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1.
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 (C 3ASH 4 and C 2ASH 8) 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.
This research provides a fundamental understanding of the early stage hydration of Portland cement paste, tricalcium aluminate
(C 3A) paste at water to cement ratio of 0.5 and C 3A suspension at water to cement ratio of 5.0 modified by 2 or 4 mass% of sodium carbonate. A high conversion of unreacted
clinker minerals to gel-like hydration products in the cement-Na 2CO 3 pastes takes place rapidly between 1 st to 24 th h. Contrary the Ca(OH) 2 formation within the same time interval is retarded in the excess of CO 32− ions due to intensive rise and growth of CaCO 3 crystals in hydrated cement. Later, the conversion of clinker minerals to the hydrate phase is reduced and higher contents
of calcite and vaterite relative to that of Ca(OH) 2 in comparison with those found in the Portland cement paste are observed. As a consequence a decrease in strength and an
increase in porosity between hardened Portland cement paste without sodium carbonate and those modified by Na 2CO 3 are observed. C 3A hydrates very quickly with sodium carbonate between 1 st and 24 th h forming hydration products rich in bound water and characterized also by complex salts of ( x)C 3A·( y)CO 2·( zH 2O type, whereas C 3A-H 2O system offers C 3AH 6 as the main hydration product. Higher content of the formed calcium aluminate hydrates in C 3A-Na 2CO 3-H 2O system also contributes to early strength increase of Portland cement paste. 相似文献
3.
The hydration of the binder, consisting of calcium aluminate cement (CAC) with Al 2O 3 >70% and with or without the additives of the FCC catalyst waste and polycarboxylate deflocculant Castament FS-20, is investigated. The methods of calorimetry, thermal analysis, XRD, electrical conductivity, SEM, as well as ultrasonic wave velocity measuring and bending strength evaluation are used. The results of the investigation show that the FCC catalyst as well as polycarboxylate deflocculant, are active additives, influencing the CAC binder??s hydration process. In the structure of the hardened binders, certain amounts of unhydrated CAC minerals, CA, and CA 2, and the hydration products, such as CAH 10, C 2AH 8 and the amorphous AH 3, are found. However, in the binder with a deflocculant, there are smaller amounts of CAH 10 and the amorphous AH 3, though the amount of C 2AH 8 is higher than that in the binder without a deflocculant additive. It has been found that in the case, when the FCC catalyst and deflocculant are simultaneously used, the FCC catalyst produces a positive effect on the formation of the CAC binder??s structure, increasing its mechanical strength. The results obtained in this article allow to predict that the FCC catalyst and deflocculant simultaneously used as the additives to the CAC binder, will enable to control the hydration process of the binder. 相似文献
4.
Differential scanning calorimeter (DSC) has been used to study the dehydration characteristics of hydrated calcium aluminates such as CA, CA 2 and C 12A 7 where C and A stand for CaO and Al 2O 3 respectively. Dehydration of CAH 10 and C 2AH 8 (where H=H 2O) occur at 160–180°C and 200–280°C respectively. These two phases are unstable and ultimately get transformed to AH 3 and C 3AH 6. Dehydration of AH 3 and C 3AH 6 occur between 290 and 350°C and overlap at lower scanning rate. The activation energy for dehydration of the stable AH 3 and C 2AH 6 phases has been found to be 107.16 and 35.58 kJ mol –1 respectively. The compressive strength of the hydrated calcium aluminates has been determined. The result shows that in the case of CA, almost 90% of ultimate strength has been attained in 1 day whereas in CA 2, ultimate strength has been attained in 14 days and in C 12A 7 in 1 day. DSC results have been correlated with the rate of strength developments. 相似文献
5.
