Effects of steel slag aggregate size and content on piezoresistive responses of smart ultra-high-performance fiber-reinforced concretes

[Display omitted] •The effects of fine steel slag aggregates on the piezoresistive responses of smart UHPCs were investigated.•Electrical resistivity of smart UHPCs containing SSAs and steel fibers decreased with increasing compressive stress.•Finer SSAs produced higher electrical conductivity and piezoelectric response of smart UHPC.•There is a linear relationship between fractional change in resistivity (FCR) and compressive stress as stress varied from 0 to 30 % of compressive strength. This study investigated the self-sensing characteristics of smart ultra-high-performance concretes (UHPCs) containing steel slag aggregates (SSAs) and steel fibers under compression. We used SSAs as functional fillers in smart UHPCs, instead of silica sands, to obtain a uniform filler distribution. We examined the effects of SSA particle size (0.39, 2, and 5 mm in max. diameter), SSA/cement ratio (SSA/C) by weight (0.5, 1, 1.5, and 2), and steel fiber content (1 and 2 vol%) on the piezoresistive response of smart UHPCs. The smart UHPC containing SSAs with a maximum diameter of 0.39 mm and a SSA/C of 0.5 and a steel fiber content of 2 vol% produced the highest fractional change in resistance (FCR = 42.9 %) and consequently the highest stress sensitive coefficient (FCR/σ = 0.298 %/MPa) under compression owing to a well-structured conductive network of functional fillers (SSAs and fibers). Coarser SSA size generated non-uniform distribution of steel fibers while high volume contents of SSA incorporating with steel fibers consequently resulted in low piezoresistive responses by exceeding the percolation threshold of functional fillers in smart UHPCs.