Fe2+ and SO4

2− to the solution. Alsochecked, in oxidation experiments of the iron sulfides with amarlstone,a limestone, and a shale, is that in pyrrhotite samples there is a highersulfate contribution than in pyrite samples.

This work is a comparative investigation of the oxidation of pyriteand pyrrhotite under simulated laboratory conditions and despitebeing a preliminary study it allows two reflections to be made aboutthe paragraph that appears in Section 6.3.2 of EN 12620:2008: It is nec-essary to take special precautions if the presence of pyrrhotite is detected(an unstable form of iron sulfide FeS). Once their presence is confirmed,the maximum total sulfur content is less than 0.1%.

First to be considered is that some reference to the significant dangerthat the presence of pyrrhotite presents respective to other iron sulfides

pH shale

time (days)

pH

pyrite pyrrhotite0

2

4

6

8

10

0 10 20 30 40 50

Fig. 12. pH evolution during solution of pyrite and pyrrhotite with shale aggregate.

80 S. Chinchón-Payá et al. / Engineering Geology 127 (2012) 75–80

of different stoichiometry (pyrite, marcasite, …) should be carried out.Secondly, it is exaggerated to state that the standards place a level of0.1% of total sulfur content when pyrrhotite is found. That may be onereasonwhy in practice, suitable aggregates have been rejected unneces-sarily on some sites.

Acknowledgments

This paper forms part of the studies carried out within the frame-work of the Horex Project. The authors want to express their gratitudeto the firm IBERDROLA for its funding.

We also would like to thank Dr Jordi Cama (ICTJA-CSIC) for hiscomments about the work and the present paper.

References

Aguado, A., Rodrigues-Ferran, A., Casanova, I., Agulló, L., 2003. Modelling time evolution ofexpansive phenomena in concrete dams as a decision-making tool. Commision Inter-nationale des Grandes Barrages, Montreal. 30 pp.

Araújo, G.S., Chinchón, S., Aguado, A., 2008. Evaluation of the behaviour of concrete gravitydams suffering from internal sulfate attack. Ibracon Structures and Materials Journal1, 17–45.

ASTM C294-05, 2005. Standard Descriptive Nomenclature for Constituents of ConcreteAggregates.

Ayora, C., Chinchón, S., Aguado, A., Guirado, F., 1998. Weathering of iron sulfides andconcrete alteration: thermodynamic model and observation in dams from CentralPyrenees. Spain, Cement and Concrete Research 28, 1223–1235.

Barnett, S.J., Macphee, D.E., Lachowski, E.E., Crammond, N.J., 2002. XRD, EDXand IR analysisof solid solutions between thaumasite and ettringite. Cement and Concrete Research32, 719–730.

Barnett, S.J., Macphee, D.E., Crammond, N.J., 2003. Extent of immiscibility in the ettringite–thaumasite system. Cement and Concrete Composites 25, 851–855.

Belzile, N., Chen, Y.W., Cai, M.F., Li, Y., 2004. A review on pyrrhotite oxidation. Journal ofGeochemical Exploration 84, 65–76.

Bensted, J., 2003. Thaumasite — direct, woodfordite and other possible formationroutes. Cement and Concrete Composites 25, 873–877.

Cement and Concrete Composites, 2003 Volume: 25 Special Issue: 8.Chiriţă, P., Descostes, M., Schlegel, M.L., 2008. Oxidation of FeS by oxygen-bearing acidic

solutions. Journal of Colloid and Interface Science 321, 84–95.Colmer, A.R., Hinkle, M.E., 1947. The role of microorganisms in acid mine drainage: a

preliminary report. Science 106, 253–256.Crammond, N., 2002. The occurrence of thaumasite in modern construction— a review.

Cement and Concrete Composites 24, 393–402.Crammond, N.J., 2003. The thaumasite form of sulfate attack in the UK. Cement and

Concrete Composites 25, 809–818.

