Negative effect of Zinc compounds on hydration kinetics of ordinary Portland cement

Con en om his wo k may be used unde he e ms o heC ea i eCommonsA ibu ion 3.0 licence. Any u he dis ibu ion o his wo k mus main ain a ibu ion o he au ho (s) and he i le o he wo k, jou nal ci a ion and DOI. Published unde licence by IOP Publishing L d ICBMPT 2020 IOP Con . Se ies: Ma e ials Science and Enginee ing 1039 (2021) 012004 IOP Publishing doi:10.1088/1757-899X/1039/1/012004 1 Nega i e e ec o zinc compounds on hyd a ion kine ics o o dina y Po land cemen L Ma ejka1, P Sile 1, R No o ny1, J S ec1, J Masilko1 and F Soukal1 1 B no Uni e si y o Technology, Facul y o Chemis y, Ins i u e o Ma e ials Chemis y, Pu kyno a 464/118, 612 00 B no, Czech Republic Email: xcma ejkal@ u b .cz Abs ac . Me als and me al con aining compounds ha e signi ican e ec on cemen hyd a ion mechanism and kine ics. The ecycling o was e ma e ials leads o inc ease o con en o me als in a ious indus ial p oduc s and isibly a ec s p ope ies o he Po land cemen . One o he me als ha has been known o d as ically inc ease he se ing ime is zinc. Zinc o ms a ious hyd oxyl species wi h calcium ca ions. Po e solu ion hus has lowe ed concen a ion o calcium which supp esses o ma ion o po landi e. Due o insu icien concen a ion o calcium he o ma ion o CSH gel and u he hyd a ion o clinke g ains is inhibi ed The aim o his s udy is o quan i y he nega i e e ec s o zinc a di e en concen a ions a ambien empe a u e a 20°C. Isope ibolic calo ime y was used o measu e he nega i e e ec s o zinc on hyd a ion kine ics o o dina y Po land cemen . Zinc was added o he cemen in he o m o wo soluble sal s Zn(NO3)2 hyd a e, ZnCl2 and a poo ly soluble compound ZnO. The concen a ion o zinc added was chosen be ween 0.1 and 1 w . % o clinke . Signi ican e a da ion o cemen hyd a ion wi h inc easing zinc con en was p o en. 1. In oduc ion Po land cemen is a hyd aulic binde p oduced by bu ning o g ound limes one, clay and o he aw ma e ials in o a y kiln. C ea ed clinke is g ound up and mixed wi h small amoun s o gypsum. P oduced clinke consis o many phases. The main clinke phases a e icalcium silica e (abb . C3S– 3CaO·SiO2 o Ca3SiO5, ali e), dicalcium silica e (abb . C2S–2CaO·SiO2 o Ca2SiO4, beli e), icalcium alumina e (abb . C3A–3CaO·Al2O3 o Ca3Al2O6, celi e) and calcium alumino e i e (abb . C4AF– 4CaO·Al2O3·Fe2O3 o Ca4Al2Fe2O10, b ownmille i e) [1]. Va ious me als can be in oduced in o cemen in all s ages o p oduc ion o applica ion. Limes one based on he speci ic deposi ends o con ain o he mine als such as sphale i e (ZnS). O dina y Po land cemen is also widely esea ched as a binde o solidi ica ion and immobiliza ion o oxic was e con aining me als. Solidi ica ion and immobiliza ion o oxic elemen s encompasses educing bioa ailabili y, leachabili y, and mobili y o haza dous elemen s [1‒5]. Zinc can be p esen in admix u es, in i s own sepa a e phase in clinke o in solid solu ion wi h main clinke phases. Solid solu ion wi h C3S seems o be p e e ed o e C2S [6]. Ions o zinc p esen in po e solu ion hyd olyse in o a ious hyd oxyl species. These compounds coa hyd a ing g ains o cemen clinke and eac wi h calcium ca ions e ol ed in o he po e solu ion du ing o ma ion o CSH gel. The esul ing insoluble Ca(Zn(OH)3)2·2 H2O deple es concen a ion o Ca2+ p e en ing he o ma ion o po landi e and se e ely supp essing sa u a ion o po e solu ion and u he hyd a ion o cemen g ains. P ecipi a ion o po landi e and CSH gel is inhibi ed un il all zinc has been con e ed in o ICBMPT 2020 IOP Con . Se ies: Ma e ials Science and Enginee ing 1039 (2021) 012004 IOP Publishing doi:10.1088/1757-899X/1039/1/012004 2 insoluble Ca(Zn(OH)3)2·2H2O. Once his p ocess eaches comple ion hyd a ion con inues once mo e. Reac ions leading o Ca(Zn(OH)3)2·2 H2O a e shown in equa ions (1) and (2) [7‒10]. ZnO + H2O + 2 OH−→Zn(OH)4 