Filtern
Erscheinungsjahr
Dokumenttyp
Sprache
- Englisch (38)
- Deutsch (3)
- Mehrsprachig (1)
Referierte Publikation
- ja (42) (entfernen)
Schlagworte
- Alkali-activated materials (16)
- Geopolymers (8)
- Concrete (7)
- Carbonation (4)
- Cement (4)
- Alkali-activation (3)
- Durability (3)
- Acid resistance (2)
- Acoustic emission (2)
- Africa (2)
- Alkali-activated slag (2)
- Blended cement (2)
- Brick clay (2)
- Calcined clay (2)
- Gas separation (2)
- Hybrid cements (2)
- MIC (2)
- Microbially induced corrosion (2)
- Microstructure (2)
- One-part formulation (2)
- One-part geopolymers (2)
- Pore structure (2)
- Rice husk ash (2)
- Silica (2)
- Sr isotopes (2)
- Steel corrosion (2)
- 27Al MAS NMR (1)
- 29Si MAS NMR (1)
- AFm phase (1)
- Accelerated testing (1)
- Alkali activated cement (1)
- Alkali activated materials (1)
- Alkali aggregate reaction (1)
- Alkali silica reaction (1)
- Aluminium hydroxide (1)
- Aluminosilicate inorganic polymers (1)
- Bio-based materials (1)
- Biogene Schwefelsäurekorrosion (1)
- Biogenic acid corrosion (1)
- Brandtest (1)
- Calcium aluminate cement (1)
- Cement membrane (1)
- Cement paste (D) (1)
- Ceramics (1)
- Chloride binding (1)
- Chloride penetration (1)
- Clean fuel (1)
- Coatings (1)
- Compressive strength (1)
- Corrosion (1)
- Cracking (1)
- Critical chloride content (1)
- Degree of reaction (1)
- Diffusion (C) (1)
- Dissolution (1)
- Drying (1)
- Education (1)
- Electrochemical methods (1)
- Feuerwiderstand (1)
- Fibre pull-out (1)
- Fire proofing (1)
- Fire protection (1)
- Fire resistance (1)
- Freeze-thaw attack (1)
- Geopolymerbeton (1)
- Heat exposure (1)
- Heat resistance (1)
- High-temperature resistance (1)
- High-temperature treatment (1)
- Hochtemperatureigenschaften (1)
- Hydration (1)
- Illite (1)
- Illitic clay (1)
- Inorganic membranes (1)
- Inorganic polymers (1)
- Instandsetzung (1)
- Intumescence (1)
- Iron speciation (1)
- Kaolinite (1)
- Laserbasierte Rautiefebestimmung (1)
- Layered double hydroxide (1)
- Leaching (1)
- Lithium aluminosilicates (1)
- Lunar regolith (1)
- Magnesium chloride (1)
- Mercury porosimetry (1)
- Mercury porosimetry (B) (1)
- Microstructure (B) (1)
- Mix-design (1)
- Monocarboaluminate (1)
- Nepheline (1)
- Nonferrous slag (1)
- Nuclear magnetic resonance (1)
- One-part mix (1)
- Permeability (1)
- Permeabilität (1)
- Physical properties (1)
- Porenstruktur (1)
- Porosity (1)
- Porous membrane (1)
- Portland clinker (1)
- Proficiency testing (1)
- Provenance (1)
- Provenancing (1)
- Quecksilberdruckporosimetrie (1)
- Raman spectroscopy (1)
- Rautiefe (1)
- Reaction products (1)
- Reaktive Brandschutzsysteme (1)
- Reinforcement corrosion (1)
- Research sub-Sahara (1)
- Round robin (1)
- Salt attack (1)
- Shear (1)
- Sintering (1)
- Softening temperature (1)
- Sol-gel (1)
- Solid-state NMR (1)
- Sorption isotherm (1)
- Spalling (1)
- Spannung-Dehnungs-Beziehung (1)
- Spectroscopy (1)
- Steel corrrosion (1)
- Steel fibres (1)
- Steel-concrete interface (1)
- Strength (1)
- Strätlingite (1)
- Sulfate attack (1)
- Sulfuric acid resistance (1)
- Supplementary cementitous materials (1)
- Temperature (1)
- Tensile strength (1)
- Testing (1)
- Thermal behavior (1)
- Thermodynamic modelling (1)
- Threshold radius (1)
- Tonerdezement (1)
- Transient thermal creep (1)
- Wastepaper sludge ash (1)
- X-ray absorption near-edge structure (1)
- X-ray absorption spectroscopy (1)
- Zeolite A (1)
- Zeolite Na-A (1)
- Zeolites (1)
Organisationseinheit der BAM
- 7 Bauwerkssicherheit (25)
- 7.4 Baustofftechnologie (25)
- 6 Materialchemie (5)
