Regulating the phase transformation of γ → β in dicalcium silicate (C 2 S) can effectively improve the hydration activity and recycling rate of AOD slag; however, the evolution law for γ → β in C 2 S has not been extensively investigated. In this study, a novel “two-step” γ → α ′ L → β phase transformation method in C 2 S was designed based on the study of the pure C 2 S phase at a nonequilibrium state in the low- and middle-temperature ranges. The “two-step” method can be used to realize the transformation from needle-like nanostructured γ -C 2 S grains to lamellar-structured β -C 2 S grains, exhibiting the trend of interlaminar peeling accompanied by expansion of the particle volume and leading to the appearance of macroscopic lamellar cracking in β -C 2 S particles. In addition, the β -C 2 S mass fraction in AOD slag treated by water cooling at 680 °C reaches a maximum value of 47.5 wt pct, while the treated AOD slag presents abundant holes and defects, which can effectively enlarge the hydration contact area.
Lu Zhu,Hanxiong Lyu,Yang Liu,Shipeng Zhang,Chi Sun Poon
Solid waste derived clinker design methodology was established based on thermodynamic simulation and experiment validation via the recycling of incinerated sewage sludge ash (ISSA) and recycled concrete fine (RCF). Compared with 1000 °C and 1100 °C, 1200 °C was the optimum temperature for C 2 S-rich clinker synthesis due to the highest simulated belite content after sintering. A utilization rate of 95 % was achieved, accomplishing the maximization of solid waste recycling. Due to the CaCO 3 phase formation by the reaction of high-content belite (46.8 %) with CO 2 , carbonated 1200ARS eco-cement showed higher compressive strength than OPC and other eco-cements. The lowest porosity (18.1 %) with dense microstructure was also obtained by carbonated 1200ARS. Benefiting from the high CO 2 reactivity of belite, 1200ARS displayed the optimum CO 2 sequestration capacity with a higher carbonation degree (30.1 %) than other batches, providing a promising direction for future development of the low-carbon cement industry to achieve environmental sustainability.
Yuanyuan Shen,Long Jiang,Peiliang Shen,Ligang Peng,Chi-sun Poon,Fazhou Wang
A new eco-friendly carbonation coating with a photocatalytic function was developed using dicalcium silicate (C 2 S) and nano TiO 2 , aiming to remove air pollution and enhance the durability of concrete at the same time. The photocatalytic performance, mechanical properties, and durability of the carbonated coatings incorporating different additions of TiO 2 were evaluated, and the development of carbonation products and microstructure were investigated. The results show that the photocatalytic efficiency was increased linearly from 2518 μmol·m −2 ·h to 4392 μmol·m −2 ·h as the TiO 2 doping amount was increased from 1% to 8%. In addition, the composition and microstructure analysis indicated that TiO 2 not only improved the carbonation degree of C 2 S but also promoted the formation of metastable calcium carbonate, including aragonite, vaterite, and amorphous calcium carbonate, leading to a densified microstructure structure. At the same time, the improved carbonation process could capture up to 15.18% CO 2 by mass. As a result, the bonding strength was improved from 3.29 MPa to 4.69 MPa after incorporating 8% TiO 2 , which is much higher than the conventional cement-based coating. Furthermore, the microhardness of the coating increased from 150 HV to 178 HV.
Zhiyong Mao,Zhijuan Lu,Jingjing Chen,Bradley D. Fahlman,Dajian Wang
In this work, tunable luminescence of dicalcium silicate doped with Eu2+ ions is demonstrated based on crystal engineering. Five types of dicalcium silicate polymorphs (γ-, β-, αL′-, αH′-, α-Ca2SiO4) are synthesized by incorporating a crystal-phase stabilizer (CPS), in order to afford variable accommodation frameworks for the Eu2+ activator. Tunable luminescence is observed as the polymorph transforms from one crystal form into another. In addition, the luminescence of Eu2+ in peculiar crystal-phase Ca2SiO4 hosts is further customized by crystal-site engineering, which regulates the coordination environment of Eu2+ in multiple types of Ca2+ sites. The luminescence properties of our Eu2+-doped dicalcium silicate polymorphs show promising prospects for LED lighting applications.
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