Study Aims to Mitigate Weak Interlayer Zones in Concrete

Brief 

A study of the interlayer fracture behavior of functionally layered concrete found multi-mix fracture behavior depended on the placement delay and the mix combination. Results also showed that an uplift of fracture properties for functionally graded specimens is possible compared to single-mix specimens.

Insight 

A paper recently published in the journal Engineering Fracture Mechanics analyzed the interlayer fracture behavior of layered concrete to prevent weak interlayer zone (ILZ) formation.

Background

Additive manufacturing (AM)/three-dimensional (3D) printing and automatization can facilitate the transition from conventional monolithic concrete forms towards more effective structural composites or functionally-graded elements, as these advances allow efficient fabrication of functionally-layered concrete (FLC).

In FLC, material layers with various mix compositions can be tailored to specific thermal or mechanical performance requirements of the layered concrete to use the concrete more efficiently, leading to cost savings and a reduction in the carbon dioxide footprint in the environment.

For instance, a lower cement lightweight concrete core in an FLC can improve the thermal performance or reduce the dead load of the layered concrete. Similarly, a higher cement mix can be utilized as the outer layer to improve the stiffness or durability of the concrete.

However, the deposition of various wet-on-hardened and wet-on-wet concrete layers induces the risk of a weak ILZ between two adjacent concretes. The ILZ is susceptible to cold joint formation and introduces a weak zone in the concrete depending on the mix compositions and casting conditions. Additionally, the fresh-state behavior and rheology and the surface quality/character of the wet layers also influence the ILZ behavior.

In 3D concrete printing applications, the ILZ is often formed between the adjacent concrete mixes with the same compositions and different print delay times. The deposition/pour delay times and mix compositions can potentially interact to influence the ILZ behavior of the FLC.