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1.
E. T. Stepkowska Z. Sulek J. L. Perez-Rodriguez A. Justo C. Maqueda 《Journal of Thermal Analysis and Calorimetry》1991,37(7):1497-1511
Mixtures of mud with various additives were studied to explain the reasons for the change in geotechnical properties. The additives were: lime, cement, fly ash, water-glass containing either Na2CO3 or CaCl2 and phosphogypsum. An increase in strength was usually associated with increase of weight loss, both on static or dynamic heating. An exothermic peak occurred between 420°C and 490°C., being especially high in the presence of water -glass, together with CaCl2. XRD indicated an increase in calcite content and the possible formation of calcium aluminate silicate hydrate. SEM showed a non-homogeneous microstructure and big pores in case of mixtures of low strength (water-glass addition). A homogeneous aggregated structure was obtained in the case of higher strength (fly ash, phosphogypsum). 相似文献
2.
Stepkowska E.T. Perez-Rodriguez J. L. Aviles M. A. Jimenez de Haro M. C. Sayagues M. J. 《Journal of Thermal Analysis and Calorimetry》2002,70(1):181-189
Specific surface, S, of CSH-gel particles of disordered layered structure, was studied by water sorption/retention in two cement pastes differing
in strength, i.e. C-33 (weaker) and C-43 (stronger), w/c=0.4. Hydration time in liquid phase was t
h=1 and 6 months, followed by hydration in water vapour either on increasing stepwise the relative humidity, RH=0.5→0.95→1.0 (WS) or on its lowering in an inverse order (WR). Specific surface was estimated from evaporable (sorbed) water
content, EV (110°C), assuming a bi- and three-molecular sorbed water layer at RH=0.5 or 0.95, respectively (WS). On WR it was three- and three- to four-molecular (50 to 75%), respectively, causing a hysteresis
of sorption isotherm. At RH=0.5 the S increased with cement strength from 146 m2 g-1 (C-33, 1 m) to 166 m2 g-1 (C-43, 1 m) and with hydration time to 163 (C-33, 6 m) and to 204 m2 g-1 (C-43, 6 m). At RH=1.0 (and 0.95), higher S-value were measured but these differences were smaller: S amounted to 190-200 m2 g-1 in C-33 (1 and 6 m) and 198-210 m2 g-1 in C-43 (1 and 6 m). Thus no collapse occurred on air drying of paste C-43 (6 m).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
Jiménez de Haro M. C. Pérez Maqueda L. A. Stepkowska E. T. Ma Martínez J. Pérez-Rodríguez J. L. 《Journal of Thermal Analysis and Calorimetry》2003,71(3):761-771
Grinding and contact with water or salt solution increased the specific surface (ssa) but lowered the first dehydration effect
(escaping up to 150°C) and increased the second dehydration effect (150 to 500°C). The dehydroxylation was moved to lower
temperatures and was only ΔM(500-1100°C)=3.7±0.3 % as compared to 5.5% in the parent vermiculite (V). Except ΔM(20-150°C),
the mass losses measured at the remaining T ranges, were consistent in the ground samples, thus the grinding for 2 min caused
the homogenization of the crystal structure of vermiculite [ΔM(150-500°C)=7.6±0.7%]. DTA curves after grinding and cation
exchange indicate an important exothermal peak at 795-870°C, its temperature depending on exchangeable cation. It indicates
the formation of high temperature phases (enstatite, forsterite, spinel). The lowest temperature of the peak (795°C) was observed
in V-gr-Li, here lithium silicate was formed. The highest peak temperature (870°C) was found in V-gr-K, where almost only
forsterite developed. These exothermal peaks were very weak in unground V with various exchangeable cations.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
E. T. Stepkowska S. Yariv J. L. Pérez-Rodríguez A. Justo A. Ruiz-Conde P. Sánchez-Soto 《Journal of Thermal Analysis and Calorimetry》1997,49(3):1449-1466
A dredged sludge was studied to investigate the influence of ageing and of pretreatment on its drying rate, water sorption/retention, thermal mass loss, XRD and microstructure (SEM).Ageing caused change in particle thickness and specific surface, a gradual aggregation to form units of the size 10–50 m, formation of macropores of similar size, unhomogeneity and fissures between aggregates and super-aggregates. Macropores were detectable by the initial drying rate especially at 45°C. They indicated a tendency of collapsing at a lower drying rate at 30°C. This is consistent with SEM observations. With ageing the aggregates were more compact and less sensitive to drying.The aggregated system indicated a higher initial drying rate (higher permeability), whereas stirring induced a lower drying rate, favouring the formation of compact laminar structure.XRD peak intensity was lowered with ageing due to decrease in crystallinity (stacking faults and/or decrease in crystallite size). The content of amorphous material was lowered as well, reducing water sorption/desorption, which indicated that the specific surface is lower.From the suitable microstructure induced by ageing some new phases may form (feldspar, zeolites), preferably in the coarser fraction of the sludge. This is disturbed by stirring which operation expels also carbonates from the particle edges and this may reduce the structural strength of the sludge. In aged bentonite suspension a similar tendency was observed of formation of specific microstructures capable of phase transformation, e.g. to feldspar. 相似文献
5.
