From micron-sized needle-shaped hydrates to meter-sized shotcrete tunnel shells: micromechanical upscaling of stiffness and strength of hydrating shotcrete |
| |
Authors: | Bernhard Pichler Stefan Scheiner Christian Hellmich |
| |
Institution: | (1) Institute for Mechanics of Materials and Structures, Vienna University of Technology (TU Wien), Karlsplatz 13/202, 1040 Vienna, Austria |
| |
Abstract: | Knowledge on the stresses in shotcrete tunnel shells is of great importance, as to assess their safety against severe cracking
or failure. Estimation of these stresses from 3D optical displacement measurements requires shotcrete material models, which
may preferentially consider variations in the water–cement and aggregate–cement ratios. Therefore, we employ two representative
volume elements within a continuum micromechanics framework: the first one relates to cement paste (with a spherical material
phase representing cement clinker grains, needle-shaped hydrate phases with isotropically distributed spatial orientations,
a spherical water phase, and a spherical air phase; all being in mutual contact), and the second one relates to shotcrete
(with phases representing cement paste and aggregates, whereby aggregate inclusions are embedded into a matrix made up by
cement paste). Elasticity homogenization follows self-consistent schemes (at the cement paste level) and Mori–Tanaka estimates
(at the shotcrete level), and stress peaks in the hydrates related to quasi-brittle material failure are estimated by second-order
phase averages derived from the RVE-related elastic energy. The latter permits upscaling from the hydrate strength to the
shotcrete strength. Experimental data from resonant frequency tests, ultrasonics tests, adiabatic tests, uniaxial compression
tests, and nanoindentation tests suggest that shotcrete elasticity and strength can be reasonably predicted from mixture-
and hydration-independent elastic properties of aggregates, clinker, hydrates, water, and air, and from strength properties
of hydrates. At the structural level, the micromechanics model, when combined with 3D displacement measurements, predicts
that a decrease of the water–cement ratio increases the safety of the shotcrete tunnel shell. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|