Although it is somewhat difficult to measure the reaction degree of slag in slag blended cement comparing with the case in Portland cement, many researchers performed experiments on this field. A large body of literature can be found on the kinetics of Portland cement/slag blends.
Based on the modification of Takashima’s salicylic acid extraction method, Taylor collected some researchers’ data on the reaction degree of slag, as is showed in Table 1.
The reaction degree of slag in blended cement is difficult to measure using those methods which are successfully applied for Portland cement. Demoulian et al. described a method based on extraction of the constituents other than unreacted slag with a reagent based on Ethylene Diamine Tetraacetic Acid (EDTA), finding it effective for determining reaction degree of slag in unhydrated blended cements.
The hydration kinetics of slag is generally divided into three stages: (1) a nucleation period during which product growth is accelerating, (2) a phase boundary controlled stage, and (3) a diffusion controlled stage.
The reaction degree of slag in blended cement is influenced by many factors. The main factors affecting the reaction of slag in blended system include the reactivity of slag that could be defined as (C+A+M)/S, the fineness of grinding (specific surface area), the vitreous fraction of slag, the replacement level of slag in blended system, the hydration temperature and the water/solids ratio.