Inlfuence of early sulfate exposure on the pore network development of mortars

Ikumi, Tai; Segura, Ignacio; Cavalaro, Sérgio Henrique Pialarissi

doi:10.1016/j.conbuildmat.2017.03.081

Cited by 15 publications

(21 citation statements)

References 36 publications

(20 reference statements)

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“…As in each group of pastes, the addition of contaminated material was made; the filler was used to ensure all pastes possessed the same proportions, considering this material is inert. The density of the carbonatic material is 2.84 g/cm 3 .…”

Section: Methodsmentioning

confidence: 99%

“…Fly ash comes from the combustion of coal mined in the Brazil and presented specific mass of 1.95 g/cm 3 , and specific BET area of 1.09 m 2 /g. Table 1 presents the results of the chemical analysis by X-ray fluorescence of the Portland cement and the fly ash.…”

Section: Methodsmentioning

confidence: 99%

“…The CP V-ARI cement employed has a density of 3.13 g/cm 3 and specific BET area of 1.07 m 2 /g. Fly ash comes from the combustion of coal mined in the Brazil and presented specific mass of 1.95 g/cm 3 , and specific BET area of 1.09 m 2 /g.…”

Section: Methodsmentioning

confidence: 99%

“…The material comes from the Paraná region (Brazil) and is a residue of the coal beneficiation process. Pyrite has density of 4.95 g/cm 3 , and after grinding, was classified as a passing material through a sieve with a mesh aperture of 2.4 mm.…”

Section: Methodsmentioning

confidence: 99%

“…The concrete structure degradation-mechanisms, attacked internally by sulphates, are caused primarily by the sulphide mineral oxidation phenomenon, which generates expansion and the appearance of cracks, due to the stress caused by crystallization of the new by-products with superior volume to the original [1][2][3]. Additionally, the products generated by this phenomenon react with the compounds of the hydrated cement, aluminate tri-calcium (C 3 A), calcium silicate hydrate (CSH) and calcium hydroxide (Ca (OH) 2 ), forming new products [4][5][6].…”

Section: Introductionmentioning

confidence: 99%

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Internal attack by sulphates in cement pastes and mortars dosed with different levels of pyrite

et al. 2017

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This study aims to investigate cementitious compound behaviour at early stages (up to 168 days), primarily when dosed with different levels of pyrite. To accomplish this, a study was conducted with cement pastes and mortars contaminated by sulphide. For the cement pastes, four contaminant levels were adopted: with one as a reference value (0%), two as cited by the standards, and one value greater than the set standards. In the mortars, two series were studied, one without contamination and the other with use of an aggregate contaminated naturally by pyrite. Pozzolanic cement was used (65% Portland cement CPV ? 35% fly ash) and the materials were submerged in curing compounds for 28 days.Subsequently, the samples were subjected to two exposure conditions: 1-a wet-dry cycle and 2-immersion in aqueous solution with aeration. To identify the products formed by pyrite oxidation, and the subsequent by-product-based reactions, and cement hydrates, scanning electron microscopy with elemental analysis was used. For the analysis of the mechanical properties, strength tests were performed to test axial compression and tensile strength in bending. Furthermore, monitoring of the dimensional variation in prisms (2.5 9 2.5 9 28.5) cm 3 was performed. In conclusion, we determined that at the exposure times tested, there were signs of sulphide oxidation in the contaminated compounds. It was proven that the higher the degree of pyrite contamination, the higher the relative expansion of the series, which was confirmed by the formation of expansive products identified in the scanning electron microscopy.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Internal attack by sulphates in cement pastes and mortars dosed with different levels of pyrite

et al. 2017

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Adhesion Study at Advanced Ages in Multipurpose Mortars

Marvila¹,

Alexandre²,

Azevedo³

et al. 2018

The Minerals, Metals &Amp; Materials Series

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Performance of Blended Cements with Limestone Filler and Illitic Calcined Clay Immediately Exposed to Sulfate Environment

et al. 2020

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The use of ternary blended cements with limestone filler and calcined clays can improve the durability of concrete structures exposed to aggressive environments and extend their service life. In sulfate-rich environments, the effects of supplementary cementitious materials depend on the replacement level and the progress of hydration. Low level of limestone filler contributes to the stabilization of AFt due to formation of monocarboaluminate. However, high replacement increases the effective w/c ratio and the capillary porosity, favoring the sulfate penetration. The use of active pozzolans improves sulfate resistance by reducing portlandite content and the permeability, which minimize ettringite and gypsum formation and sulfate penetration. It is generally assumed that curing prior to sulfate exposure should be extended to allow the pozzolanic reaction to progress. It is currently uncertain the effectiveness of calcined clay in combination with limestone filler when the cement is exposed immediately to aggressive environments. Typical structures affected by sulfate attack are commonly build in situ, thus being exposed to the aggressive environment since casting. This paper analyses external sulfate attack of blended cements with 30 % replacement by combinations of limestone filler and/or calcined clay exposed to Na2SO4 solution at two days after casting. For that, expansions, mass variation, visual appearance and compressive strength are monitored in mortars and pastes during 6 months. The evolution of microstructure was evaluated with XRD. Despite the lack of curing prior to sulfate exposure, cement with calcined clay showed an excellent resistance to external sulfate attack, while limestone cements presented a worse performance.

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Inlfuence of early sulfate exposure on the pore network development of mortars

Cited by 15 publications

References 36 publications

Internal attack by sulphates in cement pastes and mortars dosed with different levels of pyrite

Internal attack by sulphates in cement pastes and mortars dosed with different levels of pyrite

Adhesion Study at Advanced Ages in Multipurpose Mortars

Performance of Blended Cements with Limestone Filler and Illitic Calcined Clay Immediately Exposed to Sulfate Environment

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