Subject of this paper is to investigate the hydration process of Portland limestone cement containing 10-35% limestone. Cements,
produced by co-grinding of clinker, limestone and gypsum, were hydrated for periods 6 h to 28 d and were studied by means
of TG and XRD. The Ca(OH)2 content of the cements containing limestone is higher than in pure cements, specifically for 10% limestone content and ages
more than 1 day. These results are in accordance with the strength development of the studied cements. In earlier ages the
Ca(OH)2 content is slightly lower in the limestone cements and independent of the limestone content. After 1 day curing, the increase
of limestone addition causes a relative increase of the non evaporable water. The XRD patterns indicated the presence of carboaluminates
in the hydrated limestone cements.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
A new-design conduction microcalorimeter is described, which has been used to measure the heat of cement hydration evolved
in the initial period of hydration. The calorimeter is 30 cm3 in volume; the heat loss coefficient is 27.270±0.015 W V–1, the time constant is 300 s.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
Titanium dioxide (TiO2) is an excellent photocatalytic material that imparts biocidal, self-cleaning and smog-abating functionalities when added to cement-based materials. The presence of TiO2 influences the hydration process of cement and the development of its internal structure. In this article, the hydration process and development of a pore network of cement pastes containing different ratios of TiO2 were studied using two noninvasive techniques (ultrasonic and NMR). Ultrasonic results show that the addition of TiO2 enhances the mechanical properties of cement paste during early-age hydration, while an opposite behavior is observed at later hydration stages. Calorimetry and NMR spin–lattice relaxation time T1 results indicated an enhancement of the early hydration reaction. Two pore size distributions were identified to evolve separately from each other during hydration: small gel pores exhibiting short T1 values and large capillary pores with long T1 values. During early hydration times, TiO2 is shown to accelerate the formation of cement gel and reduce capillary porosity. At late hydration times, TiO2 appears to hamper hydration, presumably by hindering the transfer of water molecules to access unhydrated cement grains. The percolation thresholds were calculated from both NMR and ultrasonic data with a good agreement between both results. 相似文献
The physicochemical properties of spent fluidized bed cracking catalyst and its influence on hydration process of cement slurry
were studied. The samples were cement slurries prepared with water/solid=0.5 and additions of used catalyst amounted to 0,
5, 10, 15, 20 and 25%with resp. to the solid. After definite time they were subjected to thermogravimetric analysis (TG, DTG,
DTA) and, in order to determine the progress of reaction with water, the heat of hydration was measured by means of isotherm
calorimetry. The studies disclosed that the spent cracking catalyst is not merely an inactive filler in cement slurries, but
it modifies the course of the hydration process. The spent catalyst is a pozzolana additive and its presence leads to a decrease
of calcium hydroxide contents in the system. The spent catalyst affect on the heat of cement hydration. Small amounts additive
accelerate the process of binding.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
Summary: A new class of fibre reinforced commodity thermoplastics suited for injection moulding and direct processing applications has been developed using man-made cellulosic fibres (Rayon tire yarn, Tencel, Viscose, Carbacell) and thermoplastic commodity polymers, such as polypropylene (PP), polyethylene (PE), high impact polystyrene (HIPS), poly(lactic acid) (PLA), and a thermoplastic elastomer (TPE) as the matrix polymer. For compounding, a specially adapted double pultrusion technique has been employed which provides composites with homogeneously distributed fibres. Extensive investigations were performed with Rayon reinforced PP in view of applications in the automotive industry. The Rayon-PP composite is characterized by high strength and an excellent impact behaviour as compared with glass fibre reinforced PP, thus permitting applications in the field of engineering thermoplastics such as polycarbonate/acrylonitrile butadiene styrene blends (PC/ABS). With the PP based composites the influence of material parameters (e.g. fibre type and load, coupling agent) were studied and it has been demonstrated how to tailor the desired composite properties as modulus and heat distortion temperature (HDT) by varying the fibre type or adding inorganic fillers. Man-made cellulose fibers are also suitable for the reinforcement of further thermoplastic commodity polymers with appropriate processing temperatures. In case of PE modulus and strength are tripled compared to the neat resin while Charpy impact strength is increased five-fold. For HIPS mainly strength and stiffness are increased, while for TPE the property profile is changed completely. With Rayon reinforced PLA, a fully biogenic and biodegradable composite with excellent mechanical properties including highly improved impact strength is presented. 相似文献
This work analyzes the effect of the presence of 5 wt.% of solid sodium salts (Na2SO4, Na2CO3, and Na2SiO3) on calcium sulfoaluminate cement (CSA) hydration, addresses hydration kinetics; 2-, 28-, and 90-d mechanical strength, and reaction product microstructure (with X-ray diffraction (XRD), and Fourier transform infrared spectroscopy, (FTIR). The findings show that the anions affect primarily the reactions involved. Ettringite and AH3, are the majority hydration products, while monosulfates are absent in all of the samples. All three salts hasten CSA hydration and raise the amount of ettringite formed. Na2SO4 induces cracking in the ≥28-d pastes due to post-hardening gypsum and ettringite formation from the excess SO42– present. Anhydrite dissolves more rapidly in the presence of Na2CO3, prompting carbonation. Na2SiO3 raises compressive strength and exhibits strätlingite as one of its reaction products. 相似文献
Summary: Novel regenerated cellulose fibers have been successfully spun from the cellulose dope in NaOH/urea aqueous solution, which could rapidly dissolve cellulose. The fibers possess circular cross‐sections as well as relatively high molecular weight, and a crystallinity index with cellulose II family crystal structure, leading to good mechanical properties. This technology is simple, cheap, and environmentally friendly, promising to substitute for viscose rayon production having hazardous byproducts.
