Multi-scale evaluation of hybrid fiber restraint of alkali-silica reaction expansion in concrete

•HyFRC with PVA micro- and steel macrofibers could effectively reduce ASR damage.•ASR expansion is reduced through multi-scale crack control.•HyFRC controls ASR damage caused by aggregates of different reactivity levels.•After exposure to ASR, HyFRC retained its deflection hardening behavior. A multitude of deterioration mechanisms commonly associated with shortening the service life of conventional concrete structures are characterized by expansive internal forces for which a cementitious matrix is ill suited to resist. The addition of fibers has been shown to provide an effective mitigation scheme for several such expansive processes, most often in the form of high dosages of microfiber reinforcement. Hybridization of fibers of different sizes, to take advantage of their synergistic benefits, can provide an optimal balance of functional workability and enhanced mechanical performance. In this study one such hybrid fiber reinforced concrete (HyFRC) is evaluated for alkali-silica reaction mitigation, focusing first on the influence of the chosen microfibers and subsequently on the combined effect of micro- and macrofibers with respect to expansion potential and mechanical property retention of the concrete composite. While a low dose of the microfibers alone proved inadequate to restrain the deterioration mechanism beyond an early stage, the fiber size hybridization in HyFRC exhibited successful mitigation of expansion under standardized test conditions.