The thermal decomposition of thaumasite from Mothae kimberlite pipe, Lesotho, Southern Africa

Kresten, Peter; Berggren, G.

doi:10.1007/bf01909260

Cited by 12 publications

(4 citation statements)

References 6 publications

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“…Table 2 also collects decomposition enthalpies for a water loss obtained from experiments [8,15]. The experimental values show a relatively good agreement with our predictions.…”

Section: Methodssupporting

confidence: 66%

Model Study of Partial Structural Decomposition of Thaumasite

Scholtzová

Tunega

2015

AMM

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The DFT method was used for modeling a partial decomposition of the structure of the thaumasite mineral. The four models with a consecutive decreasing of water content were prepared (T12 – 100 %, T9 – 75 %, T6 – 50 %, T3 – 25 %) and corresponding decomposition enthalpies were calculated. The results showed a good agreement with available experimental data for the decomposition reaction of the thaumasite structure.

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“…Table 2 also collects decomposition enthalpies for a water loss obtained from experiments [8,15]. The experimental values show a relatively good agreement with our predictions.…”

Section: Methodssupporting

confidence: 66%

Model Study of Partial Structural Decomposition of Thaumasite

Scholtzová

Tunega

2015

AMM

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“…According to the TGA results of samples immersed in MgSO 4 (aq) (Fig.10), the broad trough of C-S-H was replaced by a much narrower but deeper trough at ~ 130 °C, which represented the decomposition of gypsum. The decomposition of thaumasite mainly happened between 140-200 °C (Kresten and Berggren 1976) and slightly overlapped with gypsum. M-S-H, which decomposes at ~400 °C and overlaps with hydrotalcite-like phases, was confirmed although it was not clearly detected by XRD analysis.…”

Section: Xrd and Tg Analysismentioning

confidence: 99%

Evaluation of Sulfate Resistance of Calcined Dolomite Activated Ground Granulated Blast Furnace Slag

Jin

Al‐Tabbaa

et al. 2016

J. Mater. Civ. Eng.

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Aggressive environments significantly influence the durability and serviceability of hardened cement and concrete. This paper presents an evaluation of the resistance of ground granulated blastfurnace slag (GGBS) activated with calcined dolomite, as a novel alkali activator, to 5% sodium sulfate attack and 5% magnesium sulfate attack. Two calcined dolomites, D800 and D1000, were prepared in the laboratory at 800 °C and 1000 °C respectively. The results demonstrated the good potential of using calcined dolomite activated slag in resisting sulfate attack. Immersion in Na 2 SO 4 (aq) led to an increase in strength in both the D800 (D800S) and the Portland cement CEM I 52.5N (PCS) activated slag, with a more pronounced effect in the former, while a decrease in the D1000 (D1000S) activated slag. On the Manuscript Click here to download Manuscript: Manuscript_revised.docx other hand, calcined dolomite activated slag had less strength loss than PCS after MgSO 4 attack. The products of sulfate attack and the deterioration processes are also analyzed by a range of tests including pH, weight change, corroded depth, XRD, TGA and SEM/EDS. After Na 2 SO 4 attack, the main product on D800S and D1000S was gypsum with a larger amount in the later. Gypsum, thaumasite and M-S-H were the main products of D800S and D1000S after MgSO 4 attack. The better resistance of D800S to sulfate attack was attributed to the absence of portlandite in the hydrated paste. On the other hand, the presence of portlandite in D1000S led to the inhomogeneous sulfate ions inward progression hence the severe deterioration of sample was observed.

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“…When both mineral are in cement composite, it is difficult to identify, as they belong to the same mineral group. The thermal examination of natural [19,20] and cement-forming thaumasite are studied by many researchers [18,[21][22][23][24][25][26][27][28][29], as this is achieved by comparison with ettringite. In literature, the mechanism of its thermal decomposition is shown by general description of dehydration process, presenting the solid anhydrous residuum by CaSiO 3 .CaCO 3 .CaSO 4 with valuable data from thermodynamic measurements [23][24][25][26].…”

Section: Introductionmentioning

confidence: 99%

TG/DTG-DSC and high temperature in-situ XRD analysis of natural thaumasite

et al. 2021

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This paper investigated thermal properties of natural thaumasite, such as phase composition and reaction mechanism of thermal decomposition using simultaneous TG/DTG-DSC in Ar and Air medium up to 1673 K, coupled with masspectrometer for analysis of evolving gases, and in-situ powder X-ray diffraction measurements. The transitional solid phases, grown with increasing of temperature at thaumasite thermal decomposition, are calcium hydrogen carbonate (Ca(HCO 3) 2) and hydrogen sulphate (Ca(HSO 4) 2), calcite, anhydrite, calcium silicates (wolastonite and larnite), calcium silico-carbonate (spurrite), and calcium silico-sulphate (ternesite). The thermal decomposition in both gaseous media includes the stages of dehydration, dehydroxylation, dacarbonation and desulphuration with obtaining a solid residue of varying degrees of crystallinity. The main solid phase, grown at the highest temperatures, is larnite. Based on the obtained results it was proposed the scheme of chemical reactions, which presents the reaction mechanism of thaumasite thermal decomposition. The defined scheme has both fundamental importance by adding new details of reference data, and practical application for thaumasite identification in chemical archaeology, and in the chemistry of cement and cement-based materials.

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The thermal decomposition of thaumasite from Mothae kimberlite pipe, Lesotho, Southern Africa

Cited by 12 publications

References 6 publications

Model Study of Partial Structural Decomposition of Thaumasite

Model Study of Partial Structural Decomposition of Thaumasite

Evaluation of Sulfate Resistance of Calcined Dolomite Activated Ground Granulated Blast Furnace Slag

TG/DTG-DSC and high temperature in-situ XRD analysis of natural thaumasite

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