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)

ERMSAR 2012, Cologne March 21 – 23, 2012

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.

ERMSAR 2012, Cologne March 21 – 23, 2012

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.

ERMSAR 2012, Cologne March 21 – 23, 2012

Oxidation behaviour

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

ERMSAR 2012, Cologne March 21 – 23, 2012

Fig.2: Section of the MOCKA 1.2 crucible.

ERMSAR 2012, Cologne March 21 – 23, 2012

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”!

ERMSAR 2012, Cologne March 21 – 23, 2012

Fig. 4: MOCKA 1.3 centerline concrete temperatures.

ERMSAR 2012, Cologne March 21 – 23, 2012

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.

ERMSAR 2012, Cologne March 21 – 23, 2012

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

•Axial erosion ~1 cm.•Lateral erosion ~0.5 cm.

ERMSAR 2012, Cologne March 21 – 23, 2012

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.

ERMSAR 2012, Cologne March 21 – 23, 2012

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.

ERMSAR 2012, Cologne March 21 – 23, 2012

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.

ERMSAR 2012, Cologne March 21 – 23, 2012

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.