Ewa T. Stepkowska 《Journal of Thermal Analysis and Calorimetry》2005,80(3):727-733
Summary Previous study of the hydration and ageing products of two cement pastes created the basis for the postulate of the course of solid-state reactions between the portlandite Ca(OH)2 and the CO2 from air in the hydrated and air dry cement. XRD basal spacing d(001) of portlandite exceeded the nominal value and increased with ageing, with the wetting and drying procedure and with carbonate content of the paste, indicating that a part of OH- ions was gradually substituted by CO32- ions, which are about twice bigger. IR spectroscopy showed a considerable content of portlandite, of CO32- of water and silicates. Also HCO3- H2O and CO2 in cavities between hexagonal rings and hexagonal hydrates were indicated. By MS (mass spectrometry) in vacuum the evaporation of sorbed water was detected at 100-120°C, of gel water at 350°C of portlandite water at 400°C and of high temperature water between 500 and 700°C, simultaneously with CO2 escape. Slightly higher peak temperatures were found by the TG test either in air or in argon. From these results and from geometric considerations it is postulated that the solid-state reactions take place on ageing of the cement paste and on its heating: hexagonal portlanditecalcium carbonate hydroxy hydratecalcium carbonate hydratehexagonal vaterite and/or orthorhombic aragoniterhombohedral calcite The analysis of the standard files of the calcium carbonate hydroxy hydrates supports this postulate and indicates a gradual transformation. 相似文献
6.
E. T. Stepkowska J. M. J. M. Bijen J. L. Perez-Rodriguez A. Justo P. J. Sanchez-Soto M. A. Aviles 《Journal of Thermal Analysis and Calorimetry》1994,42(1):41-65
A simple water sorption/retention (WS/WR) test, followed by stepwise static heating, was applied to the study of cement quality and the reactivity of its grain surface.
The physically bound water and hence the specific surface both in the unhydrated and in the hydrated state were estimated
as a function of the hydration time. Rehydration after heating at 220°C and contact with air was different inWS from that inWR samples, which indicates a difference in microstructure. XRD proved the formation of portlandite during the sorption test
and eventual heating at 200°C, and its transformation into carbonates on contact with air, especially on heating at 400°C.
The contents of these compounds were estimated from the mass difference between 400 and 800°C, which was compatible with the
mass change between 220 and 400°C and this indicates surface reactivity. The test may serve for the routine study of cement.
Dedicated to Professor Lisa Heller-Kallai on the occasion of her 65th birthday 相似文献
7.
Ewa T. Stepkowska 《Journal of Thermal Analysis and Calorimetry》2006,84(1):175-180
Two aged cement pastes
(7 years) were studied for H2O and CO2
evolution, the combined amounts of which were measured by TG and identified
by thermo-IR analysis. This indicated the presence of three forms of carbonates,
which decomposed at different temperatures. The displacement with time of
the evaporation of sorbed water to higher temperatures (500–700°C,
TG, MS) shows the possibility of its incorporation into carbonate hydrates
and/or hydroxy hydrates, postulated previously. The decomposition of all the
hydration products needed a thermal energy increasing with ageing (increased
temperature measured by TG). The carbonation process proceeded for 7 years
in the weaker paste, whereas it terminated before 5 years in the stronger
one. The CSH water content did not change with ageing, whereas that of portlandite
was lowered, which though did not account for the increase in carbonate content
(TG). Possibly some Ca2+ from the CSH gel was involved
in this process. In the stronger paste the growth with time of organic matter
was found (IR, TG/DTG). 相似文献
8.
