ABSTRACT
In order to evaluate the supposition (4) that fly ash only plays a significant part in the hydration reaction after a period of approximately two weeks, a series of small (12 mm diameter) cylindrical specimens containing 25% fly ash were cast over a number of days. After various hydration ages ranging from twelve hours to seven days they were broken in two to reveal a fracture surface. These specimens were then freeze-dried to arrest hydration and in order to draw off all the evaporable water with the least amount of microstructural damage (14) .
