Microstructural and permeability properties of alkali-activated slag concrete

The study consists of a series of experimental investigations concerning the microstructural and permeability properties of alkali-activated slag concrete. The object of study is the so-called F-concrete. F-cement is finely ground slag to be activated by a combination of alkali metal compounds and rendered consistent in its fresh state by means of ligno-sulphonates. The influence of different parameters on the structure of F-concrete was studied by means of thermal analysis, X-ray diffraction and mercury intrusion. In addition, strength properties and permeability properties were studied. The influence of slag binder on chloride penetration and on carbonation was investigated. The permeability properties of F-concrete were also studied by means of capillary suction, water penetration and gas penetration. The parameters considered in the experimental studies were the quality of slag and additive, the proportion of concrete constituents and the curing conditions of the concrete specimens. According to the results the hardened slag paste is very dense, but the structure contains microscopic cracks due to hydration shrinkage. The effect of the cracks on the permeability properties was found to be significant. On the basis of strength results it is possible to produce F-concrete with very good mechanical properties.