Geopolymer

About: Geopolymer is a research topic. Over the lifetime, 6776 publications have been published within this topic receiving 157991 citations. The topic is also known as: geopolymers.

Chemical optimisation of the compressive strength of aluminosilicate geopolymers synthesised by sodium silicate activation of metakaolinite

Abstract: High strength cements can be synthesised by alkali activation of materials rich in Al2O3 and SiO2. In this study, amorphous aluminosilicate polymers produced by sodium silicate activation of metakaolinite were studied, with particular reference to chemical optimisation of the compressive strength according to the relative concentrations of Si, Al and Na in the polymer. The sodium silicate was manufactured from silica fume and sodium hydroxide. The compressive strengths of polymers with Si∶Al molar ratios of 1.0–3.0 and Na∶Al molar ratios of 0.5–2.0 were considered. The polymers were cured at 75 °C for 24 h and their compressive strengths measured after aging for 7 days. The strength was found to depend systematically on the relative amounts of Si, Al and Na, with the maximum being 64 ± 3 MPa for an Si∶Al∶Na molar ratio of 2.5∶1∶1.3. X-Ray diffraction/scattering data indicate qualitatively that the bonding network in the amorphous aluminosilicate alters systematically with composition.

Physical evolution of Na-geopolymer derived from metakaolin up to 1000 °C

Abstract: The thermal shrinkage and weight loss of a systematic series of geopolymers with nominal composition of NaAlO2(SiO2) z · 5.5H2O (1.15 ≤ z ≤ 2.15) made by activation of metakaolin with sodium silicate solutions are presented. The thermal behaviour of Na-geopolymers are varied, but may be categorised into four regions of behaviour exhibited by all specimens. This investigation explores the effect of nominal Si/Al on the processes and mechanisms of thermal shrinkage and weight loss throughout constant heating of Na-geopolymer. The overall thermal shrinkage of Na-geopolymer increases with increasing nominal Si/Al, with the onset temperature of structural densification occurring at lower temperature with increasing Si/Al. Thermal shrinkage is observed to result from capillary strain, dehydroxylation and viscous sintering in different temperature regions, and is explored by use of dilatometry, thermogravimetry, nitrogen porosimetry and use of different constant heating rates.

The influence of the NaOH solution on the properties of the fly ash-based geopolymer mortar cured at different temperatures

Abstract: In this study, geopolymer mortar was produced using Class F fly ash from the thermal power plant in Kutahya Seyitomer (Turkey). The changes caused by the geopolymerization on the properties of the final product were investigated by applying curing on geopolymer mortars in different NaOH concentrations at different temperatures and for different curing times. The purpose of this process was to determine the relationship between alkali solution concentration, curing temperature and curing time. In order to determine the effect of NaOH concentration on geopolymer mortars, three different molarities of NaOH concentrations (3 M, 6 M and 9 M) were used together with sodium silicate (water glass) solution. The samples were cured at two different temperatures (65 and 85 °C). Physical properties such as porosity, bulk density, apparent density and water absorption, and mechanical properties such as flexural strength and compressive strength were determined from the 7-day geopolymer mortar samples after the curing process. As a result, this study determined that curing temperature and curing time had an effect on the physical properties of the geopolymer mortars. It was observed that NaOH concentration had a clear effect on the properties of the mortar cured at 85 °C. Compressive strength values of 21.3 MPa and 22 MPa were obtained from the mortar of 6 M concentration cured at 65 °C for 24 h and from a sample of the same mortar cured at 85 °C, respectively. Compressive strength values of the geopolymer mortars cured at 85 °C increased depending on the curing time and the increase in NaOH concentration. Given the strength values obtained, the optimal thermal curing temperature and the optimal NaOH concentration were 85 °C and 6 M, respectively.