| 1. |
- Adolfsson, Daniel, et al.
(författare)
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Hydraulic properties of sulphoaluminate belite cement based on steelmaking slags
- 2007
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Ingår i: Advances in Cement Research. - : Thomas Telford Ltd.. - 0951-7197 .- 1751-7605. ; 19:3, s. 133-138
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Adolfsson, Daniel, et al.
(författare)
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Steelmaking slags as raw material for sulphoaluminate belite cement
- 2007
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Ingår i: Advances in Cement Research. - : Thomas Telford Ltd.. - 0951-7197 .- 1751-7605. ; 19:4, s. 147-156
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Tidskriftsartikel (refereegranskat)abstract
- 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 degrees C in an air atmosphere.
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| 3. |
- Aguirre Castillo, José, et al.
(författare)
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Phase evolution and burnability of cement raw meal
- 2023
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Ingår i: Advances in Cement Research. - : ICE publishing. - 0951-7197 .- 1751-7605. ; 35:12, s. 577-587
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Tidskriftsartikel (refereegranskat)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.
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| 4. |
- Cwirzen, A., et al.
(författare)
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Properties of high yield synthesised carbon nano fibres/portland cement composite
- 2009
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Ingår i: Advances in Cement Research. - : Thomas Telford Ltd.. - 0951-7197 .- 1751-7605. ; 21:4, s. 141-146
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Tidskriftsartikel (refereegranskat)abstract
- The compressive strength and electrical resistivity of hardened pastes produced either from nanomodified Portland sulfate-resistant cement (CHH) or a mixture of nanomodified and pristine sulfate-resistant cements were determined. The nanomodification included grow carbon nanotubes (CNTs) and carbon nanofibres (CNFs) on the cement particles. Pastes having a water-to-binder ratio of 0-5 were produced. The test results revealed that partial replacement of sulfate-resistant cement by CHH cement decreased the electrical resistivity of the 28 day old specimens but worsened the mechanical properties. The lower compressive strength was attributed to a lower degree of hydration of the CHH cement. The addition of a mixture of surfactants enabled the production of specimens consisting entirely of CHH cement. The hardened material obtained was characterised by a nearly doubled compressive strength in comparison with the reference specimens made from pristine sulfate-resistant cement. This was attributed to a high degree of hydration as well as reinforcing action of the CNTs and CNFs. The electrical resistivity was lowered by one order of magnitude classifying this material as a semiconductor.
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| 5. |
- Cwirzen, A., et al.
(författare)
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Surface decoration of carbon nanotubes and mechanical properties of cement/carbon nanotube composites
- 2008
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Ingår i: Advances in Cement Research. - : Thomas Telford Ltd.. - 0951-7197 .- 1751-7605. ; 20:2, s. 65-73
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Tidskriftsartikel (refereegranskat)abstract
- The present study investigated the effects of the method of surface decoration on the wetability of multi-walled carbon nanotubes (MWCNTs) and the mechanical properties of the cement paste incorporating these dispersions. The results showed that stable and homogenous dispersions of MWCNTs in water can be obtained by using surface functionalisation combined with decoration using polyacrylic acid polymers. The cement paste specimens incorporating these dispersions revealed good workability and an increase in the compressive strength of nearly 50% even with only a small addition of the MWCNTs, namely 0-045-0-15% of the cement weight. These results indicate the existence of chemical bonds between the OH groups of the functionalised MWCNTs and probably the C-S-H phase of the cement matrix, which enhanced the transfer of stresses. A second method that was studied included decoration of MWCNTs with polyacrylic acid polymers and gum Arabic. These dispersions appeared to be homogeneous only for approximately 2 h after which a progressive sedimentation occurred. Good workability was found for the cement pastes produced with all of the dispersions; the only significant difference being the slower hydration of the cement incorporating gum Arabic. The mechanical properties of the cement pastes incorporating MWCNTs treated with polyacrylic polymers were unchanged.
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| 6. |
- Cwirzen, A.
(författare)
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The effect of the heat-treatment regime on the properties of reactive powder concrete
- 2007
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Ingår i: Advances in Cement Research. - : Thomas Telford Ltd.. - 0951-7197 .- 1751-7605. ; 19:1, s. 25-33
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the curing regime on the mechanical properties and microstructure of ultra-high-strength mortar was studied. Nine different curing procedures were applied in which the start and duration of the heat treatment were varied. The studied mortars had a water-to-binder ratio of 0·17 and additions of amorphous silica fume and fine quartz filler. The microstructure and microchemistry were investigated by electron scanning microscopy and mercury intrusion porosimetry. The results revealed that longer heating times increased the degree of hydration, refined the microstructure and resulted in higher ultimate compressive strength, Very late and very early application of the heat treatment caused a lower degree of hydration and a smaller long-term increase of compressive strength. The scanning electron microscopy investigation revealed the formation of one hydration rim around anhydrous cement particles and the presence of a hollow shell in all investigated specimens. © 2007 Thomas Telford Ltd.
