Synopsis
The effectiveness of a pfa with a high total alkali content in suppressing expansion caused by alkali silica reaction has been investigated using concrete specimens containing flint sand. The observed behaviour has been related to the effect of the pfa on pore solution composition. With such a slowly reacting aggregate, typical of those found in concrete affected by ASR in the UK, 20 or 30% of the pfa stopped any deleterious expansion. The effect of the pfa on the pore solution depended on the age and the alkalinity of the cement. At 28 days there was a net contribution to the alkalinity of moderate or high alkali cement pastes but at longer ages the pfa reduced the alkalinity below that produced by dilution with an inert material. In very low lkali cement pastes however there was a net contribution to the alkalinity at all ages up to one year.
