Abstract
In this study, the rheological properties of cement paste modified by a suspension containing both multi-walled carbon nanotubes (MWCNT) and carboxymethyl cellulose (CMC) (MWCNT/CMC suspension) with different types of plasticising admixtures (Pl), such as lignosulphonate (LS), sulfonated naphthalene formaldehyde condensate (NF), and polycarboxylate ether (PCE) were evaluated. The increase in yield stress and plastic viscosity up to 20% was established in the case of the modification of cement-based mixtures by MWCNT in the dosage up to 0.24% by weight of cement (bwoc) without Pl and with LS and NF. The complex modification of cement paste by MWCNT and PCE increases the yield stress and plastic viscosity from the MWCNT dosage of 0.06% and 0.015% bwoc, respectively. The yield stress and plastic viscosity of cement paste with PCE enhanced by 265% and 107%, respectively, in a MWCNT dosage of 0.12% bwoc. MWCNT do not have a significant influence on the flow behaviour index of cement paste; however, in the case of usage of PCE, the shear thickening effect decreased from a MWCNT dosage of 0.03% bwoc. The significant reduction in the volume coefficient of water bleeding by 99, 100, and 83% was obtained with LS, NF, and PCE, respectively, with an increase in MWCNT dosage up to 0.24% bwoc.
Highlights
The growth of demand for concrete structures of different functionality requires the development of new concrete compositions and innovative concrete technologies of transportation, handling, pumping, and compacting with a decrease in economic expenses
The maximum increase in yield stress value by 265% was obtained in the multi-walled carbon nanotubes (MWCNT) dosage of respect to the reference cement paste modified by polycarboxylate ether (PCE) without MWCNT
The proportional increase in the plastic viscosity of the cement paste modified by the suspension and PCE was observed from the MWCNT dosage of 0.015% bwoc up to 0.06% bwoc
Summary
The growth of demand for concrete structures of different functionality requires the development of new concrete compositions and innovative concrete technologies of transportation, handling, pumping, and compacting with a decrease in economic expenses. The complex admixture based on Pl and nanoparticles can improve the plasticising efficiency of Pl. Application of Pl in high dosages can lead to the occurrence of water bleeding when gravity dominates the colloidal forces between cement particles in low viscosity liquid phase [48,49]. The understanding of rheological behaviour of the plasticised cement paste with MWCNT can be valuable for further design of complex admixtures based on MWCNT and Pl. The present research is a continuation of research works [27,28,29], which generalise the research data on the rheological properties and water bleeding of cement pastes modified by MWCNT/CMC suspension in the presence of three different Pl, with application of the Herschel–Bulkley model for approximation of the experimental data; a possible explanation of the action mechanisms of MWCNT in the plasticised cement pastes is proposed
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