Effect of water/binder ratio and temperature on the hydration heat and properties of ternary blended cement containing slag and iron tailing powder

Journal of Thermal Analysis and Calorimetry - The effects of water/binder ratio and temperature on hydration heat and properties of ternary blended cement containing slag and iron tailing powder...     

Importance of quantitative thermogravimetry on initial cement mass basis to evaluate the hydration of cement pastes and mortars

Thermogravimetric analysis (TG) curves of cement pastes and mortars are obtained by default on their respective initial sample mass basis. This fact does not allow a direct comparison of TG data of percentual mass losses due to the dehydration of a same hydrated component of differently aged pastes or mortars of same cement because the initial masses of the differently aged sample usually have different initial compositions. To solve this problem, one can transform the original thermal analysis curves from the initial sample mass basis to the initial cement mass basis, to have the same composition basis for any hydration time. This paper presents in detail how this can be done graphically and analytically and applies the method to study the evolution of cement hydration during the first 28 days of pastes and mortars prepared from the same type II cement. It also shows how to compare quantitatively the main cement hydrated phases formed during solidification and setting processes of pastes and mortars with different initial compositions as a function of hydration time.     

Correlation between pore structure and low-temperature dilatation of hydrated cement pastes and mortars

The pore structure and low-temperature dilatation behavior of traditional hydrated Portland cement paste compacted by different methods were investigated. The aim of the investigation was to demonstrate the influence of the water-cement ratio and the compacting conditions on the developing pore structure and the frost dilatation during the early stage of the hydration process. A low water-cement ratio and a high compacting pressure resulted in initially low porosity, but in coarser pore sizes. Vibration resulted in lower pore volumes as compared with those of cast cement pastes, but the pore size distributions were similar. In accordance with the pore size distribution, two frost dilatation effects were measured when macro- and mesopores also occurred in the hydrated cement pastes. In the samples compacted by high pressure, a single frost dilatation effect occurred in connection with the macropores present in the sample. The magnitude of the frost dilatation effect decreased with increasing curing time. The decrease is caused by a decrease in the volume of the pores and also by an increase in matrix strength.

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Zusammenfassung Es wurde die Porenstruktur und das Tieftemperaturdilatationsverhalten von herkömmlichem, hydratiertem, durch verschiedene Methoden verdichtetem Portland-Zementleim untersucht. Das Ziel der Untersuchung bestand im Nachweis des Einflusses des Wasser-Zement-Verhältnisses und der Verdichtungsbedingungen auf die entstehende Porenstruktur und die Frostdilatation in der frühen Periode des Hydratationsprozesses. Ein niedriges Wasser-Zement-Verhältnis und ein hoher Verdichtungsdruck liefert eine geringe Porösität, aber größere Porenmaße. Vibration liefert im Vergleich zu gegossenem Zementleim ein geringeres Porenvolumen, aber die Beiträge zur Porengröße waren ähnlich. In Übereinstimmung mit dem Porengrößeeinfluß wurden zwei Frostdilatationseffekte gemessen, wenn sowohl Makroals auch Mesoporen in den hydratierten Zementleimen vorkamen. In denjenigen Proben, die unter Hochdruck verdichtet wurden, tritt in Verbindung mit der Gegenwart von Makroporen in der Probe ein einfacher Frostdilatationseffekt auf. Die Höhe des Frostdilatationseffektes sinkt mit steigender Aushärtungszeit. Dieses Sinken wird durch eine Abnahme des Volumens der Poren verursacht und ebenfalls durch ein Ansteigen der Matrixfestigkeit.

     

Correlation between pore structure and low-temperature dilatation of hydrated cement pastes and mortars

The pore structure and low-temperature dilataion behaviour of a traditional hydrated Portland cement paste and a special cement paste of high initial strength were investigated.The aim of the investigation was to demonstrate the role of the cement type in developing the pore structure and frost dilatation during the hydration process. The lower porosity and the higher strength of the special hydrated cement paste resulted in smaller frost dilatation effects in comparison with those of the traditional cement paste in the early stage of hydration.

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Zusammenfassung An einem herkömmlich hydratierten Portland Zementleim und einem Spezialzementleim mit hoher Anfangsfestigkeit wurde die Porenstruktur und das Dilatationsverhalten bei niedrigen Temperaturen untersucht. Mit dieser Untersuchung sollte gezeigt werden, welche Rolle die Zementart wÄhrend des Hydratationsprozesses bei der Ausbildung der Porenstruktur und der Ausdehnung bei Frost spielt. Die geringere PorösitÄt und höhere Festigkeit des speziell hydratierten Zementleimes ergaben bezogen auf herkömmlichen Zementleim im frühen Stadium der Hydratation geringere Dilatationseffekte bei Frost.

