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1.
Thermogravimetric (TG) analysis was applied to the characterisation of the pozzolanic reaction in mortars containing the supplementary
cementitious materials (SCMs) pitchstone fines (PF) and fly ash (FA) as partial replacements for Portland cement (PC). TG
analysis was used to determine the proportion of calcium hydroxide (CH) present from the hydration of the PC based on the
dehydroxylation of the CH present in the blended PC-SCM mortars. The consumption of CH indicated that both SCMs underwent
the pozzolanic reaction and that PF was found to compare favourably in its pozzolanic reactivity of FA, the industry and globally
accepted standard artificial pozzolan. 相似文献
2.
Present study deals with the influence of metakaolin (MK), silica fume (SF) and ground granulated blast-furnace slag (BFS) on middle hydration of ordinary Portland cement replaced by 45 mass% of particular supplementary cementitious materials (SCMs). Acceleration of cement hydration by SF and MK was proved up to the first 12 h by isothermal calorimetry as well as by thermogravimetric analyses. From the beginning of deceleratory period, when SCMs stopped to act as accelerators, more evident influence of the dilution effect was observed. Nevertheless, the presence of pozzolanic reactions was demonstrated already after 15 h of curing and even when SF and MK were used in the amount equal to 5 mass%. Synergic effect of the used SCMs allowed to increase the quantity of BFS up to 35 mass% without significant changes in their positive action. 相似文献
3.
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 Al 2O 3 and SiO 2 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
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 C 3S 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.
The rate of heat evolution as well as total heat output are strongly affected by other components of hydrating mixture, apart
from neat portland cement, such as slag, fly ash and other industrial by-products; among them the wastes from fluidised bed
combustion (FBC) has been taken into account recently. In this study the calorimeter was applied to follow the early hydration
of cements produced with these materials. They interact with cement paste in a few ways: as set controlling agent and as active
pozzolanic admixtures. Thus the rate of heat evolution/hydration is modified, depending on the composition of clinker and
percentage of waste in the mixture. After the series of measurements for clinker-waste mixture hydrated systems also some
‘model’ mixtures were investigated to separate the effects from particular waste components.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
To use flue gas desulfurization (FGD) gypsum and limestone as supplement of cement, conduction calorimetry was applied to
investigate the early hydration of ternary binder of calcium aluminate cement (CAC), Portland-limestone cement (PLC), and
FGD gypsum, supplemented with the determination of setting times and X-ray diffraction (XRD) analysis. Different exothermal
profiles were presented in two groups of pastes, in which one group (group A) sets the mass ratio of FGD gypsum/CAC at 0.25
and the other group (group B) sets the mass ratio of PLC/CAC at 0.25. Besides the two common exothermal peaks in cement hydration,
a third exothermal peak appears in the pastes with 5–15% FGD gypsum after gypsum is depleted. It is found that not PLC but
FGD gypsum plays the key role in such ternary binder where the reaction of ettringite formation dominates the hydration process.
PLC accelerates the hydration of ternary binder, which mainly attributes to the nucleating effect of fine limestone particles
and PC clinker. The modified hydration process and mechanism in this case is well visualized by the means of calorimetry and
it helps us to optimize such design of ternary cementitious material. 相似文献
7.
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
8.
The catalyst
used in fluidized catalytic cracking (FCC) units of refineries after several
recovery cycles in regeneration units, reduces its activity and it is partially
substituted by new catalyst in the process. As it has a high silicon and aluminum
oxides content, the pozzolanic properties of a Brazilian FCC spent residual
catalyst, used in different substitution degrees to cement, were evaluated
by three thermal analysis techniques during the early stages of hydration
of a type II Portland cement. NCDTA curves show in real time that the residual
catalyst, accelerates the stages of cement hydration. TG and DSC curves of
respective pastes after 24 h of hydration evidence the pozzolanic activity
of the waste, respectively, by the lower water mass loss during the dehydroxylation
of the residual calcium hydroxide and by the lower dehydroxylation endothermal
effect. Within the analyzed period, the higher is the cement substitution
degree, the higher is the pozzolanic activity of the residual catalyst. 相似文献
9.
Prediction and control of concrete temperature rise due to cement hydration is of great significance for mass concrete structures since large temperature gradients between the surface and the core of the structure can lead to cracking thus reducing durability of the structure. Cement replacement with supplementary cementitious materials (SCMs) is frequently used to reduce the concrete temperature rise. Several models have been proposed for predicting heat release of blended cements; however, none of them address incorporation of metakaolin into the mixture. Isothermal calorimetry measurements, based on statistical experimental design, were taken on pastes incorporating combinations of SCMs and chemical admixtures. The data were then used to develop equations to predict the total heat reduction with the incorporation of chemical admixtures and SCMs. Analysis of the calorimetry data indicated that chemical admixtures do not have a significant effect on heat evolution beyond 12 h. SCMs investigated in this study (fly ash, slag, silica fume and metakaolin), on the other hand, were found to have a significant effect at hydration ages of 12, 24, 48 and 72 h. 相似文献
10.
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
11.
To improve the properties of steel slag blended cements, a chemical activator was added into blended cements, the mechanical properties and durability of steel slag blended cements were investigated. The results show that steel slag in blended cement pastes presents low hydraulic activity and makes practically no contribution to strength development. After the addition of chemical activator, the mechanical properties and durability of ternary blended cements are increased significantly. The hydration process and micro-structural development of blended cement was investigated by isothermal calorimeter and scanning electric microscope, respectively. Steel slag started hydration in the first 3?days in the presence of chemical activator, steel slag and granulate blast furnace slag reacted with Ca(OH) 2 to form a dense microstructure as curing proceeded. Therefore, both early and late compressive strengths of steel slag blended cement with 35% cement clinker and 30% steel slag can be comparable with those of Portland cement. 相似文献
12.
