Hydration of cement with superabsorbent polymers

Hydration of cement is a complex thermodynamic system where a number of heterogeneous compounds interact with each other to form cement hydrates. Superabsorbent polymers (SAP) can be added to cement systems with many different reasons, so it is relevant that the basic knowledge of this new compound on the development of hydration is well understood. This paper reports basic research on thermal analysis of cement pastes with SAP—a suspension-polymerized poly acrylic acid–acrylamide copolymer. Several parameters were analysed: the concentration of SAP, the effect of particle size distribution and their influence on the hydration process with focus on ordinary Portland cement. The methodology included thermogravimetric analysis and differential scanning calorimetry. Combined water method was employed at different thermodynamic conditions, so the energy of activation in the different systems can be accessed. The introduction of SAP in cement-based materials significantly affects the chemical balance of ordinary Portland cement. The effect is not only in terms of the amount of hydrates, but also the type of hydrates being generated, thermodynamically favourable to precipitation of calcium hydroxide. This paper provides information relevant to hydration modelling and comprehension of cementitious materials when internal curing is active.     

Application of differential thermogravimetry to the hydration of expansive cement pastes

Differential thermogravimetric analysis was used to determine the hydration kinetics of expansive cement and its products at various ages of hydration. Analytical grade reagents, kaolin and Portland cement were used to prepare an expansive cement on the basis of calcium sulphoaluminate. Two mix compositions having the stoichiometric composition of trisulphate and monosulphate were synthesized from pure reagents. Three clinkers were also prepared from kaolin, gypsum and calcium carbonate with different compositions.The hydration of expansive cement prepared from the stoichiometric composition of trisulphate and Portland cement gives ettringite as the stable phase after seven days of hydration. The presence of more CaO than the stoichiometric composition of trisulphate favours the conversion of some ettringite to the monosulphate hydrate. The hydration of expansive cement prepared from the stoichiometric composition of monosulphate and Portland cement shows the presence of ettringite and the monosulphate phase. Ettringite is formed initially, and then transformed to the monosulphate form.     

Simultaneous measurements of heat of hydration and chemical shrinkage on hardening cement pastes

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.     

Influence of chromate reducers on cement hydration

Present research compared the effect of chromate reducers such as ferrous sulphate heptahydrate (FeSO₄·7H₂O) and stannous sulphate dihydrate (SnCl₂·2H₂O) on the hydration of cement paste, using water?cement ratio of 0.5 and sealed in plastic bags without curing for 28 days. Uncured hydration properties of cement paste are investigated in detail by thermogravimetric analysis (TGA) and verified with the use of scanning electron microscopy (SEM) and X-ray powder diffractometry (XRD). This research concluded that the cement paste with 0.1% additives showed better hydration in the uncured condition than the control.

     

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 ultradispersed silicas on Portland cement hydration

Solid-state ²⁹Si NMR spectroscopy was applied to examine Portland cement hydration and cement stone composition as influenced by the nature of commercial ultradispersed silicas (microsilica, precipitated silica, and colloidal silica).     

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.     

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...     

Influence of superplasticizers on the course of Portland cement hydration

A multicell isoperibolic — semiadiabatic calorimeter was used for the measurement of temperature and the determination of the hydration heat evolution at earlier period of cement pastes setting and hardening. The measurements were aimed at the determination of the effect of superplasticizers (SPs) on the course of the Portland cement hydration. Commercial polycarboxylate SP was added to the mixtures and the heat effect was measured. With the increasing content of SP, the hydration temperature increased up to a certain value and then decreased. In case of a sufficient amount of water in the mixture to achieve complete hydration of cement, samples with the highest values of the maximum hydration temperature reached the highest values of the released total heat. If there is not a sufficient amount of water to achieve complete hydration, the samples with the highest values of the maximum hydration temperature reach the lowest values of the released total heat.     

Influence of hydrothermal curing regimes on the hydration of fiber-reinforced cement composites

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, C₃AH₆, and AH₃. The second one is the process characterized by partial decomposition or interaction of primary products to form secondary products (C₂ASH₈, C₃AH_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.     

