From lime to silica and alumina: systematic modeling of cement clinkers using a general force-field

Abstract

Thirteen different cement-clinker crystalline phases present in the lime-silica-alumina system have been systematically modeled using a simple and general force field. This constitutes a new type of approach towards the study of lime-silica-alumina systems, where the simpler and more transferable Lennard-Jones potential was used instead of the more traditional Buckingham potential. The results were validated using experimental density and structural data. The elastic properties were also considered. Six amorphous phases (corresponding to calcium/silicon ratios corresponding to belite, rankinite, wollastonite and alumina-doped amorphous wollastonite with 5%, 10% and 15% alumina content) were also studied using molecular dynamics simulations. The obtained MD trajectories were used to characterize the different crystalline and amorphous phases in terms of the corresponding radial distribution functions, aggregate analyses and connectivity among silica groups. These studies allowed a direct comparison between the crystalline and amorphous phases and revealed how the structure of the silica network was modified in the amorphous materials or by the inclusion of other structural units such as alumina. The knowledge at an atomistic level of such modifications is paramount for the formulation of new cement-clinker phases.

Alternative Clinker Technologies for Reducing Carbon Emissions in Cement Industry: A Critical Review

“…The reason for that is the fact that there are significant modifications in the structure of the calcium-silicate crystalline phases as the C/S ratio decreases, from 3 (alite) to 1 (wollastonite). These changes are essentially related to the organization of the SiO x units in the crystals, as well as to the spatial distribution of the Ca atoms in the crystal network [ 27 ]. Whereas in alite and belite polymorphs, the [SiO 4 ] 4− groups are isolated and present some degree of disorder in the superstructure, in rankinite, the Si and O atoms are arranged in sorosilicate groups [Si 2 O 7 ] 6− , in which a central O connects with two SiO 3 units, whilst in wollastonite polymorphs, Si and O atoms are arranged in long parallel dreierkette-type chains of {[SiO3] 2− }n units and there is an increase in the number of the bridging oxygen atoms in comparison to rankinite [ 27 ].…”

“…These changes are essentially related to the organization of the SiO x units in the crystals, as well as to the spatial distribution of the Ca atoms in the crystal network [ 27 ]. Whereas in alite and belite polymorphs, the [SiO 4 ] 4− groups are isolated and present some degree of disorder in the superstructure, in rankinite, the Si and O atoms are arranged in sorosilicate groups [Si 2 O 7 ] 6− , in which a central O connects with two SiO 3 units, whilst in wollastonite polymorphs, Si and O atoms are arranged in long parallel dreierkette-type chains of {[SiO3] 2− }n units and there is an increase in the number of the bridging oxygen atoms in comparison to rankinite [ 27 ]. This structural shift among the four types of calcium silicate crystals (alite, belite, rankinite and wollastonite) can be summarized using the Q n terminology, that designates how a given silica tetrahedron is connected to another silica tetrahedron in a given crystal, as shown in Figure 2 : Q 0 (black), Q 1 (green), Q 2 (orange), Q 3 (blue) and Q 4 (yellow), depending on how many O-Si species are connected to the central silicon atom.…”

“… * Even though the raw material of Celitement ® are lime and quartz, their use was conducted under laboratory conditions, with high purity raw materials [ 56 , 57 ]. ** Tests performed on pastes showed that the strength of the X-Clinker, compared with OPC, is competitive at all ages [ 27 ]. However, tests performed on mortars showed that, for the X-Clinker to be competitive at early ages (2 days), a cure at temperatures around 35 °C may be required [ 99 ].…”

Analysis of relationship between optical properties of minerals and portland cement whiteness

“…Свойства материалов, в том числе оптические, определяются их структурой [2][3][4], а в случае портуландцемента, главным образом -составом и структумрой клинкера, формирующимся при обжиге сырьевой смеси [5][6][7][8][9][10]. В этой связи развитие научных представлений о технологии цемента связано с анализом фазогвого состава клинкера, формирующегося при обжиге вследствие физико-химических процессов взаимодей-ствия оксидов -продуктов разрушения решеток породообразующих минералов исходного сырья [11][12][13][14]. При этом значительное внимание уделяется исследованию условий кристаллообразования кальциевых силикатов типа алита 3CaO .…”

The Influence of Mg-Impurities in Raw Materials on the Synthesis of Rankinite Clinker and the Strength of Mortar Hardening in CO2 Environment

“…Natural rankinite only slightly varies in composition from pure Ca 3 Si 2 O 7 because ions of other metals hardly ever incorporate into its crystal lattice structure. Rankinite belongs to the silicates of the sorosilicate group (Si 2 O 7 ), in which a central O connects two SiO 3 units [ 3 ]. The interatomic distances between Ca and O show a range of values from 2.25 to 2.90 Å, while the angles O-Ca-O are between 60 and 87 degrees [ 4 ].…”