ACI 233R-03 Slag Cement in Concrete and Mortar

ACI 233R-03 Slag Cement in Concrete and Mortar. 1.7—Processing Quenching with water is the most common process for granulating slag to be used as a cementitious material. Simple immersion of the molten slag in water was often used in the past. This quenching method is sometimes called the pit process. More efficient modern granulation systems use high-pressure water jets that impinge on the stream of molten slag at a water-slag ratio of about 10 to 1 by mass. In this quenching method, called jet process granulation, the blast-furnace slag is quenched almost instantaneously to a temperature below the boiling point of water, producing slag particles with a high glass content. This material is called granulated blast-furnace slag (GBFS). A close-up view of the part of a jet-process granulator system where the water meets the molten blast-furnace slag is shown in Fig. 1.1. 1.9—Hydraulic activity There is general agreement among researchers (Smolczyk 1978) that the principal hydration product that is formed when slag cement is mixed with portland cement and water is essentially the same as the principal product formed when portland cement hydrates, that is, calcium-silicate hydrate (CSH). As seen in the phase diagram in Fig. 1.3, portland cement and slag cement lie in the same general field, although slag cement has a higher silica content. When slag cement is mixed by itself with water, initial hydration is slower than that of portland cement; therefore, portland cement, alkali salts, or lime are used to increase the reaction rate. Hydration of slag cement in the presence of portland cement depends largely upon breakdown and disso- lution of the glassy slag structure by hydroxyl ions released during the hydration of the portland cement. When slag cement hydrates, it reacts with sodium and potassium alkali and calcium hydroxide (Ca(OH) 2 ) to produce additional CSH. Regourd (1980a,b,c) showed that a small immediate reaction also takes place when slag cement is mixed with water, preferentially releasing calcium and aluminum ions to solution. The reaction is limited, however, until additional alkali, calcium hydroxide, or sulfates are available for reaction. 2.1—Storage As is the case with portland cement and most pozzolans, slag cement should be stored in bins or silos to provide protection from dampness and contamination. Color and fineness of slag cement can be similar to those of portland cement; therefore, necessary precautions should be taken to clearly mark handling and storage equipment. When compartmented...