共查询到20条相似文献,搜索用时 296 毫秒
1.
M. S. Amin S. A. Abo-El-Enein A. Abdel Rahman Khaled A. Alfalous 《Journal of Thermal Analysis and Calorimetry》2012,107(3):1105-1115
Pozzolanic cement blends were prepared by the partial substitution of ordinary Portland cement (OPC) with different percentages
of burnt clay (BC), Libyan clay fired at 700 °C, of 10, 20, and 30%. The pastes were made using an initial water/solid ratio
of 0.30 by mass of each cement blend and hydrated for 1, 3, 7, 28, and 90 days. The pozzolanic OPC–BC blend containing 30%
BC was also admixed with 2.5 and 5% silica fume (SF) to improve the physicomechanical characteristics. The hardened pozzolanic
cement pastes were subjected to compressive strength and hydration kinetics tests. The results of compressive strength indicated
slightly higher values for the paste made of OPC–BC blend containing 10% BC The results of DSC and XRD studies indicated the
formation and later the stabilization of calcium silicates hydrates (CSH) and calcium aluminosilicate hydrates (C3ASH4 and C2ASH8) as the main hydration products in addition to free calcium hydroxide (CH). Scanning electron microscopic (SEM) examination
revealed that the pozzolanic cement pastes made of OPC–BC mixes possesses a denser structure than that of the neat OPC paste.
Furthermore, the addition of SF resulted in a further densification of the microstructure of the hardened OPC–BC–SF pastes;
this was reflected on the observed improvement in the compressive strength values at all ages of hydration. 相似文献
2.
Jihui Zhao Duanle Li Shucong Liao Dongmin Wang Hao Wang Peiyu Yan 《Journal of Thermal Analysis and Calorimetry》2018,132(3):1459-1470
This paper investigates the influence of mechanical grinding on pozzolanic characteristics of circulating fluidized bed fly ash (CFA) from the dissolution characteristics, paste strength, hydration heat and reaction degree. Further, the hydration and hardening properties of blended cement containing different ground CFA are also compared and analyzed from hydration heat, non-evaporable water content, hydration products, pore structure, setting time and mortar strength. The results show that the ground CFA has a relatively higher dissolution rate of Al2O3 and SiO2 under the alkaline environment compared with that of raw CFA, and the pozzolanic reaction activity of ground CFA is gradually improved with the increase of grinding time. At the grinding time of 60 min, the pozzolanic reaction degree of CFA paste is improved from 6.32% (raw CFA) to 13.71% at 7 days and from 13.65 to 28.44% at 28 days, respectively. The relationships of pozzolanic reaction degree and grinding time of CFA also conform to a quadratic function. For ground CFA after a long-time grinding such as 60 min, the hydration heat and non-evaporable water content of blended cement containing CFA are significantly improved. Owing to relatively smaller particle size and higher activity of ground CFA, the blended cement paste has more hydration products, narrower pore size distribution and lower porosity. For macroscopic properties, with increase in grinding time of CFA, the setting time and strength of blended cement are gradually shortened and improved, respectively. 相似文献
3.
Barbara Pacewska Mariola Nowacka Valentin Antonovi? Marius Aleknevi?ius 《Journal of Thermal Analysis and Calorimetry》2012,109(2):717-726
The effect of spent FCC catalyst on early hydration (up to 48?h) of high aluminate cement (Al2O3 >70%) at different ambient temperatures (10, 20, and 30?°C) was investigated. Cement pastes with constant ratio of water/binder?=?0.35 (binder?=?cement?+?addition) and containing 0, 5, 10, and 15% mass of addition as replacement of cement were studied. The hydration kinetics was determined by calorimetric measurements and the structure of hardened binders after 2?days of curing at an appropriate temperature was also investigated using X-ray, SEM, and thermal analysis methods. Due to the fact that hydration of aluminate cements is highly sensitive to temperature conditions as well as certain changes of temperature are inevitable in practice, the evaluation of the impact of the waste catalyst addition in such conditions is justified. On the basis of obtained results, it was stated that the temperature determines the early hydration of high aluminate cement and decides about the influence of waste aluminosilicate. The introduction of the discussed addition has a big impact on the kinetics of cement hydration closely related to the curing temperature. The presence of spent catalyst accelerates the hydration at the temperatures of 20 and 30?°C, but at the temperature of 10?°C this waste aluminosilicate acts as a retarding agent. The effect of the addition on the microstructure of hardened binders after 48?h of hydration is rather insignificant, especially at 20?°C, compared to the influence of the temperature on hydration. At the temperature of 10?°C, a formation of low amount of C2AH8 can be observed because of the presence of spent catalyst, while at the temperature of 30?°C the introduction of the mineral addition prevents the hydrogarnet formation. 相似文献
4.