This paper aims to evaluate the influence of three kinds of sulfates from the green production of cement on its sintering and hydration. The properties of clinker and hydration were monitored by thermogravimetric and differential thermal analysis (TG–DTA), X-ray diffraction, X-ray fluorescence and isothermal conduction calorimeter. Results indicate that gypsum lowers the decomposition temperature of CaCO3 and all these Sulfates will enhance the solid-phase reaction but increase melting temperature. Sulfates reduce the content of C3S, but K2SO4 and 2CaSO4·K2SO4 is conducive to the formation of β-C2S. The hydration induction period is shortened by the sulfates. K2SO4 and 2CaSO4·K2SO4 improve the early hydration of clinker, but gypsum may lightly reduce the hydration reactivity of clinker in acceleration period. 2CaSO4·K2SO and K2SO can significantly accelerate the compressive strength development of cement clinker before 3 d; by contrast, gypsum is detrimental for that. The precipitation of hydration products (CH and C–S–H) in clinker with sulfates is more than that of clinker without sulfates at 9 h. K2SO4 can accelerate the hydration of clinker without forming ettringite. 相似文献
6.
The hydration products of 2.5, 5 and 10% Cl − containing metakaolin (MK)-lime pastes are compared with the same obtained from MK-lime paste to understand the chloride binding behaviour of MK during the hydration of cement. Results indicate that 2.5% Cl − addition into the MK-lime paste initially enhances the formation of Friedel's salt (Ca 2Al(OH) 6Cl·2H 2O), but Friedel's salt decomposes at later stages due to the formation of stratlingite (C 2ASH 8). In 5 and 10% chloride containing pastes, Friedel's salt is observed throughout the reaction periods along with the high amount of CSH. Small amount of stratlingite is also formed on or after 60 day hydration of 5% Cl − containing MK-lime pastes. On the other hand, MK-lime-10% Cl − containing pastes show the complete absence of stratlingite and C 4AH 13 through out the hydration period, which are the major hydration products of MK-lime paste. Mesuarements of pH of the simulated pore fliuds help to understand the decomposition behaviour of Friedel's salt. From the experimental results, chloride binding mechanism of MK-lime paste is also discussed. 相似文献
7.
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 SO 3 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 C 3A content. 相似文献
8.
The effect of spent FCC catalyst on early hydration (up to 48?h) of high aluminate cement (Al 2O 3 >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 C 2AH 8 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
9.
Simultaneous thermal analysis (DTA and TG) was applied to two fiber-reinforced cement composites cured in autoclave at 0.3, 1.2, and 2.0 MPa for 24, 72, and 168 h. Mercury intrusion porosimeter (MIP) and scanning electronic microscope (SEM) were used to complete the investigations. Thermal analysis was used to identify temperature ranges of thermal decomposition of cured samples and to characterize the nature of hydrate products. Also, fractured surface and surface microstructure were investigated by means of SEM. Based on the results of thermal analysis, three processes occurred during hydrothermal curing. The first one consists of primary hydration reaction leading to the formation of C–S–H, C 3AH 6, and AH 3. The second one is the process characterized by partial decomposition or interaction of primary products to form secondary products (C 2ASH 8, C 3AH 1.5). The last one is the carbonation of some hydrate products. Hydrothermal pressure can enhance the compressive strength, but can also cause its depletion over time. The MIP study has revealed an existence of bimodal pore size distribution that the characteristic depends on the hydrothermal curing conditions. 相似文献
10.
Journal of Thermal Analysis and Calorimetry - Generally, the early strength of hardened Portland cement paste is controlled, by changing the mineral composition of clinker and grinding fineness. By... 相似文献
11.
In the paper, the results of investigation concerning the influence of 0.3% addition of hydroxypropyl methylcellulose (MC) of 40 and 70 Pa s viscosity on the hydration process of main clinker phases C 3S and C 3A are presented. The course of hydration is documented using microcalorimetry, and formed phases were identified by XRD. The research indicated that methylcellulose inhibited the hydration process of clinker phases, analysed both, separately and in their mixture. Moreover, it was found that the presence of MC admixture also led to the reduction in calcium sulphate dihydrate reactivity in the system. 相似文献
12.
Electric arc furnace dust (EAFD) is termed as a hazardous waste due to its contamination with heavy metals. Inertization of such very fine dust can be occurred via stabilization and solidification process within the hydrated Portland cement matrix. In this paper, the effect of the addition of various ratios of EAFD on the properties of the hardened Portland cement paste was investigated. Compressive strength, chemically combine water and free lime contents were determined. In addition, phase composition using XRD; DTA analysis; as well as microstructure of the formed hydrates for some selected samples were investigated using SEM. The obtained results showed that the paste containing 1/mass% EAFD give the highest compressive strength values at most hydration ages, specially the later ages, compared to the neat Portland cement blank paste. Whileas, the pastes containing 3 and 5/mass% EAFD showed lower values of compressive strength compared to those of the blank paste. 相似文献
13.
