Influence of Particle Morphology of Ground Fly Ash on the Fluidity and Strength of Cement Paste

Abstract

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.

Fly Ash Application as Supplementary Cementitious Material: A Review

“…FA is a primary solid waste generated by coal-fired energy plants, and these plants are looking for economically viable ways to dispose of it. FA particles are generally spherical, solid/hollow in nature, mainly glassy (amorphous), with particle sizes varying from <1 µm to 150 µm [ 53 , 54 , 55 ]. The scanning electron microscopy (SEM) micrographs of the FA are shown in Figure 1 .…”

Waste material fly ash as an alternative filler for elastomers

“…116 Class F is generated by burning anthracite or bituminous coal containing SiO 2 , Al 2 O 3 , F I G U R E 4 Scanning electron microscopy (SEM) images of (A) raw fly ash (FA) (RF), (B) FA after grinding 1 h in a ball mill (BF1), (C) FA after grinding 2 h in a ball mill (BF2), and (D) FA after grinding in a vertical mill (VF), (E) the particle size distributions obtained by milling. 106 and Fe 2 O 3 concentrations greater than 70%. In addition, 50%-70% of the aforementioned compounds are found in lignite or sub-bituminous coal, which when burned, produces fly ash Class C. 35 Several inorganic materials found in FA make it suitable as an alternative filler, especially SiO 2 and CaO.…”

“…105 Generally, the original particle sizes vary from 1 to 150 μm. 22,106,107 After grinding in a ball or vertical mill, a large proportion of FA particles are broken to angular particles, and the particle size decreases with increasing grinding time, 108 as shown in Figure 4A-D. After grinding in a ball mill, the primary particles are 0-50 μm, whereas most vertical mills produce FA particles between 0 and 25 μm, as shown in Figure 4E.…”

“…A vertical mill produces finer particles because the separation system can remove appropriate size particles and increase grinding efficiency. 106 Recently, a type of FA, called FA microsphere (FAM), was compared with commercial fumed silica. 109 FAM is a type of superfine powder with sizes of 0.63-8.23 μm.…”

Experimental Study on Preparation and Performance of Concrete With Large Content of Fly Ash

“…The third is the grounding of the fly ash into much more fineness. With the changes in particle morphology and distribution of irregular grains from broken spherical particles, fly ash behaves with higher pozzolanic activity and tiny-aggregate filling effect on the improvement of composite strength (Ma et al, 2021). The fourth is making of the fly-ash composites at a hightemperature environment; this accelerates the hydration of both cement and fly ash (Hefni et al, 2018;Mei et al, 2018;Singh and Subramaniam, 2019;Yang et al, 2021).…”