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This paper deals with synthesis and assessment of the hydraulicity of C4A3Cr, analog phase C4A3S to , relevant to the phase chemistry and properties of sulfoaluminate cements. C4A3Cr, synthesized at 1250 °C is well crystallized phase, latently hydraulic, with hydration accelerated in the presence of C4A3S, or CS. Calorimetric curves show reciprocal influence of sulfate and chromate phase in hydration of C4A3S-C4A3Cr system. The total heat expressed at hydration is nearly the same for all specimens, but the rate of heat evolution depends
on the ratio of C4A3S/C4A3Cr phases. X-ray diffraction pattern and DTA curves showed that, increasing content of C4A3Cr in hydrating mixture results in a coexistence of two types of ettringite (chromate and sulfate ettringite) hydrogarnet,
gibbsite and monosulfate.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
Grounds T. Nowell D. V. Wilburn F. W. 《Journal of Thermal Analysis and Calorimetry》2003,72(1):181-190
One of the principal uses of supersulfated cement has been for structures exposed to sea water and sulfate bearing ground
waters. The resistance to such environments has been related to the absence of calcium hydroxide and the combination of much
of the free alumina into ettringite during hydration. This paper reports the resistance of SSC to sulfate solutions in which
ettringite has been decomposed. Prism samples were subjected to initial water storage at 25°C for both 28 days and 6 months.
Samples were also cured for 6 months at 95°C and at both 11% and 100% R.H. The control samples of 28 days were compared with
the 6 months samples of a more mature undecomposed SSC paste. After curing the prisms were measured and all the samples were
immersed in three sulfate solutions (0.7M Na2SO4 , 0.7M MgSO4 and saturated CaSO4), and water at the same time. Measurements of linear expansion over 6 months were carried out. Core and surface material
following immersion was examined by DTG and XRD. The study indicated that SSC is resistant to sodium and calcium sulfate solutions.
Strong magnesium sulfate solutions decomposed the samples under all conditions. A possible mechanism for this attack is suggested.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
Wieczorek-Ciurowa K. Fela K. Kozak A. J. 《Journal of Thermal Analysis and Calorimetry》2001,65(2):655-660
Attempts have been made to replace aluminium(III) by chromium(III) in the ettringite structure because of practical importance
of a waste treatment technology. The optimum conditions of Ca6[Cr(OH)6]2(SO4)3⋅26H2O formation and its thermal stability are reported.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
The system 4CaO·3Al2O3·SO3-CaSO4·2H2O-Ca(OH)2 was hydrated in the presence of ten dopants, specifically soluble salts of heavy metals.When added in 10% amount, the effect of each salt is strongly evident at shorter curing times, the hydration kinetics being more favoured in the order Pb(NO3)22CrO4< Cd(NO3)2< Zn(NO3)2t~Mn(NO3)3=K2MoO43)23)23)33)3. At longer curing times the differences among the systems decrease significantly.The 28-day compressive strength is almost the same for all the systems except those containing Pb(NO3)2, K2MoO4 and K2CrO4. 相似文献
5.
研究了不同阳离子氯盐作用下, 水泥净浆中游离氯离子浓度和结合氯离子浓度的变化, 并通过X射线衍射技术和电镜扫描分析技术观察其微观状态. 结果表明: 掺氯化钠的试件中游离氯离子浓度更高, 钙离子对氯离子的结合能力更强; 氯化钙比氯化钠更易与水泥熟料发生反应, 生成水化产物Friendel复盐和C-S-H凝胶; 掺氯化钙的试块表面晶体更为细密且结构多样. 相似文献
6.
Dweck J. Ferreira da Silva P. F. Büchler P. M. Cartledge F. K. 《Journal of Thermal Analysis and Calorimetry》2002,69(1):179-186
Thermogravimetry (TG) and derivative thermogravimetry (DTG) have been used by the authors as very effective tools to study hydration steps of cements used for solidification/stabilization of tanning wastes. The present paper presents a method which was applied to separate the peaks shown by DTG curves of type II Portland cement pastes, analyzed at different times during the first 4 weeks of setting. Through a specific software a more detailed study of the evolution of the cement hydration may be done, which allows the measurement of the amount of hydrated water present in tobermorite gel as well as in ettringite, which are the main phases formed from the original components of the cement. The number of moles of water present in the ettringite phase calculated by the method is in very good agreement with the values found in the literature, validating the method to calculate the same parameter in tobermorite gel. In the latter case the water content decreases significantly during the first day of hydration, then remains at a constant value over the rest of the analyzed period.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
7.