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The author is grateful to Dr. Ludmilla Opoczky and Mr. Imre Horváth for the samples.     

Effect of addition of nano-magnetite on the hydration characteristics of hardened Portland cement and high slag cement pastes

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 Fe₃O₄ nanoparticles by mass of cement. An aqueous stable magnetic fluid containing Fe₃O₄ 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.     

Influence of the calcined paper sludge on the development of hydration heat in blended cement mortars

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.     

Effect of substitution of blast-furnace slag by fired drinking water sludge on the properties of pozzolanic cement pastes

Journal of Thermal Analysis and Calorimetry - The effect of fired drinking water sludge (FDWS) as a mineral admixture on the physico-mechanical properties and the fire resistance of pozzolanic...     

Structure of white cement mortars with high content of marble powder

In this study, three types of cementitious composites based on (i) white Portland cement and sand (cement-to-aggregate 1:3, and water-to-cement 0.50), (ii) white Portland cement and marble powder (cement-to-aggregate 1:2, and water-to-cement 0.60), and (iii) white Portland cement and marble powder with polycarboxylate-based admixture (HRWR) (cement-to-aggregate 1:2, and water-to-cement 0.40?+?HRWR) were studied. Their states after 28 and 120?days of water curing were evaluated by measurement of physical?Cmechanical properties, such as density, compressive strength and porosity. Thermal analysis, X-ray diffraction analysis and scanning electron microscopy were used to identify the crystal phases and their morphology. The experimental data show that the white cement mortars with higher water content exhibit larder variety of newly formed phases, like hydration products of the C?CS?CH type. The structure of mortars with polycarboxylate-based admixture is so dense that there is no possibility of crystal hydrates development at late curing ages. The use of marble as filler leads to a partial inclusion of carbonate ions in the newly formed hydrated phases (carbo-aluminates).     

CO2 sequestration by high initial strength Portland cement pastes

During the formation of pastes, mortar and concretes have been used to capture CO₂. This work presents a methodology to estimate the carbon dioxide (CO₂) sequestered by high strength and sulfate-resistant Portland cement pastes during their early stages of hydration, by Thermogravimetry and Derivative Thermogravimetry. Water to cement ratio equal to 0.50 and 0.70 were evaluated and the captured CO₂ amount was determined through TG/DTG curve data on initial cement mass basis, obtained during accelerated carbonation from the fluid state and accelerated carbonation after a first hydration process. The experiments were performed in a controlled chamber, maintaining the CO₂ content at 20 vol % and the temperature at 25 °C, at different relative humidity (RH) (60 and 80 %) ambient. The procedure allows one to estimate the amount of CO₂ sequestered by the initial cement mass of a given volume of paste, as well as to evaluate the RH and W/C ratio influence on the amount of hydrated formed products, mainly on the Ca(OH)₂, important for CO₂ fixation.     

Effect of microcrystalline and microfibrillated cellulose on the evolution of hydration of cement pastes by thermogravimetry

Journal of Thermal Analysis and Calorimetry - The interest in the use of cellulose fibers of increasingly smaller sizes in cementitious materials has increased in recent years. This paper brings...     

Effect of nano-metakaolin addition on the hydration characteristics of fly ash blended cement mortar

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.     

Properties and performance of metakaolin pozzolanic cement pastes

The heating rate effect on the thermal behavior of clays from Arumetsa and Kunda deposits (Estonia) and an illitic clay from Füzérradvány (Hungary) was studied. Experiments were carried out under dynamic heating condition up to 1050 °C at the heating rates of 1.25, 2.5, 5 and 10 °C min^?1 in a stream of gas mixture containing 79 % of Ar and 21 % of O₂ with Setaram Labsys 1600 analyzer. Two different ashes were used as additives: the electrostatic precipitator ash from the first field and the cyclone ash formed, respectively, at circulating fluidized bed combustion (temperatures 750–830 °C) and pulverized firing (temperatures 1200–1400 °C) of Estonian oil shale at Estonian Power Plant. For calculation of kinetic parameters, the TG data were processed by the differential isoconversional Friedman method. The results of thermal analysis and the variation of the value of activation energy E along the reaction progress α indicated the complex character of decomposition of clays and their blends with Estonian oil shale ashes, and the certain differences in thermal behavior of different clays depending on their origin.     

Mechanical properties of high strength vanadium-base ternary alloys

High strength V-20wt.%Nb and V-10wt.%Ta base ternary alloys containing aluminium, chromium and molybdenum were studied. The fabricability and tensile properties at room temperature and in a temperature range 700–1000 °C were measured. The tensile strength values were estimated on the basis of the values for the corresponding vanadium-base binary alloys and compared with the experimental data. The estimated values are in good agreement with the experimental data. From these results, V-20wt.%Nb-5wt.%Al, V-20wt.%Nb-5wt.%Cr and V-20wt.%Nb 10wt.%Mo alloys were selected as alloys that could be recommended for their good high temperature mechanical properties.     

