Experimental Centre, Faculty of Civil Engineering, CTU in Prague, Ondřej HOLČAPEK, Pavel REITERMAN, Marcel JOGL and Petr KONVALINKA Hydrothermal conditions influence on aluminous cement pastes with metakaolin

Content  Motivation, description of contribution  Experimental program  Used components  Hydrothermal curing conditions  Temperature loading  Investigated properties and used methods  Results  Conclusion

Motivation  Analysis of refractory cement composites for high temperature application (fire protection, industrial applications, etc.).  Residual mechanical properties after temperature loading and reaction on elevated temperature (spalling).  Binder system – aluminous cement (high energy and financial intensive) and metakaolin.  Maximization of mechanical properties and durability in autoclave device (special curing conditions – high pressure, temperature up to 100°C applied at the early age of cement composite).  Investigation of the system „cement + metakaolin“ and application of results on final composite.

Experimental Program  Pastes from aluminous cement and various amount of metakaolin.  Hydrothermal curing and reference.  Exposure to elevated temperature (105°C, 600°C and 1000°C).  Study of mechanical properties.  Application of hydrothermal curing on refractory composite.  Tested pastes (weight ratio aluminous cement : metakaolin):  Water to binder ratio 0.3  100:0(A)  95:5(B)  90:10(C)  85:15(D)

Experimental Program  Used materials:  Aluminous cement Secar®71  Burdned pure artificial bauxite  Suitable for 1600°C application  CA + 10H → CAH 10  2CA + 11H → C 2 AH 8  Conversion:  3CAH 10 → C 3 AH 6 + 2AH H  3C 2 AH 8 → 2C 3 AH 6 + AH 3 + 9H  Mefisto L05  Burned clay (700°C – 900°C)  Pozzolan material  Suitable for refractories

Experimental Program Secar ®71 [% weight] Metakaolin L05 [% weight] Al 2 O %42.90 % CaO27.50 %0.17 % SiO %52.90 % Fe 2 O %1.10 % Na 2 O0.27 %0.05 % MgO0.21 %0.18 % K2OK2O0.06 %0.59 % TiO % Specific surface381 m 2 /g1306 m 2 /g  Used materials:

Hydrothermal Curing  12 hours old specimens (after first contact cement and water)  0.5 hour heating  Closing pressure valve  Increase of pressure and temperature  Hydrothermal curing cycle 4 hours 150 °C and 0.4 MPa  Release of pressure valve and cooling  End of hydrothermal curing cycle

Hydrothermal Curing

Temperature Loading  - Gradient 10°C/min  600 °C  1000 °C  180 min loading  Natural cooling dried 105°C testing 600°C and testing 1000°C and testing

Measured Parameters -Tensile strenght in bending [MPa] (specimen 40 x 40 x 160 mm) -Increase of deformation 1.0 mm/min

Measured Parameters

Results  Compressive strength

Results  Flexural strength

Results  Dynamic modulus of elasticity

Results  Fracture energy

Application  The main goal of experimental program was the development of refractory cement composite:  Aluminous cement + metakaolin  Natural crushed basalt aggregates (0/4 mm and 2/5 mm)  Water and superplasticizer (w/b = 0.25)  Basalt fibers 6.35 mm (0.75 % of volume)

Application  The main goal of experimental program was the development of refractory cement composite:  Aluminous cement + metakaolin  Natural crushed basalt aggregates (0/4 mm and 2/5 mm)  Water and superplasticizer (w/b = 0.25)  Basalt fibers 6.35 mm (0.75 % of volume)  Obtained data from hydrothermal curing of cement pastes has been applied for hydrothermal curing of composite.

Conclusion  The compressive strength decreases with higher amount of metakaolin (reference and autoclaved specimens).  Dosage of 10% and 15% means the increase of flexural strength.  Autoclaved specimens show higher mechanical properties, especially after the exposure to elevated temperatures.  Compressive strength higher by 25%  Flexural strength higher by 50% to 30%  The residual properties of pastes (especially flexural strength and fracture energy) are on excellent level.  Binder system of aluminous cement and metakaolin shows great potential for application in refractory cement composites (in combination with fibres).  Energy intensive method – suitable for highly specific applications.

Conclusion Thank you for your attention. Czech Science Foundation P104/12/0791.