USING MINERAL ADDITIONS TO IMPROVE PROPERTIES OF HIGH CALCIUM FLY ASH AS CEMENT AND CONCRETE ADMIXTURE

摘要

Use of fly ash in cement and concrete has been practiced for a long time since it is associated with technical, economical and environmental benefits, providing that the ash has the proper composition. EN 197-1, the standard for general cements, also allows the use of fly ash as a major constituent in several types of cement. According to their lime content and hydraulicity, fly ashes can be divided into high-calcium and low-calcium groups. Compared with low-calcium fly ashes, high-calcium fly ashes are known to have some disadvantages when used as an admixture in cement and concrete. Due to their relatively high lime content they may adversely affect some properties of cement and concrete such as shrinkage, sulfate resistance and freezing-thawing resistance. In Turkey, around half of the total amount of fly ash produced annually belongs to the high-calcium class. Some of these ashes also do not completely comply with the relevant standards and can have high sulfate contents. Therefore, a study was undertaken to investigate the ways to improve the properties of high calcium fly ashes some of which could also be non-standard. In this part of the study other mineral additions such as silica fume, ground sand and ground glass were mixed with the high-calcium fly ash at various proportions to improve its properties. According to the initial results, silica fume was very effective in binding the lime in high-calcium fly ash and increasing the strength of the ash mortar despite the high sulfate content of the ash. Ground sand was not effective at all while the ground waste glass seemed to have pozzolanic properties.