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Database clarifies bottom-up design of cement

An international team of scientists led by EPFL Lausanne, ETH Zurich and Rice University has created a database of molecular dynamics models that simulate the properties of cement in all its varieties.

The database is called cemff, for Cement Force Fields. It gathers methods for simulating force-field parameters for the various types of inorganic minerals present in cement, which is used to bind concrete, the most-used construction material in the world. cemff allows academic and industrial researchers to draw upon many types of force fields to make accurate simulations and predictions of purpose-built cement formulations.

cemff could help industry design stronger, more durable construction materials that also curtail carbon dioxide emissions from the manufacture of more than 3 billion tons of cement and concrete a year. Concrete manufacturing contributes as much as 8 percent of the greenhouse gas to the atmosphere.

Fifteen scientists at 11 institutions worked on the project led by Ratan Mishra of ETH Zurich, Rouzbeh Shahsavari of Rice and Paul Bowen of EPFL Lausanne. Details appear in the journal Cement and Concrete Research – leadingscientific journal in this discipline.

In this case, the force field isn't an invisible barrier from a science-fiction story. It's the collection of parameters scientists use to build computer models of atomic interactions. These parameters include the intrinsic energy of the atoms in a simulation system. They are used to calculate how atoms interacts individually and collectively with their neighbors to give the material its properties.

"This unified database is in line with the current trend towards big data and predictive computational materials science," said Shahsavari, an assistant professor of civil and environmental engineering and of materials science and engineering at Rice.

The models show how the component molecules in cement interact with each other. These microscopic interactions determine how well concrete performs in real-world applications and allow for fine-tuning the material to perform at its best for decades and in the most environmentally conscious way.

"Molecular modeling still requires multiple trade-offs," said Mishra, lead author of the paper and a materials scientist at ETH Zurich. "The typical example is time versus accuracy but, more importantly, it is essential to recognize what specific models are good at and what they may be challenged with. cemff will allow researchers to have a more comprehensive view on this question and to select the best approach for the problem they are tackling."

Cement consists primarily of calcium silicates that react with water to produce the hardened material that confers mechanical properties and durability to concrete. It was found that nearly 60 percent of carbon dioxide emissions from cement production comes from the decomposition of limestone, the source of calcium in cement, but also of carbon dioxide emissions. To reduce the carbon footprint, manufacturers often supplement the mix with clays, waste materials like fly ash and recycled materials.

These all influence the mechanical characteristics and resilience of the product. Hence the need for simulations at nanoscale that let manufacturers test mixes for strength and durability even before making real cement.

“Because of their complex structure and composition, cementitious materials are a serious challenge for atomistic simulation of their properties. This collaborative effort is a great service to a broader research community, because it provides a solid quantitative base for selecting the proper tools for accurate modeling of these important materials”- said Andrey Kalinichev, one of the co-developers of a widely used force field ClayFF, Professor at the Institut Mines-Télécom Atlantique, France, and also a Chief Research Fellow of the International Laboratory for Supercomputer Atomistic Modelling and Multi-Scale Analysis at the NRU HSE in Russia. 

"I hope the open format and international base of the cemff database will encourage both the modeling and experimental community to create solid benchmarks to help understand and predict more accurately the properties of the most used material on Earth and help us build a more sustainable future," Bowen said.

Authors of the paper include Aslam Kunhi Mohamed and David Geissbühler (EPFL Lausanne);  Hegoi Manzano (University of the Basque Country, Bilbao, Spain); Tariq Jamil and Hendrik Heinz (University of Colorado Boulder, USA); Sandra Galmarini (Swiss Federal Laboratories of Materials Science and Technology, Dübendorf); Lei Tao (Rice University); Roland Pellenq (Massachusetts Institute of Technology, USA); Adri van Duin (PennState University, USA); Stephen Parker (University of Bath, United Kingdom), and Robert Flatt (ETH Zurich).

The research was supported by the Commission for Technology Innovation, the National Science Foundation, the Swiss Competence Center for Energy Research-Supply of Electricity, the Department of Education, Linguistic Policy and Culture of the Basque Government, the ELKARTEK program, the Swiss National Foundation, the Nanocem research network, the ACS Petroleum research fund and the industrial chair “Storage and Disposal of Radioactive Waste” at the Institut Mines-Télécom Atlantique.

Read the paper at http://www.sciencedirect.com/science/article/pii/S000888461730409X

Access cemff at https://cemff.epfl.ch/