Effect of aggregate content and fibre type on the rheological behaviour and structural build-up of fibre reinforced self-compacting concrete using two binder compositions

Abstract

[Abstract:] Many parameters influence the fresh behaviour of fibre reinforced self-compacting concrete (FRSCC), such as length, aspect ratio, fibre content, solid volume fraction, and particle interaction. Most studies did not analyse rheological behaviour (just workability) and they are focused on paste or mortar. However, the analysis at the concrete level is also required to confirm the behaviour when the coarse aggregates and fibres are employed. This kind of analysis is scarce in the literature. Hence, this work aims to increase the knowledge about the effect of aggregate content and fibre type on FRSCC. To do so, the behaviour of self-compacting mixes with three different aggregate contents (550, 500, and 650 l/m3), two cementitious systems (100 % cement, and 60 % cement, 25 % limestone filler and 15 % metakaolin), and three different types of rigid fibres (two metallic and one polypropylene) were analysed. To characterise the concrete rheological performance, the stress growth test (SGT) was selected to avoid any fibre orientation. SGT was repeated twice under undisturbed and disturbed conditions to assess the structural build-up of the concrete. The results indicate that there is a critical value of the relative packing fraction that, once overcome, severely affects the fresh behaviour of FRSSC. This critical value can be calculated as the ratio between random loose packing fraction and dense packing fraction. It can be used to design a FRSCC mix guaranteeing that the fresh state remains in a suitable range where the hydrodynamic interactions dominate the behaviour and therefore, changes in the mix composition will not sharply modify the rheological performance of the concrete.