RESUMO
Hydrophobic carbon nanotubes are hardly to disperse in water and prone to agglomerate when poured with Copper Tailing-Based Cementitious Material (CTCM). Multi-walled carbon nanotubes (MWCNTs) + Arabic Gum (GA) dispersions were prepared by a novel method of synergistic optimization of concentration, controlling low-frequency ultrasonic time and setting the ambient temperature with non-toxic anionic surfactant GA as surfactant. The results of UV-Vis spectroscopy showed that the high stability MWCNTs + GA dispersion with low aggregation area (< 1.2%) and low aggregation beam size (< 219 nm) have been prepared by using 1.7 mmol/l GA. The effects of highly stable MWCNTs dispersion on the mechanical properties, microstructure and durability of CTCM were studied. The 28 days compressive strength increased by 21.5%, and the flexural strength increased by 20.5%, almost reaching the mechanical level of the control group. The results of SEM, XRD and EDS showed that GA significantly enhanced the dispersion of MWCNT in aqueous solution at a suitable concentration (mass ratio of GA:CNTs = 1:1). The microstructure of the prepared CTCM by high stability MWCNTs dispersion was optimized obviously, and the mechanical properties and durability were improved significantly. This method solves the dual problem of MWCNTs not being fully dispersed in aqueous solution and being easily re-agglomerated in cementitious materials, as well as finding a breakthrough for the low cost and industrialization of tailings cement-based composite cementitious materials.
RESUMO
In this work, one-step synthesis of high-performance C-A-S-H (calcium alumina silicate hydrate) seeds from low-calcium fly ash (FA) and carbide slag (CS) by 7 days of mechanochemical mixing was proposed and used to activate lithium slag (LS) cement. The results showed that the seeding effect of C-A-S-H seeds was increased with the increasing Ca/Si (i.e. from 1.0 to 1.5), i.e. the mortar compressive strength of 1 day and 28 days were increased by 67% and 29% with the addition of 1.0% C-A-S-H nano-seeds at Ca/Si = 1.5 in the presence of polycarboxylate superplasticizer (PCE), respectively. Moreover, the chloride resistance of lithium slag cement was improved significantly, i.e. the electric flux was decreased by more than 30% than that of plain lithium slag cement mortar. The performance difference of various C-A-S-H seeds is mainly attributed to their high proportion and polymerization degree, more stretch and three-dimensional foil-like morphology at high Ca/Si. This study provides guidance for obtaining low-cost and high-performance C-A-S-H seeds from wastes and the highly efficient utilization of LS as supplementary cementitious materials (SCMs) in the future.
Assuntos
Cinza de Carvão , Lítio , Carbono , Cálcio , Materiais de ConstruçãoRESUMO
TiO2/cement composites were prepared by a spraying method to degrade organic pollutants. After coated with waterproof liquid, pure cement pastes/mortars were sprayed with TiO2 suspensions with different TiO2 contents and spraying times. Photocatalytic properties, mechanical strength and durability were studied. Maximum photocatalytic activity and uniform TiO2 distribution were achieved at the optimal conditions of 10 wt% TiO2 content in suspension and 3 spraying times. The TiO2/cement pastes had better degradation performance over Rhodamine B (RhB) and methylene blue (MB) than that over methyl orange (MO). After 20 times of cycling degradation, the photocatalytic efficiencies had no significant reduction. The TiO2/cement mortars had good mechanical strengths, meeting the mechanical demands of wastewater treatment tanks. In durability, the TiO2/cement mortars had better water penetration resistance, chloride penetration resistance and anti-carbonation than pure cement mortars.
