The nanogranular origin of concrete creep : a nanoindentation investigation of microstructure and fundamental properties of calcium-silicate-hydrates

With an annual per capita consumption of one cubic meter, concrete is the most manufactured material on Earth. But concrete subject to sustained load creeps, like chewing gum, at a rate that deteriorates the durability and lifespan of concrete infrastructure. While it is generally agreed that concrete creep originates from the complex viscous behavior of nanometer-sized building blocks of concrete, the calcium-silicate-hydrates (C-S-H), the origin of concrete creep is still an enigma and the creep properties of C-S-H have never been measured directly since C-S-H cannot be recapitulated ex situ in bulk form. This thesis develops a comprehensive nano-investigation approach to the assessment of the microstructure and the mechanical stiffness, strength and creep properties of the fundamental building block C-S-H. This is achieved by extending the realm of classical indentation analysis of homogeneous solids to highly heterogeneous, linear-viscoelastic, cohesive-frictional materials. Applied to and validated for a wide range of sub-stoichiometric cement pastes of different composition and processing conditions, the link between material composition, microstructure and nanomechanical stiffness, strength and creep properties of cement-based materials is assessed. It is found that C-S-H, exhibiting a unique nanogranular behavior, exists in (at least) three structurally distinct but compositionally similar forms (Low-Density, High-Density and UltraHigh Density) which are characterized by packings close to limit packing densities. It is found that at the nanoscale all C-S-H phases exhibit a logarithmic creep whose magnitude depends only on the packing of 5-nanometer sized particles and not on mix proportions, processing conditions, etc. Logarithmic creep is an intrinsic creep property of C-S-H.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Civil and Environmental Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2008

Author dc:creator

• Vandamme, Matthieu

Advisor dc:contributor.advisor

• Franz-Josef Ulm.

• Civil and Environmental Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/43906

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/43906