Introduction

Alkalis, mainly potassium and sodium, are present in all portland cements, and many specifications place limits on the allowable total equivalent alkali content. The influences of potassium and sodium on cement hydration, microstructure, and performance properties has thus been a subject of considerable research for many years. ^1-6 In general, these alkalis accelerate early age cement hydration but reduce later age hydration and strength development. In recent years, numerous investigations have been performed on the addition of lithium-containing admixtures to cement-based materials, mainly as a means of mitigating the deleterious expansive cracking that occurs during alkali-silica reactions. ^7-9 These three alkali cations are each readily soluble in water and are readily incorporated into the cement hydration products.⁷ Particularly, they modify the morphology of the calcium silicate hydrate (C-S-H) gel 1, 3, 10 and thus the geometrical and percolation characteristics of the capillary pore network. ¹¹ This paper will examine the influences of four different sets of alkali compounds on degree of hydration and porosity percolation.