Evaluation of long-term behavior of concretes in high level waste repositories. An accelerated leaching test.

584 BOLETIN DE LA SOCIEDAD ESPAÑOLA DE ARTICULO Ce ámica y Vid io E alua ion o long- e m beha io o conc e es in high le el was e eposi o ies. An accele a ed leaching es . A.HIDALGO , L. FERNANDEZ, S. PETIT1, C. ANDRADE, C. ALONSO Ins i u o Edua do To oja (CSIC), 28033 Mad id, Spain. 1 Uni e si é de Poi ie s, CNRS UMR 6532 Hyd ASA, F-86022 Poi ie s Cedex, F ance The p esen wo k desc ibes an accele a ed leaching me hod ha wi h a apid p ocess allows o de elop and e alua e cemen s o use in a nuclea disposal, and he unde s anding o he long e m e ec s. The me hod has been de eloped o s udy he s abili y o cemen i ious ma e ials in con ac wi h ben oni e, o be used in high le el adioac i i y was e eposi o ies. Ni ic acid has been selec ed o simula e in an accele a ed way he pH dec easing p oduced when conc e e is in con ac wi h g oundwa e s. E aluacion del compo amien o a la go plazo de ho migones en almacenamien os de esiduos adiac i os de al a ac i idad El p esen e abajo desc ibe un ensayo acele ado de lixi iación, que median e un p oceso ápido, pe mi e desa olla y e alua cemen os pa a su uso en ins alaciones nuclea es, y la comp ensión de su compo amien o a la go plazo. El mé odo se ha desa ollado pa a es udia la es abilidad de ma e iales de base cemen o, en con ac o con ben oni a, que se án u ilizados en almacenamien os de esíduos adiac i os de al a ac i idad. Como agen e lixi ian e se seleccionó el ácido ní ico, con obje o de simula de o ma acele ada, la disminución del pH que se p oduce cuando el ho migón en a en con ac o con aguas sub e áneas. 1. INTRODUCTION The e olu ion o he mic os uc u e o cemen i ious ma e ials in con ac wi h g oundwa e s, will a y depending o he ype o cemen used o p oduce conc e e. Due o he long imescales in ol ed in labo a o y expe imen s using g oundwa e s, accele a ed leaching es s, ha e o be used o quali y he di e en conc e es o deep eposi o ies, and o e alua e hei long- e m beha iou [1,2,3]. In ealis ic condi ions o high le el adioac i e was e eposi o ies, conc e e du abili y is based on i s in e ac ion wi h clays and g ani ic g oundwa e s. In gene al g oundwa e is a e y weakly mine alised solu ion con aining dilu ed acids; howe e i s exac composi ion is si e-speci ic. In a deep eposi o y scena io o lowing wa e , cemen mass is chemically exposed mainly, o he pH o he incoming wa e ha p oduces a p og essi e neu alisa ion o he alkaline na u e o he cemen pas e, emo ing alkalis and dissol ing po landi e and CSH gel. Leaching es me hods a e in gene al used o es ima e he leachabili y, leach a e and leaching condi ions mechanisms o en i onmen ally ele an componen s. Howe e , o e alua ion o sealing ma e ials in high le el was e eposi o ies, i is necessa y o in es iga e he mine al al e a ion o ba ie s such as conc e e, and i s in e ac ion wi h o he ba ie s (ben oni e o g ani e), as well as o de ine he ype o cemen which p oduces an en i onmen compa ible wi h he su ounding ma e ials. The accele a ed me hod p oposed in his wo k, y o ep oduce equilib ium o cuasi-equilib ium condi ions, co esponding o di e en conc e e deg ada ion le els, in a sho pe iod o ime. 2. DISSOLUTION-PRECIPITATION PHENOMENA OF CEMENT PASTES. ACID NEUTRALISATION TEST (ANT). 