Kinetic and thermodynamic modeling of Portland cement hydration at low temperatures

Portland cement have to hydrate in cold climates in some particular conditions. Therefore, a better understanding of cement hydration under low temperatures would benefit the cement-based composites application. In this study, Portland cement was, therefore, kinetically and thermodynamically simulated based on a simple kinetics model and minimization of Gibbs free energy. The results of an evaluation indicate that Portland cement hydration impact factors include the water–cement ratio (w/c), temperature, and specific surface area, with the latter being an especially remarkable factor. Therefore, increasing the specific surface area to an appropriate level may be a solution to speed the delayed hydration due to low temperatures. Meanwhile, the w/c ratio is believed to be controlled under cold climates with consideration of durability. The thermodynamic calculation results suggest that low-temperature influences can be divided into three levels: irrevocable effects (<0 °C), recoverable effects (0–10 °C), and insignificant effects (10–20 °C). Portland cement was additionally measured via X-ray diffraction, thermal gravity analysis, and low-temperature nitrogen adsorption test in a laboratory and comparisons were drawn that validate the simulation result.     

Influence of borax and citric acid on the hydration of calcium sulfoaluminate cement

The hydration of calcium sulfoaluminate cement in the presence of borax and citric acid has been studied using isothermal calorimetry, X-ray diffraction, thermogravimetric analysis, Fourier transfer infrared spectrometry and mercury intrusion porosimetry. The results suggest that the formation of complex between calcium and citrate in the solution adsorbed on the solid surface delayed the C₄A₃ \( \bar{S} \) and anhydrite dissolution and AFt nucleation. At the same time, the presence of borate replaced sulfate anion in ettringite (AFt) to form B-AFt. These reactions have an effect on the setting times and the mechanical strength values. The setting times of the calcium sulfoaluminate cement increased when the mineral admixtures increased in the cement. The effect of borax and citric acid on the strength development at different hydration stages presented different results, namely a decreased strength in an early stage and an increased strength at 3 and 28 days.     

Synthesis and characterization of glass-containing superabsorbent polymers

By embedding hollow glass spheres of different sizes and densities into a matrix of crosslinked sodium polyacrylate, superabsorbent polymers were synthesized using a water-in-oil suspension polymerization. These glass-containing superabsorbents were capable of taking up water not only in form of a swollen polyacrylate gel, but also in form of additional free water between the glass spheres and the surrounding polyacrylate matrix. According to swelling measurements the maximum volume swelling degree of the glass-containing superabsorbents is in certain cases nearly double as large as the value of a superabsorbent without embedded glass spheres.     

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.     

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.     

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.

     

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.     

Characterisation of cement pastes by inverse gas chromatography

Two cement pastes, commonly used in concrete formulations, were characterised by IGC at 35-80 degrees C before and after coating with an epoxy resin and a hardener. The cements are mixtures of hydrates in various proportions, such as calcium silicate hydrate (CaO-SiO2-H2O) and calcium hydroxide Ca(OH)2. Apolar and polar probes were used to determine the dispersive and acid-base characteristics of the cement pastes. These materials have high surface energy as judged from the dispersive contribution to the surface free energy (gamma(s)d) values lying in the 50-70 mJ/m2 range at 60-80 degrees C. Examination of the specific interactions permitted to show that the cement pastes are strongly amphoteric species with a substantial predominant Lewis basicity that is in line with the basic pH of their aqueous suspensions. Following coating with an epoxy resin (DGEBA) and a hardener (triethylene tetramine), the surface energy of the cements decreases substantially with the mass loading of the organic material. The surface thermodynamic properties were also correlated with the surface chemical composition as determined by X-ray photoelectron spectroscopy.     

Study on the hydration product of ettringite in cement paste with ethanol-diisopropanolamine

Journal of Thermal Analysis and Calorimetry - Ettringite (AFt) is a very important hydration product of hardened cement pastes in the early stage. The effect of ethanol-diisopropanolamine (EDIPA)...