ABSTRACT The double punch test (DPT) is increasingly used internationally for quality control of steel fiber reinforced shotcrete (SFRS). This study intends to verify the influence of the DPT specimens’ diameter on the residual strength behavior of the SFRS. The experimental program aims to evaluate the dynamics of the test in terms of the results obtained from the analytical conversion of the axial displacement into total circumferential opening displacement (TCOD). The results are compared to those obtained through the 3D digital image correlation (DIC3D) to evaluate its applicability as a quality control method of the SFRS. The results demonstrated that the TCOD could be easily obtained by analytical conversion with reliable accuracy. The analysis of the DPT results could consider the crack opening level to obtain constitutive equations. The diameter of the DPT specimens directly influences the structural parameters of the SFRS. Smaller specimens may show a 35% reduction in residual strength associated with the service limit state. As the coefficient of variation of the residual strength associated with the ultimate limit state practically doubles when smaller specimens are used, for the same reliability, the sample sizing of the specimens of 10 cm is twice the quantity of the 15 cm.

The present study proposes a methodology to characterize the mechanical properties of synthetic macrofibres, which are used as a reinforcement of new composites applied in civil construction industry. Some standards suggest that this characterization should be performed on original filaments and others propose using the current methodology used to characterise metallic fibres. These recommendations turn difficult the quality control procedure, so it was developed a methodology to characterize the mechanical properties of the macrofibres as they are supplied in the construction site, using the tensile test. In that sense, two types of macrofibres were evaluated obtaining their tensile strength and elastic modulus. Additionally, the macrofibres were mixed with aggregates in order to study how the abrasion affects their mechanical properties. Summing up, the proposed methodology is feasible, especially to estimate the tensile strength allowing its application in ordinary laboratories. Regarding the elastic modulus results, they may be underestimated using this method. Finally, it was observed that the abrasion between the macrofibre and the aggregates during the mixing process compromises the mechanical properties decreasing both the tensile strength and the elastic modulus.