Silica polymer bonding of stressed silica grains: An early growth of intergranular tensile strength

•Micro-damaged amorphous silica grains under stress release silicic acid into near contact water.•Within 3–4 weeks above initial concentration of 300 ppm, silicic acid polymerizes and forms polymer bridges between the grains.•The force at rupture in a single polymer branch reaches up to 0.03 mN.•The cumulative force at rupture of the polymer network between the grains reaches 1–1.5 mN.•The latter value is 2–3 times higher than an analogous capillary bridge force.

Laboratory tests on microscale are reported in which millimeter-sized amorphous silica cubes were kept highly compressed in a liquid environment of de-ionized water solutions with different silica ion concentrations for up to four weeks. Such an arrangement simulates an early evolution of bonds between two sand grains stressed in situ. In-house designed Grain Indenter-Puller apparatus allowed measuring strength of such contacts after 3–4 weeks. Observations reported for the first time confirm a long-existing hypothesis that a stressed contact with microcracks generates silica polymers, forming a bonding structure between the grains on a timescale in the order of a few weeks. Such structure exhibits intergranular tensile force at failure of 1–1.5 mN when aged in solutions containing silica ion concentrations of 200- to 500-ppm. The magnitude of such intergranular force is 2–3 times greater than that of water capillary force between the same grains.