Comparative Physical Characteristics of Fine and Coarse Shotcrete

摘要

The conclusions concerning hardened shotcrete tested at ages from 7 to 28 days are considered valid for the particular mixtures used, but are not necessarily applicable to all hardened shotcrete. The density of fine shotcrete (3/8-inch maximum-size aggregate) varies as much as three times that of coarse shotcrete (3/4-inch maximum-size aggregate). Size and type of test specimen are insignificant relative to testing the density of shotcrete. Poisson's ratio of either fine or coarse shotcrete, and flexural strength of coarse shotcrete, are not affected by size of test specimen. Young's modulus, flexural strangth, compressive strength, and strength of bond to steel tend to increase with age in both fine and coarse shotcrete. The position of reinforcing bars at the time of gunning has no bearing on bond strength. Three-inch cubical, pull-out test specimens are not sufficient for ascertaining the bond strength of shotcrete walls 6 inches thick. It is recommended that methods of producing ready-mixed mortar for use as fine shotcrete be revised to improve the distribution of cement throughout the mass when the mortar is discharged from the truck mixer. Also recommended is the use of large shotcrete test specimens for verifying flexural strength and the use of cylindrical rather than cubical test specimens for verifying compressive strength of shotcrete. (Author)