Sulphoaluminate Belite Cement Research Articles

The influence of variable gypsum and water content on the strength and hydration of a belite-calcium sulphoaluminate cement

ABSTRACTThe relative impact and interaction of two components, gypsum and water, in high ye’elimite containing calcium sulphoaluminate-belite cement pastes at an age of 7 days was studied to find the optimum conditions for compressive strength. Using statistical analysis of 149 compressive strength results having a range of water and gypsum contents, the statistical significance of the variables was investigated. X-ray diffraction analysis demonstrated the different hydration processes occurring within samples based on water and gypsum contents, while mercury intrusion porosimetry comparison confirmed the importance of pore structure towards determining ultimate paste strength. Thermodynamic modelling was also used to contribute to the understanding of the microstructural development. The compressive strengths of cement pastes with varying gypsum and water content were shown to be influenced by both factors, with a non-linear dependence on gypsum content observed.

Characteristics of cement pastes containing sulphoaluminate and belite prepared from nano-materials

The sulphoaluminate phase C4A3S¯ as well as β-C2S represent an important factor for the preparation of rapid hardened sulphoaluminate–belite cement. The hydration of C4A3S¯ forms ettringite and monosulphate hydrates in addition to the liberation of aluminium hydroxide. The hydration rate of belite is much slower than that of C4A3S¯, but becomes significant at later ages. Two mixes containing sulphoaluminate (C4A3S¯) and monosulphate mix (C4A3S¯, with 8CS¯+6C) in addition to belite (β-C2S) were synthesized from nano-materials after firing at 1250°C. The hydration characteristics of 10% C4A3S¯ or 10% C4AS¯ in addition to 10% β-C2S on the expanse of OPC were studied. The results revealed that the substitution of OPC with sulphoaluminate mixes as well as belite shortens the setting times. The rate of hydration of OPC with sulphoaluminate–belite phases is increased from the formation of more sulphoaluminate hydrates and the consumption of protlandite. Also, these mixes give higher chemically combined water contents. The monosulphate hydrate is deposited in some of open pores in the dormant period of hydration that tends to increase the compressive strength of sulphoaluminate–belite cement pastes.

Steelmaking slags as raw material for sulphoaluminate belite cement

In the present study, slags from the steelmaking industry are described and considered as a potential raw material within the field of sulphoaluminate belite cement. The objective of the study was to investigate the possibility of using a substantial amount of steelmaking slags as raw meal in the manufacture of a sulphobelitic clinker. A further aim was to compare the influence of different slags in relation to the formation of sulphoaluminate and the other clinker phases required. The behaviour of high temperature reactions was investigated by using thermogravimetric analysis coupled with a quadrupole mass spectrometer. Mineralogical observations were carried out through X-ray powder diffraction, and scanning electron microscopy. Three different mixtures and a single ladle slag were prepared using modified Bogue calculations, which are characterised by the assessment of a potential phase composition in order to produce belite-rich cement activated with sulphoaluminate. The results so far prove that steelmaking slags have the potential to be used as raw material, since sulphoaluminate along with polymorphs of dicalcium silicate and ferrite phases were detected after firing at 1200°C in an air atmosphere.

Hydraulic properties of sulphoaluminate belite cement based on steelmaking slags

Based on modified Bogue calculations, steelmaking slags were combined in order to produce a belite-rich clinker activated with sulphoaluminate. The experiments were conducted on two different mixtures based on steelmaking slags together with additives, namely MixA and MixB. The objective of the present study was to investigate the hydraulic properties of the specimens, using conduction calorimetry, X-ray diffraction and differential scanning calorimetry, and also to measure the mechanical strength of the specimens when hydrated for 2 and 28 days. The compressive strength was satisfactory in relation to the estimated compositions. Both mixtures behaved the same with regard to heat development as well as the amount of ettringite formed during the first 24 h of the hydration.

Microwave sintering of sulphoaluminate cement with utility wastes

Class C flyash, baghouse dust and scrubber sludge have been successfully used for sulphoaluminate belite (SAB) cement preparation by microwave sintering. For proper raw mix proportioning, the modulus of gehlenite (C 2AS) 1 1 Conventional cement notation is used here, i.e. C=CaO, S=SiO 2, etc. formation (MG) and modulus of calcium sulphosilicate (2C 2S·C S̄) formation (MS) were put forward. The results indicated that, when MG and MS were 0.90–1.10, C 2AS and 2C 2S·C S̄ could be chemically eliminated when microwave-sintered at low temperature; with the 1150°C/10 min sintering condition, microwave-prepared sample had developed into SAB cement clinker with the main phases of C 4A 3S and β-C 2S, while a conventionally fired one had not; with proper gypsum addition, microwave-prepared SAB cement developed strength similar to Type-I cement in 28-day hydration.