Thermogravimetry of ternary cement blends

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.     

Differential thermal studies of polymethyl methacrylate-impregnated cement pastes

Differential thermal curves have been obtained for two polymethyl methacrylate-impregnated cement pastes prepared at a water/cement ratio of 0.37 and 0.70. Complex thermal effects, including a substantial decrease in the endothermal peak for Ca(OH)₂ decomposition, were observed in samples heated in air. These effects originate in the portland cement paste, in the polymer, and from interactions between the polymer and the hydrated cement during heating. Less complex effects resulted when DTA was carried out in N₂. There was no evidence of a reaction between the hydrated cement and PMMA during impregnation.     

Microgravimetric measurements of water vapour sorption on hydrated cement pastes

To study the pore structure of hydrated cement pastes, differing in pretreatment and chemical composition, water vapour sorptlon experiments have been used. The experiments were carried out at 25.0°C in a pure water vapour atmosphere, up to relative vapour pressures of 0.98. The amount of water adsorbed or desorbed was determined gravimetrically using a Cahn 2000 microbalance. The set-up developed for this purpose and some experimental results are presented.     

Low frequency dielectric behaviour of Portland cement pastes

Summary Dielectric constants and loss tangents of a Portland cement paste were measured during and after hardening in the frequency range 60 c/s-300 kc/s. One day after preparation two loss areas were observed; during hydration (at 20 °C; 65% R. H.) a h. f. maximum moved slowly to lower frequencies; a l. f. loss increased in magnitude during the first few days of curing, but disappeared during further hardening. Results for a cement paste cured under water for 6 weeks, showed that the h. f. maximum had come to a stop at about 10 kc/s. From the continuous shift of this maximum with temperature in passing the freezing-point it is concluded that the h. f. loss is caused by water of crystallization; the activation energy is 13 kcal/mole. The l. f. loss is believed to be caused by water in open pores. Cement exposed to air during hardening appears to have more open pores than cement hardened under water.

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Zusammenfassung Dielektrische Konstante und dielektrische Verluste von Portland-Zement Pasta wurden w?hrend und nach Aush?rtung im Frequenzbereich zwischen 60 und 3.10⁵ Hz gemessen und diskutiert. Ein Tag nach der Bereitung der Paste zeigt diese zwei Verlustgebiete. W?hrend der Aush?rtung verschiebt sich das hochfrequente Verlustmaximum nach niederen Frequenzen. Es kommt schlie?lich bei etwa 10⁴ Hz zum Stillstand, wie Messungen an unter Wasser ausgeh?rtetem Zement zeigen. Die Temperaturverschiebung dieses Maximums verl?uft stetig beim Durchgang durch den Gefrierpunkt mit einer Aktivierungsenergie von 13 kcal/Mol. Aus diesen Tatsachen ergibt sich ein Deutungsvorschlag dieses Maximums: Es wird Dipolverlusten von gebundenem Kristallwasser zugeschrieben. Das zweite, niederfrequente, Verlustgebiet erh?ht sich innerhalb der ersten Tage der Aush?rtung, um dann wieder zu verschwinden. Es wird als ein Maxwell-Wagner-Sillars-Maximum von in Poren absorbiertem Wasser gedeutet.

     

Thermal resistance,microstructure and mechanical properties of type I Portland cement pastes containing low-cost nanoparticles

This study aimed to utilize laboratory-prepared nano-silica (NS) and nano-alumina (NA) as low-cost nano-oxides additions for improving the mechanical properties and thermal resistance of hardened ordinary Portland cement (OPC) pastes. NS was synthesized from rice husk ash in the absence of any surfactant, while NA was synthesized from AlCl₃ in the presence of CTAB as a surfactant. The average particle sizes of synthesized NS and NA were 30 and 40 nm, respectively. Nano-silica or nano-alumina was added to OPC as a single phase with different ratios of 0.5, 1, 2 and 3 by mass % of OPC. The physico-chemical characteristics of different OPC-NS and OPC-NA hardened pastes were studied after 1, 3, 7, 14, 28 and 90 days of hydration. The resistance of the hardened composites for firing was evaluated for specimens cured for 28 days under tap water and then fired at 300, 600 and 800 °C for 3 h. The fired specimens were cooled by two methods: gradual cooling and rapid cooling. The compressive strength test was performed for all mixes at each firing temperature. The compressive strength results revealed that the optimum addition of NS is 1, whereas the optimum addition of NA is 0.5 by mass % of OPC. XRD, TG/DTG and SEM results indicated that ill-crystalline and nearly amorphous C–S–H, C–A–S–H and C–A–H were the main hydration products.     

Study on optimization of hydration process of blended cement

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.