Revealing the effect of silica fume on the flexural behavior of ultra-high-performance fiber-reinforced concrete by acoustic emission technique

Abstract

Silica fume (SF), a commonly used supplementary cementitious material for preparing ultra-high-performance fiber-reinforced concrete (UHPFRC), is known to greatly influence the microstructure of cementitious materials and the interfacial properties of fibers in cement matrix. These effects can be crucial to the mechanical properties of UHPFRC. This paper studied the effect of SF on the four-point flexural behaviors of UHPFRC. It was found that the load (strength)-deflection curve showed a more pronounced hardening branch and a steeper softening branch by SF addition, indicating potentially both increased toughness and brittleness properties at the respective stages. To reveal the implicit mechanism inducing these changes, the microstructural alteration during the flexural deformation of UHPFRC was analyzed by acoustic emission (AE) technique. Two types of acoustic events, i.e., matrix cracking and steel fiber vibration, were clearly distinguished, and the results suggest a two-fold effect brought by SF addition: The fiber-matrix interface was toughened but the cement matrix became more brittle. The flexural behaviors of UHPFRC were predominantly impacted by the latter effect with 10% SF addition, whilst the former effect played a dominant role at higher SF dosage rates (≥20%).