Mechanical behaviour at high temperature of alkali-activated aluminosilicates (geopolymers)

Abstract

g r a p h i c a l a b s t r a c t a b s t r a c tThis study was designed to determine the effect of temperature on the mechanical strength (in both in vivo and post-exposure trials) of two alkaline cements (without OPC): (a) 100% fly ash (FA) and (b) 85% FA + 15% bauxite, the activated alkaline solution used was 85% 10-M NaOH + 15% sodium silicate. A Type I 42.5 R Portland cement was used as a control. Two series of trials were conducted: (i) in vivo trials in which bending and compressive strength, fracture toughness and modulus of elasticity were determined at different temperatures; and (ii) post-firing trials, assessing residual bending and compressive strength after a 1-h exposure to high temperatures and subsequent cooling. The findings showed that from 25 to 600 °C, irrespective of the type of test (in vivo or post-firing), compressive mechanical strength rose, with the specimens exhibiting elastic behaviour and consequently brittle failure. At temperatures of over 600 °C, behaviour differed depending on the type of test: (i) in the in vivo trials the high temperature induced pseudo-plastic strain and a decline in mechanical strength that did not necessarily entail specimen failure; (ii) in the post-firing trials, compressive strength rose.

Effect of high temperatures on the mechanical behaviour of hybrid cement

“…The better mechanical behaviour of HYC at 600 °C might be related to the alkaline (sodium), fly ash and in general high amorphous phase content in the matrix ( Table 2). In earlier studies, pseudo-viscous phases were observed to form in fly ash-based alkaline cement at around 500 °C (34). Vitreous transition at 560 °C (52) and hightemperature softening have also been reported in fly ash alkaline cement (53).…”

“…In the DT tests, cracks formed unstably and after extending rapidly under loading, grew spontaneously with no need to raise the load (34). Greater OPC deterioration was nonetheless obviously related to the presence of general cracking in the matrix.…”

“…Post thermal treatment porosity was found on a Micromeritics AutoPore IV 9500 mercury intrusion porosimeter, featuring a maximum pressure of 227 MPa at a contact angle of 141.3° and a surface tension of 485 dynes/cm (34). The untreated 28 d pastes were also ground to powder for thermogravimetric/differential thermal analysis (TG/DTA) on a Labsys SETARAM analyser, in which the air temperature was ramped up from 25 °C to 1000 °C at a rate of 10 °C/min.…”

Waste Stream Porous Alkali Activated Materials for High Temperature Application

“…The existing publications on fire resistance and performance of AAM under high temperature conditions are promising. The stability at high temperatures of binders made by the alkaline activation of aluminosilicate precursors is clearly distinct from the behavior observed in Portland cement at high temperatures (Martin et al, 2015). The shrinkage of AAM up to 600 • C temperature occurs due to evaporation of the adsorbed and weakly bound water.…”

“…On one hand, high alkali content in activation solution (8 to 12 M NaOH solutions) is necessary to accelerate the activation reactions of precursors and to obtain AAM with high initial strength, but at the same time increased concentration of alkalis could act as fluxes at high temperatures. Therefore, the content of alkalis in the alkali activation solution must be limited to generate thermally stable materials (Martin et al, 2015). It has been reported that the alkali concentration in the activation solution could be reduced event to 2 M (Huiskes et al, 2016).…”