Dehaan, S.B., 1991. A review of the rate of pyrite oxidation in aqueous systems at low-temperature. Earth-Science Reviews 31, 1–10.

EHE, 1999. Instrucción de Hormigón Estructural. Real decreto 2661/1998. BOE 11 de13/01/99, pp. 1525–1526. and Anexo.

EHE-08, 2008. Instrucción de Hormigón Estructural. Real Decreto 1247/2008, de 18de julio.

EN 12620, 2002. Aggregates for Concrete.EN 12620, 2008. Aggregates for Concrete.Gravotta, C.A., Trahan, M.K., 1999. Limestone drains to increase pH and remove dissolved

metals from acidic mine drainage. Applied Geochemistry 14, 581–606.Köhler, S., Heinz, D., Urbonas, L., 2006. Effect of ettringite on thaumasite formation. Cement

and Concrete Research 36, 697–706.Macphee, D.E., Barnett, S.J., 2004. Solution properties of solids in the ettringite–thaumasite

solid solution series. Cement and Concrete Research 34, 1591–1598.Moses, C., Nordstrom, D.K., Herman, J.S., Mills, A.L., 1987. Aqueous pyrite oxidation by dis-

solved oxygen and by ferric iron. Geochimica et Cosmochimica Acta 51, 1561–1571.Neville, A., 2004. The confused world of sulfate attack on concrete. Cement and Concrete

Research 34, 1275–1296.Reid, J.M., Avery, K., 2009. Measuring the Potential Reactivity of Sulfides in Aggregates,

Mineral Industry Sustainable Technology, Final Report May 2009.Santomartino, S.,Webb, J.A., 2007. Estimating the longevity of limestone drains in treating

acid mine drainage containing concentrations of iron. Applied Geochemistry 22,2344–2361.

Steguer, H.F., 1982. Oxidation of sulphide minerals: VII. Effect of temperature and relativehumidity on the oxidation of pyrrhotite. Chemical Geology 35, 281–295.

Taylor, H.F.W., 1997. Cement Chemistry, 2nd ed. Thomas Telford Publishing, London.TheUKGovernment Thaumasite ExpertGroup, 1999. The Thaumasite Formof SulfateAttack:

Risks, Diagnosis, Remedial Works and Guidance on New Construction, Report of theThaumasite Expert Group, Department of the Environment, Transport and the Regions:London. January.

Thomas, J.E., Jones, C.F., Skinner,W.M., Smart, R.S., 1998. The role of surface sulfur species inthe inhibition of pyrrhotite dissolution in acid conditions. Geochimica et CosmochimicaActa 62, 1555–1565.

Thomas, J.E., Smart, R.S., Skinner, W.M., 2000. Kinetic factors for oxidative and non-oxidative dissolution of iron sulfides. Minerals Engineering 13, 1149–1159.

Thomas, J.E., Skinner, W.M., Smart, R.S., 2001. A mechanism to explain sudden changes inrates and products for pyrrhotite dissolution in acid solution. Geochimica et Cosmochi-mica Acta 65, 1–12.

Torres, S.M., Kirk, C.A., Lynsdale, C.J., Swamy, R.N., Sharp, J.H., 2004. Thaumasite–ettringite solid solutions in degraded mortars. Cement and Concrete Research34, 1297–1305.

Zhou, Q., Byars, E.W., Lynsdale, C.J., Cripps, J.C., Hill, J., Sharp, J.H., 2007. Relative Resistanceof Portland and Pozzolanic Cements to the Thaumasite Form of Sulfate Attack (TSA)12th International Congress on the Chemistry of Cement. Montreal. July.

Ziemkiewicz, P.F., Skonsen, J.G., Brant, D.L., Sterner, P.L., Lovett, R.J., 1997. Acid drainage treat-ment with armored limestone in open limestone channels. Journal of EnvironmentalQuality 26, 1017–1024.