The U phase formation in cement-based systems containing high amounts of Na2SO4

Li, G.; Bescop, P. Le; Moranville, Micheline

doi:10.1016/0008-8846(95)00189-1

Cited by 80 publications

(50 citation statements)

References 8 publications

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“…Hydrates formed in sprayed pastes are hexagonal plates presenting an Al/S ratio equal to 7.0 and an elevated sodium content. This aluminate hydrate may be an AFm phase denominated U-phase and was also reported by [37][38][39] in cement systems containing sodium concentration above 0.40 mol/l. The sprayed paste CEM I_ALK_SP_0.32 presents a propitious sodium concentration in the liquid phase for U-phase formation (0.58 mol/L, Table 5).…”

Section: Sem and Eds Microanalysismentioning

confidence: 78%

Influence of spraying on the early hydration of accelerated cement pastes

Salvador

Cavalaro

Cano³

et al. 2016

Cement and Concrete Research

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In practice, most of the studies about the interaction between cement and accelerators is performed with hand-mixed pastes. However, in many applications mixing occurs through spraying, which may affect accelerators reactivity and the microstructure of the hardened paste. The objective of this study is to analyze how the mixing process influences the early hydration of accelerated cement pastes. Isothermal calorimetry, X-ray diffraction, thermogravimetry and SEM imaging were performed on cement pastes produced by hand-mixing and by spraying, using equivalent doses of an alkali-free and an alkaline accelerator and two types of cement. Results showed a great influence of the spraying process on the reactivity of accelerators and on the morphology of the precipitated hydrates. Variations in hydration kinetics caused by the mixing method are explained and the results obtained might have a significant repercussion on how future research on the behavior of accelerated mixes will be performed.Peer ReviewedPostprint (author's final draft

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Section: Sem and Eds Microanalysismentioning

confidence: 78%

Influence of spraying on the early hydration of accelerated cement pastes

Salvador

Cavalaro

Cano³

et al. 2016

Cement and Concrete Research

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“…even the appearance of moderate amounts of ettringite in FAN‐4 pastes could be surprising as these authors failed to observe ettringite in a pure system comprised solely of Na 2 SO 4 and C 3 A. Although Na 2 SO 4 is not alkaline in itself (a solution of Na 2 SO 4 should have a pH of around 7), when mixed with hydrating C 3 A, the formation of phase U, only considered stable at very high pH′s, has recently been observed . Although Phase U or AFm was not observed in FAN‐4 paste XRD, it should be noted that in our pastes, the estimated C 3 A content is only ~1%, making it impossible to observe any alternative C 3 A hydration products that are poorly crystalline.…”

Section: Discussionmentioning

confidence: 98%

Very High Volume Fly Ash Cements. Early Age Hydration Study Using Na₂SO₄ as an Activator

2013

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The early age ambient temperature hydration of a hybrid cement formulation containing very high volumes of coal fly ash (~80% by dry mass) and activated by Na2SO4 is presented. The Na2SO4 salt acts as a safe and convenient in situ source of alkali to activate fly ash glassy phases without undesirable effects on cement clinker hydration. Comparison to a reference paste with gypsum instead of sodium sulfate revealed that Na2SO4 reduced setting times, shortened the induction period, and increased early alite hydration and compressive strength development, but also restricted ettringite formation. When replacing the active fly ash component for milled sand of a similar particle size, the Na2SO4‐activated pastes set even quicker, no ettringite was observed, and early strengths were considerably reduced. Possible reaction mechanisms in the hybrid pastes are discussed.