In order
to evaluate the pozzolanic activity of metakaolin, several pastes were prepared,
by mixing metakaolin with hydrated lime, in different ratios. The pastes were
stored in standard conditions ( RH=99±1%, T=25±1°C) and evaluated using thermal
analysis (DTA/TG), X-ray diffraction (XRD), compressive strength tests and
mercury intrusion porosimetry (MIP), in time. The obtained results revealed
that the compounds formed are CSH, C 2ASH 8
and C 4
11
while C 4AH 13 was not detected
up to 270 days of curing. The calcium hydroxide consumption increases as the
initial amount of the metakaolin in the paste augments. The maximum strength
development is obtained for metakaolin/lime ratio:1. 相似文献
14.
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 C 2S. 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
15.
The hydration properties of slag sulfate cement (SSC), slag Portland cement (PSC), and ordinary Portland cement (POC) were compared in this study by determining the compressive strength of pastes, the hydration heat of binders within 72 h, the pore structure, the hydration products, and the hydration degree. The results indicated that main hydration products of PSC paste and POC paste are calcium hydroxide and C–S–H gel, while those of SSC paste are ettringite and C–S–H gel from the analyses of XRD, TG–DTA, and SEM. At the early curing age, the compressive strength depends on the clinker content in the cementitious system, while at the late curing age, which is related to the potential reactivity of slag. From hydration heat analysis, the cumulative hydration heat of PSC is lower than that of POC, but higher than that of SSC. Slag can limit chemical reaction and the delayed coagulation of gypsum, which also plays a role in the early hydration. So SSC shows the lowest heat release and slag can’t be simulated without a suitable alkaline solution. Based on MIP analysis, the porosity of POC paste is the smallest while the average pore size is the biggest. At the age of 90 days, the compressive strength of SSC can get higher development because of its relative smaller pore size than that of PSC and POC paste. 相似文献
16.
This paper studies the addition (0–40% w/w) of natural zeolite (NZ, 84% clinoptilolite) in blended cements made with Portland cement (PC) with low and medium C 3A content. The isothermal calorimetry was used to understand the effect of NZ on the early cement hydration. For low C 3A cement, the addition of NZ produces mainly a dilution effect and then the heat released curve is similar to plain cement with lower intensity. For medium C 3A cement, the curve shows the C 3S peak in advance and a high intensity of third peak attributed to C 3A hydration. The high cation fixed of NZ reduces the ions concentration (especially alkalis) in the mixing water stimulating the PC hydration. The flowability decreases when the NZ replacement level increases. Results of Fratini’s test show that NZ with both PCs used presents slow pozzolanic activity. At early age, XRD and FTIR analyses confirm that hydration products are the same as that of the corresponding PC and the CH is progressively reduced after 28 days and some AFm phases (hemi- and monocarboaluminate) appear depending on the NZ percentage and the PC used. For low replacement levels, the compressive strength is higher than the corresponding PC from 2 to 28 days. For high replacement levels, the early compressive strength is lower than that of corresponding plain PC and the pozzolanic reaction improves the later compressive strength of blended cements. 相似文献
17.
In this investigation the effect of addition of magnetite nanoparticles on the hydration characteristics of both ordinary Portland cement (OPC) and high slag cement (HSC) pastes was studied. The cement pastes were prepared using a water/solid (W/S) mass ratio of 0.3 with addition of 0.05, 0.1, and 0.3 % of magnetic fluid Fe 3O 4 nanoparticles by mass of cement. An aqueous stable magnetic fluid containing Fe 3O 4 nanoparticles, with a mean diameter in the range of super-paramagnetism, was prepared via co-precipitation method from ferrous and ferric solutions. The admixed magnetite-cement pastes were examined for compressive strength, chemically combined water content, X-ray diffraction analysis, and differential scanning calorimetry. The results of compressive strength revealed that the hardened pastes made from OPC and HSC admixed with different amounts of magnetic fluid have higher compressive strength values than those of the neat cement OPC and HSC cement pastes at almost all ages of hydration. The results of chemically combined water content for the admixed cement pastes showed almost the same general trend and nearly comparable values as those of the neat cement pastes. From the XRD diffractograms obtained for the neat OPC and HSC cement pastes, the main hydration products identified are calcium silicate hydrates, portlandite, and calcium sulfoaluminate hydrates. Addition of magnetic fluid nanoparticles to both of OPC and HSC did not affect the main hydration products of the neat OPC or HSC cement in addition to one main basic difference, namely, the formation of calcium iron hydroxide silicate as a new hydration product with a reasonable hydraulic character. 相似文献
18.
