Polycarboxylate ether (PCE) plasticizer possesses by high water-reduction capability of about 30-40%. Despite the superior water reduction capability, the high dosages of PCE may cause the bleeding in cement systems, which is not suitable for high workability and self-compacting concrete. The current research is devoted to the studying of multi-walled carbon nanotubes (MWCNT) suspension prepared in combination with PCE plasticizer on the rheological properties of cement pastes. The bleeding of cement pastes modified by different dosages of MWCNT was estimated as well. The increase of yield stress in 3.7 and 3.5 times was obtained for cement paste modified by MWCNT suspension in dosage of 0.12% by weight of cement (bwoc) in 5 and 120 min after cement paste mixing, respectively. The increase of plastic viscosity in 2.95 and 1.55 times was obtained for cement paste modified by MWCNT suspension in dosage of 0.12% bwoc in 5 and 120 min after cement paste mixing, respectively. Modification of cement pastes by MWCNT suspension in the dosage of 0.24 % bwoc led to the decrease of bleeding water volume by 21.7% in comparison with cement pastes modified only by PCE plasticizer.
The evaluation of rheological properties of cement systems is getting more relevant with growing interest to self-consolidating concrete (SCC), high-performance concrete (HPC) and ultrahigh-performance concrete (UHPC). The rheology models are a perspective tool to predict and manage the properties of cement systems in the fresh and hardened state. The current research is focused on the rheological test of cement systems modified by multiwalled carbon nanotubes (MWCNT) dispersion with and without polycarboxylate ether (PCE). The content of dispersion with 1% concentration of MWCNT in cement pastes varied from 0.125 to 0.5% by weight of cement. The dosage of PCE was taken as 0.6% by weight of cement. The cement pastes were prepared based on Portland cement without mineral additives. The rheological test was carried out at 5, 30, 60, and 120 min after mixing of cement paste. The rheological test established that modification of cement pastes by MWCNT dispersion in dosage 0.25% leads to the decrease of yield stress by 30.7% and increase of plastic viscosity by 29.6%. The combined modification by PCE and MWCNT dispersion shows the decrease in plastic viscosity of cement pastes by 9.90% in dosage of MWCNT equal to 0.5% by weight of cement, reduction of water demand by 20% for the same workability, and decrease of yield stress till 0 Pa. It gives the ability to obtain the self-compacting mixtures. The cement pastes with and without MWCNT dispersion revealed the shear-thinning behavior during 120 min after mixing. The modification of cement pastes by PCE with and without MWCNT dispersion showed the shear-thickening behavior which remains during 120 min after mixing.
Condensation of enynones readily available from cheap starting material with pyrazolamines provides easy access to fluorescent 7-(trimethylsilylethynyl)pyrazolo[1,5-a]pyrimidines. The reaction is straightforward, does not require the use of any additional reagents or catalysts, and can be performed without inert atmosphere. Various substituents and functional groups in both enynone and pyrazolamine are tolerated. The presented method features full regioselectivity, high isolated yields, and simplicity of both setup and product purification. Fluorescent properties of the obtained pyrazolopyrimidines were studied.
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