Pozzolanic Index and lime requirement of low calcium fly ashes in high volume fly ash mortar

The major drawback for High Volume Fly Ash Concrete (HVFAC) is low strength development. It is because of the production of less lime by the hydration due to less cement present. However, the exact amount of the lime required for HVFAC system is an unsolved problem so far due to the complexity of hydration and pozzolanic reactions. This paper presents the application of the theory of a logical Pozzolanic Index proposed by Dunstan R Edwin in 2006 for three fly ashes of different chemical and physical properties. Based on the procedure used to find the Strength Activity Index proposed by ASTM C 618, an experimental analysis is conducted on mortar compressive strength, whose results are used to determine the Pozzolanic Index. Thereby calculates the required lime for each replacement of cement with fly ash ranging from 0 to 80% for the three fly ashes. It also concludes that the finer the fly ash the more reactive and consumes more lime at certain age of concrete

Durability of basalt fibers in concrete medium

This study investigates the durability of basalt fiber following immersion in a range of chemical solutions representative of the concrete medium. The tests were conducted over a 62-day period and the solutions were sodium hydroxide, sodium chloride, sodium sulfate and combinations of the three. Weight loss was observed in all alkali solutions, with the worst being the combination of sodium hydroxide with sodium sulfate. The impact of chloride was minimal in the alkaline environment and reduced the impact of the sulfate when both were present. Microstructure analysis using a Scanning Electron Microscope (SEM) found that the silica structure present in basalt fibers was degraded by the OH- from an alkaline medium. The study suggests the need for modification or treatment of basalt fibers before use as fiber reinforcement in concrete