Factors affecting the performance of metakaolin geopolymers exposed to elevated temperatures

The effects of geopolymer binder systems exposed to elevated temperatures are examined. Geopolymers investigated were synthesized from metakaolin, activated by combinations of sodium/potassium silicate and sodium/potassium hydroxide. The specimens were then exposed to temperatures of 800 °C. The factors studied were: (1) calcining temperatures of kaolin; (2) Si/Al ratio of the geopolymer; (3) activator/metakaolin ratio; (4) curing temperature; and (5) alkali cation type. Altogether 30 geopolymer formulations were studied. The samples were subjected to compressive strength, thermogravimetry, and scanning electron microscopy tests. Results showed that Si/Al ratio has a significant influence on elevated temperature exposure deterioration. Lesser strength loss due to elevated temperature exposures were observed in geopolymer with high Si/Al ratios (>1.5). The geopolymer binders activated by potassium-based activators showed an enhanced post-elevated temperature exposure performance compared to sodium-based systems. The optimum calcining temperature of kaolin and curing temperatures for improved temperature performance are also reported.

[1]  Salman Azhar,et al.  Performance of metakaolin concrete at elevated temperatures , 2003 .

[2]  Grant C. Lukey,et al.  Physical evolution of Na-geopolymer derived from metakaolin up to 1000 °C , 2007 .

[3]  Hua Xu,et al.  Ab Initio Calculations on the Five-membered Alumino-silicate Framework Rings Model: Implications for Dissolution in Alkaline Solutions , 2000, Comput. Chem..

[4]  T. Bakharev,et al.  Geopolymeric materials prepared using Class F fly ash and elevated temperature curing , 2005 .

[5]  T. Cheng,et al.  Fire-resistant geopolymer produced by granulated blast furnace slag , 2003 .

[6]  J. Deventer,et al.  The geopolymerisation of alumino-silicate minerals , 2000 .

[7]  J. Phair,et al.  Effect of silicate activator pH on the leaching and material characteristics of waste-based inorganic polymers , 2001 .

[8]  J. Davidovits.  Geopolymers : inorganic polymeric new materials , 1991 .

[9]  S. Alonso,et al.  Alkaline activation of metakaolin and calcium hydroxide mixtures: influence of temperature, activator concentration and solids ratio , 2001 .

[10]  J. Deventer,et al.  Understanding the relationship between geopolymer composition, microstructure and mechanical properties , 2005 .

[11]  B. Vijaya Rangan,et al.  ON THE DEVELOPMENT OF FLY ASH-BASED GEOPOLYMER CONCRETE , 2004 .

[12]  K. Sagoe-Crentsil,et al.  Relationships between composition, structure and strength of inorganic polymers , 2005 .

[13]  G. Kakali,et al.  Metakaolin as supplementary cementitious material , 2005 .

[14]  G. Brown,et al.  Polymerization of silicate and aluminate tetrahedra in glasses, melts, and aqueous solutions—I. Electronic structure of H6Si2O7, H6AlSiO71−, and H6Al2O72− , 1980 .

[15]  K. Sagoe-Crentsil,et al.  Relationships between composition, structure and strength of inorganic polymers , 2005 .

[16]  H. Rahier,et al.  Low-temperature synthesized aluminosilicate glasses: Part III Influence of the composition of the silicate solution on production, structure and properties , 1997 .

[17]  Waltraud M. Kriven,et al.  The effect of alkali and Si/Al ratio on the development of mechanical properties of metakaolin-based geopolymers , 2007 .