Blast Effects of a Shear Thickening Fluid-Based Stemming Material

The Trauzl test is widely used to measure the explosive power of a substance by determining the volume increase produced by the detonation of a tested explosive charge in the cavity of a lead block with defined quality and size. In this study, the Trauzl lead block test and a high-speed 3D digital image correlation (3D-DIC) system were used to evaluate the effect of stemming on a blast hole. The blasting experiments were conducted with emulsion explosives. The stemming materials adopted in this study were sand, aggregate, and shear thickening fluid (STF)-based stemming materials. The results of the blasting experiments and numerical analysis showed that the expansion rate of the lead block was most affected by STF-based materials, followed by aggregates and sand stemming. Furthermore, the displacement and surface strain on the block were the highest in the experimental case using STF-based stemming materials. The STF-based stemming material developed in this study in open pit mining or various blasting constructions is expected to increase rock fragment efficiency, compared to that of general blasting stemming methods, and reduce blasting vibration by decreasing the amount of explosive per blast hole used for blasting

Evaluation of Self-Healing Performance of PE and PVA Concrete Using Flexural Test

The self-healing performance of PE and PVA concrete was evaluated, by using the three-point bending test with a notch. Four different crack inducement days were applied (7, 28, 49, and 91 days), and the same 21 days of healing period were applied to each case. The self-healing environments were in 20°C water, and in the curing room with 20°C temperature and 60% humidity. The flexural strength and the initial flexural stiffness of before and after healing were compared. As a result, both the strength recovery effect and the stiffness recovery effect decreased with the delay of crack inducement, and specimens in the water environment showed higher healing effect than those in the air environment. PVA fiber showed a relatively greater recovery effect than PE fiber