Interlayer fracture behaviour of functionally layered concrete

Abstract

Automatization and additive manufacturing provide a platform to move away from traditional monolithic concrete forms towards more material efficient functionally-graded or structural composite elements. This has a great potential to tailor the element’s mechanical or thermal performance which allows to efficiently use material and furthermore safe costs and reduce the environmental footprint of an element. However, the deposition of different wet-on-wet and wet-on-hardened concrete layers introduces the risk of a weak interlayer zone (ILZ). Furthermore, functionally layered concrete made of multi-mixes introduces a new dimension whereby the mix compositions and the deposition delay times potentially interact to influence the interlayer behaviour.To provide a better insight on the interlayer zone behaviour of functionally graded concrete, a detailed investigation of the interlayer fracture properties of multi-mix concrete elements cast in layers and the effect of the pour delay between layers is presented. Wedge-splitting-tests are used to infer the fracture behaviour of layered specimens fabricated using three different concrete mixes in single and multi-mix combinations. The influence of a pour delay between layers of up to 4.0 h is also interrogated. The results show that the multi-mix fracture behaviour depends on not only the mix compositions but also on the pour delay time. Cases where the fracture properties were at least as good as, or even better, than those of the comparator weaker single mix suggest that judicious mix designs and controlled fabrication processes for functionally layered concrete can mitigate the formation of weak ILZs.