Influence of aggregate fraction in the mix on the reliability of the rapid chloride permeability test

Abstract

The present paper elucidates the influence of aggregate content of the mix on the reliability of rapid chloride permeability test (RCPT) results. For this purpose, test specimens prepared with mixes varying in total aggregate content were subjected to soaking test, RCPT and electrical resistivity measurements, and the results from these tests were compared and conclusions drawn. The RCPT results indicated the plain cement concrete to be relatively more resistant against chloride penetration than the plain cement mortar, whilst the opposite was true according to the 90-day soaking test results. The above trend did not change despite the addition of silica fume (SF) to the concrete and mortar mixes. The lower aggregate content or higher paste content of plain cement mortar and the mortar with SF is shown to mislead the RCPT results. The higher paste content in the above mix promotes the conduction of higher charge as a result of lower electrical resistivity. Thus the results derived from the present investigation emphasize the need to consider the volume fraction of aggregate in the mix with and without SF while interpreting the RCPT results. Furthermore, regardless of the total aggregate and SF content in the mix, the total charge passed (from the RCPT) through the mix decreased exponentially with increasing electrical resistivity. On the other hand, for those mixes containing either SF or a high volume fraction of aggregates the linear correlation between the total charge passed and chloride penetration coefficient (K) was poor. However, for the mix with relatively lower aggregate content and with no SF the charge passed was well correlated linearly with K. © 1999 Published by Elsevier Science Ltd.