Using micro-XRF to characterize chloride ingress through cold joints in 3D printed concrete.

Concrete 3D printing has advanced rapidly, but weaknesses at printed layer interfaces remain poorly understood. Established knowledge shows that cold joints form between layers, often leading to reduced strength. However, the long-term durability of these interfaces has not been thoroughly explored. Chloride ingress is a known durability threat in traditional concrete, but its behavior in 3D printed systems is unclear. Prior research has focused on mechanical properties rather than transport phenomena. This gap motivated the need for new methods to study chloride movement through cold joints. No prior work had resolved how curing conditions affect chloride transport in printed concrete. This paper introduces a novel approach using μXRF to address this issue. The study aims to bridge the knowledge gap between material strength and durability in 3D printed concrete.

This study aimed to investigate chloride ingress through cold joints in 3D printed concrete using a novel imaging method. The specific problem is understanding how chloride ions penetrate weak interfaces between printed layers. The motivation stems from the lack of data on durability in 3D printed concrete. Cold joints are suspected to act as pathways for aggressive agents like chlorides. The authors propose using μXRF to visualize chloride ingress at high spatial resolution. This method allows direct detection of chloride ions without destructive sample preparation. The study also compares μXRF results with neutron imaging of moisture uptake. The goal is to assess the effectiveness of μXRF in durability analysis of printed concrete.

The researchers used μXRF to image chloride ingress in 3D printed concrete specimens. Specimens were produced with varying layer deposition time intervals. The cold joints formed after a 1-day interval were analyzed for chloride susceptibility. Neutron imaging was also used to compare moisture uptake patterns. The μXRF method provides spatial resolution and direct analysis of chloride ions. Specimens were exposed to chloride solutions to simulate ingress conditions. Curing conditions were varied to assess their impact on transport rates. The method allows non-destructive visualization of chloride distribution across interfaces.

Cold joints formed after a 1-day interval showed high susceptibility to chloride ingress. Curing conditions significantly influenced the speed of chloride transport. μXRF imaging revealed detailed chloride distribution at layer interfaces. Neutron imaging showed complementary moisture uptake patterns. The highest chloride concentration was observed at weak interfaces between printed layers. Specimens with longer curing intervals showed reduced chloride penetration. The μXRF method successfully detected chloride ions at micrometer resolution. These findings suggest that cold joints act as preferential pathways for aggressive agents.

The study demonstrates that μXRF is a useful tool for analyzing chloride ingress in 3D printed concrete. Cold joints formed after a 1-day interval are highly vulnerable to chloride transport. Curing time strongly affects the rate of chloride ingress through interfaces. The μXRF method offers spatial resolution and direct detection of aggressive species. Neutron imaging complements μXRF by showing moisture distribution. The findings suggest that cold joints function as chloride transport channels. The authors propose that μXRF can be used to study transport phenomena in printed concrete. These results may inform future strategies to improve the durability of 3D printed structures.