Effect of organic alkali on compressive strength and hydration of wet-grinded granulated blast-furnace slag containing Portland cement

Abstract

In this study, a commercially available ground granulated blast-furnace slag (GGBS) was further processed by wet grinding, and WGGBS (wet-grinded GGBS) slurry with superfine particles was obtained. To avoid self-hydration of slag and augment the grinding efficiency, one commercially available polycarboxylate superplasticizer was added. The binder, composed of 10.0% cement and 90.0% WGGBS with the addition of 0.05% triethanolamine (TEA) and 0.05% triisopropanolamine (TIPA), was designed; the cement was added to provide alkali environment and calcium ions, and organic alkali was used to promote the dissolution of GGBS. The compressive strength of mortar and hydration mechanism was investigated. The results showed that wet grinding exhibited high grinding efficiency; D(50) value of particle size distribution of WGGBS was reduced from 18 μm to 2.10 μm by wet grinding for one hour. Compressive strength of hardened WGGBS mortar was 20 MPa and 28 MPa at 7 d and 28 d, and 10% cement replacement ratio of the WGGBS increased the strength to 24.6 MP at 7 d and 32.2 MPa at 28 d. Furthermore, in C-WGGBS, 0.05% TEA increased the 7 d strength by 23%, with the value of 30.27 MPa, but 0.05%TIPA slightly reduced it to 23.5 MPa, with a decrease by 5%. Mechanism behind the increase was due to the accelerated formation of hydrotalcite-like phase, despite the retarding effect on formation of C-(A)S-H gel; the slight decline by TIPA was mainly because of the retarding effect of formation of C-(A)S-H gel as well as its air-entraining effect. Moreover, both TEA and TIPA increased the 28 d strength of cement-WGGBS system, because TEA and TIPA were able to facilitate ferric and aluminum dissolution and expedite the formation of C-(A)S-H gel as well as hydrotalcite-like phase. Additionally, it was worth noting that 0.05% TEA could make 28 d strength of the binder, composed of only 10% cement, reach 43.7 MPa, in accordance with the requirement of 42.5 grade cement.