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1.
The properties of high-strength concrete under standard curing condition (20 °C, 95% RH), high-temperature curing condition (50 °C) and temperature match curing condition were comparatively investigated. The cumulative hydration heat of composite binder containing fly ash and silica fume is lower than that of composite binder containing the same amount of slag. Addition of fly ash and silica fume clearly reduces the adiabatic temperature rise of concrete, but adding slag leads to higher adiabatic temperature rise than Portland cement concrete. High-temperature curing condition and temperature match curing condition lead to the sustainable increase in compressive strength of concrete containing mineral admixture, but they hinder the later-age strength development of Portland cement concrete. For cement–slag paste and cement–fly ash–silica fume paste, the non-evaporable water contents increase significantly and the pore structures are much finer under high-temperature curing condition and temperature match curing condition, which negatively affect the pore structure of Portland cement paste. The differences in properties of concrete among three curing conditions become smaller with time. The properties obtained under standard curing condition can approximately reflect the long-term properties of high-strength concrete in the real structure. The concrete prepared with cement–fly ash–silica fume composite binder has the highest compressive strength, finest pore structure and best resistance to chloride permeability under any curing condition. This composite binder is very suitable to prepare the high-strength concrete with large volume. 相似文献
2.
The difference among the effects of high-temperature curing on the early hydration properties of the pure cement, the binder containing fly ash, the binder containing GGBS, and the binder containing steel slag was investigated by determining the compressive strength, non-evaporable water content, hydration heat, and Ca(OH) 2 content. Results show that the order of the influence degrees of high-temperature on the early hydration of different binders is the binder containing GGBS > the binder containing steel slag > the binder containing fly ash > the pure cement. In the case of short period of high-temperature curing (only 1 day), the strength growth rate of the concrete containing GGBS is the greatest. Though the influence of increasing high-temperature curing period on the hydration degree of the binder containing fly ash is not the most significant, the strength growth rate of the concrete containing fly ash is the most significant due to the excessive consumption of Ca(OH) 2 by reaction of fly ash. In the case of high-temperature curing, the Ca(OH) 2 content of the paste containing steel slag is much higher than those of the paste containing GGBS and the paste containing fly ash, so though high-temperature curing promotes the hydration of the binder containing steel slag significantly, its influence on the strength growth rate of the concrete containing steel slag is not so significant. 相似文献
3.
The hydration heat of pure cement, fly ash single-doped cement, as well as fly ash and fluorgypsum co-doped cement were investigated
by means of micro-calorimetry with an eight-channel micro-calorimeter. The results showed that the hydration heat and the
hydration rate could be reduced significantly by fly ash and fluorgypsum. However, the reduction was not proportional to the
loading of dopant. The exothermic peak of the co-doped cement was appeared earlier than that of the single-doped cement. As
the temperature decreased, the hydration heat and the hydration rate of both the doped cement were reduced, and the exothermic
peak appeared later. The effect of fly ash and fluorgypsum on the compressive strength of cement was also investigated. The
results revealed that the early compressive strength of concrete made up of the co-doped cement was largely higher than that
of the single-doped cement. Based on the experiment results obtained in this article, we could conclude that fluorgypsum is
a suitable additive for the single-doped cement. 相似文献
4.
There is a pre-curing period before the freshly made concrete elements were exposed to steam curing in the steam curing process. In this paper, the influence of pre-curing time on the hydration of binder and the properties of concrete under steam curing condition was investigated. Three binders were used: the pure cement, the binder containing high content of GGBS, and the binder containing high content of fly ash. Three pre-curing times (1, 3, and 6 h) and one steam curing period at 60 °C (over 8 h) were adopted. Results show that pre-curing time has limited influence on the hydration degree of binder, and compressive strength and pore structure of paste. The influence of pre-curing time has limited influence on the compressive strength and chloride permeability of the pure cement concrete and the concrete containing high content of GGBS at whether early or late ages, indicating that the proper pre-curing time can be as short as 1 h for these two concretes. Increasing pre-curing time enhances the late-age compressive strength of the concrete containing high content of fly ash significantly, but it has limited influence on the late-age permeability. 相似文献
5.
