Comparative analysis of structural build-up in one-component stiff and two-component shotcrete-accelerated set-on-demand mixtures for 3D concrete printing

Figures & data

Table 1. Mix proportion (kg/m³).

Mix name	Water	OPC-I	Fly ash	Silica fume	Sand	Water reducer	Viscosity Modifying Admixture	Accelerator
Stiff mixture (1 K)	222.9	602.7	172.7	86.5	1190.5	17.8
Set-on-demand (2 K)	251.1	439.4	125.6	62.7	1253.1	6.3	0.6	47.1

Figure 1. Experimental tests: (a) unconfined uniaxial compression test (b) shear vane test, (c) ultrasonic pulse velocity test, (d) slow penetration test, and (e) printing test.

Table 2. Printing strategy for 3DCP with the selected mixtures.

Mix name	Print geometry	Printing test ID	Building rates	Time gap (sec)	Print speed (mm/sec)	Nozzle type
Stiff mix (1 K)	Cylinder diameter = 500 mm, layer thickness = 10 mm, height = 450 mm	I	0.8 m/hr	45	34.89	Circular
		II	1.44 m/hr	25	62.80
Set-on demand (2 K)	Cylinder diameter = 250 mm, layer thickness = 10 mm, height = 1100 mm	III	2.57 m/hr	14	56.04	Circular
		IV	5.14 m/hr	7	112.08

Figure 2. Printing setups for set on demand and stiff mixtures.

Figure 3. Green strength evolution measured with Uniaxial Unconfined Compression Test for stiff mix (1 K) versus set-on-demand mix (2 K).

Figure 4. Young's modulus evolution measured with Uniaxial Unconfined Compression Test for stiff mix (1 K) versus set-on-demand mix (2 K).

Figure 5. Yield stress measured with shear vane test: stiff mix (1 K) versus set-on-demand mix (2 K).

Figure 6. Ultrasonic Pulse Velocity profile of stiff mix (1 K) vs set-on-demand mix (2 K) during early age.

Figure 7. Slow penetration resistance profile of stiff mix (1 K) during vs set-on-demand mix (2 K).

Figure 8. Buildability test using stiff mixture: (a) successful print with the building rate of 0.8 m/hr and (b) plastic failure at the building rate of 1.44 m/hr.

Figure 9. Buildability tests using set-on-demand mixture: (a) successful printing with the building rate of 2.57 m/hr, (b) elastic buckling failure at the building rate of 5.14 m/hr.

Table 3. Direct printing test results.

Mix name	Print geometry	Printing Test ID	Building rates	Printing Performance (achieved maximum layer number)
Stiff mix (1 K)	Cylinder diameter = 500 mm, layer thickness = 10 mm, height = 450 mm	I	0.8 m/hr	Stable, no failure detected within the limit of gantry printer (45 layers)
		II	1.44 m/hr	Plastic failure at 16th layer
Set-on demand (2 K)	Cylinder diameter = 250 mm, layer thickness = 10 mm, height = 1100 mm	III	2.57 m/hr	Stable, no failure within the limit of robotic arm printer (110 layers)
		IV	5.14 m/hr	Elastic buckling failure at 88th layer

Figure 10. Predicted number of layers for plastic failures using the UUCT and shear vane test for the stiff mixture.

Figure 11. Predicted number of layers for buckling failure using the UUCT result for the set-on-demand mixture.

Table 4. Comparison of predicted print failure layer counts from test methods versus actual failure triggering layer counts in direct 3D printing tests.

Mix name	Printing rate (m/hr)	UUCT	Shear vane	Failure detection
Stiff mixture (1 K)	0.8	89	26	No failure (stable up to 45 layers)
	1.44	47	20	16^th layer
Set-on-demand mixture (2 K)	2.57	136	-	No failure (Stable up to 110 layers)
	5.14	119	-	88th layer

Data availability statement

The authors confirm that the data supporting the findings of this study are available within the article.