Discrete element modeling and electron microscopy investigation of fatigue-induced microstructural changes in ultra-high-performance concrete

Enthalten in
Materials 
Volume
14
Issue
21
Article Number
6337
Citation
Materials 14 (21): 6337 (2021-10-23)
Publisher DOI
10.3390/ma14216337
Scopus ID
2-s2.0-85117802862
Publisher
MDPI
In view of the growing demand for sustainable and lightweight concrete structures, the use of ultra-high-performance concrete (UHPC) is becoming increasingly important. However, fatigue loads occur more frequently in nature than static loads. Despite the impressive mechanical properties of UHPC, a reduced tolerance for cyclic loading is known. For this reason, our paper deals with experimental and numerical investigations regarding the main causes for crack initiation on the meso, micro, and nanoscale. After mechanical fatigue tests, we use both scanning (SEM) and transmission electron microscopy (TEM) to characterize microstructural changes. A new rheological model was developed to apply those changes to the mesoscopic scale. The origins of fatigue damaging can be traced back to a transformation of nanoscale ettringite, resulting in a densification of the surrounding binder matrix. Additionally, a higher content of unhydrated cement clinker in the matrix benefits fatigue resistance. On the mesoscale, stress peaks around aggregate grains expand into the surrounding binder with increasing load cycles and lead to higher degradation.
Schlagworte
ultra-high-performance concrete
fatigue
electron microscopy
ettringite transformation
bonded particle model
discrete element method
rheological model
crack propagation
DDC Class
530: Physik
540: Chemie
600: Technik
620: Ingenieurwissenschaften
690: Hausbau, Bauhandwerk
Projekt(e)
SPP2020: Cyclic damage processes in high-performance concretes in the Experimental Virtual Lab 
Funding Organisations
Deutsche Forschungsgemeinschaft (DFG) 
More Funding Information
This research was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation), grant number 353408149, as part of the priority program “SPP2020: Cyclic damage processes in high-performance concretes in the Experimental Virtual Lab”.