Suggested modified testing techniques to the ACI 544-R repeated drop-weight impact test

Abstract

Experimental tests were conducted in this study to introduce two simplified modifications to the setup of the ACI 544-2R repeated impact test aiming to reduce the results scattering of this test. The first modification is the using of sand bedding as a replacement to the steel baseplate, while the second is the using of notched specimens that are either centrally line notched or cross notched and loaded through a line or cross knife-like load transferring steel plate. Hence, the drop impact load is distributed along the specimen’s notch using the topping knife-like plate. To evaluate the proposed modification techniques, 90 cylindrical high performance concrete specimens were tested in six groups. The test results showed that, in notched specimens, the cracks were formed along the projections of notches, while several random cracks were formed in those without notches. The results also showed that the effect of fine sand bedding depends on the loading pattern, and that the dispersion of results can be reduced by using notched specimens with the load distributed along these notches. Using line notched specimens with sand bedding was found to exhibit the lowest results dispersion among the six investigated loading cases. The COV reduced by more than 60% compared to the current ACI 544-2R testing technique. At 90% level of confidence with a maximum error of 10%, the minimum required number of specimens is 55 for the ACI 544-2R test procedure, while only 7 specimens are required if sand bedding with line notch specimens are used.