A New Method to Measure Available Alkalis of Cementitious Blends

The amount of available alkalis to the pore solution is an important property for alkali-silica reaction (ASR) prevention when supplementary cementitious materials (SCMs) are used. Supplementary cementing materials (SCM) are known to produce cement hydrates that increase alkali binding compared to portland cement only systems. The alkali-binding capacity of a specific SCM coupled with the alkali threshold of an aggregate will determine the required SCM dosage to prevent deleterious ASR for that specific reactive aggregate., Pore solution extraction (PSE) and analysis has been the most direct and reliable way to determine available alkalis of cementitious pastes. PSE requires advanced equipment and can be time intensive. In addition, the representativity of the pore solution extracted is a matter of debate. This paper introduces a new method called the alkali leaching test (ALT) to determine the available alkalis of binders containing portland cement and SCMs. Cement pastes at different alkali levels and containing various types and dosages of SCMs were tested. The results of the test showed different alkali-binding capacity for different fly ashes; also as the replacement level of SCMs increased, the available alkalis of cement pastes decreased.