Investigation of bentonite characteristics for application in geopolymers and hybrid cement binders

Abstract

Since the late seventies of twentieth century geopolymers have been investigated as a new type of aluminosilicate binders which will eventually replace traditional cement based structural materials. Geopolymers are the three-dimensional synthetic inorganic polymers, which contain amorphous and semi-amorphous crystal microstructures. Hybrid binders are structural materials which combine alkali activated raw materials and cement in its mixdesign. In this paper the characteristics of bentonite, which are important for its application in geopolymers and hybrid cement binders, were thoroughly investigated in order to evaluate its proneness to alkali activation. Bentonite samples from three different deposits were submitted to detail testing. Elaborate physico-chemical and mineralogical characterization was The Nineth Serbian Ceramic Society Conference »Advanced Ceramics and Application« September 20-21, 2021 Serbian Academy of Sciences and Arts, Knez Mihailova 35, Belgrade, Serbia 83 conducted. Determined moisture contents in bentonite samples were from 20.54 % to 24.15 %. Hygroscopic moisture was in range 7.99 - 8.99 %, and specific mass was in range 2.42 - 2.52 g/cm3 . Grain-size analysis of the bentonite samples was conducted using Sympatec laser sizer. Mineralogical analysis highlighted smectite, α-crystbalite, quartz, and feldspar as the most aboundant mineral phases. DTA/TG analyses were conducted to monitor thermal behavior of the bentonite samples in thermal range 20 – 1000 °C. Cation exchange capacity, CEC, (Ca2+, Mg2+, Na+ , and K+) was also conducted. Obtained total CEC values were from 66.16 meq/100g to 78.97 meq/100g. Plasticity of bentonite samples was determined using Atterberg – Casagrande methodology. Also Moisture absorption coefficient (using Enslin –Neff methodology), pH values and dioxin content in samples were tested. It was determined that investigated bentonite samples showed high potential for application in construction materials, i.e. geopolymers and hybrid binders.