Abstract
This paper reports on the effect of cellulose nanofibrils (CNFs) on the fresh-state properties of alkali activated ground granulated blast-furnace slag (GGBS). Surface functionalized (oxidized) CNFs were added to alkali activated GGBS water suspensions (hydraulic pastes). The rheological behaviour of the pastes was compared with OPC and interpreted based on the CNF-mineral surface interaction, and on the CNF-water interaction and swelling. The water dispersion of CNFs with different surface functionalization degrees resulted in gels of different viscosity and yield stress, due to their different hydrophilicity and water adsorption properties. On increasing the CNFs surface oxidation degree, the viscosity of the CNF water dispersion decreases and the CNF water adsorption increases, while the viscosity of fresh pastes increases because of the reduced amount of available mixing water. In the hardened state, the hydraulic pastes show differences in mechanical strength related to the type and the amount of CNF influencing the porosity of the matrix as evidenced by the microstructural investigation performed by X-ray microtomography. The presence of higher amounts of CNFs induces the formation of porous agglomerates that may act as stress concentrators due to the swelling ability of nanofibrils.
Highlights
Alkali activated binders are actively researched since earlier than the half of last century as a possible alternative to Portland cement [1, 2]
One inherent problem of alkali activated binders is their low effectiveness towards viscosity modifiers. In this context we have evaluated the effect of the addition of cellulose nanofibrils (CNFs) to alkali activated materials, in comparison with the effects of the same addition to ordinary Portland cement (OPC), to assess the suitability of their use as viscosity modifiers or reinforcing agents
The objectives of this paper are to investigate the influence of cellulose nanofibrils (CNFs) on the rheological properties of alkali activated ground granulated blast-furnace slag (AAS) matrix and to compare it with ordinary Portland cement (OPC) considering different degrees of oxidation for the CNF
Summary
Alkali activated binders are actively researched since earlier than the half of last century as a possible alternative to Portland cement [1, 2] The interest in such materials spans from their higher resistance to acid corrosion and aggressive environmental conditions [3, 4] to reduced economic and environmental costs [5, 6]. The use of alkali hydroxide or silicate solutions raises concerns about their corrosive properties and the related health and safety on the working sites [10] These alkaline solutions have high embedded energy and emission values, limiting the benefits of introducing the alkali activated binders [9, 11]. A suitable alternative to alkaline solutions is the use of solid alkali-activators such as sodium carbonate or sulphate because of their lower environmental impact and costs [8, 9, 11]. An investigation on the effect of some specific cementitious viscosity modifiers on sodium carbonate activated GGBS can get considerable attention to assess their use in different industrial applications
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