Stepkowska E. T. Perez-Rodriguez J. L. Jimenez de Haro M. C. Sayagues M. J. 《Journal of Thermal Analysis and Calorimetry》2002,69(1):187-204
Main hydration products of two cement pastes, i.e. CSH-gel, portlandite (P) (and specific surface S) were studied by static heating, and by SEM, TEM and XRD, as a function of cement strength (C-33 and C-43) hydration time (th) and subsequent hydration in water vapour.Total change in mass on hydration and air drying, Mo, increased with strength of cement paste and with hydration time. Content of water escaping at 110 to 220°C, defined as water bound with low energy, mainly interlayer and hydrate water, was independent on cement strength but its content increased with (th). Content of chemically bound (zeolitic) water in CSH-gel, escaping at 220-400°C, was slightly dependent on strength and increased with (th). It was possibly derived from the dehydroxylation of CSH-gel and AFm phase. Portlandite water, escaping at 400-500°C, was independent on cement strength and was higher on longer hydration. Large P crystals were formed in the weaker cement paste C-33. Smaller crystals were formed in C-43 but they increased with (th). Carbonate formated on contact with air (calcite, vaterite and aragonite), decomposed in cement at 600-700oC. It was high in pastes C-33(1 month) and C-43(1 month), i.e. 5.7 and 3.3%, respectively; it was less than 1% after 6 hydration months (low sensitivity to carbonation) in agreement with the XRD study showing carbonates in the air dry paste (1month), and its absence on prolonged hydration (6 months) and on acetone treatment. Water vapour treatment of (6 months) pastes or wetting-drying increased this sensitivity.Nanosized P-crystals, detected by TEM, could contribute to the cement strength; carbonate was observed on the rims of gel clusters.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
9.
Ewa T. Stepkowska M. A. Aviles J. M. Blanes J. L. Perez-Rodriguez 《Journal of Thermal Analysis and Calorimetry》2007,87(1):189-198
The low temperature
of decomposition of some calcium carbonates and the bending of the TG curves
of hydrated cement between 500 and 800°C suggested the presence of some
complex compound(s), which needed complementary investigation (XRD, TG). Stepwise
transformation of portlandite (and/or lime) into calcium carbonate, with intermediate
steps of calcium carbonate hydroxide hydrates (CCH-1 to CCH-5), was indicated
by the previous study of two OPC.
This was checked here on four
cements ground for t
g=15,
20, 25 and 30 min and hydrated either in water vapour, successively at RH=1.0,
0.95 and 0.5 for 2 weeks each (WR1, WR2 and WR3, respectively) or as mortars
in liquid water (1m), followed by WR as above. The d[001] spacing of portlandite
was confirmed to vary: here between the lowest and the highest standard values.
The diffractograms of n=32 different samples
were analyzed for presence of standard CCH peaks, generally slightly displaced.
These were: CCH-1 [Ca3(CO3)2(OH)2]: N=11 peaks, of three different d[hkl] spacings, CCH-2 [Ca6(CO2.65)2(OH657)7(H2O)2]: N=10 for two d[hkl], CCH-3 [Ca3(CO3)2(OH)2·1.5H2O]: N=14 for five d[hkl], CCH-4,
ikaite [CaCO3(H2O)6]: N=13 for six d[hkl], CCH-5[CaCO3(H2O)]: N=15 for five d[hkl]. Thus the most probable is the presence of the
last three. The stepwise transformation of Ca(OH)2
into CaCO3 was confirmed: 相似文献
10.
E. T. Stepkowska J. M. Blanes F. Franco C. Real J. L. Prez-Rodríguez 《Thermochimica Acta》2004,420(1-2):79-87
The standard cement paste (C-43-St) was studied previously by static heating, SH, immediately after 1 month hydration at w/c = 0.4 [J. Therm. Anal. Calorim. 69 (2002) 187]. This paste after 5-year ageing (unprotected from contact with air) was subject to thermal analysis in air and in argon (DTA, DTG and TG), to XRD at various temperatures, T, in a high temperature chamber, to mass spectroscopy (MS) and to IR spectroscopy. The aim of this study was to compare the results of SH (fresh paste) and of TG (the aged one), to verify the assumptions made on SH interpretation and to check the change in hydration products with ageing as measured by phase transformation on heating (ΔM versus the final mass). The sorbed water (EV), escaping at 110 °C from the fresh paste, was bound on ageing with a higher energy and escaped at higher temperatures. The joint water content of hydrates and of C-S-H gel increased on ageing by 1–2% in the dense paste C-43-St and did not change in the less compact one C-43-I. C-S-H gel transformed on heating above 600 °C into C2S and C3S. Portlandite content did not change on ageing. In the air atmosphere it became partly carbonated, which was accompanied by an increase in mass between 500 and 600 °C. Carbon dioxide and/or carbonate ions to form carbonates, were sorbed during ageing and were present in the aged paste in some form undetectable by XRD (amorphous or crypto-crystalline). Sensitivity to carbonation ΔM(700–800 °C) increased highly with ageing. 相似文献