2− (1) 2 Zn(OH)4 2− + Ca2+ + 2 H2O → Ca(Zn(OH)3)2∙ 2 H2O + 2 OH− (2) The pu pose o his s udy is o show he e ec o zinc compounds ZnCl2, Zn(NO3)∙6 H2O and poo ly soluble compound ZnO a di e en concen a ions on he hyd a ion induc ion pe iod o o dina y Po land cemen a lowe ambien empe a u e han mos s udies and compa e esul s wi h s udies using highe ambien empe a u e. Exposu e o zinc oxide o humidi y a ec s bo h solubili y and pa icle size dis ibu ion. Mois u e p esen in chemicals can lead o misleading esul s by al e ing he concen a ion o zinc in he zinc sou ce. These pa ame e s can also a ec eac ion kine ics o zinc oxide in po e solu ion. Moni o ing o hese e ec s is done using isope ibolic calo ime y. I is appa en ha ambien empe a u e has signi ican in luence on bo h hyd a ion o cemen and mechanisms behind zinc induced p olonging o induc ion pe iods. 2. Expe imen al 2.1. Ma e ials and Sample P epa a ions All samples we e p epa ed using cemen CEM I 42,5 R p oduced by Mok á—Českomo a ský cemen , a.s., Heidelbe g Cemen Czech Republic. Chemical composi ion o his cemen is p o ided in echnical documen a ion and is shown in able 1 [11]. Each cemen sample con ained a speci ic amoun o zinc equal o weigh % o cemen (1, 0.5 and 0.1%) and 0.4 wa e o cemen a ion. Cemen pas es we e p epa ed using s anda d ki chen aid mixe acco ding o he no m ČSN EN 196-1. Table 1. Chemical composi ion o used cemen [11]. Componen Cemen (w . %) CaO 63.7 SiO2 19.6 Al2O3 4.8 Fe2O3 3.3 MgO 1.4 SO3 3.1 Cl- 0.040 K2O 0.75 Na2O 0.19 Insoluble 0.7 LOI 3.4 Zinc was in oduced in o cemen pas e in a o m o soluble sal s ZnCl2 and Zn(NO3)2∙6 H2O and poo ly soluble compound ZnO in concen a ions 0.1; 0.5 and 1 w . % o pu e zinc in cemen . The humidi y o he oxide was de e mined wi h Ke n MLS 50-D humidi y analyse . Zinc oxide used as one o zinc sou ces con ained on a e age 0.35 weigh % o mois u e. ZnO was used in s ock and d ied o m. ZnO was d ied a 80°C o 72 h. Zinc chlo ide and zinc ni a e hexahyd a e we e pu chased om Lach-Ne , s. .o. wile zinc oxide was pu chased om Lachema, s. .o.. 2.2. Isope ibolic Calo ime y One o he bes me hods o e alua ing hyd a ion o cemen is mul icell isope ibolic calo ime y. This ype o de ice allows moni o ing o mul iple samples and e e ences allowing easy compa ison o di e en cemen mix u es. This me hod is widely used o he s udy o he e ec s o di e en admix u es such as supe plas icize s, ha dening accele a o s and a ious seconda y indus ial p oduc s on se ing o cemen pas es [12]. ICBMPT 2020 IOP Con . Se ies: Ma e ials Science and Enginee ing 1039 (2021) 012004 IOP Publishing doi:10.1088/1757-899X/1039/1/012004 3 Cemen mix u es we e weigh ed (300 g) in o polys y ene cup wi h he mocouples and co e ed wi h he mo-insula ing op. Calo ime ic cu es showing cemen hyd a ion and di e ences be ween a ious samples we e ob ained using isope ibolic calo ime y in a oom wi h ambien empe a u e a 20°C. 3. Resul s and discussion Mix u es o samples we e p epa ed ou side o he calo ime e hus he i s peak on hyd a ion cu e was no measu ed in i s en i e y. Ne e heless, he ea ly s ages o cemen hyd a ion a e no signi ican o his s udy and do no signi ican ly con ibu e o any changes du ing hyd a ion. Figu e 1. Isope ibolic calo ime y cu es o samples wi h 1% weigh concen a ion o zinc. F om calo ime ic cu es shown in igu e 1 i is appa en ha cemen hyd a ion o samples doped wi h zinc compounds was se e ely inhibi ed as peaks a e shi ed o he igh o he e e ence peak. The e also appea s o be a small wide peak a a ound 25 h on a cu e o sample wi h zinc ni a e. The hea e olu ion causing his peak was p obably a esul o dissolu ion o he zinc sal o c ys alliza ion on he su ace o he cemen g ains as explained in wo ks [13, 14]. Maximum empe a u es eached by sample peaks we e also lowe han ha o e e ence. Maximum empe a u es eached by he samples we e 32.9°C o cemen