Phase evolution of C-(N)-A-S-H/N-A-S-H gel blends investigated via alkali-activation of synthetic calcium aluminosilicate precursors

Stoichiometrically-controlled alkali-activated pastes containing calcium-(sodium) aluminosilicate hydrate (C-(N)-A-S-H) and sodium aluminosilicate hydrate (N-A-S-H) gels are produced by alkali-activation of high-purity synthetic calcium aluminosilicate powders. These powders are chemically comparable to the glass in granulated blast furnace slag, but without interference from minor constituents. The physiochemical characteristics of these gels depend on precursor chemical composition. Increased Ca content of the precursor promotes formation of low-Al, high-Ca C-(N)-A-S-H with lower mean chain length as determined by quantification of solid state nuclear magnetic resonance spectra, and less formation of calcium carboaluminate ‘Alumino-ferrite mono’ (AFm) phases. Increased Al content promotes Al inclusion and reduced crosslinking within C-(N)-A-S-H, increased formation of calcium carboaluminate AFm phases, and formation of an additional N-A-S-H gel. Small changes in precursor composition can induce significant changes in phase evolution, nanostructure and physical properties, providing a novel route to understand microstructural development in alkali-activated binders and address key related durability issues

Solid-state nuclear magnetic resonance spectroscopy of cements

Cement is the ubiquitous material upon which modern civilisation is built, providing long-term strength, impermeability and durability for housing and infrastructure. The fundamental chemical interactions which control the structure and performance of cements have been the subject of intense research for decades, but the complex, crystallographically disordered nature of the key phases which form in hardened cements has raised difficulty in obtaining detailed information about local structure, reaction mechanisms and kinetics. Solid-state nuclear magnetic resonance (SS NMR)spectroscopy can resolve key atomic structural details within these materials and has emerged as a crucial tool in characterising cement structure and properties. This review provides a comprehensive overview of the application of multinuclear SS NMR spectroscopy to understand composition–structure–property relationships in cements. This includes anhydrous and hydrated phases in Portland cement, calcium aluminate cements, calcium sulfoaluminate cements, magnesia-based cements, alkali-activated and geopolymer cements and synthetic model systems. Advanced and multidimensional experiments probe 1 H, 13 C, 17 O, 19 F, 23 Na, 25 Mg, 27 Al, 29 Si, 31 P, 33 S, 35 Cl, 39 K and 43 Ca nuclei, to study atomic structure, phase evolution, nanostructural development, reaction mechanisms and kinetics. Thus, the mechanisms controlling the physical properties of cements can now be resolved and understood at an unprecedented and essential level of detail

Temperature measurement in a Paris-Edinburgh cell by neutron resonance spectroscopy

Neutron resonance spectroscopy is demonstrated as a viable and reliable method for the determination of sample temperatures in high-pressure, high-temperature neutron diffraction studies at neutron spallation sources. The technique operates by characterizing the thermally induced Doppler broadening of neutron absorption resonances of heavy nuclei present within the sample assembly observed in transmission. Accuracies of ±10 K have been readily achieved with data acquisition times of approximately 40 min. It is shown that the temperatures determined by this technique are independent of the sample pressure provided that the sample temperature is kept above the Debye temperature of the material whose resonances are being examined. A short list of candidate resonances for temperature measurement by neutron resonance spectroscopy is presented and suggestions volunteered for the combinations of elements most suitable for temperature measurement based on the experience of the authors

Remote determination of sample temperature by neutron resonance spectroscopy

The Doppler broadening ofthe lower energy neutron absorption resonances ofnatural hafnium, tantalum, iridium and rhenium have been studied for the purpose of measuring temperature in remote or isolated environments. Three methods for the determination of sample temperature from neutron transmission data were studied and a critical comparison ofthe efficacy ofeach method made. Fitting the observed resonance line shapes with analytical expressions incorporating instrument resolution and resonance parameters provided the most accurate measure ofsample temperature with an estimated uncertainty of 10 C at 1000 C and did not require prior calibration experiments to be performed