Exothermic Hydration Research Articles

Numerical simulation of temperature rise of highstrength concrete incorporating silica fume and superplasticiser

A numerical model is proposed to predict the process of adiabatic temperature rise of high-strength concrete (HSC) incorporating silica fume (SF) and superplasticisers. On the basis of predicting the exothermic hydration process of plain concrete, the proposed numerical model takes the retardation caused by the superplasticisers and the effect caused by the SF into consideration. The verification of the proposed model is carried out with several groups of experimental data on concrete at different water to cementitious material ratios and initial temperatures. This numerical model is able to predict the adiabatic temperature history of HSC with SF and superplasticiser. The computing model requires the following relevant material parameters, namely, the mineral composition of Portland cement, the amount of SF, the dosage of superplasticiser, mix proportions and initial placing temperature of concrete. The model is useful in the prediction of heat of hydration, temperature distribution in mass concrete providing useful information on de-moulding at early ages and on controlling the potential thermal cracking.

Theory and example of a small‐molecule motor

AbstractConceptual principles for operation of a molecular motor stipulate that such a species must consist of an energy‐consuming catalyst that exhibits within its mechanism temporal overlap of successive catalytic cycles, so as to induce irreversible intramolecular motion during operation. The exothermic hydration reaction of MeCOCHCNCMe3 brought about by catalyst HO2CCH2OCMe(CO2H)2 qualifies as such a process, in the form of serial conversion between canonical carboxylic anhydride structures within the catalyst. The steady‐state kinetic behavior and inactivation by methanol demonstrate the operation of an appropriate repetitive catalytic loop in this case. Copyright © 2003 John Wiley & Sons, Ltd.

Simulation of the exothermic hydration process of Portland cement

A numerical model is proposed to simulate the exothermic hydration process of cement and temperature rise in mass concrete pours. The hydration reaction of each major mineral compound found in Portland cement, C3S, C2S, C3A and C4AF, is considered. The hydration of each mineral compound is characterised by its two material functions, namely, the thermal activity and the reference rate of heat of hydration. The influences of various factors on the exothermic hydration process are taken into consideration. The applicability of the proposed model is verified by a series of adiabatic temperature rise tests. With the establishment of this approach, it is possible to simulate the exothermic hydration process of Portland cement and the temperature rise directly on the basis of intrinsic mechanism of hydration, chemical composition of cement and mix proportion of concrete mixture.

Simulation of the exothermic hydration process of Portland cement

A numerical model is proposed to simulate the exothermic hydration process of cement and temperature rise in mass concrete pours. The hydration reaction of each major mineral compound found in Portland cement, C3S, C2S, C3A and C4AF, is considered. The hydration of each mineral compound is characterised by its two material functions, namely, the thermal activity and the reference rate of heat of hydration. The influences of various factors on the exothermic hydration process are taken into consideration. The applicability of the proposed model is verified by a series of adiabatic temperature rise tests. With the establishment of this approach, it is possible to simulate the exothermic hydration process of Portland cement and the temperature rise directly on the basis of intrinsic mechanism of hydration, chemical composition of cement and mix proportion of concrete mixture.

Solvent Effect on the Protonation of Acetylene and Ethylene – Continuum Solvent Quantum Chemical Calculations

The protonation of acetylene and ethylene (yielding the vinyl and ethyl cation, respectively) was investigated computationally by ab initio calculations [B3LYP/6–31G(d,p)], in the gas phase and in water, as modeled by the IPCM and SCIPCM continuum methods. The structures and NBO atomic charges were thus determined for the neutral bases and their protonated forms, while the comparison of gas-phase and aqueous basicities afforded the hydration energies of the protonated bases. It was found that the aqueous protonation of acetylene is more endothermic than that of ethylene by 5 kcal/mol, owing to the lower intrinsic basicity of the former (by 7.4 kcal/mol), which is only partly compensated for by the more exothermic hydration (by 3.8 kcal/mol) of the vinyl cation.

Solvent Effect on the Protonation of Acetylene and Ethylene – Continuum Solvent Quantum Chemical Calculations

The protonation of acetylene and ethylene (yielding the vinyl and ethyl cation, respectively) was investigated computationally by ab initio calculations [B3LYP/6–31G(d,p)], in the gas phase and in water, as modeled by the IPCM and SCIPCM continuum methods. The structures and NBO atomic charges were thus determined for the neutral bases and their protonated forms, while the comparison of gas-phase and aqueous basicities afforded the hydration energies of the protonated bases. It was found that the aqueous protonation of acetylene is more endothermic than that of ethylene by 5 kcal/mol, owing to the lower intrinsic basicity of the former (by 7.4 kcal/mol), which is only partly compensated for by the more exothermic hydration (by 3.8 kcal/mol) of the vinyl cation.

Catalytic converter heating by reversible chemical reaction of CaO/Ca(OH)2. Simulation study of exhaust emission reduction with prototype heater.

