Synergistic effects of C-S-H–PCE and triethanolamine on the hydration kinetics and rheological behaviours of lithium slag composite binder

Molybdenum tailings powder (MTs) has potential pozzolanic activity and can be used as a mineral admixture. In order to comprehend the influence of MTs powder on the cement hydration process, the hydration heat and kinetics of composite cementitious materials (CCMs) were investigated using an isothermal calorimeter and the Krstulovic–Dabic model. Furthermore, the influences of fly ash (FA), slag (SL), and MTs powder on hydration heat were compared and analyzed, considering the same content. The results show that the proper amount of MTs can promote the hydration of CCMs. When the content of MTs is 5% and 15%, the second exothermic peak of the CCMs appears 2.30% and 4.27% earlier, and the exothermic peak increases by 2.72% and 1.34%, respectively. The cumulative heat release of CCMs gradually decreases with an increasing content of MTs powder. When the replacement of MTs, FA, and SL is 15%, respectively, the second exothermic peak of CCMs increases by 1.34%, −16.13%, and −12.04% for MTs, FA, and SL, respectively. The final heat release of MTs is higher than that of FA, but lower than that of SL. The hydration process of CCMs undergoes three stages: nucleation and crystal growth (NG), interactions at phase boundaries (I), and diffusion (D).

Triisopropanolamine (TIPA) was used as an early strength component to study its effects on mortar strength, cement paste setting time and early hydration characteristic of cement. And the early strength mechanism of TIPA at low temperature of 5 °C was also discussed. The results showed that, at 5 °C, the incorporation of TIPA promoted the condensation of cement paste, shortened the initial and final setting time, and accelerated the strength development of specimens at all ages, among which the strength after 3 d increased significantly. The 1, 3, 7, and 28 d compressive strength ratios of the mortars mixed with 1% TIPA could reach 196%, 179%, 160% and 110% respectively, and the mortar strength after 3 d exceeded that of the contrast sample cured at 20 °C. Under low temperature condition, TIPA could promote the hydration reaction of cement, shorten the induction period and advance the acceleration period. Furthermore, the maximum heat release rate and cumulative heat release quantity would be all increased, and the cumulative heat release of the cement mixed with TIPA hydrated for 12 h and 7 d increased 73% and 38% respectively. TIPA could shorten the nucleation and crystal growth (NG) stage and increase its hydration degree significantly, so it promoted cement hydration reaction. Additionally, the hydration reaction rates in phase boundary reaction (I) phase and diffusion reaction (D) phase were increased, and the duration of I process was prolonged, thereby the development of specimen strength would be accelerated. TIPA did not obviously change the types of hydration products, but increased the content of Ca(OH)2 in the samples and the degree of cement hydration. After hydration to 7 d, large amounts of hydration products, whose surface was smooth, were formed and bonded into sheets, and the structural density of samples improved significantly.

The calorimetric data of composite binder containing slag or fly ash at different water-to-binder ratios were measured at 298 and 333 K by an isothermal calorimeter. The influences of water-to-binder ratio on the hydration heat characteristics of composite binder were analyzed. Based on the hydration kinetics model, the controlling processes during hydration, nucleation and crystal growth (NG), interactions at phase boundaries (I) and diffusion (D), were determined, and the kinetics parameters were calculated and discussed. The results show that water-to-binder ratio slightly affects the early-stage hydration heat evolution rate and cumulative hydration heat, but a lower water-to-binder ratio results in a lower hydration heat evolution rate and cumulative hydration heat at later stage. The water-to-binder ratio has a great effect on the hydration of composite binder at elevated temperature. Decreasing water-to-binder ratio does not change the hydration mechanism of composite binder, which is NG → I → D at 298 K and becomes NG → D at 333 K. The decrease in water-to-binder ratio increases the apparent rate constant of composite binder containing slag, but the inverse trend is obtained for composite binder containing fly ash during NG process at 298 K. The lower water-to-binder ratio leads to the lower apparent rate constant for composite binder containing large amount of slag or fly ash during NG process at 333 K. Decreasing water-to-binder ratio decreases the apparent rate constant during D process for all samples. The apparent activation energy of composite binder decreases with decreasing water-to-binder ratio.

Kinetic and thermodynamic enhancement of crystal nucleation and growth rates in amorphous Si film during ion irradiation

Effects of TEA on rheological property and hydration performance of lithium slag-cement composite binder

Fly ash has been widely used as supplementary cementitious material in concrete industry. Hydration mechanism of composite binder containing fly ash is much more complicated due to the mutual effect of the hydration of cement and the pozzolanic reaction of fly ash. This paper involves the hydration kinetics of composite binder containing up to 65 % of fly ash and comparison of the results with data on composite binder containing slag that are previously published. The hydration heat evolution rate and cumulative hydration heat of composite binder containing fly ash were measured at 298, 318 and 333 K with an isothermal calorimeter. Based on the hydration kinetics model, three hydration processes, namely nucleation and crystal growth (NG), interactions at phase boundaries (I) and diffusion (D) were characterized, the relationship between the hydration rate and hydration degree was discussed at different stages, and kinetics parameters, n, K and Ea, were calculated and analyzed. Results show that the hydration heat evolution rate and cumulative hydration heat of composite binder obviously decrease with increasing the replacement ratio of fly ash. Elevated temperatures promote the hydration process, especially for composite binder containing high amount of fly ash. The kinetics model could simulate the hydration process of composite binder containing no more than 65 % of fly ash, whose hydration process sequence is NG → I → D at 298 and 318 K, but it becomes NG → D at 333 K. Fly ash has relatively smaller effect on the overall reaction of composite binder than slag. The reaction rates of composite binder containing fly ash at different stages are higher than those of composite binder containing slag at the same replacement ratio. The value of Ea for the overall reaction of composite binder decreases first and then increases with increasing the content of fly ash, and it is lower than that of composite binder containing slag at the same replacement ratio.

