Influence of cellulose micro-fibers on hydration characteristics of cementless UHPC using CaO-activated GGBFS

This study aimed to investigate the influence of natural cellulose fibers (NCFs) on improving the hydration characteristics of cementless ultra-high performance concrete (UHPC) using CaO-activated ground granulated blast furnace slag (GGBFS). The NCFs were added in a saturated condition as an internal-curing agent so as to supply additional water to the UHPC matrix and subsequently increase the reactivity of unhydrated phases. To evaluate the hydration characteristics, saturated NCFs were added at 0 to 1.5 wt% of the GGBFS plus CaO. TGA and FTIR analyses showed that, as the amount of NCFs increased, the formation of hydration products was improved as evidenced by an increase in heat of hydration, indicating that more reactions of unhydrated phases occurred. Similarly, morphologies of the samples revealed the formation of hydration products on and near the surfaces of the NCFs due to the additional water exerted during the process of internal curing. Moreover, the compressive and tensile strengths were not compromised by the incorporation of weak and flexible NCFs, but rather a slight improvement was observed with a certain content of NCFs.