New Insights into the Dissolution Kinetics of Alite Powder and the Effects of Organic Toughening Materials

Alite dissolution plays a crucial role in cement hydration. However, quantitative investigations into alite powder dissolution are limited, especially regarding the influence of chemical admixtures. This study investigates the impact of particle size, temperature, saturation level, and mixing speed on alite powder dissolution rate, considering the real-time evolution of specific surface area during the alite powder dissolution process. Furthermore, the study delves into the influence of two organic toughening agents, chitosan oligosaccharide (COS) and anionic/non-ionic polyester-based polyurethane (PU), on the kinetics of alite powder dissolution. The results demonstrate a specific-surface-area change formula during alite powder dissolution: SS0=0.348e1-m/m0/0.085+0.651. Notably, the temperature and saturation level significantly affect dissolution rates, whereas the effect of particle size is more complicated. COS shows dosage-dependent effects on alite dissolution, acting through both its acidic nature and surface coverage. On the other hand, PU inhibits alite dissolution by blocking the active sites of alite through electrostatic adsorption, which is particularly evident at high temperatures.

Influence of alumina ratio on reactions at the surface of alite crystals during cooling

Microstructural features of industrial Portland cement clinker samples are presented to illustrate the influence of the clinker melt chemistry on the reactions taking place on the surfaces of alite crystals during cooling at high temperatures. While clinker melts rich in Al₂ O₃ are usually undersaturated with respect to CaO, leading to corrosion of alite crystals and formation of secondary belite, clinker melts rich in Fe₂ O₃ are oversaturated with respect to CaO. This leads to a final growth step of alite during cooling, as long as the clinker temperature is still in the stability field of alite (>1250°C). In the first case, the microstructural features of the alite surface permits conclusions on the length of the precooling zone in the rotary kiln, which is closely connected to the flame shape. In the latter case, such conclusions cannot be drawn.

Combining Raman Spectroscopy, DFT Calculations, and Atomic Force Microscopy in the Study of Clinker Materials

Raman spectroscopy and Raman mapping analysis, combined with density functional theory calculations were applied to the problem of differentiating similar clinker materials such as alite and belite. The Portland cement clinker 217 (further: clinker) was analysed using colocalised Raman mapping and atomic force microscopy mapping, which provided both spatial and chemical information simultaneously. The main constituents found in the clinker were alite, belite, portlandite, amorphous calcium carbonate, and gypsum. Since phonon bands of alite and belite greatly overlap, and their distinction is important for the hydration process during cement setting, we provided the calculated phonon density of states for alite Ca3SiO5 (Pc structure) and belite Ca2SiO4 (β P21/n structure) here for the first time. Both calculated phonon densities have similar distribution of phonon modes, with a gap between 560 and 810 cm-1. A comparison of the calculated phonon frequencies for Ca3SiO5 and Ca2SiO4 shows that the lowest calculated phonon frequency of β-Ca2SiO4 lies at 102 cm-1, while for Pc alite the lowest phonon frequency is predicted at 27 cm-1. Low frequency Raman spectroscopy could therefore be used for a clearer distinction of these two species in a clinker material.

Development of Crystallinity of Triclinic Polymorph of Tricalcium Silicate

Tricalcium silicate phase is one of the main components of modern Portland cements. One of the major industrial challenges in the field of cement production is mapping the influence of individual clinker minerals and their polymorphs on the properties of industrially produced clinkers. The primary goal of this work is to improve the fundamental knowledge of understanding the process of alite formation and development from a crystallographic point of view. This study focuses on the observation of the crystallization process of triclinic alite during the firing process, which to date has not been thoroughly described. The effects of a wide range of temperatures and sintering periods on crystallinity were assessed on samples fired in platinum crucibles in a laboratory furnace. X-ray analysis-together with calculation of crystallinity using Scherrer's equation-was used for observing the crystallite size changes of T1 alite polymorph. According to the acquired results, among the most technologically and economically advantageous regimes of production of a high-quality triclinic alite is the temperature of 1450 °C and sintering time of two hours. The most significant changes in the crystallite size occurred within the first hour of sintering for the whole investigated temperature range.

Reactivity of Different Crystalline Surfaces of C3S During Early Hydration by the Atomistic Approach

Early hydration of tricalcium silicate (C₃S) has received great attention over the years due to the increased use of composite cement with a reduced number of clinker phases, especially the addition of what should be very reactive C₃S to guarantee early strength. Although many mechanisms have been proposed, the dissolution of polygonal C₃S at the material interface is not yet fully understood. Over the last decade, computational methods have been developed to describe the reaction in the cementitious system. This paper proposes an atomistic insight into the early hydration and the dissolution mechanism of calcium from different crystalline planes of C₃S using reactive force field (ReaxFF) combined with metadynamics (metaD). The reactivity and thermodynamic stability of different crystal planes were calculated from the dissolution profile of calcium during hydration at 298 K. The simulation results, clearly describe the higher reactivity of (01¯1¯), (011), (100), and (1¯00) surfaces of C₃S due to the strong interaction with the water, whereas, the dissolution profile explains the lower reactivity of (1¯1¯0), (110), (01¯0) and the effect of water tessellation on the (001), (010) planes.