RYC Peer-to-Peer Webinar: Past, present, and future of cement-based materials: from the strength origin of cement hydrate to the mechanical behaviors of advanced concrete structures incorporating hybrid nanomaterials

Theme of the Peer-to-Peer Webinar: Past, present, and future of cement-based materials: from the strength origin of cement hydrate to the mechanical behaviors of advanced concrete structures incorporating hybrid nanomaterials.

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Speaker 1: Zhang Zhe, National University of Singapore, Singapore

Title: Strength origin of calcium silicate hydrate

Calcium silicate hydrate (C-S-H) is the main strength contributor in modern concrete. Despite the increased knowledge of its multiscale structure, little is known about the origin of its macroscale strength. In our recent study we successfully endow macro strength (tensile strength >20 MPa) to hydrothermal synthesized C-S-H powder. Relative humidity (RH) condition, Ca/Si ratio and porosity were studied as influencing factors to the strength, which enables an insight of the origin of strength in C-S-H matrix. The mechanical properties of C-S-H at different length scales were evaluated. There is a finding that hardness is not only influenced by porosity but also influenced by amounts of particle contacting boundaries especially with low porosity. Excessive water between C-S-H particles seemed to reduce the inter-particle bonding and hence the overall mechanical properties. An increase in hardness was witnessed while Ca/Si ratio decreasing. Inter-particle cohesion was measured using atomic force microscope to further explain this phenomenon. This work adds new insights to correlate the bulk strength of C-S-H with its microstructure and surface chemistry.

Speaker 2: Donghee Son, Hanyang University, South Korea

Title: Mechanical performance of concrete incorporated with triple hybrid of graphene oxide, functionalized carbon nanotube, and nano-silica: assessment on the bond characteristics

Nanomaterials have received great attention owing to their ability to control the cement-based structure at the nanoscale. The incorporation of nanomaterial hybrids in cement paste, mortar, and concrete indicated that they possess a synergistic effect owing to their interaction among themselves. The improved dispersity and increased mechanical strength of the hybrids compared with those of single nanomaterials leads to a possibility of a triple hybrid with their synergistic effects while maintaining the advantages of each nanomaterial.
The purposes of this study are (i) to evaluate the mechanical properties of triple hybrid-reinforced concrete mixed with carbon nanotubes, nano-silica, and graphene oxide and (ii) to determine the effect of these properties on the bond strength. The flexural strength of concrete increases and the Poisson's ratio and volumetric strain decrease with the incorporation of nano-materials, and the effect is most pronounced when graphene oxide is added.  Next, pull-out tests were conducted using a total of 21 specimens of triple hybrid-reinforced concrete. Similarly to the material test results, the bond performance of triple hybrid-reinforced concrete was found to be the highest, which can be attributed to the minimal volumetric deformation of the concrete. 

This webinar is brought to you by the RILEM Youth Council (RYC) and is hosted by Seongmin Cho, RYC East Asia Representative.