2.1. Leaching es p ocedu e The expe imen al p ocedu e consis s o a ba ch es ; ha is, a closed sys em [4, 5, 6]. Hyd a ed cemen mixes a e g ound and sie ed un il a pa icle size less han 32 mm is ob ained; hen 10 g o his solid (S) a e mixed wi h deionised wa e (L) in a a io S/L=1, p oducing an homogeneous slu y. Accele a ed es s a e pe o med in hese slu ies by adding an acid (HNO3, 1N), a a a e o 0.5 ml.min-1 wi h an au oma ed i a o (Ne Ti ino 721 om Me ohm), and s i ing he sample igo ously o a o con inuous mix u e o leachan and sample. In he case o ni ic a ack, a N2 low is main ained du ing he p ocess o a oid ca bona ion. The e olu ion o pH is con inuously eco ded and liquid and solid phases a e aken a di e en pHs co esponding o p og essi e deg ada ion s ages. The p ocess o hyd a ion is in e up ed in each case by “ eezing” he sample wi h ace one and e hanol; hen samples a e acuum il e ed h ough a 0.45 mm il e . Fu he analysis o he leacha es and solid phases a e ca ied ou . 2.1. Ma e ials A Spanish cemen (CEM I-SR acco ding o he Eu opean S anda d ENV 197-1) and wo ypes o mine al addi ions ( ly ash and silica ume) we e used o his es ing p og am. Cemen pas es we e ab ica ed wi h w/c=0.35 and hey we e hyd a ed du ing 7 days in sealed condi ions (98% ela i e humidi y and 20±2 oC ). Fo mula ions o pas es we e: 100% CEM I-SR, 59% CEM I-SR + 41% FA, and 73% CEM I-SR + 7% FA + 20% SF. 2.2. De e mina ions and calcula ions Chemical analysis esul s o he leacha es we e in oduced in PHRQPITZ code using he da abase HATCHES [7], in o de o calcula e he he modynamic s a us o such solu ions; ha is he sa u a ion indexes o mine al phases. Mid In a ed spec a o e e ence and deg aded cemen mixes, we e ob ained using a Nicole Magna 750 Fou ie ans o m IR spec ome e (FTIR) equipped wi h a DTGS de ec o . Fo each sample, 256 scans we e eco ded in he 4000-250 cm-1 spec al ange wi h a Bol. Soc. Esp. Ce am. V., 43 [2] 584-586 (2004) (c) Sociedad Española de Ce ámica y Vid io, Consejo Supe io de In es igaciones Cien í icas. Licencia C ea i e Commons 3.0 España (by-nc) h p://ce amicay id io. e is as.csic.es 585 esolu ion o 4 cm-1. The spec a o all he samples we e measu ed using he 12 mm diame e KB pelle s (0.1 mg o sample and 150 mg o KB ). Solid s a e 27Al M.A.S N.M.R was eco ded a oom empe a u e wi h a Va ian VXR 300S spec ome e a 78.1393 MHz, wi h a spinning speed o 4 kHz in a double bea ing 7mm Z O2 o o . Spec a we e accumula ed using Bloch decay pulse sequences o Π/8 ad pulses and a ecycle ime o 1 s we e used. NMR chemical shi o 27Al we e e e enced o 1.0 M aqueous Al(H2O) 6 3+. 3. RESULTS AND DISCUSSION F om he modynamic calcula ions, i was conside ed ha he po en ially p ecipi a ing mine als will be hose wi h he highes sa u a ion indexes. In all cases solu ions we e o e sa u a ed in di e en mine al phases; a pH=10, mine als wi h he highe sa u a ion indexes we e obe mo i e and also chabazi e; a pH=7 hey we e chabazi e and Ca-Pzeoli e. Resul s om some cemen mixes a e p esen ed in Table 1. In Fig. 1 he compa ison o 27Al MAS NMR spec a om a blended cemen pas e, be o e and a e he leaching in HNO3 medium, and a di