Elucidating the nano-mechanical behavior of multi-component binders for ultra-high performance concrete. (20th May 2020)

• Record Type: Journal Article
• Authors: Ford, Emily; Arora, Aashay; Mobasher, Barzin; Hoover, Christian G.; Neithalath, Narayanan
• Is Part Of: Construction & building materials. Volume 243(2020)
• Publication Date: 2020-05-20
• Subjects: Nanoindentation -- Ultra-high performance concrete -- C-S-H -- Heterogeneity -- Homogenization; Building materials -- Periodicals; 624.18
• DOI: 10.1016/j.conbuildmat.2020.118214
• Languages: English
• ISSNs: 0950-0618

Abstract

Highlights: Nanomechanical response of highly heterogeneous ultra-high performance cement pastes. Elucidates the influence of very low w/b and high volume of cement replacement materials on the nanoscale response. Explains the reasoning for an ultra-high stiffness phase in UHPC pastes. Models to upscale elastic modulus from nanoscale measurements and their applicability. Abstract: 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.