State-of- the-art, opportunities and challenges for nanotechnology in concrete materials

Marco GOISIS, Italcementi - HeidelbergCement Group

The performance of concrete materials depends to a great extent on structural elements and phenomena which are effective on a micro and nanoscale. C-S-H is the hydrated dominant component of cement and has a local structure with nanoscale features with size in the few nanometer range. It is the main strength giving phase in the hardened cement paste. Advanced modification of the C-S-H structure at the nanoscale to create hybrid, organic, cementitious nanocomposites has been proposed with the object of obtaining enhanced engineering properties and improvement of durability even if much research remains to be done on this route. Substantial improvements in the properties of concrete have been achieved by use of silica fume along with use of superplasticizers in concrete mixes, leading to very high and ultra-high strength concretes. Incorporation of nanoparticles, especially nano-SiO2, in concrete is indicated to result in further improvements in strength and durability characteristics. Admixtures are capable to modify and control properties of ordinary and special mixtures such as self-compacting concrete and high performance concrete. Non-conventional properties such as self-cleaning ability, air pollution reduction, bactericidal capacity can be achieved by the use of nano-TiO2 particles. Advanced strategies for self-healing of micro-cracks based on hollow fibers, microencapsulation, expansive agents, bacteria and shape memory materials have been proposed. Nano carbon materials appears to be among the most promising candidates for enhancing mechanical properties of cement-based composites and their resistance to crack propagation while providing such novel properties as electromagnetic field shielding and self-sensing. Carbon nanotubes can be used as sensing devices permitting to monitor concrete stresses during structures service life and even during exceptional events (impact, earthquake etc…). Incorporation of graphene and graphene-oxide in cementitious matrix is a very recent field of research where studies have shown modifications of cement hydration products with formation of regular flower-like or polyhedron-like structures. Applications of graphenic materials to enhance electrical and thermal conductivity of hydrated graphene-cement composites are currently addressed.

 
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