Rapid activation of three-way catalyst is very effective to reduce harmful substances in exhaust gas. For heating the catalyst of a car, feasibility study of CaO/Ca(OH)2 reversible exothermic reaction has been done. In this paper, experimental results of prototype heater with exothermic hydration and dehydration reaction are described. Furthermore, the performance of exhaust emission reduction with the prototype heater and Ca(OH)2 dehydration are estimated by simulation study. It is predicted that the prototype heater reduces unburned exhaust emission by 37% in LA-4 test cycle simulation.

Catalytic Converter Heating by Reversible Chemical Reaction of CaO/Ca(OH)2. Prototype Heater with Exothermic Hydration Reaction.

Catalytic Converter Heating by Reversible Chemical Reaction of CaO/Ca(OH)2. Prototype Heater with Exothermic Hydration Reaction.

Dependence of Acridine Adsorption on Ligand Hydration Enthalpy

The effect of the aqueous solution pH and ligand type (H2PO-4, HPO2-4, H2CO3, HCO-3 Cl-, and ClO-4) on acridine adsorption to silica was studied in a series of continuous-flow column experiments. The extent of acridine adsorption at solution pH's above its pKa was enhanced when H2CO3/HCO-3 was used as a buffer rather than H2PO-4/HPO2-4, due to more exothermic hydration enthalpy of the H2CO3/HCO-3 buffer. The greater polarity of the acridinium cation and/or acridinium cation/ligand complexes at solution pH's below the pKa of acridine minimized the effect of differences in ligand hydration enthalpies on acridine adsorption. These results suggest that acridine mobility in groundwater would be buffer dependent.

Structure and thermodynamic properties of water–methanol mixtures: Role of the water–water interaction

Thermodynamic properties and structures of water–methanol mixtures at various temperatures have been investigated by means of Monte Carlo simulations and subsequent analyses. The OPLS model by Jorgensen was used for the methanol–methanol interaction and both the Caravetta–Clementi (CC) potential and TIP4P potential by Jorgensen et al. were used for the water–water interaction. We show that the role of water–water interaction is very important in discussing aqueous solutions of alcohols, and examine the origin of the exothermic mixing processes. We have investigated the sensitivity of the temperature dependence of the enthalpy of mixing to the water–water interaction. The CC potential is able to reproduce the temperature dependence observed in experiments, although the absolute values of the mixing enthalpy were larger than the experimental ones. While the TIP4P potential results in better agreement for the excess enthalpy and volume near room temperature, the temperature dependence of the excess enthalpy did not agree with experiment. The difference in the magnitude of the exothermic hydration for different water–water interactions is explained in terms of the energetic stability of the clathrate hydrate compared with ice, on the basis that the structure of water in the vicinity of a methanol molecule is similar to the clathrate hydrate. It is found that the energetic stability of the clathrate hydrate for the CC model is higher than that for TIP4P, and this is responsible for the larger exothermic hydration. The higher stability of the clathrate hydrate structure for the CC potential, in turn, arises from the difference in the pair interaction energy surface between two kinds of potential functions; the minimum energy structure and the flexibility of the hydrogen bonded pair.

Hydrophobic hydration of inert gases: Thermodynamic properties, inherent structures, and normal-mode analysis

Computer simulations on water and aqueous solutions of noble gases have been carried out in order to study the structures of water around a solute. The hydration energy and free energy evaluated for neon (Ne) and xenon (Xe) solutions in the present study were in good agreement with those by experiments. The detailed hydration structures were investigated by means of the so called inherent structures and normal-mode analyses. It was found that the positive excess free energy in the hydration of Xe arises from a decrease in the number of distinct potential-energy minima in configuration space and that the free energy increase in the Ne solution is due partly to the decrease in the number of the potential minima and partly to the anharmonic modes which are harder than those in pure water. The soft anharmonic modes in the Xe solution were almost equivalent to those in pure water. The introduction of a Xe solute gives rise to a change in water structure to a clathrate-like structure and yields an increase in population of the cyclic pentamer connected by hydrogen bonds, which leads to the exothermic hydration.

Effect of Curing Temperature on the Properties of Cementitious Waste Forms

ABSTRACTCurrent plans for disposing various low-level radioactive and/or hazardous liquid wastes include solidification of the waste using cementitious materials. One process, known as grouting, involves mixing liquid wastes with a blend of cementitious materials and pumping the resultant slurry to lined, underground concrete vaults. As the grout slurry begins to solidify and harden, the temperature within the grout increases due to exothermic hydration reactions. Depending on the the particular grout composition and on the disposal conditions, the grout may be exposed to temperatures of around 90°C for extended time periods. Studies are being conducted to determine the effects of high-temperature curing on selected properties of grouts prepared with a simulated low-level liquid waste. Grout samples cured at temperatures up to 950C in the laboratory absorbed water during curing. The resultant leach resistance and compressive strength of these grouts decreased with increases in curing temperature and curing time.

