Evaluating shrinkage of fly ash - slag geopolymers

Geopolymers;Autogenous Shrinkage;Drying Shrinkage;Chemical Shrinkage;Fly Ash;Slag

Mosale Vijayakumar, Ranjani ; Mondal ; Paramita

关键词: Geopolymers;    Autogenous Shrinkage;    Drying Shrinkage;    Chemical Shrinkage;    Fly Ash;    Slag;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/46792/Ranjani_Mosale%20Vijayakumar.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The objective of current work is to investigate the volume changes that accompany the geo-polymerization reaction in order to evaluate geopolymer as a sustainable alternative binder. This study will help in evaluating the mechanical behavior of geopolymers when used in field. Since shrinkage causes volume change, any volume change after the binder has stiffened will cause stresses to develop and this will cause cracks and reduction in the load carrying capacity of the mix. The study was performed on a user-friendly geopolymer made with Class F fly ash, slag, potassium silicate, and potassium hydroxide. Slag used was constant at 5% of the total mass of the mix. The SiO2 to Al2O3 ratio was kept constant at 3.6, the K2O to SiO2 ratio varied between 0.9 - 2.4 for molarity variations between 4 to 10, and the water to solids ratio was kept constant at 0.35. Various types of shrinkage are investigated by performing shrinkage tests using corrugated tubes, studying the volume change in prisms which were sealed using aluminum tapes and placing in Ziploc bags and an attempt at quantifying the chemical shrinkage was made. Proctor penetration tests were performed on each of the mix to identify the start time of the corrugated tube test. Cubes of size 1 in. by 1 in. were cast in order to look at the compressive strength variation with mixes. Isothermal calorimetry was performed on each of the sample to study the heat evolution that accompanies the reaction process and it was seen that at lower molarities, the initial rate of heat evolution was higher as compared to the higher molarities. It was seen that the higher molarity specimens (M8, M10) showed lower autogenous shrinkage as compared to the lower molarity specimens (M4, M6).The chemical shrinkage results were not very conclusive and need to be repeated in order to have confidence on the results. The compressive strength was higher for lower molarities initially and then the rate of strength gain decreases at higher ages. At 28 days, the higher molarities show higher strength as compared to the lower molarities.