- 6.3 Strukturanalytik (5)
- 7.1 Baustoffe (3)
- 1 Analytische Chemie; Referenzmaterialien (2)
- 1.1 Anorganische Spurenanalytik (2)
- 7.6 Korrosion und Korrosionsschutz (2)
- 5 Werkstofftechnik (1)
- 5.4 Multimateriale Fertigungsprozesse (1)
Paper des Monats
- ja (2)
Diffusional gas transport of a H2/CO2 mixture versus N2 in the pore system of hardened cement pastes was studied at four temperatures up to 350 °C in a Wicke-Kallenbach cell. The pastes possessed separation factors αH2,CO2 from 1.42 to 3.43, i.e. the diffusion of hydrogen took place considerably faster than the diffusion of carbon dioxide. The separation factors depended on the threshold radii of the pastes, smaller threshold radii leading to higher separation factors. The Knudsen numbers of the controlling constrictions of the pore system and the temperature dependence of the effective diffusion coefficients of the gases show that gas transport in these constrictions takes place in the transient regime between Knudsen diffusion and bulk diffusion, smaller constriction widths leading to predominating Knudsen diffusion. It is therefore possible to use cement paste membranes to separate gas components of low molecular weight from higher weight components.
A silica residue from waste treatment of chlorosilane production was used together with solid sodium aluminate to test its applicability for the production of one-part geopolymers. The blend was activated with water and cured at 70 °C. The degree of reaction and strength were determined after 1, 3, and 7 days. The reaction products were analyzed by XRD and SEM/EDX. Until the third day of curing the degree of reaction of the residue reached 51 % and the strength was 8.9 MPa. The reaction product was identified as geopolymer containing zeolite A. Thus, the results confirmed that the residue may be used in the production of geopolymers. However, after 3 days of curing no further progress of reaction was observed and the strength slightly decreased, which was attributed to changes in the structure of the geopolymeric gel. It was further observed that even harsh vacuum drying left some water (presumably zeolitic water and surface hydroxyl groups) in the geopolymer.
The conversion of hydrated calcium aluminate cement (CAC) leads to an increase of its porosity which results in lower strength and higher permeability. Due to particular failures in the past, caused by conversion of CAC concretes, their use is sometimes considered to be not reliable. To evaluate the durability of converted CAC, pastes of two CACs were prepared at low w/c ratios (0.25 and 0.35), heated to 105 °C for 15 days and investigated by means of helium pycnometry, mercury porosimetry and nitrogen adsorption as well as by air permeability measurements. The results were compared to the pore structure properties and permeabilities of hardened Portland cement (OPC) pastes. At identical w/c, CAC pastes and OPC pastes exhibited similar open and total porosities. The threshold radii of the CAC pastes were about one order of magnitude greater while the hydraulic radii of their open pore system were smaller. The CAC pastes possessed somewhat smaller permeabilities than the OPC pastes and can thus be regarded as being as durable as the latter in this respect. From comparison of pore structure parameters and permeabilities it was furthermore concluded that significant pore structure damage occurs in the CAC pastes during mercury porosimetry measurements and therefore the measured threshold radii have to be considered as unreliable.
