| dc.description.abstract | Addition of cement to the soil is a common method to improve the geotechnical properties of soils in construction. However, it is generally known that 8% of the total CO2 emissions is from the Portland cement production. In order to reduce the usage of cement and its environmental impact, waste materials, such as fly ash, have become popular in geotechnical applications. Also, using waste materials can decrease the environmental threat caused by the disposal of huge quantities of these waste materials. Some types of fly ash lack adequate cementitious properties, therefore, they can be mixed with other additives such as lime or alkali activators to improve the mechanical properties of soils. Alkali activated waste materials are found comparable to cement in terms of strength performance. Therefore, they have the potential to replace cement in soil stabilisation. However, a current gap is noticed in detailed investigations of soils stabilised with fly ash and alkali activated fly ash. For soils stabilised with fly ash, triaxial and consolidation analyses are limited, while for soils stabilised with alkali activated fly ash, inconsistency is observed between the alkali ratios of sodium silicate/sodium hydroxide.
In this research, the effects of class C fly ash, class F fly ash, and alkali activated fly ash, as stabilising agents, were studied in stabilising clay soil. The thesis investigated the role of different fly ash and alkali activated fly ash contents on the physical, mechanical, and chemical behaviour of the stabilised soil. The experimental programme included compaction, unconfined compressive strength, one-dimensional consolidation, and consolidated-undrained triaxial tests as well as scanning electron microscopy and X-Ray diffraction analysis on the control and stabilised samples at 1 day, 7 days, and 28 days of curing times.
This research contributes to this context in 2 phases. In the first phase, the effects of class C and class F fly ash were compared considering the mechanical and microstructural behaviour of the stabilised soil. The results showed that the strength parameters of stabilised soil improved and swelling and compression indices decreased with the addition of fly ash and with the increase of curing time. A higher permeability was observed at 1 day of curing and the permeability decreased with the curing time. It was observed that class C fly ash can be used as a soil stabilisation agent whereas class F fly ash need to be mixed with different additives such as alkali activators to stabilise the soil.
In the second phase, class F fly ash was used with alkali activators (sodium silicate and sodium hydroxide) as a soil stabilising agent. For the alkali activated class F fly ash, a rigorous dosage method using parameters such as alkali dosage and silica modulus was applied to determine soil mix proportions and produce replicable samples. After the designation of the optimal parameters, mechanical tests, microstructural and mineralogical analysis were carried out. The results showed that the strength improvement of stabilised soil was considerable when the fly ash was activated. The recommended optimal strength parameters were alkali dosages of 12% and silica modulus of 1.25. The addition of either alkali activated fly ash or fly ash to the soil led to a decrease of compression and swelling indices, while yield stress increased. Stress-strain behaviour of soil was modified from ductile to brittle strain-softening response with the addition of alkali activated fly ash and curing time, whereas stress-strain behaviour had ductile response at all curing times with the addition of non-activated fly ash. X-Ray diffraction analysis indicated a decrease in the peak intensities of illite and kaolinite, while scanning electron microscopy analysis showed a modification with the addition of alkali activated fly ash. | en_GB |