The influence of time on the mechanical behavior of concrete after exposure to elevated temperatures has been studied. Twenty-one self-compacting high-performance concrete mixtures with different incorporation amounts of coarse recycled concrete aggregate (RCA) and three unprocessed waste powder materials have been tested at age of 270 days for residual compressive and flexural strength after exposure to fire. The results have been compared to the results for the same concrete, which have been studied at age of 90 days. A new parameter has been introduced for comparing the responses of concrete to elevated temperatures at different ages; this parameter was the “heat resistance” which expresses the total area under the curve of the relative residual strength (compressive or flexural) after exposing to six temperature degrees (20, 150, 300, 500, 600, and 800 °C). The results showed that the age of concrete has an influence on the response of concrete to elevated temperatures. The heat resistance of compressive strength enhanced with age but the concrete behaved with a tendency different to that at the age of 90 days. The heat resistance of flexural strength has not been affected or slightly decreased but not with more than 10% to that at the age of 90 days. The used waste powder materials were unprocessed waste fly ash, waste cellular concrete powder and waste perlite powder; they proved that using any of them up to 15% as a replacement for cement with 0% or 25% of RCA enhanced the concrete resistance for the fire with time. The main two reasons for changing of residual strength with the time were the changing of water content and the proceeding of hydration of the binder. In general, long ages testing properties of concrete simulate the real behavior of concrete structures accurately. 相似文献
6.
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
7.
This study reports the microstructure characteristic and compressive strength of multi-blended cement under different curing methods. Fly ash, ground bottom ash, and undensified silica fume were used to replace part of cement at 50 % by mass. Mortar and paste specimens were cured in air at ambient temperature, water at 25, 40, and 60 °C and sealed with plastic sheeting for 28 days. In addition, these specimens were cured in an autoclave for 6, 9, and 12 h. Results indicated that the compressive strength of multi-blended mixes containing silica fume 10 % by mass cured with plastic sealed and cured in water at 25 and 40 °C was similar to or higher than the corresponding Portland cement control at 28 day. Moreover, the mixes containing silica fume 10 % by mass cured in water at 60 °C had higher compressive strength than Portland cement control. X-ray diffraction and thermogravimetry results confirmed that there was increased pozzolanic reaction with increasing silica fume content which relates to the increasing in strength. For autoclaved curing, the compressive strength of multi-blended cement specimens with silica fume (total of 50 % replacement) was noticeably higher than control Portland cement mix and was highest when autoclaving time was 9 h. X-ray diffraction results showed the pattern of 0.9, 1.1, and 1.4 nm tobermorite crystalline phases as the main product of this curing. Thermogravimetry results showed dehydration of 1.4 nm tobermorite and 1.1 nm tobermorite at about 80–90 and 135–150 °C, respectively. Tobermorite (also shown by scanning electron microscope) thereby as a result lead to significant compressive strength improvement in the short time of autoclaved curing. 相似文献
8.
The heat of hydration evolution of eight paste mixtures of various water to binder ratio and containing various pozzolanic
(silica fume, fly ash) and latent hydraulic (granulated blast furnace slag) admixtures have been studied by means of isothermal
calorimetry during the first 7 days of the hydration process and by means of solution calorimetry for up to 120 days. The
results of early heat of hydration values obtained by both methods are comparable in case of the samples without mineral admixtures;
the values obtained for samples containing fly ash and granulated blast furnace slag differ though. The results from isothermal
calorimetry show an acceleration of the hydration process by the presence of the fine particles of silica fume and retarding
action of other mineral admixtures and superplasticizer. The influence of the presence of mineral admixtures on higher heat
development (expressed as joules per gram of cement in mixture) becomes apparent after 20 h in case of fly ash without superplasticizer
and after 48 h for sample containing fly ash and superplasticizer. In case of samples containing slag and superplasticizer
the delay observed was 40 h. The results obtained by solution calorimetry provide a good complement to the ones of isothermal
calorimetry, as the solution calorimetry enables to study the contribution of the mineral admixtures to the hydration heat
development at later ages of the hydration process, which is otherwise hard to obtain by different methods. 相似文献
9.
