Inmobilization of Zn(II) in Portland cement pastes. Determination of microstructure and leaching performance

The aim of this paper is to study the solidification/ stabilization potential of cementitious matrices on the immobilization of Zn(II) before its disposal into the environment by determining the mechanisms of interaction between the Zn(II) ions and the binder. The results of structural and mineralogical characterization of cement pastes formed with different amounts of immobilized Zn(II) ions are presented and the study includes results from thermogravimetric analysis (TG), scanning electron microscopy, X-ray diffraction, and leaching performance. Zn(II) ions delay the hydration reaction of Portland cement due to the formation of mainly CaZn2(OH)6 2H2O , as well as Zn5(CO3)2(OH)6, Zn(OH)2, and ZnCO3 in minor proportion. Correlations between total mass loss in TG analysis and leached Zn(II) ions in long-term curing pastes have been obtained. This result is important because in a preliminary approach from a TG on an early-aged cement paste containing Zn(II), it could be possible to perform an estimation of the amount of Zn(II) ions that could be leached, thus avoiding costly and time-consuming tests.Mellado Romero, AM.; Borrachero Rosado, MV.; Soriano Martinez, L.; Paya Bernabeu, JJ.; Monzó Balbuena, JM. (2013). Inmobilization of Zn(II) in Portland cement pastes. Determination of microstructure and leaching performance. Journal of Thermal Analysis and Calorimetry. 112(3):1377-1389. doi:10.1007/s10973-012-2705-8S137713891123Mojumdar SC, Sain M, Prasad RC, Sun L, Venart JES. Selected thermoanalytical methods and their applications from medicine to construction, Part I. J Therm Anal Calorim. 2007;90:653–62.Perraki M, Perraki T, Kolovos K, Tsivilis S, Kakali G. Secondary raw materials in cement industry. Evaluation of their effect on the sintering and hydration processes by thermal analysis. 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J Therm Anal Calorim. 2001;64:1011–6.Melchert MBM, Viana MM, Lemos MS, Dweck J, Buchler PM. Simultaneous solidification of two catalyst wastes and their effect on the early stages of cement hydration. J Therm Anal Calorim. 2011;105:625–33.Vessalas K, Thomas PS, Ray AS, Guerbois JP, Joyce P, Haggman J. Pozzolanic reactivity of the supplementary cementitious material pitchstone fines by thermogravimetric analysis. J Therm Anal Calorim. 2009;97:71–6.Tommaseo CE, Kersten M. Aqueous solubility diagrams for cementitious waste stabilization systems. 3. Mechanism of zinc immobilization by calcium silicate hydrate. Environ Sci Technol. 2002;36:2919–25.Peyronnard O, et al. Study of mineralogy and leaching behavior of stabilized/solidified sludge using differential acid neutralization analysis. Cem Conc Res. 2009. doi: 10.1016/j.cemconres.2009.03.016 .Moulin I, et al. Lead, zinc and chromium (III) and (VI) speciation in hydrated cement phases. 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Zastosowanie żużli o długim czasie składowania jako składników cementów powszechnego użytku

