Characterization of early age behavior of cemented paste backfill through the magnitude and frequency spectrum of ultrasonic P-wave

Abstract Cemented paste backfill (CPB) is broadly used for underground backfilling, improving the mechanical performance through the modification of its composition and, therefore, its microstructure and characteristics. In order to assess the applicability of ultrasonic waves to better comprehend relations among composition-microstructure-characteristics; an experimental program was realized using the magnitude and frequency spectrum of ultrasonic P-wave which is considered as an effective system for characterizing the hardening processes of cementitious materials. In this study, different binder contents (3, 5 and 7 wt%) and curing temperatures (20 and 35 °C) were tested for investigating CPB’s hardening processes. Silica fume (0, 5 and 20 wt% of binder) was used as an additive in replace of binder to determine its effect on behavior of ultrasonic waves. Component (TG and DTG) and microanalysis (SEM) were adopted to improve the understanding of ultrasonic behavior. Results show that there is a positive relationship between the strength and magnitude of ultrasonic P-wave in CPB, except for the sample with 3 wt% binder. The magnitude and frequency spectrum of ultrasonic P-wave is more sensitive than P-wave velocity to reflect the variation in the backfill strength. Higher binder content can densify the microstructure of CPB with longer curing time and reduce the energy attenuation of ultrasonic P-wave, resulting higher magnitude obtained. The addition of silica fume makes CPB having a finer pore structure enhanced, thereby improving in the strength, P-wave velocity and magnitude. The energy attenuation of ultrasonic P-wave can be notably weakened at a curing temperature of 35 °C due to a dense network formed by both hydration products and tailings. The magnitude and frequency spectrum of ultrasonic P-wave can be capable of reflecting and characterizing the pore structure, hydration processes and water content in CPB comprehensively. Consequently, the proposed technique can be well used to illustrate the hardening processes of CPB and hence improve the understanding of its early-age behavior.