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| 7. |
- Dubina, Elina, et al.
(författare)
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Impact of environmental moisture on C(3)A polymorphs in the absence and presence of CaSO4 center dot 0.5 H2O
- 2014
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Ingår i: Advances in Cement Research. - : Thomas Telford Ltd.. - 0951-7197 .- 1751-7605. ; 26:1, s. 29-40
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Tidskriftsartikel (refereegranskat)abstract
- The phenomenon of water vapour sorption by anhydrous C(3)A polymorphs both in the absence and in the presence of CaSO4 center dot 0.5 H2O was studied utilising dynamic and static sorption methods. It was found that orthorhombic C(3)A starts to sorb water at 55% relative humidity (RH) and cubic C(3)A at 80% RH. Also, C(3)Ao sorbs a higher amount of water which is predominantly physically bound, whereas C3Ac preferentially interacts with water by chemical reaction. In the presence of calcium sulfate hemihydrate, ettringite was observed as the predominant pre-hydration product for both C(3)A modifications: that is, ion transport had occurred between C(3)A and sulfate. Environmental scanning electron microscopic imaging revealed that in a moist atmosphere, a liquid water film condenses on the surface of the phases as a consequence of capillary condensation between the particles. C(3)A and sulfate can then dissolve and react with each other. Seemingly, pre-hydration is mainly facilitated through capillary condensation and less through surface interaction with gaseous water molecules.
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| 8. |
- Ghasemi, Yahya, 1982-, et al.
(författare)
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A theoretical study on optimal packing in mortar and paste
- 2019
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Ingår i: Advances in Cement Research. - 0951-7197 .- 1751-7605.
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Tidskriftsartikel (refereegranskat)abstract
- Packing density of particles is regarded as a key factor affecting workability of cementitious mixtures. While the value can be easily measured, and several models exist for estimating the parameter, no generally accepted definition exist for the optimal packing. Current study aims at exploring the concept of optimal packing in mortars and paste using particle packing and excess water layer theories. A semiempirical method is used for calculating water demand of mixtures based on their specific surface area. The approach allows for estimating optimal packing considering water demand and water to cement ratio of mixtures in addition to packing density.
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| 9. |
- Hökfors, Bodil, 1971-, et al.
(författare)
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Modelling the cement process and cement clinker quality
- 2014
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Ingår i: Advances in Cement Research. - : ICE Publishing. - 0951-7197 .- 1751-7605. ; 26:6, s. 311-318
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a recently developed simulation model that can be used as a tool for evaluating sustainable development measures for cement and lime production processes. Examples of such measures are introducing new combustion technologies such as oxy-fuel combustion, using biomass fuel and using alternative materials in the raw material feed. One major issue when introducing process changes is the need to maintain product quality. In some ways, oxygen-enriched air combustion resembles oxy-fuel combustion. The model results were validated and found to be consistent with full-scale operational data for normal running conditions and for a full-scale test with oxygenenriched air. The model shows, for example, that with an additional 1500 m3/h of oxygen, fuel addition at the calciners can increase up to 108% and the raw material feed rate can increase up to 116% for a process with a raw meal feed of 335.5 t/h.
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| 10. |
- Hökfors, Bodil, 1971-, et al.
(författare)
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On the phase chemistry of Portland cement clinker
- 2015
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Ingår i: Advances in Cement Research. - : Thomas Telford. - 0951-7197 .- 1751-7605. ; 27:1, s. 50-60
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes the formation of a phosphorous belite solid solution and its impact on alite formation. A sub-solidus phase relation for the ternary system silicon dioxide–calcium oxide–phosphorus pentoxide (SiO2–CaO–P2O5) is reported. The ternary system is based on Rietveld refinements of X-ray diffraction patterns from experimental tests. The overall picture is based on known phase diagrams, relevant Rietveld refinements models, stoichiometric relationships as a function of increasing phosphorus pentoxide concentration and vacancy theories for solid solutions of phosphate belites. A tool is developed for predicting the chemistry of the product as well as the chemistry during heating when producing Portland cement clinker. A thermodynamic database for phase chemistry calculations of clinkering reactions has been created and evaluated. Suitable compounds and solution species have been selected from the thermochemical database included in FactSage software. Some solution compositions have been uniquely designed to allow for the proper prediction of the cement clinker chemistry. The calculated results from the developed database for heating raw materials in cement clinker production and cooling of the product are presented in this paper. The calculated results provide a good prediction of the phases and quantities formed during heating and non-equilibrium cooling. The prediction of the amounts of alite, belite and aluminoferrite phases in the product according to the Scheil method is good. The temperature interval for the existence of all of the major phases is relevant. The thermodynamic data for a solution phase of alite with substituting ions of primarily magnesium oxide and phosphorus pentoxide would improve the predictability of the developed database.
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