Comparative Study on Traditional vs. Pre-Placed Aggregate Methods for Reducing Segregation in Heavy-Weight Concrete

One of the major challenges in using heavy-weight concrete is the occurrence of segregation due to differences in the specific gravity of its constituent materials. In this study, the effectiveness of two concrete production methods (traditional and pre-placed aggregate) in controlling segregation was investigated. Additionally, to improve segregation resistance in both methods, the incorporation of silica fume (equivalent to ۱۰% of cement weight) and steel fibers (۱.۵% by volume) was evaluated. Tests performed on hardened concrete included compressive strength, ultrasonic pulse velocity, flexural tensile strength, and gamma-ray attenuation coefficient. To monitor segregation, cubic specimens with dimensions of ۱۵۰×۱۵۰×۴۵۰ mm, cast along a ۴۵۰ mm height, were analyzed. Ultrasonic waves were transmitted through the upper, middle, and lower levels of the specimens, and compressive strength at these levels was estimated using calibration relationships to assess segregation. Results indicated that adding silica fume in both methods reduced the variation in compressive strength across different levels. Although silica fume had no significant impact on the gamma-ray attenuation coefficient, the reduced variation in this coefficient across specimen levels demonstrated improved homogeneity of the heavy-weight concrete. Furthermore, the pre-placed aggregate method effectively controlled segregation. Overall, findings highlight the significant role of silica fume in mitigating segregation and enhancing the uniformity of heavy-weight concrete.

کلیدواژه ها:

heavy-weight concrete ، segregation ، traditional ، pre-placed aggregate ، Magnetite