Reaction products and strength development of wastepaper sludge ash and the influence of alkalis
(2014)
Wastepaper sludge ash (WSA) from a newsprint paper mill was investigated for its mineralogical composition and its reaction products and strength development after activation with water and sodium and potassium hydroxide solutions. The results showed the WSA to consist of calcite, free lime, gehlenite, tricalcium aluminate, belite, talc, quartz and probably a glassy phase. The principle reaction product was monocarboaluminate (CO3–AFm) for the water- as well as for the alkali-activated WSA. Formation of monocarboaluminate and strength gain was more rapid for the alkali-activated WSA until 1 day of curing. However, afterwards reactions proceeded much slower when alkali solutions were used, leading to an about twice as high compressive strength for water-activated WSA mortars after 28 days of curing. The observed behavior is tentatively ascribed to a less uniform microstructure of the alkali-activated WSA. Significant differences between NaOH- and the KOH-activated WSA were not observed.
Gas separation is a key issue in various industrial fields. Hydrogen has the potential for application in clean fuel technologies. Therefore, the separation and purification of hydrogen is an important research subject. CO2 capture and storage have important roles in 'green chemistry'. As an effective clean technology, gas separation using inorganic membranes has attracted much attention in the last several decades. Membrane processes have many applications in the field of gas separation. Cement is one type of inorganic material, with the advantages of a lower cost and a longer lifespan. An experimental setup has been created and improved to measure twenty different cement membranes. The purpose of this work was to investigate the influence of gas molecule properties on the material transport and to explore the influence of operating conditions and membrane composition on separation efficiency. The influences of the above parameters are determined, the best conditions and membrane type are found, it is shown that cementitious material has the ability to separate gas mixtures, and the gas transport mechanism is studied.
Metakaolin-based alkali activated mortars (AAM) - with and without CuSO4·5H2O and ZnO addition (mass ratio Mn+/solid binder 0.08% to 1.7%) - were casted and exposed within an extensive long-term field campaign over the period of 20 months to a sewer basin, strongly affected by biogenic acid corrosion. (Un-)exposed AAM were tested regarding their physicochemical and microstructural properties, bioreceptivity and overall durability. Metal addition led to a retarding effect during alkali-activation reaction, as well as to an increase in open porosity of up to 3.0% and corresponding lower compressive strength of up to 10.9%. Reduced microbial colonization and diversity were observed on AAM with Cu, while Zn addition led to increased biodiversity. We propose that the observed higher durability of Cu-doped AAM is due to antibacterial effects and associated reduction of biogenic acid production, superseding overall negative effects of metal-dosage on physical material properties. Observed lower durability of Zn-doped AAM was related to combined negative physicochemical and microbial effects.
Hybrid cements are composites made of Portland cement or Portland clinker and one or more supplementary cementitious materials like slag, fly ash or metakaolin, activated with an alkali salt. To date, their hydration mechanism and the phase formation at various temperatures is insufficiently understood, partly due to the large variability of the raw materials used. In the present study, three hybrid cements based on ground granulated blast furnace slag, fly ash, Portland clinker and sodium sulfate, and an alkali-activated slag/fly ash blend were cured at 10 and 21.5°C, and subsequently analyzed by XRD, 27Al MAS NMR, and TGA. The compressive strength of the hybrid cements was higher by up to 27% after 91-day curing at 10°C, compared to curing at 21.5°C. The experimental results as well as thermodynamic modeling indicate that the differences in compressive strength were related to a different phase assemblage, mainly differing amounts of strätlingite and C-N-A-S-H, and the associated differences of the volume of hydration products. While the strätlingite was amorphous to X-rays, it could be identified by 27Al MAS NMR spectroscopy, TGA and thermodynamic modeling. The microstructural properties of the hybrid cements and the alkali-activated slag/fly ash blend as well as the compatibility between thermodynamic modeling results and experimental data as a function of curing temperature and time are discussed.
