Fracture properties of the alkali silicate gel using microscopic scratch testing

We carry out a multi-scale investigation of the fracture properties of the gel produced by the alkali-silica reaction in concrete. Milimeter-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 Kc=0.62 MPam. In turn, by combining micro-indentation and scratch tests, we can estimate the fracture energy Gf=11.2 J/m2. These experimental results are important for the multi-scale modeling of the alkali-aggregate reaction.