e en pHs has been p esen ed. 27Al MAS NMR spec a o blended cemen pas es including ly ash on hei o mula ion, show he cha ac e is ic peaks o e ahed al and oc ahed al aluminium [8]; whe e he obse ed chemical shi s a e espec i ely cen e ed abou 55 ppm and –10 ppm. These spec a appea o be ela ed o he aluminosilica es. The p esence o e ahed al and oc ahed al aluminium in he un ea ed sample, in ol es laye aluminosilica es o ec oaluminosilica es om ly ash. Table 1. SaTu aTion indexeS o poTenTially p ecipiTaTing Solid pha- SeS o cemenT mixTu eS. Mine al Fo mula pH 100% CEM I-SR 59% CEM I-SR 41% FA 73% CEM I-SR 7% FA 20% SF Tobe mo i e Ca5Si6O17.5H2O 10 9.7657 9.1116 8.3644 Chabazi e CaAl2Si4O12.6H2O 10 3.4057 3.1847 5.0327 Chabazi e CaAl2Si4O12.6H2O 7 10.7107 9.6196 9.9802 CaP CaAl2Si2.6O9.2.3.2H2O 7 7.5134 6.7377 6.9522 B ownmille i e (C4AF), which emains unhyd a ed in cemen pas e, con ains also some Al in e ahed al si es. Howe e , leaching inc eases he a io Al e a/Aloc a. This ac can be ela ed wi h he inco po a ion o e ahed al aluminium in o he silica chains o he C-S-H gel [9, 10]. Figu e 1. 27Al MAS NMR spec a o a blended cemen pas e wi h ly ash E ALUATION OF LONg-TERM BEHA IOR OF CONCRETES IN HIgH LE EL wASTE REPOSITORIES. AN ACCELERATED LEACHINg TEST. Bol. Soc. Esp. Ce am. V., 43 [2] 584-586 (2004) (c) Sociedad Española de Ce ámica y Vid io, Consejo Supe io de In es igaciones Cien í icas. Licencia C ea i e Commons 3.0 España (by-nc) h p://ce amicay id io. e is as.csic.es 586 Figu e 2 shows he mid-IR spec a in he lowe equencies; in his case he obse ed ea u es p o ide use ul in o ma ion abou Ca/Si a io in CSH, silica e polyme isa ion, and he p esence o TO4 e ahed a (T=Si o Al). Main in o ma ion ex ac ed om esul s is: - Fo he CSH gels, he mid-IR bands occu a 950-1100, 810-830, 660-670, and 440-450 cm-1. These mid-I bands change sys ema ically wi h Ca/Si a io in silica es which is also ela ed wi h silica e polyme isa ion. The displacemen o he band occu ing a 976 cm- 1, o 1030 o 1080 cm-1, in he case o leached samples, is due o an inc easing in silica e polyme isa ion and a dec easing in Ca/Si a io. The appea ance o a shoulde a ∼1200 cm-1 occu s when we ha e hyd a ed silica es wi h Ca/Si<0.7. - The 660-670 cm-1 (Si-O-Si bending) band, inc eases in in ensi y o Ca/Si <0.88, consis en wi h an inc easing in polyme isa ion. - Bands in he ange 400-500 cm-1 a e due o de o ma ion o TO4 e ahed a (T=Si o Al), and he inc easing in in ensi y o his band when leaching p oceeds, is also consis en wi h an inc easing in polyme isa ion (mo e b idging TO4 uni s linking dime s). - Band a 1140 cm-1 can be a ibu ed o e ingi e which has comple ely disappea ed in he sample leached un il pH=7. - Bands in he ange 700-850 cm-1 can be a ibu ed o he in oduc ion o Al in e ahed al coo dina ion , which is signi ican o samples leached a pH=7, and consis en wi h p e ious esul s ob ained by au ho . - Bands a 875 and 320 cm-1, a e due o CO3 2- g oups in calci e. Addi ionally, he disappea ing o po landi e could be ollowed by he disappea ing o he band a 3640 cm-1, due o Ca-OH species in such compound. Analyses o MID-IR spec a o cemen pas es including mine al addi ions (59% CEM I-SR + 41% FA and 73% CEM I-SR + 7% FA + 