SEM micrograph of the cross‐section of the novel cellulose fibers generated here. 相似文献
Summary: A feasible method for the preparation of antimicrobial ultrafine fibers with silver nanoparticles was developed by direct electrospinning of a cellulose acetate (CA) solution with small amounts of silver nitrate followed by photoreduction. Silver nanoparticles in ultrafine CA fibers were stabilized by interactions with carbonyl oxygen atoms in CA. Ultrafine CA fibers with silver nanoparticles showed very strong antimicrobial activity.
TEM image of an ultrafine CA fiber electrospun from 10 wt.‐% CA solution with 0.5 wt.‐% AgNO3. 相似文献
In the present work, a Portland cement blended with calcium carbonate is being used to study the solidification/stabilization
(S/S) of a Brazilian tanning waste arising from leather production. Chromium is the element of greatest concern in this waste,
but the waste also contains a residual organic material. Using thermogravimetry (TG) and derivative thermogravimetry (DTG)
to identify and quantify the main hydrated phases present in the pastes, this paper presents a comparative study between the
effects of Wyoming and Organophilic bentonites (B and OB) on cement hydration. Samples containing combinations of cement, B, OB and waste have been subjected to thermal analysis after different setting times during the first 28 days of the waste S/S
process. Both bentonites affect the cement hydration, with no significant differences in hydration degree after 1 week. This
work shows further examples of the great utility of thermal analysis techniques in the study of very complex systems containing
both crystalline and amorphous mineral materials as well as organics.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
A facile method for the fabrication of inorganic hollow materials from cuprammonium cellulose composite filaments based on fast pyrolysis has been developed. Unlike Ostwald ripening, approaches based on the Kirkendall effect, and other template methods, this process yielded hollow materials within 100 s. The heterogeneous structure of the cellulose composite fibers and the gradient distribution of the metal oxides are the main reasons for the formation of the hollow structure. The diameter, wall thickness, and length of the hollow microfibers could be conveniently controlled. With their perfect morphology, these hollow structural materials have great potential for use in various fields. 相似文献
Nuclear Magnetic Resonance (NMR) relaxometry is a valuable tool for investigating cement-based materials. It allows monitoring of pore evolution and water consumption even during the hydration process. The approach relies on the proportionality between the relaxation time and the pore size. Note, however, that this approach inherently assumes that the pores are saturated with water during the hydration process. In the present work, this assumption is eliminated, and the pore evolution is discussed on a more general basis. The new approach is implemented here to extract information on surface evolution of capillary pores in a simple cement paste and a cement paste containing calcium nitrate as accelerator. The experiments revealed an increase of the pore surface even during the dormant stage for both samples with a faster evolution in the presence of the accelerator. Moreover, water consumption arises from the beginning of the hydration process for the sample containing the accelerator while no water is consumed during dormant stage in the case of simple cement paste. It was also observed that the pore volume fractal dimension is higher in the case of cement paste containing the accelerator. 相似文献
Thermal methods are used extensively in investigating cements and effects of additives on their hydration behaviour. Calcium chloride is the most effective and widely used accelerator for cement hydration, but the result is largely dependent on the rate at which it is added. In this study the influence of calcium chloride dosage on the hydration behaviour of OPC pastes aged for different periods has been investigated by means of differential scanning calorimetry (DSC), thermogravimetry (TG) and X-ray diffraction (XRD) methods. The results are discussed in relation to the relative amounts of calcium hydroxide and total reaction product formed. Chloroaluminate was a product of hydration in the samples dosed with greater than 1% calcium chloride. XRD was unable of itself to differentiate between monochloroaluminate and the calcium aluminate hydrate C4AH13 when present in small amounts. Thermal methods proved effective in characterising the products of hydration in the presence of chloride.
