Influence of water-to-binder ratio on top-bar effect and on bond variation across length in Self-Compacting Concrete specimens

Abstract

The present study is investigating the impact of five different water-to-binder (w/b) ratios on bond capacity of Self-Compacting Concrete (SCC) specimens, with a focus on top-bar effect and on bond variation across horizontal specimens with a single casting point at one edge. One 600mm high vertical specimen and one 1780mm long horizontal specimen with transverse reinforcement bars that were distributed over height and across length, respectively, were cast and tested by pull-out for each of five SCC mixtures, and compared to three Normally Vibrated Concrete (NVC) mixtures with similar aggregate grading curves and compressive strength. The bond–slip curves were evaluated on the basis of analytical models for NVC, proposed by major international building codes and literature. SCC develops an improved bond capacity, a less intense top-bar effect and a lower scatter compared to NVC. The analytical bond–slip model curves appear to underestimate bond stiffness and overestimate the assumed maximum bond stress. Water increase leads to lower stresses and a more intense top-bar effect, which is though always less significant in SCC. The code provisions concerning the top-bar effect of rebars close to the poor bond conditions zone seem to overestimate the actual bond reduction. Bond capacity of SCC is not decreased across length up to the measured rebar distance (1.60m) from the casting point and the scatter of the resulting stresses is significantly lower compared to NVC, especially for higher w/b ratios.