mocka experiments on concrete erosion by a metal and oxide melt

ERMSAR 2012, Cologne March 21 – 23, 2012

MOCKA Experiments on Concrete Erosion by a Metal and

Oxide Melt

J. J. FOIT, T. CRON, B. FLUHRER, A. MIASSOEDOV,

T. WENZ

Karlsruhe Institute of Technology, Germany (KIT)


Behaviour of Concrete under Thermal Load

Decomposition of concrete during heat-up starts with evaporation of physically bound water around 100°C.

• Dehydration of chemically bound water occurs up to 550°C.

• Decarbonation of CaCO3 from the cement and carbonate aggregates occurs from 700 to 900°C.

Consequently, loss of mechanical and thermal strength.

Liquid phases start to form between 1100-1250 °C.


MOCKA experiments

Melt: 39 kg Fe (collapsed melt height: 13 cm) and 70 kg oxide (initially Al2 O3 , CaO): (MOCKA 1.1, 1.2; 1-dim and MOCKA 1.3; 2-dim),

(MOCKA 1.4 with 3 kg Zr at the bottom of the crucible to avoid the outcome of the MOCKA 1.2 test (Fig. 2)!; 2-dim).

Initial melt temperature ~ 1900 °C.

Siliceous cylindrical crucible with 25 cm inner diameter. Experimental findings:

MOCKA 1.1: 3 cm axial erosion.

MOCKA 1.2: Compact metal layer embedded in a ~ 0.2 mm thick oxide layer

(never seen before)

no detectable concrete erosion.


Oxidation behaviour

Fig. 1: Time dependent composition of oxide and metal melts in BETA V 5.2.


Fig.2: Section of the MOCKA 1.2 crucible.


Fig. 3: Section of the MOCKA 1.4 crucible.

MOCKA 1.4:

Axial erosion: 2,5 cm.

Lateral erosion: 1.5 cm:

ratio ~ 1.7.

Approx. 2.5 cm thick

mechanically unstable

concrete layer due to

long-term thermal load.

Remelting of the melt

would lead to a fast

concrete “erosion”!


Fig. 4: MOCKA 1.3 centerline concrete temperatures.


MOCKA 1.5:

• Initial 3 kg Zr not at

the bottom.

• ejection of approx.

49 kg Al2O3 during the

thermite reaction

leading to low tempe-

rature of the oxide melt

(crust formation at

4 min after thermite

ignition).

• Rather small fraction

of the added 8.3 kg Zr

(start at 1 min, end

at 4 min after ignition)

was oxidized, Fig. 3.b.

• Axial erosion: 2,5 – 3 cm

Lateral erosion:

1-1.5 cm, ratio ~ 2-3. Fig. 5: Section of the MOCKA 1.5 crucible with unmelted Zr tubes.


Fig. 6: Section of the MOCKA 1.3 crucible (without Zr).

•Axial erosion ~1 cm.

•Lateral erosion ~0.5 cm.


MOCKA 1.6

• 110 kg thermite (→ 42 kg Fe + 38 kg Al2O3 + 30 kg CaO - 17 kg losses

from the oxide phase) with 4 kg Zr at the bottom of the crucible; Tin ~ 2193

K.

• After the completion of the thermite reaction alternating additions of thermite

and Zr.

• Total added masses: 63 kg thermite and 24 kg Zr within approx. 11 minutes.

MOCKA 1.7

• Total added masses: 117,5 kg thermite and 34 kg Zr within approx. 18 min.


Fig. 7: Section of the MOCKA1.6 crucible.

Max. concrete erosion:

• Metal: axial 10 cm, lateral 5 cm;

• Oxide: lateral 4,5 cm.

• Significant concrete erosion by the oxide melt: approx. 9 l (Edec= 41 MJ).

• Ver(met.)~ 9 l (Edec= 41 MJ).

• Oxidation of 1 kg Zr

with SiO2 + H2O + CO2, released

from approx. 0.8 kg eroded

concrete; ~0.74 cm axial erosion,

generates ~3.07*106 J mainly in the

oxide phase.

The Zr+SiO2 gives 0,26 kg Si. The

subsequent oxidation of that Si

amount delivers 7.9*106 J.

• The thermite reaction of 1 kg

gives 0.524 kg Fe with 7.5*105 J

and 0.476 kg Al2O3 with 1.5*106 J.


Max. concrete erosion:

• Metal: axial 15 cm, lateral 6,5 cm;

• Oxide: lateral 5 cm.

• Significant concrete erosion by the oxide melt: approx. 17 l (Edec= 76 MJ).

• Ver(met.)~ 15 l (Edec= 69 MJ).

Fig. 8: Section of the MOCKA1.7 crucible.


Conclusions

• Destruction of the concrete structure at low heat fluxes.

• BETA/COMET like ratio of axial to lateral concrete erosion by a metal melt for a

siliceous concrete.

• Significant lateral concrete erosion by the oxide melt (not observed in BETA/COMET

experiments).

Possible future tests:

• Study of the MCCI on a siliceous concrete with rebars.

• Investigate the concrete ablation ratio in rectangular, half-cylinder and inverse

crucibles.

mocka experiments on concrete erosion by a metal and oxide melt

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