A study was carried out comparing silica fume (SF) and dealuminated kaolin (DK) as pozzolanic materials in blended cements. Ten, 20 or 30 wt% of SF or DK were substituted for Portland cement. The kinetics of hydration up to 45 h were studied using isothermal conduction calorimetry. Blends containing pozzolanic materials usually have decreased heats of hydration compared to pure cement during the period of C3S hydration, i.e. during the main hydration peak. Depending on the chemical composition and the activity of the pozzolan, the reaction taking place with the lime typically contributes to the heat output after the main hydration peak.The pozzolanic activity of DK is the principal factor and heat evolution increases with respect to pure PC mortar, during the first 15 h. The presence of hydrated silica (silanol groups) in DK increases the pozzolanic activity especially before and during induction period. The acidic silanol sites are capable of a fast acid-base reaction with the alkalis and with any Ca(OH)2 present in cement during the induction period. 相似文献
5.
M. Kuliffayová L’. Krajči I. Janotka V. Šmatko 《Journal of Thermal Analysis and Calorimetry》2012,108(2):425-432
The kaolin sand containing 36 wt% of kaolinite was thermally transformed at 650 °C/L h to the burnt kaolin sand (BKS) with
relevant content of metakaolinite. Thermal behaviour of composites with substitution of Portland cement (PC) by the BKS containing
0, 5, 10 and 15 wt% of metakaolinite and water-to-solid ratio of 0.5 kept for 90 days in 20 ± 1 °C water was studied by thermal
analysis. TG/DTA/DTG studies concerned calciumsilicate hydrate and calciumaluminate hydrate formation, portlandite dehydroxylation
and calcite decarbonation. The influence of curing time and metakaolinite content were estimated. The reduction in portlandite
content was observed in PC–BKS composites opposite to that found in the reference PC system. Compressive strength uptakes
were observed in PC–BKS composites relative to that of reference PC system. BKS is characterized as effective pozzolanic material
giving cement composites of high performance. The above findings were confirmed by X-ray diffraction analysis (XRD) and scanning
electron microscopy (SEM) results. 相似文献
6.
L’. Krajči S. C. Moujmdar M. Kuliffayová I. Janotka 《Journal of Thermal Analysis and Calorimetry》2010,100(3):779-787
Two types of raw materials, original kaolin sand OKS I and OKS II were used for experiment. They were transformed (1 h at 650 °C with 10 °C/min temperature increase) to burnt kaolin sand (BKS I and BKS II) with pozzolanic properties. Contents of decisive mineral—metakaolinite—in BKSs are as follows: BKS I (fraction below 0.06 mm) 20%; BKS II (fraction below 0.06 mm) 36% and BKS II (fraction below 0.1 mm) 31% by mass. Mortars with blends of Portland cement (PC) and BKS were prepared announced as: MK I (0.06) with 5 and 10% cement substitution by metakaolinite; MK II (0.06) with 5 and 10% cement substitution by metakaolinite and MK II (0.1) with 5, 10, 15 and 20% cement substitution by metakaolinite. The reference mortar with 100% of PC was made for comparison. All mortars were adjusted on the constant workability 180 ± 5 mm flow. Besides significant increase in compressive strengths—the refinement of pore structure in mortars with BKS connected with decreases in permeability and Ca(OH)2 content were revealed. The above facts confirm pozzolanic reaction of BKS in contact with hydrated PC and indicate perceptiveness of BKS for the use in cement-based systems as a pozzolanic addition. 相似文献
7.