The hydration and hardening processes of Portland cements prepared from clinkers mineralized with sodium fluoride and/or oxides
(SnO 2 or CuO) was studied. Type I cements (CEM I) were prepared by grinding with gypsum (5%) of clinkers obtained by the burning
of an industrial raw mix with different mineralizers: sodium fluoride, oxides (CuO and SnO 2) or mixtures of sodium fluoride and oxide (NaF + CuO or NaF + SnO 2). The influence of foreign ions on the clinker morphology was assessed by scanning electronic microscopy (SEM) and energy
dispersive X-ray spectrometry (EDX). The hydration processes of modified cements were examined by X-ray diffraction analysis
(XRD) and thermal analysis techniques (TG and DTA). The main properties of the cements, i.e., flexural and compressive strengths,
setting time, and soundness were also determined. A good correlation between the chemically bound water or portlandite content
in pastes hydrated 2–28 days and compressive strength developed by mortars was observed. The influence of mineralizers on
the kinetic of hydration processes and main properties of cements is different—0.5% NaF and 0.5% SnO 2 and their mixture increase the rate of cement hydration and hardening processes, opposite to 0.5% CuO that reduce the rate. 相似文献
19.
Molasses is generally used as a grinding aid in cement and as a water reducer and retarder in concrete. In China, the output primarily consists of sugarcane molasses. In this paper, the effects of sugarcane molasses on the physical performance and hydration chemistry of conventional Portland cement were investigated. The setting times, the normal consistency of cement pastes, the compressive strengths and fluidities of the mortars were respectively determined according to Chinese Standard GB/T 1346, GB/T17671 and GB/T 2419. The effect of molasses on the hydration kinetics of cement was investigated using a calorimeter. The hydration products and pore size distribution of the cement pastes were analysed by X-ray powder diffraction, differential scanning calorimetry and a mercury injection apparatus. The results show that a small amount of sugarcane molasses retards the setting and hardening of cement paste and increases the fluidity of cement mortar, while excess molasses accelerates the setting and hardening. Molasses improves significantly the compressive strength at 3d due to the decrease of porosity. The addition of 1.0 % molasses accelerates the formation of ettringite, prevents the second hydration of aluminate phase and delays the hydration of C 3S. 相似文献
20.
In this research, the influences of nano-limestone (NC) on tricalcium silicate (C 3S) hydration, including early hydration rate, setting time, Ca(OH) 2 content, quantification of C–S–H, micrographs of hydration products and compressive strength, were investigated by different methods. Calorimetry results show that the first and second exothermic peak of C 3S with 1 mass% NC is ~29 and ~5% higher than that of control sample and the second peak appears 32 min in advance. Besides, the total hydration heat of C 3S with 1 mass% NC increases by 10.08% compared to control sample at 72 h. The initial and final setting time of C 3S with 1 mass% NC shortens by 23 and 17 min, respectively. In addition, thermal analysis results show that adding NC leads to higher Ca(OH) 2 and C–S–H content at all ages (1, 3 and 28 days). All of the above results imply that the hydration progress of C 3S is accelerated by NC. Correspondingly, the compressive strength of C 3S with 1 mass% NC increases by 9.88% at 28 days. Besides, EDS results reveal that the Ca/Si ratio of C–S–H gel decreases after NC modification. However, excessive content NC (4 mass%) reduces the acceleration effect of NC on C 3S hydration and finally leads to relative low content of Ca(OH) 2 and C–S–H compared with C 3S sample containing 1 mass% NC. 相似文献
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