wi h chlo ide, 29.9°C o ni a e, 34.0°C o un ea ed zinc oxide and 33.2°C o samples wi h d ied zinc oxide. This is p obably a esul o zinc compounds slowing hyd a ion o clinke g ains. A he same concen a ion o zinc, ZnCl2 seems o show lowe inhibi o y abili y han zinc ni a e. zinc oxide showed he highes inhibi ion o hyd a ion. The di e ence in beha iou o samples doped wi h zinc oxide is due o lowe solubili y in wa e han zinc chlo ide and zinc ni a e. Smalle inhibi ion by chlo ide and ni a e is due o he abili y o chlo ide and ni a e ions o accele a e cemen hyd a ion wi h chlo ide being mo e e ec i e accele a o a his concen a ion [15]. When compa ed wi h simila s udies done by Šile e al. [16, 17] who used 25°C (as opposed o 20°C in his s udy) as ambien empe a u e, i s no iceable di e ences a e wide hyd a ion peaks wi h highe ICBMPT 2020 IOP Con . Se ies: Ma e ials Science and Enginee ing 1039 (2021) 012004 IOP Publishing doi:10.1088/1757-899X/1039/1/012004 4 maximum empe a u e when highe ambien empe a u e is used. This co esponds wi h accele a ed hyd a ion o cemen and o ma ion o hyd a ion p oduc s. Samples con aining chlo ides show compa able induc ion pe iod wi h samples in his s udy bu had eached signi ican ly highe maximum empe a u e a a ound 37 and in con as wi h 32.9°C o ou samples. Maximum empe a u es o samples wi h zinc oxide a e compa able wi h samples in his s udy bu he leng h o induc ion pe iod was di e en . This could be explained by lowe solubili y o d ied zinc oxide, bu he di e ence does no seem o be e y signi ican . In s udy published by Kolářo á e al. [18] hese cemen sys ems we e s udied using iso he mal calo ime y. Induc ion pe iod measu ed by his me hod was a a ound 80 h which is e y simila o 77.8 h wi h d ied zinc oxide and 73.3 h wi h un ea ed zinc oxide. Summa y o de e mined induc ion pe iods is shown in able 2. Figu e 2. Isope ibolic calo ime y cu es o samples wi h 0.5% weigh concen a ion o zinc. Beha iou o samples wi h concen a ion o zinc equal o 0.5% o weigh o he clinke isibly changed as is demons a ed in igu e 2. Peaks belonging o he zinc oxide samples shi ed o he le indica ing sho e induc ion pe iod. Bo h zinc oxide peaks we e hinne han hose o samples wi h concen a ion o 1%. This indica es as e hyd a ion ela i e o he p e ious samples. Peaks o chlo ide and ni a e samples we e isibly hinne han hose o p e ious samples. The maximum empe a u e eached by ni a e sample was highe han maximum empe a u e o he e e ence. This indica es accele a ed hyd a ion in compa ison o he samples wi h highe concen a ion o zinc. Signi ican di e ence was obse ed in induc ion pe iods o ni a e and chlo ide samples. O e all leng hs o induc ion pe iods o all samples a e in able 2. While he induc ion pe iod o ni a e sample d opped om 48.2 h o 29 h wi h dec ease in concen a ion o zinc, he induc ion pe iod o chlo ide sample inc eased om 38.9 h o 56 h wi h dec ease in concen a ion o zinc. This could be esul o chlo ide and ni a e anions accele a ing hyd a ion h ough di e en mechanisms. While chlo ide anions a e said o a ec hyd a ion by inco po a ion in o CSH gel, dis up ing i , allowing mo e wa e o be a ailable o hyd a ion eac ions, ni a es a ec o ma ion o e ingi e and he hyd a ion ICBMPT 2020 IOP Con . Se ies: Ma e ials Science and Enginee ing 1039 (2021) 012004 IOP Publishing doi:10.1088/1757-899X/1039/1/012004 5 o β-C2S. Nex pa ame e o conside is solubili y o a ious ion species in po e solu ion wi h di e ing concen a ions o chlo ides and ni a es in such complica ed sys ems [19, 20]. Resul s o Šile [16, 17] measu emen s co esponding o 0.5% chlo ide show highe maximum empe a u e in compa ison wi h 1% chlo ide, while he induc ion pe iod was simila . In con as wi h measu emen s in his s udy whe e induc ion pe iod inc eased. This could be explained by loss o inhibi o y e ec wi h dec easing zinc ion concen a