Abstract
3D printing of concrete and related digital fabrication techniques are enjoying rapid growth. For these technologies to be broadly accepted in structural applications and to be economically competitive, quality control methods of the process will be required. Additive concrete manufacturing processes are sensitive to process settings and conditions, which calls not only for preprint structural modelling to establish printability, but also for in-print monitoring to ensure expected properties are indeed achieved. Non-destructive test methods are highly suitable for this aspect of quality control, as they usually allow efficient, high frequent digital measurements that require relatively little effort. However, as they generally do not directly measure the appropriate parameter(s), correlations between non-destructive and destructive testing have to be established. The preprint structural modelling is based on a number of time-dependent mechanical properties, including the compressive strength and the Young's modulus. If concrete is still in the dormant state, as it often is in 3D concrete printing, these properties require difficult, time consuming destructive tests to establish. In the present work, the correlation between these two mechanical properties on the one hand, and the pulse velocity on the other, was studied. A (destructive) unconfined uniaxial compression test was applied to determine the former, while a (non-destructive) ultrasonic wave transmission test was used for the latter. As expected from previous research on a similar mortar, both the compressive strength and the Young's modulus were found to increase linearly in a time frame of 5–90 min after extrusion. This is attributed to thixotropic build-up. Within that time frame, the pulse velocity also grew in a linear fashion. Thus, a simple linear correlation between the destructive and non-destructive test results could be established. For now, this allows continuous quality control on simply obtainable control batches. Furthermore, it stimulates the development of ultrasonic online monitoring methods for the objects during printing.
| Original language | English |
|---|---|
| Pages (from-to) | 447-454 |
| Number of pages | 8 |
| Journal | Construction and Building Materials |
| Volume | 181 |
| DOIs | |
| Publication status | Published - 30 Aug 2018 |
Funding
The support of the staff of the Structures Laboratory Eindhoven is greatly acknowledged. The assistance in the 3DCP research of Master track students Structural Design at the TU/e Department of the Built Environment is highly valued. For this paper, the authors appreciate the work of R. Crombez, C. Simpelaar and M. van de Ven in particular, on whose MSc project the material presented is partially based. The TU/e research program on 3D Concrete Printing is co-funded by a partner group of enterprises and associations, that on the date of writing consisted of (alphabetical order) Ballast Nedam, BAM Infraconsult bv, Bekaert, Concrete Valley, CRH, Cybe, Saint-Gobain Weber Beamix, SGS Intron, SKKB, Van Wijnen, Verhoeven Timmerfabriek, and Witteveen + Bos. Their support is gratefully acknowledged.
Keywords
- 3D Printing
- Compression test
- Fresh concrete
- Mechanical properties
- Ultrasonic testing