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

Abstract

A large amount of coal fly ash produced in thermal power plants is disposed of in landfills which causes many environmental problems. The utilization of fly ash can be encouraged in geotechnical engineering projects. In this paper, the effects of class C and class F fly ash on the mechanical and microstructural behavior and stabilization of clay soil were evaluated through a program of laboratory experiments. The experiments included compaction, unconfined compressive strength, consolidated-undrained triaxial, one-dimensional consolidation tests, and scanning electron microscopy analysis on samples of fly ash-stabilized clay soil after 1, 7, and 28 days of curing. The tests were conducted on mixtures of clay with class C or class F fly ash, ranging from 0% to 30% of the soil. Experimental results showed that the strength parameters and permeability of the stabilized soil improved while the compression and swelling indices decreased by the addition of fly ash and by the increase of curing days. The results obtained from the mechanical tests agreed with the results from the SEM analysis. Based on the results, the soil could be successfully stabilized by using class C fly ash. The improvements in strength, swelling, and permeability parameters of the stabilized soil were higher with the class C fly ash compared with class F fly ash.

Effects of Fly Ash Inclusion and Alkali Activation on Physical, Mechanical, and Chemical Properties of Clay

“…However, the results for the soils stabilised with alkali-activated fly ash at 1 day of curing, and for the soils stabilised with fly ash at 1, 7, and 28 days of curing, were found to be insignificant. This might be due to the fact that class F fly ash has very low reactive calcium content, and this results in a lack of a chemical reaction with soil [56]. On the other hand, the UCS of the soils stabilised with alkali-activated fly ash increased considerably with the increase in fly ash content at 7 and 28 days of curing.…”

“…On the other hand, the soils stabilised with neat fly ash showed a very slight increase with the increase in curing time (Figure 7a). The increase in UCS in soils stabilised with fly ash with the curing time is due to the pozzolanic properties of fly ash [56].…”

“…On the other hand, the soils stabilised with neat fly ash showed a very slight increase with the increase in curing time (Figure 7a). The increase in UCS in soils stabilised with fly ash with the curing time is due to the pozzolanic properties of fly ash [56]. Figure 8a-c show the stress-strain behaviour of the control sample, soils stabilised with 15% and 25% fly ash, and soils stabilised with 15% and 25% alkali-activated fly ash with a constant SM of 1.25 and an M+ of 12% and an M+ of 16%, cured for 1, 7, and 28 days.…”

“…Even though the reaction products observed in the system improved the mechanical properties of stabilised soil, the presence of unreacted fly ash at 28 days of curing showed the insignificant improvement in the soils stabilised with class F fly ash. Turan et al [56] indicated that due to the low Ca content in class F fly ash, it has a lack of cementitious properties; hence, class F fly ash is not able to give a strong reaction Figure 15a-f show the results of the SEM analysis on the soils stabilised with neat class F fly ash. Unreacted fly ash particles were observed in the stabilised soils at each curing time.…”

Geotechnical Characteristics of Fine-Grained Soils Stabilized with Fly Ash, a Review

“…In terms of swelling reduction, 30% class F fly ash was found comparable to 10% class C fly ash. Turan et al [51] conducted a series of tests to analyze the effects of class C and class F fly ash on the shear strength, consolidation, and microstructural behavior of clay. They argued that class C fly ash is more effective in improving the mechanical and microstructural properties of the soil compared to class F fly ash.…”