New Trends and Technologies in Characterizing, Controlling, and Predicting the Workability of 3D Printed Concrete, Part 2 of 2

Sunday, October 29, 2023  10:30 AM - 12:30 PM, W-Marina Ballroom III

3D printing has exploded onto the scene of concrete construction technologies, bringing with it a renewed appreciation for workability in all its aspects. This session will cover advances and challenges in characterizing, controlling, and predicting the workability of 3D-printed concrete, from case studies to research applications. This session is suitable for people new to 3D printing, as well as those experienced with 3D printing.

Learning Objectives:
1) Identify quality control methods in testing and monitoring 3D printed concrete filaments;
2) Review practical considerations for field-testing of the rheology of extruded concrete;
3) Discuss the effect of mix design and admixtures on the rheology of printable concrete and mortars;
4) Examine the correlation between printing properties and cement rheology.

This session has been approved by AIA and ICC for 2 PDHs (0.2 CEUs). Please note: You must attend the live session for the entire duration to receive credit. On-demand sessions do not qualify for PDH/CEU credit.

Development of a Real-Time Geometric Quality Monitoring System for 3D Printed Concrete Filaments Using a Rotating Nozzle and 2D Laser Detection

Presented By: Jung-Hoon Kim
Affiliation: Yonsei University
Description: Effective geometric quality assurance for 3D Concrete Printing (3DCP) requires automated, real-time, cost-effective and non-destructive methods. In this regard, this study presents the working operation of a newly developed automated test for monitoring the width, thickness, and cross-sectional area of extruded filaments. The hardware of the quality monitoring system consists of a rotating nozzle and a laser triangulation-type 2D laser detection system, which consists of a 2D line laser and a CMOS camera. It is specifically designed for real-time use while considering the requirements for the camera's field of view (FOV), minimum object distance (MOD), physical dimensions and weight requirement suitable for the rotating nozzle. Unlike previous research, the rotatable nozzle attached to the 3D printer allows monitoring the extrusion for all directions along the printing path. The proposed processing algorithm to compute the profile information of extruded filament involves image segmentation, extraction, and clustering for laser profile, coordinate transformation, estimation of reference ground line, and calculation of the geometry of the filament. The basic performance test under static conditions shows a sufficient accuracy of 0.087mm in FOV, and the experimental results demonstrate the feasibility of the developed system for in-situ quality monitoring during the 3DCP process.

Matric Suction and its Effect on the Shape Stability of 3D Printed Concrete

Presented By: Jae Hong Kim
Affiliation: KAIST
Description: The mix design of 3D printed concrete has adopted various types of binders and additives to enhance its casting performance and shape stability. Matric suction, as an attractive force among partially unsaturated particles of the binders and additives, influences the shape stability of firm cement paste composing 3D printed concrete. Higher matric suction induces higher compressive strength (or green strength) and higher elastic modulus. The extended Mohr–Coulomb failure envelope describes the stress state of the 3D printed concrete considering its matric suction. Variation of the matric suction takes parallel shifting and rotation of the shape failure envelope. The test results on the matric suction finally confirm the effect of binders and additives. Change in the water-to-binder ratio contributes to higher matric suction related to the parallel shift of the Mohr-Coulomb failure envelope, while incorporating nanoclay or polycarboxylate ether affects the internal friction angle of the binder

Using Vibration to Control the Rheology of Concrete for 3D Printing

Presented By: KARTHIK PATTAJE
Affiliation: WIE
Description: Concrete mixtures which are 3D printed typically do not contain coarse aggregates. In this study, vibration was used to manipulate the rheology of concrete mixtures which included coarse aggregates. Using an experimental design method called Box-Wilson central composite design (CCD), the rheology of the concrete was statistically modelled both during vibration and without vibration. The sensitivity of the mixture design parameters (volume of paste, volume of sand, and water to cement ratio) on the rheology of concrete was investigated. It was found that aggregates play a significant role in the behavior of concrete in its fresh state. The volume of total aggregates in a mixture and its water to cement ratio were found to have the greatest influence on the rheology. The equations developed from this statistical model can help guide changes to be made to printable mixture designs.

Rheological Characterization of 3D Printable Mixtures Beyond Flow Initiation

Presented By: Ala Eddin Douba
Affiliation: Purdue University
Description: The innovations in 3D printing concrete generated an accelerated interest in cement rheology targeting maximizing structural buildup while maintaining rapid shear thinning. As a result, various rheological admixtures and extrusion methods were developed to meet the complex and demanding rheological profile of 3D printing concrete. Literature shows great emphasis on flow initiation measurements via shear rheology to prevent buildability collapse. However, there is still limited literature on the impact of the rheological characterization method and the underlying 3D printing admixtures mechanisms on the true in-situ rheological properties. In this work, we compare the effects of different types of rheological admixtures on shear and extensional rheological properties. In addition, we highlight a number of other rheological properties such as colloidal elastic modulus and critical strain in identifying other printing properties such as shape stability.