Zusammenfassung Bei der Untersuchung von Zement und des Einflusses von Additiven auf das Hydratationsverhalten von Zement finden thermoanalytische Methoden eine breite Anwendung. Der effektivste und meistbenutzte Beschleuniger für die Hydratation von Zement ist Calciumchlorid, aber die Ergebnisse hängen stark von der Dosiergeschwindigkeit ab. In vorliegender Studie wird mittels DSC-, TG- und Röntgendiffraktionsmethoden der Einflu\ der Dosierung von Calciumchlorid auf das Hydratationsverhalten von verschieden alten OPC-Zementbreiproben untersucht. Die Ergebnisse wurden in Bezug auf die relativen Mengen Calciumhydroxid und das gebildete Gesamtreaktionsprodukt gewertet.Bei Dosen von mehr als 1% Calciumchlorid konnte als Hydratationsprodukt Chloraluminat festgestellt werden. Sind Monochloraluminat und das Calciumaluminathydrat C4AH13 in geringen Mengen vorhanden, kann man zwischen den beiden mittels Röntgendiffraktion nicht unterscheiden. Thermoanalytische Methoden erwiesen sich als effektives Hilfsmittel bei der Charakterisierung der Produkte der Hydratation in Gegenwart von Chlorid.
Biodegradable polymer composites consisting of poly(lactic acid) (PLA) and cellulose fibers (CF) were prepared by our newly developed method. L-Lactic acid (LA) was reacted by ring-opening polymerization with aluminum triflate as a catalyst, glycerol as an initiator and CF as a filler, in simple plastic tubes at 100 °C for 6 hours. By this method, CF could be mixed with the polymer matrix easily and homogeneously. The molecular weight and molecular weight distribution of the PLA matrix were determined by gel permeation chromatography (GPC). The Mn of the composite samples decreased from 6200 to 2800 with increasing CF content. The molecular weight distribution of composites was around 2.5 regardless of the CF content. Biodegradation of samples was determined by measuring the results from the Microbial Oxidative Degradation Analyzer (MODA) and the weight loss in compost. Biodegradation of composite samples of PLA with CF increases with increasing CF content as measured by the MODA. Apparent density of composite samples was calculated by using the weight and sizes of column shape specimens. The density of the composite samples was a bit lower than that of PLA pure samples without CF. Mechanical properties such as the elastic modulus and strength were investigated by compression tests using column shape specimens. For the sample with filter paper as CF, the strength of composite samples increases with increasing CF content. 相似文献
Summary: Cellulose was dissolved rapidly in 9.5 wt.‐% NaOH and 4.5 wt.‐% thiourea aqueous solution pre‐cooled to −5 °C to prepare a transparent solution. Novel cellulose multi‐filament fibers were spun successfully, for the first time, from the cellulose dope on an extended laboratory scale. The results from 13C NMR, scanning electron microscopy and wide angle X‐ray diffraction (WAXD) patterns indicated that the fibers exhibited cellulose II character and possessed a circular cross‐section and smooth surface. The tensile strength of the novel fibers reached 1.9–2.2 cN · dtex−1. 2D WAXD and SAXS patterns revealed that, with a drawing progress, the orientation factor increased and mechanical properties were improved.
SEM micrographs of the novel multi‐filament fibers spun from cellulose solution in a NaOH/thiourea aqueous system pre‐cooled to −5 °C on an extended laboratory scale. 相似文献
Four paste mixtures with varying replacement level of the cement content by fly ash have been studied. Due to fly ash, the
acceleration period decreased and a third hydration peak was noticed with isothermal calorimetry. The total heat after 7 days
increased with increasing fly ash content. From 1 to 7 days, thermogravimetry showed a higher chemically bound water and Ca(OH)2-content for the pastes with fly ash. Between 7 and 14 days the calcium hydroxide started to be depleted due to the pozzolanic
reaction. A unique relation was found between calcium hydroxide and total heat development. 相似文献
Investigations of physico-chemical properties
of three kinds of fly ash and their influence on cement hydration were performed
in this work. Thermal analysis, microcalorimetry, infrared absorption and
others were used. It was confirmed that the kind of coal and combustion conditions
essentially influence physico-chemical properties of fly ash and in consequence
influence cement hydration. Investigated fly ashes show in cement system so-called
pozzolanic activity. Fly ash from combustion of brown coal in fluidized furnace
revealed better activity compared to other investigated ones. This work is
an introduction to more extensive investigation of fly ash activation. 相似文献