M. Ischia C. Perazzolli R. Dal
Maschio R. Campostrini 《Journal of Thermal Analysis and Calorimetry》2007,87(2):567-574
The pyrolysis of
an urban plant sewage sludge carried out under He atmosphere was studied by
thermogravimetric-mass spectrometric (TG-MS) and thermogravimetric-gas chromatographic-mass
spectrometric (TG-GC-MS) analyses. The sludge was thermally degraded with
a heating rate of 10°C min–1 in the 20–1000°C
interval; its mass loss is 51.8% up to 600°C and 61.4% up to 1000°C.
Gas chromatographic analyses of the gas released during major thermogravimetric
events allow the identification of various chemical species. Water, carbon
mono- and di-oxide, several hydrocarbons (up to C5, both saturated and unsaturated)
were the major detected species. Minor amount of pollutant species, such as
cyano-compounds, were also detected. Among the released species hydrocarbons
constituted the major fraction (53%), thus suggesting their immediate exploitation
as fuel gas. The pyrolysis behaviour of this sample was then compared with
other sewage sludge arising from wastewater treatment plants subjected to
anaerobic digestion as found in literature data. 相似文献
8.
E. J. Kim H. Y. Xu J. S. Lim J. W. Kang J. H. Gim Vinod Mathew Jaekook Kim 《Journal of Solid State Electrochemistry》2012,16(1):149-155
LiCoPO4 nanoparticles were synthesized by standard and glucose-assisted sol–gel methods for use as cathodes in lithium-ion batteries.
The effect of glucose on the characteristics of the formed LiCoPO4 nanoparticles was investigated by TGA, XRD, and FESEM. The TGA results indicated gradual decomposition of glucose in the
temperature range 400–700 °C. The XRD results showed olivine phases in addition to small traces of Co3O4 for samples calcined at 400 °C while pure olivine phases were confirmed for the 700 °C calcined samples. The addition of
glucose strongly suggests promotion of LiCoPO4 crystallization, as revealed by FESEM studies. The electrochemical measurements pertaining to LiCoPO4 samples calcined at 400 °C suggested an enhancement of initial discharge capacity from 103.3 to 144.6 mAh/g for the standard
and glucose-based electrodes, respectively. Further, the effects of conductive additive and excess lithium on the electrochemical
performance of LiCoPO4 have also been investigated. 相似文献
9.
Tongsheng Zhang Qijun Yu Jiangxiong Wei Pingping Zhang Peixin Chen 《Journal of Thermal Analysis and Calorimetry》2012,109(1):265-271
Owing to poor bonding between coarse fly ash particles and hydration products, gap-graded blended cements with fly ash usually show lower compressive strengths than Portland cement. Surface cementitious properties of coarse fly ash were improved by dehydration and rehydration processes in the present study. The results show that during the calcination at 750?°C, C?CS?CH gel is mainly transformed into a new nesosilicate, which is similar to a less crystalline C2S. The formation of melilite from hydration products is also noticed at 900?°C, however, this will not contribute to rehydration of calcined fly ash. Rehydration of new generated nesosilicate on the surface of coarse fly ash leads to a better bonding between coarse fly ash particles and hydration products. As a result, both early and late mechanical properties of gap-graded blended cements containing 25% cement clinker and 39% calcined coarse fly ash are higher than those of 100% Portland cements. 相似文献
10.
V. Rahhal O. Cabrera R. Talero A. Delgado 《Journal of Thermal Analysis and Calorimetry》2007,87(2):331-337
The use of active mineral additions is an important alternative in concrete
design. Such use is not always appropriate, however, because the heat released
during hydration reactions may on occasion affect the quality of the resulting
concrete and, ultimately, structural durability. The effect of adding up to
20% silica fume on two ordinary Portland cements with very different mineralogical
compositions is analyzed in the present paper. Excess gypsum was added in
amounts such that its percentage by mass of SO3 came
to 7.0%.
