ABSTRACT
When the hydroxyl ions are produced solely as a consequence of the hydration of a Portland cement (PC), the rate of reaction is greatest at the time when the reactants first come into contact and thereafter, it declines. The reaction ceases when either of the reactants are depleted or when the hydroxyl ion concentration is reduced to a threshold level. In a high cement content concrete with an original alkali content of 5kg/m3 expressed as equivalent Na2O, the reaction of about 2.5 per cent by mass of total aggregate is sufficient to reduce either the hydroxyl ion concentration or alkali
FIGURE 9.1 Gel filled cracks and gel saturated paste. (Magnification 100.) (With permission from British Cement Association.)
concentration to a threshold level or, alternatively, to deplete all the available sodium and potassium alkalis [4].
