Mesocrystalline calcium silicate hydrate: A bioinspired route toward elastic concrete materials.

Calcium silicate hydrate (C-S-H) is the binder in concrete, the most used synthetic material in the world. The main weakness of concrete is the lack of elasticity and poor flexural strength considerably limiting its potential, making reinforcing steel constructions necessary. Although the properties of C-S-H could be significantly improved in organic hybrids, the full potential of this approach could not be reached because of the random C-S-H nanoplatelet structure. Taking inspiration from a sea urchin spine with highly ordered nanoparticles in the biomineral mesocrystal, we report a bioinspired route toward a C-S-H mesocrystal with highly aligned C-S-H nanoplatelets interspaced with a polymeric binder. A material with a bending strength similar to nacre is obtained, outperforming all C-S-H-based materials known to date. This strategy could greatly benefit future construction processes because fracture toughness and elasticity of brittle cementitious materials can be largely enhanced on the nanoscale.

Identification of binding peptides on calcium silicate hydrate: a novel view on cement additives.

Phage display experiments on industrially important calcium silicate hydrates (C-S-H), the main hydration product of ordinary Portland cement, suggest fundamentally different specific binding motifs compared to hitherto existing commercial cement additives. According to that, a strong and specific adsorbing additive on C-S-H should have three features which are a negative charge, H-bond formers (especially amide functions) and a hydrophobic part.

A straightforward treatment of activity in aqueous CaCO3 solutions and the consequences for nucleation theory.

The aqueous calcium carbonate system is rigorously investigated with respect to ionic activity. Ideal treatment is found to be a good approximation at relevant concentrations. The data further show that bound CaCO3 species cannot be regarded as "inactive" during nucleation but rather appear to play a key role in the phase-separation process, and that amorphous calcium carbonate (ACC) can be precipitated from much lower levels of supersaturation than previously believed.

Polymer vesicles as microreactors for bioinspired calcium carbonate precipitation.

Giant polymer vesicles made by electroformation have been shown to encapsulate salts up to concentrations of about 10 mM. The impermeability of these "polymersomes" to calcium ions is demonstrated by the use of fluorescent probes dedicated to calcium analysis. Permeability to calcium ions can be triggered by the addition of calcimycin, an ionophore molecule that is able to transport cations selectively through the membrane. As a result, we show that the mineralization of calcium carbonate can be induced within the polymersomes, which were previously loaded with carbonate ions. This is a further step toward the use of polymersomes as microreactors and the study of mineralization schemes, including biomimetic ones, in confined environments.