The grinding process has become widely used to improve the fineness and performance of fly ash. However, most studies focus on the particle size distribution of ground fly ash, while the particle morphology is also an important factor to affect the performance of cement paste. This article aims at three different kinds of ground fly ash from the ball mill and vertical mill, and the particle morphology is observed by scanning electron microscopy (SEM) to calculate the spherical destruction (the ratio of spherical particles broken into irregular particles in the grinding process of fly ash), which provides a quantification of the morphology change in the grinding process. The fluidity of cement paste and the strength of cement mortar are tested to study the relation of spherical destruction and fluidity and strength. The results show that the spherical destruction of ground fly ash in a ball mill is more than 80% and that in a vertical mill with a separation system is only 11.9%. Spherical destruction shows a significant relation with the fluidity. To different addition of ground fly ash, the fluidity of cement paste decreases with the increase of spherical destruction. To the strength of cement paste, particle size distribution and spherical destruction are both the key factors. Therefore, spherical destruction is an important measurement index to evaluate the grinding effect of the fly ash mill.

Separating finer particles from raw fly ash is a popular method to produce high-performance admixture of concrete. However, the supply of separated fly ash is obviously behind the demand and the residue fly ash is difficult to be disposed. Ground fly ash is another method to improve the particle size and reactivity, but the change of particle morphology during grinding may affect the rheological properties of cement paste and concrete, which limits the application of ground fly ash in concrete projects. In this study, the raw fly ash, separated fly ash, and ground fly ash of the same particle size range were studied and the particle morphology was analyzed by Image-Pro Plus process and spherical particles proportion calculation. On this basis, the fluidity and rheological properties of cement paste with different fly ash content were tested and the mechanism was discussed by packing density and zeta potential analysis. The results showed that the total amount of spherical particles in fly ash-cement paste system was reduced due to the spherical particles of ground fly ash being destroyed during the grinding process. Thus, compared with the separated fly ash of similar particle size range, the fluidity of ground fly ash was significantly decreased while the yield stress and plastic viscosity increased significantly, which indicated that the rheological properties of fly ash cement paste are closely related to the particle morphology of fly ash. The results provide theoretical basis and technology support to the application of ground fly ash.

The carbonation of steel slag (SS) can enhance its performance while capturing CO₂. The synergistic effect of combining multi-solid waste materials improves SS’s carbon sequestration efficiency, thereby contributing to reduce carbon emissions. This study investigates the synergistic carbonation mechanism of SS when combined with calcium carbide slag (CCS) and desulfurization gypsum (DG) under various water-to-binder ratios (w/bs). The mineral evolution, carbon sequestration performance, and carbon footprint of the multi-solid waste composite system are comprehensively analyzed. The results indicate that, at different w/bs, most SS-CCS-DG composite pastes exhibit a significant strength increase after carbonation compared to carbonated SS paste. Specifically, the strength of the 89%SS-5%CCS-6%DG paste is 44% and 60% higher than that of carbonated SS pastes at 0.15 and 0.3 w/bs, respectively. Carbon sequestration and carbon footprint analysis show that after carbonation, the composite system effectively sequesters 12.2% CO₂, with an actual carbon sequestration rate surpassing 70% of its theoretical value. Compared to the SS system, the composite system achieves a higher negative carbon emission of -279.93 kg CO₂/t.

As one of the main raw materials of engineered cementitious composite (ECC), fly ash exerts the “ball effect” and “pozzolanic effect” in concrete, which improves the working performance of concrete and enhances the strength of the concrete matrix. Polyvinyl alcohol (PVA) fiber has been widely used in the preparation of ECC, while ground fly ash can be used to enhance the performance of ECC as a kind of high-activity admixture. In this paper, the compressive strength, flexural strength and flexural toughness of ECC prepared from different types of fly ash (raw fly ash, sorted fly ash and ground fly ash) are compared, and the rheological properties of the ECC are analyzed by studying the two parameters of yield stress and plastic viscosity. The results show that the smaller the particle size of fly ash is, the more sufficient it reacts with Ca(OH)₂ produced by cement hydration, and the more it can improve the compressive strength and flexural strength of the matrix. In addition, the smaller the particle size of fly ash, the higher the yield stress and plastic viscosity of ECC; therefore, the distribution of PVA fiber in ECC is more uniform, thereby improving the flexural toughness and ductility of ECC.

Using fly ash (FA) solid wastes as economical carriers to construct Fenton-like catalytic composites with additional functions is more practical than the use of a single catalyst. Understanding the structure and properties of catalysts and carriers is vital to improve performance. Tetranitro iron phthalocyanine (TNFePc) is a highly active molecular catalyst, whose immobilization and Fenton-like heterogeneous catalysis remain unclear. In this study, magnetically recyclable composites of TNFePc@Fe₃O₄@FA were successfully fabricated. Further, Fe₃O₄ nanocrystals decorated on FA surfaces could be used as special functional layer for composite recycling and simultaneous in situ TNFePc synthesis. Peroxides of H₂O₂, KHSO₅, and tert-butyl hydrogen could be effectively activated by composites and transformed into highly reactive radicals. Moreover, molecular oxygen could be activated as well. Model pollutants, methylene blue and oxytetracycline, could be synergistically degraded by the radical oxidation of superoxide, hydroxyl, alkoxy, and sulfate radicals and non-radical oxidation of high-valent iron-oxo species of TNPcFe^IV=O. To the best of our knowledge, this is the first design of FA-based composites with dual function, Fenton-like heterogeneous catalysis and magnetic recyclability, for environmental decontamination. Graphical abstract