Hydrous lithium aluminosilicate (L–A–S–H) and lithium aluminate (L–A–H) gels are candidate precursors for glass-ceramics and ceramics with potential advantages over conventional processing routes. However, their structure before calcination remained largely unknown, despite the importance of precursor structure on the properties of the resulting materials. In the present study, it is demonstrated that L–A–S–H and L–A–H gels with Li/Al ≤ 1 can be produced via an organic steric entrapment route, while higher Li/Al ratios lead to crystallization of gibbsite or nordstrandite. The composition and the structure of the gels was studied by thermogravimetric analysis, X-ray diffraction, 27Al and 29Si magic-angle spinning nuclear magnetic resonance, and Raman spectroscopy. Aluminium was found to be almost exclusively in six-fold coordination in both the L–A–H and the L–A–S–H gels. Silicon in the L–A–S–H gels was mainly in Q4 sites and to a lesser extent in Q3 sites (four-fold coordination with no Si–O–Al bonds). The results thus indicate that silica-rich and aluminium-rich domains formed in these gels.
The current understanding of the carbonation and the prediction of the carbonation rate of alkali-activated concretes is complicated inter alia by the wide range of binder chemistries used and testing conditions adopted. To overcome some of the limitations of individual studies and to identify general correlations between mix design parameters and carbonation resistance, the RILEM TC 281-CCC ‘Carbonation of Concrete with Supplementary Cementitious Materials’ Working Group 6 compiled and analysed carbonation data for alkali-activated concretes and mortars from the literature. For comparison purposes, data for blended Portland cement-based concretes with a high percentage of SCMs (≥ 66% of the binder) were also included in the database. The analysis indicates that water/CaO ratio and water/binder ratio exert an influence on the carbonation resistance of alkali-activated concretes; however, these parameters are not good indicators of the carbonation resistance when considered individually. A better indicator of the carbonation resistance of alkali-activated concretes under conditions approximating natural carbonation appears to be their water/(CaO + MgOeq + Na2Oeq + K2Oeq) ratio, where the subscript ‘eq’ indicates an equivalent amount based on molar masses. Nevertheless, this ratio can serve as approximate indicator at best, as other parameters also affect the carbonation resistance of alkali-activated concretes. In addition, the analysis of the database points to peculiarities of accelerated tests using elevated CO2 concentrations for low-Ca alkali-activated concretes, indicating that even at the relatively modest concentration of 1% CO2, accelerated testing may lead to inaccurate predictions of the carbonation resistance under natural exposure conditions.
The current understanding of the carbonation of alkali-activated concretes is ham-pered inter alia by the wide range of binder chemistries used. To overcome some of the limitations of individual studies and to identify general correlations between their mix design parameters and carbonation resistance, the RILEM TC 281-CCC working group 6 compiled carbonation data for alkali-activated concretes and mortars from the literature. For comparison purposes, data for blended Portland cement-based concretes with a high percentage of SCMs (≥ 66 % of the binder) were also included in the database. A preliminary analysis of the database indicates that w/CaO ratio and w/b ratio exert an influence on the carbonation resistance of alkali-activated concretes but, contrary to what has been reported for concretes based on (blended) Portland cements, these are not good indicators of their carbonation resistance when considered individually. A better indicator of the carbonation resistance of alkali-activated concretes under conditions approxi-mating natural carbonation appears to be their w/(CaO + Na2O + K2O) ratio. Furthermore, the analysis points to significant shortcomings of tests at elevated CO2 concentrations for low-Ca alkali-activated concretes, indicating that even at a concentration of 1 % CO2, the outcomes may lead to inaccurate predictions of the carbonation coefficient under natural exposure conditions.