| 1. |
- Aguirre Castillo, José, et al.
(author)
-
Phase evolution and burnability of cement raw meal
- 2023
-
In: Advances in Cement Research. - : ICE publishing. - 0951-7197 .- 1751-7605. ; 35:12, s. 577-587
-
Journal article (peer-reviewed)abstract
- The use of high-temperature X-ray diffraction (HT-XRD) to study the mass transfer of raw meal constituents towards forming clinker phases and the occurrence of free lime (calcium oxide), also known as burnability, was assessed. A measuring strategy with temperature ranging from 1000°C to 1450°C was developed and compared with a conventional burnability method. The free lime determined by the methods showed that HT-XRD produced good results for the evaluation of burnability. In addition, HT-XRD revealed the formation of intermediate phases, providing insight into early reactions in a cement kiln. The particle size of quartz was found to affect crystal expansion of the phase at a high temperature, subsequently affecting the formation of silica polymorphs. The different raw meals used in this study also indicate that the formation of different silica polymorphs affects the formation of C2S. The lack of knowledge regarding the influence of β-quartz on the reduction of free lime is highlighted.
|
|
| 2. |
- Kothari, Ankit, et al.
(author)
-
Partial replacement of OPC with CSA cements – effects on hydration, fresh-, hardened-properties
- 2023
-
In: Advances in Cement Research. - : ICE Publishing. - 0951-7197 .- 1751-7605. ; 35:5, s. 207-224
-
Journal article (peer-reviewed)abstract
- The effects of a partial replacement of Ordinary Portland cement (OPC) with three types of calcium sulfoaluminate (CSA) cements (40 wt% and 20 wt%) were investigated. The obtained results were generally in agreement with previously published data but with few interesting exceptions. Setting times were shortened due to the formation of ettringite. The maximum hydration temperature increased for concretes containing 40 wt% of CSA but decreased when 20 wt% replacement was used. The decrease was related to the deficiency of the available sulfates, which limited the formation of ettringite. The presence of extra anhydrite and calcium oxide was associated to the delayed establishment of the second temperature peak in contrast to OPC-based concretes. Their surplus delayed calcium aluminate and belite reactions, and triggered renewed formation of ettringite, C-S-H and portlandite. Effects of aluminum hydroxide were also indicated as possibly important, although not proved experimentally in this research. The slightly lower compressive strength measured for mixes containing 40 wt% of CSA were linked with more formed ettringite. The same factor was indicated as the key to the reduction of the total shrinkage in mixes containing 40 wt% of CSA and increased for the lower CSA replacement level. In that case, the insufficient amount of formed ettringite caused too small expansion, which could not efficiently mitigate or compensate the developed shrinkage.
|
|
| 3. |
|
|
| 4. |
- Viggh, Erik, et al.
(author)
-
Early formation of belite in cement clinker raw materials with slag
- 2021
-
In: Advances in Cement Research. - : ICE Publishing. - 0951-7197 .- 1751-7605. ; 33:6, s. 249-256
-
Journal article (peer-reviewed)abstract
- Analytical methods for characterising cement raw meal during heating in different atmospheres were investigated. The effect of replacing limestone with 10 wt% slag on the formation of incipient belite and precursors of the clinker liquid in the temperature range 600–1050°C was quantified using thermogravimetry, X-ray diffraction and equilibrium calculations. The results showed that when calculating the lime saturation factor, slags were favoured to sand, resulting in lower amounts of quartz and C2S in the samples containing slag than the reference sample. This suggests that silicon dioxide in slag minerals did not react in this temperature range. The multi-component equilibrium results supported the phase formation sequence established. Allowing for the possible kinetic influences the potential solids solutions offered with the software was a valuable asset. The results showed that the effect of using slags to reduce the carbonate and sand content in a raw meal on potential amounts of incipient C2S was negative. At present, more detailed knowledge is needed regarding how blast-furnace slag and basic oxygen furnace slag contribute to the formation of intermediary compounds such as incipient C2S, C3A, C2F and C4AF in the solid phase at temperatures over 1050°C and affect the formation of C3S.
|
|
| 5. |
- Wen, Rongjia, et al.
(author)
-
Molecular dynamics study on coupled ion transport in aluminium-doped cement-based materials: Effect of concentration
- 2023
-
In: Advances in Cement Research. - : ICE Publishing. - 0951-7197 .- 1751-7605. ; 35:2, s. 81-95
-
Journal article (peer-reviewed)abstract
- The mutual inhibition effect of transport of sulphate and chloride in concrete specimen was determined in a macroscopic experiment. Higher concentration of sulphate has a better inhibition effect on chloride transport and the opposite is also true. In this paper, molecular dynamics (MD) simulation was performed to explore the effect of concentration (0, 0.5, 1.0 mol/L) on the transport of mixed solutions (NaCl and Na2SO4) in the main hydration products of aluminium-doped cement-based materials (i.e., calcium-aluminium-silicate-hydrate (C-A-S-H) gel). Sulphate was found to promote the aggregation of other ions to form ion clusters, which can reduce the effective width of the channel entrance and create a “necking” effect, thus reducing the overall transport rate of the solution. With the increase of NaCl concentration, sulphate ions in the mixed solution can adsorb more Na+ and Cl+ ions, and then form larger ion clusters to block the nanopores. Moreover, with increasing Na2SO4 concentration, higher amount of sulphate ions existing in the solution makes it possible to form more ion clusters. The results can provide a reasonable nanoscale explanation for macroscopic experiment.
|
|