In this work, the hydration rate and products of blended zeolite cements were studied for periods up to 360 days. Thermoanalytical
methods (TG/DTG and DTA) were applied in order to evaluate the hydration rate of blended cements, while. X-ray diffraction
and FTIR spectroscopy were used in order to identify the hydrated products. As it is concluded the incorporation of zeolite
in cement contributes to the consumption of Ca(OH) 2 formed during the cement hydration and the formation of cement-like hydrated products. The pozzolanic reaction of the zeolite
is rather slow during the first days of hydration but it is accelerated after the 28 days. 相似文献
13.
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
14.
Calorimetry has been used in the investigations of cementitious systems with different set controlling admixtures. The kinetics
and mechanism of hydration process was thus characterized on two different cement clinkers mixed with calcium sulphate containing
materials. These admixtures were collected as a residue in the fluidised bed combustion (FBC) of coals with simultaneous desulphurisation
process - so-called bottom ash. Apart from anhydrite/gypsum, they were composed mainly of alumina and silica containing material
of disordered structure, originating from the coal contaminations of clay character. Anhydrite/gypsum acts as set controlling
admixture. The aluminosilicate component reacts with calcium ions released to the solution from the calcium silicate clinker
minerals.
It has been found that fluidised bed combustion wastes can be successfully used as set controlling admixture. There is no
other harmful effects; those could be easily detectable by calorimetry. However the effect is dependent upon the composition
of cement clinker. At low calcium aluminate content a slight acceleration of hydration process can be easily observed, particularly
at higher amount of admixture. In the mixtures with high calcium aluminate clinker the heat evolved is slightly reduced in
the presence of admixture. The dominating role of aluminate phase in heat evolution process within the first hours of hydration
process has been thus proved.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
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
16.
The present study is based on the influence of the addition of a pozzolanic material as a result of the activation of an industrial
waste coming from the Spanish paper industry on the heating as well as hydration heat of the cement mortars made with 10 or
20% of active addition.
Once the sludge has been calcined at different temperatures (700–800°C) and stays in furnace (2 and 5 h), the calcined products
showed high pozzolanic activity. The maximum activity corresponded to the paper sludge calcined at 700°C for 2 h (S1). Besides,
it can be proved that there was an increase both of the heating and also of the hydration heat in the first 23–25 h for both
additions (10 and 20% of S1) regarding the reference cement mortar. This behaviour would be related to the influence of different
effects: filler and pozzolanic during the first hours of reaction, and by the dilution effect for longer hydration times,
mainly when 20% of S1 was added. 相似文献
17.
Journal of Thermal Analysis and Calorimetry - Two Portland cement (PC) replacement levels (35, 45 mass%) and three locally available supplementary cementitious materials (SCMs; metakaolin... 相似文献
18.
The effect of nano-metakaolin (NMK) addition on hydration characteristics of fly ash (FA) blended cement mortar was experimentally investigated. The amorphous or glassy silica, which is the major component of a pozzolan, reacts with the calcium hydroxide liberated during calcium silicate hydration. It is believable to add FA and NMK particles in order to make high performance concrete. The physico-mechanical properties of FA blended cement mortars made with different percentages of NMK were investigated. The experimental results showed that the compressive and flexural strengths of mortars containing NMK are higher than those of FA blended cement mortar at 60 days of hydration age. It is demonstrated that the nanoparticles enhances strength than FA. In addition, the hydration process was monitored using scanning electron microscopy and thermal gravimetric analysis (TG). The results of these examinations indicate that NMK behaves not only as a filler to improve microstructure, but also as an activator to promote the pozzolanic reaction. 相似文献
19.
Isothermal calorimetry and chemical shrinkage measurements are two independent techniques used to study the development of
hydration in cementitious systems. In this study, calorimetry and chemical shrinkage measurements were combined and simultaneously
performed on hydrating cement paste samples. Portland cement pastes with different water to cement ratios and a cement paste
containing calcium sulfoaluminate clinker and anhydrite were studied. The combined calorimetry/chemical shrinkage test showed
good reproducibility and revealed the different hydration behavior of sealed samples and open samples, i.e., samples exposed
to external water during hydration. Large differences between sealed and open samples were observed in a Portland cement paste
with low water to cement ratio and in the calcium sulfoaluminate paste; these effects are attributed to self-desiccation of
the sealed pastes. Once the setup is fully automatized, it is expected that combined calorimetry/chemical shrinkage measurements
can be routinely used for investigating cement hydration. 相似文献
20.
When cement hydrated compositions are analyzed by usual initial mass basis TG curves to calculate mass losses, the higher
is the amount of additive added or is the combined water content, the higher is the cement ‘dilution’ in the initial mass
of the sample. In such cases, smaller mass changes in the different mass loss steps are obtained, due to the actual smaller
content of cement in the initial mass compositions. To have a same mass basis of comparison, and to avoid erroneous results
of initial components content there from, thermal analysis data and curves have to be transformed on cement calcined basis,
i.e. on the basis of cement oxides mass present in the calcined samples or on the sample cement initial mass basis.
The paper shows and discusses the fundamentals of these bases of calculation, with examples on free and combined water analysis,
on calcium sulfate hydration during false cement set and on quantitative evaluation and comparison of pozzolanic materials
activity. 相似文献
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