=+71. Curing concrete is known to be vulnerable to shock vibrations, which may cause cracking or hidden damage to the material. As part of a study of vibration phenomena, the paper “Shock Vibration Test of Concrete” (ACI Materials J., 2002:

361–370) reported the accompanying data on peak particle velocity (mm/sec) and ratio of ultrasonic pulse velocity after impact to that before impact in concrete prisms:

Obs ppv Ratio Obs ppv Ratio 1 160 .996 16 708 .990 2 164 .996 17 806 .984 3 178 .999 18 884 .986 4 252 .997 19 526 .991 5 293 .993 20 490 .993 6 289 .997 21 598 .993 7 415 .999 22 505 .993 8 478 .997 23 525 .990 9 391 .992 24 675 .991 10 486 .985 25 1211 .981 11 604 .995 26 1036 .986 12 528 .995 27 1000 .984 13 749 .994 28 1151 .982 14 772 .994 29 1144 .962 15 532 .987 30 1068 .986 Transverse cracks appeared in the last 12 prisms, whereas there was no observed cracking in the first 18 prisms.