ion, loss o accele a ion by chlo ide ions bu wi h added accele a ion caused by highe ambien empe a u e. Samples doped wi h ni a es measu ed by Šile show signi ican inc ease in maximum empe a u e wi h dec ease o concen a ion o ni a e. This co ela es wi h p esen ed esul s. Al hough sample o 0.5% ni a e measu ed a highe empe a u e showed sho e induc ion pe iod han ou esul s, he dec ease in induc ion pe iod wi h dec easing concen a ion was no as high as in ou expe imen . [16, 17]. Figu e 3. Isope ibolic calo ime y cu es o samples wi h 0.1% weigh concen a ion o zinc. Table 2. Summa y o induc ion pe iods measu ed based on isope ibolic cu es. Induc ion pe iod (hou ) Concen a ion o zinc (w .%) ZnCl2 Zn(NO3)2 ZnO un ea ed ZnO d ied Cemen 0.0 4.9 0.1 27.1 13.7 14.9 22.6 0.5 56.0 29.0 63.5 56.5 1.0 38.9 48.2 73.3 77.8 Di e ences be ween leng hs o induc ion pe iods and maximum empe a u es eached dec ease wi h dec easing concen a ion o zinc. Peaks o all samples shi ed o he le indica ing sho e induc ion pe iods as seen in igu e 3. Samples doped wi h zinc oxide eached highe maximum empe a u e han ICBMPT 2020 IOP Con . Se ies: Ma e ials Science and Enginee ing 1039 (2021) 012004 IOP Publishing doi:10.1088/1757-899X/1039/1/012004 6 he e e ence cemen . Induc ion pe iods o all samples anged be ween 13.7 h and 27.1 h. These a e signi ican ly longe induc ion pe iods han he induc ion pe iod o e e ence sample. These esul s a e compa able wi h li e a u e [16, 17]. Induc ion pe iods measu ed by Kolářo á [18] anged be ween 10 and 20 h. Sample doped wi h zinc chlo ide had signi ican ly longe induc ion pe iod han hose doped wi h zinc ni a e. This phenomenon co ela es wi h esul s o Kolářo á. Samples doped wi h zinc oxide had he longes induc ion pe iod ou o he measu emen s. These esul s a e e y simila o ou measu emen wi h un ea ed zinc oxide samples. Ou samples o cemen wi h d ied zinc oxide show signi ican ly longe induc ion pe iod han samples wi h un ea ed oxide. 4. Conclusion The aim o his s udy was o moni o he e ec s o a ious zinc compounds on induc ion pe iod o cemen hyd a ion a 20°C ambien empe a u e as opposed o 25°C used in o he s udies [16‒18]. Compounds used as zinc sou ce in his s udy we e soluble sal s ZnCl2 a Zn(NO3)∙6 H2O and insoluble compound ZnO in d ied and no d ied o m. • The leng h o induc ion pe iod was inc easing wi h inc easing concen a ion o speci ic zinc sou ce excep o sample wi h 1 weigh % o zinc in a o m o ZnCl2 due o accele a ion e ec o chlo ide anions a his concen a ion. • Ambien empe a u e o 20°C was used du ing measu emen s (as opposed o o 25°C as used in s udies [16‒18]) which esul ed in signi ican ly highe peak empe a u es eached a high concen a ions o zinc. • Di e ences in he leng h o induc ion pe iods be ween zinc chlo ide and zinc ni a e samples a e bigge a 20°C ambien empe a u e as opposed o 25°C used in s udies [16‒18]. • The di e ence be ween induc ion pe iods and maximum empe a u es eached by cemen samples wi h d ied and un ea ed zinc oxide was ela i ely small. Induc ion pe iod o bo h samples we e simila wi h consis en di e ence be ween 5 o 7 h. Un ea ed zinc oxide con ained 0.35 weigh % o wa e . This is insigni ican amoun ha p obably would no in luence he esul s. The di e ence in hyd a ion induc ion pe iods was p obably caused by di e en pa icle size dis ibu ion o hea ea ed and un ea ed zinc oxide and di e en le el o homogeniza ion o sample pas es. Acknowledgmen This esea ch has been achie ed wi h he inancial suppo by he p ojec : GA19-16646S “The elimina ion o he nega i e impac o zinc in Po land cemen by accele a ing conc e e admix u es”, wi h inancial suppo om he Czech Science Founda ion. Re e ences [1] Lea F and Hewle T P 1998 Lea's chemis y o cemen and conc e e 4 h ed. (New Yo k: Copublished in No h, Cen al, and Sou h Ame ica) by J. 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