New Developments in In-Place Testing of Shotcrete

TL;DRAbstract

Present methods of quality control are briefly reviewed and one method, the pullout test method, is discussed in detail. The testing of cores from the lining which is the most representative of the present methods has some shortcomings: damage in drilling small cores; cores cannot be drilled at early ages. Two commercially available testing devices are described. The Windsor Probe method consists of shooting a probe into the shotcrete with a calibrated explosive and measuring penetration which is then correlated to compressive strength. The rebound hammer measures the rebound of a rod that is forced against the shotcrete or concrete surface by a calibrated spring. These rebound values are then related to compressive strength. The apparatus used in the pullout test method is illustrated. A bolt with a washer brazed to the head is embedded in the fresh shotcrete or concrete. At the time of testing this bolt is pulled from the material through a steel ring and a truncated cone of shotcret

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