The chief techniques used in this study were heat conduction
calorimetry and the Frattini test, supplemented with the determination of
setting times and X-ray diffraction. The results obtained showed that replacing
up to 20% of Portland cement with silica fume affected the rheology of the
cement paste, measured in terms of water demand for normal consistency and
setting times; the magnitude and direction of these effects depended on the
mineralogical composition of the clinker. Hydration reactions were also observed
be stimulated by silica fume, both directly and indirectly – the latter
as a result of the early and very substantial pozzolanic activity of the addition
and the former because of its morphology (tiny spheres) and large BET specific
surface. This translated into such a significant rise in the amounts of total
heat of hydration released per gram of Portland cement at early ages, that
silica fume may be regarded in some cases to cause a synergistic calorific
effect with the concomitant risk of hairline cracking. The addition of excess
gypsum, in turn, while prompting and attenuation of the calorimetric pattern
of the resulting pastes in all cases, caused the Portland cement to generate
greater heat of hydration per gram, particularly in the case of Portland cement
with a high C3A content. 相似文献
11.
E. Kraleva M. L. Saladino R. Matassa E. Caponetti S. Enzo A. Spojakina 《Journal of Structural Chemistry》2011,52(2):330-339
Pure titania, zirconia, and mixed oxides (3–37 mol.% of ZrO2) are prepared using the sol-gel method and calcined at different temperatures. The calcined samples are characterized by
Raman spectroscopy, X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen
adsorption porosimetry. Measurements reveal a thermal stability of the titania anatase phase that slightly increases in the
presence of 3–13 mol.% of zirconia. Practically, the titania anatase-rutile phase transformation is hindered during the temperature
increase above 700°C. The mixed oxide with 37 mol.% of ZrO2 treated at 550°C shows a new single amorphous phase with a surface area of the nanoparticles double with respect to the other
crystalline samples and the formed srilankite structure (at 700°C). The anatase phase is not observed in the sample containing
37 mol.% of ZrO2. The treatment at 700°C causes the formation of the srilankite (Ti0.63Zr0.37Ox) phase. 相似文献
12.
Marta Worzakowska 《Journal of Thermal Analysis and Calorimetry》2008,93(3):799-803
The preliminary studies of the thermal behaviour of polyester obtained in polycondensation process of cyclohex-4-ene-1,2-dicarboxylic
anhydride and ethylene glycol and its new epoxidized form have been performed. The thermal characterization of initial polyester
and its completely oxidized form was done by using differential scanning calorimetry (DSC) and thermogravimetric analysis
(TG). The non-isothermal DSC was applied to determine the influence of time and the temperature on the chemical modification
of initial polyester using 38-40% solution of peracetic acid. On the basis of DSC profiles it has been found that the endothermic
transition, due to the degradation process of initial polyester was characteristic feature under controlled heating program.
The two characteristic transitions for the new epoxidized polyester, the exothermic peak corresponded to the thermal crosslinking
of epoxidized polyester (322.8–336.4°C) and the endothermic decomposition peak of the cured material (363.8–388.9°C) were
observed. The peak maximum temperatures (Tmax) and the heat of cross-linking reaction (ΔHc) for epoxypolyester prepared at 20–60°C under 1–4 h were evaluated. The Tmax1 were almost independent from epoxidation conditions,
while, the values of ΔHc were dependent from conditions of synthesis. The ΔHc values of this process decreased when time of oxidation increased. The highest values of ΔHc at 40°C were obtained. Additionally, TG experiments confirmed two separated degradation steps of the new epoxidized polyester
indicating the ester (370–380°C) and ether (450–460°C) bond breakdown. 相似文献
13.
D. Choudhury R. C. Borah R. L. Goswamee H. P. Sharmah P. G. Rao 《Journal of Thermal Analysis and Calorimetry》2007,89(3):965-970
Pyrolysis of petroleum refinery sludge has received global acclamation as a clean conversion technique for providing solution
of sludge disposal as well as efficient resource utilization. This communication reports the kinetics study of pyrolysis of
petroleum refinery sludge. Experiments were carried out by means of thermogravimetric analysis at different heating rates
of 5, 10 and 20°C min−1. The pyrolytic reaction is significant in the temperature range of 200–350°C and analysis and evaluation of kinetic parameters
is done in the 100–500°C region of non-isothermal TG curves obtained in nitrogen atmosphere.
