On The Mechanical Behavior of Metakaolin Based Geopolymers Under Elevated Temperatures

Abstract

Geopolymers may be described as solid and stable synthesized aluminosilicate materials, whose properties are generally believed to provide a superior durability behavior. The work in hand presents the results of an experimental investigation on the thermomechanical behavior of geopolymer matrices composed by metakaolin (MK), silica fume (SF) and blast furnace slag (BFS). The alkaline activator solution consisted of sodium silicate and sodium hydroxide. The use of different aggregates was also investigated, by replacing natural sand with chamotte. Samples were submitted to different temperatures at predetermined intervals to a maximum of 1000ºC. Compression tests were performed, before and after the exposure to elevated temperatures. X-ray diffraction, thermal analysis (TGA and DTA) and scanning electron microscopy (SEM) were used to investigate the microstructural characteristics of the studied materials. The results showed that the presence of BFS in the geopolymer mixture significantly increases its mechanical response. However, the incorporation of SF presents inferior behavior in regular conditions and when exposed to elevated temperatures. The replacement of sand with chamotte results in higher compatibility above 500ºC, when a better tolerance to extreme environmental temperature conditions was observed.

Effect of Filler Type on the Thermo-Mechanical Properties of Metakaolinite-Based Geopolymer Composites

“…The addition of fillers mitigates the shrinkage of the geopolymer binders (the material does not crack due to heating). The results indicate decreases in compressive strength of geopolymer composites with increasing temperature, which were also previously published [23,25,30,47,56]. A slight increase in compressive strength after exposure to 200 • C was observed with GC, GS, and GR samples.…”

“…Hemra et al [30] examined the geopolymer composite based on metakaolin and sodium activator with the addition of cordierite (30 wt %) and the compressive strength was 57.5 MPa at room temperature. Rovnaník et al [25,47] [23] also revealed a descending paths of compressive strength of geopolymer composites based on metakaolin and sodium activator with the addition of chamotte or quartz (50 wt %) with increasing temperature. The described results of compressive strength of geopolymer composites were 72 MPa for quartz and 62 MPa for chamotte at laboratory temperature and 7 MPa for quartz and 18 MPa for chamotte after the exposure to 1000 • C. The reason for the high values of compressive strength of the prepared geopolymer composites was probably the appropriate binder composition, especially its low viscosity, which made it possible to achieve a high fill rate (high content of filler in the composite) and thus excellent mechanical properties after thermal exposure.…”

“…The type of filler material used can influence phase transformation at a high temperature, and minimize porosity and shrinkage of the material [20]. Various kinds of inert fillers in geopolymer composites-including quartz sand [2, 16,[21][22][23][24][25], crushed brick [26], corundum [26][27][28], kaolinite [26], chamotte [20,23,25,29], cordierite [30], vermiculite [31], carbon fiber [32,33], or silicon carbide [11]-were investigated in many studies. Buchwald et al [20] described the influence of fillers on the mechanical properties of geopolymers.…”

“…The geopolymer prepared from the potassium silicate solution promoted thermally more stable material than from the sodium silicate solution. There have been numerous studies which tested the thermo-mechanical properties of geopolymer binders or geopolymer composites after exposure to elevated temperatures (after cooling) [9,22,23,25,28,35]. Nearly no research has been done under real conditions, i.e., at the required elevated temperature (in situ).…”

Mechanical behavior of K‐geopolymers reinforced with silane‐coated basalt fibers

“…Geopolymers exhibit a fragile behavior with low deformation capacity as is typical of ceramics 10 . The use of reinforcements has been well explored in distinct forms to enhance their strength and ductility, such as additions of: sand 10 and chamotte 10‐12 as particulate reinforcements; as well as incorporations of synthetic (PVA, 13 PE, 14 carbon, 15 glass, 16 steel 9 ), mineral (basalt 11,17 ) and natural (bamboo, 18 jute, 8 sisal 19 ) fibers. Basalt fibers appear to be an interesting compatible material to be incorporated into geopolymer binders due to their high tensile strength, alkali resistance, 11 durability, and resistance to elevated temperatures 16 …”