EFFECT OF PFA ON FRESH AND HARDENED CONCRETE

Abstract

Mass concrete structures, such as dams, always require special measures to be taken to produce a qualified concrete. The use of PFA in concrete has become an accepted practice partly due to the large body of research work conducted in the area of blended cement(1) to have a consistent concrete and to eliminate heat of hydration as well as to improve the quality of concrete. This research was formulated to evaluate the performance of concrete when PFA was used, at Merowe Dam Project, as a replacement of cement in the range 0 to 35% and changing the water-cement ratio from 0.45 to 0.65 adding 0.05. In a trial mix stage samples of 180 cubes, and 180 cylinders were taken for maximum size 38 mm of coarse aggregate and the same numbers for 76mm and tested for 3,7,and 28 days. After full curing a compressive strength tests were performed. The results showed low strength recorded in the early age with the increment of PFA dosage and qualified strength at 28 days. Based on that results it was recommended to use 15% of PFA replacing of the cement, but at early of the construction period increased to 25% to mitigate alkali-silica reaction. At the construction period the records of heat of hydration read by the sensors embedded in concrete were showed below the maximum limit.