The activation energy is calculated by iso-conversional method, then other kinetic parameters are determined by considering
single reaction and two reaction global kinetic model. Two-reaction model is found to fit satisfactorily the experimental
results. 相似文献
14.
Study on optimization of hydration process of blended cement 总被引:1,自引:0,他引:1
Tongsheng Zhang Qijun Yu Jiangxiong Wei Peng Gao Pingping Zhang 《Journal of Thermal Analysis and Calorimetry》2012,107(2):489-498
To optimize the hydration process of blended cement, cement clinker and supplementary cementitious materials (SCMs) were ground
and classified into several fractions. Early hydration process of each cementitious materials fraction was investigated by
isothermal calorimeter. The results show fine cement clinker fractions show very high hydration rate, which leads to high
water requirement, while fine SCMs fractions present relatively high hydration (or pozzolanic reaction) rate. Cement clinker
fractions in the range of 8–24 μm show proper hydration rate in early ages and continue to hydrate rapidly afterward. Coarse
cement clinker fractions largely play “filling effect” and make little contribution to the properties of blended cement regardless
of their hydration activity (or pozzolanic activity). The hydration process of blended cement can be optimized by arranging
high activity SCMs, cement clinker, and low activity SCMs in fine, middle, and coarse fractions, respectively, which not only
results in reduced water requirement, high packing density, and homogeneous, dense microstructure, but also in high early
and late mechanical properties. 相似文献
15.
Calorimetry in the studies of cement hydration 总被引:1,自引:0,他引:1
Marek Gawlicki Wiesława Nocuń-Wczelik Łukasz Bąk 《Journal of Thermal Analysis and Calorimetry》2010,100(2):571-576
Calorimetry was applied to an investigation of the early hydration of Portland cement (PC)–calcium aluminate cement (CAC)
pastes. The heat evolution measurements were related to the strength tests on small cylindrical samples and standard mortar
bars. Different heat-evolution profiles were observed, depending on the calcium aluminate cement/Portland cement ratio. The
significant modification of Portland cement heat evolution profile within a few hours after mixing with water was observed
generally in pastes containing up to 25% CAC. On the other hand the CAC hydration acceleration effect was also obtained with
the 10% and 20% addition of Portland cement. As one could expect the compressive and flexural strength development was more
or less changed—reduced in the presence of larger amount of the second component in the mixture, presumably because of the
internal cracks generated by expansive calcium sulfoaluminate formation. 相似文献
16.
M. R. Barati 《Journal of Sol-Gel Science and Technology》2009,52(2):171-178
Nanocrystalline Mg–Cu–Zn ferrite powders were successfully synthesized through nitrate–citrate gel auto-combustion method.
Characterization of the nitrate–citrate gel, as-burnt powder and calcined powders at different calcination conditions were
investigated by using XRD, DTA/TG, IR spectra, EDX, VSM, SEM and TEM techniques. IR spectra and DTA/TGA studies revealed that
the combustion process is an oxidation–reduction reaction in which the NO3
− ion is oxidant and the carboxyl group is reductant. The results of XRD show that the decomposition of the gel indicated a
gradual transition from an amorphous material to a crystalline phase. In addition, increasing the calcination temperature
resulted in increasing the crystallite size of Mg–Cu–Zn ferrite powders. VSM measurement also indicated that the maximum saturation
magnetization (64.1 emu/g) appears for sample calcined at 800 °C while there is not much further increase in M
s at higher calcination temperature. The value of coercivity field (H
c) presents a maximum value of 182.7 Oe at calcination temperature 700 °C. TEM micrograph of the sample calcined at 800 °C
showed spherical nanocrystalline ferrite powders with mean size of 36 nm. The toroidal sample sintered at 900 °C for 4 h presents
the initial permeability (μ
i) of 405 at 1 MHz and electrical resistivity (ρ) of 1.02 × 108 Ω cm. 相似文献
17.