以粉煤灰和蔗糖为原料,浓硫酸为炭化剂,制备了一种新型的C/粉煤灰复合吸附材料。 采用X光电子能谱、红外吸收光谱、场发射扫描电子显微镜、X射线衍射及N2气吸附实验对所制备复合材料进行了表征。 结果表明,粉煤灰表面被类石墨态炭纳米颗粒所包裹,复合材料表面密集分布着大量的介孔,Brunauer-Emmett-Teller(BET)比表面积SBET=5.4 m2/g,并且在该复合材料表面含有丰富的-SO3H、-COOH和-OH等含氧官能团。 考察了所制备的复合材料对典型阳离子型染料亚甲基蓝及重金属离子的吸附能力,结果表明,该复合材料具有优异的吸附性能,其对亚甲基蓝的吸附能力达到活性炭的83.7%,对典型重金属离子的吸附能力优于市售活性炭。 所制备复合材料可作为活性炭的一种替代品,用于水中有机染料和重金属离子的吸附处理。 相似文献
10.
G-Oil Well cement was modified by blending it with blast furnace slag and silica fume at various ratios. The hydration was carried out under the hydrothermal conditions (200 °C and 1.2 MPa) up to 7 days. TG and DTG were performed on cured pastes to identify the hydrated products, their quantity and their stability under given hydrothermal curing conditions. The microstructure of samples was observed by a scanning electron microscope. The mechanical compressive strength was determined and the pore structure was analyzed using mercury intrusion porosimeter. It was found out that the compressive strength values of blend G-Oil Well cements markedly increased with increasing blast furnace/silica ratio. The pore structure was consolidated, as demonstrated by the displacement of pore size distribution to the region of micro and nano pores. 相似文献
11.
The hydration properties of the binder containing low quality fly ash or limestone powder were compared in this study. Isothermal calorimetry was performed to measure the hydration heat of the binders during the first 3 days. Mercury intrusion porosimetry, scanning electron microscope, and thermogravimetry–differential thermal analysis were all used to determine the pore structure and hydration products of paste. The compressive strength of the pastes of age 3, 7, 28, and 90 days was also tested. The results indicate that the ground low quality fly ash can improve the mechanical properties of composite cementitious material and ameliorate the hydration properties and microstructure compared with the inert admixture limestone powder. The chemical activity of low quality fly ash presents gradually and appears high pozzolanic effect at later period, and it can accelerate the generation of hydration products containing more chemically bonded water. This leads to the higher rate of strength growth and cement hydration degree, the more compact microstructure and reasonable pore size distribution. Additionally, low quality fly ash delays the induction period, but shortens the acceleration period, therefore there is no significant influence on the second exothermic peak occurrence time. 相似文献
12.
利用烧失量和酸溶法测定不同固体废物蒸压样品的结合水量和溶出差,研究固体废物蒸压样品中水化产物量、结晶度与其强度的关系。结果表明,粉煤灰、废玻璃、废混凝土蒸压样品的结晶度较低,钢渣蒸压样品的结晶度较高。蒸压样品的溶出差、结合水量和结晶度与水化产物种类有关。蒸压样品的结晶度可间接表达结晶良好的水化产物占总水化产物量的多少,并可用来确定不同蒸压制品的合理养护制度,指导蒸压制品的工艺优化。蒸压样品的结晶度存在合理范围。 相似文献
13.
The effect of calcium hydroxide (CH) on the properties of Portland–fly ash cement pastes, at up to high-volume fly ash mixes
has been investigated using normal consistency, setting time, compressive strength, thermal analysis and scanning electron
microscope. CH as an additive material (5 and 10 wt%), lignite fly ash (FA) up to 50 wt% was used to produce Portland cement
(PC)–FA–CH pastes at w/PC + FA ratio of 0.5. Water requirement for normal consistency was found to increase with increasing
CH content while a decrease in initial setting time was found. Furthermore, the compressive strengths of all FA mixes with
CH were found to be higher than the mixes without CH. Thermal analysis and scanning electron microscope were used to study
the hydration of PC–FA–CH system. The results showed that the first phase transition detected by thermal analyses was attributed
to ettringite, calcium silicate hydrate, gehlenite hydrate and was found to be higher in PC–FA–CH mixes than in pure Portland–FA
cement paste resulting in an increase in compressive strength. Moreover, the hydration phases were also found to increase
with increasing curing time. Overall, the results show that the additional of 5 wt% CH in Portland–FA mixes especially at
high-volume FA mixes was found to accelerate FA pozzolanic reaction at early ages (7 and 28 days), resulting to an increase
in compressive strength. 相似文献
14.
