The Effect of Changing Fly Ash Content on the Modulus of Compression of Stabilized Soil

Abstract

Adding a curing agent can enhance the mechanical properties of soil including its compressive strength. However, few studies have quantitatively analyzed the compressive strength and microstructure of soils to explore the impact of changes in the microstructure on compressive strength. In addition, the cost of curing agents is too high to be widely used. In this study, curing agents with different proportions of fly ash were added to dredger fill to reduce the amount of curing agents needed. The quantitative analysis of the relationships between the modulus of compression Es and microstructures of stabilized soil samples is presented. The modulus of compression Es was gauged from compression tests. Microscopic images acquired using a scanning electron microscope were processed using the Image-Pro Plus (IPP) image processing software. The microscopic parameters, obtained using IPP, included the average equivalent particle size Dp, the average equivalent aperture size Db, and the plane pore ratio e. This research demonstrated that the fly ash added to the curing agent achieved the same effect as the curing agent, and the amount of curing agent required was reduced. Therefore, the modulus of compression for stabilized soil can be improved. This is due to the hydration products (i.e., calcium silicate hydrate, calcium hydroxide, and ettringite), produced by the hydration reaction, and which adhere to the surface of the particles and fill the spaces among them. Thus, the change in the pore structure and the compactness of the particles helps to increase the modulus of compression. In addition, there was a good linear relationship between the modulus of compression and the microscopic parameters. Using the mathematical relationships between the macroscopic and microscopic parameters, correlations can be built for macro–microscopic research.

The Influence Mechanism of Ettringite Crystals and Microstructure Characteristics on the Strength of Calcium-Based Stabilized Soil

“…As shown in Figure 3 a, abundant flocculated CSH gels [ 10 , 11 , 18 , 19 , 20 , 21 , 22 ] were generated in PC100S, which coated the outer surface of soil particles and cemented the soil particles together to form a whole structure. However, some large pores can still be observed.…”

“…However, some large pores can still be observed. Moreover, a little of needle-like AFt crystals and monosulfate calcium sulfoaluminate hydrate (AFm) crystals [ 10 , 11 , 12 , 18 , 20 , 21 , 23 ] can be detected in the pores, together with individual hexagonal plate-shaped CH crystals [ 18 , 19 , 20 , 21 ] and cubic-shaped CAH crystals [ 20 ]. The AFt crystals were about 1–2 μm in length and 0.1 μm in diameter.…”

Effects of Class C and Class F Fly Ash on Mechanical and Microstructural Behavior of Clay Soil—A Comparative Study

“…Over 65% of the produced fly ash is disposed of in landfills [ 4 ]. If the fly ash, as a waste material, is not managed well, it can lead to serious environmental and health problems [ 4 , 5 ]. However, many characteristics of fly ash such as low compressibility, high shear resistance, high strength and pozzolanic characteristics offer it an important role in improving the properties of soil in geotechnical applications [ 2 , 6 ].…”

Special Issue: “Microstructures and Durability of Cement-Based Materials”

“…The performance of concrete can be improved by incorporating various admixtures, as demonstrated by [ 6 ], which investigated the durability and strength of casein-cemented sand incorporating slag. The use of fly ash is highlightable for enhancing the compression modulus of stabilized soil [ 7 ] and coastal soil [ 8 ]. In addition to typically employed and widely investigated SCMs, the use of other by-products can be beneficial.…”