Third phase of this research, aims at finding the optimum length of the airdeck. For this purpose, another series of experiments wasconducted at the already determined middle position of explosive column but with varying lengths of airdeck.
Experiments were conducted at four different airdeck lengths of 10 %, 20 %, 30%, and 40% of the total column charge. The results are shown in Table 5.
These results suggested that airdeck length equivalent to 20% of total column charge produced the best fragmentation. Figure 8 shows the cumulative percentage plot for the blasted block fragments for all
the experiments in this phase.
The mean fragment size for the blasted block was calculated and
presented in Table 6. The mean fragment size decreases gradually with increase of airdeck size from 0 to 20% and then increases with increasing airdeck size. The Figure 9 shows that 20% airdeck produces the smallest mean fragment size, which has significant economic effect on subsequent size reduction processes, and then mean fragment size increases with increasing airdeck size.