Leveraging clay formwork 3D printing for reinforced concrete construction

Figures & data

Figure 1. Commercial ready-to-use terracotta clay block (left), slump flow test of the SCC mix with a spread range of 500–600 mm (center), and steel fibers (right).

Table 1. Terracotta clay properties.

Wet density ($\mathrm{kg}/{\mathrm{m}}^3$)	Natural moisture content (%)	Atterberg limits (%)		Unconfined compression strength (kPa)	Undrained shear strength (kPa)
2003.9	26.7	LL=38	PL=17	41.5	20.7

Table 2. Concrete composition (% of the total mix weight).

Sand (0.3–2 mm)	Aggregate (4.75–9.5 mm)	Portland cement(I/II)	Water	Limestone	Superplastisizer	Retarder	Accelerator
39.5	30.2	14.1	8.7	5.2	0.2	0.2	1-2

Figure 2. Sample trials to fine-tune the SCC mix, and adjust the retarder and accelerator proportions.

Figure 3. Cylinder samples used in the compression test; samples 2 and 4 showed lower compressive strengths.

Figure 4. Stress-strain curves under the direct tension for three #5 rebars (Ø = 15.95 mm, $A=198{\mathrm{mm}}^2$) including the average dynamic values for yield stress $f_y$, ultimate stress $f_u$, and ultimate strain ${ϵ}_u$.

Figure 5. Overview of the fabrication process: (top) printing and casting sequence, and (bottom) removal of the self-detached external formwork, installation of the longitudinal rebars (after the removal of the internal formwork), grouting the void, and the finished beam before screwing the anchorage bolts.

Figure 6. Beam properties and structural test configuration, the dashed lines show the casting layers (dimensions in mm).

Figure 7. Formwork cross-section with four stiffeners and an internal void: interlayer (left) and mixed (right) fibers.

Figure 8. Recycling process: demolded formwork (left), crushed pieces in the fabric (center), kneaded clay ready for extrusion (right).

Table 3. Overview of the beam specimens.

Beam ID${}^{\ast }$	Formwork	Steel fibers	Rebars
B1-CL-I	clay	interlayer	yes
B2-CL-M	clay	mixed	yes
B3-RCL-I	recycled clay	interlayer	yes
B4-RCL-M${}^{\ast \ast }$	recycled clay	mixed	yes
B5-WD-M	wood	mixed	yes
B6-WD-M	wood	mixed	yes

Notes:

${}^{\ast }$Beam ID abbreviations – B#: beam number, CL: clay formwork, RCL: recycled clay formwork, WD: wood formwork, M: mixed fibers, and I: interlayer fibers.

${}^{\ast \ast }$Failed specimen.

Figure 9. Four-point bending test setup with four pairs of kinematic tracking markers installed on the beam's surface.

Figure 10. The three beams fabricated with 3D-printed clay formwork; the beam with recycled and reused clay is on the right side, with the exterior formwork just removed.

Table 4. Terracotta clay properties (non-recycled vs. recycled${}^{\ast }$).

Wet density ($\mathrm{kg}/{\mathrm{m}}^3$)	Natural moisture content (%)	Atterberg limits (%)		Unconfined compression strength (kPa)	Undrained shear strength (kPa)
2003.9	26.7	LL=38	PL=17	41.5	20.7
1968.7${}^{\ast }$	29.2*	LL=41${}^{\ast }$	PL=18${}^{\ast }$	27.1${}^{\ast }$	13.6${}^{\ast }$

Figure 11. Formwork deformations as: (top) histograms with a bin size of 0.5 mm, and (bottom) heat maps with reported average (μ), median (η), and standard deviation (σ). The continuous vertical red/yellow lines in the heat maps are related to ridges caused by the formwork stiffeners and can be ignored.

Figure 12. Load-displacement behaviour. Table 5 shows the values at the ultimate load marked with circles and their corresponding deformation. The curve for B1-CL-I is not presented because of the premature anchorage failure.

Table 5. Summary of the test results presented in Figure 12, $F_u$ is the ultimate load and ${\mathrm{\Delta }}_u$ is the mid-span deflection at $F_u$.

Beam ID	$F_u$ (kN)	${\mathrm{\Delta }}_u$ (mm)	Failure mode
B1-CL-I	–	–	anchorage failure
B2-CL-M	37.95	1.14	shear
B3-RCL-I	40.48	2.29	shear
B5-WD-M	48.87	1.57	shear
B6-WD-M	46.09	2.04	shear

Figure 13. Diagonal tension shear failure of the four tested beams close to failure (80-90% of the peak load).

Data availability statement

The data for this study is available at the following DOI link: https://doi.org/10.34770/d6kk-qt95

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