Evaluation of the repeatability and reproducibility of the double punch test

Abstract

The constant advances in the use of fiber reinforced concrete (FRC) bring the need of developing practical tests for quality control programs. The double punch test (DPT) is a promising alternative technique in relation to the flexural test of notched beams as proposed by the fib Model Code 2010. In that sense, this work aims to investigate the possibility of finding repeatability and reproducibility of the crack and residual loads determined by DPT. For the repeatability study, an experimental program was developed in a single laboratory, involving two steel fiber contents (30 kg/m3 and 55 kg/m3) in three equivalent concrete batches. For the reproducibility study, an interlaboratory program was developed, involving the same fiber and contents and the same concrete matrix, tested in six different laboratories. In both parts, analysis of variance and the ASTM E691 method were used to compare average and variance values. In addition, the minimum number of specimens necessary to provide adequate results of average and variance was determined. The results showed that the DPT is sensitive to variations in the mechanical properties after cracking of the FRC that are of special interest for structural application. In addition, it is possible to find repeatability and reproducibility of residual loads in terms of average values with a limited number of specimens. The crack load was repeatable in the same fiber content, but not reproducible. Despite this, DPT can be considered as efficient for the ordinary control of the quality of the FRC.