Resistance to freezing and thawing of mortar specimens made from sulphoaluminate—belite cement

Resistance to freezing and thawing of mortar specimens made from sulphoaluminate-belite cement (M-SAB) is compared with that of mortars made from portland cement (M-PC). The results suggest that larger median radius of the pores and total porosity of M-SAB compared to those of M-PC are primarily caused by the rapid setting of the SAB cement. The ‘coarsening’ of pore structure of mortar specimens under action of freezing and thawing is proved by the increase in the macropores portion, median pore radius, and total porosity values. This process is more intense in M-SAB. The effect of the frost attack is confirmed by lower compressive strength and dynamic modulus of elasticity on the one hand and higher absorption capacity, expansion, and crack propagation of M-SAB compared with those of M-PC on the other hand. Besides the decreased frost resistance of M-SAB as compared with that of M-PC, unsatisfactory passivation of steel in M-SAB was found. The reason of this fact is the pH value decrease to less than 11.5 of the M-SAB extract

Effects of sulphate, calcium and aluminum ions upon the hydration of sulphoaluminate belite cement

In the model sulphoaluminate belite cement, the process of hydration is governed by the diffusion and transport phenomena of the main ionic species. The sulphate components and combined sulphate and aluminium ions, exert an accelerating effect upon the kinetics of sulphoaluminate belite cement hydration. Aluminium and calcium ions delay the hydration by creating a retarding layer which can be considered a co-precipitate of aluminium and calcium hydroxides. This is revealed in the calorimetric curves by the duration of induction period and also by the intensities of the main peaks. The appearance of small additional peaks characterizes the formation of 'primary ettringite', due to the presence of sulphate ions in aqueous solution. The intensities of these peaks depend on the ion concentration too.

Application of conduction calorimetry for study of the reactivity of C2S in the system C2S-C4A3¯S-C¯S-H

A conduction calorimeter was used to determine the effect of the ignition temperature on the hydration reactivity of C2S in the system C2S-C4A3¯S-C¯S relevant to sulphoaluminate belite cement. The results thus obtained showed that the kinetics and mechanism of hydration of the system C2S-C4A3¯S-C¯S are influenced by the temperature of C2S synthesis. The hydration reactivity of C2S increases with increasing temperature of ignition.

Preparation of sulphoaluminate belite cement from fly ash

Sulphoaluminate belite cements containing the phases C 2S, C 4A 3 S , C 4AF, C S were synthesised from limestone, fly ash and gypsum at 1200 °C. The correspondence between the predicted phase composition and real phase composition were checked. The influence of quantities of different phases in the hydration behaviour and strength development were verified. Results show that an optimum proportion of phase quantities help in high strenght development in early age. These cements fulfill all the requirement of Portland cement and have very high early strength. Porosity measurements show that the total pore volume in early period is comparatively less than that of Ordinary Portland Cement. Thus these cements can be usable for special purposes.

Relationship between raw mixture and mineralogical composition of sulphoaluminate belite clinkers in the system CaOSiO 2Al 2O 3Fe 2O 3SO 3

The mineralogical (phase) composition of sulphoaluminate belite cement clinkers was calculated using phase compatibility data of the relevant portion of the five component oxide system CaOSiO 2Al 2O 3Fe 2O 3SO 3 and was plotted in the plane of three component raw mix. In result a phase fields map (PFM) was obtained showing equilibrium changes in phase composition of clinkers on changes in the raw mixture composition.

Phase compatibility in the system CaOSiO 2Al 2O 3Fe 2O 3SO 3 referred to sulphoaluminate belite cement clinker

The individual subsystems of the basic five component oxide system CaOSiO 2Al 2O 3Fe 2O 3SO 3 are analysed for their subsolidus phase relationship. The study is confined to the portion of the system in which C 2S, the key mineralogical component of belite clinker is present. As a result eighteen equilibrium phase assemblages, each containing five phases relevant to belite clinkers were identified.

Influence of particle sizes of individual minerals on the hydration processes in the system C 2S-C 4A 3[formula omitted]-C [formula omitted

The influence of particle size distribution of individual minerals of a modelled sulphoaluminate belite cement clinker containing the phases C 2S, C 4A 3 S and C S on the hydration kinetics was studied by X-ray diffraction analysis, and differential calorimetry. The surface area of the phases controls the concentrations of different ions in the non-equilibrium liquid phase and by this way determines the mechanism of formation of hydrated products in the system. Results show that the particle sizes of the anhydrite influence significantly on the kinetics and mechanism of precipitation of hydrates in the initial period. Whereas in the presence of fine particles of C 2S leads to the retardation of reaction processes.

Hydration behaviour of sulphoaluminate belite cement in the presence op various calcium sulphates

The Sulphoaluminate belite cement clinker with the main phases C 2S, C 4A 3S̄, C 4AF, was synthesised from limestone, fly ash and gypsum. Its hydration was studied in the presence of different admixed calcium sulphates (anhydrites calcined at 750°C, 1200°C, hemidrate, gypsum) by differential calorimetry at room temperature. Results show that predominantly the solubility and to lesser extent the content of calcium sulphate influences the early period-of hydration process.