Concrete, made from Portland cement (PC), water, aggregates, mineral additions and chemical admixtures, is the most manufactured world commodity, 5 t/person/yr. PCs are environmentally contentious, accounting for 8% of anthropogenic CO2 emissions. Hence, developing more durable concretes with lower embodied carbon contents is central to maintaining our well-being. The main drawback of the most ambitious proposals for sustainable low-carbon cements is their slow hydration kinetics in the first three days.

Following our breakthrough in synchrotron ptychographic nanotomography for building materials, syn4cem will tailor coherence-based submicron 4D (3D+time) techniques for in situ hydration studies. These techniques should simultaneously provide: - spatial resolution better than 100 nm, - time resolution better than 100 minutes, and – very good electron density contrast. If attained, it will allow a better understanding of cement hydration at early ages. Chiefly, the transition from the accelerated to the decelerated stage will be understood which should allow a rational enhancement of the early age reactivity through admixtures like C-S-H seeding and alkanolamines.

Based on the 4D understanding of cement hydration, syn4cem will develop binders with lower CO2 footprints. The focus will be on limestone calcined clay cements, where the highest possible amount of clinker will be replaced by these abundant supplementary cementitious materials. The hydration reactions of these systems must be accelerated to have competitive mechanical strengths at one day which is key for on-site applications.

The proposed approach will allow ground-breaking interdisciplinary advances like a) quantification of etch-pit growth rates as a function of the particle sizes, b) mass transport in confined spaces, and c) water/air porosity evolution. The X-ray tools will zoom in during early hydration to optimise the admixture performances for attaining more sustainable buildings and infrastructures