Synergistic efects of MWCNTs and chemical admixtures on the foam stability and rheological behavior of lightweight cement pastes

Abstract

The development of lightweight and functional cement-based materials is essential for sustainable construction solutions. This study investigates the combined eect of multi-walled carbon nanotubes (MWCNTs), air-entraining admixtures (AEAs), and three types of superplasticizers – lignosulfonate (LS), polyacrylate (PA), and polycarboxylate ether (PCE) – on the foam stability and rheological behavior of cement pastes. MWCNTs, known for their high surface area and bridging capabilities, were shown to significantly enhance foam stability and suspension viscosity by forming filament-like networks that entrap air bubbles. When used together with AEAs, a pronounced synergistic increase in viscosity and initial foam volume was observed, especially at higher MWCNT dosages (up to 0.5% bwoc). However, the eectiveness of this synergy was found to be highly dependent on the type of superplasticizer. SP(LS) preserved foam stability, while SP(PA) and SP(PCE) reduced it due to interference with bubble formation. Electrical conductivity and setting time measurements revealed that increasing MWCNT content delays hydration, reduces ion mobility, and extends setting time up to 2.8-fold in the presence of PCE. Spreadability tests confirmed a reduction in flowability with MWCNTs, partially recovered by SP(PCE). Overall, this work presents new insights into multicomponent nano-admixture interactions and highlights pathways for tailoring foamed cementitious systems for structural and thermal eiciency.