Department of Mechanics: Seminar: Abstract Bazant 2018

Centurial Durability of Concrete Structures: Creep, Hydration and Hygrothermal Effects

Zdeněk P. Bažant, Northwestern University, Evanston, Illinois 60208, USA

Large meeting room (B169), Faculty of Civil Engineering, Czech Technical University in Prague

Friday, 23 February 2018, 10:30-11:30

Concrete structures, especially the large ones, are planned for service life over a century, but all too often they have to be repaired or replaced in a few decades. The lecture reviews recent mathematical models that should allow better assessment and control of the physico-chemical processes compromising the centurial durability, and focusses on creep, drying effects, autogenous shrinkage, and alkali-silica reaction (ASR). Since they all are profoundly affected by aging, the aging due to chemical hydration and the aging due to relaxation of nanoscale microprestress are analyzed in detail. A new model for hydration evolution from hours to centuries, controlled by water and ion diffusion through growing barrier shells of C-S-H surrounding the remnants of cement grains, is outlined, and an improved microprestress-solidification theory governing the relaxation of microprestress (or disjoining pressures) is presented. New semi-empirical equations for predicting centurial self-desiccation and autogenous shrinkage, based on a large data set, are reported and used to update the nonlinear diffusion equation for moisture in concrete, and to extract pure creep and pure drying shrinkage from a large database. A complete model for the ASR, including microcracking and the relaxation of pore pressure due to local diffusion of ASR gel into micropores is described. All these formulations are incorporated on the microplane level into model M7. For the local diffusion of ASR gel, an algorithm of unconditionally stability, important for century-long predictions, is formulated. The predictions are calibrated and validated by extensive test data collected from the literature. These data are of much shorter durations, which makes a solid theoretical basis, attempted here, essential. Finally, some necessary updates RILEM model B4 are adumbrated.

References:

• Rahimi-Aghdam, S., Bažant, Z.P., and Qomi, M.J.A. (2017). “Cement hydration from hours to centuries controlled by diffusion through barrier shells of C-S-H." J. of the Mechanics and Physics of Solids 99, 211-224.
• Sinko, R., Vandamme, M., Bažant, Z.P., Keten, S. (2016). “Transient effects of drying creep in nanoporous solids: understanding the effects of nanoscale energy barriers." Proc. Royal Soc. A 472:20160490; doi: 10.1098/rspa.2016.0490.
• Bažant, Z.P., and Rahimi-Aghdam, S. (2016). “Diffusion-controlled and creep-mitigated ASR damage via microplane model: I. Mass concrete". J. of Engineering Mechanics ASCE 142 (10); pp. 04016108-1--04016108-10; DOI: 10.1061/(ASCE)EM.1943-7889.0001186.
• Rahimi-Aghdam, S., Bažant, Z.P., and Caner, F.C. (2016). “Diffusion-controlled and creep-mitigated ASR damage via microplane model: II. Material degradation, drying, and verification". J. of Engineering Mechanics ASCE 142 (10); pp. 04016109-1--04016109-10; DOI: 10.1061/(ASCE)EM.1943-7889.0001185; doi: 10.1002/suco.201500126.

Born and educated in Prague (Ph.D. 1963), Bažant joined Northwestern in 1969, where he has been W.P. Murphy Professor since 1990 and simultaneously McCormick Institute Professor since 2002, and Director of Center for Geomaterials (1981-87). He was inducted to NAS, NAE, Am. Acad. of Arts & Sci., Royal Soc. London; to the academies of Italy, Austria, Spain, Czech Rep., India and Lombardy; to Academia Europaea and Eur. Acad. of Sci. & Arts. Honorary Member of: ASCE, ASME, ACI, RILEM. Received: Austrian Cross of Honor for Science and Art I. Class; 7 honorary doctorates (Prague, Karlsruhe, Colorado, Milan Poly, Vienna, Ohio State); ASME Medal; ASME Timoshenko, Nadai and Warner Medals; ASCE von Karman, Newmark, Biot, Mindlin and Croes Medals and Lifetime Achievement Award; SES Prager Medal; RILEM L’Hermite Medal; Exner Medal (Austria); Torroja Medal (Madrid); Šolin and Bažant, Sr., Medals (Prague), etc. He authored eight books, on scaling of structural strength, inelastic analysis, fracture and size effect, stability of structures, concrete at high temperatures, concrete creep, hygrothermal effects, and quasibrittle probabilistic fracture mechanics. H-index: 117, citations: 61,200, i10 index: 584 (on Google, incl. self-cit.). In 2015, ASCE established ZP Bažant Medal for Failure and Damage Prevention. He is one of the original top 100 ISI Highly Cited Scientists in Engrg.