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“…The XRD patterns for system B2-BFS hydrated in the presence of activator B differed from the foregoing (see Figure 3(b)). In addition to calcite and ettringite, another calcium sulfoaluminate hydrate appeared, phase "u" (Arbi et al 2013;Li et al, 1996). The secondary products identified in systems hydrated in the presence of alkaline activators differ scantly from the ones traditionally detected in ordinary portland cement hydration (Lea, 1974;Taylor, 1997).…”

Section: Mineralogical and Microstructural Characterisationmentioning

confidence: 95%

Cementos híbridos de bajo impacto ambiental: Reducción del factor clinker

García-Lodeiro

Fernández-Jiménez

Palomo

2015

Revista de la Asociación Latinoamericana de Control de Calidad,

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The environmental problems posed by portland cement manufacture have prompted the scientific committee to seek more eco-efficient binders with the same technological features as OPC; hybrid cements are among such alternative materials. Hybrid alkaline cements are multi-component systems containing a high mineral addition (fly ash (FA), metakaolin (MK), blast furnace slag (BFS)) content, low proportions (<30 %) of portland clinker and moderately alkaline activators. The substantially lower amount of clinker needed to manufacture these binders than ordinary portland cement is both economically and ecologically beneficial. The present study explored strength development and the reaction products generated by several hybrid cements, consisting of a number of industrial by-products and very low portland clinker contents. Keywords: alkaline activation; geopolymer; hybrid cements; mechanical strength; NMR. RESUMENLa problemática medioambiental en torno a la fabricación de cemento portland, ha llevado a la comunidad científica a buscar nuevos materiales cementantes alternativos, mas ecoeficientes, y con las mismas prestaciones tecnológicas que las del cemento portland tradicional, en este sentido se ha desarrollado los cementos híbridos. Los cementos híbridos alcalinos son interesantes sistemas multicomponente que incorporan elevados contenidos de adiciones minerales (cenizas (FA), metacaolin (MK), escorias (BFS)…) y bajos contenidos de clinker portland (CK) (< 30 %), junto con activadores de moderada alcalinidad. El desarrollo de estos cementos permite una importante reducción en el factor clinker, con el beneficio tanto económico como medioambiental que ello supone. En el presente trabajo se investiga tanto el desarrollo resistente como los productos de reacción generados en diferentes cementos híbridos, constituidos por diversos subproductos industriales y muy bajos contenidos en clinker portland. Palabras clave: activación alcalina; geopolimero; cementos híbridos; resistencia mecánica; RMN. RESUMOA questão ambiental em torno da fabricação do cimento Portland levou a comunidade cientifica a buscar por novos materiais cimentícios alternativos, porém ecoeficientes e com prestações tecnológicas semelhantes às do cimento Portland tradicional. Uma alternativa, nesse sentido se desenvolveram os cimentos híbridos. Os cimentos híbridos alcalinos são interessantes sistemas multicomponentes que incorporam elevados conteúdos de adições minerais (cinzas (FA), metacaulim (MK), escórias (BFS)...) e baixos conteúdos de clínquer Portland (CK) (<30%), junto com ativadores de moderada alcalinidade. O desenvolvimento destes cimentos permite uma importante redução do fator clínquer, com benefício econômico e também ambiental. Neste presente trabalho é investigado tanto o desenvolvimento da resistência como os produtos das reações gerados dos cimentos híbridos, constituídos por diferentes produtos industriais e conteúdos baixos de clínquer Portland.

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The U phase formation in cement-based systems containing high amounts of Na2SO4

Cited by 80 publications

References 8 publications

Influence of spraying on the early hydration of accelerated cement pastes

Influence of spraying on the early hydration of accelerated cement pastes

Very High Volume Fly Ash Cements. Early Age Hydration Study Using Na₂SO₄ as an Activator

Cementos híbridos de bajo impacto ambiental: Reducción del factor clinker

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The U phase formation in cement-based systems containing high amounts of Na2SO4

Cited by 80 publications

References 8 publications

Influence of spraying on the early hydration of accelerated cement pastes

Influence of spraying on the early hydration of accelerated cement pastes

Very High Volume Fly Ash Cements. Early Age Hydration Study Using Na2SO4 as an Activator

Cementos híbridos de bajo impacto ambiental: Reducción del factor clinker

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Very High Volume Fly Ash Cements. Early Age Hydration Study Using Na₂SO₄ as an Activator