Size effect of ultra-high-performance concrete under compression: effects of steel fiber characteristics and water-to-binder ratio

Understanding the size effect of UHPC under compression is fundamental and essential for component and/or structure design and analysis. This paper investigated the size effect of UHPC cubes (40, 70.7, 100, and 150 mm) under compression through considering the steel fiber characteristics (1%, 2%, 3% short straight, short hooked, and long hooked steel fibers) and water-to-binder ratios (0.16, 0.18, 0.2 and 0.22). Bazant size effect law (SEL) and Weibull statistical theory of size effect were employed to analyze the influence of those factors on the size effect of compressive behavior of UHPC. Results showed the size effect of compressive strength of UHPC increased with the increase of short straight fiber content, but decreased with the increase of w/b ratio. Given the fiber content, UHPC with short hooked fiber showed the greatest size effect, while that with long hooked fiber exhibited the lowest size effect. SEL was more robust and reliable in predicting the change in compressive strength of UHPC with specimen size. The fitted compressive strength from SEL was more accurate with the increase in fiber content and the decrease in w/b ratio.

Automated summary

Understanding the size effect of UHPC under compression is essential for design and analysis purposes. This study investigated the size effect of UHPC cubes through variations in steel fiber content and water-to-binder ratios. The results indicate that the compressive strength size effect of UHPC increases with an increase in short straight fiber content, but decreases with an increase in water-to-binder ratio. UHPC with short hooked fiber exhibits the largest size effect, while UHPC with long hooked fiber shows the smallest size effect. The Bazant size effect law is a more reliable predictor of the change in UHPC compressive strength with specimen size.