Prevention of potential strength degradation due to conversion of C(2)AH(8) formed in CaO-Ca(HCOO)(2)-activated GGBFS binder using CaSO4

Abstract

Recently, the combined use of calcium oxide (CaO) and calcium formate (Ca(HCOO)(2)) has been proposed as an alternative activator for ground granulated blast furnace slag (GGBFS) (referred to as CaO-Ca(HCOO)(2)-activated GGBFS system). However, this clinker-free binder system produces calcium aluminate hydrate (C(2)AH(8)), generally leading to the degradation of cementitious binder systems by its conversion to other phases. Thus, in this study, attempts to remove C(2)AH(8) from this system without losing the strength are suggested by the use of two additives (i.e., calcium sulfate (CaSO4) and calcium nitrate (Ca(NO3)(2)), respectively). Results revealed that the above-mentioned additives completely remove C(2)AH(8) in the initial curing stage via its conversion to ettringite or NO3- and NO2-AFm, respectively. In addition, the additives reduced the extent of the total shrinkage and the standard deviation of strength results of triplicate samples. However, CaSO4 exerted a beneficial effect on the strength, while Ca(NO3)(2) exerted a marginal or detrimental effect on the strength. Therefore, this study suggested a new mixture form of an activator, comprising CaO, Ca(HCOO)(2), and CaSO4, to activate GGBFS for maintaining strength without the conversion issue of C(2)AH(8). (C) 2020 Elsevier Ltd. All rights reserved.