Carbonation and freeze-thaw resistance of geopolymer-zeolite cementitious composites

Abstract

Geopolymer-zeolite cementitious composites (GZCC) are emerging materials which can find applications as self-supported cementitious adsorbents, self-cleaning composite panels, etc. Considering the carbonation and free-thaw attack tendency of GZCC, this study assessed the carbonation and freeze–thaw resistance of geopolymer-zeolite cementitious composites (GZCC). GZCC samples with different activator-to-binder ratios (0.8 or 1), activator composition (sodium silicate-to NaOH ratio of 0.17 or 0.5 and NaOH molarity of 5 or 8 M), and hydrothermal duration (24 or 48 h), were prepared. Samples were exposed to accelerated carbonation environment after 3 and 14 days of curing. The physical and chemical characteristics of samples before and after carbonation were assessed by means of compressive strength, x-ray diffraction (XRD), and mercury intrusion porosimetry (MIP). Free-thaw exposure was started after 14 days of initial curing. Samples were put at -20 °C during freezing and immersed in water during thawing. The test results revealed that the carbonation resistance of samples was dependent on the mix proportion. A higher activator and lower silicate content resulted in lower residual strength which can be related to the higher porosity and lower compressive strength values of reference uncarbonated samples. However, zeolitic phases were still present which directs that the functionality of GZCC might not be affected much. All the samples broke after freeze–thaw exposure between 2 to 20 cycles. The formation of zeolitic crystals enhanced the open porosity of GZCC samples which caused their poor freeze–thaw resistance owing to easy penetration of water.