Mauricio H. Cornejo Jan Elsen Cecilia Paredes Haci Baykara 《Journal of Thermal Analysis and Calorimetry》2014,115(1):309-321
Two Ecuadorian zeolite-rich tuffs, coded as Zeo1 (Mordenite) and Zeo2 (Clinoptilolite–Heulandite–Mordenite), were treated and used as supplementary cementitious materials (SCM) so as to study the effect of the thermal and mechanical treatments on pozzolanic reaction in mortars. The treatment was carried out by means of thermomechanical process according to a central composite-blocked cube-star experimental design. In this experimental design as independent factors the milling time (48, 60, 90, 120 and 132 min) and the heating temperatures (559, 600, 700, 800 and 841 °C) were used but keeping a constant heating time (5 h), and zeolite-rich tuffs as experimental blocks. The proportion of SCM was kept constant i.e. 15 %. On the other hand, the compressive strength, fixed lime, normalized water in hydrates and mg Ca(OH)2 per mg Cement at 7, 28 and 45 days, as well as hydration products related to dehydration degree of the zeolitic tuffs (DOD) were used as dependent factors. In addition, Quantitative and High-temperature chamber XRD, TG-DSC, particle size distribution and SEM-EDS were also carried out. The most significant factor was calcination leading to increase in the compressive strength compared to control, but just up to 800 °C because of recrystallization. As a conclusion, a meaningful loss of crystal structure of zeolites was not observed; but instead, the treatment could only lead to removing the water in cages and voids, thus improving the reaction with Ca(OH)2, producing more hydrates. In addition, lime was not only fixed by pozzolanic reaction, but also by carbonation. 相似文献
18.
Monica Ari Kimberly J. Miller Bojan A. Marinkovic Paula M. Jardim Roberto de Avillez Fernando Rizzo Mary Anne White 《Journal of Sol-Gel Science and Technology》2011,58(1):121-125
Aluminum molybdate was successfully synthesized using a simplified PVA assisted sol–gel method resulting in highly crystalline,
monophasic (monoclinic P21/a) samples. These materials could readily be obtained at temperatures of 600 and 700 °C after calcining for as little as
15–20 min. Scanning electron microscopy and X-ray powder diffraction indicated that even the sample calcined at 600 °C for
20 min was free of impurities and composed of submicron sized particles (~300 nm). Transmission electron microscopy was used
to confirm the monophasic character and submicron dimensions of the as-prepared powders. In addition to producing high quality
samples, it was also observed that the metal to PVA ratio used during this simplified synthesis, could be used as a control
parameter for tailoring the particle sizes of the final product. 相似文献
19.
M. García de Lomas M. I. Sánchez de Rojas M. Frías 《Journal of Thermal Analysis and Calorimetry》2007,90(2):443-447
This work presents the relation between the pozzolanic activity, the hydration heat and the compressive strength developed by blended mortars containing 10 and 35% of a spent fluid catalytic cracking catalyst (FCC). The results show that, in comparison with 100% Portland cement mortar, a mortar with 10% FCC increases the hydration heat all over the period of testing. This hydration heat increasing is due to the pozzolanic effect, therefore the resulting compressive strength is higher than the reference mortar. Whereas, in a mortar with 35% of FCC, the hydration heat is higher than 100% PC mortar, until 10 h of testing. After this age, the substitution degree predominates over the pozzolanic activity, showing in this case, lower hydration heat and developing lower compressive strength than 100% PC mortar. 相似文献
20.
M. V. Bukhtiyarova A. S. Ivanova G. S. Litvak L. M. Plyasova 《Kinetics and Catalysis》2009,50(6):824-829
Hexaaluminates synthesized by precipitation and calcined at 700–1400°C have been characterized by atomic absorption spectroscopy, thermal analysis, X-ray powder diffraction, and adsorption methods. The heat treatment of the Mn-substituted and unsubstituted materials at 1100 and 1200°C yields a hexaaluminate phase. The specific surface area of the samples calcined at 1100°C is 20–49 m2/g. The texture of the samples calcined at 1000°C is characterized by a unimodal mesoporous pore size distribution with a mean pore diameter of 290 Å. 相似文献