Free Online Education Presentations

Browse from hundreds of recorded presentations from ACI Conventions and other concrete industry events.

This Week's Featured Presentation

Stainless Steel Strands for Pretensioned Concrete Girders
by Anwer Al-Kaimakchi, Florida State University

Session details

Research in Progress, Part 1 of 2 (ACI Fall 2020 Convention, Virtual Sessions) This session will feature presentations of original, unpublished results from ongoing research projects and leading-edge concrete technology and research throughout the world.

Upcoming Presentation

May 10 - 16

Expanding Working Domain of Cement Based Matrices via Molecular Scale Engineered C-S-H
by Konrad Krakowiak, University of Houston

Presentation details

Why Nanofibers in Concrete? (ACI Fall 2020 Convention, Virtual Sessions) Coupling of organic and inorganic chemistry presents a new degree of freedom in nano-engineering of thermo-mechanical properties of cement-based materials. Despite these vast technological benefits, molecular scale cross-linking of calcium-silicate-hydrate (C-S-H) gel with organic molecules still presents a significant challenge. Herein, we report experimental results on sol-gel synthesis, structure and morphology of nanocrystalline C-S-H cross-linked with dipodal organosilanes. These novel organic-inorganic gels have layered turbostratic molecular structure with similarities to C-S-H precipitating in hydrating cement paste. The organic molecules’ chain length controls the interlayer spacing, which shows little to no shrinkage upon dehydration up to 105ºC. However, the structure gets distorted in the basal crystallite plane, in which dimer and trimer Si-polyhedra structures condense on a 2D hexagonal Ca-polyhedra layer. Cross-linked C-S-H gels display plate-like morphology with tendency toward stacking into agglomerates at the larger scale. If successfully realized in cement environment, e.g. high concentration seed, such novel organic-inorganic C-S-H gels could potentially provide cement-based matrices with unique properties unmatched by classical inorganic systems.

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