Microwave‐assisted, solvent‐free alkylation and acylation of 2‐mercaptobenzothiazole has been attempted using silica gel, alumina, and a new solid support, fly ash. Fly ash, a waste generated at thermal power stations, could be used as solid support just as efficiently as commercial supports. The additional features of methodology include a much faster reaction, easy workup, higher yields, higher purity of the products, and an ecofriendly approach. 相似文献
15.
The work aims to study the effect of polycarboxylate type of super plasticizer on the hydration of composite cements. In this
paper we have studied the hydration of 20 wt% fly ash (FA) blended Portland cement in the presence of 0.1 wt% super plasticizer
(SP). Water consistency, setting times, non-evaporable water contents, compressive strength, water percolation, and air content
measurements were carried out. In addition, X-ray diffraction studies were carried out to understand the hydration process.
The results indicated the increase in compressive strength of the FA blended Portland cement in the presence of SP and with
the increase of the hydration time. 相似文献
16.
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
17.
The calorimetric data of binders containing
pure Portland cement, 20% fly ash, 20% slag and 10% silica fume respectively
are determined at different initial casting temperatures using an adiabatic
calorimeter to measure the adiabatic temperature rising of concrete. The calorimetric
data of binders with different dosages of fly ash at two water binder ratios
( w/ b)
are determined, too. Elevation of initial casting temperature decreases the
heat evolution of binder, enhances the heat evolution rate of binder and increases
the heat evolution rate of binder at early age. The dosage of fly ash in concrete
has different effects on the heat evolution of binder with different w/ b. At high w/ b ratio the
heat evolution of binder decreases when dosage of fly ash increases. At low w/ b ratio the
heat evolution of binders increases when dosage of fly ash increases from
0 to 40% of total binder quantity. The heat evolution of binder decreases
after the dosage of fly ash over 40%. An appropriate dosage of fly ash in
binder benefits the performance of concrete at low w/ b ratio. 相似文献
18.
采用晶种静电吸附-诱导转化技术,成功地将选自工业废弃物粉煤灰的空心微 球转化为具有沸石/莫来石双层复合球壳结构的空心球,用XRD和SEM等手段对产物 进行了表征,并对球壳的转化机理进行了讨论。 相似文献
19.
The study of γ‐neutrons attenuation and mechanical characteristics of modified concrete are vital and crucial parameters for the construction of civilian radiological, nuclear shielding, and/or shelters. In this work, fifteen samples of ordinary concretes with five different additives; steel fibers, polypropylene, silica fume, and fly ash, with variation of cement percentages, were prepared and used for performing the mechanical and radiation attenuation investigations. The compressive strength, tensile strength, slump test, bulk density, and water permeability were also carried out for the prepared concrete mixes. Collimated coherent beams from 60Co and Pu‐Be fast neutron sources were used to check the radiation penetrability through the syntheized mixed concrete‐additives. Very sensitive and well calibrated gamma‐neutron pulse shape discriminating spectrometer with its electronic componenets and stilbene organic detector and 3′′ × 3′′ NaI scintillation crystal was used to measure the radiation before and after attenuation and transmission. The integrated fast neutron removal macroscopic cross section ( Σr) and linear attenuation coefficient of total gamma rays ( μ) were calculated for all the analysed concrete mixes. The results of measurements, tests, analyses and calculations are given and explained. The investigated modified concrete mixes show good workability and properties from the view point of mechanical loads and γ‐fast neutrons penetrability and resistance. These results can be used for shielding and sheltering design. 相似文献
20.
以三个正在运行的垃圾发电厂的除尘器飞灰为研究对象,实验测出它们的化学组成、热灼减率、灰熔点等物化特性和浸出毒性、腐蚀性等有害特性,对三种灰样的特性进行了对比、分析。结果表明,飞灰的物化特性主要受飞灰中MgO、CaO、SiO2和CaCl2等几种主要成分质量分数的影响。MgO和Al2O3质量分数较高而CaCl2质量分数较低的飞灰其灰熔点相对较高;CaO和CaCl2质量分数较高的飞灰其水分和热灼减率也相对较高;SiO2质量分数较高的飞灰其重金属的浸出率相对较低;CaO和Al2O3等碱性氧化物质量分数较高的飞灰其浸出液的pH值相对较高。 相似文献
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