Reactivation of a Retarded Suspension of Ground Granulated Blast-Furnace Slag

Abstract

An effective retarded suspension of ground granulated blast-furnace slag (GGBFS) needs a strong activator to reactivate the hydration. In this research study, sodium hydroxide (NaOH) as an alkali activator in two different concentrations (30 and 50 wt.%) was used to overcome the retardation and give the hardened GGBFS the reasonable strength. The study was carried out with a mixture of GGBFS, a solution of 1.0 wt.% d-gluconic acid (C6H12O7) as a retarder in the mixing water and a methyl cellulose as a stabilizer. The reactivation was executed after seven different periods (up to 28 days) after the system was retarded. The following investigations were performed: slump test, measurement of ultrasonic (US) velocity, compressive strength and gross density, thermogravimetry (TG) and scanning electron microscopy (SEM). The analyses of the hardened samples were carried out seven, 28 and 90 days after the reactivation. The result of the study is an effective reactivation of a retarded suspension. In this case, the activator with 50 wt.% NaOH shows a very high performance. The setting time of the reactivated binders is much longer compared to the reference, but, in the longer term, the compressive strength and the progress of the hydration exceed the performance of the reference.

Studying the Hydration of a Retarded Suspension of Ground Granulated Blast-Furnace Slag after Reactivation

“…The difference in the hydration degree can be mainly regulated by the activator concentration (cf. [6,27,28]). To a certain extent, the decrease of the retarder concentration can also contribute to a higher hydration degree; however, this is probably because of the earlier overcoming of the retarded state (compare (c) and (e) in Figure 7).…”

“…The alkaline activator for the activation of GGBFS also plays an important role. The main factors of the alkaline activator are the type and the concentration [3,4,28,47,48,49,50,51,52,53,54]. So, the hydration process is controllable by the specific use and the suitable content [25,28,55].…”

“…The main factors of the alkaline activator are the type and the concentration [3,4,28,47,48,49,50,51,52,53,54]. So, the hydration process is controllable by the specific use and the suitable content [25,28,55]. Thereby, the prior-ranking factor is the pH value, which controls the dissolution of the vitreous form of the slag, whereby the formation of C-S-H phases is initiated [4,24,48,50,53,56,57,58,59,60,61].…”

“…Based on the hydration control, individual reactivation of the retarded binder can be achieved by the addition of an activator (cf. [ 27 , 28 ]). The concept of the combination is based on the recycling process of fresh concrete.…”

“…Generally, the strength is strongly dependent on the retarder concentration. Therefore, a high concentration increases the advanced strength and decreases the early strength; it has the same performance for low retarder concentrations [ 11 , 13 , 22 , 28 ].…”