Performance Characteristics of Concrete Produced with Fluidized Bed Combustion Ash Residue

ABSTRACTOver the last five years, the Kentucky Energy Cabinet (KEC) and the Tennessee Valley Authority (TVA) have developed and demonstrated the production of concrete from atmospheric fluidized bed combustion (AFBC) spent bed (SB) ash, and pulverized fuel ash (PFA). This AFBC concrete contains no cement and relies on the reaction of residual lime in the SB ash to react with the pozzolan PFA to form cementitious products. The SB ash is prehydrated in order to reduce exothermic lime hydration reactions and minimize molar volume expansion. Laboratory tests were conducted to establish the performance characteristics of AFBC concretes relative to conventional concrete. AFBC concretes exhibit slower strength gain characteristics, but long term (60 day), unconfined compressive strengths of 5,000 psi have been documented. This slow strength development is typical of pozzolanic concretes. AFBC concrete is more flexible and less brittle than conventional Portland cement concrete, as evidenced by its much lower modulus of elasticity. Setting times for AFBC concretes are extended, requiring the use of accelerators under certain applications. Field demonstrations of the AFBC concretes in ready mix concrete, masonry units, and road base applications have indicated excellent workability and finishing characteristics and confirm the laboratory performance characteristics.The paper describes the results of the testing program with emphasis on the ash chemistry/conditioning, the performance characteristics and field demonstrations.

Integral equation and Monte Carlo study on hydrophobic effects: Size dependence of apolar solutes on solute–solute interactions and structures of water

Hydrophobic effects for various solute sizes have been investigated by the RISM equation and Monte Carlo simulation. It is shown that the association of solute molecules is enhanced by the hydrogen bonds among water molecules. The degree of association depends on the solute size. For a large apolar solute, the structure of water is enhanced, resulting in the exothermic hydration and the negative entropy change in hydration. For a solute comparable with the water size, the hydrogen bonds among water molecules are strengthened but the net hydrogen bonds number does not increase. These results are also confirmed by the analysis of the geometric patterns formed by the hydrogen bond network. It is shown that the ordered structure of water in the solution of the large solutes gives rise to the larger enthalpy of the hydration, and thus they are more soluble in water than the smaller solutes.

Heat-release characteristics of CaO packed bed accompanied by exothermic hydration.

Ca (OH) 2/CaO系熱化学反応の化学蓄熱への適用性を調べるための1段階としてCaO蓄熱材充填層の水和発熱反応に伴う放熱特性を検討した.その結果, 本実験範囲ではCaO充填層は水蒸気流入と同時に水和反応を開始し, 層温度は水蒸気分圧に相当する反応平衡温度にまで上昇した後, 反応期間中ほぼこの一定温度に保たれることを認め, また, 放熱持続時間は, 大略, 流入水蒸気温度に比例し, 水蒸気流量に逆比例することがわかった.本実験結果はある仮定のもとで求めた計算結果と比較的良好な一致を示し, 充填層内放熱特性を理論的に説明できた.さらに, 本蓄熱材充填層の蓄熱/放熱繰返し実験によって得られる放熱特性は繰返しサイクルによらずほぼ一定であった.

Enthalpy of mixing of hydrated melts. II. Evidence for an endothermic step in the chlorocomplex formation of zinc

The enthalpies of mixing measured for the systems x(ZnCl2+RH2O)-(1−x)(LiCl+RH2O) are reported. In contrast to the exothermic effects for R=4, the mixing processes at R=6 are considerably endothermic. For R=5, the sign of ΔH M depends on the composition. The mixing enthalpies of these hydrated melts are controlled by an endothermic step in the chlorocomplex formation of zinc and the exothermic hydration of lithium cations.

Maturation Anomalies in Cretaceous Sediments Underlying Volcanic Plateaus in Oregon: ABSTRACT

Vitrinite reflectance profiles from three drill holes in Oregon, supplemented by independent data from Oregon and northern California, suggest that a thick sequence of volcanics may lead to a significant thermal input into underlying sediments. Anomalous, nearly vertical maturation profiles, in sedimentary sequences over 4000 ft thick, imply that large volumes of mature source rocks may lie under the volcanic cover of the Pacific Northwest. Several factors may be involved in this vertical homogenization of the temperature field. Although a convective hydrothermal mechanism would be the most effective form of thermal input, this is not considered to be the dominant mechanism due to the low permeabilities of the volcanogenic sediments underlying the volcanics. However, the cooling of intrusive and extrusive volcanics, thermal slip at abrupt changes in lithology, and exothermic hydration reactions of the altering volcanics can all be considered viable mechanisms for the thermal input. These mechanisms can lead to the uniform maturation of the entire sedimentary column and may account for the gas fields in Mist, Oregon. There, poor and immature source rocks give no indication of the actual origin of the gas. However, a mature sedimentary column underlying volcanic cover to the north and east could providemore » a plausible source for the gas. Other settings in which potentially hydrocarbon-bearing sediments underlie volcanics occur elsewhere in the US, and in India, Argentina, Brazil, Russia, and eastern and southern Africa.« less