Suchergebnisse

Trabajo presentado al 15th International Congress on the Chemistry of Cement (ICCC), celebrado en Praga (República Checa) del 16 al 20 de septiembre de 2019. ; The microstructural development of alkali-activated slag cements, and the electrochemical conditions prevailing within these materials, depend on many synthesis parameters, in particular the curing conditions applied. The aim of this study is to evaluate the effect of curing time (28, 90 and 180 days of curing) on the mineralogical, physical and mechanical development, and resistance to chlorideinduced corrosion, in steel-reinforced alkali-activated blast furnace slag mortars. The compressive strengths and chloride migration coefficients of alkali activated blast slag mortars increase and decrease respectively, with longer curing, and the mineralogy evolves toward the formation of more hydrotalcite-group phases. Corrosion potential values decrease with time of immersion in an alkaline chloride-rich solution, and this reduction is independent of the curing time, which would usually be taken to indicate susceptibility to breakdown of the passive film on the rebar. However, the actual corrosion activity observed in embedded rebars indicated that corrosion initiation and propagation are not taking place. The presence of sulfide in the pore solution, supplied by the slag and/or ionexchanging between the pore solution and the layered hydration products, reduces the redox potential but does not induce steel corrosion. ; The research leading to these results received funding from the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013) / ERC Grant Agreement #335928.

Trabajo presentado a la 39th Cement and Concrete Science Conference, celebrada en la Universidad de Bath (UK) del 9 al 10 de septiembre de 2019. ; The physical and chemical interaction between CO2 and cementitious materials is referred to as carbonation, and is considered one of the main threats to our built environment. In alkali-activated materials, carbonation reactions can lead to significant changes in phase assemblages, an increase in porosity, and a loss in mechanical strength; however, the kinetics of carbonation are strongly dependent on factors controlling phase assemblage evolution in these systems, such as the type of precursor used in their production, the nature and amount of the activator utilised, and the curing conditions adopted. In this study the structural changes of sodium carbonate activated slag cements induced by accelerated carbonation under controlled exposure conditions (1% CO2, 65% relative humidity and 23¿C) are evaluated. The results are compared with those obtained for specimens exposed to natural carbonation conditions, to identify any changes in the type of carbonation products forming, as a function of CO2 concentration. Conversely to what has been reported for silicate activated slag systems, when using sodium carbonate as activator, negligible carbonation of the specimens is identified upon natural or accelerated carbonation. The outcomes of this study demonstrate that the development of highly durable and carbonation resistant alkali-activated cements is feasible when using sodium carbonate as the alkali source. ; This research was funded by the European Research Council under the European Union's Seventh Framework Programme (FP7/2007 2013) / ERC Grant Agreement #335928 (GeopolyConc). XK is grateful to U. Bath for her Prize Fellow ship. The participation of SAB in this research was partially funded by EPSRC through ECF EP/R001642/1.

The reaction kinetics of four commercial ground granulated blast furnace slags with varying percentages of MgO (6 to 14 wt.%), activated with four different doses of sodium metasilicate, were evaluated using isothermal calorimetry. The reaction kinetics were strongly dependent on the dose of the alkaline activator used, and the chemical and physical properties of the slag. When using low concentrations of sodium metasilicate as an activator, the MgO content in the slag influences the kinetics of the reaction, while the CaO content plays a more significant role when the concentration of metasilicate is increased. This study elucidated a close relationship between the dose of the alkali-activator and the chemistry of the slag used, although it was not possible to identify a clear correlation between any of the published chemically-based "slag quality moduli" and the calorimetry results, highlighting the complexity of blast furnace slag glass chemistry, and the importance of the physical properties of the slag in defining its reactivity. ; This research was funded in part by the European Research Council under the European Union's Seventh Framework Program (FP7/2007–2013)/ERC Grant Agreement #335928 (GeopolyConc), and in part by the Engineering and Physical Sciences Research Council (EP/P013171/1). Participation of SAB in this study was sponsored by EPSRC through ECF EP/R001642/1. ; Peer reviewed

The aim of RILEM TC 247-DTA 'Durability Testing of Alkali-Activated Materials' is to identify and validate methodologies for testing the durability of alkali-activated concretes. To underpin the durability testing work of this committee, five alkali-activated concrete mixes were developed based on blast furnace slag, fly ash, and flash-calcined metakaolin. The concretes were designed with different intended performance levels, aiming to assess the capability of test methods to discriminate between concretes on this basis. A total of fifteen laboratories worldwide participated in this round robin test programme, where all concretes were produced with the same mix designs, from single-source aluminosilicate precursors and locally available aggregates. This paper reports the mix designs tested, and the compressive strength results obtained, including critical insight into reasons for the observed variability in strength within and between laboratories. ; The participation of J. L. Provis and S. A. Bernal (at U. Sheffield), S. Nanukuttan and D. Bondar (at Queen's University) in this research was sponsored by the Engineering and Physical Sciences Research Council (EPSRC; UK) under Grant Number EP/M003272/1. Participation of V. Ducman was financially supported by the Slovenian Research Agency Programme Group P2-0273. The work and research of K. Dombrowski-Daube in RILEM TC-247 DTA was supported by ZIM - Central Innovation Program, German Federal Ministry of Economic Affairs and Energy (BMWi) by order of the German Bundestag. The contribution of the team at TU Delft led by G. Ye was supported by the Materials innovation institute M2i/Netherlands Organisation for Scientific Research (STW/M2i Project 13361). The contributions of K. Arbi were also supported by Delta Concrete Consult BV. ; Peer reviewed