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.

Geopolymer as well cement and the variation of its mechanical behavior with curing temperature

Abstract: Anthropogenic emissions of greenhouse gases are a major problem for all nations, and carbon dioxide (CO2) sequestration is one of the best practical solutions to reduce greenhouse gases. A large amount of CO2 is injected through sequestration wells into injection reservoirs. The injection wells play an important role; well integrity is an important part of any CO2 sequestration projects and well cement is the key to maintaining well integrity. To date, Ordinary Portland cement (OPC)-based well cement has been used and there are many problems associated with this, including cement degradation, durability issues, and sustenance in acid-rich environments. Therefore, this paper aims to study geopolymer as a well cement and the variation of its mechanical properties with different curing temperatures. Temperatures from ambient level (23 °C) up to 80 °C were considered, as well cement undergoes a range of temperatures from the ground surface to deep underground with a geothermal gradient of 30 °C/km. Stress-strain variations and crack propagation stress thresholds were studied using stress-strain and acoustic emission (AE) methods, and failure strain and orientation were studied using ARAMIS photogrammetry software for samples cured at different curing temperatures. The results show that the optimal curing temperature for higher strength is 60 °C; Young's modulus and Poisson's ratio generally increase with curing temperature. In general, crack closure, crack initiation, and crack damage thresholds increase with curing temperature. ARAMIS image capture showed that failure modes of low-temperature cured samples are diagonal, whereas elevated-temperature cured samples start to fail at the top and bottom compression plates. In addition, low-temperature cured samples exhibit higher strain (6–8%) at failure, while elevated-temperature cured samples exhibit low strain (0.8–3.5%) at failure. © 2011 Society of Chemical Industry and John Wiley & Sons, Ltd

Phase evolution of Na2O–Al2O3–SiO2–H2O gels in synthetic aluminosilicate binders

Abstract: This study demonstrates the production of stoichiometrically controlled alkali-aluminosilicate gels (‘geopolymers’) via alkali-activation of high-purity synthetic amorphous aluminosilicate powders. This method provides for the first time a process by which the chemistry of aluminosilicate-based cementitious materials may be accurately simulated by pure synthetic systems, allowing elucidation of physicochemical phenomena controlling alkali-aluminosilicate gel formation which has until now been impeded by the inability to isolate and control key variables. Phase evolution and nanostructural development of these materials are examined using advanced characterisation techniques, including solid state MAS NMR spectroscopy probing 29Si, 27Al and 23Na nuclei. Gel stoichiometry and the reaction kinetics which control phase evolution are shown to be strongly dependent on the chemical composition of the reaction mix, while the main reaction product is a Na2O–Al2O3–SiO2–H2O type gel comprised of aluminium and silicon tetrahedra linked via oxygen bridges, with sodium taking on a charge balancing function. The alkali-aluminosilicate gels produced in this study constitute a chemically simplified model system which provides a novel research tool for the study of phase evolution and microstructural development in these systems. Novel insight of physicochemical phenomena governing geopolymer gel formation suggests that intricate control over time-dependent geopolymer physical properties can be attained through a careful precursor mix design. Chemical composition of the main N–A–S–H type gel reaction product as well as the reaction kinetics governing its formation are closely related to the Si/Al ratio of the precursor, with increased Al content leading to an increased rate of reaction and a decreased Si/Al ratio in the N–A–S–H type gel. This has significant implications for geopolymer mix design for industrial applications.

High-Calcium Bottom Ash Geopolymer: Sorptivity, Pore Size, and Resistance to Sodium Sulfate Attack

Abstract: The resistance to sulfate attack, compressive strength, sorptivity, and pore size of high-calcium bottom ash geopolymer mortars were studied. Ground lignite bottom ashes (BAs) with median particle sizes of 16, 25, and 32 μm were used. NaOH, sodium silicate, and temperature curing were used to activate the geopolymerization. Results showed that relatively high strengths of 40.0–54.5 MPa were obtained for the high-calcium bottom ash geopolymer mortars. The use of fine BA improved the strength and resistance to sulfate attack of mortars. The good performances were attributable to the high degree of reaction of fine BA and the associated low amount of large pores (0.05–100 μm) compared with those of coarse BA. The incorporation of water improved the workability of mixes, and the compressive strength, sorptivity, and resistance to sulfate attack decreased due to the increase in large pores.