PSI - Issue 10

M. Papachristoforou et al. / Procedia Structural Integrity 10 (2018) 155–162 M. Papachristoforou et al. / Structural Integrity Procedia 00 (2018) 000 – 000

160

6

8000

40

30

6000

20

4000

10 Vicat (mm)

2000

Yield Stress (Pa)

0

0

10

15

20

25

10

15

20

25

Expansion (cm)

Expansion (cm)

Fig. 5. Flow table expansion versus Vicat along .

Fig. 4. Flow table expansion versus Yield stress.

Limestone aggregate River sand aggregate 50% Limestone + 50% River sand

800

500kg/m³ 830kg/m³

30

750

25

700

20 Expansion (cm)

650 Power (W)

600

15

0

10

20

30

15

20

25

Expansion (cm)

Time (min)

Fig. 6. Electric power consumption of screw extruder motor vs. flow table expansion for mixtures with 500 and 830 kg/m³ .

Fig. 7. Loss of workability with time of concretes with different cement aggregates quantity.

presented in Fig.7. Concrete with limestone filler lost workability in a higher rate than ones with river sand or com bination with limestone and river sand. This can be explained by the granulometry of aggregates. Limestone filler has more fines that absorb more water from the mixture. Regarding hardened conc rete properties, density of concrete was measured, between 1.9 and 2.1 g/cm³, depending on the aggregate and binder. Density decreased when limestone filler rate increased, or when cement is replaced by FA or LFS. Compressive strength and UPV, as expected, are significantly affected by the type and proportions of raw materials in the mixtures. As seen in Fig.8, compressive strength is decreased when the Water/Binder ratio is increased and a maximum strength of 70 MPa was achieved for W/B ratio of 0.4. Regarding the type of aggregates, when the W/B ratio was kept constant, mixture with river sand and limestone filler showed the best strength results followed by the one with 100% river sand. An example of strength development for mixtures with 500 kg/m³ cement and differ ent aggregates is given in Fig.9. The substitution of part of cement by supplementary materials such as FA and LFS decreased compressive strength. In Fig.10, mixtures with combination of river sand and limestone as aggregates, 500 kg/m³ quantity of total binder and different binders is given. When FA or LFS replaced part of cement, compressive strength was reduced by 30%. UPV, a non destructive method for estimation of strength, was also measured and corre lated with experimental results of compressive strength (Fig.11). Soundness of selected printable mixtures was also tested according to EN 196-3:2005. The difference of distance measured between the indicator points after boiling was low (0.5-1.5 mm), which means that the possibility of expansion of concrete due to free CaO and MgO is also low.

4. Conclusions

Workability of fresh concrete used as material for additive manufacturing was measured according to four different tests. By measuring a wide range of mixtures produced with various raw materials (aggregates, binders) with different