A thermo-hygro computational model to determine the factors dictating cold joint formation in 3D printed concrete

TL;DR

This paper introduces a computational model that simulates drying and hydration processes in 3D printed concrete to predict cold joint formation, aiding in understanding and mitigating structural heterogeneity.

Contribution

The study presents a novel thermo-hygro model that integrates drying kinetics and cement hydration to estimate cold joint formation timing in 3D printed concrete.

Findings

Model accurately predicts cold joint formation timing.

Environmental and geometric factors influence drying severity.

Recommendations for cold joint mitigation are provided.

Abstract

Cold joints in extruded concrete structures form once the exposed surface of a deposited filament dries prematurely and gets sequentially covered by a layer of fresh concrete. This creates a material heterogeneity which lowers the structural durability and shortens the designed service life. Many factors concurrently affect cold joint formation, yet a suitable tool for their categorization is missing. Here, we present a computational model that simulates the drying kinetics at the exposed structural surface, accounting for cement hydration and the resulting microstructural development. The model provides a time estimate for cold joint formation as a result. It allows us to assess the drying severity for a given structure's geometry, its interaction with the environment, and ambient conditions. We evaluate the assessed factors and provide generalized recommendations for cold joint mitigation.