PSI - Issue 64

300

a) FFT

H. Varela et al. / Procedia Structural Integrity 64 (2024) 1427–1434 Varela et al./ Structural Integrity Procedia 00 (2019) 000 – 000

1432

6

300

conventional specimens, it was observed that 3DP increased D ap in all cases, again due to particle squeezing during extrusion. Figure 6 summarizes capillary water absorption index ( i ) on conventional and 3DP specimens capillary absorption. Conventional specimens of reference mortar M0 and mortar with larger VF of longer SF M3 showed the highest i at 24h reaching values around 0.3 g/cm 2 . Lower VF of long SF showed lower i . M4, the mortar with shorter SF, was the mixture with the lowest i (0.21 g/cm 2 ). 3DP samples showed a faster i evolution at the initial time, reaching 0.15g/cm 2 in less time than conventional samples. This effect could be produced by fiber alignment and water retention capacity, which accords to Hamback et al. (2016), Varela et al. (2023a) and Toledo Filho et al. (2009). Furthermore, 3DP samples showed more similarity between mixtures evolution than conventional samples which showed a higher behavior range of i evolution. Alternatively, all 3DP samples reached i of 0.25 to 0.3 g/cm 2 , except M1 (0.23 g/cm 2 ). The most remarkable change between conventional casting and 3DP specimens was observed for M4 (short SF fiber) related again to extrusion and particle squeezing as in Wolfs et al. 2019, Varela et al. (2023a) and Liu et al. (2023). a) FFT 300 a) FFT 300 a) FFT

R FS-0.5% FS-1% FS-1.5% FS(6.5)-1.0% M4

3DP R FS-0.5% FS-1% FS-1.5% FS(6.5)-1.0% 100 10 M3

10 R FS-0.5% FS-1% FS-1.5% FS(6.5)-1.0% M2

10 R FS-0.5% FS-1% FS-1.5% FS(6.5)-1.0%

Final Diamter (mm)

Conventional R_stirred FS-0.5%-Stirred FS-1%_stirred FS-1.5%-Stirred FS(6.5)-1.0% 100 Final Diamter (mm) 100 M0 M1

Final Diamter (mm)

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 100

Time (min)

Final Diamter (mm)

Time (min)

90

i (g/cm 2 )

i (g/cm 2 )

Time (min)

90

Time (min)

10

90

0

1

2

3

4

5

0

1

2

3

4

5

time (h 1/2 )

time (h 1/2 )

Fig. 6. Capillary water absorption index ( i ) of conventional and 3DP specimens.

Figure 7 presents the mechanical parameters measured on conventional and 3DP specimens. Regarding compressive strength results ( F c ), a reduction regarding conventional casting was measured for all 3DP samples and the reference mortar (M0) presented the highest values for both conventional casting and 3DP (29 and 22 MPa respectively). SF addition reduced F c in both conventional and 3DP specimens, according to Wolfs et al. (2019) and Van Overmier et al. (2023). Among SF mixtures, M1 and M4 showed the highest F c value in in both conventional and 3DP specimens, showing values similar to reference mortar (M0) for 3DP specimens. On the other hand, samples with higher 13 mm length fibers amounts (M2 and M3) showed the lowest F c values (conventional around 20 MPa and 3DP around 17 MPa). The highest the dosage of 13 mm fibers, the lowest the F c . Flexural strength results showed two values related to the effect of fibers (figure 7): flexural strength at first crack ( F f1 ) and flexural strength remaining after first crack ( F f2 ). F f1 varied between 6 and 8.5 MPa. 3DP specimens showed higher F f1 than conventional specimens for Reference mixture and shorter SF, while 3DP reduced F f1 for longer SF, independently of the VF. F f2 was only measured for specimens with SF. 3DP specimens showed higher values, due to the alignment of fibers produced by 3DP process, as described by Hamback (2016), reaching an increase of 70 % for 3DP specimens compared to conventional casting specimens (from 2.1 MPa to 3.4 MPa) for mortar M3. Higher SF VF further increased F f2 , according to Li et al. (2024). However, M4 showed lower values than M1 despite of its higher fibers volume, due to their shorter fiber length.