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.

The deterioration mechanisms of sulfate attack on concrete under sustained loading and wet-dry cycling were investigated based on micro and macroobservations. The mass fraction of sodium sulfate solution was 6.9%. Three loading levels of 20, 40, and 60% of ultimate flexural load were considered, and the load was mechanically applied to the specimens under four-point bending. Microobservations included the analysis of the chemical products formed using thermal analysis and the determination of the sulfate-ion content profile using the modified barium sulfate gravimetric method (chemical titration). Macroobservations primarily included visual observations and flexural strength changes. Test results showed that under alternate action of wet-dry cycling, concretes are attacked by expansive products such as ettringite and gypsum during the wetting cycle, and crystallization damage, induced by evaporation, is superposed during the drying cycle. Results also showed that the tensile stresses can increase ...