Microstructure–toughness relationships in calcium aluminate cement–polymer composites using instrumented scratch testing
- 404 Downloads
We investigate the influence of the microstructure on the fracture properties of calcium aluminate cement/polymer composites. We carry out microscopic scratch tests during which a Rockwell C diamond probe pushes across the surface of a polished specimen under a linearly increasing vertical force. We extend the scratch fracture method to heterogeneous materials. The scratch test induces a ductile-to-brittle transition as the penetration depth increases. Scanning electron microscopy imaging shows that the low porosity and the strong cement-binder interphase favor toughening mechanisms such as crack trapping and bridging. Nonlinear fracture mechanics theory yields the fracture toughness in the fracture-driven regime. The fracture toughness of macro-defect-free (MDF) cement is found to decrease as the polymer-to-cement ratio increases. This decrease in the fracture resistance can be explained by the decrease in anhydrous cement content and the increase in the inter-particle distance between cement grains. By evaluating the fracture toughness of the micro-constituents of MDF cement, we show that the high value of the fracture toughness at the composite level stems from tough calcium aluminate phases and a highly packed non-porous granular microstructure.
We acknowledge the support of the Department of Civil and Environmental Engineering and the UIUC CEE Structural Engineering group that provided a fellowship to Kevin Anderson during his Master studies. This investigation was funded by Prof. Akono’s start-up funds which were sponsored by the Department of Civil and Environmental Engineering and the College of Engineering at the University of Illinois at Urbana-Champaign. We are grateful to Prof. Leslie J. Struble for invaluable insights into the chemistry and microstructure of macro-defect-free cement. We acknowledge the generosity of industrial partners such as Kerneos and Kuraray that have provided free calcium aluminate cement and poly(vinyl alcohol-co-acetate) samples. Finally, part of this research was carried out at the Frederick Seitz Research Materials Laboratory.
- 3.Robson TD (1962) High-alumina cements and concretes. Wiley, New YorkGoogle Scholar
- 5.Alford NM, Birchall JD (1985) The properties and potential applications of macro-defect-free cement. In: MRS proceedings, vol 42. doi 10.1557/PROC-42-265
- 14.Birchall JD, Howard AJ, Kendall K (1981) Flexural strength and porosity of cements. Nature 289Google Scholar
- 19.Zhang W (2014) Synthesis and fracture toughness of macro-defect-free-cement. M. Sc. Thesis, University of Illinois at Urbana-ChampaignGoogle Scholar
- 31.Theophrastus, On Stones, c. 300 BCGoogle Scholar
- 39.Irwin GR (1964) Structural aspects of brittle fracture. Appl Mat Res 3:65–81Google Scholar
- 45.Net S, Vandembroucq D, Roux S, Quantitative prediction of effective toughness at random heterogeneous interfaces(2013) Phys Re Lett, 110Google Scholar