Fracture Properties of the Alkali Silicate Gel Using Microscopic Scratch Testing

Abstract

The alkali-silica reaction, ASR, can cause significant distress in concrete structures. Several methods have been proposed to measure the mechanical properties of ASR gel. The challenge is that the gel is often intermixed with hydration products in the complex cement matrix. We carry out a multi-scale investigation of the fracture properties of the gel produced by the alkali-silica reaction in concrete. Millimeter-sized alkali gels are tested via scratch tests at the micrometer level. Scanning electron microscopy reveals curved fracture surfaces produced during the scratch test, warranting a fracture mechanics analysis. By application of a nonlinear fracture mechanics model to the recorded load and depth data, we estimate the fracture toughness of ASR gel to be . In turn, by combining micro-indentation and scratch tests, we can estimate the fracture energy . These experimental results are important for the multi-scale modeling of the alkali-aggregate reaction.

Bio

Jiaxin Chen is a 4th-year Ph. D. candidate studying Mechanics, Materials, and Structures at the department of Civil and Environmental Engineering within the Sustainability and Nanomechanics group at Northwestern University. She obtained undergraduate degree in Road and Bridge Engineering in the department of Transportation Science and Engineering. She earned a Master of Science in structure engineering in Civil and Environmental Engineering at University of Illinois at Urbana-Champaign (2017). Her current research interests focus on additive manufacturing, material characterization including geopolymer composites, cement nanocomposites using data-driven approach and depth sensing experiments.