Journal
CONSTRUCTION AND BUILDING MATERIALS
Volume 243, Issue -, Pages -Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.conbuildmat.2020.118214
Keywords
Nanoindentation; Ultra-high performance concrete; C-S-H; Heterogeneity; Homogenization
Categories
Funding
- U.S. National Science Foundation [CMMI: 1463646]
- Arizona Department of Transportation [ADOT: SPR 745]
- Arizona State University
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The nanomechanical signature of highly heterogeneous ultra-high performance (UHP) cement pastes are explored in this paper. The UHP pastes are proportioned using 30% or 50% (by mass) of commonly available cement replacement materials including fly ash, microsilica, and fine limestone. Nanoindentation experiments coupled with a Bayesian information criterion-based statistical approach is used to develop modulus-hardness (M-H) clusters for the UHP pastes. While typical low-density (LD) and high-density (HD) C-S-H phases are present in early-age UHP pastes, it is shown that an ultra-high stiffness (UHS) phase, which is a composite of HD C-S-H and nanoscale CH, is predominant at later ages. Nanoindentation data points to the presence of significantly higher proportions of mixed phases in the UHP pastes, comprising of cement hydrates/pozzolanic reaction products and unreacted phases including fine limestone and microsilica acting as micro-aggregates to enhance the stiffness of the paste. The presence of such mixed phases complicates upscaling of the elastic modulus using multi-scale homogenization models, which is to be carefully accounted for in such highly heterogeneous systems. (C) 2020 Elsevier Ltd. All rights reserved.
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