The effect of varying cement replacement level on alkali metal distribution in cement pastes

Abstract

This study investigates how the level of Portland cement (PC) replacement affects the distribution of alkali metals in cement pastes, and how this relates to alkali silica reaction (ASR). Pore solution and hydrates were analysed for pastes with 22 % and 35 % PC replaced with limestone, fly ash (FA), and volcanic pozzolan (VP), cured for 180 days at 20, 38, and 60 °C. A significant portion of Na in VP is likely bound in non-reactive minerals. Curing temperature had limited effect on the distribution, mostly related to increased reaction of FA and VP. Higher replacement level increased pore solution volume and decreased concentration of K, but not of Na. It also did not change the amount of Na and K bound by C-A-S-H, as less C-A-S-H formed while (Na,K)/Si ratios increased to compensate. Adding more SCM did not lead to more reacted SCM, thus the additional SCM mainly acted as filler.