The physical and chemical properties of cements with slag originated from the storage yards of different age, added as a supplementary cementing material are highlighted. The materials after 20-year storage, the crushed slag after approximately 2-year storage and the new slag from the ongoing production were compared. The materials supplied by the same metallurgical plant were characterized. The blended cements were produced by Portland cement clinker grinding with gypsum and slags added as 5 to 50% of binder mass. The standard properties of cements were examined, as well as some experiments related to the kinetics of hydration and hydration products were carried out. The addition of granulated blast furnace slag (GBFS) stored for a long time, as a component of cement, affects the properties of material in such a way that the early compressive strength is not specially altered but at longer maturing the strength decreases generally with the storage time and percentage of additive. This is related to the reduction of the vitreous component, as well as to the presence of weathered material of altered activity. At the additive content up to 50% the binder complying with the requirements of the European standards for CEM III/A or CEM II/(A,B)-S common cements can be produced. The cements with the old slag meet the requirements of EN 197-1 relating at least to the class 32,5. The role of calcium carbonate, being the product resulting from the slag weathering process, acting as a grindability and setting/hardening modifying agent, should be underlined.Praca dotyczy właściwości cementów zawierających granulowane żużle wielkopiecowe o różnym czasie składowania, z jednego źródła (huty żelaza). Porównano właściwości materiału z żużlem pochodzącym sprzed 20 lat, żużlem składowanym około 2 lat i żużlem z bieżącej produkcji. Cementy wyprodukowano poprzez przemiał klinkieru cementu portlandzkiego z gipsem; udział żużla stanowił od 5% do 50% masy spoiwa. Otrzymane cementy poddano badaniom standardowym; przeprowadzono również ocenę kinetyki i produktów hydratacji. Ustalono w pierwszej kolejności, że wprowadzenie żużla składowanego przez długi czas w charakterze składnika cementów powszechnego użytku wpływa na właściwości cementów w taki sposób, że wytrzymałości wczesne nie ulegają znaczącym zmianom, natomiast wytrzymałość po 28 dniach twardnienia zmniejsza się. Zredukowanie wytrzymałości jest wyraźniejsze w przypadku żużla o długim czasie składowania i przy większym jego udziale. Jest to powiązane ze zmniejszeniem zawartości fazy szklistej w żużlu i obniżeniem aktywności w następstwie procesów wietrzenia. Jednakże i tak przy odpowiednich udziałach żużla w granicy do 50% jest możliwe otrzymanie cementów powszechnego użytku typu CEM III/A lub CEM II/(A,B)-S spełniających wymagania normy EN 197-1 klasy przynajmniej 32,5. Należy podkreślić, że rolę modyfikującą pozytywnie właściwości cementów takie, jak mielność oraz generalnie proces wiązania i twardnienia wydaje się pełnić węglan wapnia tworzący się jako produkt wietrzenia żużli

Lekkie zaprawy cementowe z dodatkiem perlitu ekspandowanego, modyfikowane domieszkami

The lightweight insulating cement mortars with expanded perlite reveal high porosity bound with the presence of this filler. However, their properties are lowered due to the absorption of water. The studies were performed with aim to improve the composition of cement – perlite mortars and their parameters, such as, density and the percentage of absorbed water by use of admixtures. The three series of mortars of similar consistency were produced with cement to perlite volume ratio of 1/3, 1/5 and 1/7 respectively. The water repellent and air entraining agents were used. The density and water absorption were measured and the observations of microstructure were carried out under SEM. The transport of water in the mortars was significantly slower and limited by use of admixtures. The proportions giving the lowered density at fairly low absorbability complying with the standard requirements have been pointed out. The advantageous effect of water repellent and air entraining agent has been proved.Lekkie zaprawy ciepłochronne sporządzone z udziałem perlitu ekspandowanego charakteryzują się podwyższoną porowatością, co skutkuje pogorszeniem niektórych właściwości użytkowych w obecności wilgoci. Praca stanowi podsumowanie badań mających na celu poprawę właściwości termoizolacyjnych tworzyw perlitowych poprzez wprowadzenie domieszek o działaniu hydrofobizującym i modyfikującym mikrostrukturę materiału. Sporządzono kilka serii zapraw cementowo-perlitowych o różnej zawartości perlitu. Przeprowadzono pomiary podciągania kapilarnego i standardową ocenę nasiąkliwości. Dokonano obserwacji pod elektronowym mikroskopem skaningowym, podczas których potwierdzono zwartą mikrostrukturę warstwy na granicy rozdziału: wypełniacz perlitowy – matryca cementowa. Ustalono proporcje cement/perlit/domieszka, zapewniające istotne zmniejszenie nasiąkliwości. Wskazano też na korzyści wynikające z zastosowania domieszki hydrofobizującej i napowietrzającej