Evaluating the impact of specimen and punch sizes on the tensile strength of UHPC through double punch testing

Abstract

Many studies have shown that direct tensile tests are fraught with numerous challenges. The Double Punch Test (DPT) is considered a more reliable alternative for evaluating tensile properties among the indirect tensile methods. While DPT is efficient and reliable, its size effect should not be overlooked. Previous studies on DPT size effects have primarily focused on specimen size, with little discussion on the impact of punch size variations. Additionally, with the evolution of construction materials, the applicability of the generalized DPT formula to new materials, such as Ultra-High-Performance Concrete (UHPC), with its exceptional strength, toughness, durability, and crack resistance, needs to be evaluated. This study conducts experimental research on UHPC, focusing on the relationship between specimen and punch sizes and their impact on tensile strength measurements. By designing experiments with 12 different specimen sizes and punch ratios, we explore the differences between actual experimental results and simplified formula calculations. Bažant's theoretical methods are also applied to analyze the size effects of specimen and punch dimensions on DPT. The results indicate that, with appropriate specimen size and punch ratio, DPT can provide tensile strength measurements closer to those of Direct Tensile Tests (DTT). It was also found that tensile strength, strain, and toughness decrease with increasing specimen size. When the ratio of UHPC specimen to punch size (d/D) is 1/3, the results align well with the predictions of the simplified formula. This indicates that the optimal punch ratio is not fixed for different specimen sizes. These findings offer valuable references for designing related experiments and improving quality control and structural performance in various engineering fields.