Iskanje po repozitoriju

A+ | A- | | SLO | ENG

Povzetek: Belite-sulfoaluminate (BCSA) cements are low-carbon mineral binders, which require low energy consumption and allow the incorporation of various secondary raw materials in the clinker raw meal. In this study two types of unprocessed steel slags, coming from stainless steel production, were incorporated in the BCSA clinkers. The clinker phase composition, clinker reactivity, and the compressive strength of the cement were studied to evaluate the possible use of the slag in BCSA clinkers. The cement clinkers were synthesized by using natural raw materials, white titanogypsum, mill scale, as well as two different steel slags: (i) EAF S slag, which is a by-product of melting the recycled steel scrap in an electric arc furnace, and (ii) la dle slag as a by-product of the processes of secondary metallurgy, in various quantities. Raw mixtures with two different targeted phase compositions varying in belite, calcium sulfoaluminate and ferrite phases were sintered at 1250 °C. Clinker phases were determined by Rietveld quantitative phase analysis, while their distribution, morphology and incorporation of foreign ions in the phases were studied by SEM/EDS analysis. The clinker reactivity was determined by isothermal calorimetry. BCSA cements were prepared by adding titanogypsum. The compressive strength of the cement pastes was determined after 7 days of hydration. The presence of a predicted major clinker phases was confirmed by Rietveld analysis, however periclase was also detected. Microscopy revealed subhedral grains of belite and euhedral grains of calcium sulfoaluminate phases, while ferrite occurred as an interstitial phase. The results showed differences in the microstructure and reactivity of the clinker and cement, which can be attributed to varying amounts of ettringite due to different slag types
Ključne besede: belite-sulfoaluminate cement, cement clinker, steel slags, clinker microstructure, cement reactivity
Objavljeno v DiRROS: 19.01.2024; Ogledov: 184; Prenosov: 81
Celotno besedilo (18,89 MB)
Gradivo ima več datotek! Več...

Povzetek: The RILEM technical committee TC 247-DTA ‘Durability Testing of Alkali-Activated Materials’ conducted a round robin testing programme to determine the validity of various durability testing methods, originally developed for Portland cement based-concretes, for the assessment of the durability of alkali-activated concretes. The outcomes of the round robin tests evaluating sulfate resistance, alkali-silica reaction (ASR) and freeze–thaw resistance are presented in this contribution. Five different alkali-activated concretes, based on ground granulated blast furnace slag, fly ash, or metakaolin were investigated. The extent of sulfate damage to concretes based on slag or fly ash seems to be limited when exposed to an Na2SO4 solution. The mixture based on metakaolin showed an excessive, very early expansion, followed by a dimensionally stable period, which cannot be explained at present. In the slag-based concretes, MgSO4 caused more expansion and visual damage than Na2SO4; however, the expansion limits defined in the respective standards were not exceeded. Both the ASTM C1293 and RILEM AAR-3.1 test methods for the determination of ASR expansion appear to give essentially reliable identification of expansion caused by highly reactive aggregates. Alkali-activated materials in combination with an unreactive or potentially expansive aggregate were in no case seen to cause larger expansions; only the aggregates of known very high reactivity were seen to be problematic. The results of freeze–thaw testing (with/without deicing salts) of alkali-activated concretes suggest an important influence of the curing conditions and experimental conditions on the test outcomes, which need to be understood before the tests can be reliably applied and interpreted.
Ključne besede: alkali-activated materials/geopolymers, sulphate resistance, alkali silica reactivity, freeze-thaw resistance, Rilem TC
Objavljeno v DiRROS: 17.08.2023; Ogledov: 221; Prenosov: 161
Celotno besedilo (560,56 KB)
Gradivo ima več datotek! Več...

