![]() ![]() It is also becoming increasingly apparent that a combination of the properties of “geopolymer”-like (alkali aluminosilicate) and GBFS-based systems can show advantages over either of the end-member systems in terms of the formation of desirable microstructures and mechanical properties, ,, ,, ,, and so this work is focused on one such system: a blend of GBFS with a small amount of MK, activated by sodium silicate (waterglass) solution. ![]() The dominant binder phases in these systems are generally identified to be calcium silicate hydrate (C–S–H) gels which are relatively low in Ca. Of the different materials that have been subjected to alkali activation, granulated blast furnace slag (GBFS) has been the most widely studied, and alkali-activated binders based on GBFS have been used in large-scale applications in regions including Eastern Europe and China. More recent advances in instrumentation, particularly in the areas of electron microscopy, nuclear magnetic resonance spectroscopy and synchrotron radiation-based analysis, ,, ,, , have provided the ability to understand alkali-activated binders on a detailed level, which is essential to the understanding and prediction of their performance and durability. The possible value of alkali-activated binders has been reported since the 1940s, , although it was not until the 1960s that the understanding of the chemistry of these materials began to be established. Infrared spectroscopy carried out over a period of 180 days shows the development of the gel structure, with aluminum incorporation leading to an increase in the extent of crosslinking, and higher alkalinity giving a more depolymerized gel structure.Īlkali-activated binders are a class of materials that use an alkaline activator in conjunction with a solid (usually pozzolanic or cementitious) silicate powder to initiate a reaction sequence which results in the formation of a solid material with properties comparable to traditional hydraulic cements. A secondary reaction product (Na-substituted C–S–H) is also identified in pastes activated with a modulus of solution of 2.0. No hydrotalcite-type phases are observed in these samples, which are synthesized from a low-Mg slag. High-energy synchrotron X-ray diffractometry reveals that the main reaction products in alkali-activated GBFS/MK blends are segregated and partially crystalline calcium silicate hydrate and aluminosilicate phases, including a small component with a zeolitic (gismondine) structure. This effect is more significant when an activating solution with a higher silicate modulus is used, and leads to a slight reduction in the final mechanical strength of mortars but a significant increase in setting time, which is valuable in the development of alkali-activated slag binders as these are known to sometimes harden more rapidly than is desirable. In the initial period of the reaction, the addition of MK leads to an increase in the total setting time, reduces the heat release, and affects the reaction mechanism by introduction of a large quantity of additional Al. Structural evolution in pastes produced from alkali silicate-activated granulated blast furnace slag (GBFS)/metakaolin (MK) blends is assessed. ![]()
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |