Due to their remarkable mechanical properties, graphene nanoplatelets (GNPs) are widely employed to reinforce matrix components such as cement materials. Recent findings have indicated that GNPs can be used as additives to improve the mechanical properties of cement. However, the enhancement mechanism is still indefinite. In order to investigate the reinforcement mechanism, this work studied the effect of GNPs on the hydration behaviour of Portland cement through an experimental investigation with isothermal calorimetry and thermogravimetric analysis. The results indicate that the addition of GNPs has little effect on the cement hydration process and the degree of hydration. As revealed by scanning electron microscopy and mini-slump tests, the GNPs were mechanically dispersed in the cement matrix. Special attention was paid to the physical functions between GNPs and cement and a possible mechanism is proposed to explain the formation pathway for GNP–cement composites. This research provides deeper understanding regarding the use of GNPs for reinforcing and toughening cement-based composites.
Calcium sulphoaluminate cement (CSA) has the characteristics of quick hardening, high early strength and high impermeability, however its strength growth persistence in the middle and late stages (after the age of 3 days) is poor. In order to improve this disadvantage, the pilot production of alite (C3S) modified CSA (AMCSA) clinker was carried out by liquid phase manipulation and barium ion doping technology. The effects of different dosages of gypsum on the hydration and hardening properties of AMCSA, such as setting time, hydration rate, compressive strength and hydration products, were studied. The results show that the mineral content of ye’elimite, C2S, C3S and iron phase in the calcined AMCSA clinker are 48.5 wt.%, 32.6 wt.%, 11.7 wt.% and 7.2 wt.% respectively, which are close to the designed mineral composition. The stable coexistence of ye’elimite and C3S in the same clinker system is realized. The initial and final setting time of AMCSA are retarded with the increasing gypsum dosage. When the gypsum dosage is 15 wt.% under the experimental conditions in this study, the AMCSA mortar reaches the highest compressive strength at every age. The strength of AMCSA mortar at 28 days is still significantly improved compared with that at 3 days, which indicates that the shortcoming of the low strength growth persistence of CSA in the middle and late stages is improved.
Ca 2 SiO 4 is a phase-change material, and γand β-Ca 2 SiO 4 usually coexist in the sintered product. The overlap of the diffraction data between the two polymorphs makes the relevant phase identification difficult. In this work, the Eu 3+ rear-earth fluorescence probe is introduced in the preparation of Ca 2 SiO 4 , and the obtained result indicates that the introduction of Eu 3+ ions facilitates the increase in the content of β-Ca 2 SiO 4 in the final product. In addition, the differences of the local coordination environments between the two Ca 2 SiO 4 phases obviously influence the crystal-field splittings of Eu 3+ ions, especially in the 5 D 0 → 7 F 0 nondegenerate and 5 D 0 → 7 F 1 magnetic dipole transition regions. On the basis of the excitation from the Eu 3+ −O 2− charge-transfer band, the low-temperature spectral changes are systematically discussed. The transition area ratios of
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