Povzetek: Alkali-activated materials (AAMs) represent a promising alternative to conventional building materials and ceramics. Being produced in large amounts as aluminosilicate-rich secondary products, such as slags, they can be utilized for the formulation of AAMs. Slags are partially crystalline metallurgical residues produced during the high temperature separation of metallic and non-metallic materials in the steelmaking processes. In the present study, the electric arc furnace carbon or stainless steel slag (EAF) and secondary metallurgical slag such as ladle furnace basic slag (LS) were used as precursors in an alkali-activation process. EAF slag, with its amorphous fraction of about 56%, presented higher contents of soluble Si and Al species with respect to ladle slag R (35%). However, both are suitable to produce AAM. The leaching behavior shows that all the release values are below the regulation limit. All the bivalent ions (Ba, Cd, Cu, Ni, Pb, and Zn) are well immobilized in a geopolymeric matrix, while amphoteric elements, such as As and Cr, show a slight increase of release with respect to the corresponding slag in alkaline and aqueous environments. In particular, for Sb and As of AAM, release still remains below the regulation limits, while Mo presents an increase of leaching values that slightly exceeds the limit for landfill non-dangerous waste.
Ključne besede: slag, aluminosilicate materials, chemical reactivity, cold consolidation, alkali activation, leaching test, open access
Objavljeno v DiRROS: 22.05.2023; Ogledov: 327; Prenosov: 169
Celotno besedilo (4,49 MB)
Gradivo ima več datotek! Več...

Povzetek: The results of phase 1 of an interlaboratory test, coordinated by the RILEM TC 267-TRM “Tests for Reactivity of Supplementary Cementitious Materials” showed that the R3 (rapid, relevant, reliable) test method, by measurement of heat release or bound water, provided the most reliable and relevant determination of the chemical reactivity of supplementary cementitious materials (SCMs), compared to other test methods. The phase 2 work, described in this paper aimed to improve the robustness of the test procedure and to develop precision statements for the consolidated test procedure. The effect of the pre-mixing and mixing conditions, and the impact of the mix design on the test method robustness were assessed and fixed for optimal conditions to carry out the R3 heat release test. The effect of the drying step was evaluated to define the R3 bound water test procedure in more detail. Finally, the robustness of the consolidated final test methods was determined by an interlaboratory study to define the precision statements.
Ključne besede: supplementary cementitious materials, reactivity test, bound water
Objavljeno v DiRROS: 26.04.2023; Ogledov: 304; Prenosov: 118
Celotno besedilo (1,07 MB)
Gradivo ima več datotek! Več...

Povzetek: Background. The European baseline series (EBS) of contact allergens is subject to change. An allergen is considered for inclusion when routine patch testing of patients with suspected contact dermatitis results in ≥ 0.5% prevalence rate. Objectives. We aimed to determine the frequency of sensitizations to 30 EBS allergens and 10 locally added allergens. Additionally, we assessed the strength and evolution of reactions to all tested allergens and co-reactivity of additional allergens. Methods. Patch testing with our baseline series of 40 allergens was done in 748 consecutive adults. Tests were applied to the upper back and removed by patients after 48 hours. Readings were done on day 3 (D3) and D6 or D7 (D6/7). Positive reactions fulfilled the criteria of at least one plus (+) reaction. Retrospective analysis was done. Results. Eight allergens not listed in the EBS had ≥ 0.5% prevalence rate (i.e., cocamidopropyl betaine, thiomersal, disperse blue mix 106/124, 2-bromo-2-nitropropane-1,3-diol, diazolidinyl urea, propylene glycol, Compositae mix II, and dexamethasone-21-phosphate), and 16.6% of positive reactions would have been missed without D6/7 readings. Conclusion. We propose further studies to evaluate whether cocamidopropyl betaine, disperse blue mix 106/124, 2-bromo-2-nitropropane-1,3-diol, diazolidinyl urea, and Compositae mix II need to be added to the EBS.
Ključne besede: allergy and immunology -- diagnosis, hypersensitivity -- diagnosis, skin tests, clinical epidemiology, baseline series, contact sensitization, patch tests, simultaneous reactivity
Objavljeno v DiRROS: 24.06.2022; Ogledov: 561; Prenosov: 206
Povezava na datoteko