Luís Urbano D. Tambara Júnior Janaíde C. Rocha Malik Cheriaf Pilar Padilla-Encinas Ana Fernndez-Jimnez Angel Palomo 《Molecules (Basel, Switzerland)》2021,26(7)
This work analyzes the effect of the presence of 5 wt.% of solid sodium salts (Na2SO4, Na2CO3, and Na2SiO3) on calcium sulfoaluminate cement (CSA) hydration, addresses hydration kinetics; 2-, 28-, and 90-d mechanical strength, and reaction product microstructure (with X-ray diffraction (XRD), and Fourier transform infrared spectroscopy, (FTIR). The findings show that the anions affect primarily the reactions involved. Ettringite and AH3, are the majority hydration products, while monosulfates are absent in all of the samples. All three salts hasten CSA hydration and raise the amount of ettringite formed. Na2SO4 induces cracking in the ≥28-d pastes due to post-hardening gypsum and ettringite formation from the excess SO42– present. Anhydrite dissolves more rapidly in the presence of Na2CO3, prompting carbonation. Na2SiO3 raises compressive strength and exhibits strätlingite as one of its reaction products. 相似文献
8.
In the present study, the average modulus of delayed ettringite is evaluated by an experimental method combined with theoretical analysis. Firstly, the delayed ettringite crystal is synthesized by chemical reaction of Aluminum sulfate and calcium hydroxide. Secondly, specimens are obtained by compressing the delayed ettringite crystal under different pre-loads. Thirdly, the variation of the modulus of the specimen with different pre-loads is tested using Instron material test machine and the SHPB technique, respectively. It is found that the experimental data may be suitably fitted by Boltzmann Function. Finally, the porosity of the specimen is detected using the saturation method, and the effect of the porosity on the modulus is analyzed by the Eshelby's equivalent inclusion method and the Mori-Tanaka's scheme. The static and dynamic modulli of the equivalent homogeneous ettringite obtained in present study are approximately 10.64 GPa and 24.61 GPa, respectively. 相似文献
9.
Ubbrìaco P. Bruno P. Traini A. Calabrese D. 《Journal of Thermal Analysis and Calorimetry》2001,66(1):293-305
In this study the process of hydration of fly ash, produced by a municipal solid waste (MSW) incinerator, is examined in water
and in a solution enriched with Ca(OH)2. The examined fly ash samples are characterized by a high content of alkaline chlorides and anhydrite and by remarkable amounts
of heavy metals. Investigations using differential thermal analysis/thermogravimetry (DTA/TG) and X-ray diffractometry (XRD)show
particular kinetics of the formation of the ettringite phase. The development of such a hydrated phase is much more intense
in the presence of an excess of Ca(OH)2so as to consume the ‘free’ sulphate in the case of the more reactive fly ash. Experimental results from thermal analysis
and X-ray diffractometry show the presence of different hydrated phases during the interaction between fly ash and aqueous
solution. The analytical determinations, related to the aqueous solution, point out an interesting decrease in concentration
of metals Pb, Zn and Cr(VI), relating to the middle period of the interaction.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
DTA/TG
and X-ray investigations were carried out on different building composites
in order to examine their relative hydration processes. The presence of lime,
hemihydrate gypsum, ferosilicate, and some other wastes as leaner and hydrophobic
additive in different proportions into composites provokes hydration reactions,
leading to calcium silicate hydrate (CSH), ettringite and an intermediate
phase formation with varying chemical composition of calcium, aluminum, silicon
and sulfur.
DTA curves indicate several transformations taking
place between composites components, related to hydration of some phases.
The content of ettringite component corresponds to the properties and it is
used as an indicator for the possibility of industrial application. It is
found out that gypsum based cementitious binders could be used as building
material in the industry. The same time it is confirmed that the selected
wastes could be considered as secondary raw materials. 相似文献
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