A novel optical real-time method for evaluating the castability of glass forming melts for laboratory furnaces is presented. The method is based on the analysis of top view images of the melt surface inside the crucible during melting after being subjected to a small mechanical impulse. In this way, the melt surface is excited to oscillate. The difference in contrast between two images taken in quick succession scales with the viscosity, with a larger diffe­rence occurring at lower viscosities. The method is designed as an instrument for the in-line evaluation of the castability for a high-throughput glass melting system as part of the joint project “GlasDigital” in the framework of the German Platform Material Digital initiative but is applicable to other laboratory furnaces as well.

The process of viscous flow sintering is a phenomenon that is closely linked to the surface properties of the glass particles. In this work, we studied the extreme case of acid-leaching of soda-lime-silicate glass beads of two different particle size distributions and its effects on non-isothermal viscous sintering of powder compacts. Depth profiling of the chemical composition after leaching revealed a near-surface layer depleted in alkali and alkaline earth ions, associated with concurrent hydration as mass loss was detected by thermogravimetry. Heating microscopy showed that acid treatment of glasses shifted the sinter curves to higher temperatures with increasing leaching time. Modelling of the shrinkage with the cluster model predicted a higher viscosity of the altered surface layer, while analysis of the time scales of mass transport of mobile species (Na+, Ca2+ and H2O) during isochronous sintering revealed that diffusion of Na+ can compensate for concentration gradients before sintering begins. Also, exchanged water species can diffuse out of the altered layer, but the depletion of Ca2+ in the altered surface layer persists during the sinter interval, resulting in a glass with higher viscosity, which causes sintering to slow down.

An increasing number of studies are being presented demonstrating that volcanic glasses can be heterogeneous at the nanoscale. These nano-heterogeneities can develop both during viscosity measurements in the laboratory and during magma eruptions. Our multifaceted study identifies here total transition metal oxide content as a crucial compositional factor governing the tendency of basalt melts and glasses towards nanolitization: at both anhydrous and hydrous conditions, an undercooled trachybasalt melt from Mt. Etna readily develops nanocrystals whose formation also hampers viscosity measurements, while a similar but FeO- and TiO 2 -poorer basalt melt from Stromboli proves far more stable at similar conditions. We therefore outline a procedure to reliably derive pure liquid viscosity without the effect of nanocrystals, additionally discussing how subtle compositional differences may contribute to the different eruptive styles of Mt. Etna and Stromboli.

Ground granulated blast furnace slags (GGBS) are glasses (>99%) of the CaO-Al 2 O 3-SiO 2 compositional system and are widely used as supplementary cementitious materials. Differences in reactivity of GGBS were screened by modifying the content of 11 minor elements (namely Ba, Ce, Cs, Cr, Mn, P, Sn, Sr, Ti, V, Zr). SEM observations showed that most elements entered the silicate glass matrix, only Sn was reduced to its metallic form and P accumulated in minor minerals. Mortar strength tests showed that 2d-compressive strength was reduced by > 50% for a TiO 2 content of 2.5 wt.% in the slag. At 28 days the loss in compressive strength was still > 40%. Calorimetric tests on other element additions showed that network modifiers (Ba, Cs and Sr) and GGBS reactivity are positively correlated, whereas Ce, Cr, V and Zr significantly decreased reactivity. It is shown that these effects can be well estimated by the weighted field strength of the added element.

Together with about 1180 million tons of hot metal (2017) about 380 million tons of blast furnace slag are produced yearly worldwide. Most of it (about 280 million tons) is quenched forming the glassy granulated blast furnace slag (GBS). For more than 130 years, this by-product is used as a clinker substitute in cement and concrete. Many approaches exist to evaluate the reactivity of ground granulated blast furnace slag (GGBS) in cementitious systems based on glass content, chemical composition, fineness, etc. But all approaches fail to define a suitable tool for judging an unknown GBS in a way that its strength contribution can be predicted. Only a rough differentiation might be possible. Compared to other parameters influencing GBS reactivity, the thermal history and the glass structure are mostly not investigated so far. However, from thermodynamic and kinetic points of view it is obvious that the thermal history of the slag should have a significant influence on glass structure and reactivity. The basic idea of the research project was to use analytical techniques being already established, for example, lime–soda–silica glasses. The differential scanning calorimetry and viscosity measurements have been combined for GBS characterization in order to measure the fictive temperature Tf (glass transition temperature on cooling during industrial quenching process) and to calculate retroactively the unknown cooling rates of liquid slags. Using these methods in combination with classical cementitious tests, it was possible to verify a correlation between the thermal history of GBS and its reactivity in a cementitious system.

The effect of Ti and other minor elements on the reactivity of granulated ground blast furnace slag (GGBS) in blended cements SIMON BLOTEVOGEL1, LAURENT STEGER1,2, HANSJÖRG BORNHÖFT3, JOACHIM DEUBNER3, LOLA DOUSSANG2, FRANCK FAYON4, DANIEL HART3, JUDIT KAKNICS5, VALERIE MONTOUILLOUT4, CEDRIC PATAPY1, GIUSEPPE SALDI7, JACQUES SCHOTT7, MARTIN CYR1 1 LMDC, UPS/INSA Toulouse, France 2 Ecocem Materials, Dublin, Ireland 3 Clausthal University of Technology, Germany 4 CNRS CEMHTI, Orléans, France 5ArcelorMittal Research, Maizières-les-Metz, France 6GET-CNRS-IRD, Toulouse, France