We evaluated the effects of hydration heat inhibitors on the early hydration heat release process of cement and its main mineral components. We used a microcalorimetric method to determine the effects of various proportions and properties of hydration heat inhibitors on the hydration of portland cement, tricalcium silicate, and tricalcium aluminate: concentration (C) = 40% m/m hydroxydiphosphonic acid (HEDP) (1-hydroxyethylidene-1,1-diphosphonic acid) and C = 40% m/m diethylene triamine pentonyphosphonic acid (DTPMPA) (diethylenetriaminepentamethylene phosphonic acid). We also analyzed and tested the heat release rate and cumulative heat release during the hydration of cement and its main mineral components. The hydration heat inhibitors decreased the heat release rate of cementitious materials by means of adsorption, chelation, precipitation, complex formation, and control of calcium hydroxide crystals. Among these materials, the hydration heat inhibitor had the most substantial effect on the composition of tricalcium silicate clinker, reducing the peak temperature at the initial stage of hydration and delaying its occurrence time. These results are pertinent to controlling and selecting the early hydrothermal release process of cement systems.

Fluidity and hydration evolution of cement-LS binder in the function of Mg/Al-LDH-PCE

Early-age hydration heat evolution and kinetics of Portland cement containing nano-silica at different temperatures

Hydration heat effect of cement pastes and mechanism of hydroxypropyl methyl cellulose ether (HPMC) and expanded perlite in cement pastes were studied by means of hydration exothermic rate, hydration heat amount, FTIR and TG-DTG. The results show that HPMC can significantly delay the hydration induction period and acceleration period of cement pastes. As mixing amount increased, hydration induction period of cement pastes enlarged and accelerated period gradually went back. At the same time, the amount of hydration heat gradually decreased. Expanded perlite had worse delay effects and less change of hydration heat amount of cement pastes than HPMC. HPMC changed the structure of C-S-H during cement hydration. The more amount of HPMC, the more obvious effect. However, EXP had little influence on the structure of C-S-H. At the same age, the content of Ca (OH)2 in cement pastes gradually decreased as the mixing amount increase of HPMC and expanded perlite, and had better delay effect than that single-doped with HPMC or expanded perlite when HPMC and expanded perlite were both doped in cement pastes.

The effect of 3,4 dihydroxy benzoic acid (3,4 DHBA) on the precipitation of alumina trihydrate

The hexacelsian-celsian transformation from grains of 1/4 in. (0.635 cm) size is slow and erratic. This is because the rate of heterogeneous nucleation in such grains is low and is influenced by contamination present in the furnace. When the grain size is reduced to a −200 mesh powder, heterogeneous nucleation becomes a dominant factor and the transformation is accelerated. The transformation has three stages: the first is controlled by the rate of crystal growth, the second is controlled by the rates of nucleation and crystal growth, and the third is controlled by the rate of nucleation.

The driving force of the cooling crystallization process is supersaturation, where the supersaturation level during the crystallization process is crucial to grow the crystal sufficiently. Nucleation and crystal growth rates are two concurrent phenomena occurring during crystallization. Both are supersaturation functions that determine the growth of seed crystals and the formation of fine crystals. Trade-offs between nucleation and crystal growth are essential for achieving the large size of seed crystals with the minimum number of fine crystals. Thus, the objective of this study is to analyze the effects of nucleation and crystal growth rates on final product quality, which is crystal size distribution (CSD). Modeling of the crystallization process using a potash alum case study is highlighted and simulated using Matlab software. Then, the effects of nucleation rate, crystal growth rate, and both nucleation and crystal growth rates on CSD are evaluated using local sensitivity analysis based on the one-factor-at-a-time (OFAT) method. Based on simulation results for all strategies, a low combined rate delivers the best performance of the final CSD compared to others. Its primary peak has a mean crystal size of 455 µm with 0.0078 m3/m volume distribution. This means that the grown seed crystals are large with high volume distribution compared to the nominal strategy, which is at the mean crystal size of 415 µm and 0.00434 m3/m. Meanwhile, the secondary peak has the mean crystal size of 65 µm, 0.00028 m3/m in volume distribution. This corroborates the least number of fine crystals at the considerably small size compared to nominal’s (0.00151 m3/m, 35 µm). Overall, the low nucleation and crystal growth rates strategy provides useful insights into designing temperature profiles during the linear cooling crystallization process, whereby achievable supersaturation levels in obtaining large crystals with fewer crystal fines are provided via simulation.

In order to provide theoretical guidance for sulfoaluminate cement as grouting material used for coal mines, the purpose of this paper is to trace the hydration process and study the hydration kinetics of sulfoaluminate cement. The influence of the water/cement ratio (W/C) on the hydration exothermic characteristics of sulfoaluminate cement was studied by TAM air hydration microcalorimeter, Raman spectrum and compressive strength test, respectively. The results show that the rapid hydration of sulfoaluminate cement can be divided into three hydration processes: acceleration period, deceleration period and stability period. With the increase of W/C, the maximum heat release rate of cement decreases, while the cumulative heat release increases. In addition, increasing W/C can affect the microstructure of the cement paste, increase the porosity and further decrease the strength. Meanwhile, the Krstulović–Dabić model was used to analyse the hydration kinetics of sulfoaluminate cement with different W/C. The results show that the hydration mechanism of sulfoaluminate cement is not affected by increasing W/C. The hydration kinetics process can include three stages: nucleation and growth mechanism, phase boundary reaction and diffusion reaction.

Early hydration characteristics and kinetics model of cement pastes containing internal curing materials with different absorption behaviors