20% SF), ga e he same in o ma ion. Small di e ences wi h he p e iously analysed da a, could be a ibu ed o ini ial di e ences in he Ca/Si a io in silica es Resul s demons a ed ha he main p ocesses occu ed in leaching o samples based in Po land cemen when exposed o a pH dec easing a e: - Alkalies elease. - Dissolu ion o po landi e. - Decalci ica ion o CSH gel. - Silica e polyme isa ion o ming a gel wi h a highe in e laye wa e con en . - Possible inco po a ion o e ahed al aluminium in polyme ised gel esul ing in he o ma ion o an alumino-silica e gel. REFERENCES 1. H. A. Van de Sloo ; “Leaching beha iou o was e and s abilised was e ma e ials; cha ac e iza ion o en i onmen al assessmen pu poses”, Was e Managemen & Resea ch, 22 181-186 (2002). 2. M. Andac, F. P. Glasse ; “Long- e m leaching mechanisms o Po land ce- men -s abilized municipal solid was e ly ash in ca bona ed wa e ”, Cemen and Conc e e Resea ch, 29 179-86 (1999). 3. E. Re e ega , F. Adeno , C. Riche , L. Wu, F. P. Glasse , D. Damido , S. A. S onach; “Theo e ical and expe imen al s udy o deg ada ion mechanisms o cemen in he eposi o y en i onmen ”, CEC Con ac nº FI2W-CT90- 0035, Final Repo . ISBN 92-828-0394-5, 1997. 4. A. Hidalgo e al.; “E ec s o cemen on clay ba ie pe o mance. Ecoclay P ojec ”. CEC con ac nº FI4W-CT96-0032, Nuclea Science and Technology Se ies, Eu opean Communi ies, B ussels 2000, Pages 1-140. ISBN: 92-828- 9774-5. 5. A. Hidalgo, C. And ade, C. Alonso; “Role o alkaline ese e in he acidic esis ance o cemen pas es” in “Reac ions o calcium hyd oxide in conc e- e”, J. Skalny, J. Gebaue , I. Odle eds., The Ame ican Ce amic Socie y (Ohio) 2001, Pages, 93-111, ISSN: 1042-1122; ISBN: 1-57498-128-5. 6. A. Hidalgo, C. And ade, C. Alonso; ”E alua ion o he long e m beha iou o conc e e used in high le el nuclea was e disposal (HLW). An accele a ed leaching es ” in “En i onmen al and Technical Implica ions o Cons uc ion wi h Al e na i e Ma e ials. Wascon 2003”, G. O iz de U bina, H. Goumans eds., 2003, Pages 857-860, ISBN: 84-95520-00-1. 7. J. E. C oss, F. T. Ewa ; “HATCHES a The modynamic Da abase and Mana- gemen Sys em Rep in ”. Radiochimica Ac a, 52/53, 421-422 (1991). 8. G. Engelha d , D. Michel; High-Resolu ion Solid-S a e NMR o Silica es and Zeoli es., John Wiley & Sons, Chiches e , 1987. 9. P. Faucon, T. Cha pen ie , A. Nona , and J. C. Pe i ; “T iple-Quan um Two- Dimensional 27Al Magic Angle Nuclea Magne ic Resonance S udy o he Aluminum Inco po a ion in Calcium Silica e Hyd a es”, Jou nal o he Ame ican Chemical Socie y, 120(46), 12075-12082 (1998). 10. P. Faucon, A. Delag a e, J. C. Pe i , C. Riche , J. M. Ma chand, and H. Zanni; “Aluminum inco po a ion in calcium silica e hyd a es (C-S-H) depending on hei Ca/Si a io”, Jou nal o Physical Chemis y B, Ma e ials, Su aces, In e aces & Biophysical, 103(37), 7796-7802 (1999). Recibido: 1.2.03 Acep ado: 30.11.03 Figu e 2. Mid-IR spec a o a 100% CEM I-SR cemen pas e. Silica e en i onmen s. A.HIDALgO , L. FERNANDEZ, S. PETIT, C. ANDRADE, C. ALONSO Bol. Soc. Esp. Ce am. V., 43 [2] 584-586 (2004) (c) Sociedad Española de Ce ámica y Vid io, Consejo Supe io de In es igaciones Cien í icas. Licencia C ea i e Commons 3.0 España (by-nc) h p://ce amicay id io. e is as.csic.es