The current drive to drastically reduce carbon emissions from cement production is promoting the exploration of cementitious materials with new and "greener" chemistries. The challenge is to predict how cements with new chemistries will behave (and degrade) in the long term. To do this, we must first understand the main chemo-mechanical processes taking place at the nanoscale and we must learn how to include them in engineering mechanics models at larger scales.
Our research is centred on particle-based simulations addressing the mesoscale between the nanometer and the micrometre. The simulations reproduce the mechanical response of particle aggregates, representing the cement hydrates, and consider also alterations to the particles due to chemical reactions, e.g. precipitation and dissolution. All this is fully coupled in an original Kinetic Monte Carlo framework (Shvab et al, 2017). Key inputs for the simulations are obtained from molecular dynamics simulations (e.g. Lolli et al 2018), whereas key outputs are used in larger-scale continuum models of cement paste mechanics (e.g. Masoero et al 2018).
The particle-based simulations have been shown to capture the hydration rate of fresh ordinary cement paste (Shvab et al, 2017). The simulations are now ready to be applied to cements with greener chemistries, in particular geopolymers. The conditions to address geopolymers have emerged only recently, thanks to molecular simulations that will provide key inputs to the mesoscale model (Lolli et al 2018). At the larger scale, the structures obtained with the mesoscale simulations have provided data on size distributions of the gel pores in the cement hydrates. These data have been used to show that the nano-morphology of the hydration products is key to explain the experimentally observed self-desiccation during cement hydration (Masoero et al 2018).
Our research provides insight into the fundamental mechanisms of cement formation and ageing. This supports the development of constitutive laws for new, more sustainable cementitious materials, and helps building confidence in their long-term performance, thus accelerating standardization and uptake in construction. Furthermore, the methodology developed for the cementitious materials is being extended to other materials, such as scaffolds for bone regeneration, and is suggesting new ways to address the fundamental question of covering long timescales in simulations at the nanometre level.
- Shvab, I., Brochard, L., Manzano, H. and Masoero, E., 2017. Precipitation mechanisms of mesoporous nanoparticle aggregates: off-lattice, coarse-grained, kinetic simulations. Crystal Growth & Design, 17(3), pp.1316-1327.
- Lolli, F., Manzano, H., Provis, J.L., Bignozzi, M.C. and Masoero, E., 2018. Atomistic simulations of geopolymer models: the impact of disorder on structure and mechanics. ACS applied materials & interfaces.
- Masoero, E., Cusatis, G. and Di Luzio, G., 2018. C-S-H gel densification: The impact of the nanoscale on self-desiccation and sorption isotherms. Cement and Concrete Research, 109, pp.103-119.
- Ioannidou, K., Krakowiak, K.J., Bauchy, M., Hoover, C.G., Masoero, E., Yip, S., Ulm, F.J., Levitz, P., Pellenq, R.J.M. and Del Gado, E., 2016. Mesoscale texture of cement hydrates. Proceedings of the National Academy of Sciences, p.201520487.
- Pinson MB, Masoero E, Bonnaud PA, Manzano H, Ji Q, Yip S, Thomas JJ, Bazant MZ, Van Vliet KJ, Jennings HM. Hysteresis from multiscale porosity: modeling water sorption and shrinkage in cement paste. Physical Review Applied. 2015 Jun 17;3(6):064009.