AMORPH · Analysis and Modelling of the Reactivity of Pozzolans during Cement Hydration

Analysis and Modelling of the Reactivity of Pozzolans during Cement Hydration

Currently, the annual global cement production is estimated to be 3.3 billion tons. Even though the CO2 emissions associated with the final product, concrete, are low, the massive scale of production means that the cement industry accounts for 5-8 % of the global annual anthropogenic CO2 emissions. One of the most effective ways to improve sustainability is the blending of Portland cement with supplementary cementitious materials (SCMs). To scientifically support the transition of the cement industry to a more sustainable production of blended cements that can incorporate a wide range of industrial by-product, societal waste or low-energy natural materials, the AMORPH project aimed to: 1. Document the interaction between the SCM surface and the Portland cement pore solution in terms of surface chemistry processes (adsorption and leaching of components, dissolution and precipitation reactions) and SCM dissolution rate. 2. Integrate kinetics, experimental results of the hydration reactions in a model of blended cement hydration with thermodynamic modelling. 3. Devise improved methods to measure and predict the reactivity of a wide range of SCMs in blended cement systems. The AMORPH project adopted a novel interdisciplinary approach, building on the geochemical background of the fellow combined with the materials science perspective of the host. Novel concepts of surface chemistry, recently developed in geochemistry, were applied to the study of the behaviour of SCMs in cement. The focus of the project was the investigation of the effect of SCM and solution chemistry on the rate of the nanoscale surface processes of dissolution, leaching and precipitation. This goal was achieved, and delivered new insights into parameters controlling the reactivity of SCMs in high pH, Ca-rich systems such as hydrating Portland cements. The novel insights indicate that significant gains in resource-efficiency can be gained by exploiting synergy effects between SCMs to enhance their reactivity. Boosting the reactivity of SCMs enables to use smaller fractions of Portland cement clinker and strongly reduces the environmental impact of cement production. Simultaneously, higher fractions of SCMs will enable the transformation of waste streams that are currently land-filled into added value construction materials (Figure 1). The results were published in a series of peer-reviewed publications 1–3 and presented at several international and national scientific gatherings. Figure 1 (attached). Flow chart summarizing the socio-economic impact of enhancing SCM reactivity by beneficiation treatment of waste streams and subsequent activation and synergetic design for hydration of blended cement mixes. The impact of reacting SCMs on the hydration product assemblage of the hardened cement was further modelled and compared to experiment, exploiting recent breakthroughs in thermodynamic modelling of hydrating cement systems. Furthermore, links between thermodynamic properties of aqueous solutions and reaction kinetics were established. This generic approach will lead to an improved understanding and prediction of the reactivity of potentially interesting secondary resources as cement replacement materials and thus contribute to the transformation of the EU-economy from a primary resource intensive economy to a sustainable economy based on the reuse and recycling of waste streams into new, high-quality products. Finally, a number of improvements in measurement techniques and strategies to assess the reactivity and suitability for reuse of a potential SCM were developed. Practical methodologies for testing of SCM reactivity in a basic laboratory environment are essential to further implement and transfer into practice new, more sustainable and more environment-friendly cementitious binders. In this respect, two important contributions were made. On the one hand a fast X-ray powder diffraction data treatment method was developed to directly measure the reaction of previously non-quantifiable amorphous phases in hydrating cement systems. On the other hand much progress was made into the development of an accelerated reactivity test for supplementary cementitious materials by using simple and straightforward calorimetry measurements that show very good correlations with compressive strength results. More on: wiki.epfl.ch/amorph e-mail: ruben.snellings@epfl.ch References 1 R. Snellings, “Solution-controlled dissolution of supplementary cementitious material glasses at pH 13: The effect of solution composition on glass dissolution rates,” J. Am. Ceram. Soc., 96 [8] 2467–2475 (2013). 2 R. Snellings, T. Paulhiac, and K. Scrivener, “The effect of Mg on slag reactivity in blended cements,” Waste Biomass Valoris., 5 369–383 (2014). 3 R. Snellings and K.L. Scrivener, “Dissolution kinetics as a method to assess the reactivity of supplementary cementitious materials (SCMs): the effect of solution composition and SCM structure”; in XIII Int. Conf. Durab. Build. Mater. Sao Paulo, 2014.

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